Patient-ventilator asynchrony during assisted mechanical ventilation

Abstract

During mechanical ventilatory assistance, patient-ventilator asynchrony occurs frequently. To avoid patient-ventilator asynchrony, the ventilator gas delivery pattern must match the patient's breathing pattern. Asynchrony may cause one or more of the following: poor gas exchange; hyperinflation of the lung; increased work of breathing owing to ventilator-induced diaphragmatic dysfunction; increased duration of both mechanical ventilation and ICU length of stay; and greater mortality. However, patient-ventilator asynchrony is easily overlooked. There are three general types of asynchrony: trigger asynchrony, cycling asynchrony, and flow asynchrony. Trigger asynchrony - caused by auto-triggering, ineffective inspiratory efforts (missed triggering), double triggering, and reverse triggering - occurs when the ventilator does not start pressurization in synchrony with the patient’s inspiratory effort. Cycling asynchrony occurs when the inspiratory time of patient, ventilator do not match, and may occur as premature cycling or delayed cycling. Flow asynchrony occurs when ventilator flow delivery does not match the inspiratory demand of the patient. To deal with this common problem, bedside clinicians need better understanding of causes, graphical characteristics and appropriate management of each asynchrony.