, Alan A. Aitkenhead2 and Brendon J. Coventry3
(1)
Department of Anaesthesia, Royal Adelaide Hospital, University of Adelaide, Adelaide, Australia
(2)
Department of Anesthesia, Nottingham University, Nottingham, UK
(3)
Discipline of Surgery, Royal Adelaide Hospital, University of Adelaide, Adelaide, Australia
Abstract
Anesthesia has defined the capability of surgical practice within a very short time frame and has grown from a mere adjunct of surgery into a separate specialty which has significantly advanced medical practice. We now have the commonplace luxury of relatively painless surgery on a usually cooperative patient, whether under general, regional, or local anesthesia or some combination of these. Even major feats of surgery that would have been impossible in the past can be performed, and surgery continues to advance alongside that of anesthesia in a symbiotic process. While not aiming to be fully comprehensive, this chapter explains and discusses many important aspects and principles of anesthesia that are essential for surgical practice.
General Perspective and Overview
The relative risks and complications increase proportionately according to preexisting comorbidities of the patient and the length and difficulty of anesthesia and surgery. The age of the patient is often more related to the previously mentioned issues, but in itself increased age (or very premature age) carries risk of mortality. Loose teeth, difficult airways, poor access, emergency procedures, and repeated intubation attempts all carry some degree of increased risk of airway trauma.
Anesthetists argue the benefits of one approach over the other, but data are unclear to demonstrate differences in terms of the observed or reported complications in many cases.
Possible reduction in the risk of misunderstandings over complications or consequences from anesthesia might be achieved by:
Good explanation of the risks, aims, benefits, and limitations of the procedure(s)
Careful planning considering the anatomy, approach, alternatives, and method
Avoiding likely problems
Adequate clinical follow-up (especially if problems arise)
With these factors and facts in mind, the information given in this chapter must be appropriately and discernibly interpreted and used.
Important Note: It should be emphasized that the risks and frequencies that are given here represent derived figures. These are often representative of a number of studies, which include different patients with differing comorbidities. As such, the risks of complications in lower or higher risk patients may lie outside these estimated ranges, and individual clinical judgement is required as to the expected risks communicated to the patient and staff, or for other purposes. The range of risks is also derived from experience and the literature; while risks outside this range may exist, certain risks may be reduced or absent due to certain variations of procedures or approaches. It is recognized that different patients, practitioners, institutions, regions, and countries may vary in their requirements and recommendations.
For risks and complications associated with anesthesia assessment, monitoring, or safety, see Chapters 3 and 8, or the relevant volume or chapter.
Introduction
Historically, surgical procedures until the mid-nineteenth century were initially performed without anesthesia of any type. Inevitably, severe pain was the limiting factor, with the consequence of significant restriction in the type, timing, and extent of surgery possible. Pain caused significant movement and muscle spasm, which severely limited operative ease and duration. Early battlefield surgeons noted the relative ease of performing surgery on the unconscious patient and sought this “ideal” state for elective surgery in civilian life. Early anesthetics in Western cultures included the use of cold compresses applied to the region preoperatively, herbal preparations to “numb” nerves, induced concussion, alcohol, opium extracts, and other sedatives and in many Eastern cultures, hypnosis, acupuncture, opiates, deep meditation, and other herbal medicines. Even as recently as the 1800s, alcohol and a “good dose of courage” comprised the sole anesthetic used by naval and military surgeons before amputation of limbs. “Biting the bullet” offered diversionary advantage from pain for the patient while surgery was being performed. However, patient movement and maintenance of a satisfactory airway with sufficient oxygenation remained significant problems using any available method involving central nervous system depression.
