Respiratory Disorders

INTRODUCTION

The respiratory system distributes air to the alveoli, where gas exchange—the addition of oxygen (O₂) and the removal of carbon dioxide (CO₂) from pulmonary capillary blood—takes place. Certain specialized structures within this system play a vital role in preparing air for use by the body. The nose, for example, contains vestibular hairs that filter the air and an extensive vascular network that warms it. The nose also contains a layer of goblet cells and a moist mucosal surface; water vapor enters the airstream from this mucosal surface to saturate inspired air as it’s warmed in the upper airways. Ciliated mucosa in the posterior portion of the nose and nasopharynx as well as major portions of the tracheobronchial tree propel particles deposited by impaction or gravity to the oropharynx, where the particles are swallowed.

EXTERNAL RESPIRATION

The external component of respiration— ventilation or breathing—delivers inspired air to the lower respiratory tract and alveoli. Contraction and relaxation of the respiratory muscles move air into and out of the lungs. Ventilation begins with the contraction of the inspiratory muscles: the diaphragm (the major muscle of respiration) descends, while external intercostal muscles move the rib cage upward and outward.

Air then enters the lungs in response to the pressure gradient between the atmosphere and the lungs. The lungs adhere to the chest wall and diaphragm because of the vacuum created within the pleural space. As the thorax expands, negative pressure is created in the intrapleural space, causing the lungs to also expand and draw in the warmed, humidified air. The accessory muscles of inspiration, which include the scalene and sternocleidomastoid muscles, raise the clavicles, upper ribs, and sternum. The accessory muscles aren’t used in normal inspiration but may be used in some pathologic conditions.

Normal expiration is passive; the inspiratory muscles cease to contract, the diaphragm rises, and the elastic recoil of the lungs causes the lungs to contract. These actions raise the pressure within the lungs above atmospheric pressure, moving air from the lungs to the atmosphere. Active expiration causes pleural pressure to become less negative. (See Mechanics of ventilation, page 90.)

An adult lung contains an estimated 300 million alveoli; each alveolus is supplied by many capillaries. To reach the capillary lumen, O₂ must cross the alveolocapillary membrane, which consists of an alveolar epithelial cell, a thin interstitial space, the capillary basement membrane, and the capillary endothelial cell membrane. The O₂ tension of air entering the respiratory tract is approximately 150 mm Hg. In the alveoli, inspired air mixes with CO₂ and water vapor, lowering the O₂ pressure to approximately 100 mm Hg. Because alveolar partial pressure of O₂ is higher than that present in mixed venous blood entering the pulmonary capillaries (approximately 40 mm Hg), O₂ diffuses across the alveolocapillary membrane into the blood.

O₂ AND CO₂ TRANSPORT AND INTERNAL RESPIRATION

Circulating blood delivers O₂ to the cells of the body for metabolism and transports metabolic wastes and CO₂ from the tissues back to the lungs. When oxygenated arterial blood reaches tissue capillaries, O₂ diffuses from the blood into the cells because of the O₂ tension gradient. The amount of O₂ available is determined by the concentration of hemoglobin (Hb; the principal carrier of O₂), the percentage of O₂ saturation of the Hb, regional blood flow, arterial O₂ content, and cardiac output.

Internal (cellular) respiration occurs as a part of cellular metabolism, which can take place with O₂ (aerobic) or without O₂ (anaerobic). The most efficient method for providing fuel (highenergy compounds such as adenosine triphosphate [ATP]) for cellular reactions is aerobic metabolism, which produces CO₂ and water in addition to ATP. Anaerobic metabolism is less efficient because a cell produces only a limited amount of ATP and yields lactic acid as well as CO₂ as a metabolic by-product.

Because circulation is continuous, CO₂ doesn’t normally accumulate in tissues. CO₂ produced during cellular respiration diffuses from tissues into regional capillaries and is transported by systemic venous circulation. When CO₂ reaches the alveolar capillaries, it diffuses into the alveoli, where the partial pressure of CO₂ is lower; CO₂ is removed from the alveoli during exhalation.

MECHANISMS OF CONTROL

The central nervous system’s (CNS’s) control of respiration lies in the respiratory center, located in the lateral medulla oblongata of the brain stem. Impulses travel down the phrenic nerves to the diaphragm, and down the intercostal nerves to the intercostal muscles, where the impulses change the rate and depth of respiration. The
inspiratory and expiratory centers, located in the posterior medulla, establish the involuntary rhythm of the breathing pattern.

Mechanics of ventilation

Breathing results from differences between atmospheric and intrapulmonary pressures, as described below.

Before inspiration, intrapulmonary pressure equals atmospheric pressure (approximately 760 mm Hg). Intrapleural pressure is 756 mm Hg.

The intrapulmonary atmospheric pressure gradient pulls air into the lungs until the two pressures are equal.

During inspiration, the diaphragm and external intercostal muscles contract, enlarging the thorax vertically and horizontally. As the thorax expands, intrapleural pressure decreases and the lungs expand to fill the enlarging thoracic cavity.

During normal expiration, the diaphragm slowly relaxes and the lungs and thorax passively return to resting size and position. During deep or forced expiration, contraction of internal intercostal and abdominal muscles reduces thoracic volume. Lung and thorax compression raises intrapulmonary pressure above atmospheric pressure.

Apneustic and pneumotaxic centers in the pons influence the pattern of breathing. Stimulation of the lower pontine apneustic center (e.g., by trauma, tumor, or stroke) produces forceful inspiratory gasps alternating with weak expiration. The apneustic center continually excites the medullary inspiratory center and thus facilitates inspiration. Signals from the pneumotaxic center as well as afferent impulses from the vagus nerve inhibit the apneustic center and “turn off” inspiration. The apneustic pattern doesn’t occur if the vagus nerves are intact.

Partial pressure of arterial oxygen (Pao₂), pH, and pH of cerebrospinal fluid (CSF) influence output from the respiratory center. When CO₂ enters the CSF, the pH of CSF falls, stimulating central chemoreceptors to increase ventilation.

The respiratory center also receives information from peripheral chemoreceptors in the carotid and aortic bodies. These chemoreceptors respond primarily to decreased Pao₂ but also to decreased pH. The peripheral
chemoreceptors have little control over respirations until the Pao₂ is less than 60 mm Hg.

During exercise, stretch receptors in lung tissue and the diaphragm prevent overexpansion of the lungs. During swallowing, the cortex can interrupt automatic control of ventilation. During sleep, respiratory drive may fluctuate, producing hypoventilation and periods of apnea. External sensations, drugs, chronic hypercapnia, and changes in body temperature can also alter the respiratory pattern.

DIAGNOSTIC TESTS

Diagnostic tests evaluate physiologic characteristics and pathologic states within the respiratory tract.

Noninvasive tests include:

Chest X-ray shows such conditions as atelectasis, pleural effusion, infiltrates, pneumothorax, lesions, mediastinal shifts, pulmonary edema, and chronic obstructive pulmonary disease (COPD).
Computed tomography (or CT) scan provides a three-dimensional picture that’s 100 times more sensitive than a chest X-ray.
Magnetic resonance imaging (or MRI) identifies obstructed arteries and tissue perfusion, but movement of the heart and lungs reduces the image’s clarity.
Sputum specimen analysis assesses sputum quantity, color, viscosity, and odor; microbiological stains and culture of sputum can identify infectious organisms; and cytologic preparations can detect respiratory tract neoplasms. Sensitivity tests determine antibiotic sensitivity and resistance.
Pulmonary function tests (or PFT) measure lung volume, flow rates, and compliance. Normal values, individualized by body stature, ethnicity, and age, are reported in percentage of the normal predicted value. Static measurements are volume measurements that include tidal volume, volume of air contained in a normal breath; functional residual capacity, volume of air remaining in the lungs after normal expiration; vital capacity, volume of air that can be exhaled after maximal inspiration; residual volume, air remaining in the lungs after maximal expiration; and total lung capacity (TLC), volume of air in the lungs after maximal inspiration. Dynamic measurements characterize the movement of air into and out of the lungs and show changes in lung mechanics. They include measurement of forced expiratory volume in 1 second, maximum volume of air that can be expired in 1 second from total lung capacity; maximal voluntary ventilation, volume of air that can be expired in 1 minute with the patient’s maximum voluntary effort; and forced vital capacity, maximal volume of air that the patient can exhale from TLC. (Peak flow rate, which can be obtained at the bedside, is also a dynamic measurement of pulmonary function.)
Methadholine challenge is one method of assessing airway responsiveness and is used to determine a diagnosis of asthma.
Exercise stress test evaluates the ability to transport O₂ and remove CO₂ with increasing metabolic demands.
Polysomnography can diagnose sleep disorders.
Lung scan (ventilation-perfusion or scintiphotography scan) demonstrates ventilation and perfusion patterns. It’s used primarily to evaluate pulmonary embolus.
Arterial blood gas (ABG) analysis assesses gas exchange. Decreased Pao₂ may indicate hypoventilation, ventilation-perfusion mismatch, or shunting of blood away from gas exchange sites. Increased partial pressure of arterial carbon dioxide (Paco₂) reflects marked ventilation-perfusion mismatch or hypoventilation; decreased Paco₂ reflects increased alveolar ventilation. Changes in pH may reflect metabolic or respiratory dysfunction.
Pulse oximetry is a noninvasive assessment of arterial oxygen saturation.
Capnography may be used either transcutaneously or in ventilator circuit to determine Paco₂ trends.

