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

Abstract

Study Objective: To compare circulatory variables to an abrupt increase in isoflurane concentration via mask in patients who received either upper thoracic or lumbar epidural anesthesia, or neither. Design: Prospective study. Setting: Operating room at a university hospital Patients: 45 ASA physical status I female patients scheduled for elective surgeries with general anesthesia. Interventions: Patients received thoracic (TEA group) or lumbar (LEA group) epidural anesthesia, or neither (control group) ( n = 15 per group). An epidural catheter was inserted through the T 1-T 2 intervertebral space in the TEA group or L 2-L 3 in the LEA group, and 10 mL of 2% lidocaine without epinephrine was injected. Two minutes after induction of anesthesia with thiamylal, the inspired isoflurane concentration was rapidly increased from 0.5% to 5% and maintained for 5 minutes. Measurements and Main Results: Heart rate and mean arterial pressure (MAP) were measured every minute. Mean analgesic levels obtained by epidural block were C 4-T 6 and T 10-S 1 in the TEA and LEA groups, respectively. Heart rate increased after the increase in isoflurane concentration in all groups, but increased significantly less in the TEA group than in the control or LEA groups ( p < 0.05). Isoflurane also increased MAP in the control group throughout the 5-minute period, but only at the first minute of inhalation in the TEA and LEA groups. The increases in MAP in the TEA and LEA groups were significantly less than that in the control group ( p < 0.05). Conclusion: Epidural anesthesia can blunt circulatory responses to a sudden increase in isoflurane concentration.