Efficacy of noninvasive pulse co-oximetry as compared to invasive laboratory-based hemoglobin measurement during spinal anesthesia

Abstract

BACKGROUND The Masimo Radical 7 (Masimo Corp., Irvine, CA, USA) pulse co-oximeter(R) noninvasively determines the hemoglobin concentration using the principle of transcutaneous spectrophotometry. We compared hemoglobin levels determined using this device (SpHb) with those determined using an invasive laboratory-based technique (tHb) during spinal anesthesia. METHODS Thirty patients received spinal anesthesia with 0.5% hyperbaric bupivacaine. The pulse co-oximeter probe was mounted on the second toe, and arterial blood samples were obtained from a radial artery catheter. SpHb, tHb, and perfusion index (PI) values were recorded before and 20 and 40 min after intrathecal injection of bupivacaine. RESULTS Before spinal anesthesia, the SpHb and tHb showed a significant difference of -2.86 +/- 1.56 g/dl (P < 0.005), but no significant differences were found between tHb and SpHb at 20 and 40 min after spinal anesthesia (-0.16 +/- 2.45 g/dl and 0.29 +/- 2.68 g/dl). Additionally, PI was significantly increased at 20 and 40 min after spinal anesthesia compared to the pre-anesthetic value (P < 0.001). CONCLUSIONS The toe is not the monitoring site for pulse co-oximetry in adult patients, but the pulse co-oximetry on the toe appears to be appropriate as a noninvasive hemoglobin monitoring device after spinal anesthesia.