Some problems involved in using hemoglobin oxygen saturation in arterial blood to detect hypoxemia and hyperoxemia in newborn infants

Abstract

The recent renewed interest in using hemoglobin oxygen saturation (s_O2) as an alternative to oxygen tension (pO₂) in arterial blood has been largely stimulated by the advent of the pulse oximeter for in vivo s_O2 measurement. This has also extended to monitoring newborn premature infants with respiratory insufficiency. Two problems confronting clinicians and manufacturers are discussed here on the basis of measurements made on sick newborn premature infants. 1. Confusion overthe definition of s_O2 and allied quantities. Here there is a need for clear internationally agreed definitions and symbols. 2. Difficulties in establishing reference/alarm limits for s_O2 in newborn infants, with regard to detecting both hypoxemia and hyperoxemia. It is concluded that (a) the position of the hemoglobin-oxygen dissociation curve should be established in each individual before setting an s_O2limit for hypoxemia, and (b) very high accuracy in s_O2 measurements are required to detect hyperoxemia. Though in vivo calibration may help, the latter is not achievable at present with pulse oximetry, and even blood s_O2 measurement may be insufficiently accurate due to changes in the absorption spectra of oxyhemoglobin due to fetal hemoglobin and pH effects.

Key-words:

• Blood gases
• hemoglobin-oxygen dissociation curve
• pulse oximetry
• reference values
• oxyhemoglobin fraction