During the twentieth century there were massive and rapid advances in general, regional, and local anesthetic methods, ventilation, drugs, and intensive care support, and this has continued into the twenty-first century. Surgeons initially performed the basic initial forms of “anesthesia,” but this developed into an art and clinical science as the present day specialty of anesthesia or anesthesiology. Enormous improvements and refinements in anesthesia, patient safety, and comfort have permitted much more complex surgical procedures, many now undertaken as day-case surgery. In reality, these have provided some dramatic reductions in surgical complications, risks and consequences, and notable economic advantages for healthcare systems.
These advances will extend even further into this century as electronic, chemical, robotic, and nanotechnology developments become a reality.
The term “anaesthesia” (also anesthesia) means without feeling, derived from the Greek words an, without, and aesthesia, feeling (normal ability to experience sensation, perception, or sensitivity). The precise definition of what “anesthesia” means continues to evolve as different agents and techniques are being developed.
Assessment of the complications and overall risk of general anesthesia, or anesthesia of any type, is not always straightforward. Effectively it is the compounded risk of:
1.
The administration of general (or other) anesthetic and associated agents
2.
The surgery being performed
3.
The comorbidities of the individual patient
These may not be easily separable. For this reason, different definitions of anesthetic morbidity and mortality exist.
Whether the problem was classified as due to anesthesia alone as the primary cause or anesthesia as either the primary or an associated cause is an important consideration. The time frame is important also. For example, general anesthesia might be assumed to be from the time of “induction” to regaining “full awareness and airway control.” It may include the period from entry to departure from theatre. However, it might also include preoperative sedation and postoperative recovery back to the ward. It might also include an intensive care or surgical high-dependency period, where anesthetic effects might still be operational. Coroners often use “death within 24 h of an anesthetic.” All of these time periods have been used in calculations of “anesthetic” or “anesthesia-related” complications. The term perioperative mortality is also often used, but again this varies appreciably in reports. It can mean operative death, combined pre-/intra-/immediate postanesthetic mortality, 24 or 48 h mortality from induction, or even 30-day hospitalization mortality. The denominator and its accuracy are important also, as some studies use per 100,000 of population and others use per 100,000 of anesthetics delivered or surgical procedures performed. These and other factors can account for reported mortality (and morbidity) differences between studies.
There is an increasing awareness that pre- and postoperative factors are closely, if not inextricably, linked to the intraoperative factors (selection of mode(s) of anesthesia, duration, temperature control, surgical factors, events, etc.) and that these might more usefully be considered collectively in measuring and improving outcomes.
Current Anesthesia or Anesthesiology
Types of Anesthesia
The main types of anesthesia are as follows:
General Anesthesia
Full and complete depression of consciousness by gaseous or intravenous agents is usually termed general anesthesia, whereas “partial” or “light” depression of consciousness is often termed sedation. States of consciousness between these levels are obtainable, if required, and occur during induction of and recovery from anesthesia.
Regional Anesthesia
Epidural anesthesia is instillation of local anesthetic, narcotic, or other agents into the epidural space around the spinal cord in order to create anesthesia of the area below or around the level of injection.
Spinal anesthesia is instillation of local anesthetic, narcotic, or other agents into the subarachnoid (containing cerebrospinal fluid, CSF) space around the spinal cord in order to create anesthesia of the area below or around the level of injection.
Nerve blocks are instillation of local anesthetic with or without adrenaline (epinephrine) or close to peripheral nerves (e.g., sciatic, popliteal, anterior/posterior tibial, orbital, trigeminal, axillary, median, ulnar, intercostal, femoral, ankle, digital) in order to block conduction in those nerves.
Local Anesthesia
Local anesthesia is injection of local anesthetic agents intradermally or subcutaneously, intramuscularly, intratendinously, intra-articularly, or similarly into tissues or spaces to directly block nerves, causing local anesthesia of the area for surgery and/or pain relief.
Combinations of the types of anesthesia, it should be noted, are not infrequent, for example, general anesthesia followed by local anesthesia, to maximize surgical ease, pain relief, and comfort for the patient. Indeed, such combinations are increasingly used.
