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Surgical start time impacts incidence of postoperative blood transfusion in RYGB patients

Gastric bypass patients who had a late surgical start time (SST) had a greater incidence of postoperative blood transfusion despite having similar demographic and operative characteristics, according to study by researchers from the University of Virginia, Charlottesville, VA.

Figure 1: Distribution of surgical case start times (doi:

The authors stated that SST has resulted in conflicting effects on perioperative outcomes due to confounding factors, previous research has hypothesised that clinical response to an intervention is significantly impacted by circadian variations at the cellular level. They stated that gastric bypass surgery results may offer significant insight into the association between SST and postoperative complications, as this surgery represents a truly elective, non-urgent surgery with modifiable SST.

Therefore, the investigators designed a study to investigate the effect of SST on blood transfusion after gastric bypass surgery, a complication-prone elective surgical procedure. This retrospective cohort study included 299 patients undergoing gastric bypass surgery at the University of Virginia from 2016 through 2021. The primary independent variable was SST (before vs. after 15:00). The primary outcome was blood transfusion. Secondary outcomes included postoperative respiratory failure, length of stay, acute kidney injury and mortality.


The aggregate range of SSTs was 07:53–18:43 - there were 259 patients in the 07:53–14:59 SST cohort and 40 patients in the 15:00–18:43 SST cohort (Figure 1). The average age was 46.76±11.23 years, male sex comprised 14.0% of patients, and the average BMI was 48.33±10.64 kg/m2. There were no significant differences in these baseline characteristics when comparing the 07:53–14:59 SST and 15:00–18:43 SST cohorts. In addition, medical comorbidities (diabetes, hypertension) and baseline laboratory values (creatinine, haemoglobin) were comparable between the two SST cohorts. Distribution of surgeon, distribution of surgical approaches (open, laparoscopic, robotic), operative time, volatile aesthetic use, and estimated blood loss were all found to be similar between the 07:53–14:59 SST and 15:00–18:43 SST cohorts.

The investigators found that there was a greater incidence of postoperative blood transfusion in the 15:00–18:43 SST cohort (4/40 vs. 6/259, relative risk 4.32, 95% confidence interval 1.27 to 14.63, p=0.032). Additionally, there was a greater incidence of weekend operation (including Friday after 15:00) in the 15:00–18:43 SST cohort (17/40 vs. 1/259, relative risk 110.07, 95% confidence interval 15.06 to 804.54, p<0.001). There was no difference in postoperative respiratory failure, acute kidney injury, hospital length of stay and mortality between the two SST cohorts. Postoperative sepsis (n=2), venous thromboembolism (n=0), stroke (n=0), and myocardial infarction (n=0) were ultimately excluded from analysis due to a rare event rate (n<3).

The only preoperative or operative characteristics associated with postoperative blood transfusion on univariate testing were SST (4/10 vs. 36/289, relative risk 4.32, 95% confidence interval 1.27 to 14.63, p=0.032) and mean expired sevoflurane (1.46 ± 0.31 vs. 1.62 ± 0.49, absolute difference 0.17, 95% confidence interval 0.01 to 0.42, p=0.044). Weekend operation (including Friday after 15:00), primary surgeon and surgical approach (open versus laparoscopic versus robotic) were not associated with postoperative blood transfusion. After adjusting for covariates ultivariate analysis, SST was the only independent predictor of postoperative blood transfusion (adjusted odds ratio 4.32, 95% confidence interval 1.06 to 15.96, p=0.029). The model discrimination was fair (c-statistic=0.638).

There was no difference in nadir haemoglobin concentration or discharge haemoglobin concentration between the two SST cohorts. Compared to the non-transfused cohort, the transfused cohort had a lower postoperative haemoglobin concentration (9.61 ± 1.72 vs. 12.01 ± 1.36 g/dL, p=0.002), lower nadir haemoglobin concentration (6.46 ± 0.53 vs. 11.36 ± 1.62 g/dL, p<0.001), greater 48 hour reduction in haemoglobin concentration (3.57 ± 1.52 vs. 0.57 ± 0.90 g/dL, p<0.001), and lower discharge haemoglobin concentration (9.61 ± 2.10 vs. 11.81 ± 1.57 g/dL, p=0.009).

“While it is difficult to determine whether the reason for increased blood transfusion rate in the late SST cohort is mostly surgical, the need for transfusion appeared to be related to the index surgery in seven of ten (70.0%) cases, suggesting that surgical cause is the major reason for blood transfusion in patients after gastric bypass surgery” the authors write.

“The present study demonstrates an increased risk of postoperative transfusion with later SST in the gastric bypass population. Earlier SST may decrease the incidence of postoperative blood transfusions in elective cases,” the authors concluded. “Further research is warranted to investigate the morbidity and mortality attributable to late SSTs in elective cases.”

The outcomes were report in the paper, ' Late surgical start time is associated with increased blood transfusion following gastric bypass surgery', published in PlosOne. To access this paper, please click here


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