Intravenous isoproterenol: rationale for bronchial asthma

Intravenous isoproterenol was infused into 7 adult asthmatic patients with refractory bronchial obstruction. Over a dose range of 0.0375 to 0.225 mug per kilogram per minute, maximal bronchodilator effect (or reversal of effect) occurred within 2 to 5 minutes of starting (or stopping) the infusion. Obstruction to airflow improved with each increment of dose. Average heart rate reached a maximum at 0.075 mug per kilogram per minute. Over the lower dose range alveolar to arterial oxygen gradients widened and heart rate increased; over the higher dose range, as heart rate plateaued, bronchodilator effect continued and oxygen gradient narrowed. When combined with adequate oxygenation and continual monitoring of cardiac rhythm and blood pressure, intravenous isoproterenol appears safe for asthmatic patients. Major advantages are (1) administration of bronchodilator to airways not reached by inhalation, (2) prompt onset and offset of effects, and (3) reversal of undesirable side effects. The use of intravenous isoproterenol may obviate the need for intubation and ventilatory assist.