Efficacy of maintaining low-tidal volume mechanical ventilation as compared to resting lung strategy during coronary artery bypass graft cardiopulmonary bypass surgery: A post-hoc analysis of the MECANO trial

Abstract

Study objective: To compare a low-tidal-volume with positive end-expiratory pressure strategy (VENT strategy) to a resting-lung-strategy (i.e., no-ventilation (noV) strategy) during cardiopulmonary bypass for coronary artery bypass graft surgery on the incidence of postoperative pulmonary complications.

Design: Post-hoc analysis of the MECANO trial which was a prospective single-center, blind, randomized, parallel-group controlled trial.

Setting: Tertiary care cardiac surgery center.

Patients: Patients who underwent isolated on-pump coronary bypass surgery were randomized either to VENT or noV group.

Intervention: During the cardiopulmonary bypass phase of the cardiac surgery procedure, mechanical ventilation in the VENT group consisted of a tidal volume of 3 mL/kg, a respiratory rate of 5 per minute and a positive end-expiratory pressure of 5 cmH₂O. Patients in the noV group received no ventilation during this phase.

Measurements: Primary composite outcome combining death, early respiratory failure, ventilation support beyond day 2 and reintubation.

Main results: In this post-hoc analysis, we retained 725 patients who underwent isolated CABG surgery, from the 1501 patients included in the original study. There were 352 in the VENT group and 373 patients in the noV group. Post-hoc comparison yielded no differences in baseline characteristics between these two groups. The primary outcome occurred less frequently in the VENT group than in the noV group, with 44 (12.5%) and 76 (20.4%) respectively (odds-ratio (OR) = 0.56 (0.37-0.84), p = 0.004). There were fewer early respiratory dysfunctions and prolonged respiratory support in the VENT group (respectively, OR = 0.34 (0.12-0.96) p = 0.033 and OR = 0.51 (0.27-0.94) p = 0.029). Complications related to mechanical ventilation were similar in the two groups.

Conclusions: In this post-hoc analysis, maintaining low-tidal ventilation compared to a resting-lung strategy was associated with fewer pulmonary postoperative complications in patients who underwent isolated CABG procedures.

Keywords: Cardiac surgery; Cardiopulmonary bypass; Coronary artery bypass graft; Mechanical ventilation; Randomized controlled trial; Respiratory complications.