Noninvasive mechanical ventilation in acute on chronic respiratory failure: determinants of success and failure

Mechanical ventilation (MV) has been indicated in the treatment of acute respiratory failure (ARF) if conservative treatment fails. The recent innovations of noninvasive methods of mechanical ventilation (NMV) make it possible to avoid the complications of invasive MV, at the same time ensuring a similar degree of efficacy. A review of the literature from 1989 to 1996 shows that use of NMV in ARF has been reported in several studies involving more than 500 patients, mostly with chronic obstructive pulmonary disease (COPD). NMV was successful in 51-91% of cases, the severity of ARF being widely different among the different studies. Only three prospective, controlled, randomized studies compared the effectiveness of NMV with "conventional" medical therapy. Controlled studies of NMV versus endotracheal (ET) intubation are lacking. Success with NMV was associated with less severely abnormal baseline clinical and functional parameters and with less severe levels of acidosis assessed during an initial trial of NMV. Therefore, NMV may be useful in selected patients with ARF. Patients should have clinical and physiological evidence of ARF, and should be sufficiently co-operative. It is commonly said that NMV should be avoided and ET intubation performed in patients with haemodynamic instability, uncontrolled arrhythmias, gastrointestinal bleeding, or high risk for aspiration. With these limitations, NMV in selected patients with ARF is well-tolerated and may be useful in avoiding ET intubation in most cases of COPD, and with a wide range of success rates in other diseases. This in turn has several advantages in terms of avoiding complications of invasive MV, reducing the length of stay in the Intensive Care Unit (ICU), and probably the number of ICU readmissions. Side-effects of NMV appear less severe than those induced by invasive MV.