Pulse oximetry during lumbar epidural anesthesia: reliability of values measured at the hand and the foot.

Pulse oximetry is dependent upon the presence of a pulsating vascular bed. The signal detection will be impaired in the presence of vasoconstriction or venous congestion, conditions which may occur readily in clinical practice. We compared the oximetric measurements (SpO2) at the hand and the foot with arterial hemoglobin saturation (SaO2) during lumbar epidural anesthesia. After administration of a crystalloid solution (20 mL/kg body weight lactated Ringer's solution), 40 adult male patients, scheduled for inguinal hernioplasty, received 15 mL of 0.50% plain bupivacaine into the lumbar epidural space. Two pulse oximeter probes were applied to the index finger and toe of the patients, and the SpO2 values were recorded continuously. Arterial hemoglobin saturation (SaO2) was measured using a co-oximeter 5 min before and 30 min after the onset of sensory block. No significant differences were detected between SaO2 (97.7%, SD 0.4%) and SpO2 basal values recorded from the hand (97.8%, SD 0.8%) and the foot (98.1%, SD 0.4%). After the onset of epidural anesthesia, a progressive decrease of SpO2 value recorded from the hand was observed: at 30 min it was 92.3% +/- 1.3% (P < 0.01 compared with baseline). At the same time, the SaO2 value was 97.5% +/- 0.9% (P < 0.01 compared with SpO2 from the hand). On the contrary, no significant difference from both basal value and SaO2 was detected in SpO2 measurements from the toe during the epidural block. In all patients intraoperative decrease of heart rate and arterial blood pressure was < or = 15% from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)