Acute exacerbations in patients with COPD: predictors of need for mechanical ventilation

Predictive factors in mechanically-ventilated patients with acute exacerbations of chronic obstructive pulmonary disease (COPD) have been extensively studied but not in spontaneously breathing patients. The aim of this retrospective study was to evaluate the contribution of parameters of respiratory mechanics, clinical and nutritional status in predicting the need for mechanical ventilation (MV) in COPD patients treated with medical therapy for an acute exacerbation. Anthropometric data, Acute Physiology and Chronic Health Evaluation (APACHE) II score, bedside spirometry, breathing pattern, respiratory mechanics and blood gases were measured in 39 COPD patients upon hospital admission for exacerbation of their disease. Fourteen patients in whom MV was necessary were compared with 25 patients in whom medical therapy was enough for a good outcome. The discriminant analysis showed, with decreasing order of power, that nutritional prognostic index (NPI), APACHE II score, forced expiratory volume in one second/forced vital capacity (FEV1/FVC) ratio, vital capacity (VC) (% predicted) and FVC (% pred) provided a significant distinction between the two groups. The discriminant equation considering NPI, and FVC (% pred) could correctly predict the success in 76% of the patients. A multiparametric stepwise regression analysis showed that APACHE II score was significantly correlated with NPI, VC (% pred), pressure time index (PTI) and duty cycle, i.e. fraction of inspiration to duration of total breathing cycle (tl/ttot). In conclusion, underlying general conditions as assessed by malnutrition and APACHE II score were shown to be unfavourable indices of outcome for chronic obstructive pulmonary disease patients who experienced an exacerbation of their disease and were treated with medical therapy. Flow limitation data as assessed by the forced expiratory manoeuvre may provide additional information.