Effects of 15% oxygen on breathing patterns and oxygenation in infants

An article in this week’s issue raises the spectre that exposing a young infant to the relative hypoxia of an airline flight may increase the risk of sudden infant death (p 887).¹ The authors base this claim on their findings that exposing 3 month old infants to 15% oxygen for about six hours led to an increase in the time spent in periodic respiration and the number of episodes of mild desaturation. In addition, four of the 34 infants had more prolonged hypoxia, with transcutaneous arterial saturation values below 80% for more than one minute, for which they were given oxygen therapy. They could not predict which infants were likely to develop the more prolonged pattern of desaturation from their baseline cardiorespiratory monitoring. They conclude that further research is urgently needed into the effects of airline flights or holidays at high altitude on infants, particularly as they had contact with two families who had experienced sudden infant death syndrome within two days of intercontinental flights. Even more urgent is the need to decide the relevance of their findings and what advice we should give to parents about to set out on flights with their young infants.

We already have a considerable amount of information on the effects of hypoxia on infants. All aircraft used for medium and long flights are pressurised so that the pressure within the cabin is equivalent to that found at about 1700 m in Boeing 747s and 2500 m in the older DC9s.² At 2500 m the atmospheric pressure is 0.75 bar compared with 100 bar at sea level. This has the effect of reducing the arterial oxygen tension from 12.7 to 7.5 kPa in healthy adults, and the arterial oxygen saturation from 97 to 89%.² In early infancy the relatively high concentration of fetal haemoglobin will have a protective effect, so that newborn infants in Tibet at altitudes of over 3600 m have arterial saturations of 92% in quiet sleep compared with only 85% at 4 months of age.³

The physiological effects of breathing hypoxic gas mixtures have been well investigated in early infancy. Unlike adults, who have prolonged stimulation of ventilation in response to hypoxia, newborn infants have initial stimulation followed by suppression.⁴ However, this secondary suppression is seen only in the first 10-14 days of life.⁵ Babies born very preterm become apnoeic in response to hypoxia⁶ and take a variable time to develop the adult response pattern. There is evidence that viral respiratory tract infections cause these infants to revert to the immature pattern with episodes of prolonged apnoea.⁷ There have also been several studies on infants into the cardiorespiratory effects of life at high altitudes. The increase in periodic breathing noted in this study has previously been documented in infants living in Denver and Tibet.³ Of concern is the report that infants of Chinese parents who had moved to Tibet were at greater risk of dying from pulmonary hypertension, at a mean age of 2.3 months, than infants of Tibetan parents.⁸

Before creating widespead concern about the possible risk to infants it is important to put these considerations into context. According to British Airways, who fly over 34 million passengers a year, no cases of sudden infant death have been recorded during flight (personal communication). They claim that if one had occurred there would certainly have been a full investigation and the results publicised. It is difficult to obtain information on how many of these 34 million are infants, but assuming it is 1 in 500, the number would be over 750 000 over 10 years.

The only relevant recommendation given by the Aerospace Medical Association and the Air Transport Committee is that, although physiologically newborn infants should be able to fly quite safely, it would be prudent to wait about a week after birth to be sure that the infant is healthy.⁹ Obviously sensible precautions need to be taken for babies who have reduced respiratory reserve—who may need oxygen for the flight. However, all the epidemiological evidence indicates that, whatever the effect of relative hypoxia on breathing patterns, flying appears to be safe for healthy children in the first year of life.

Papers p 887