Effects of isoflurane anesthesia and muscle paralysis on respiratory mechanics in normal man

Abstract

In 5 healthy adult male volunteers in the supine position, respiratory mechanics and functional residual capacity (FRC) were studied in the awake state (control) and with muscle paralysis and mechanical ventilation during isoflurane anesthesia (inspired concentrations, 1 and 2%). In 8 of 9 instances, FRC was less during isoflurane anesthesia compared with control. Static compliance of the total respiratory system [C(rs)] decreased consistently during anesthesia and that of the lung (C1) decreased in 8 of 9 instances; static compliance of the chest wall [C(w)] did not change. Average pulmonary resistance (R1) was significantly higher during anesthesia. The decrease in FRC and increase in R1 appear to be somewhat less than those reported for other anesthetics. Increasing the inspired isoflurane concentration to 2% had no further significant effect on FRC, C(rs), C1, C(w) and R1. Arterial blood pressure was decreased significantly and heart rate remained unchanged during anesthesia with 1% isoflurane; with 2% isoflurane, blood pressure was further significantly decreased and heart rate did not change significantly.