Cardiopulmonary effects of halothane in hypovolemic dogs

Abstract

Summary Cardiopulmonary effects of halothane administration were studied in hypovolemic dogs. Baseline cardiopulmonary data were recorded from conscious dogs after instrumentation. Hypovolemia was induced by withdrawal of blood from dogs until mean arterial pressure of 60 mm of Hg was achieved. Blood pressure was maintained at 60 mm of Hg for 1 hour, by further removal or replacement of blood. Halothane was delivered by face mask, dogs were intubated, then halothane end-tidal concentration of 1.13 ± 0.02% was maintained, and cardiopulmonary effects were measured 3, 15, 30, and 60 minutes later. After blood withdrawal and prior to halothane administration, systemic vascular resistance index, oxygen extraction, and base deficit increased. Compared with baseline values, these variables were decreased: mean arterial pressure, mean pulmonary arterial pressure, pulmonary arterial occlusion pressure, cardiac index, oxygen delivery index, oxygen consumption index, mixed venous oxygen tension, mixed venous oxygen content, venous admixture, arterial bicarbonate concentration, and mixed venous pH. At all times after intubation, arterial and venous oxygen tensions and mixed venous carbon dioxide tensions were increased. Three minutes after intubation, base deficit and mixed venous carbon dioxide tension increased, and mean arterial pressure and arterial and venous pH decreased, compared with values measured immediately prior to halothane administration. Fifteen minutes after intubation, systemic vascular resistance index decreased and, at 15 and 30 minutes, mean arterial pressure and arterial and venous pH remained decreased. At 60 minutes, mean pulmonary arterial pressure and pulmonary arterial occlusion pressure were increased and mixed venous pH was decreased, compared with values measured before halothane administration. Results of this study indicated that induction of anesthesia with halothane and maintenance at an end-tidal halothane concentration of 1.13% induced significant changes in blood pressure, with minimal effects on cardiac output and pulmonary function, when administered to hypovolemic dogs.