An anesthesiologist takes care of patients in the periods immediately before, during, and immediately after surgery, which are known as the preoperative, perioperative, and postoperative periods, respectively. In the perioperative period, the goals of an anesthesiologist can be broadly broken down into three components:
Keeping the patient safe, above all else. This includes monitoring the patient’s vital signs and responding to changes that may be harmful to the patient, as well as anticipating any changes that may be brought about because of the specific stage of surgery.
Ensuring patient comfort, which includes providing analgesia (a state of minimal pain) and amnesia (a state of minimal recall).
Creating a favorable surgical environment for the procedurist (within reason). This typically involves ensuring immobility of the patient during the operation.
General Anesthesia vs Sedation
Anesthesia can be thought of as existing on a continuum, ranging from light sedation to general anesthesia, separated according to the patient’s ability to maintain respirations and responsiveness to verbal, tactile, and painful stimulation ( Table 6.1 ).
|Minimal Sedation||Moderate Sedation||Deep Sedation||General Anesthesia|
|Responsiveness||Unaffected||Intentional movements with verbal/tactile stimulation||Intentional movements with repeated tactile or noxious stimulation only||No intentional movements to repeated noxious stimulation|
|Ability to maintain airway||Yes||Yes||May require assistance (jaw thrust maneuver, inserting OPA or NPA)||Usually requires advanced airway (LMA vs ETT)|
|Spontaneous ventilation||Yes||Yes||May not be insufficient||Usually insufficient|
General anesthesia is the deepest level of anesthesia that can be provided, and it involves putting the patient to sleep (known as “induction”) using a combination of medications. Propofol is most commonly used for patients who are expected to have the ability to increase their cardiac output to handle some myocardial suppression and vasodilation caused by this agent. Patients who would not fit into this category include any patient in extremis (e.g., actively exsanguinating, cardiac tamponade or experiencing large pulmonary embolism) and patients with severe heart failure, severe cardiac valvular disorders (particularly stenotic lesions), severe pulmonary hypertension, severe sepsis, or shock of any etiology. Following induction, an advanced airway device, such as an endotracheal tube (ETT) or a laryngeal mask airway (LMA), is placed to assist the patient’s respirations. An ETT sits in the patient’s trachea below the epiglottis, and an LMA sits above the patient’s epiglottis. To facilitate the placement of an ETT, the patient is almost always paralyzed, usually with succinylcholine (which acts and wears off quickly but has several contraindications, the most serious being hyperkalemia and subsequent hyperkalemic cardiac arrest in certain patient populations) or with rocuronium. Paralysis is not typically needed for placement of an LMA. Placement of an ETT vs an LMA is dependent on a variety of factors, such as risk of gastric regurgitation entering the lungs, known as aspiration, and the need for paralysis. An ETT has a tracheal cuff that minimizes the chance that gastric contents can enter the trachea, whereas the LMA does not. In patients receiving paralytics during the procedure, the risk of aspiration is higher if using LMA due to positive pressure ventilation insufflating the stomach (this is more of a concern when using higher inspiratory pressures), whereas nearly all of the inspiratory gases given through an ETT will be entering the patient’s lungs instead of the stomach. In contrast, the LMA results in improved hemodynamic stability during placement, a lower incidence of postoperative hoarse voice, and decreased rates of coughing and laryngospasm (resulting in obstruction of the airway) as the patient wakes up. , Patients are usually kept asleep with an inhalational anesthetic (desflurane, sevoflurane, isoflurane, and nitrous oxide are most commonly used) but can be kept asleep with the use of only IV anesthetics, called total IV anesthesia (TIVA), which is often employed as well. The agents chosen for TIVA can include, but are not limited to, propofol and a fentanyl analogue (e.g., sufentanil, alfentanil, remifentanil). As the procedure nears its conclusion, the inhaled anesthetic or TIVA is weaned off and any residual paralysis can be reversed with sugammadex (if rocuronium was used) or neostigmine with glycopyrrolate.
Procedures done under sedation, in contrast, would not require an advanced airway device and would not require paralysis. The medications used in these cases include, but are not limited to, opioids (e.g., fentanyl, hydromorphone), propofol, dexmedetomidine, ketamine, and midazolam.
The appropriate depth of anesthesia to administer is based on a combination of factors including the patient’s past medical history, the patient’s preference, the procedure itself, and the procedurist’s individual preference. The anesthesiologist will take all of this into consideration and develop a plan that will keep the patient safe and comfortable while providing a favorable surgical environment for the procedurist (which involves a state of minimal movement from the patient when under sedation and possibly relaxing muscles with paralytics when under general anesthesia).
