Cardiovascular and Metabolic Sequelae of Inducing Anesthesia with Ketamine or Thiopental in Hypovolemic Swine

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Abstract
If further sympathetic stimulation is neither possible nor desirable during moderate hypovolemia, anesthetic agents capable of sympathetic stimulation would not be advantageous for induction of anesthesia during hypovolemia. To test this hypothesis, 21 swine were studied during normovolemia and after 30% of their estimated blood volume was removed. Swine were divided randomly into 3 equal groups to receive no anesthetic or the minimal anesthetic dose of ketamine [K] (6.65 .+-. 0.38 mg/kg, i.v.) or thiopental [T] (5.77 .+-. 0.21 mg/kg, i.v.). After the initial response to hypovolemia, animals given no drug did not exhibit further changes during the hypovolemic period. Five min after induction of anesthesia in the hypovolemic state, K but not T caused large increases in plasma epinephrine, norepinephrine and renin activity. Despite these differences, both anesthetics equally depressed systemic vascular resistance, mean systemic arterial blood pressure, heart rate and cardiac output. K but not T decreased stroke volume. Neither anesthetic affected O2 consumption. Both anesthetics caused similar increases in blood lactate concentration. Thirty min after induction of anesthesia, plasma epinephrine, norepinephrine and renin activity remained higher in animals give K than in those given T. Stroke volume, systemic vascular resistance, cardiac output and O2 consumption did not differ among groups: only the animals given K showed further increase in blood lactate concentration and base-deficit. Thirty min after infusion of shed blood, cardiac output and blood lactate concentration were greater in the animals given K than in those given T or no anesthetic. Ninety min after infusion of shed blood, no differences existed among groups. Apparently, after moderate hemorrhage, further increase in circulating catecholamines is possible but the levels achieved either exceed the maximal effective concentration at site(s) of action or their effect are overwhelmed by the depressant effects of K. K has no advantage over T when used in the minimal anesthetic dosage for induction of anesthesia during hypovolemia.