Hypercapnia Test and Weaning outcome from Mechanical Ventilation in COPD Patients

Abstract

We evaluated the hypercapnia response test as a weaning outcome predictor from mechanical ventilation in patients with chronic obstructive pulmonary disease (COPD). We studied 44 COPD intubated patients considered ready for a weaning trial. The hypercapnia test was based on the modified method of re-inhalation of expired air. Through the hypercapnic test we calculated the ratio of the change in minute volume (VE) to the change in PaCO2 (ΔVE/ΔPaCO2), the change in airway occlusion pressure at 0.1 second of inspiration (P0.1) to change in PaCO2 (ΔP0.1/ΔPaCO2), the ratio of the change in P0.1 to baseline PaCO2 (ΔP0.1/PaCO2) and the ratio of the change in VE to baseline PaCO2 (ΔVE/PaCO2). Nineteen patients were successfully weaned and 25 patients failed. No differences in baseline clinical characteristics were found between the two groups. Weaning failure COPD patients had lower ΔP0.1/ΔPaCO2 (0.19±0.11 and 0.34±0.20 cm H2O/mmHg respectively, P=0.006) and lower ΔVE/ΔPaCO2 (0.21±0.15 and 0.40±0.22 l/min/mmHg respectively, P=0.002) than successfully weaned patients. The area under the receiver operating characteristic curve to discriminate weaning outcome was for the baseline PaCO2 0.81 (95% confidence interval: 0.66 to 0.91), hypercapnic PaCO2 0.76 (0.61 to 0.88), hypercapnic drive response 0.74 (0.59 to 0.86), hypercapnic ventilatory response 0.76 (0.60 to 0.87), ΔP0.1/PaCO2 0.76 (0.60 to 0.87) and for the ΔVE/PaCO2 0.81 (0.67 to 0.91). COPD patients with weaning failure have a significantly more blunted response to the hypercapnia response test than weaning success patients. This test could be useful to predict weaning failure patients if the combined values of the hypercapnic drive and hypercapnic ventilatory response were below the threshold values.

Hypercapnic Ventilatory Response in the Weaning of Patients with Prolonged Mechanical Ventilation

“…Hypercapnic ventilatory response has been used to predict weaning outcomes in ICU patients on short durations of mechanical ventilation [ 14 , 18 ] and in various other populations [ 16 – 18 ]. However, to the best of our knowledge, this study was the first to focus on subjects with PMV.…”

“…Any impairment of the respiratory system (ventilatory or neuromuscular apparatus and metabolic control) can reduce the hypercapnic ventilatory response [ 19 ]. ICU patients ready for weaning from mechanical ventilation but failing a spontaneous breathing trial have lower carbon dioxide (CO 2 ) response than successfully weaned patients [ 6 , 14 , 18 , 20 ]. Patient's age [ 21 ] and muscular weakness induced by mechanical ventilation [ 22 ] may contribute to the low hypercapnic ventilatory response.…”

CO2Response and Duration of Weaning From Mechanical Ventilation

“…Critically ill patients ready for weaning from mechanical ventilation but who fail a spontaneous breathing trial (SBT) have higher airway-occlusion pressure 0.1 s after the start of inspiratory flow (P 0.1 ) [1][2][3][4][5] and lower carbon dioxide (CO 2 ) response [6][7][8][9] than successfully weaned patients. However, those studies did not analyze the relationship between the CO 2 response and the duration of weaning.…”

The effects of acute carbon dioxide on behavior and physiology in Procambarus clarkii

“…A phenomena not well understood in humans, particularly people inflicted with chronic obstructive pulmonary disease, is the unresponsiveness to chronic increased levels of pCO 2 in the blood. Such people become more responsive to hypoxia (low pO 2 ) for respiratory drive than to elevated pCO 2 (Raurich et al, 2009; Zapata et al, 2009; Samolski et al, 2010). In fact, if O 2 ventilation is provided to relieve hypoxia, the respiratory rate will decrease further despite a large rise in pCO 2 .…”