Importance of radiant flux in the treatment of hyperbilirubinemia: failure of overhead phototherapy units in intensive care units.

Prior to 1972, radiation used to treat neonatal hyperbilirubinemia was based upon the photometric unit, the foot-candle, a measure of light illumination. Measurements in terms of microwatts per square centimeter for selective wavelengths is more precise. We compared the effectiveness of phototherapy provided by overhead phototherapy units in intensive care modules vs. conventional phototherapy units. Forty-two infants were studied over a six-month period and divided into three groups based upon radiant flux measurements as follows: Group 1 (No. = 6), 1.0 muw to 1.9 muw/sq cm/nm; group 2 (No. = 15), 2.0 muw to 3.9 muw/sq cm/nm; group 3 (No. = 21), 4.0 muw to 6.0 muw/sq cm/nm. All flux determinations were made within the 400- to 500-nm range. All infants in group 1 were treated with overhead phototherapy units in the intensive care modules. Because of multiple factors known to increase the risk of kernicterus, evaluation of effectiveness of phototherapy at low radiant flux was limited in group 1. Significant changes in bilirubin were noted by 48 hours when comparing group 3 with groups 1 and 2. A minimum of 4.0 muw/sq cm/nm appears necessary for effective phototherapy. As designed, phototherapy units in intensive care modules are ineffective in delivering this therapeutic level of radiant flux.