Oxygen consumption and resting energy expenditure during phototherapy in full term and preterm newborn infants.(Statistical Data Included)

Abstract

Objectives--To determine the effect of phototherapy on the oxygen consumption and resting energy expenditure of term and preterm newborn infants.

Methods--A total of 202 infants (gestation 30-42 weeks; body weight 1270-4100 g) requiring phototherapy for the treatment of neonatal hyperbilirubinaemia were enrolled in a randomised crossover study. In random sequence, the oxygen consumption and resting energy expenditure were measured twice in each infant by indirect calorimetry, once at the end of six hours of continuous phototherapy and once after a control period of at least six hours without phototherapy. Anterior abdominal wall temperature was servocontrolled at 36.5[degrees]C throughout the study.

Results--At the end of six hours of continuous phototherapy, oxygen consumption (mean (SD): 6.21 (1.35) v 6.26 (1.51) nil/kg, p = 0.555) and resting energy expenditure (178.11 (37.62) v 180.37 (43.14) kJ/kg/24 h, p = 0.382) did not differ significantly from those measured after the control period. There were also no significant differences in heart rate, respiratory rate, or rectal temperature. Subgroup analysis of those of gestation [less than] 37 weeks or [less than] 34 weeks also showed no effect of phototherapy on either oxygen consumption or resting energy expenditure.

Conclusion--Phototherapy has no effect on the metabolic rate of thermally stable term or preterm infants.

Keywords: phototherapy; oxygen consumption; resting energy expenditure; preterm

Phototherapy may affect the energy metabolism and oxygen consumption of newborn infants by a number of mechanisms. The photo-oxidation of bilirubin in the skin is an oxygen consuming process, and it has been shown that photo-energy accelerates the oxidation of fatty acids. [1] The metabolic effect of phototherapy, however, appears to be mediated mainly through changes in the infant's thermal environment. Part of the photo-energy, especially that near the infrared range, is converted into heat energy which increases the environmental and skin temperature of the infant. [2,3] Overheating may increase metabolic rate as a result of elevation of the body temperature and increase in insensible water loss. A profound increase in evaporative water loss is seen when sweating is elicited by a rise in body temperature in newborns. [4] Even without apparent sweating, infants undergoing phototherapy exhibit a significant increase in peripheral blood flow [5] and transepidermal insensible water loss. A rise in body tempera ture may also increase respiratory rate and minute ventilation, [5,6] leading to increased respiratory water loss. [5,7] The increase in evaporative water loss through the skin and respiratory tract consumes a substantial amount of heat energy in the form of latent heat of evaporation, and the increase in muscle activity caused by increased respiratory rate and the discomfort resulting from overheating also increases metabolic rate. [8] It has been estimated that, in newborns, approximately 2.42 J of heat is dissipated for each gram of water evaporated. [9,10] The thermal effect on insensible water loss is particularly pronounced in preterm and low birth weight infants [5,7,9,11,12] because of skin factors, including larger surface area in relation to body weight, thinner epidermis, larger water content, and greater permeability.

The thermal effect of phototherapy can be minimised by maintaining a stable environmental …