‘Safe oxygen’ in acute asthma: prospective trial using 35% Ventimask prior to admission

There is still some uncertainty as to the best inspired oxygen concentration to use in the treatment of acute asthma before measurement of arterial blood gases can be made. In the absence of published data, we report a prospective study in which 35% oxygen was the initial therapy given to patients with moderate to severe asthma, and arterial blood gases were taken to assess the adequacy of oxygenation and the safety of this method. Fortyfive episodes were analyzed and a wide range of Pa o 2 was observed (8·8–21·3 kPa 66–160 mmHg). No relationship was shown between Pa co 2 and either Pa o 2 or duration of oxygen treatment. It was concluded that 35% oxygen given in acute asthma is both safe and probably adequate. A lesser concentration of oxygen could expose asthmatics to an unacceptable risk of significant hypoxaemia.