Association between preoperative hemoglobin with length of hospital stay among non-cardiac and non-obstetric surgery patients: a secondary analysis of a retrospective cohort study

Background Previous studies concerning the association between preoperative Hemoglobin (HB) level and the Length Of hospital Stay (LOS) in patients with non-cardiac surgery and non-obstetric surgery remain inconclusive. Herein, the objective of this study was to analyze whether and to what extent the preoperative HB level was connected with the LOS in non-cardiac and non-obstetric surgery patients. Methods This retrospective cohort study was performed at a single institution, involving patients who underwent elective non-cardiac, non-obstetric surgery from April 2007 to September 2013. Clinical characteristics of patients such as demographics, comorbidities, preoperative HB level, LOS, mortality, procedure length, and pulmonary hypertension (PHTN) Severity Class data were collected. A univariate analysis was used to determine the association between clinical characteristics and LOS. Multivariate regression analysis was conducted to investigate the relationship between preoperative HB level and LOS. Results and discussion In this study, 311 patients were included. We observed that compared with the LOS > 7 days group, the average HB level of patients in the LOS <= 7 days group was higher (12.04 +/- 2.20 g/dl vs. 10.92 +/- 2.22 g/dl, p < 0.001). In addition, there were fewer patients with moderate-to-severe anemia in LOS <= 7 days group than the LOS > 7 days group (32.74% vs 58.82%, p < 0.001). In addition, we found that patients with LOS <= 7 days were accompanied with lower mortality (0.44% vs. 7.06%, p < 0.001) and lower mean combined pulmonary artery systolic pressure (PASP) and right ventricular systolic pressure (RVSP) than that in patients with LOS > 7 days (42.56 +/- 11.97 vs. 46.00 +/- 12.37, p < 0.05). After controlling for relevant confounders, we discovered a nonlinear association between preoperative HB level and LOS as well as a threshold effect based on LOS. Specifically, when preoperative HB level was less than 11.9 g/dL, LOS decreased by 2 days for each 1 g/dL increase in HB level. However, LOS did not alter substantially with the rise of preoperative HB level when it was higher than 11.9 g/dL. Conclusion Our study showed a close non-linear association between preoperative HB level and LOS in patients with non-cardiac surgery and non-obstetric surgery. In particular, for patients with preoperative HB less than 11.9 g/dL, increasing the preoperative HB level can help shorten the LOS after operation.