Cardiac Arrhythmias
Cardiac arrhythmias may arise spontaneously, or they may be associated with myocardial ischemia, respiratory depression, metabolic disorders, or other physiological derangements. Some anesthetic agents can cause or contribute to arrhythmias, particularly in susceptible individuals. Arrhythmias may be divided based on rate into tachyarrhythmias and bradyarrhythmias, or based on location of origin – supraventricular ectopic rhythm generation versus ventricular arrhythmias. Some cardiac rhythm abnormalities such as premature ventricular contractions and premature atrial contractions occur spontaneously in an otherwise normal population and require no intervention. Likewise, certain instances of tachycardia (mild, associated with anxiety) and bradycardia (due to chronic treatment with beta‐blockers, or in a competitive athlete) may be within acceptable limits. Any arrhythmia that is symptomatic, that carries a risk of conversion to a more dangerous cardiac rhythm, or that is accompanied by hemodynamic instability should be promptly addressed, however. If the arrhythmia is attributable to an underlying physiological disturbance, efforts should be made to treat the underlying condition. Otherwise, the management strategies for cardiac arrhythmias include pharmacological interventions or cardioversion/defibrillation.
Tachycardia due to stress, anxiety, or pain usually responds to a deepening of anesthesia and additional analgesia. The administration of a beta‐adrenergic blocking medication can be considered for refractory cases. Selective beta‐1 medications are preferred so as to avoid undesirable bronchoconstriction. Esmolol is a beta blocker with a fast onset and short acting duration. Metoprolol is another beta‐1‐selective medication with a longer acting duration. Both are available for IV use and may be titrated to effect. In general, beta blockers are best avoided in patients with low cardiac output states such as acute MI or acute exacerbation of congestive heart failure due to negative inotropic effects. When tachycardia is secondary to hypotension, hypovolemia, or fever, it is preferable to treat the underlying physiological derangement.
For cases of paroxysmal supraventricular tachycardia, vagal maneuvers may be attempted first. These include ice packs applied to the face or Valsalva maneuver. Pharmacological intervention involves the medication adenosine. Supraventricular tachycardias that do not respond to drug therapy or wide complex tachycardia (ventricular tachycardia) should be treated with synchronized/unsynchronized cardioversion (electric shock). Cardioversion is also preferred for tachycardia associated with hemodynamic instability. Cardiac rhythms associated with cardiac arrest, i.e., ventricular fibrillation or pulseless electrical activity, should be treated according to the ACLS protocols.
Bradycardia, defined as a heart rate <60 bpm, may occur in sinus rhythm (sinus bradycardia) or as a result of heart block (atrial–ventricular dissociation). Any new onset of heart block is cause for evaluation by a specialist. Chronic heart block can be a stable condition in patients with cardiac pacemakers. Sinus bradycardia during ambulatory anesthesia can be a sign of myocardial depression and is cause for concern. It may be treated with atropine or glycopyrrolate (both vagolytics), or with sympathomimetic drugs such as ephedrine or epinephrine.
Hypertension and Hypotension
During the course of an anesthetic, both hypertension and hypotension may be encountered. Hypertension is typically associated with patient anxiety, painful stimulus, or anesthesia that is too light. Hypertension may also be seen in the hypertensive patient who neglects to take their regular antihypertensive medications the day of the surgical procedure. Hypertension may be treated by deepening the anesthesia or by judicious use of an antihypertensive medication. Labetalol, a combined alpha‐adrenergic and beta‐adrenergic blocker, is often preferred, but selective beta‐blocking agents such as metoprolol or vasodilating agents such as hydralazine may also be used. In patients whose baseline blood pressure is elevated (above 120/80), it is important not to decrease blood pressure too rapidly or profoundly so as to avoid inducing a decrease in cardiac output.
Hypotension may also be encountered in the course of an anesthetic. Several commonly used medications such as propofol can induce a transient decrease in blood pressure, particularly when given as a bolus. In a young patient without underlying cardiac disease, small to moderate decreases in blood pressure are usually well tolerated. However, because hypotension may also be a sign of low volume status or of impending cardiovascular collapse, it should be closely monitored and treated aggressively when indicated. In pediatric patients particularly, hypotension typically precedes cardiac arrest and is an important warning sign [20]. Decreasing the anesthetic depth, increasing the rate of IV fluid infusion, and giving a bolus of IV fluids are all appropriate first steps in the management of hypotension. If these steps are not corrective, a vasopressor medication such as ephedrine or phenylephrine may be given while also investigating for any causative factors such as an underlying medical condition, anaphylaxis/allergic reaction, or increased vagal stimulation.
GASTROINTESTINAL COMPLICATIONS
Nausea and Vomiting
Postoperative nausea and vomiting (PONV) is frequently cited as the most common complication of anesthesia, and it is one that patients frequently complain about. Many drugs used in ambulatory anesthesia are potentially capable of causing nausea and vomiting, particularly the halogenated gases (isoflurane, halothane, sevoflurane) and anticholinesterases. Narcotic medications such as morphine and fentanyl may also cause nausea and vomiting, as do barbiturates. Benzodiazepine medications have not been cited as a cause of PONV, and propofol is known to have antiemetic properties.
In addition to the effects of the anesthetic drugs, there are several patient factors that are known to increase the risk of PONV. Female gender, past history of PONV or motion sickness, nonsmoking status, postoperative opioid use, and younger age [21] may all predispose toward nausea and vomiting post‐anesthesia. Dehydration may also be a factor.
Prevention is an important consideration given that PONV is a frequent cause of delayed discharge to home after ambulatory anesthesia procedures [16]. Treatment of nausea and vomiting once it occurs is more difficult and less successful than efforts at prophylaxis. Avoiding dehydration and hypoglycemia by maintaining a reasonable preoperative fasting period and giving IV fluids during surgery will benefit most patients. Avoiding volatile anesthetics and nitrous oxide, favoring the use of propofol, and limiting opioids in the postoperative period can all help prevent PONV. In addition, screening prospective patients to identify those at risk of PONV will allow the surgeon to consider pharmacological methods of nausea and vomiting prophylaxis. Several effective medications are available that can be given by mouth or intravenously in order to prevent and/or treat nausea and vomiting (see Table 1.4).
Table 1.4. Common antiemetic medications
PO: by mouth; IV: intravenous; IM: intramuscular; PR: rectal suppository.
| Dolasetron, ondansetron, granisetron | 5‐HT3 receptor antagonist (PO, IV); given at end of surgery |
| Droperidol, haloperidol | butyrophenones (IV); given at end of surgery |
| Aprepitant, casopitant, rolapitant | NK‐1 receptor antagonists (PO); given before surgery |
| Perphenazine | Phenothiazine derivative (PO, IV, IM, PR) |
| Dimenhydrinate, meclizine | Antihistamine (IV, PO) |
| Scopolamine |