Review Of Currently Used Inhalation Anesthetics: Part I

Abstract

SIDE EFFECTS OF INHALED ANESTHETICS CARDIOVASCULAR SYSTEM Blood pressure: All volatile anesthetics with the exception of nitrous oxide produce a dose-dependent decrease in blood pressure. Nitrous oxide produces either no change or only a slight increase in blood pressure. The decrease in blood pressure produced by halothane and enflurane results mainly from negative inotropy (decrease in myocardial contractility), whereas hypotension produced by desflurane, isoflurane, and sevoflurane mainly result from a decrease in systemic vascular resistance. Heart rate: Isoflurane and desflurane produce a dosedependent increase in heart rate. This increase occurs at low doses of isoflurane or high doses of desflurane. It might be blunted by simultaneous use of opioids during balanced anesthesia. Nitrous oxide, halothane and sevoflurane are not associated with substantial changes in heart rate. Cardiac performance: As mentioned earlier, halothane and enflurane produce a dose dependent decrease in cardiac output due to decrease in myocardial contractility. Administration of nitrous oxide can modestly increase cardiac output because its sympathomimetic effect. High doses may cause myocardial depression. Isoflurane, desflurane and sevoflurane do not significantly alter cardiac output. Systemic vascular resistance: Isoflurane, desflurane, and sevoflurane produce dose dependent decreases in systemic vascular resistance. Pulmonary vascular resistance: Nitrous oxide is known to increase pulmonary vascular resistance, especially in patients with pre-existing pulmonary hypertension. All other inhalation agents may decrease pulmonary vascular resistance and blunt the Hypoxic Pulmonary Vasoconstriction Reflex (HPV). Coronary blood flow: Isoflurane is known to be a potent coronary artery vasodilator. Isoflurane induced coronary artery vasodilatation can lead to redistribution of coronary blood flow away from diseased areas to areas with normal responsive coronary arteries. This phenomenon is called the coronary steal syndrome. However, most clinical studies failed to prove a higher incident of myocardial ischemia due to isoflurane. Enflurane, halothane, desflurane, and sevoflurane are all weaker coronary artery vasodilator than isoflurane. Cardiac dysrhythmias: Especially halothane is known for its dysrhythmic effect in combination with catecholamines such as epinephrine. All cardiac depressant effects of volatile anesthetics are able to recover. Cardiac output, heart rate, and systemic vascular resistance usually return to base value if these agents are administered for five hours or longer.