The effect of posture on the induction of epidural anesthesia for peripheral vascular surgery.

ABSTRACT

BACKGROUND AND OBJECTIVES: A study was done to determine whether a difference existed in the quality and time to maximum anesthesia between the induction of lumbar epidural anesthesia in the sitting and supine position in patients undergoing infrainguinal arterial reconstruction. METHODS: An epidural catheter was inserted at L3-L4 in 40 patients who were randomly assigned to two groups. In group 1, with the patient sitting, 3 mL lidocaine 1.5% with 5 micrograms/mL epinephrine was given as a test dose, followed 3 minutes later by 12 mL bupivacaine 0.75% injected over 2 minutes through the catheter. After remaining in the sitting position for 5 minutes, the patient was placed supine and the quality of anesthesia assessed at 3-minute intervals for 30 minutes. Anesthesia was assessed by loss of sensation to pinprick and the Bromage scale for loss of motor function. In group 2, after placement of the catheter, the patient was immediately placed supine, the same doses of local anesthesia were given at the same time intervals as in group 1, and the onset of anesthesia was similarly assessed. In addition to a comparison between groups in the quality and time to maximum anesthesia, a correlation was sought between these variables and the age, weight, height, and body surface area (BSA) of the patients in each group. RESULTS: The demographically similar groups showed no difference in maximum cephalad spread of anesthesia (median, interquartile range; group 1 T4, T2.5-T6; group 2 T4, T2.5-T7), motor block (group 1 3, 2-4; group 2 4, 4-6), or time to maximum motor block (mean +/- SD; group 1, 17.4 +/- 8.7 minutes; group 2, 17.9 +/- 6.8 minutes). The time to maximum cephalad spread of anesthesia was shorter in group 1 (13.8 +/- 6.9 minutes; group 2, 18.6 +/- 6.6 minutes; P = .03). Neither the age nor weight of the patients in either group had any influence on the quality and time to maximum anesthesia. There was, however, a significant correlation between the height (r = 0.48, P = .0303) and BSA (r = 0.48, P = .0318) of the patients in group 1 and the time to maximum cephalad spread of anesthesia. CONCLUSIONS: When lumbar epidural anesthesia was induced in the sitting rather than supine position, the time to maximum cephalad spread was shorter and correlated directly with the height and BSA of the patient. The position of the patient during induction had no effect on the final level of cephalad spread and degree of motor block.