Letters

Ethical commentaries must be based on sound science

EDITORIt is unfortunate that the scientific basis of Savulescu's commentary on the ethics of the study by Parkins et al, in which infants were exposed to 15% oxygen, is so weak.¹ Savulescu states that evidence exists that exposure to hypoxia is related to sudden infant death; he refers to a study in piglets to support his assertion.² In fact, this study he cites shows no such thing. Parkins et al cogently explain the scarcity of evidence on the effects of exposure to 15% oxygen.

Savulescu also argues that piglets should be used as a model for infants. He is clearly unaware of the important differences that exist between species in terms of ventilatory responses to hypoxia; this is an area of debate in respiratory physiology.³ For example, the depressant effect of hypoxia on the respiratory system of many animals is thought to be due to an action of hypoxia on the central nervous system. In contrast, the depressant effect of hypoxia in humans is thought to be due to an action on the carotid body.³ It is misleading therefore to extrapolate all studies in animals to humans.

Savulescu discusses the possibility that hypobaric hypoxia somehow differs from isobaric hypoxia. There is no evidence in humans that barometric pressure affects ventilatory responses over and above the reduction in the partial pressure of oxygen.⁴ Birds might be expected to show some differences in ventilatory responses since they possess aerodynamic valves which prevent inspired air from being shunted past the gas exchange surfaces. The efficiency of these valves depends on gas density, and thus efficiency might be reduced in hypobaria. However, studies in ducks show minimal differences between hypobaric hypoxia and isobaric hypoxia.⁵

The fact that seems to have been overlooked is that an inspired oxygen fraction of 15% is equivalent to breathing air at an altitude of about 2300 metres (7000 feet). Many cities, such as Pretoria and Mexico City, are at or near this altitude, and many infants live in and visit these places. The ethical arguments about studying infants exposed to mild hypoxia might be elaborate. However, it follows that the same ethical issues must then apply to allowing infants to visit, reside in, or even be born in cities at high altitude. It is perhaps at this point that many of the ethical arguments become untenable.

Parkins et al's study was interesting, necessary, safe, and ethical. The real lesson of Savulescu's commentary is that proper discussion of ethical issues in research needs good acquaintance with the underlying science.

Jaideep J Pandit, Visiting instructor.  .
Department of Anesthesiology, University Hospital, Box 0048, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0048, USA

1. Parkins KJ, Poets CF, O'Brien LM, Stebbens VA, Southall DP. Effect of exposure to 15% oxygen on breathing patterns and oxygen saturation in infants: interventional study. BMJ 1998; 316: 887-894[Abstract/Free Full Text]. [With commentaries by Savulescu J; Hughes V.] (21 March.)
2. Waters KA, Beardsmore CS, Paquette J, Meehan B, Cote A, Moss IR. Respiratory responses to rapid-onset, repetitive vs continuous hypoxia in piglets. Respir Physiol 1996; 105: 135-142[Medline].
3. Robbins PA. Hypoxic ventilatory decline: site of action. J Appl Physiol 1995; 79: 373-374[Abstract/Free Full Text].
4. Loeppky JA, Scotto P, Roach RC. Acute ventilatory response to simulated altitude, normobaric hypoxia, and hypobaria. Aviat Space Environ Med 1996; 67: 1019-1022[Medline].
5. Shams H, Powell FL, Hempleman SC. Effects of normobaric and hypobaric hypoxia on ventilation and arterial blood gases in ducks. Respir Physiol 1990; 80: 163-170[Medline].