Invasive tests include:

Bronchoscopy permits direct visualization of the trachea and mainstem, lobar, segmental, and subsegmental bronchi. It may be used to localize the site of lung hemorrhage, visualize masses in these airways, and collect respiratory tract secretions. Brush biopsy may be used to obtain specimens from the lungs for microbiological stains, culture, and cytology. Lesion biopsies may be performed by using small forceps under direct visualization (when present in the proximal airways) or with the aid of fluoroscopy (when present distal to regions of direct visualization). Bronchoscopy can also be used to clear secretions and remove foreign bodies.
Thoracentesis permits removal of pleural fluid for analysis.
Pleural biopsy obtains pleural tissue for histologic examination and culture.
Pulmonary artery angiography, the injection of dye into the pulmonary artery, can locate pulmonary embolism. This is considered

the gold standard for diagnosing pulmonary emboli.
Positron emission tomography (or PET) scan uses a short-life radionuclide. Increased uptake of the substance is seen in malignant cells.

Characterizing and interpreting percussion sounds

Percussion may produce several kinds of sounds. Known as flat, dull, resonant, hyperresonant, or tympanic, these sounds indicate the location and density of various structures. During percussion, determining other tonal characteristics, such as pitch, intensity, and quality, also will help identify respiratory structure. Use this chart as a guide to interpreting percussion sounds.

Characteristic

Sound	Pitch	Intensity	Quality	Implications
Flatness	High	Soft	Extremely dull	These sounds are normal over the sternum. Over the lung, they may indicate atelectasis or pleural effusion.
Dullness	Medium	Medium	Thudlike	Normal over the liver, heart, and diaphragm, these sounds over the lung may point to pneumonia, tumor, atelectasis, or pleural effusion.
Resonance	Low	Moderate to loud	Hollow	When percussed over the lung, these sounds are normal.
Hyperresonance	Lower than resonance	Very loud	Booming	These are normal findings with percussion over a child’s lung. Over an adult’s lung, these findings may indicate emphysema, chronic bronchitis, asthma, or pneumothorax.
Tympany	High	Loud	Musical, drumlike	Over the stomach, these are normal findings; over the lung, they suggest tension pneumothorax.

ASSESSMENT

Assessment of the respiratory system begins with a thorough patient history. Ask the patient to describe his respiratory problem. How long has he had it? How long does each attack last? Does one attack differ from another? Does any activity in particular bring on an attack or make it worse? What relieves the symptoms? Always ask whether the patient was or is a smoker, what and how often he smoked or smokes, and how long he smoked or has been smoking. Record this information in pack years—the number of packs of cigarettes per day multiplied by the number of smoking years. Remember to ask about the patient’s occupation, hobbies, and travel; some of these activities may involve exposure to toxic or allergenic substances.

If the patient has dyspnea, ask if it occurs during activity or at rest. What position is the patient in when dyspnea occurs? How far can he walk? How many flights of stairs can he climb? Has his exercise tolerance been decreasing? Can he relate dyspnea to allergies or environmental conditions? Does it occur only at night, during sleep? If the patient has a cough, ask about its severity, persistence, and duration; ask if it produces sputum and, if so, how much and what kind. Have the patient’s cough habits and character of sputum changed recently?

PHYSICAL EXAMINATION

Use inspection skills to check for clues to respiratory disease, beginning with the patient’s general appearance. If he’s frail or cachectic, he may have
a chronic disease that has impaired his appetite. If he’s diaphoretic, restless, or irritable or protective of a painful body part, he may be in acute distress. Also, look for behavior changes that may indicate hypoxemia or hypercapnia. Confusion, lethargy, bizarre behavior, or quiet sleep from which he can’t be aroused may point to hypercapnia. Watch for marked cyanosis, indicated by bluish or ashen skin (usually best seen on the lips, tongue, earlobes, and nail beds), which may be due to hypoxemia or poor tissue perfusion.

Assess chest shape and symmetry at rest and during ventilation. Increased anteroposterior diameter (“barrel chest”) characterizes emphysema. Kyphoscoliosis also alters chest configuration, which in turn restricts breathing. Assess respiratory excursion and observe for accessory muscle use during breathing. The use of upper chest and neck muscles is normal only during physical stress.

Observe the rate and pattern of breathing because certain disorders produce characteristic changes in breathing patterns. For example, an acute respiratory disorder can produce tachypnea (rapid, shallow breathing) or hyperpnea (increased rate and depth of breathing); intracranial lesions can produce Cheyne-Stokes and Biot’s respirations; increased intracranial pressure can result in central hyperventilation and apneustic or ataxic breathing; metabolic disorders can cause Kussmaul’s respirations; and airway obstruction can lead to prolonged forceful expiration and pursed-lip breathing.

Also observe posture and carriage. A patient with COPD, for example, usually supports rib cage movement by placing his arms on the sides of a chair to increase expansion and leans forward during exhalation to help expel air.

Palpation of the chest wall detects areas of tenderness, masses, changes in fremitus (palpable vocal vibrations), or crepitus (air in subcutaneous tissues). To assess chest excursion and symmetry, place your hands in a horizontal position, bilaterally on the posterior chest, with your thumbs pressed lightly against the spine, creating folds in the skin. As the patient takes a deep breath, your thumbs should move quickly and equally away from the spine. Repeat this with your hands placed anteriorly, at the costal margins (lower lobes) and clavicles (apices). Unequal movement indicates differences in expansion, seen in atelectasis, diaphragm or chest wall muscle disease, or splinting due to pain.

Percussion should detect resonance over lung fields that aren’t covered by bony structures or the heart. A dull sound on percussion may mean consolidation or pleural disease. (See Characterizing and interpreting percussion sounds.)

Auscultation normally detects soft, vesicular breath sounds throughout most of the lung fields. Absent or adventitious breath sounds may indicate fluid in small airways or interstitial lung disease (crackles), secretions in moderate and large airways (rhonchi), and airflow obstruction (wheezes).

SPECIAL RESPIRATORY CARE

The hospitalized patient with respiratory disease may require an artificial upper airway, chest tubes, chest physiotherapy, and supervision of mechanical ventilation. In cardiopulmonary arrest, establishing an airway always takes precedence. In a patient with this condition, airway obstruction usually results when the tongue slides back and blocks the posterior pharynx. The head-tilt method or, in suspected or confirmed cervical fracture or arthritis, the jaw-thrust maneuver can immediately push the tongue forward, relieving such obstruction. Endotracheal (ET) intubation and, sometimes, a tracheotomy may be necessary.

CHEST TUBES

An important procedure in patients with respiratory disease is chest tube drainage, which removes air or fluid from the pleural space. This allows the collapsed lung to reexpand to fill the evacuated pleural space. Chest drainage also allows removal of pleural fluid for culture. Chest tubes are commonly used after thoracic surgery, penetrating chest wounds, pleural effusion, and empyema. They’re also used for evacuation of pneumothorax, hydrothorax, or hemothorax. Sometimes chest tubes are used to instill sclerosing drugs into the pleural space to prevent recurrent malignant pleural effusions.

