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.