The clinical characteristics at the onset of a severe asthma attack and the effects of high frequency jet ventilation for severe asthmatic patients

To clarify the relationship between the clinical characteristics and the effects of high frequency jet ventilation based on the differences in the speed of deterioration in severe asthmatic patients who required intubation and mechanical ventilation, we classified 37 severe asthmatics into two groups (acute onset group: n= 20, intubated within 24 hours; slow onset group: n= 17, intubated over 3 days) and measured the arterial blood gas values, the duration of mechanical ventilation, and the peak inspiratory pressure during synchronized intermittent mechanical ventilation with or without high frequency jet ventilation. The acute onset group showed a significantly higher incidence of cyanosis (75 vs. 41, p< 0.05), an acute loss of consciousness (90 vs. 53, p< 0.05), severe mixed acidosis with extreme hypercapnoea (pH 7.11 ± 0.19, PaCO294.1 ± 10.7 mmHg, BE −8.3 ± 1.7 mEq/1), and a more elevated peak inspiratory pressure (59.7 ± 1.8 mmHg vs. 41.1 ± 1.8 mmHg, p< 0.05) during synchronized intermittent mechanical ventilation at admission, compared with the slow onset group (p< 0.05). The slow onset group required a more prolonged mechanical ventilation than the acute onset group (5.4 ± 4.0 vs. 3.0 ± 2.4 days, p< 0.05), in spite of a lower peak inspiratory pressure than that observed in the acute onset group, because of either a large amount of secretion or an infection in the airway. Both the high peak inspiratory pressure and the severe mixed acidosis with markedly elevated hypercapnoea were significantly reduced by the application of high frequency jet ventilation between the intra- and the inter-groups. These findings thus indicated the existence of significant differences in the clinical features and pathogenesis of airway hyperreactivity between these two groups, and the application of high frequency jet ventilation to the status asthmaticus was thus found to be effective.