Commonly, the chest tube is placed in the sixth or seventh intercostal space, in the axillary region. Occasionally, in pneumothorax, the tube is placed in the second or third intercostal space, in the midclavicular region.

Follow these guidelines when caring for a patient with a chest tube:

Monitor changes in suction pressure.
Make sure that all connections in the system are tight and secured with tape.
Never clamp the chest tube unless checking for air leaks or changing the drainage system.
Record the amount, color, and consistency of drainage. Watch for signs of shock, such as tachycardia and hypotension, if drainage is excessive.
Encourage the patient to cough and breathe deeply every hour to enhance lung expansion.

Additionally, if a water seal-wet suction system is in place:

Check for fluctuation in the water-seal chamber as the patient breathes. Normal fluctuations of 2” to 4” (about 5 to 10 cm) reflect pressure changes in the pleural space during respiration.
Watch for intermittent bubbling in the waterseal chamber. This bubbling occurs normally when the system is removing air from the pleural cavity. Absence of bubbling indicates that the pleural space has sealed.
Check the water level in the suction-control chamber. If necessary, add sterile water to bring the level to the ordered level.
Check for gentle bubbling in the suction-control chamber, which indicates that the proper suction level has been reached.

If a dry-suction system is in place, check that the rotary dry-suction control dial is turned to the ordered suction mark and verify that the appropriate indicator is present, indicating that the desired amount of suction is applied.

VENTILATOR METHODS

Mechanical ventilators are typically used for CNS problems, hypoxemia, or failure of the normal bellows action provided by the diaphragm and rib cage. Positive-pressure ventilators cause inspiration while increasing tidal volume (VT). The inspiratory cycles of these ventilators may vary in volume, pressure, time, or frequency. For example, a volume-cycled ventilator—the type most commonly used—delivers a preset volume of air each time, regardless of the amount of lung resistance. A pressure-cycled ventilator generates flow until the machine reaches a preset pressure regardless of the volume delivered or the time required to achieve the pressure. A time-cycled ventilator generates flow for a preset amount of time. A highfrequency ventilator uses high respiratory rates and low VT to maintain alveolar ventilation. Positive end-expiratory pressure (PEEP) is used to retain a certain amount of pressure in the lungs at the end of expiration. By keeping small airways and alveoli open with this method, functional residual capacity is increased and oxygenation is improved.

Implement strategies to prevent ventilatorassociated pneumonia and plan to remove the patient from ventilator support as soon as the cause of respiratory failure has resolved (see Preventing ventilator-associated pneumonia). Several weaning methods are used. The patient may be taken off the ventilator and supplied with a T-piece (ET tube O₂ adapter) that provides O₂ and humidification. The patient then breathes spontaneously without the ventilator for gradually increasing periods.

With intermittent mandatory ventilation, the ventilator provides a specific number of breaths, and the patient is able to breathe spontaneously between ventilator breaths. The frequency of ventilator breaths is gradually decreased until the patient can breathe on his own. Pressure support ventilation, in which the patient receives a preset pressure boost with each spontaneous breath, has proved effective. Vital signs, ABG levels, physical findings, and subjective symptoms should be monitored periodically during weaning to assess respiratory status.

Chest physiotherapy

In respiratory conditions marked by excessive accumulation of secretions in the lungs, chest physiotherapy may enhance removal of secretions. Chest physiotherapy includes chest assessment, effective breathing and coughing exercises, postural drainage, percussion, vibration, and evaluation of the therapy’s effectiveness. Before initiating treatment, review X-rays and physical assessment findings to locate areas of secretions.

Deep breathing maintains diaphragm use, increases negative intrathoracic pressure, and promotes venous return; it’s especially important when pain or dressings restrict chest movement. An incentive spirometer can provide positive visual reinforcement to promote deep breathing.
Pursed-lip breathing is used primarily in obstructive disease to slow expiration and prevent small airway collapse. Such breathing slows air through smaller bronchi, maintaining positive pressure and preventing collapse of small airways and resultant air trapping.
Segmental breathing or lateral costal breathing is used after lung resection and for localized disorders. Place your hand over the lung area on the affected side. Instruct the patient to try to push that portion of his chest against your hand on deep inspiration. You should be able to feel this with your hand.
Coughing that’s controlled and staged gradually increases intrathoracic pressure, reducing pain and bronchospasm of explosive coughing. When wound pain prevents effective coughing, splint the wound with a pillow, towel, or your hand during coughing exercises.
Postural drainage uses gravity to drain secretions into larger airways, where they can
be expectorated. This technique is used in the patient with copious or tenacious secretions. Before performing postural drainage, auscultate the patient’s chest and review chest X-rays to determine the best position for maximum drainage. To prevent vomiting, schedule postural drainage at least 1 hour after meals.
Percussion moves air against the chest wall, enhancing the effectiveness of postural drainage by loosening lung secretions. Percussion is contraindicated in severe pain, extreme obesity, cancer that has metastasized to the ribs, crushing chest injuries, bleeding disorders, spontaneous pneumothorax, spinal compression fractures, and in patients with temporary pacemakers.
Vibration can be used with percussion or alone when percussion is contraindicated.
PEEP therapy maintains positive pressure in airways, preventing small airway collapse.

PREVENTION Preventing ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is the leading cause of death among all hospitalacquired infections. VAP also prolongs time spent on the ventilator, length of critical care unit (CCU) stay, and length of hospital stay after discharge from the CCU. Research has shown that the mortality rate due to VAP can be reduced by early recognition of pneumonia and consistent application of evidence-based practices. The Ventilator Bundle is a group of interventions related to ventilator care that, when implemented together, achieve significantly better outcomes than when implemented individually. The key components of the Ventilator Bundle include:

elevating the head of the bed 30 to 45 degrees
interrupting sedation daily and assessing the readiness to extubate
instituting peptic ulcer disease prophylaxis
instituting deep vein thrombosis prophylaxis
providing daily oral care with chlorhexidine

Various other best practices can be combined with the bundle to prevent VAP. They include:

adhering to Centers for Disease Control and Prevention or World Health Organization hand hygiene guidelines to prevent the spread of infection
using noninvasive ventilatory support, such as bilevel positive-airway ventilation instead of endotracheal (ET) intubation and mechanical ventilation, to eliminate the risk of VAP
using the oral route instead of the nasal route for ET intubation to prevent sinusitis
maintaining ET tube cuff pressure at 20 cm or more to prevent aspiration
using a cuffed ET tube with in-line and subglottic suctioning to prevent secretion aspiration
avoiding gastric distention to reduce the risk for aspiration
avoiding unexplained extubation and reintubation to prevent secretion aspiration
minimizing equipment contamination (by removing condensate from ventilator circuits, keeping the circuit closed during removal, changing the ventilator circuit only when visibly soiled or malfunctioning, and disinfecting and storing respiratory equipment properly) to prevent airway contamination
teaching the patient and family about measures to prevent VAP and involving them in monitoring

Before and after chest physiotherapy, auscultate the patient’s lung fields and assess for sputum production to evaluate the effectiveness of therapy.

CONGENITAL AND PEDIATRIC DISORDERS

Respiratory distress syndrome

Respiratory distress syndrome (RDS), also called hyaline membrane disease, is the most common cause of neonatal mortality. In the United States alone, it kills 40,000 neonates every year. RDS occurs in premature neonates and, if untreated, is fatal within 72 hours of birth in up to 14% of neonates weighing less than 5½ lb (2.5 kg). Aggressive management using mechanical ventilation can improve the prognosis, but some surviving neonates may develop some degree of bronchopulmonary dysplasia.

CAUSES AND INCIDENCE

Although airways and alveoli of a neonate’s respiratory system are present by 27 weeks’
gestation, the intercostal muscles are weak and the alveolar capillary system is immature. The preterm neonate with RDS develops widespread alveolar collapse due to a lack of surfactant, a lipoprotein present in alveoli and respiratory bronchioles. Surfactant lowers surface tension and helps prevent alveolar collapse. This surfactant deficiency results in widespread atelectasis, which leads to inadequate alveolar ventilation with shunting of blood through collapsed areas of lung, causing hypoxemia and acidosis.

