Intraoperative Mechanical Ventilation and Postoperative Pulmonary Complications After Cardiac Surgery

Michael R. Mathis, M.D.; Neal M. Duggal, M.D.; Donald S. Likosky, Ph.D.; Jonathan W. Haft, M.D.; Nicholas J. Douville, M.D., Ph.D.; Michelle T. Vaughn, M.P.H.; Michael D. Maile, M.D., M.S.; Randal S. Blank, M.D., Ph.D.; Douglas A. Colquhoun, M.B., Ch.B., M.Sc., M.P.H.; Raymond J. Strobel, M.D., M.S.; Allison M. Janda, M.D.; Min Zhang, Ph.D.; Sachin Kheterpal, M.D., M.B.A.; Milo C. Engoren, M.D.

Disclosures

Anesthesiology. 2019;131(5):1046-1062. 

In This Article

Abstract and Introduction

Abstract

Background: Compared with historic ventilation strategies, modern lung-protective ventilation includes lower tidal volumes (VT), lower driving pressures, and application of positive end-expiratory pressure (PEEP). The contributions of each component to an overall intraoperative protective ventilation strategy aimed at reducing postoperative pulmonary complications have neither been adequately resolved, nor comprehensively evaluated within an adult cardiac surgical population. The authors hypothesized that a bundled intraoperative protective ventilation strategy was independently associated with decreased odds of pulmonary complications after cardiac surgery.

Methods: In this observational cohort study, the authors reviewed nonemergent cardiac surgical procedures using cardiopulmonary bypass at a tertiary care academic medical center from 2006 to 2017. The authors tested associations between bundled or component intraoperative protective ventilation strategies (VT below 8 ml/kg ideal body weight, modified driving pressure [peak inspiratory pressure – PEEP] below 16 cm H2O, and PEEP greater than or equal to 5 cm H2O) and postoperative outcomes, adjusting for previously identified risk factors. The primary outcome was a composite pulmonary complication; secondary outcomes included individual pulmonary complications, postoperative mortality, as well as durations of mechanical ventilation, intensive care unit stay, and hospital stay.

Results: Among 4,694 cases reviewed, 513 (10.9%) experienced pulmonary complications. After adjustment, an intraoperative lung-protective ventilation bundle was associated with decreased pulmonary complications (adjusted odds ratio, 0.56; 95% CI, 0.42–0.75). Via a sensitivity analysis, modified driving pressure below 16 cm H2O was independently associated with decreased pulmonary complications (adjusted odds ratio, 0.51; 95% CI, 0.39–0.66), but VT below 8 ml/kg and PEEP greater than or equal to 5 cm H2O were not.

Conclusions: The authors identified an intraoperative lung-protective ventilation bundle as independently associated with reduced pulmonary complications after cardiac surgery. The findings offer insight into components of protective ventilation associated with adverse outcomes and may serve as targets for future prospective interventional studies investigating the impact of specific protective ventilation strategies on postoperative outcomes after cardiac surgery.

Introduction

Postoperative pulmonary complications, a well-documented group of complications after cardiac surgery, are associated with a fourfold increase in mortality,[1,2] extended intensive care unit (ICU) and hospital lengths of stay,[2,3] and more than $20,000 in institutional expenses per event.[3–5] In the cardiac surgery population, measurable derangements in pulmonary function occur in nearly all patients,[6,7] and approximately 10% to 25% develop postoperative pulmonary complications requiring substantial healthcare resource utilization.[1,6]

Cardiopulmonary bypass (CPB), mechanical ventilation, and surgical manipulation of the thoracic cavity each play major roles in the evolution of pulmonary injury.[1] Preoperative, intraoperative, and postoperative factors impact a patient's ability to cope with these insults.[7,8] Several externally validated risk scores incorporating these factors have been developed to improve risk stratification for postoperative pulmonary complications after cardiac surgery.[9,10] Despite rigorous model development, shortcomings of postoperative pulmonary complication prediction models remain evident. One recent multicenter study demonstrated that a large proportion of variation in pneumonia rates remains unexplained by prediction models focused on surgical technique and underlying patient risk, suggesting that other unmeasured practices may account for the differences observed.[11] One such process of care associated with postoperative pulmonary complications, yet not accounted for in current prediction models, is the practice of intraoperative lung-protective ventilation. Compared with historic intraoperative ventilation techniques, modern lung-protective ventilation strategies use lower tidal volumes (VT),[1,4,5,12–15] lower driving pressures,[16–18] and positive end-expiratory pressure (PEEP).[13,15,19] These techniques have already gained acceptance in ICUs after large studies have demonstrated reduced morbidity and mortality.[18,20] However, the contributions of each component to an overall intraoperative lung-protective ventilation strategy aimed at reducing postoperative pulmonary complications (postoperative pulmonary complications) have not been comprehensively studied in an adult cardiac surgical population.

Although ICU ventilation after cardiac surgery has been assessed,[21,22] scarce data currently exist evaluating the relationship between intraoperative ventilator management during cardiac surgery, postoperative pulmonary complications, and mortality. Because the post-CPB intraoperative period represents a unique transition from often nonventilated to ventilated lungs, optimizing respiratory mechanics to reduce lung injury is of critical concern. To better characterize this currently understudied relationship, we performed an observational cohort study using the Society of Thoracic Surgeons and Multicenter Perioperative Outcomes Group databases at our institution. We hypothesized that a bundled intraoperative lung-protective ventilation strategy (i.e., lower VT, driving pressure, and application of PEEP) was independently associated with decreased odds of postoperative pulmonary complications after cardiac surgery, when adjusted within a novel, robust multivariable model leveraging data uniquely available from each database. We additionally hypothesized that when studied as separate exposures, components of the intraoperative bundled lung-protective ventilation strategy had differential associations with postoperative pulmonary complications.

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