[Acute respiratory failure in chronic obstructive lung disease. Effective weaning and excess base]

To establish whether the weaning from assisted mechanical ventilation (AMV) should be accompanied by continuous respiratory support (synchronized intermittent mandatory ventilation [SIMV]) or discontinuous support (O2 in T) in patients affected by chronic obstructive lung disease (COLD) who are recovering from acute respiratory failure (ARF), and also to identify any possible predictive value of gasometric measurements. Sixteen patients with COLD and ARF were studied prospectively during their stay in the intensive care unit. Ten had acute bronchitis, 3 had left ventricular failure and 2 had pneumonia. In 1 case the etiology was unknown. The following protocol was used for the first attempt at weaning: 1) SIMV for 30 min, 2) return to rest period with AMV for 2 hours, 3) O2 in T-tube for 30 min. After 30 min both SIMV and O2 in T had produced a rise in PaCO2 to 55.1 and 54.6 mmHg, respectively (p < 0.001), with a subsequent lowering of pH to 7.32 and 7.36 (p < 0.001). When weaning was well tolerated, pH decreased significantly due to an increase in PaCO2 with both techniques, while base excess (BE) remained stable. Values of pH also decreased significantly when weaning was poorly tolerated, and the fall was greater with SIMV; increases in PaCO2 were similar, but decreases in BE were significant. When pH is kept within normal range by a high BE, the withdrawal of AMV, accompanied by either support system, is usually well-tolerated.