EFFECT OF EPIDURAL BLOCK ON THE LAG TIME OF PULSE OXIMETER RESPONSE

Thirty-six healthy patients, ASA 1, aged 16-41 years, scheduled for el ective plastic surgery were studied to determine if thoracocervical or lumbar epidural blocks affected the lag time of the pulse oximeter re sponse. Patients were allocated to receive thoracocervical epidural bl ock (n = 20) (group 1) (lignocaine 1%) or lumbar epidural block (n = 1 6) (group 2) (lignocaine 1.5%). Epidural block was performed with a 17 -gauge Tuohy needle inserted in the midline between C-4-T-2) vertebrae in group 1 and between L(3)-S-1 in group 2 and an epidural chatheter was introduced. Arterial oxygen saturation (SpO(2)) was measured conti nuously using a Datex pulse oximeter. The lag time of the pulse oximet er response was measured while breathing oxygen (100%) after breath-ho lding. Values were obtained 10 min before and 5, 10, 15, 20, 30, and 4 0 min after epidural injection of a test dose. There was a progressive decrease in the lag time of the pulse oximeter response so that by 30 min after epidural injection the mean (SD) value had decreased from 2 9 (6.1) to 14 (3.4) in Group 1 and 41 (12.8) to 23 (7.9) s in group 2 (p < 0.01).