Anesthesia: Choices and Complications

Introduction

Hospitalists are often involved in perioperative patient care and should be familiar with techniques and complications of anesthesia, as well as preoperative and postoperative considerations. Current modalities include general anesthetics, neuraxial techniques (spinal and epidural), regional anesthetics (nerve blocks), and monitored anesthetic care (MAC), or so-called conscious sedation. Each mode of anesthesia has benefits and risks that must be weighed in view of the operative procedure and the condition and comorbidities of each patient. The administration of regional or local anesthetics does not preclude the necessity for general anesthesia in the event of unforeseen events or complications. Therefore, patients undergoing all but the most minor procedures should be assessed as potential candidates for general anesthesia.

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Practice Point

Cardiovascular and psychiatric medications in the perioperative period

Beta-blockers, calcium channel blockers, and amiodarone should be continued in the perioperative period. Patients who receive perioperative angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may be at greater risk of intraoperative hypotension. Some authorities recommend holding these drugs on the day of surgery, particularly for operations with significant fluid shifts or using techniques associated with systemic inflammatory responses, such as cardiopulmonary bypass. It is traditionally recommended to stop monoamine oxidase inhibitors (MAOIs) two weeks prior to surgery. Patients who take MAOIs perioperatively are at risk of serotonergic toxicity and hypertension, especially with vasopressor use, as well as excessive sedation from inhibition of opioid metabolism by MAOIs. Some anesthesiologists continue MAOIs perioperatively, avoiding indirect-acting sympathomimetics such as ephedrine, and using narcotics such as morphine with lesser degrees of interaction with MAOIs, instead of meperidine. Tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs) may be continued perioperatively. TCAs have rarely been associated with intraoperative hypotension, requiring norepinephrine for reversal. SSRIs are occasionally implicated in perioperative serotonin syndrome, particularly when given with serotonin 5-HT3 receptor antagonists such as ondansetron, and phenylpiperidine opioids such as fentanyl.

General Anesthesia

General anesthesia is usually induced with a short-acting intravenous agent such as propofol and maintained with inhaled halogenated ethers or intravenous propofol. The mechanism of action of inhalational anesthetics remains unclear and may be a membrane effect, a receptor effect, or both. These agents may be used in conjunction with narcotics and muscle relaxants to achieve balanced anesthesia and may also be supplemented with inhaled nitrous oxide. Airway protection may be obtained by endotracheal intubation; airway patency, but not protection, may be ensured with a laryngeal mask airway, or oropharyngeal airway with mask.

Complications of general anesthesia include postoperative nausea and vomiting (PONV); aspiration; complications of intubation, such as dental, mucosal, or laryngeal trauma; atelectasis and complications of positive pressure ventilation, such as barotrauma; complications of positioning during surgery; and allergic or idiosyncratic reactions to anesthetic agents. Additionally, ischemic or thromboembolic events may occur perioperatively because of physiologic stresses from surgery or anesthesia.

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Practice Point

Side effects of anesthesia induction

Propofol is the most commonly used agent for anesthesia induction. A common side effect is hypotension from vasodilation and decreased cardiac output, which occurs in up to 16% of patients. Barbiturates such as methohexital and thiopental sodium are occasionally used for anesthesia induction but also have cardiovascular depressant effects. Etomidate and ketamine are sometimes used for anesthesia induction in patients at higher risk of hypotension from propofol, such as the elderly. Etomidate rarely has significant cardiovascular side effects, but it does inhibit 11-betahydroxylase, an enzyme involved in steroid synthesis, thus attenuating the adrenal stress response and potentially leading to postoperative hypotension. This effect may persist for up to 24 hours in elderly patients after a single dose for anesthesia induction. Ketamine does not depress respiratory drive, unlike most anesthetic agents, and it actually has bronchodilator effects that make its use attractive in patients with reactive airway disease. However, ketamine has side effects that make its use in elderly patients problematic, including increases in heart rate and blood pressure, myocardial depression that is masked by its sympathomimetic effects, postoperative delirium and hallucinations, and neurodegenerative apoptosis in animal models.

Postoperative Nausea and Vomiting

PONV occurs after approximately 10% of surgeries. Risk factors include younger age; female gender; intraabdominal, ophthalmic, or ear, nose, and throat (ENT) surgery; past history of PONV or motion sickness; and being a nonsmoker. Strategies to lower the risk of PONV include avoidance of general anesthesia in favor of regional anesthesia, use of propofol, avoidance of nitrous oxide and volatile anesthetics, minimization of opioids, and adequate hydration. Intraoperative prophylaxis and postoperative treatment may include central dopaminergic antagonists such as prochlorperazine, peripheral dopaminergic antagonists such as metoclopramide, serotonin 5-HT3 receptor antagonists such as ondansetron, and corticosteroids such as dexamethasone. These agents may also be used as rescue agents after emesis to prevent further symptoms. PONV usually abates in 24–48 hours. The examination of a patient with presumed PONV should assess for bowel sounds and the presence or absence of abdominal distention to avoid missing a diagnosis of postoperative ileus.

Aspiration

Aspiration is the entry of gastric contents into the trachea and lower airways. It may occur prior to or during induction of anesthesia, intraoperatively if the airway is unprotected, or during emergence from anesthesia and postoperatively. A chemical pneumonitis usually results with severity increasing with lower pH or particulates. Risk factors include a full stomach, preexisting gastroesophageal reflux disease (GERD), obesity, intraabdominal obstruction or other pathology, pregnancy, and trauma. American Society of Anesthesiologists guidelines for nil per os (NPO) status preoperatively recommend two hours for clear fluids, six hours for a light meal (essentially toast and clear fluids), and eight hours for full meals. These guidelines are for healthy elective patients with no GERD or other risks. Routine antireflux prophylaxis is not recommended, but in patients with GERD, histamine H2-receptor antagonists, proton pump inhibitors, physical antacids, or promotility agents such as metoclopramide may be indicated. Patients on these medications should have them ordered preoperatively.

Complications of Intubation and Airway Maintenance

In closed claim studies, the most common awards for anesthetic complications are those for dental trauma (approximately 1 in 5000). Laryngeal injury may have an incidence as high as 6% in general anesthesia but is usually minor and self-limiting, such as sore throat or vocal cord hematoma. Hoarseness lasting longer than 7 days should be evaluated by an otolaryngologist. Mucosal lacerations have an incidence of 1 in 1000, but again are usually self-limiting.

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