Evaluate the accuracy of criteria for diagnosing pressure overassistance during pressure support ventilation.
Prospective clinical study.
Adults under mechanical ventilation for 48 hours or more using pressure support ventilation and without any sedative for 6 hours or more. Overassistance was defined as the occurrence of work of breathing less than 0.3 J/L or 10% or more of ineffective inspiratory effort. Two alternative overassistance definitions were based on the occurrence of inspiratory esophageal pressure-time product of less than 50 cm H2O s/min or esophageal occlusion pressure of less than 1.5 cm H2O.
The pressure support was set to 20 cm H2O and decreased in 3-cm H2O steps down to 2 cm H2O.
The following parameters were evaluated to diagnose overassistance: respiratory rate, tidal volume, minute ventilation, peripheral arterial oxygen saturation, rapid shallow breathing index, heart rate, mean arterial pressure, change in esophageal pressure during inspiration, and esophageal and airway occlusion pressure. In all definitions, the respiratory rate had the greatest accuracy for diagnosing overassistance (receiver operating characteristic area = 0.92; 0.91 and 0.76 for work of breathing, pressure-time product and esophageal occlusion pressure in definition, respectively) and always with a cutoff of 17 incursions per minute. In all definitions, a respiratory rate of less than or equal to 12 confirmed overassistance (100% specificity), whereas a respiratory rate of greater than or equal to 30 excluded overassistance (100% sensitivity).
A respiratory rate of 17 breaths/min is the parameter with the greatest accuracy for diagnosing overassistance. Respiratory rates of less than or equal to 12 or greater than or equal to 30 are useful clinical references to confirm or exclude pressure support overassistance.
1Pulmonary Division, Heart Institute (InCor), Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil.
2Intensive Care Unit, AC Camargo Cancer Center, São Paulo, Brazil.
3Sírio-Libanês Teaching and Research Institute, São Paulo, Brazil.
*See also p. 488.
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Work was performed at the Heart Institute (InCor), Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil.
Supported and funded by Fundação de Amparo a Pesquisa do Estado de São Paulo (Fapesp) (2012/09170-3 and 2010/08947-9), a governmental nonprofit agency. No restrictions were placed on authors regarding the statements made in the manuscript.
Dr. de Albuquerque received support for article research from FAPESP - Fundação de Amparo à Pesquisa do Estado de São Paulo, and he disclosed government work. The remaining authors have disclosed that they do not have any potential conflicts of interest.
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