General Anesthesia
History
Historically, use of gaseous agents for anesthesia was attempted by a number of dentists in the UK, USA, and Europe in the early 1820s, with experimentation using carbon dioxide-induced coma and then the use of nitrous oxide. Diethyl ether, although discovered in 1540, was not used for inhalational induction of anesthesia until about 1842 when a dentist, William Clarke, used it for teeth extractions, and soon afterwards, Crawford Long used inhaled ether for excision of a neck cyst, although this went unreported. In October 1846, at the Massachusetts General Hospital in Boston, USA, William Morton gave the first public demonstration of the use of ether anesthesia to Gilbert Abbott for excision of a neck tumor, and Oliver Holmes proposed the name anesthesia for the ether induction procedure, which gained rapid popularity across Europe, as well as the USA. In Britain, chloroform was used by James Simpson in 1847 for anesthesia, and this was associated with less problematic vomiting and flammability than with ether. Chloroform gained Royal approval in 1853 when John Snow successfully administered anesthesia to Queen Victoria for the birth of Prince Leopold. For many years, both ether and chloroform were used for induction of general anesthesia, with nitrous oxide gradually regaining popularity as an additive agent. The main problem was control of the amount of gas inhaled/delivered to maintain uniform and safe depth of anesthesia. Dr. H.E.G. Boyle developed a machine in 1917 to deliver mixed gases, including oxygen, and this was later modified to allow extraction of CO2 using soda lime. This method remained the standard approach to induction of anesthesia for many years. Airway management then took another leap forward with the development of the cuffed endotracheal tube and a range of ventilation devices. The cuffed tube permitted positive-pressure ventilation and improved airway protection. Later refinements have included double-lumen endotracheal tubes, which permit selective deflation of one lung during thoracic surgical procedures, and more recently the inflatable laryngeal mask airway (LMA) by Dr. Archie Brain. Muscle relaxant agents were used to permit adequate muscle relaxation. Analgesics were utilized intraoperatively to provide better pain relief. The development of effective and safe anesthetic techniques and the training of specialist anesthetists have enabled a massive expansion in the range and complexity of surgical procedures.
General Anesthetic Procedures
The main elements of modern general anesthesia are adequate:
1.
General anesthesia (general ± regional or local)
2.
Analgesia
3.
Muscle relaxation (this is less important for superficial surgery)
4.
Anti-emesis
5.
Monitoring of particularly BP, oxygen saturation, and end-tidal CO2 concentration
General Anesthesia
Rapid sequence induction of general anesthesia is a technique where pressure is placed directly over the cricoid cartilage to push it backwards, blocking off the esophagus against the cervical vertebral bodies, thereby limiting the risk of regurgitation of gastric contents and aspiration into the respiratory system. It is also called crash induction and is used most frequently in the unprepared, non-fasted patient in the emergency setting for safer airway, intensive care, or surgical management. It is always used for obstetric patients, in whom the risk of reflux and aspiration is increased.
A period of preoxygenation prior to general anesthetic induction has become standard practice for most anesthetists, because it achieves a higher concentration of oxygen in the lungs and offers a greater reserve of oxygen in case of difficulty in achieving control of the airway. Maximal hemoglobin O2 loading and higher dissolved O2 levels allow a greater time before desaturation and oxygen depletion. This may afford a significant advantage during intubation by trainees, or if a difficult intubation is encountered unexpectedly.
Endotracheal Intubation
In 1543, the Italian anatomist and surgeon Andreas Vesalius reported endotracheal intubation of an animal with life-sustaining artificial respiration, but this went virtually unnoticed until the German surgeon Friedrich Trendelenburg reported the first tracheal intubation through a tracheostomy in 1869. However, the first human oral intubation appears to have been performed in 1878 by Macewen, a Glasgow surgeon. The finer historical details of tracheal intubation and tracheostomy appear unclear but were mentioned and illustrated as far back as ancient Greece, Rome, and Egypt. After the First World War, Magill and Macintosh (subsequently professors of anesthesia in Cardiff and (Nuffield) Oxford) refined endotracheal intubation, also devising the Macintosh spatula with a curved blade for direct laryngoscopy, Magill forceps, Magill introducer, and the curved form of the endotracheal tube.
