Intensive Alveolar Recruitment Protocol After Cardiac Surgery

Study Overview
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Brief Summary
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The purpose of this study was to evaluate prospectively the impact of two protective mechanical ventilation strategies, both using low tidal volume ventilation (6 mL/kg/ibw) after cardiac surgery. The study selected patients presenting signals of deficient gas exchange (PaO2/FIO2 < 250 at a PEEP [positive end expiratory pressure] of 5 cmH2O) in the immediate post-operative period. An aggressive alveolar recruitment protocol applying opening pressures of 45 cmH2O, followed by ventilation with PEEP = 13 cmH2O, was compared to the standard alveolar recruitment protocol of the institution, where an opening pressure of 20 cmH2O in the airways is followed by ventilation with PEEP = 8 cmH2O. After a stabilizing period of four hours of controlled mechanical ventilation, the patients followed the routine weaning protocol and physiotherapy protocol of the institution.

Detailed Description
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The postoperative period of cardiac surgery is associated with the development of pulmonary complications. Functional residual capacity can be reduced up to 50% and pulmonary volumes may be decreased until three months after surgery. Lung injury is the result of pulmonary inflammation (activated by cardiopulmonary bypass, the surgical procedure itself and ischemia-reperfusion injury), the adopted mechanical ventilation strategy and a consequence of previous cardiac and/or pulmonary dysfunction. The use of protective mechanical ventilation strategies with low tidal volumes since the immediate postoperative period, or since the operating room, has been shown to attenuate and prevent lung injury in previous studies selecting with high-risk patients. A more complex topic, however, has been the proof of the additional benefit of alveolar recruitment maneuvers during the brief period of mechanical ventilation after surgery. While the experimental evidence suggests that the use of an open lung approach could minimize the shearing forces in the lung parenchyma, enhancing the protection afforded by low tidal volume ventilation, innumerous concerns about the hemodynamic side effects, and the possibility of barotrauma have prevented the routine use of intensive alveolar recruitment protocols. Another matter of concern is the net efficacy of a recruitment maneuver applied in the post-operative period, instead of the intra-operative period. Thus, this study compared the impact of two protective mechanical ventilation strategies, both using low-tidal volume ventilation (6 mL/kg/ibw) after cardiac surgery, in a selective population of patients presenting signals of deficient gas exchange (PaO2/FIO2 < 250 at a PEEP of 5 cmH2O) in the immediate post-operative period. In a previous study at this institution, this subgroup of patients was shown to be at higher risks of postoperative pulmonary complications. During the short period of controlled mechanical ventilation after the patient arrival from the operating theater, an aggressive alveolar recruitment protocol applying opening pressures of 45 cmH2O, followed by ventilation with PEEP = 13 cmH2O, was compared to the standard alveolar recruitment protocol of the institution, where an opening pressure of 20 cmH2O in the airways is followed by ventilation with PEEP = 8 cmH2O. After an stabilizing period of four hours of controlled mechanical ventilation, the patients followed the routine weaning protocol and physiotherapy protocol of the institution. Our hypothesis was that the aggressive alveolar recruitment strategy might help in the reversal of collapse created during the surgery and short term mechanical ventilation during anesthesia and patient transportation. Previous studies have shown that this effect may extend to the post-extubation period, impairing lung function for a few days. Thus, we tested if the effect of an aggressive alveolar recruitment protocol was translated in a better lung compliance, better gas exchange, and fewer pulmonary complications in the post-operative periods (this latter was our primary outcome). Analysis of the length of stay was also scrutinized, consisting in our secondary outcome. All hemodynamic complications was reported, since we also anticipated that events of hemodynamic impairment might be more frequent in the aggressive recruitment arm, eventually obscuring the expected benefits .

Official Title
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Comparison of Two Protective Mechanical Ventilation Strategies After Cardiac Surgery: Aggressive Versus Moderate Alveolar Recruitment Strategies

Conditions
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Ventilator Induced Lung Injury, Cardiac Disease, Acute Lung Injury

Intervention / Treatment
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* Other: Intensive Alveolar Recruitment
* Other: Moderate Alveolar Recruitment


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Immediate postoperative period of myocardial revascularization and/or heart valve surgery (aortic and/or mitral) Age > 18 years and < 80 years No previous pulmonary disease Left ventricular ejection fraction > 35% Body mass index < 40 kg/m2 Oxygen index (PaO2/FiO2) < 250 Corrected volemic status (negative raising legs mean arterial pressure [MAP] variation < 10%) Written inform consent Exclusion Criteria: MAP (mean arterial pressure) < 60 mmHg Noradrenaline > 2 micrograms/Kg/min Acute arrhythmias Blooding associated to hemodynamic instability Need of re-surgery and/or mechanical circulatory assistance Suspicion of neurological alteration Chest tube with persistent air leak

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 80 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Intensive Alveolar Recruitment<br>Recruitment with opening pressures of 45 cmH2O in the airways. | Other: Intensive Alveolar Recruitment<br>* Recruitment with opening pressures of 45 cmH2O in the airways, followed by ventilation with PEEP = 13 cmH2O, during 4 hours of protective mechanical ventilation with tidal volume (VT) = 6 mL/kg/pbw.<br>|
| Active Comparator: Moderate Alveolar Recruitment<br>Recruitment with opening pressures of 20 cmH2O in the airways. | Other: Moderate Alveolar Recruitment<br>* Recruitment with opening pressures of 20 cmH2O in the airways, followed by ventilation with PEEP = 8 cmH2O, during 4 hours of protective mechanical ventilation with VT = 6 mL/kg/pbw.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Severity of Pulmonary Complications in the Post-operative Period | Score of pulmonary complications adapted from previous publications, with 5 degrees, where the higher one means death before hospital discharge, degree (4) means the need of mechanical ventilation for more than 48 hours after surgery or after reintubation, degree (3) means pneumonia or intense noninvasive ventilation need, degree (2) means hypoxemia and abnormal lung findings, degree 1 means simple atelectasis and degree (0) means no complication. The comparison used this ordinal variable, representing the highest score achieved during the post-operative period. The comparison between arms was made through the Mann-Whitney U test. Data shown are percentage of participants with pulmonary complications grade ≥ 3. | Participants were followed for the duration of hospital stay. | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Length of ICU Stay | Days since surgery until ICU discharge, analyzed through Kaplan-Meyer curves (log-Rank test), where the time to event is the time of discharge from the ICU. The censoring was performed at 28 days. Patients dying before leaving the ICU were censored as not discharged from ICU at day 28. | From the day of surgery up to ICU discharge, maximum censoring at day 28 after surgery | 
| Length of Hospital Stay | Days since surgery until Hospital discharge, analyzed through Kaplan-Meyer curves (log-Rank test), where the time to event is the time of discharge from the Hospital. The censoring was performed at 28 days. Patients dying before leaving the Hospital were censored as not discharged from Hospital at day 28. | From the day of surgery up to Hospital discharge, maximum censoring at day 28 after surgery | 
| Incidence of Barotrauma | Confirmed by X-ray. Test with logistic regression | Five days after surgery | 
| Hospital Mortality | Deaths occurred during hospital stay, tested with logistic regression. | From the day of surgery up to Hospital discharge or death, with no maximum censoring. | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Mechanical ventilation, Open lung approach, Blood gases, Cardiac surgery, Pulmonary complications