Isoflurane Epinephrine

Isoflurane is a respiratory depressant (71). At concentrations which are associated with surgical levels of anesthesia, there is Htde or no depression of myocardial function. In experimental animals, isoflurane is the safest of the oral clinical agents (72). Cardiac output is maintained despite a decrease in stroke volume. This is usually because of an increase in heart rate. The decrease in blood pressure can be used to produce "deHberate hypotension" necessary for some intracranial procedures (73). This agent produces less sensitization of the human heart to epinephrine relative to the other inhaled anesthetics. Isoflurane potentiates the action of neuromuscular blockers and when used alone can produce sufficient muscle relaxation (74). Of all the inhaled agents currently in use, isoflurane is metabolized to the least extent (75). Unlike halothane, isoflurane does not appear to produce Hver injury and unlike methoxyflurane, isoflurane is not associated with renal toxicity. 

Desflurane is less potent than the other fluorinated anesthetics having MAC values of 5.7 to 8.9% in animals (76,85), and 6% to 7.25% in surgical patients. The respiratory effects are similar to isoflurane. Heart rate is somewhat increased and blood pressure decreased with increasing concentrations. Cardiac output remains fairly stable. Desflurane does not sensitize the myocardium to epinephrine relative to isoflurane (86). EEG effects are similar to isoflurane and muscle relaxation is satisfactory (87). Desflurane is not metabolized to any significant extent (88,89) as levels of fluoride ion in the semm and urine are not increased even after prolonged exposure. Desflurane appears to offer advantages over sevoflurane and other inhaled anesthetics because of its limited solubiHty in blood and other tissues. It is the least metabolized of current agents. 

Enflurane produces a dose-related decrease in systemic arterial blood pressure secondary to reductions in cardiac output and systemic vascular resistance. There is evidence that cardiac output is partially maintained by a compensatory increase in heart rate. This effect seems dependent on a degree of hypercardia and does not occur during controlled ventilation. Enflurane and halothane depress myocardial contractility to a similar extent and less than isoflurane. Enflurane does not sensitise the heart to the effects of catecholamines to any significant extent and adrenaline (epinephrine) may be given subcutaneously for control of bleeding. 

Moore MA, Weiskopf RB, Eger El 2nd, Wilson C, Lu G. Arrhythmogenic doses of epinephrine are similar during desflurane or isoflurane nesthesia in humans. Anesthesiology 1993 79(5) 943-7. 

Isoflurane ha.s similar actions to halothane but is less cardiodepre.s-sant and doe.s not sensitize the heart to epinephrine (adrenaline). It causes dose-related hypotension by decreasing systemic vascular resistance. Only 0.2%i of the absorbed dose is metabolized and so isoflurane Ls very unlikely to cause hepatotoxiciiy,... 

Patients anaesthetised with inhalational anaesthetics (particularly cyclopropane and halothane, and to a lesser extent desflurane, enflurane, ether, isoflurane, methoxyflurane, and sevoflurane) can develop cardiac arrhythmias if they are given adrenaline (epinephrine) or noradrenaline (norepinephrine), unless the dosages are very low. Children appear to be less susceptible to this interaction. file addition of adrenaline to intrathecal tetracaine enhances the sedative effects of propofol. 

Johnston RR, Eger El, Wilson C, A comparative interaction of epinephrine with enflurane, isoflurane, and halothane in man. Anesth Analg (1976) 55, 709-12. 

A 22-year-old woman in good health was anaesthetised for surgery with nitrous oxide/oxygen and isoflurane. Twenty minutes after induction she was given an injeetion of 0.2 units of vasopressin into the eervix. Within seeonds she developed severe hypotension and bradycardia, and over the next 30 minutes blood pressures as low as 70/35 mmHg and heart rates as low as 38 bpm were recorded. She was treated with atropine and adrenaline (epinephrine), and eventually made a full recovery. This patient was wearing a transdermal nicotine patch. ... 

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