Ventilatory and metabolic responses to acute hypoxia in infants assessed by transcutaneous gas monitoring

Abstract

Transcutaneous PO2, transcutaneous PCO2 and respiratory pattern were monitored during acute mild hypoxia (15% O2) in quiet sleep. Eighteen healthy infants were studied sequentially at 1-5 days, 4-8 weeks and 10-14 weeks of age. The transcutaneous PCO2 changes (delta PCO2) related to the transcutaneous PO2 fall, were used as an index of the total ventilatory and metabolic response during the test. This calculated index was related to the occurrence of arousal and periodic breathing. Transcutaneous PCO2 increased above control levels in infants 1-5 days old, decreased markedly in infants 4-8 weeks of age, and decreased slightly or remained unchanged in the 10-14 weeks old infants. The changes in response pattern were significant (P less than 0.006). These differences in response were not reflected in the lowest values of transcutaneous PO2 attained during the test. The lowest transcutaneous PO2 levels did not differ significantly between the age groups, indicating that the mechanisms maintaining PO2 during hypoxia may change during development. Periodic breathing was always associated with a decrease in transcutaneous PCO2 and in 8 out of 10 tests where it occurred it commenced at the lowest transcutaneous PCO2 level recorded. These results do not support the concept that periodic breathing is a sign of hypoventilation. Arousal was observed in less than half of the infants and was not related to the degree of hypoxaemia. We conclude that hypoxic arousal in infants may not be the important escape mechanism as suggested previously.