Novel application of respiratory muscle index obtained from chest computed tomography to predict postoperative respiratory failure after major non-cardiothoracic surgery

Background: Postoperative respiratory failure (PRF) is a serious complication associated with significant morbidity and mortality. We propose a new method to predict PRF by utilizing computed tomography (CT) of the chest to assess degree of respiratory muscle wasting prior to surgery. Methods: Patients who received a chest CT and required invasive mechanical ventilation (MV) after major non-cardiothoracic surgery were included. Exclusion criteria included cardiothoracic surgery. Respiratory muscle index (RMI) was calculated at the T6 vertebra measured on Slice-O-Matic® software. Results: Thirty three patients met inclusion with a mean (±SD) age, BMI, and APACHE II score of 62.2 years (±12.1), 28.1 kg/m² (±7.8), and 14.1 (±4.7). Most patients were female (n = 22 [67%]). Eleven patients (33%) developed PRF with a mean of 6.0 (±10.7) initial ventilation days. There was no difference in baseline demographics between groups. RMI values for the PRF group were significantly lower when compared to the non-PRF group: 22.7 cm²/m² (±5.3) vs. 28.5 cm²/m² (±5.9) (p = 0.008). Conclusion: Presence of respiratory muscle wasting prior to surgery was found to be associated with postoperative respiratory failure.