Risk factors for near-fatal asthma.

Background: There is a paucity of lung function data in patients, both before and after episodes of near-fatal asthma (NFA), requiring transient endotracheal intubation and mechanical ventilation.

Methods: Lung function was initially measured in 43 asthmatic patients (age range, 16 to 49 years), who were observed and treated in a tertiary referral asthma clinic and were clinically stable at the time of study. Subsequently, clinical and physiologic follow-up studies were obtained over > 5 years. The primary outcomes were to determine (1) the integrity of lung elastic recoil and (2) the severity of expiratory airflow limitation, and (3) to correlate these outcomes with adverse clinical complications.

Results: Fourteen of 26 asthmatic patients (54%) [age range, 30 to 49 years] had significantly reduced lung elastic recoil pressures at all lung volumes compared to 3 of 17 asthmatic patients (18%); p = 0.02 [chi(2) test and Fisher exact test] [age range, 16 to 26 years]. In asthmatic patients between the ages of 30 and 49 years, significant loss of lung elastic recoil was noted in 4 of 10 patients with mild reduction in FEV(1) (FEV(1), > 79% predicted), 6 of 12 patients with moderate reduction in FEV(1) (FEV(1), 61 to 79% predicted), and all 4 patients with severe reduction in FEV(1) (FEV(1), < 61% predicted). In asthmatic patients between the ages of 16 and 26 years, significant loss of lung elastic recoil was noted in 0 of 11 patients with mild reduction in FEV(1), 2 of 5 patients with moderate reduction in FEV(1), and 1 of 1 patient with severe reduction in FEV(1). A subgroup of 10 asthmatic patients (7 men) [mean (+/- SD) age, 37 +/- 11 years] were studied when clinically stable, both before and after an episode of NFA in 8 cases and only after an episode of NFA in 2 additional cases. In 1 of 10 cases, the FEV(1) was mildly reduced, in 4 cases it was moderately reduced, and in 5 cases it was severely reduced, both before and after an episode of NFA. The sensitivity was 90%, the specificity was 61%, the positive predictive value was 41%, and the negative predictive value was 95% for NFA with an FEV(1) < or = 79% predicted or FEV(1)/FVC ratio of < 75%. Prior to an episode of NFA, all 8 asthmatic patients had significant loss of lung elastic recoil pressure, and afterward all 10 had significant loss of lung elastic recoil pressure (ie, less than the predicted normal mean minus 1.64 SD at a total lung capacity [TLC] of 100 to 70% predicted). The sensitivity was 100%, the specificity was 79%, the positive predictive value was 59%, and the negative predictive value was 100% for NFA with the loss of lung elastic recoil. The mean TLC measured with a plethysmograph in 10 patients with NFA was 7.2 +/- 1.41 (124 +/- 16% predicted). The sensitivity for TLC of > 115% predicted was 70%, the specificity was 70%, the positive predictive value was 88%, and the negative predictive value was 41% for NFA.

Conclusion: A persistent reduction in FEV(1) of < or = 79% predicted or an FEV(1)/FVC ratio of < 75%, and, especially, the loss of lung elastic recoil and hyperinflation at TLC are risk factors for NFA. The loss of lung elastic recoil in asthmatic patients was associated with increased age, duration of disease, and progressive expiratory airflow limitation.