BACKGROUNDS: Previous reports have revealed a high morbidity and mortality in fatal asthma patients, especially those treated in the medical intensive care unit(MICU). But it has not been well known about the predictable factors for the mortality of fatal asthma(FA) with acute respiratory failure. In order to define the predictable factors for the mortality of FA at the admission to MICU, we analyzed the relationship between the clinical parameters and the prognosis of FA patients. METHODS: A retrospective analysis of all medical records of 59 patients who had admitted for FA to MICU at a tertiary care MICU from January 1992 to March 1997 was performed. RESULTS: Over all mortality rate was 32.2% and 43 patients were mechanically ventilated. In uni-variate analysis, the death group had significantly older age (66.2 +/- 10.5 vs. 51.0 +/- 18.8 year), lower FVC(59.2 +/- 21.1 vs. 77.6 +/- 23.3%) and lower FEV1(41.4 +/- 18.8 vs. 61.1 +/- 23.30%), and longer total ventilation time (255.0 +/- 236.3 vs. 98.1 +/- 120.4 hour)(p<0.05) compared with the survival group (PFT : best value of recent 1 year). At MICU admission, there were no significant differences in vital signs, PaCO2, PaO2/FiO2 and AaDO2 in both groups. However, on the second day of MICU, the death group had significantly more rapid pulse rate (121.6 +/- 22.3 vs. 105.2 +/- 19.4 rate/min), elevated PaCO2(50.1 +/- 16.5 vs. 41.8 +/- 12.2 mmHg), lower PaO2/FiO2(160.8 +/- 59.8 vs. 256.6 +/- 78.3mmHg), higher AaDO2(181.5 +/- 79.7 vs. 98.6 +/- 47.9mmHg), and higher APACHE III score (57.6 +/- 21.1 vs. 20.3 +/- 13.2) than survival group (p<0.05). The death group had more frequently associated with pneumonia and anoxic brain damage at admission, and had more frequently developed sepsis during disease progression than the survival group (p<0.05). Multi-variate analysis using APACHE III score and PaO2/FiO2 ratio on first and second day, age, sex, and pneumonia combined at admission revealed that APACHE III score (40) and PaO2/FiO2 ratio (<200) on second day were regarded as predictive factors for the mortality of fatal asthma (p<0.05). CONCLUSIONS: APACHE III score (>or=40) and PaO2/FiO2 ratio (<200) on the second day of MICU, which might reflect the response of treatment, rather than initially presented clinical parameters would be more important predictable factors of mortality in patients with FA.