Pulmonary hemodynamics during induction of anesthesia

Abstract

Changes in pulmonary hemodynamics and acid-base balance were recorded during induction of anesthesia using either intravenous administration of a barbiturate (28 patients) or inhalation of N2O-O2-halothane (12 patients). The two types of induction resulted in equal elevations of pressure within the pulmonary circulation. The increase, proportional on the two sides of the heart, was most pronounced immediately before endotracheal intubation. Cardiac index decreased before and during intubation but subsequently increased to levels above control values. Systemic blood pressure increased more during barbiturate than during inhalation induction. Changes in acid-base balance were similar during the two types of induction: arterial blood P(CO2) and P(O2) increased, pH decreased, and standard bicarbonate remained unchanged. Changes in pulmonary arterial mean pressure and central venous pressure were correlated with changes in Pa(CO2). Pulmonary capillary filtration pressure (i.e., pulmonary capillary wedge pressure minus plasma colloid osmotic pressure) was negative in every patient before anesthesia. During induction of anesthesia, filtration pressures became positive in half the patients. Observed changes in circulation may have been caused by hypercapnia alone or by a combination of hypercapnia and vascular reflexes associated with instrumentation during intubation. The increased strain on the heart during induction of anesthesia may lead to cardiac failure in patients with diminished cardiac reserve.