ARTERIAL OXYGEN-SATURATION IN ACUTE CHILDHOOD ASTHMA - INTERPRETATIONOF CHANGE FOLLOWING SALBUTAMOL NEBULIZATION

The significance of change in SaO2 (DELTASaO2) following initialf bron chodilator therapy in acute childhood asthma is not clear. Increase in SaO2 following initial bronchodilator therapy has been advocated as a measure of improvement in acute asthma. We hypothesized that the init ial level of SaO2 would be inversely related to DELTASaO2 and would ch ange very little for most children with mild or moderate asthma. There fore, we measured SaO2 before and 30 min after salbutamol inhalation i n 135 children (age range 1-14.5 yr) presenting to an emergency room w ith mild/moderate (SaO2 > 91%) and severe (SaO2 less-than-or-equal-to 91%) asthma. DELTASaO2 was inversely related to initial SaO2 (p < 0.01 ) with the greatest rise (7%) occurring in children with the lowest in itial level (84%). SaO2 increased more in the severe group than the mi ld to moderate group-2.3% versus 0.6% respectively (p < 0.01)-although the change in peak expiratory flow (PEF) was similar for both groups. DELTASaO2 expressed as a percent of potential increase increased with decreasing SaO2 indicating that a small DELTASaO2 at a higher initial SaO2 could not be fully explained by a ''ceiling'' effect. We postula te that varying contributions of bronchoconstriction and ventilation p erfusion inequality could explain this observation. Thus, salbutamol u sually improves hypoxia in severe asthma, but SaO2 is not a reliable g uide to response to initial bronchodilator therapy in the majority of children with asthma (SaO2 greater-than-or-equal-to 91%) as it usually increases little and does not reflect increase in PEF.