EFFECT OF EXPOSURE TO 15-PERCENT OXYGEN ON BREATHING PATTERNS AND OXYGEN-SATURATION IN INFANTS - INTERVENTIONAL STUDY

Objective: To assess the response of healthy infants to airway hypoxia (15% oxygen in nitrogen). Design: Interventional study. Settings: Inf ants' homes and paediatric ward. Subjects: 34 healthy infants (20 boys ) born at term; mean age at study 3.1 months. 13 of the infants had si blings whose deaths had been ascribed to the sudden infant death syndr ome. Intervention: Respiratory variables were measured in room air (pr e-challenge), while infants were exposed to 15% oxygen (challenge), an d after infants were returned to room air (post-challenge). Main outco me measures: Baseline oxygen saturation as measured by pulse oximetry, frequency of isolated and periodic apnoea, and frequency of desaturat ion (oxygen saturation less than or equal to 80% for greater than or e qual to 4 s), Exposure to 15% oxygen was terminated if oxygen saturati on fell to less than or equal to 80% for greater than or equal to 1 mi n. Results: Mean duration of exposure to 15% oxygen was 6.3 (SD 2.9) h ours. Baseline oxygen saturation fell from a median of 97.6% (range 94 .0% to 100%) in room air to 92.8% (84.7% to 100%) in 15% oxygen. There was no correlation between baseline oxygen saturation in room air and the extent of the fall in baseline oxygen saturation on exposure to 1 5% oxygen. During exposure to 15% oxygen there was a reduction in the proportion of time spent in regular breathing pattern and a 3.5-fold i ncreasein the proportion of time spent in periodic apnoea (P < 0.001). There was an increase in the frequency of desaturation from 0 episode s per hour (range 0 to 0.2) to 0.4 episodes per hour (0 to 35) (P < 0. 001). In 4 infants exposure to hypoxic conditions was ended early beca use of prolonged and severe falls in oxygen saturation. Conclusions: A proportion of infants had episodes of prolonged (less than or equal t o 80% for greater than or equal to 1 min) or recurrent shorter (less t han or equal to 80% for greater than or equal to 4 s) desaturation, or both, when exposed to airway hypoxia. The quality and quantity of thi s response was unpredictable. These findings may explain why some infa nts with airway hypoxia caused by respiratory infection develop more s evere hypoxaemia than others. Exposure to airway hypoxia similar to th at experienced during air travel or on holiday at high altitude may be harmful to some infants.