Pulse oximetry during lumbar epidural anesthesia: reliability of values measured at the hand and the foot
Peduto, V.A.; Tani, R.; Pani, S.
Anesthesia and Analgesia 78(5): 921-924
1994
ISSN/ISBN: 0003-2999 PMID: 8160991 Document Number: 422636
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 (SpO-2) at the hand and the foot with arterial hemoglobin saturation (SaO-2) 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 SPO-2 values were recorded continuously. Arterial hemoglobin saturation (SaO-2) was measured using a co-oximeter 5 min before and 30 min after the onset of sensory block. No significant differences were detected between SaO-2 (97.7%, SD 0.4%) and SpO-2 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 SpO-2 value recorded from the hand was observed: at 30 min it was 92.3% +- 1.3% (P lt 0.01 compared with baseline). At the same time, the SaO-2 value was 97.5% +- 0.9% (P lt 0.01 compared with SpO-2 from the hand). On the contrary, no significant difference from both basal value and SaO-2 was detected in SPO-2 measurements from the toe during the epidural block. In all patients intraoperative decrease of heart rate and arterial blood pressure was ltoreq 15% from baseline. The decrease of SpO-2 values recorded from sympathetically unaffected areas during epidural anesthesia could be related to vasoconstriction, counterbalancing lumbar preganglionic sympathetic block, which occurred despite perioperative crystalloid volume loading. Because of this compensatory vasoconstriction, pulse oximetry during lumbar epidural anesthesia gives a falsely low reading when the oximetric sensor is placed at the upper limbs.