RDS occurs almost exclusively in neonates born before 37 weeks’ gestation (in 60% of those born before the 28th week). The incidence is greatest in those with birth weights of 1,000 to 1,500 g. Infants of diabetic mothers, those born by cesarean delivery, second-born twins, infants with perinatal asphyxia, and those delivered suddenly after antepartum hemorrhage are more commonly affected.

SIGNS AND SYMPTOMS

Although a neonate with RDS may breathe normally at first, he usually develops rapid, shallow respirations within minutes or hours of birth, with intercostal, subcostal, or sternal retractions; nasal flaring; and audible expiratory grunting. This grunting is a natural compensatory mechanism designed to produce positive end-expiratory pressure (PEEP) and prevent further alveolar collapse.

Severe disease is marked by apnea, bradycardia, and cyanosis (from hypoxemia, left-toright shunting through the foramen ovale, or right-to-left intrapulmonary shunting through atelectatic regions of the lung). Other clinical features include pallor, frothy sputum, and low body temperature as a result of an immature nervous system and the absence of subcutaneous fat.

DIAGNOSIS

Chest X-ray may be normal for the first 6 to 12 hours (in 50% of neonates with RDS), but 24 hours after birth it will show the characteristic ground-glass appearance and air bronchograms.
ABG analysis shows decreased partial pressure of arterial oxygen; normal, decreased, or increased partial pressure of arterial carbon dioxide; and decreased pH (from respiratory or metabolic acidosis or both).
Chest auscultation reveals normal or diminished air entry and crackles (rare in early stages).

When a cesarean birth is necessary before 36 weeks’ gestation, amniocentesis enables the determination of the lecithin/sphingomyelin (L/S) ratio and the presence of phosphatidylglycerol. An L/S ratio of more than 2:1 and the presence of phosphatidylglycerol decrease the likelihood of RDS.

TREATMENT

Treatment of an infant with RDS requires vigorous respiratory support. Warm, humidified, oxygen-enriched gases are administered by oxygen hood or, if such treatment fails, by mechanical ventilation. Severe cases may require mechanical ventilation with PEEP or continuous positive airway pressure (CPAP), administered by nasal prongs or, when necessary, endotracheal (ET) intubation. Special ventilation techniques are now used on the patients refractory to conventional mechanical ventilation. These include highfrequency jet ventilation and high-frequency oscillatory ventilation. Extracorporeal membrane oxygenation is the last choice for ventilation and is only available in certain specialized facilities. Treatment of RDS also includes:

a radiant warmer or isolette for thermoregulation
I.V. fluids and sodium bicarbonate to control acidosis and maintain fluid and electrolyte balance
tube feedings or total parenteral nutrition if the neonate is too weak to eat
administration of surfactant by an ET tube (Studies show that this treatment can prevent or improve the course of RDS as well as reduce mortality.)

SPECIAL CONSIDERATIONS

Neonates with RDS require continual assessment and monitoring in an intensive care nursery.
Closely monitor ABGs as well as fluid intake and output. If the neonate has an umbilical
catheter (arterial or venous), check for arterial hypotension or abnormal central venous pressure. Watch for complications, such as infection, thrombosis, or decreased circulation to the legs. If the neonate has a transcutaneous oxygen monitor, change the site of the lead placement every 2 to 4 hours.
To evaluate his progress, assess skin color, rate and depth of respirations, severity of retractions, nostril flaring, frequency of expiratory grunting, frothing at the lips, and restlessness.
Regularly assess the effectiveness of oxygen or ventilator therapy. Evaluate every change in fraction of inspired oxygen and PEEP or CPAP by monitoring arterial oxygen saturation or ABG levels. Adjust the PEEP or CPAP as indicated, based on findings.
Mechanical ventilation in neonates is usually done in a pressure-limited mode rather than the volume-limited mode used in adults.
When the neonate is on mechanical ventilation, watch carefully for signs of barotrauma (an increase in respiratory distress and subcutaneous emphysema) and accidental disconnection from the ventilator. Check ventilator settings frequently. Be alert for signs of complications of PEEP or CPAP therapy, such as decreased cardiac output, pneumothorax, and pneumomediastinum. Mechanical ventilation increases the risk of infection in the preterm neonate, so preventive measures are essential.
As needed, arrange for follow-up care with a neonatal ophthalmologist to check for retinal damage. Preterm neonates in an oxygen-rich environment are at increased risk for developing ROP.
Teach the parents about their neonate’s condition and, if possible, let them participate in his care (using sterile technique), to encourage normal parent-infant bonding. Advise parents that full recovery may take up to 12 months. When the prognosis is poor, prepare the parents for the neonate’s impending death and offer emotional support.
Help reduce mortality in the neonate with RDS by detecting respiratory distress early. Recognize intercostal retractions and grunting, especially in a premature neonate, as signs of RDS; make sure the neonate receives immediate treatment.

Give corticosteroids to the mother 2 to 3 days before delivery to help the infant’s lungs mature in preterm deliveries.

Sudden infant death syndrome

A medical mystery of early infancy, sudden infant death syndrome (SIDS), also called crib death, is the unexpected, sudden death of an infant or child younger than age 1 year. Reasons for the death remain unexplained even after an autopsy. Typically, parents put the infant to bed and later find him dead, commonly with no indications of a struggle or distress of any kind. Incidence has decreased with the practice of teaching parents to place an infant on his back to sleep.

CAUSES AND INCIDENCE

SIDS is the third leading cause of death in infants between age 1 month and 1 year. It occurs more commonly in winter months. The incidence is higher in males, preterm neonates, and those who sleep on their stomachs or in cribs with soft bedding. Incidence is also higher among neonates born in conditions of poverty and to those who were one of a single multiple birth, such as twins and triplets, and to mothers who smoke, take drugs, or failed to seek prenatal care until late in the pregnancy. SIDS may also result from an abnormality in the control of ventilation that allows carbon dioxide to build up in the blood, thereby causing prolonged apneic periods with profound hypoxemia and serious cardiac arrhythmias. It’s also thought to be associated with problems in sleep arousal.

SIGNS AND SYMPTOMS

Although parents find some victims wedged in crib corners or with blankets wrapped around their heads, autopsies rule out suffocation as the cause of death. Autopsy shows a patent airway, so aspiration of vomitus isn’t the cause of death. Typically, SIDS babies don’t cry out and show no signs of having been disturbed in their sleep. However, their positions or tangled blankets may suggest movement just before death, perhaps due to terminal spasm.

Depending on how long the infant has been dead, a SIDS baby may have a mottled complexion with extreme cyanosis of the lips and fingertips or pooling of blood in the legs and feet that may be mistaken for bruises. Pulse and respirations are absent, and the diaper is wet and full of stool.

DIAGNOSIS

Diagnosis of SIDS requires an autopsy to rule out other causes of death. Characteristic histologic findings on autopsy include small
or normal adrenal glands and petechiae over the visceral surfaces of the pleura, within the thymus, and in the epicardium. Autopsy also reveals extremely well-preserved lymphoid structures and certain pathologic characteristics that suggest chronic hypoxemia such as increased pulmonary artery smooth muscle. Examination also shows edematous, congestive lungs fully expanded in the pleural cavities, liquid (not clotted) blood in the heart, and curd from the stomach inside the trachea.

TREATMENT

If the parents bring the infant to the emergency department (ED), the physician will decide whether to try to resuscitate him. An “aborted SIDS” infant is one who’s found apneic and is successfully resuscitated. Such an infant, or any infant who had a sibling stricken by SIDS, should be tested for infantile apnea. If tests are positive, a home apnea monitor may be recommended. Because the infant usually can’t be resuscitated, however, treatment focuses on providing emotional support for the family.

