Phototherapy of neonatal jaundice

Abstract

In approximately 10% of new-born infants a jaundice which is more severe than the classical physiological jaundice may lead to the use of phototherapy in order to prevent the neurological complications linked to hyperbilirubinemia. The apparent simplicity of this treatment, and a lack of knowledge of the physical rules which apply, have been for a long time responsible for the poor conditions of its use and notably the use of any available source of light. The development of radiometers which were specifically designed for quantification of the 'blue' energy illumination produced by phototherapy installations used in jaundice has enabled the poor quality of this therapy to be understood. The systematic recourse to light sources which are currently the most effective, the special blue TL20/52 or failing that the white TL18/86, together with a reduction in the distance between these sources and the infant, enabled energy levels of 1 to 2 mW/cm2 to be attained, which considerably improved the results of this treatment. The concept of dose dependance has led to the development of a phototherapy termed 'intensive' which delivers an illumination of 3 to 4 mW/cm23 and which enables a reduction in the plasma bilirubin levels to be obtained that is equally as rapid and significant as that following an exsanguino transfusion, but which does not carry the risks of complications of this latter technique. The photons in the visible part of the solar spectrum act on bilirubin in different fashions. The principal action appears to be an isomerisation leading to the formation of lumirubin, a hydrosoluble photoderivative, which would be very rapidly excreted in the new-born. Theory and practice confront each other for deciding which of the zones of the spectrum, green or blue, is the most effective on bilirubin. Although theory favours green light in practice it is a fluorescent tube used in industry, TL/52, which has been shown to be the most effective. Further studies are thus necessary to explain these surprising results.