Accuracy of Continuous and Noninvasive Hemoglobin Monitoring in the Presence of CO2 Insufflation: An Observational Pilot Study

Abstract

BACKGROUND Laparoscopic surgery has several benefits, but it requires prolonged carbon dioxide (CO₂) insufflation. Several factors affect the accuracy of continuous and noninvasive hemoglobin (SpHb) monitoring, but the effects of CO₂ insufflation are undetermined. This study investigated the effect of CO₂ insufflation on SpHb monitoring in laparoscopic surgery. MATERIAL AND METHODS Twenty patients undergoing laparoscopic gastrectomy were enrolled. Anesthesia was maintained using sevoflurane and remifentanil within an end-tidal CO₂ of 30-45 mmHg. The CO₂ insufflation was maintained at 12 mmHg using CO₂. SpHb was monitored with a Radical-7 Pulse CO-Oximeter, and laboratory hemoglobin (tHb) was analyzed using a satellite blood analyzer. RESULTS Forty paired measurements were analyzed. The mean perfusion index, SpHb, and tHb were 3.10±1.77%, 10.92±1.48 g/dL, and 11.51±0.88 g/dL, respectively. SpHb underestimated tHb with a bias (precision) of -0.59 (1.28 g/dL), and the 95% limit of agreement was wide (-3.11 to 1.92 g/dL). SpHb was moderately correlated with tHb (r=0.50, 95% CI: 0.23 to 0.70). The concordance rate was 67%. ΔSpHb was not correlated with ΔtHb (r=0.29, 95% CI: -0.18 to -0.65). A similar bias, wider limits of agreement, a higher |SpHb-tHb|, but more significant correlation between SpHb and tHb were observed for the "PaCO2 <40 mmHg" range compared with the "40 mmHg ≤PaCO₂" range. CONCLUSIONS SpHb may have an acceptable accuracy but has a weak trending ability in the presence of CO₂ insufflation, and it can be affected by PaCO₂. Further research on the effects of CO₂ insufflation on SpHb is needed.

Figure 1

Flow diagram for patient enrollment.

Figure 2

Error grid analysis for the data points of the SpHb and tHb pairs. Zone A represents a clinically acceptable difference (±10%) for hemoglobin from 6 g/dL to 10 g/dL. Zone B represents differences greater than ±10% with a potential for therapeutic error. Zone C represents differences with a major therapeutic error. SpHb – continuous and noninvasive hemoglobin monitoring; tH – laboratory hemoglobin

Figure 3

Bland-Altman analysis. The solid line represents the bias (SpHb–tHb), and the dotted line represents the 95% limit of agreement. SpHb – continuous and noninvasive hemoglobin monitoring; tHb – laboratory hemoglobin.

Figure 4

The 4-quadrant plot. It shows the directionality of the trend with a central exclusion zone of 1 g/dL hemoglobin. SpHb – continuous and noninvasive hemoglobin monitoring; tHb – laboratory hemoglobin