Noninvasive Ventilation after Surgical Myocardial Revascularization for Left-Ventricular Dysfunction: A Hypothesis-Generating Study

To the Editor:

Noninvasive ventilation (NIV) affects both the pulmonary and the cardiovascular systems. Indeed, it restores lung volume by opening atelectatic areas, increases alveolar ventilation, and reduces the work of breathing. Moreover, NIV reduces left ventricle afterload and improves cardiac output.

Currently, high-quality evidence supports the use of NIV after cardiac surgery because it significantly improves the patient's oxygenation and decreases the need for endotracheal intubation without significant complications. However, data about improvement of cardiovascular function are scarce, and a mild reduction of the cardiac function due to NIV has been reported. Thus, a judicious application is wise, with constant hemodynamic monitoring in case of reduced left ventricular function. In this line, we read with great interest the study by Marcondi et al,¹ which evaluated the acute effects of NIV on central-venous oxygen saturation (S_c̄vO2) and blood lactate in subjects with left ventricular dysfunction during the early postoperative phase of coronary artery bypass graft surgery.¹ The authors found that NIV acutely improved S_c̄vO2 and decreased lactatemia, two known determinants of survival.² The authors are to be commended for their pioneering approach, nevertheless a few key aspects require comment to strengthen the message of the paper.

The timing of NIV implementation (ie, early after extubation) and the short duration of the application (ie, 1 h) raise clinical and physiological concerns. Similarly, there was no mention of the intra-operative course, data from hemodynamic monitoring, or concomitant medical or invasive therapy (eg, inotropic drugs, intra-aortic balloon pumping). Without these data, the interpretation of mere biochemical markers might be misleading.³ Moreover, the study sample is ample but poorly characterized, and stratification according to surgical technique might introduce further bias. Indeed, according to institutional practice, an on-pump technique might be a surrogate marker of more demanding revascularization, lower hemodynamic stability, less atherosclerotic burden, or surgeon expertise. A new target population has been clearly identified, but the inherent merits of NIV require further investigation.

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