Patient-ventilator asynchrony in adult critically ill patients

Patient-ventilator asynchrony is considered as a major clinical problem for mechanically ventilated patients. It occurs during partial ventilatory support, when the respiratory muscles and the ventilator interact to contribute generating the volume output. In this review article, we consider all studies published on patient-ventilator asynchrony in the last 25 years. We selected 62 studies. The different forms of asynchrony are first defined and classified. We also describe the methods used for detecting and quantifying asynchronies. We then outline the outcome variables considered for evaluating the clinical consequences of asynchronies. The methodology for detection and quantification of patientventilator asynchrony are quite heterogeneous. In particular, the Asynchrony Index is calculated differently among studies. Sixteen studies established some relationship between asynchronies and one or more clinical outcomes, such as duration of mechanical ventilation (7 studies), mortality (5 studies), length of intensive care and hospital stay (4 studies), patient comfort (4 studies), quality of sleep (3 studies), and rate of tracheotomy (3 studies). In patients with severe patient-ventilator asynchrony, 4 of 7 studies (57%) report prolonged duration of mechanical ventilation, one of 5 (20%) increased mortality, one of four (25%) longer intensive care and hospital lengths of stay, 4 of 4 (100%) worsened comfort, three of four (75%) deteriorated quality of sleep, and one of three (33%) increased rate of tracheotomy. Given the varying outcomes considered and the erratic results, it remains unclear whether 1) asynchronies really affects patient outcome, and 2) the relationship between asynchronies and outcome is causative or associative.