OBJECTIVE: To compare respiratory mechanics estimated by the (pulse) technique in spontaneously breathing patients during proportional assist ventilation (PAV) with load-adjustable 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 Rint). 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 Rint (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.
OBJECTIVE: To compare respiratory mechanics estimated by the (pulse) technique in spontaneously breathing patients during proportional assist ventilation (PAV) with load-adjustable 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 Rint). 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 Rint (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.