Mechanical ventilation in circulatory failure: Effects on biventricular function and on tissue oxygenation

Abstract

This review summarizes the cardiocirculatory effects of mechanical ventilation (MV) with or without a positive end-expiratory pressure (PEEP) in patients with myocardial dysfunction or failure. Special emphasis is given on the effects of MV on: a) myocardial function in case of left or right ventricular failure, b) myocardial oxygenation, and c) on oxygen consumption of the respiratory muscles and their consequence to oxygen delivery to other tissues. According to the clinical studies published in this field, the effects of MV on cardiocirculatory function are neither simple nor predictable. In critically ill patients, the magnitude and the consequences of the classical hemodynamic effects of MV may be substantially modulated by the presence of preexisting alterations in respiratory mechanics, biventricular function, sympathetic-adrenal activity, vasomotor tone and state of intravascular hydration of the patient. Especially in patients with circulatory failure and inefficient oxygen delivery to the tissues, a high oxygen cost of breathing may either deprive the rest of the body of desperately needed energy supplies or induce anaerobic metabolism and eventually fatigue of the respiratory muscles. Placing the respiratory muscles at rest by appropriately adjusted MV appears to be the best solution in case of circulatory failure. We conclude that, in mechanically ventilated patients the multifactorial nature of the mechanisms involved on heart lung interaction makes an individualized approach necessary and indicates that it is the evolution of the hemodynamic profile with treatment, rather than single measurements, that should lead to a diag-nosis.