Evaluation of respiratory exchange ratio (RER) for predicting postoperative outcomes in elderly patients undergoing oncological resection for gastrointestinal malignancies – A prospective cohort study

BACKGROUND AND AIMS: Predicting complications after major oncosurgery is particularly daunting in the elderly subcategory of patients owing to factors like preexisting age-related immune cellular senescence and a significant imbalance of oxygen delivery (DO(2)) and consumption (VO(2)) characteristic of major oncological surgeries. The respiratory exchange ratio (RER) indicates DO(2)–VO(2) balance and onset of anaerobic metabolism. We evaluated the ability of RER in predicting the occurrence of postoperative complications following geriatric oncosurgery. MATERIALS AND METHODS: In the study, we enrolled 96 patients aged 65 years and above undergoing definitive surgery for gastrointestinal malignancy. The RER was calculated at predefined time points by a non-volumetric method from the respiratory parameters as RER = (end-tidal fractional carbon dioxide [FetCO(2)] – fraction of inspired carbon dioxide [FiCO(2)]/fraction of inspired oxygen [FiO(2)] – end-tidal fractional oxygen [FetO(2)]). Other indices of tissue perfusion, like central venous oxygen saturation and lactate levels, were also recorded. The patients were followed up for postsurgical complications. The predictive value of RER and other perfusion parameters was assessed and compared by appropriate statistical methods. RESULTS: The patients who sustained major complications had a higher RER than the patients who did not sustain complications (1.47 ± 0.99 vs. 0.90 ± 0.31, P = 0.001). An intraoperative cutoff value of RER ≥0.89 was found to best predict postoperative complications at a specificity and sensitivity rate of 81.2% and 76%, respectively. End-operative partial pressure of carbon dioxide (pCO(2)) gap of >5.2 mm and elevated arterial lactate could also predict postsurgical complications in this age group. CONCLUSION: The RER can serve as a noninvasive, real-time and sensitive indicator of tissue hypoperfusion and postoperative complications in geriatric gastrointestinal oncosurgery.