CO2 response and duration of weaning from mechanical ventilation

Abstract

BACKGROUND: The CO2 response test measures the hypercapnic drive response (which is defined as the ratio of the change in airway-occlusion pressure 0.1 s after the start of inspiratory flow [ΔP0.1] to the change in PaCO [ΔPaCO2]), and the hypercapnic ventilatory response (which is defined as the ratio of the change in minute volume to ΔPaCO2). OBJECTIVE: In mechanically ventilated patients ready for a spontaneous breathing trial, to investigate the relationship between CO2 response and the duration of weaning. METHODS: We conducted the CO2 response test and measured maximum inspiratory pressure (PImax) and maximum expiratory pressure (PEmax) in 102 non-consecutive ventilated patients. We categorized the patients as either prolonged weaning (weaning duration > 7 d) or non-prolonged weaning (≤ 7 d). RESULTS: Twenty-seven patients had prolonged weaning. Between the prolonged and non-prolonged weaning groups we found differences in hypercapnic drive response (0.22 ± 0.16 cm H2O/mm Hg vs 0.47 ± 0.22 cm H2O/mm Hg, respectively, P 0.19 cm H2O/mm Hg, and 6.3 times higher if hypercapnic ventilatory response was > 0.15 L/min/mm Hg. Other variables (P0.1, PImax, and PEmax) were not associated with the duration of the weaning. CONCLUSIONS: Decreased CO2 response, as measured by hypercapnic drive response and hypercapnic ventilatory response, are associated with prolonged weaning. © 2011 Daedalus Enterprises.