Comparison of automated and static pulse respiratory mechanics during supported ventilation

Objective: To compare respiratory mechanics estimated by the pulse technique in spontaneously breathing patients during proportional assist ventilation (PAV) with loadadjustable gain factor (PAV+) mode with those measured using the flow-interruption technique during controlled ventilation. Design, participants and setting: Observational study of 21 haemodynamically stable post-cardiac surgery patients with routine weaning from mechanical ventilation (Puritan- Bennett 840 ventilator) in the intensive care unit of a tertiary hospital. Main outcome measures: Bland-Altman and linear correlation of respiratory system compliance and inspiratory resistance estimated during PAV+ (C _pulse and R _pulse ) with that measured during controlled mechanical ventilation (C _int and R _int ). Results: C _pulse overestimated C _int (67.4 [SD, 27.7] v 51.6 [SD, 9.7] mL/cmH ₂ O; P = 0.02), although the correlation between C _int and C _pulse was strong. Using the Bland-Altman method, the bias and limits of agreement were outside a clinically useful range. R _pulse underestimated R _int (9.3 [SD, 3.0] v 11.5 [SD, 3.0] cmH ₂ O/L/s; P = 0.02), with a weak positive correlation. Although the bias calculated by the Bland-Altman method was small, the limits of agreement were too large to be clinically useful. Conclusion: Based on these data, respiratory mechanics estimated from the pulse technique are too inaccurate to be clinically useful.