Effects of thermoregulatory vasoconstriction on pulse hemoglobin measurements using a co-oximeter in patients undergoing surgery ★★★

Study ObjectiveTo validate intraoperative pulse hemoglobin (SpHb) measurements in anesthetized patients with large forearm temperature – fingertip temperature gradients.Designprospective and observational study.SettingOperating room of a university hospital.Patients28 patients undergoing surgery during general anesthesia, requiring arterial blood withdrawal.InterventionsRadial arterial blood pressure, forearm and fingertip skin surface temperatures, and SpHb were monitored.MeasurementsPaired SpHb and arterial hemoglobin (Hb) measurements at different skin-surface temperature gradients.Main ResultsA total of 175 paired SpHb and arterial Hb measurements were analyzed. The mean SpHb to arterial Hb differences in each group were 0.33 ± 1.41 g/dL in the < 1°C group of the forearm temperature – fingertip temperature gradient, -0.31 ± 1.24 g/dL in the 1 - 2°C group, - 0.59 ± 1.11 g/dL in the 2 - 3°C group, and - 0.53 ± 0.87 g/dL in the > 3°C group (P < 0.05). The percentage of nonmeasurable SpHb due to low perfusion state was 0% (0 of 115 paired measurements) in the < 1°C group, 6.7% (2 of 30 pairs) in the 1 - 2°C group, 16.7% (3 of 18 pairs) in the 2 - 3°C group, and 66.7% (8 of 12 pairs) in the > 3°C group.ConclusionSpHb measured at fingertip was significantly affected by the perfusion state, with lower perfusion associated with lower SpHb. Thermoregulatory vasoconstriction affects measurement of SpHb.