Determinants of near fatality in acute severe asthma

The data extrapolated from cases of acute severe asthma that narrowly miss being fatal may prove valuable in the identification of the factors implicated in mortality. The purpose of this study was, therefore, to identify determinants of near fatality in patients with acute severe asthma.

We studied 81 patients with acute severe asthma in whom mechanical ventilation was required. Near fatality was defined as the occurrence of respiratory arrest and/or coma necessitating emergency tracheal intubation and resuscitation. In the cases that were not regarded as near fatal, tracheal intubation was performed electively because of deteriorating arterial blood gas values and/or the anticipation of exhaustion. Various continuous and categorical variables were compared in these two groups of patients. Patients with a hyperacute attack (period from onset of attack to mechanical ventilation less than 3 hours) were specifically sought and studied to determine the impact of such a course on near fatality.

The "attack duration" (period from onset of attack to mechanical ventilation) was an important determinant of near fatality and of the subsequent clinical course. It was shorter in the group with a near-fatal episode (p < 0.03), and hyperacute attacks were uniformly near fatal. The attack duration correlated positively with the duration of the requirement for mechanical ventilation (p < 0.01). A longer attack duration was associated with an increased likelihood of the occurrence of major atelectasis (p < 0.01). There was no evidence of a relationship between near fatality and the side effects of bronchodilators as regards hypokalemia, arrhythmias, or cardiotoxicity. There was evidence of considerable under-treatment in the patient population as a whole, particularly in regard to the use of corticosteroids.

A short attack duration is associated with an increased risk of near fatality in acute severe asthma. This is particularly evident in hyperacute attacks. Hyperacute attacks resolve rapidly once bronchodilator therapy has been instituted, suggesting that smooth muscle spasm is the predominant pathogenetic mechanism. The importance of routine anti-inflammatory therapy in mild to moderate asthma requires re-emphasis but, in addition, all patients should be provided with, and educated in the use of, bronchodilator rescue therapy, which should be available at all times. Despite current trends, the use of regular, prophylactic bronchodilator therapy in strict conjunction with anti-inflammatory agents may still be indicated. There is little evidence in the present data obtained from near-fatal cases to support the concept that cardiotoxicity related to bronchodilators contributes significantly to mortality from asthma.