Impact of Increased End-Tidal Carbon Dioxide on Continuous Noninvasive Hemoglobin Monitoring during Laparoscopic Gastrectomy: A Randomized Controlled Study

The pulse CO-Oximetry allows continuous, noninvasive monitoring of hemoglobin (SpHb). We assessed the impact of increased end-tidal carbon dioxide (EtCO2) on the accuracy and trending ability of SpHb in laparoscopic surgery. Participants (n = 64) were randomly allocated to the low carbon dioxide (CO2) group (EtCO2: 30–35 mmHg) or the high CO2 group (EtCO2: 40–45 mmHg). The SpHb and laboratory hemoglobin (tHb) were obtained during surgery. The correlation coefficient (r) between SpHb and tHb showed greater tendency in the low CO2 group (r = 0.68) than in the high CO2 group (r = 0.43). The bias (precision) was −1.18 (1.09) with a limit of agreement (LOA) of −3.31 to 0.95 in low CO2 group and −1.02 (1.24) with a LOA of −3.45 to 1.42 in high CO2 group; they did not differ significantly between the groups (p = 0.246). The low CO2 group showed a high concordance rate of 95.9% and a moderate correlation between ΔSpHb and ΔtHb (r = 0.53). However, the high CO2 group showed a concordance rate of 77.8% and no correlation between ΔSpHb and ΔtHb (r = 0.11). In conclusion, increased EtCO2 significantly reduced the trending ability of SpHb during laparoscopic surgery. Caution should be executed when interpreting SpHb values during laparoscopic surgery in patients with hypercapnia.