Physiologic correlates of intraoperative blood transfusion among patients undergoing major gastrointestinal operations.

BACKGROUND: Guidelines for transfusion focus on nadir levels of hemoglobin. Hemoglobin triggers may not be helpful, however, in defining appropriate intraoperative use of packed red blood cells. We sought to define the use of intraoperative packed red blood cells relative to quantitative physiologic factors at the time of operation. METHODS: Prospective intraoperative data on patients undergoing a major gastrointestinal operation between 2010 and 2014 were analyzed. Risk of intraoperative transfusion was assessed with multivariable extended Cox models using baseline clinical covariates and time-varying intraoperative covariates. RESULTS: Among 2,316 patients, the mean preoperative hemoglobin was 12.6 g/dL (standard deviation = 2.0 g/dL), while the median estimated blood loss was 200 mL (interquartile range: 100-55 mL). Overall, 357 (15.4%) patients received a transfusion intraoperatively. A greater hazard of transfusion was associated with a greater American Society of Anesthesiologists class (ref: American Society of Anesthesiologists class I-II; American Society of Anesthesiologists class III-IV; hazard ratio = 1.44, 95% confidence interval, 1.18-1.77, P < .001), and a lesser preoperative hemoglobin level (per 1 g/dL increase; hazard ratio = 0.70, 95% confidence interval, 0.65-0.74, P < .001). In addition, an increase in heart rate of 10 beats/min above the cumulative average at any measurement was associated with up to a 30% increased probability of transfusion (hazard ratio = 1.30, 95% confidence interval, 1.15-1.47, P < .001); similarly, an increase in mean arterial pressure of 10 mm Hg was associated with an 8% decreased likelihood of transfusion (hazard ratio = 0.92, 95% confidence interval, 87-0.99, P = .017). In contrast, nadir hemoglobin was not associated with the risk of receiving a transfusion (hazard ratio = 1.10, 95% confidence interval, 0.97-1.23, P = .129). Among patients who received an intraoperative transfusion, 9.2% (n = 33) never had a hemoglobin nadir below 10 g/dL, nor an average mean arterial pressure less than 65 mm Hg or a heart rate greater than 100 beats/min around the time of transfusion. CONCLUSION: Among the intraoperative factors, heart rate, and mean arterial pressure were strongly associated with the likelihood of receiving a transfusion, despite the observation that 9.2% of patients never had a physiologic indicator for transfusion or a nadir hemoglobin below 10 g/dL, suggesting a subset of patients could benefit from a decrease in intraoperative rate of transfusion.