LOCAL AND REGIONAL ANESTHESIA
Some procedures can be performed under either sedation (with a component of local or regional anesthesia) or general anesthesia. Local anesthesia, otherwise known as a field block, is the injection of a local anesthetic (e.g., lidocaine, bupivacaine) around the incision site. In contrast, in regional anesthesia (also known as a nerve block), local anesthetic is deposited around the specific nerve or bundle of nerves that is responsible for the sensation of the surgical area, often with the help of ultrasound imaging. Take, for example, a surgical procedure in the forearm, as would be performed for the creation of an arteriovenous fistula for hemodialysis. Such a procedure can be performed with local anesthetic deposited in the forearm around the expected incision site, with a targeted nerve block of the brachial plexus (the nerve bundle that is responsible for sensation in the arm) under ultrasound guidance, or with general anesthesia. Since inducing light or moderate sedation will require less medication than inducing general anesthesia and because the most common agents used to induce general anesthesia can all cause some degree of hypotension (via myocardial depression and/or vasodilation), moderate sedation can be expected to cause fewer perturbations in vital signs than inducing general anesthesia in the majority of cases. However, other factors to consider include:
Can the patient remain motionless in the required position for the entirety of the procedure? Patients with conditions such as anxiety, back pain, or heart failure may be unable to lay supine for prolonged periods.
Does the patient look potentially difficult to intubate? Under all circumstances, an anesthesiologist should be prepared to convert to general anesthesia within 1 or 2 minutes. If the patient has risk factors for being potentially difficult to intubate, such as a history of sleep apnea, morbid obesity, retrognathia, a small mouth opening, a large tongue, or a history of neck radiation, then the anesthesiologist may opt to induce general anesthesia from the beginning of the procedure. In these patients, inserting an ETT in a controlled environment with optimal positioning, adequate preoxygenation (having the patient breathe 100% oxygen until their expired oxygen concentrations are >80%), nearby emergency intubation equipment (such as a video laryngoscope, fiberoptic scope, or bougie), and perhaps a second anesthesiologist in the room for assistance may be desirable compared with suddenly needing to intubate in the middle of a procedure when a patient becomes compromised. If a patient is already desaturating (meaning that oxygen levels in the blood are decreasing), repositioning and lack of emergency equipment and personnel can waste precious seconds, which can lead to an adverse outcome. It is for this reason that an anesthesiologist may elect to administer a general anesthetic for the excision of a small back lipoma (to be done with prone positioning), even though the surgery may only last a few minutes.
Anesthetic Complications and the Inpatient
There are a number of anesthetic-related complications that can be influenced or encountered by inpatient practitioners. A few common scenarios are listed below. It is recommended to check local institution-specific guidelines that may exist regarding any of these medications/situations.
Generally speaking, oral antihypertensives should not be held prior to surgery. For some antihypertensives, such as alpha-2 agonists, withdrawal may precipitate an intraoperative reflex hypertensive event. Withholding preoperative beta blockers may result in ischemia in patients who have coronary artery disease and has been associated with increased morbidity and mortality. One possible exception to this rule is suspending angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) on the day of the procedure (some centers may hold them beginning 24 hours prior to surgery), as some studies have found that these medications are associated with increased rates of hypotension when continued into the perioperative period. There is no general consensus as the data is conflicted with regard to 30-day mortality, so it is reasonable to consider holding ACEIs and ARBs prior to surgery.
Administering opioids and/or benzodiazepines prior to transporting the patient to the procedure area may hinder the ability of the patient to consent to both the procedure and to being anesthetized if they cannot verbalize their understanding of the risks and benefits of undergoing anesthesia. In addition, one must also be wary of these medications and any others that have a potential for sedation in the immediate postoperative hours, particularly if the patient is obese and/or has obstructive sleep apnea (OSA) and was placed under general anesthesia. These include the aforementioned benzodiazepines and opioids, in addition to barbiturates, antipsychotics, and common sleep medications. The reasoning for this is as follows:
The most common method of administering general anesthetic is via the inhaled route. The termination of action of these anesthetics requires sufficient gas exchange at the level of the alveoli (the most downstream segment of the lung). Therefore, when a patient with OSA, or presumed to have OSA because of obesity, has an episode of airway obstruction and hypoventilation during sleep, accumulation of the inhaled anesthetic can occur in the alveoli and can reanesthetize the patient. In addition, benzodiazepines and opioids also decrease the ventilatory response (which can be thought of as the desire to breathe) to hypoxia and hypercarbia. Further compounding this is the lethargy and sedation that occurs with hypercapnia. All of these factors can result in a positive feedback loop that can ultimately cause hypercapnic respiratory failure requiring reintubation. Unfortunately, this desaturation is often not acutely detected and there have been instances in which floor nurses have discovered patients expired overnight or having suffered irreparable brain injury with this as a contributing factor. Some methods that can interrupt this cycle are the use of continuous positive airway pressure (CPAP) in the postoperative period, which can minimize the episodes of airway obstruction and help the patient maintain ventilation; use of continuous pulse oximetry to alert medical personnel of desaturations under 90%; encouraging patients to sleep in a nonsupine position, as lateral or semi-recumbent positioning is associated with less pharyngeal collapse and subsequently less airway obstruction; and use of patient-controlled (instead of provider-controlled) analgesia, in which the patient can deliver their own small doses of opioids with a set minimum time limit between doses in addition to a set limit of doses in a given time period, with the caveat of avoiding background basal infusions. See Chapter 44: Oxygen Supplementation for details about continuous positive airway pressure. See Chapter 45: Patient-Controlled Analgesia for more details about this practice. In summary, one should exercise caution when administering sedating medications, particularly benzodiazepines and opioids, in patients with morbid obesity and/or OSA in the immediate postoperative day/night after having received general anesthesia and should consider giving these medications only on an as-needed basis instead of prophylactically.
