We read with great interest the paper by Longo et al.1 on lung recruitment after cardiopulmonary bypass. The study focused on the correlation between two of the most dreaded complications of cardiac surgery: lung injury and perioperative right ventricular dysfunction.
Several pathogenic mechanisms are involved in postoperative lung injury. Some are specific to the cardiac surgery setting (median sternotomy, cardiopulmonary bypass, hypothermia, route of myocardial protection, mammary artery harvesting). Others relate to drawbacks of general anaesthesia and mechanical ventilation as well as to the transfusion of blood products. The complex and unpredictable interplay between the above reported factors and patient baseline pulmonary function leads to both anomalies in gas exchange and alterations in lung mechanics (affecting vital capacity, functional residual capacity along with static and dynamic compliance). Several preventive strategies have been advocated, including minimisation of cardiopulmonary bypass time, enhanced biocompatibility of extracorporeal circuits and associated perfusion technologies, pharmacological manipulations and the adoption of protective ventilation algorithms.2
Alveolar recruitment manoeuvres judiciously increase transpulmonary pressure to promote the opening of the largest possible number of alveoli. A growing body of knowledge clearly underscored the clinical benefits of alveolar recruitment manoeuvres in the cardiac surgery setting. Reduction of atelectasis and intrapulmonary shunting, improvements in ventilation–perfusion ratio and overall arterial oxygenation have been consistently reported. Nevertheless, there is still no consensus on several aspects of the recruitment technique, adverse events and contraindications have been definitively highlighted.3
Mechanisms of right ventricular failure in the non-transplant surgical setting include preexisting dysfunction, myocardial ischemia, ischemia–reperfusion injury, postoperative pulmonary hypertension, excessive volume loading and pericardial constriction. Identification of high-risk surgical candidates along with early recognition and management of right ventricular dysfunction are mandatory to reduce the incidence of refractory failure of the right ventricle (RV) with its inherent morbidity and mortality.
Optimisation of ventilation settings is mandatory in patients with overt right ventricular dysfunction to increase preload and decrease afterload. Hyperinflation is indeed strictly linked to an abrupt increase in pulmonary vascular resistance and narrowing of the capillaries of well ventilated areas with worsening of ventilation–perfusion matching. Avoidance of hypoxemia, and hypercapnia and correct pH management are similarly crucial to avoid refractory failure.
In the study by Longo et al.1, low-risk elective cardiac surgical patients were randomised to determine whether recruitment manoeuvre improved right ventricular function by reaerating the lung after cardiopulmonary bypass. The study is elegant and timely, and the authors should be commended for their efforts in linking haemodynamic and ventilator data to physiopathological patterns and extrapolating clinical advice. Nevertheless several limitations, as noted in the relevant paragraph in the manuscript, are to be considered for a thorough evaluation of the implications of that study. Despite being classified as low-risk elective patients the study population was not entirely homogenous. Differences in aetiology imply different surgical approaches, which in turn determine a variable degree of myocardial ischemia and intraoperative volume loading as well as postoperative ventricular loading conditions. Implications of coronary surgery are definitely different from mitral or valve repair or aortic valve replacement. Isolated ultrasound imaging for haemodynamic monitoring and detection of atelectasis has limitations. Finally, the time frame of the study was strictly limited to the very early perioperative phase. The observed ameliorations of the performance of the RV were also linked to targeted drug manipulations. All in all, the study largely confirms previous observations and reappraises the strict link between lung function and the performance of the RV along with the need for close patient monitoring and extensive use of preventive measures.
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1. Longo S, Siri J, Acosta C, et al. Lung recruitment improves right ventricular performance after cardiopulmonary bypass: a randomised controlled trial. Eur J Anaesthesiol
2. Huffmyer JL, Groves DS. Pulmonary complications of cardiopulmonary bypass. Best Pract Res Clin Anaesthesiol
3. Padovani C, Cavenaghi OM. Alveolar recruitment in patients in the immediate postoperative period of cardiac surgery. Rev Bras Cir Cardiovasc