SPECIAL CONSIDERATIONS

Make sure that parents are present when the child’s death is announced. They may lash out at ED personnel, the babysitter, or anyone else involved in the child’s care—even each other. Stay calm and let them express their feelings. Reassure them that they weren’t to blame.
Let the parents see the baby in a private room. Allow them to express their grief in their own way. Stay in the room with them if appropriate. Offer to call clergy, friends, or relatives.
After the parents and family have recovered from their initial shock, explain the necessity for an autopsy to confirm the diagnosis of SIDS (in some states, this is mandatory). At this time, provide the family with some basic facts about SIDS and encourage them to give their consent for the autopsy. Make sure that they receive the autopsy report promptly.
Find out whether your community has a local counseling and information program for SIDS parents. Participants in such a program will contact the parents, ensure that they receive the autopsy report promptly, put them in touch with a professional counselor, and maintain supportive telephone contact. Also, find out whether there’s a local SIDS parent group; such a group can provide significant emotional support. Contact the National Sudden Infant Death Foundation for information about such local groups.
If your facility’s policy is to assign a public health nurse to the family, she will provide the continuing reassurance and assistance the parents will need.
If the parents decide to have another child, they’ll need information and counseling to help them through the pregnancy and the first year of the new infant’s life.
Infants at high risk for SIDS may be placed on apnea monitoring at home.
All new parents should be informed of the American Academy of Pediatrics’ recommendation that infants be positioned on their back, not on their stomach or side, for sleeping.

Tell parents infants should sleep on a firm mattress and shouldn’t have soft objects in the crib; like stuffed toys and blankets.
Tell parents infants shouldn’t sleep in the same bed as their parents.
Tell parents to give infants pacifiers at bedtime.
Tell parents infants shouldn’t be exposed to secondhand smoke.

Croup

Croup is a severe inflammation and obstruction of the upper airway, occurring as acute laryngotracheobronchitis (most common), laryngitis, and acute spasmodic laryngitis; it must always be distinguished from epiglottiditis. It’s derived from an old German word for “voice box” and refers to swelling around the larynx or vocal cords. Recovery is usually complete.

CAUSES AND INCIDENCE

Croup usually results from a viral infection but can also be caused by bacteria, allergens, and inhaled irritants. Parainfluenza viruses cause 75% of such infections; adenoviruses, respiratory syncytial virus (RSV), influenza, and measles viruses account for the rest.

Croup is a childhood disease affecting more boys than girls (typically between ages 3 months and 5 years) that usually occurs during the winter. Up to 15% of patients have a strong family history of croup.

SIGNS AND SYMPTOMS

The onset of croup usually follows an upper respiratory tract infection. Clinical features include inspiratory stridor, hoarse or muffled vocal sounds, varying degrees of laryngeal obstruction and respiratory distress, and a characteristic sharp, barking, seal-like cough. These symptoms may last only a few hours or persist for a day or two. As it progresses, croup causes inflammatory edema and, possibly, spasm, which can obstruct the upper airway and severely compromise ventilation. (See How croup affects the upper airway, page 100.)

Each form of croup has additional characteristics:

In laryngotracheobronchitis, the symptoms seem to worsen at night. Inflammation causes edema of the bronchi and bronchioles as well as increasingly difficult expiration that frightens the child. Other characteristic features include fever, diffusely decreased breath sounds, expiratory rhonchi, and scattered crackles.

Laryngitis, which results from vocal cord edema, is usually mild and produces no respiratory distress except in infants. Early signs include a sore throat and cough, which, rarely, may progress to marked hoarseness, suprasternal and intercostal retractions, inspiratory stridor, dyspnea, diminished breath sounds, restlessness and, in later stages, severe dyspnea and exhaustion.

Acute spasmodic laryngitis affects a child between ages 1 and 3, particularly one with allergies and a family history of croup. It typically begins with mild to moderate hoarseness and nasal discharge, followed by the characteristic cough and noisy inspiration (that usually awaken the child at night), labored breathing with retractions, rapid pulse, and clammy skin. The child understandably becomes anxious, which may lead to increasing dyspnea and transient cyanosis. These severe symptoms diminish after several hours but reappear in a milder form on the next one or two nights.

DIAGNOSIS

The clinical picture is very characteristic, so the diagnosis should be suspected immediately. When bacterial infection is the cause, throat cultures may identify the organisms and their sensitivity to antibiotics and rule out diphtheria. On a posterior-anterior X-ray of the chest, narrowing of the upper airway (“steeple sign”) may be apparent. Laryngoscopy may reveal inflammation and obstruction in epiglottal and laryngeal areas. In evaluating the patient, assess for foreign body obstruction (a common cause of crouplike cough in a young child) as well as masses and cysts.

TREATMENT

For most children with croup, home care with rest, cool mist humidification during sleep, and antipyretics, such as acetaminophen, relieve symptoms. However, respiratory distress that’s severe or interferes with oral hydration requires hospitalization and parenteral fluid replacement to prevent dehydration. If bacterial infection is the cause, antibiotic therapy is necessary. Oxygen therapy may also be required. Increasing obstruction of the airway requires intubation and mechanical ventilation.

Inhaled racemic epinephrine and corticosteroids may be used to alleviate respiratory distress.

SPECIAL CONSIDERATIONS

Monitor and support respiration, and control fever. Because croup is so frightening to the child and his family, you must also provide support and reassurance.

Carefully monitor cough and breath sounds, hoarseness, severity of retractions, inspiratory stridor, cyanosis, respiratory rate and character (especially prolonged and labored respirations), restlessness, fever, and cardiac rate.
Keep the child as quiet as possible. However, avoid sedation because it may depress respiration. If the patient is an infant, position him in an infant seat or prop him up with a pillow; place an older child in Fowler’s position. If an older child requires a cool mist tent to help him breathe, explain why it’s needed.
Isolate patients suspected of having RSV and parainfluenza infections if possible. Wash your hands carefully before leaving the room, to avoid transmission to other children, particularly infants. Instruct parents and others involved in the care of these children to take similar precautions.
Control fever with sponge baths and antipyretics. Keep a hypothermia blanket on hand for temperatures above 10°F (38.9°C). Watch for seizures in infants and young children with high fevers. Give I.V. antibiotics as ordered.
Relieve sore throat with soothing, waterbased ices, such as fruit sherbet and ice pops. Avoid thicker, milk-based fluids if the child is producing heavy mucus or has great difficulty in swallowing. Apply petroleum jelly or another ointment around the nose and lips to soothe irritation from nasal discharge and mouth breathing.
Maintain a calm, quiet environment and offer reassurance. Explain all procedures and answer any questions.

When croup doesn’t require hospitalization:

Teach the parents effective home care. Suggest the use of a cool mist humidifier (vaporizer). To relieve croupy spells, tell parents to carry the child into the bathroom, shut the door, and turn on the hot water. Breathing in warm, moist air quickly eases an acute spell of croup.
Warn parents that ear infections and pneumonia are complications of croup, which may appear about 5 days after recovery. Stress the importance of immediately reporting earache, productive cough, high fever, or increased shortness of breath.

Give diphtheria, tetanus, and pertussis (DpT); Haemophilus influenzae B (Hib); and measles, mumps, and rubella (MMR) vaccines to children.

Epiglottiditis

Acute epiglottiditis, also known as epiglottitis, is an acute inflammation of the epiglottis that tends to cause airway obstruction. A critical emergency, epiglottiditis can prove fatal unless it’s recognized and treated promptly.

CAUSES AND INCIDENCE

Epiglottiditis usually results from infection with Haemophilus influenzae type B (Hib) and, occasionally, pneumococci and group A streptococci. It typically strikes children between ages 2 and 6 years. (However, immunosuppression can predispose adults to epiglottiditis.) Since the advent of the Hib vaccine, epiglottiditis is becoming more rare.

SIGNS AND SYMPTOMS

Sometimes preceded by an upper respiratory infection, epiglottiditis may rapidly progress to complete upper airway obstruction within 2 to 5 hours. Laryngeal obstruction results from inflammation and edema of the epiglottis. Accompanying symptoms include high fever, stridor, sore throat, dysphagia, irritability, restlessness, and drooling. To relieve severe respiratory distress, the child with epiglottiditis may hyperextend his neck, sit up, and lean forward with his mouth open, tongue protruding, and nostrils flaring as he tries to breathe. He may develop inspiratory retractions and rhonchi.

DIAGNOSIS

In acute epiglottiditis, throat examination reveals a large, edematous, bright red epiglottis.
Such examination should follow lateral neck X-rays and, generally, shouldn’t be performed if the suspected obstruction is great. Special equipment (laryngoscope and endotracheal [ET] tubes) should be available because a tongue blade can cause sudden complete airway obstruction. Trained personnel (such as an anesthesiologist) should be on hand during the throat examination to secure an emergency airway. On the lateral soft tissue X-ray of the neck, a large, thick but indistinct (“thumbprint”) epiglottis will be seen. Blood or throat culture may show H. influenzae or other bacteria.