Indications for nasal intubation include dental or oral surgery; oral injury; endolaryngeal, tracheal, or esophageal surgery; oral obstruction from jaw fractures; jaw wiring; and oral tumor obstruction. Nasal intubation may be used also in patients with reduced cervical spine mobility (e.g., fracture instability, arthritis, fusion), when intubation may be achieved by fiberoptic endoscopy.
Modern endotracheal (ET) tubes are streamlined devices with collapsible, slim cuffs that permit good visualization of the larynx during the procedure. A variety of introducing bougies are available for “railroading” the ET tube through the larynx into the trachea. In difficult cases, fiberoptic laryngoscopy, using a narrow flexible or rigid endoscope device, can be used to locate the larynx and direct the ET tube in the correct direction. Longer-term effects of the ET tube remaining in place in the intensive care setting include ulceration of the trachea, bleeding, stenosis, and even perforation. These complications are usually avoided by ET tube changes, good care, low seal pressures, and tracheostomy. Laryngeal masks were developed to avoid the need for endotracheal intubation, reduce trauma, yet protect the airway from aspiration. These devices are placed over the larynx, within the pharynx, and are, in effect, an oropharyngeal tube with an inflatable cuff to secure the airway in place, creating a seal. These have replaced the ET tube in many settings, especially for peripheral, short elective procedures as they provide a clear, protected airway, without passing through the vocal cords. Problems with laryngeal masks include failure to adequately seal, dislodgement, aspiration around the cuff, failure to adequately suck secreted material out before removal, and unexpected cuff deflation.
Some Adverse Effects Associated with Laryngoscopy and Endotracheal Intubation
Injury to lips and teeth
Injury to tongue, hard palate, gums, and pharynx
Injury to larynx
Hoarse voice
Sore throat
Tracheal injury
Esophageal intubation
Tube retraction
Tube distal migration
Air leakage
Cervical spine injury
Nasal injury (with nasal intubation)
Base of skull, meningeal injury (nasal method especially with basal skull fracture)
Inhalation of foreign material (teeth, plates, plastic, etc.)
Vomiting and aspiration pneumonitis
Airway bleeding
Some Adverse Effects Associated with Intubation and Ventilation
Air leakage
Pneumothorax
Surgical emphysema
Pulmonary edema
Inhalation of foreign material (teeth, plates, plastic, etc.)
Vomiting and aspiration pneumonitis
CO2 accumulation and CO2 retention (hypercapnia)
Circuit disconnection
Overinflation
Underinflation
Basal atelectasis
Stages of Anesthesia
Historically, the four stages of general anesthesia relating to the depth of CNS depression are:
1.
Induction where unconsciousness is “induced” in the patient
2.
Excitation phase where the somatic and autonomic responses become erratic, with breath holding, gagging, respiratory irregularity, twitching, limb movements, spasticity, and pupillary dilation
3.
Surgical plane where stability returns with regular breathing (unless muscle relaxant is used), and this plane can further be subdivided into four planes based on eye movements, eye reflexes, and pupillary size
4.