For a patient requiring a surgery in which a regional nerve block may be used as either the primary anesthetic or as an adjunct for postoperative pain control, the risk and benefit of suspending pharmacologic venous thromboembolism prophylaxis must be weighed. Surgical procedures involving the extremities and/or hips or those requiring large abdominal incisions are primary examples for which suspending the anticoagulant is considered. The basis of using nerve blocks is the principle that with better pain control, there are fewer intraoperative hemodynamic changes and less postoperative opioid use. This has been shown to result in less constipation, less delirium, less nausea and vomiting, increased tidal volumes (the size of a particular breath) resulting in less postoperative atelectasis and fewer pulmonary complications, and faster hospital discharge.
Patients are made nil per os (NPO), Latin for nothing by mouth, prior to surgery as a protective measure against aspiration. Aspiration occurs when food or gastric contents enter the trachea and lungs, possibly resulting in chemical pneumonitis, pneumonia, acute respiratory distress syndrome, and even death. This can occur with anesthesia because as patients lose consciousness, there is a loss of the cough reflex that would otherwise protect the airway from aspiration as well as a decline in the tone of both the upper and lower esophageal sphincter (the bundle of muscles that prevent gastric contents from entering the oropharynx and esophagus, respectively). The exact recommended duration of NPO status prior to surgery depends on the fluid/food ingested. The American Society of Anesthesiologists recommends at least 2 hours for clear liquids (which include water, coffee, tea, carbonated beverages, and pulpless fruit juice); 4 hours for breast milk; 6 hours for light meals (those with minimal amounts of fat and/or meat), nonhuman milk, formula, and other liquids not classified under clear liquids; and 8 hours for heavy meals.
Patients with diabetes who are to be NPO have their own specific needs with regard to dosing of their basal insulin. Assuming a daytime surgery, patients taking twice-daily NPH should take their regular bedtime dose of NPH the night before surgery and a daytime dose of NPH reduced by 50%. For patients using once-daily basal insulin such as insulin glargine or insulin detemir, their dose prior to surgery should be reduced by 25%. Those who are taking twice-daily insulin glargine or insulin detemir should reduce both the dose the morning of surgery and the dose the evening prior to surgery by 25%. Patients who take >80 units/day of insulin, have >60% of their total daily insulin as basal, or are otherwise at high risk for hypoglycemia (those with kidney or liver impairment, a history of hypoglycemia, or advanced age) should have their doses decreased by 50% to 75%. Regardless, blood glucose should still be checked every 4 to 6 hours throughout the day of surgery in these patients. Nutritional insulin (mealtime standing bolus doses) should be held as the patient will not be eating a meal, but correctional bolus insulin should still be administered. Consider consulting with an endocrinologist if the patient is particularly sensitive to changes in their diabetes regimen. See Chapter 5: Glycemic Considerations for Tests and Procedures for details.
Patients who undergo cardiac catheterization and have a stent placed in their coronary artery are usually started on dual antiplatelet therapy (DAPT), such as aspirin with a P2Y 12 inhibitor (e.g., clopidogrel), to prevent stent thrombosis and myocardial infarction. When these patients are to have a procedure, the necessity of the procedure, the risk of bleeding if continued on DAPT, and the risk of stent thrombosis if discontinuing DAPT must be taken into consideration. Suspending DAPT after a recent stent placement when superimposed on the general prothrombotic/proinflammatory state that is associated with surgery puts the patient at a very high risk for stent thrombosis. The current recommendations from American College of Cardiology/American Heart Association (AHA) are as follows: completely elective surgeries should be delayed for at least 30 days after bare metal stent placement and 6 months following drug-eluting stent placement. For patients with drug-eluting stents who require a time-sensitive surgical procedure, the procedure should be delayed for at least 3 months following stent placement, if possible. However, if the risk of delaying the surgery is greater than the risk of stent thrombosis, then the surgery should be performed. Ideally, DAPT would be continued in these patients, but for procedures in which bleeding would have catastrophic consequences—such as in intracranial or intraocular surgeries—it may be necessary to hold one (typically the P2Y 12 inhibitor) or both medications , ( Fig. 6.1 ). This decision should be made on a case-by-case basis and only after a discussion with the surgeon and cardiologist. See Chapter 4: Anticoagulation Management in the Periprocedural Period and Chapter 46: Percutaneous Coronary Intervention .