Pulmonary gas exchange response to weaning with pressure-support ventilation in exacerbated chronic obstructive pulmonary disease patients

Abstract

Objective: To assess if pressure-support ventilation (PSV) can improve ventilation-perfusion (VA/Q) imbalance observed during the transition from positive-pressure ventilation to spontaneous breathing in intubated chronic obstructive pulmonary disease (COPD) patients during weaning. Design: Prospective study. Setting: Respiratory intensive care unit of a tertiary university hospital. Patients: Seven mechanically ventilated COPD male patients (age 68±6 (SD) years; FEV1 26±6% predicted) during weaning. Interventions: Patients were studied during three ventilatory modalities: (1) assist-control ventilation (ACV), tidal volume (VT), 8-10 ml. kg-1; (2) PSV aimed to match VT in ACV, 15±1 cmH2O and (3) spontaneous breathing. Measurements and results: Arterial and mixed venous respiratory blood gases, VA/Q distributions, hemodynamics and breathing pattern were measured. Compared with both ACV and PSV, during spontaneous breathing patients exhibited decreases in VT (of 43%, p<0.001) and increases in respiratory rate (of 79%, p<0.001), PaCO2 (of 8.5 mmHg, p=0.001), cardiac output (of 27%, p<0.001) and mixed venous oxygen tension (of 3.4 mmHg, p=0.003), while PaO2 remained unchanged throughout the study. Except for a shift of the pulmonary blood flow distribution to areas with lower VA/Q ratios (p=0.044) and an increase of dead space (of 25%, p=0.004) during spontaneous breathing, no other changes in VA/Q distributions occurred. No differences were shown between ACV and PSV modalities. Conclusion: In COPD patients during weaning, PSV avoided VA/Q worsening during the transition from positive-pressure ventilation to spontaneous breathing. Hemodynamics, blood gases or VA/Q mismatch were no different between ACV and PSV when both modalities provided similar levels of ventilatory assistance.