TREATMENT

A child with acute epiglottiditis and airway obstruction requires emergency hospitalization; he may need emergency ET intubation or a tracheotomy with subsequent monitoring in an intensive care unit. Respiratory distress that interferes with swallowing necessitates parenteral fluid administration to prevent dehydration. A patient with acute epiglottiditis should always receive a complete course of parenteral antibiotics—usually a secondor third-generation cephalosporin. (If the child is allergic to penicillin, a quinolone or sulfa drug may be substituted.) Corticosteroids should be used to decrease swelling of the throat.

SPECIAL CONSIDERATIONS

Keep equipment available in case of sud den complete airway obstruction to secure an airway. Be prepared to assist with intubation or tracheotomy, as necessary.

After a tracheotomy, anticipate the patient’s needs because he won’t be able to cry or call out; provide emotional support. Reassure the patient and his family that the tracheotomy is a short-term intervention (usually from 4 to 7 days). Monitor the patient for rising temperature and pulse rate and hypotension—signs of secondary infection.
The bacterial infection causing epiglottiditis is contagious, and airborne or droplet precautions should be followed. Family members should be screened.

Administer the Hib vaccine to children.

ACUTE DISORDERS

Acute respiratory distress syndrome

A form of noncardiogenic pulmonary edema that causes acute respiratory failure, acute respiratory distress syndrome (ARDS), also called shock lung or adult respiratory distress syndrome, results from increased permeability of the alveolocapillary membrane. Fluid accumulates in the lung interstitium, alveolar spaces, and small airways, causing the lung to stiffen. Effective ventilation is thus impaired, prohibiting adequate oxygenation of pulmonary capillary blood. Severe ARDS can cause intractable and fatal hypoxemia. However, patients who recover may have little or no permanent lung damage. (See Alveolar changes in ARDS, page 102.)

CAUSES AND INCIDENCE

ARDS results from many respiratory and nonrespiratory insults, such as:

aspiration of gastric contents
sepsis (primarily gram-negative), trauma, or oxygen toxicity
shock
viral, bacterial, or fungal pneumonia or microemboli (fat or air emboli or disseminated intravascular coagulation)
drug overdose (barbiturates, glutethimide, or opioids)
blood transfusion
smoke or chemical inhalation (nitrous oxide, chlorine, or ammonia)
hydrocarbon and paraquat ingestion
pancreatitis, uremia, or miliary tuberculosis (rare)
near drowning
severe traumatic injuries, such as head injury or pulmonary contusions

Altered permeability of the alveolocapillary membrane causes fluid to accumulate in the interstitial space. If the pulmonary lymphatic glands can’t remove this fluid, interstitial edema develops. The fluid collects in the peribronchial and peribronchiolar spaces, producing bronchiolar narrowing. Hypoxemia occurs as a result of fluid accumulation in alveoli and subsequent alveolar collapse, causing the shunting of blood through nonventilated lung regions. In addition, alveolar collapse causes a dramatic increase in lung compliance, which makes it more difficult to achieve adequate ventilation.

PATHOPHYSIOLOGY Alveolar changes in ARDS

The alveoli undergo major changes in each phase of ARDS.

Phase 1

In phase 1, injury reduces normal blood flow to the lungs. Platelets aggregate and release histamine (H), serotonin (S), and bradykinin (B).

Phase 2

In phase 2, those substances— especially histamine—inflame and damage the alveolocapillary membrane, increasing capillary permeability. Fluids then shift into the interstitial

Phase 3

In phase 3, as capillary permeability increases, proteins and fluids leak out, increasing interstitial osmotic pressure and causing pulmonary edema.

Phase 4

In phase 4, decreased blood flow and fluids in the alveoli damage surfactant and impair the cell’s ability to produce more. As a result, alveoli collapse, impeding gas exchange and decreasing lung compliance.

Phase 5

In phase 5, sufficient oxygen can’t cross the alveolocapillary membrane, but carbon dioxide (CO₂) can and is lost with every exhalation. Oxygen (O₂) and CO₂ levels decrease in the blood.

Phase 6

In phase 6, pulmonary edema worsens, inflammation leads to fibrosis, and gas exchange is further impeded.

ARDS affects 10 to 14 people per 100,000, with a mortality rate of 36% to 52%.

SIGNS AND SYMPTOMS

ARDS initially produces rapid, shallow breathing and dyspnea within hours to days of the initial injury (sometimes after the patient’s condition appears to have stabilized). Hypoxemia develops, causing an increased drive for ventilation. Because of the effort required to expand the stiff lung, intercostal and suprasternal retractions result. Fluid accumulation produces crackles and rhonchi; worsening hypoxemia causes restlessness, apprehension, mental sluggishness, motor dysfunction, and tachycardia (possibly with transient increased arterial blood pressure).

Severe ARDS causes overwhelming hypoxemia. If uncorrected, this results in hypotension, decreasing urine output, respiratory and metabolic acidosis, and eventually ventricular fibrillation or standstill.

DIAGNOSIS

On room air, arterial blood gas (ABG) analysis initially shows decreased partial pressure of arterial oxygen (Pao₂; less than 60 mm Hg) and partial pressure of arterial carbon dioxide (Paco₂; less than 35 mm Hg). The resulting pH usually reflects respiratory alkalosis. As ARDS becomes more severe, ABG analysis shows respiratory acidosis (increasing Paco₂ [more than 45 mm Hg]), metabolic acidosis (decreasing bicarbonate [less than 22 mEq/L]), and a decreasing Pao₂ despite oxygen therapy.

Other diagnostic tests include the following:

Pulmonary artery catheterization helps identify the cause of pulmonary edema (cardiac versus noncardiac) by evaluating pulmonary artery wedge pressure; allows collection of pulmonary artery blood, which shows decreased oxygen saturation, reflecting tissue hypoxia; measures pulmonary artery pressure; measures cardiac output by thermodilution techniques; and provides information to allow calculation of the percentage of blood shunted through the lungs.
Serial chest X-rays initially show bilateral infiltrates. In later stages, a ground-glass appearance and eventually (as hypoxemia becomes irreversible), “whiteouts” of both lung fields are apparent. Medical personnel can differentiate ARDS from heart failure by noting the following on serial chest X-rays:

normal cardiac silhouette
diffuse bilateral infiltrates that tend to be more peripheral and patchy, as opposed to the usual perihilar “bat wing” appearance of cardiogenic pulmonary edema
fewer pleural effusions

Differential diagnosis must rule out cardiogenic pulmonary edema, pulmonary vasculitis, and diffuse pulmonary hemorrhage. To establish the etiology, laboratory work should include sputum Gram stain, culture and sensitivity tests, and blood cultures to detect infections; a toxicology screen for drug ingestion; and, when pancreatitis is a consideration, a serum amylase determination.

TREATMENT

When possible, treatment is designed to correct the underlying cause of ARDS as well as to prevent progression and the potentially fatal complications of hypoxemia and respiratory acidosis. Supportive medical care consists of administering humidified oxygen with continuous positive airway pressure. Hypoxemia that doesn’t respond adequately to these measures requires ventilatory support with intubation, volume ventilation, and positive end-expiratory pressure (PEEP). Other supportive measures include fluid restriction, diuretics, and correction of electrolyte and acid-base abnormalities.

When ARDS requires mechanical ventilation, sedatives, opioids, or neuromuscular blocking agents may be ordered to optimize ventilation. Treatment to reverse severe metabolic acidosis with sodium bicarbonate may be necessary, although in severe cases this may worsen the acidosis if carbon dioxide can’t be cleared adequately. Use of fluids and vasopressors may be required to maintain blood pressure. Infections require appropriate anti-infective therapy.

SPECIAL CONSIDERATIONS

ARDS requires careful monitoring and supportive care.