Recovery where the anesthetic is gradually eliminated and the patient reenters the previous phases in reverse and then regains all reflexes and respiratory drive
Current Agents Used for General Anesthesia
Current inhalational general anesthetic agents include:
Nitrous oxide
Isoflurane
Sevoflurane
Desflurane
Less commonly, xenon and halothane (enflurane1)
Current IV general or sedative agents include:
Thiopental
Propofol
Etomidate
Ketamine
Diazepam
Midazolam
General Anesthesia: Some Associated Adverse Effects
The overall population-based risk of anesthesia is very low. This does not imply that there is negligible risk or no room for improvement(s). Complications and adverse consequences of general anesthesia (± regional or local) and intubation are well described. Some of these represent “iatrogenic” injury, while others are the consequences or side effects of the techniques or agents used or more related to the surgery being performed or to underlying patient comorbidities. It is estimated that some component of human error occurs in 70–80 % of anesthetic injury, but the contribution may be small; studies of complex systems have revealed that up to 85 % are primarily due to deficiencies in the layout and processes of the system (Runciman et al. 1993). Analysis of 13,389 anesthetics identified 116 errors: 9 (7.8 %) were human errors and 107 (92.2 %) were system errors (Lagasse et al. 1995). Although many complications can occur, some of these are shown in Table 5.1 with estimated frequency ranges.
Table 5.1
General anesthesia complications
Complications, risks, and consequences | Estimated frequency (%) |
|---|---|
Most significant/serious complications | |
Nausea and vomiting after surgery (hours to rarely several days)a | 1–5 % |
Dizziness, blurred visiona | 1–5 % |
Confusion or memory loss (increases with age or dementia)a | 1–5 % |
Rare significant/serious problems | |
Awareness during anesthesiaa | 0.1–1 % |
Esophageal intubationa (unrecognized) | 0.1–1 % |
Chest infection (higher in smokers) | a0.1–1 % |
Bladder problems | a0.1–1 % |
Damage to teeth, lips, or tonguea | 0.1–1 % |
Exacerbation of an existing medical conditiona | 0.1–1 % |
Respiratory depression | 0.1–1 % |
Aspiration pneumonitisa | <0.1 % |
Damage to the eyes | <0.1 % |
Serious allergy to drugsa | <0.1 % |
Nerve damagea | <0.1 % |
Equipment failurea | <0.1 % |
Deatha | <0.1 % |
Less serious complications | |
Pain or discomfort during injection of drugsa | 5–20 % |
Hematoma and soreness | 5–20 % |
Sore throata | 5–20 % |
Minor allergy to drugsa | 0.1–1 % |
Shiveringa | 1–5 % |
Headachea | 1–5 % |
Itchinga | 1–5 % |
Aches, pains, and backachea | 1–5 % |
Oral/Nasal Injury
Injuries to the lips, teeth, nose, gums, palate, tongue, pharynx, larynx, and esophagus have all been reported. Dislodgement of teeth and inhalation becomes a major complication, if recognized, often requiring immediate bronchoscopic retrieval.
Ocular Injury
This includes corneal abrasions, lacerations, contamination, contusions, blunt and sharp eyeball, and eyelid trauma.
Positioning and Pressure Injuries
Positioning should be a priority before and after induction of anesthesia, and because the position may change during surgery, all staff should reappraise the situation regularly to ensure that positioning is safe, not contacting metal or hard surfaces and not straining joints or other anatomy. Nerve compression and traction injuries are reported including the ulnar, common peroneal, brachial plexus, facial, trigeminal, median, radial, sciatic, and plantar nerves from atypical positioning or direct compression. Special attention is required for patients with casts or braces, or when raising or lowering the bed. The possibility exists that some of the later postoperative complications, such as sacral, heel, malleolar, and buttock decubitus ulcers, may have a component of their genesis during anesthesia/surgery from the pressure of the firm operating table and immobility. Backache and neck ache are common postoperative musculoskeletal sequelae.
Neck Injury
Soft Tissue
Neck stiffness can occur from lack of support and occasionally dry retching.
Cervical Spine Injury
This is very rare as the head is routinely carefully protected. However, it can occur after trauma or in association with rheumatoid or congenital instability.
Burns
Diathermy or static electricity in the presence of oxygen can ignite volatile gases, including vaporized alcohol from skin preparations and methane from the bowel, causing flash burns and even fire externally on the skin or internally within the airway or bowel. Direct burns can arise from contact with the metal of the operating table, from surgical instruments touching exposed wires, or wet drapes, to complete an electrical circuit.
