[Effects of a pressure support ventilation of 6 cm H2O on oxygen consumption of the respiratory muscles during weaning of mechanical ventilation].

OBJECTIVE: To determine the effects of a pressure support ventilation (PSV) of 6 cm H(2)O during spontaneous breathing on oxygen consumption of the respiratory muscles (VO(2) resp), gas exchange, respiratory rate, tidal volume and to determine if these low levels of PSV can reduce or cancel the increase in work of breathing induced by the resistances of the endotracheal tube and the circuit of the respirator. PATIENTS AND METHODS: Prospective study. Twenty intubated patients were studied. The VO(2) resp was assessed by measurements of inspired and expired concentrations of oxygen (O(2)) and carbon dioxide (CO(2)) in patients during controlled ventilation and spontaneous breathing. Gas exchange, respiratory rate, minute ventilation, tidal volume and VO(2) resp were collected during spontaneous breathing with a PSV level of 6 cm H(2)O and without PSV. SETTING: Respiratory Intensive Care Unit, Amiens, University Hospital 80054 Amiens. RESULTS: A PSV level of 6 cm H(2)O significantly increased the spontaneous tidal volume (+12%) without any modification in respiratory rate, minute ventilation, tidal volume and gas exchange. No significant improvement in VO(2) resp was found when a PSV level of 6 cm H(2)O was added. CONCLUSION: Despite a significant increase in spontaneous tidal volume, adding a PSV level of 6 cm H(2)O did not improve VO(2) resp. Thus, low level of PSV did not reduce the increased work of breathing induced by the resistances of the ventilator tubing and the endotracheal tube.