RISK-FACTORS FOR MORBIDITY IN MECHANICALLY VENTILATED PATIENTS WITH ACUTE SEVERE ASTHMA

Acute severe asthma is associated with significant morbidity and mortality. We retrospectively quantified hypotension, pulmonary barotrauma, and cardiac arrhythmias in all patients with severe asthma admitted to the intensive care unit (ICU) and prospectively evaluated the predictive value of a measurement of dynamic hyperinflation (DHI) in those patients who required mechanical ventilation. In the first study, 88 ICU admissions tor severe asthma over 5 yr (73 patients, 40 +/- 18 yr, 36 men, 37 women) were evaluated. Fifty-one admissions wore mechanically ventilated, 29 were not, and 8 previously ventilated patients remained briefly intubated but were not ventilated in the ICU. Hypotension (18/88, 20%), pulmonary barotrauma (12/88,14%), and arrhythmias (9/88, 10%) were entirely confined to patients who had been mechanically ventilated. There were no significant differences in ventilatory parameters, airway pressures, or blood gases between mechanically ventilated patients with and without complications. Two patients with previous severe hypoxic cerebral damage died from this complication after ICU discharge. In the second study, the end-inspiratory lung volume (VEI) (1) was compared with standard ventilatory parameters in 22 patients. There were no ICU deaths, but high incidences of pulmonary barotrauma (27%) and hypertension (41%) were found. Both minute ventilation (VE and VEI) were significantly higher in patients who developed complications (VE 13.7 +/- 3.0 versus 11.2 +/- 2.5 L/min, VEI 28.1 +/- 4.7 versus 20.0 +/- 7.4 ml/kg, p < 0.05) but only VEI had a threshold value significantly predictive of complications. For VEI < 1.4 L, 0/5 (0%) patients had complications; for VEI greater-than-or-equal-to 1.4 L, 11/17 (05%) had complications (p = 0.03). We concluded that a causal relationship between mechanical ventilation and complications is probable, that risk of hypotension and barotrauma is best predicted by VEI, and that alteration of ventilatory pattern based on this measurement is most likely to reduce morbidity in mechanically ventilated patients with severe asthma.