Cardiac Complications
Most inhalational anesthetic agents depress myocardial function to some degree, with relatively greater effects from halothane and enflurane. This can reduce blood pressure, which may be countered partially by the effects of surgical stimulation. A wide range of drugs used by either the anesthetist or surgeon can influence cardiac rate, rhythm, or function. Simple examples are adrenaline (epinephrine), lignocaine, atropine, and antibiotics. Vasovagal episodes from mesenteric traction, or handling of the gut or heart, can occur, leading to bradycardia and hypotension or cardiac asystole, which may respond to atropine but may require cessation of surgery and cardiac compression. Severe bradycardia can also occur from peritoneal distension during laparoscopy. Atrial fibrillation, supraventricular tachycardia, atrioventricular block, and ventricular arrhythmias can occur during surgery and require urgent attention to correct the problem to restore adequate cardiac output. Ketamine typically has a cardiovascular stimulatory effect and maintains blood pressure better than other agents.
Respiratory Complications
Inhalational anesthetic agents may irritate the airways during induction, producing coughing and laryngospasm if the reflexes are not sufficiently depressed prior to inhalation. Inhalational induction is used commonly in pediatric anesthesia, usually with sevoflurane, which is less irritating than other volatile anesthetic drugs. Inadvertent distal migration of the endotracheal tube may obstruct one main bronchus, usually the left, and lead to lung collapse. This can lead to hypoventilation, atelectasis, and pulmonary consolidation, in addition to intraoperative hypoxemia. Pulmonary barotrauma can arise from excessively high ventilation pressures and volumes leading to pulmonary contusion, edema, and even pneumothorax. Tension pneumothorax is a surgical emergency requiring immediate pleural catheterization to equalize the pressure, reduce cardiac compression, and restore venous return. Airway occlusion with marked negative pressures during inspiratory efforts may result in pulmonary edema. Dislodgement of the endotracheal tube is potentially catastrophic, requiring immediate restoration of the airway with urgent reintubation. Similarly, endotracheal tube obstruction requires immediate attention; the commonest cause is inspissated secretions, which require aspiration. Cuff deflation may occur due to a faulty cuff or inflation valve. Accidental disconnection of the anesthetic breathing system is another potential disaster, usually heralded by alarms on the anesthetic monitoring system. Similarly, a rising CO2 level in the circuit is typically detected by the in-line CO2 monitor (capnography), and a fall in the inspired oxygen tension is detected by the in-line O2 monitor or pulse oximeter, both of which are programed to alarm when abnormal levels are reached. Narcotic analgesics can produce respiratory depression, which may be initially reversed in the recovery ward by naloxone, but which may recur when the shorter half-life of naloxone permits further respiratory depression from the residual narcotic. Labile asthma during surgery can be problematic and is often unpredictable. Prophylactic nebulized bronchodilator and steroids are sometime useful before surgery in averting an episode in susceptible individuals. Ventilation pressures may rise intraoperatively, and lung compliance may reduce, indicating airway obstruction.
Hepatotoxicity
In a small number of patients, halothane can produce an acute hepatic inflammation and even liver failure in some situations. Some antibiotics can also cause hepatitis, or cholestasis.
Renal Toxicity
Methoxyflurane (now unavailable in most Western countries) releases fluoride ions when metabolized and can induce nephrotoxicity, leading to renal impairment and renal failure, on occasions. Sevoflurane can react with alkali in the CO2 absorber to produce a vinyl chloride compound, which can cause acute tubular necrosis, usually of an apparently clinically insignificant level unless renal function is already impaired.
Drug Complications
These are multitudinous and can be idiosyncratic. Fortunately, despite the large number of procedures and many drugs used, the incidence of complications is relatively small. However, a real risk of a minor or major drug reaction remains for any patient undergoing anesthesia.
