Mechanisms of Cardiovascular Changes of Phototherapy in Newborns with Hyperbilirubinemia.

During phototherapy of jaundiced newborns, vasodilation occurs in the skin circulation compensated by vasoconstriction in the renal and mesenteric circulation. Furthermore, there is a slight decrease in cardiac systolic volume, and blood pressure, as well as an increase in heart rate and discrete changes in the heart rate variability (HRV). The primary change during phototherapy is the skin vasodilation mediated by multiple mechanisms: 1) Passive vasodilation induced by direct skin heating effect of the body surface and subcutaneous blood vessels, modified by myogenic autoregulation. 2) Active vasodilation mediated via the mechanism provided by axon reflexes through nerve C-fibers and humoral mechanism via nitric oxide (NO) and endothelin 1 (ET-1). During and after phototherapy is a rise in the NO:ET-1 ratio. 3) Regulation of the skin circulation through the sympathetic nerves is unique, but their role in skin vasodilation during phototherapy was not studied. 4) Special mechanism is a photorelaxation independent of the skin heating. Melanopsin (opsin 4) - is thought to play a major role in systemic vascular photorelaxation. Signalling cascade of the photorelaxation is specific, independent of endothelium and NO. The increased skin blood flow during phototherapy is enabled by the restriction of blood flow in the renal and mesenteric circulation. An increase in heart rate indicates activation of the sympathetic system as is seen in the measures of the HRV. High-pressure, as well as low-pressure baroreflexes, may play important role in these adaptation responses. The integrated complex and specific mechanism responsible for the hemodynamic changes during phototherapy confirm adequate and functioning regulation of the neonatal cardiovascular system, including baroreflexes.

Cardiovascular changes during phototherapy in newborns.

Phototherapy is the most effective non-invasive method of neonatal hyperbilirubinemia treatment. Application of this method can be associated with side effects including changes in the cardiovascular system. During phototherapy, the primary effects in the cardiovascular system include cutaneous vasodilation leading to skin hyperperfusion and subsequent redistribution of blood. The increased blood flow through the skin is associated with increased transepidermal water loss. Further effects include an increase in cerebral blood flow. Redistribution of blood to the cutaneous bed is compensated by hypoperfusion in the splanchnic area (mostly postprandial) and a significant reduction of the renal blood flow. Regarding closure/reopening of the ductus arteriosus, the results suggest that that phototherapy does not affect ductal patency. During phototherapy the cardiac output can be slightly reduced due to a decreased stroke volume, especially in preterm newborns. Systemic blood pressure is decreased and heart rate is elevated in both preterm and term newborns during phototherapy. The heart rate variability is slightly reduced. Symbolic dynamics analysis of the short-term HRV showed that during phototherapy the activity of the ANS regulating the heart rate is shifted towards the dominancy of the sympathetic activity. The responses in the cardiovascular system of premature/mature newborns without other pathology confirm a well physiologically functioning control of this system, even under specific conditions of phototherapy.

Accuracy of transcutaneous bilirubin measurement in newborns after phototherapy.

OBJECTIVE: We tested the accuracy of transcutaneous bilirubin (TcB) measure in newborns undergoing phototherapy. STUDY DESIGN: In a prospective study of 150 term Caucasian neonates, 255 measurements of total serum bilirubin (TSB) and TcB concentration were obtained 2 h after discontinuing phototherapy. TcB measurements obtained on the forehead, sternum, abdomen and covered lower abdomen were statistically compared with the corresponding TSB. RESULT: TcB consistently underestimated TSB levels significantly. The smallest but significant difference between TSB and TcB was found on the lower abdomen. The correlation between TSB and TcB was found to be moderately close (r=0.4 to 0.5). TcB measurements were inaccurate, regardless of phototherapy technique (Bilibed, conventional phototherapy). CONCLUSION: Phototherapy significantly interferes with the accuracy of transcutaneous bilirubinometry. TcB measurements performed 2 h after stopping phototherapy were not reliable, even if they were carried out on the unexposed body area. TSB assessment remains necessary, if treatment of hyperbilirubinemia is being considered.

Transcutaneous bilirubinometry in preterm neonates.

This prospective study was conducted to evaluate the accuracy of transcutaneous bilirubinometry in preterm newborns less than 32 weeks of gestation. Serum bilirubin values measured by direct spectrophotometry were considered as standard, the range was 2.2-12.5 mg/dL. 32 jaundiced infants of less than 32 weeks of gestation without phototherapy, including 10 ELBW neonates, were enrolled. Close correlation (R=0.933) existed between total serum bilirubin and transcutaneous bilirubin values measured over sternum.