Blood pressure decreases with induction of anesthesia but returns toward normal with surgical stimulation. Progressive increases in depth of anesthesia produce corresponding decreases in blood pressure. Nitrous oxide diminishes the inspiratory concentration of Isoflurane required to reach a desired level of anesthesia and may reduce the arterial hypotension seen with Isoflurane alone. Heart rhythm is remarkably stable. With controlled ventilation and normal PaCO2, cardiac
output is maintained despite increasing depth of anesthesia, primarily through an increase in heart rate, which compensates for a reduction in stroke volume. The hypercapnia, which attends spontaneous ventilation during Isoflurane anesthesia further increases heart rate and raises cardiac output above awake levels. Isoflurane does not sensitize the myocardium to exogenously administered epinephrine in the dog. Limited data indicate that subcutaneous injection of 0.25 mg of epinephrine (50 mL of 1:200,000 solution) does not produce an increase in ventricular arrhythmias in patients anesthetized with Isoflurane.