Allergy and Anaphylaxis
Any drug can trigger allergy, but of the anesthetic drugs, muscle relaxants are the most common group. Atypical allergic (anaphylactic) reactions present most commonly with one or more of three signs: bronchospasm, hypotension, and edema. A wide range of drugs and blood products can cause allergic reactions during anesthesia. The most effective treatment is IV adrenaline (epinephrine) 1–2 (micro) μg/kg body weight, repeated with dose doubling every 3–5 min, as required. A severe allergy may require an overall total dose of 2 mg or more of adrenaline. Allergic responses vary from minor skin rashes and postoperative nausea to asthmatic episodes where ventilation is difficult, ranging to severe anaphylaxis where laryngeal edema, asthma, severe angioedema, and circulatory collapse may occur. Minor reactions may be treated with an antihistamine, like IM Phenergan, moderate allergy may respond well to IV hydrocortisone, whereas anaphylaxis requires IM or IV adrenaline (epinephrine). Patients with an established or strongly suspected latex rubber allergy should have a full history taken and blood testing for Hevea braziliensis (rubber) antibody may be useful. Ideally, such patients must be preplanned for the beginning of a morning operating list where a non-latex anesthetic circuit and equipment setup is used (including non-latex gloves) to avoid exposure.
Venous Stasis, Deep Venous Thrombosis (DVT), and Pulmonary Thromboembolism (PTE)
The precise effect of general anesthesia on the genesis of deep venous thrombosis is difficult to determine. The analysis is confounded by the effects of the surgical illness, other medical conditions, preoperative immobility and stasis, surgery, genetics, dehydration and postoperative hypercoagulability, and possible further stasis. However, it is assumed that there is a contributing effect of stasis from the immobility induced by unconsciousness due to anesthesia. The effect may be increased by positive-pressure ventilation and head-up positioning and during laparoscopic procedures where insufflation pressure may impede venous return from the lower limbs.
The use of:
is prophylactic measures that have been shown to reduce the incidence of DVT. Pulmonary embolism is reduced in situations where DVT can be reduced. However, a small, low residual incidence of PTE has remained despite diligent application of these prophylactic measures. Risk factors include prior history of DVT, cancer, prolonged surgery, hip and pelvic surgery, lower-limb joint replacement surgery, obesity, pregnancy, hormone therapy, prolonged immobility pre- or postoperatively, increasing age over 45, smoking, and trauma, especially multiple fractures.
Intraoperative full leg support stockings
Intermittent pneumatic calf compression devices
Preoperative fractionated or unfractionated subcutaneous heparin
Hypothermia
Low core temperature during anesthesia has become a significant risk factor for increased risk of surgical infection. Recent evidence shows that maintenance of a core temperature above 36 °C is associated with reduced wound infection and improved wound healing, especially in situations where anaerobic bacterial contamination has occurred intraoperatively. For this reason, patients should be considered for a hot-air blanket, covering as much of the body as is practicable, and the warming of all IV fluids during surgery.
Malignant Hyperthermia (Hyperpyrexia)
This relatively rare condition is also termed malignant hyperpyrexia (MH). It is an autosomal dominant genetic condition where the control of Ca++ release with skeletal muscle contraction is impaired in the presence of volatile anesthetics or after the administration of suxamethonium. The leaking of Ca++ triggers continual muscle contraction and generates heat, causing hyperthermia and lethal hyperkalemia. Any family history needs to be treated seriously and investigated further. Any possible drugs that can trigger MH should be avoided, which includes all of the volatile anesthetic agents, but not the gases nitrous oxide and xenon. Intravenous anesthetic agents are safe, as are all of the muscle relaxants except suxamethonium (succinylcholine). If a general anesthetic is required, then it can be achieved using nitrous oxide and intravenous agents such as midazolam and fentanyl or total intravenous anesthesia using propofol and an analgesic, such as remifentanil.
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