Frequently assess the patient’s respiratory status. Be alert for retractions on inspiration. Note the rate, rhythm, and depth of respirations; watch for dyspnea and the use of accessory muscles of respiration. On auscultation, listen for adventitious or diminished breath sounds. Check for clear, frothy sputum, which may indicate pulmonary edema.
Observe and document the hypoxemic patient’s neurologic status (level of consciousness and mental status).
Maintain a patent airway by suctioning, using sterile, nontraumatic technique. Ensure adequate humidification to help liquefy tenacious secretions.
Closely monitor heart rate and blood pressure. Watch for arrhythmias that may result from hypoxemia, acid-base disturbances, or electrolyte imbalance. With pulmonary artery catheterization, know the desired pressure levels. Check readings often and watch for decreasing mixed venous oxygen saturation.
Monitor serum electrolytes and correct imbalances. Measure intake and output; weigh the patient daily.
Check ventilator settings frequently, and empty condensate from tubing promptly to ensure maximum oxygen delivery. Monitor ABG studies and pulse oximetry. The patient with severe hypoxemia may need controlled mechanical ventilation with positive pressure. Give sedatives, as needed, to reduce restlessness.
Because PEEP may decrease cardiac output, check for hypotension, tachycardia, and decreased urine output. Suction only as needed to maintain PEEP or use an in-line suctioning apparatus. Reposition the patient often and record an increase in secretions, temperature, or hypotension that may indicate a deteriorating condition. Monitor peak pressures during ventilation.
Because of stiff, noncompliant lungs, the patient is at high risk for barotrauma (pneumothorax), evidenced by increased peak pressures, decreased breath sounds on one side, and restlessness.
Monitor nutrition, maintain joint mobility, and prevent skin breakdown. Accurately record calorie intake. Give tube feedings and parenteral nutrition, as ordered. Perform passive rangeof-motion exercises or help the patient perform active exercises, if possible. Provide meticulous skin care. Plan patient care to allow periods of uninterrupted sleep.
Provide emotional support. Warn the family and the patient who’s recovering from ARDS that recovery will take some time and that he will feel weak for a while.
Watch for and immediately report all respiratory changes in the patient with injuries that may adversely affect the lungs (especially during the 2- to 3-day period after the injury, when the patient may appear to be improving).

Acute respiratory failure in COPD

In patients with essentially normal lung tissue, acute respiratory failure (ARF) usually means partial pressure of arterial carbon dioxide (Paco₂) above 50 mm Hg and partial pressure of arterial oxygen (Pao₂) below 50 mm Hg. These limits, however, don’t apply to patients with chronic obstructive pulmonary disease (COPD), who usually have a consistently high Paco₂ and low Pao₂. In patients with COPD, only acute deterioration in arterial blood gas (ABG) values, with corresponding clinical deterioration, indicates ARF.

CAUSES AND INCIDENCE

ARF may develop in patients with COPD as a result of any condition that increases the work of breathing and decreases the respiratory drive. Such conditions include respiratory tract infection (such as bronchitis or pneumonia). The most common precipitating factor is bronchospasm, or accumulating secretions secondary to cough suppression. Other causes of ARF in COPD include the following:

Central nervous system (CNS) depression— head trauma or injudicious use of sedatives, opioids, tranquilizers, or oxygen (O₂)
Cardiovascular disorders—myocardial infarction, heart failure, or pulmonary emboli
Airway irritants—smoke or fumes
Endocrine and metabolic disorders— myxedema or metabolic alkalosis
Thoracic abnormalities—chest trauma, pneumothorax, or thoracic or abdominal surgery

The incidence of ARF increases markedly with age and is especially high among people age 65 and older.

SIGNS AND SYMPTOMS

In patients who have COPD with ARF, increased ventilation-perfusion mismatch and reduced alveolar ventilation decrease Pao₂ (hypoxemia) and increase Paco₂ (hypercapnia). This rise in carbon dioxide (CO₂) lowers the pH. The resulting hypoxemia and acidemia affect all body organs, especially the CNS and the respiratory and cardiovascular systems.

Specific symptoms vary with the underlying cause of ARF but may include these systems:

Respiratory—Rate may be increased, decreased, or normal depending on the cause; respirations may be shallow, deep, or alternate between the two; and air hunger may occur. Cyanosis may or may not be present, depending on the hemoglobin (Hb) level and arterial oxygenation. Auscultation of the chest may reveal crackles, rhonchi, wheezing, or diminished breath sounds.
CNS—When hypoxemia and hypercapnia occur, the patient may show evidence of restlessness, confusion, loss of concentration, irritability, tremulousness, diminished tendon reflexes, and papilledema; he may slip into a coma.
Cardiovascular—Tachycardia, with increased cardiac output and mildly elevated blood pressure secondary to adrenal release of catecholamine, occurs early in response to low Pao₂. With myocardial hypoxia, arrhythmias may develop. Pulmonary hypertension, secondary to pulmonary capillary vasoconstriction, may cause increased pressures on the right side of the heart, jugular vein distention, an enlarged liver, and peripheral edema. Stresses on the heart may precipitate cardiac failure.

DIAGNOSIS

Progressive deterioration in ABG levels and pH, when compared with the patient’s “normal” values, strongly suggests ARF in COPD. (In patients with essentially normal lung tissue, pH below 7.35 usually indicates ARF, but patients with
COPD display an even greater deviation from this normal value, as they do with Paco₂ and Pao₂.)

Other supporting findings include:

Bicarbonate—Increased levels indicate metabolic alkalosis or reflect metabolic compensation for chronic respiratory acidosis.
Hematocrit (HCT) and Hb—Abnormally low levels may be due to blood loss, indicating decreased oxygen-carrying capacity. Elevated levels may occur with chronic hypoxemia.
Serum electrolytes—Hypokalemia and hypochloremia may result from diuretic and corticosteroid therapies used to treat ARF.
White blood cell count—Count is elevated if ARF is due to bacterial infection; Gram stain and sputum culture can identify pathogens.
Chest X-ray—Findings identify pulmonary pathologic conditions, such as emphysema, atelectasis, lesions, pneumothorax, infiltrates, or effusions.
Electrocardiogram—Arrhythmias commonly suggest cor pulmonale and myocardial hypoxia.

TREATMENT

ARF in patients with COPD is an emergency that requires cautious O₂ therapy (using nasal prongs or Venturi mask) to raise the Pao₂. In patients with chronic hypercapnia, O₂ therapy can cause hypoventilation by increasing Paco₂ and decreasing the respiratory drive, necessitating mechanical ventilation. The minimum fraction of inspired air (FIO₂) required to maintain ventilation or O₂ saturation greater than 85% to 90% should be used. If significant uncompensated respiratory acidosis or unrefractory hypoxemia exists, mechanical ventilation (through an endotracheal [ET] or a tracheostomy tube) or noninvasive ventilation (with a face or nose mask) may be necessary. Treatment routinely includes antibiotics for infection, bronchodilators, and possibly steroids.

SPECIAL CONSIDERATIONS

Because most patients with ARF are treated in an intensive care unit, orient them to the environment, procedures, and routines to minimize their anxiety.
To reverse hypoxemia, administer O₂ at appropriate concentrations to maintain Pao₂ at a minimum of 50 to 60 mm Hg. Patients with COPD usually require only small amounts of supplemental O₂. Watch for a positive response— such as improvement in the patient’s breathing, color, and ABG levels.
Maintain a patent airway. If the patient is retaining CO₂, encourage him to cough and to breathe deeply. Teach him to use pursed-lip and diaphragmatic breathing to control dyspnea. If the patient is alert, have him use an incentive spirometer; if he’s intubated and lethargic, turn him every 1 to 2 hours. Use postural drainage and chest physiotherapy to help clear secretions.
In an intubated patient, suction the trachea as needed after hyperoxygenation. Observe for a change in quantity, consistency, and color of sputum. Provide humidification to liquefy secretions.
Observe the patient closely for respiratory arrest. Auscultate for chest sounds. Monitor ABG levels and report any changes immediately.
Check the cardiac monitor for arrhythmias. If the patient requires mechanical ventilation:
Check ventilator settings, cuff pressures, and ABG values often because the FIO₂ setting depends on ABG levels. Draw specimens for ABG analysis 20 to 30 minutes after every FIO₂ change or oximetry check.
Prevent infection by performing hand hygiene and using sterile technique while suctioning.
Stress ulcers are common in the intubated patient. Check gastric secretions for evidence of bleeding if the patient has a nasogastric tube or if he complains of epigastric tenderness, nausea, or vomiting. Monitor Hb level and HCT; check all stools for occult blood. Administer antacids, histamine-2 receptor antagonists, or sucralfate, as ordered.

