Effects of epidural anesthesia on the cardiovascular response to a rapid increase in isoflurane concentration

Hemodynamic and catecholamine response to a rapid increase in isoflurane or sevoflurane concentration during a maintenance phase of anesthesia in humans

PURPOSE

The purpose of this study was to compare hemodynamic and catecholamine changes due to a sudden increase in inhalation anesthetic concentrations (isoflurane and sevoflurane) during surgery.

METHODS

Thirty patients aged 40-70 years scheduled for lower abdominal surgery were anesthetized with either isoflurane or sevoflurane with nitrous oxide and epidural block. During surgery the isoflurane or sevoflurane concentration was kept at 0.5 minimum alveolar concentration (MAC) (end-tidal concentration) for 15 min. Then the isoflurane or sevoflurane concentration (inhalation concentration) was changed to 1.5 MAC and maintained at that level for 10 min. Thereafter, it was decreased to 0.5 MAC for 10 min. Blood pressure, heart rate, and plasma concentrations of epinephrine and norepinephrine were measured.

RESULTS

The blood pressure decreased significantly in both groups after increasing the anesthetic concentration, and it increased after decreasing the concentration. The decrease in systolic blood pressure was significantly larger in the isoflurane group. The heart rate increased significantly after increasing the anesthetic concentration only in the isoflurane group. Plasma concentrations of epinephrine and norepinephrine increased significantly in the isoflurane group, whereas the epinephrine concentration (but not the norepinephrine concentration) decreased in the sevoflurane group.

CONCLUSION

During surgery a sudden increase in isoflurane concentration induced larger changes in hemodynamics and sympathetic nerve activity than sevoflurane.

Values of the bispectral index do not parallel the hemodynamic response to the rapid increase in isoflurane concentration

PURPOSE

To investigate the changes in hemodynamic variables and bispectral index (BIS) in response to a rapid increase in isoflurane or sevoflurane concentration.

METHOD

Thirty adult patients were anesthetized with either isoflurane (isoflurane group) or sevoflurane (sevoflurane group). Two minutes after induction of anesthesia with thiamylal, the inspired concentrations of isoflurane and sevoflurane were rapidly increased from 0.5 minimum alveolar anaesthetic concentration (MAC) to 3 MAC and maintained for five minutes. Heart rate (HR), mean arterial pressure (MAP), and BIS were measured every minute.

RESULTS

An increase in the anesthetic concentration caused increases in HR and MAP in the isoflurane group and a decrease in MAP in the sevoflurane group. Consequently, HR and MAP in the isoflurane group were significantly higher than those in the sevoflurane group. After inhalation of high concentrations, BIS significantly and progressively decreased in both groups.

CONCLUSION

BIS values decrease after a step increase in volatile agent concentration, whether or not a hyperdynamic action occurs.