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

Study Objective: To compare circulatory variables to an abrupt increase in isoflurane concentration via mask in patients who received either upper tho racic 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 s urgeries with general anesthesia. Interventions: Patients received thoracic (TEA group) or lumbar (LEA group) epidural anesthesia, or neither (control group) (n = 15 per group). An epi dural 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 e pinephrines was injected. Two minutes after induction of anesthesia with th iamylal, 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 ny epidural bloc k 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 TEA and LEA gro ups. 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. (C) 2000 by Elsevier Science Inc.