Intensive Alveolar Recruitment Protocol After Cardiac Surgery

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 .

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