Objective: We propose that higher airway occlusion pressure (P0.1) responses to hypercapnic challenge (HC) indicate less severe injury. The study aim was to determine whether P0.1 responses to HC were associated with successful weaning after prolonged mechanical ventilation (PMV) in patients with brainstem lesions and to determine a reference value for clinical use.
Design and setting: Forty-two patients with brainstem lesions on PMV were recruited. Breathing parameters and P0.1 were measured before HC. Three-minute HC challenges with increasing CO(2) concentrations were initiated and P0.1, respiratory rate, minute ventilation (V (e)), tidal volume (V (t)) and end tidal CO(2) were measured.
Measurements and results: Patients were classified into high (group I) and low (group II) response groups on the basis of P0.1 responses to HC. Increases in V (e) and V (t) after HC were significantly greater in group I patients (12.22 +/- 8.22 vs. 3.08 +/- 4.84 L/min, P < 0.001 and 399.11 +/- 278.18 vs. 110.54 +/- 18.275 ml, P < 0.001). P0.1 levels were significantly higher in group I compared to group II before HC (2.69 +/- 1.81 vs. 1.28 +/- 1.04 cmH(2)O, P = 0.003). The increase in P0.1 following HC was significantly greater in group I compared to group II patients (11.05 +/- 4.06 vs. 2.90 +/- 2.53 cmH(2)O, P < 0.001). Weaning success was significantly higher in group I compared to group II patients (72.2% vs. 33.3%, P = 0.02). A P0.1 increase of >6 cmH(2)O following HC was significantly associated with successful weaning.
Conclusions: Assessing the P.01 response to serial increases in the level of HC may be a safe means to ascertain whether patients with brainstem lesions are ready for ventilator weaning.