Neural control of mechanical ventilation in respiratory failure

Mechanical ventilation is a life-saving intervention for the management of acute respiratory failure. Its objective is to reduce excessive respiratory effort while improving gas exchange. By applying positive pressure to the airway, the mechanical ventilator assumes to a varying extent the work necessary to breathe, thereby unloading the respiratory muscles. In its most basic form, called controlled mechanical ventilation, a pre-set tidal volume is delivered at a fixed rate, irrespective of the patient's own breathing pattern. If the mechanical and natural respiratory cycles are not matched, however, the patient `fights' the ventilator, causing discomfort, gas exchange deterioration and cardiovascular impairment. To avoid discoordination between the patient and the ventilator, it is often necessary to suppress the patient's intrinsic respiratory drive with the use of hyperventilation, sedation or even muscle paralysis, which increase the risk of complications due to excessive ventilation, drug-related adverse effects and muscle disuse atrophy. Assisted modes of mechanical ventilation, in which the mechanical breath is triggered by the patient's own inspiratory effort, were developed to address this. These modes enable the patient to influence the machine cycling to a varying extent, depending on the specific mode utilized. Although it is believed that assisted modes can reduce side effects and complications associated with controlled mechanical ventilation, coordination between spontaneous breathing and mechanical assistance is not guaranteed. Poor interaction between the patient and the ventilator remains one of the main problems in the management of patients with acute respiratory failure.