Prevent tracheal erosion, which can result from artificial airway cuffoverinflation. Use the minimal leak technique and a cuffed tube with high residual volume (low-pressure cuff), a foam cuff, or a pressure-regulating valve on the cuff.
To prevent oral or vocal cord trauma, make sure that the ET tube is positioned midline or moved carefully from side to side every 8 hours.
To prevent nasal necrosis, keep the nasotracheal tube midline within the patient’s nostrils and provide good hygiene. Loosen the tape periodically to prevent skin breakdown. Avoid excessive movement of any tubes; make sure the ventilator tubing is adequately supported.

Pulmonary edema

Pulmonary edema is the accumulation of fluid in the extravascular spaces of the lung. In cardiogenic pulmonary edema, fluid accumulation results from elevations in pulmonary venous
and capillary hydrostatic pressures. A common complication of cardiac disorders, pulmonary edema can occur as a chronic condition or it can develop quickly to cause death. (See How pulmonary edema develops.)

CAUSES AND INCIDENCE

Pulmonary edema usually results from left-sided heart failure due to arteriosclerotic, hypertensive, cardiomyopathic, or valvular cardiac disease. In such disorders, the compromised left ventricle is unable to maintain adequate cardiac output; increased pressures are transmitted to the left atrium, pulmonary veins, and pulmonary capillary bed. This increased pulmonary capillary hydrostatic force promotes transudation of intravascular fluids into the pulmonary interstitium, decreasing lung compliance and interfering with gas exchange. Other factors that may predispose the patient to pulmonary edema include:

excessive infusion of I.V. fluids
decreased serum colloid osmotic pressure as a result of nephrosis, protein-losing enteropathy, extensive burns, hepatic disease, or nutritional deficiency
impaired lung lymphatic drainage from Hodgkin’s lymphoma or obliterative lymphangitis after radiation
mitral stenosis, which impairs left atrial emptying
pulmonary veno-occlusive disease
lung damage from a severe infection or exposure to poisonous gas
kidney failure

SIGNS AND SYMPTOMS

The early symptoms of pulmonary edema reflect interstitial fluid accumulation and diminished lung compliance: dyspnea on exertion, paroxysmal nocturnal dyspnea, orthopnea, and coughing. Clinical features include tachycardia, tachypnea, dependent crackles, jugular vein distention, and a diastolic (S₃) gallop. With severe pulmonary edema, the alveoli and bronchioles may fill with fluid and intensify the early symptoms. Respiration becomes labored and rapid, with more diffuse crackles and coughing that produces frothy, bloody sputum. Tachycardia increases, and arrhythmias may occur. Skin becomes cold, clammy, diaphoretic, and cyanotic. Blood pressure falls and the pulse becomes thready as cardiac output falls.

Symptoms of severe heart failure with pulmonary edema may also include signs of hypoxemia, such as anxiety, restlessness, and changes in the patient’s level of consciousness.

DIAGNOSIS

Clinical features of pulmonary edema permit a working diagnosis. Arterial blood gas (ABG) analysis usually shows hypoxia; the partial pressure of arterial carbon dioxide is variable. Profound respiratory alkalosis and acidosis may occur. Chest X-ray shows diffuse haziness of the lung fields and, commonly, cardiomegaly and pleural effusions. Ultrasound (echocardiogram) may show weak heart muscle, leaking or narrow heart valves, and fluid surrounding the heart. Pulmonary artery catheterization helps identify left-sided heart failure by showing elevated pulmonary artery wedge pressures. This helps to rule out acute respiratory distress syndrome—in which pulmonary wedge pressure is usually normal.

TREATMENT

Treatment measures for pulmonary edema are designed to reduce extravascular fluid, improve gas exchange and myocardial function and, if possible, correct any underlying pathologic conditions.

Administration of high concentrations of oxygen by a cannula, a face mask and, if the patient fails to maintain an acceptable partial pressure of arterial oxygen level, assisted ventilation improves oxygen delivery to the tissues and usually improves acid-base disturbances. Diuretics—furosemide and bumetanide, for example—promote diuresis, which reduces extravascular fluid.

Treatment of heart failure includes angiotensin-converting enzyme inhibitors, diuretics, inotropic drugs such as digoxin, antiarrhythmic agents, beta-adrenergic blockers, and human B-type natriuretic peptide. Vasodilator drugs, such as nitroprusside, may be used to reduce preload and afterload in acute episodes of pulmonary edema.

Morphine is used to reduce anxiety and dyspnea as well as dilate the systemic venous bed, promoting blood flow from pulmonary circulation to the periphery.

SPECIAL CONSIDERATIONS

Carefully monitor the vulnerable patient for early signs of pulmonary edema, especially tachypnea, tachycardia, and abnormal breath sounds. Report any abnormalities. Assess for peripheral edema and weight gain, which may also indicate that fluid is accumulating in tissue.
Administer oxygen as ordered.
Monitor the patient’s vital signs every 15 to 30 minutes while administering nitroprusside in dextrose 5% in water by I.V. drip. Protect the nitroprusside solution from light by wrapping the bottle or bag with aluminum foil, and discard unused solution after 4 hours. Watch for arrhythmias in the patient receiving cardiac glycosides and for marked respiratory depression in the patient receiving morphine.
Assess the patient’s condition frequently, and record response to treatment. Monitor ABG levels, oral and I.V. fluid intake, urine output and,
in the patient with a pulmonary artery catheter, pulmonary end-diastolic and wedge pressures. Check the cardiac monitor often. Report changes immediately.
Carefully record the time and amount of morphine given.
Reassure the patient, who will be anxious due to hypoxia and respiratory distress. Explain all procedures. Provide emotional support to his family as well.

Cor pulmonale

The World Health Organization defines chronic cor pulmonale as “hypertrophy of the right ventricle resulting from diseases affecting the function or the structure of the lungs, except when these pulmonary alterations are the result of diseases that primarily affect the left side of the heart or of congenital heart disease.” Invariably, cor pulmonale follows some disorder of the lungs, pulmonary vessels, chest wall, or respiratory control center. For instance, chronic obstructive pulmonary disease (COPD) produces pulmonary hypertension, which leads to right ventricular hypertrophy and right-sided heart failure. Because cor pulmonale generally occurs late during the course of COPD and other irreversible diseases, the prognosis is generally poor.

CAUSES AND INCIDENCE

Approximately 85% of patients with cor pulmonale have COPD, and 25% of patients with COPD eventually develop cor pulmonale.

Other respiratory disorders that produce cor pulmonale include:

obstructive lung diseases—for example, bronchiectasis and cystic fibrosis
restrictive lung diseases—for example, pneumoconiosis, interstitial pneumonitis, scleroderma, and sarcoidosis
loss of lung tissue after extensive lung surgery
congenital cardiac shunts—such as a ventricular septal defect
pulmonary vascular diseases—for example, recurrent thromboembolism, primary pulmonary hypertension, schistosomiasis, and pulmonary vasculitis
respiratory insufficiency without pulmonary disease—for example, in chest wall disorders such as kyphoscoliosis, neuromuscular incompetence due to muscular dystrophy and amyotrophic lateral sclerosis, polymyositis, and spinal cord lesions above C6
obesity hypoventilation syndrome (pickwickian syndrome) and upper airway obstruction
living at high altitudes (chronic mountain sickness)

Pulmonary capillary destruction and pulmonary vasoconstriction (usually secondary to hypoxia) reduce the area of the pulmonary vascular bed. Thus, pulmonary vascular resistance is increased, causing pulmonary hypertension. To compensate for the extra work needed to force blood through the lungs, the right ventricle dilates and hypertrophies. In response to low oxygen content, the bone marrow produces more red blood cells (RBCs), causing erythrocytosis. When the hematocrit (HCT) exceeds 55%, blood viscosity increases, which further aggravates pulmonary hypertension and increases the hemodynamic load on the right ventricle. Right-sided heart failure is the result.

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Tags: Professional Guide to Diseases

Aug 27, 2016 | Posted by drzezo in PATHOLOGY & LABORATORY MEDICINE | Comments Off

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