Breathe easy? Investigating HCO3-as a biochemical predictor of postoperative pulmonary complications.

Abstract

Introduction: Despite advances in perioperative care, postoperative pulmonary complications (PPCs) remain a significant concern in major surgeries, contributing to prolonged hospital stays and increased mortality rates [1]. Identifying a biomarker that could predict patients at higher risk of developing PPCs would be extremely beneficial in helping clinicians appropriately allocate resources for pre-operative optimisation and/or higher acuity post-operative care. Raised baseline serum bicarbonate (HCO3-) levels have been associated with obstructive sleep apnea (OSA), a risk factor for PPCs [2]. However, the potential predictive value of HCO3- in identifying patients at risk of PPCs remains unclear. This study aims to investigate the association between preoperative serum bicarbonate levels and PPCs in various non-cardiac surgical disciplines, using data from a post-hoc analysis of a large RCT that was published in JAMA. Methods: The local ethics committee approved the study (HREC approval number HREC/14/Austin260). Written informed consent was obtained from all participating patients. A post-hoc analysis of a single-center, randomized clinical trial [3] was conducted, involving 1206 patients undergoing laparoscopic surgery. Serum bicarbonate levels were measured pre-operatively, and patients were followed up for the development of PPCs within 7 days post-surgery. Multivariable logistic regression was used to assess the association between baseline HCO3- levels and outcomes, adjusting for potential confounders. Results: Data from 1206 patients were analyzed. In the univariable analysis, higher baseline HCO3- was associated with reduced risk of PPCs but not of acute respiratory failure. On multivariable analysis, baseline HCO3- was not significantly associated with increased risk of PPCs (odds ratio, 0.89 [95% CI, 0.78 to 1.01]; p = 0.075) or acute respiratory failure odds ratio, 0.89 [95% CI, 0.76 to 1.04]; p = 0.158) after adjusting for other confounders. Intraoperative variables such as peak pressures, driving pressures, and respiratory rates were higher in patients who developed PPCs, while duration of surgery was longer. Baseline HCO3- showed mild correlation with HCO3- levels at induction, prior to closure, and in recovery. Discussion/Conclusion: While elevated serum bicarbonate levels are associated with reduced risk of PPCs on univariable analysis, this association did not remain significant after adjusting for confounders. Despite its potential utility in identifying OSA patients, HCO3- alone may not sufficiently predict PPC risk due to the multifactorial nature of postoperative respiratory complications.