Higher Intraoperative Mechanical Power Linked to Impaired Oxygenation and Pulmonary Complications After Orthopedic Surgery

This post hoc analysis of a cluster factorial randomized trial investigated the association between intraoperative mechanical power normalized to predicted bodyweight and postoperative respiratory outcomes in patients undergoing orthopedic surgery. The study included 2,582 patients (2,860 surgeries) with a mean age of 63 ± 14 years, 53% female, 83% White, and a mean BMI of 31 ± 7 kg/m². Most patients were ASA Physical Status III (72%). The intervention was intraoperative mechanical power normalized to predicted bodyweight, and no comparator was reported. The primary outcome was not reported; secondary outcomes included impaired oxygenation in the postanesthesia care unit (PACU) and ward, postoperative pulmonary complications (PPCs), and length of postoperative hospital stay (LoS). Follow-up duration was not reported.

For the outcome of SF-TWA (a measure of oxygenation impairment) in the PACU, each 0.1 J/min/kg increment in mechanical power was associated with a reduction of -11 (95% CI, -14 to -8; P < 0.001). Similarly, in the wards, the reduction was -8 (95% CI, -11 to -5; P < 0.001). For PPCs, each 0.1 J/min/kg increment was associated with higher odds (odds ratio 1.55; 95% CI, 1.05 to 2.27; P = 0.026). Length of hospital stay was unrelated to mechanical power (effect size 1.01; 95% CI, 0.97 to 1.05; P = 0.68). Safety outcomes, including adverse events, serious adverse events, discontinuations, and tolerability, were not reported.

These results should be interpreted in the context of prior studies. Previous research has suggested that higher mechanical power during mechanical ventilation may contribute to ventilator-induced lung injury, but data specific to orthopedic surgery are limited. This analysis extends those findings to a surgical population, though the observational nature of the analysis precludes causal inference.

Key methodological limitations include the post hoc design, which increases the risk of bias and confounding. The study did not report a primary outcome, and the analyses were exploratory. Additionally, the population was predominantly White and had high ASA physical status, which may limit generalizability. The lack of reported follow-up duration and safety data further limits interpretation.

For clinical practice, these findings suggest that intraoperative mechanical power may be a modifiable factor associated with postoperative respiratory outcomes. However, given the associative nature of the evidence, clinicians should not change practice based solely on these results. Prospective trials are needed to confirm whether reducing mechanical power improves outcomes.

Several questions remain unanswered. The optimal threshold for mechanical power, the impact of different ventilation strategies, and whether these associations are causal are unknown. Additionally, the role of patient-specific factors and the generalizability to other surgical populations require further investigation.