Effect of Intraoperative Low Tidal Volume vs Conventional Tidal Volume on Postoperative Pulmonary Complications in Patients Undergoing Major Surgery: A Randomized Clinical Trial

Abstract

Importance: In patients who undergo mechanical ventilation during surgery, the ideal tidal volume is unclear.

Objective: To determine whether low-tidal-volume ventilation compared with conventional ventilation during major surgery decreases postoperative pulmonary complications.

Design, setting, and participants: Single-center, assessor-blinded, randomized clinical trial of 1236 patients older than 40 years undergoing major noncardiothoracic, nonintracranial surgery under general anesthesia lasting more than 2 hours in a tertiary hospital in Melbourne, Australia, from February 2015 to February 2019. The last date of follow-up was February 17, 2019.

Interventions: Patients were randomized to receive a tidal volume of 6 mL/kg predicted body weight (n = 614; low tidal volume group) or a tidal volume of 10 mL/kg predicted body weight (n = 592; conventional tidal volume group). All patients received positive end-expiratory pressure (PEEP) at 5 cm H2O.

Main outcomes and measures: The primary outcome was a composite of postoperative pulmonary complications within the first 7 postoperative days, including pneumonia, bronchospasm, atelectasis, pulmonary congestion, respiratory failure, pleural effusion, pneumothorax, or unplanned requirement for postoperative invasive or noninvasive ventilation. Secondary outcomes were postoperative pulmonary complications including development of pulmonary embolism, acute respiratory distress syndrome, systemic inflammatory response syndrome, sepsis, acute kidney injury, wound infection (superficial and deep), rate of intraoperative need for vasopressor, incidence of unplanned intensive care unit admission, rate of need for rapid response team call, intensive care unit length of stay, hospital length of stay, and in-hospital mortality.

Results: Among 1236 patients who were randomized, 1206 (98.9%) completed the trial (mean age, 63.5 years; 494 [40.9%] women; 681 [56.4%] undergoing abdominal surgery). The primary outcome occurred in 231 of 608 patients (38%) in the low tidal volume group compared with 232 of 590 patients (39%) in the conventional tidal volume group (difference, -1.3% [95% CI, -6.8% to 4.2%]; risk ratio, 0.97 [95% CI, 0.84-1.11]; P = .64). There were no significant differences in any of the secondary outcomes.

Conclusions and relevance: Among adult patients undergoing major surgery, intraoperative ventilation with low tidal volume compared with conventional tidal volume, with PEEP applied equally between groups, did not significantly reduce pulmonary complications within the first 7 postoperative days.

Trial registration: ANZCTR Identifier: ACTRN12614000790640.

Figure 1.. Participant Flow Through the Randomized Clinical Trial

Discrepancy exists in the number of patients between groups because the study was undertaken in 2 phases, and in both phases, a randomization permuted by blocks of random size ranging from 4, 6, and 10 was used. In the first pilot phase of the study, recruitment was undertaken by a group of 10 anesthesiologists, each with an allocated permuted randomization sequence to follow. The second phase of the study occurred after securing additional funding support, which led to expansion of recruitment to all anesthesiologists. This also involved a combined permuted randomization sequence. ^aReasons for anesthesiologist decline were not collected. ^bAnesthesiologist withdrew patient after randomization (lack of clinical equipoise or when an arterial line was not inserted).

Figure 2.. Absolute Differences of Postoperative Respiratory Complications in Prespecified Subgroups

Sizes of data markers are proportional to the numbers of patients entering the analysis. P values are for the interaction between the subgroup and the treatment group. Lack of a significant interaction implies that the results are consistent across subgroups and that the overall effects estimated are the most appropriate estimates of treatment effect within each subgroup. ^aCalculated as weight in kilograms divided by height in meters squared. ^bRisk of complications is defined according to the Assess Respiratory Risk in Surgical Patients in Catalonia score as higher (≥26) or lower (<26).