PEDIATRICS Vol. 105 No. 2 February 2000, pp. 350-353

Changes in Mesenteric Blood Flow Response to Feeding: Conventional Versus Fiber-optic Phototherapy

Marco Pezzati, MD^*, Roberto Biagiotti, MD, Venturella Vangi, MD^*, Enrico Lombardi, MD^*, Lisa Wiechmann, MD^*, and Firmino F. Rubaltelli, MD^*

From the ^* Department of Pediatrics, Division of Neonatology, University of Firenze School of Medicine, Firenze, Italy; and the  Department of Obstetrics and Gynecology, University of Firenze School of Medicine, Firenze, Italy.

	ABSTRACT

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Objective.  To evaluate whether fiberoptic phototherapy influences the postprandial increase in mesenteric blood flow velocity similarly to conventional phototherapy in preterm infants.

Patients and Methods.  With the use of Doppler color ultrasonography, blood flow velocity in the superior mesenteric artery was measured both preprandially and postprandially in 19 preterm infants during and after conventional phototherapy, and in 20 preterm infants during and after fiber-optic phototherapy. The mean arterial blood pressure/mean flow velocity ratio was calculated as an estimate of relative vascular resistance of the superior mesenteric artery.

Results.  The study shows that conventional phototherapy blunts the postprandial mesenteric blood flow response to feeding in preterm infants. Furthermore, it shows that the postprandial increase in intestinal blood flow is not attenuated when fiber-optic phototherapy is administered, and that such postprandial increase of blood flow is significantly greater than in infants receiving conventional phototherapy. During and after fiber-optic phototherapy, a significant reduction in postprandial relative vascular resistance was found; such reduction was significantly greater than during conventional phototherapy.

Conclusions.  Fiber-optic phototherapy is preferable to conventional phototherapy for the treatment of hyperbilirubinemia in preterm infants because it does not affect the physiologic postprandial redistribution of blood flow from the periphery to the gastrointestinal system as does conventional phototherapy.  Key words:  conventional phototherapy, fiber-optic phototherapy, mesenteric blood flow velocity, newborn.

Doppler ultrasonography is the method currently used for the clinical assessment of velocity and volume of superior mesenteric artery (SMA) blood flow.^1-5 Recently, several reports have shown that enteral feeding induces a significant and progressive increase in blood flow velocity (BFV) in the SMA that peaks 30 to 45 minutes after the meal.^5-12 Oh et al¹³ have shown that infants receiving phototherapy (PT) present an increase in peripheral blood flow with changes in body temperature and Yao et al¹⁴ have shown that PT blunts the postprandial mesenteric blood flow response to feeding in full-term infants. The changes in blood flow distribution are probably because of the fact that PT induces peripheral vasodilation.¹⁴ In the last few years a new device, the fiber-optic phototherapy (FO-PT) apparatus, has been introduced into neonatal care. We hypothesized that this kind of PT, by using cold light and irradiating a minimal quantity of ultraviolet and infrared rays,¹⁵ would not induce peripheral vasodilation as does conventional phototherapy (CPT). Consequently, we hypothesized that FO-PT would not induce significant alterations on pre- and postprandial intestinal blood flow. Color Doppler ultrasonography was used in this study to evaluate whether FO-PT influences the postprandial increase in mesenteric BFV similarly to CPT in preterm infants.

	PATIENTS AND METHODS

A group of 39 hyperbilirubinemic (bilirubin >171.0 µmol/L [>10 mg/dL]) but otherwise healthy preterm infants were eligible for enrollment in a study performed from December 1997 to April 1998. All were of appropriate size for gestational age. Infants with malformations, perinatal asphyxia, respiratory distress, renal or gastrointestinal abnormalities, patent ductus arteriosus, hypo- or hypertension, infection, anemia (venous Hb < 10 g/dL), polycythemia (venous Hb > 22 g/dL) were excluded from the study. Infants whose mothers presented significant complications during pregnancy or delivery were also excluded. We used a sequential study design in which all eligible preterm newborns for the study were enrolled. Twenty-one patients were females (53.8%) and 18 were males (46.2%). The mean gestational age was 34.3 weeks (range, 31.3-36.5 weeks) and mean birth weight was 2101 g (range, 1260-2750 g). Hyperbilirubinemia was a consequence of exaggerated physiologic jaundice in 33 cases (84.6%), of ABO incompatibility in 3 cases (7.7%), of Rh incompatibility in 1 case (2.6%), and of scalp hematoma in 2 cases (5.1%). None of the infants required exchange transfusion. The mean peak serum bilirubin concentration was 244.5 µmol/L (range, 198.3-311.2 µmol/L [14.3 mg/dL; range, 11.6-18.2 mg/dL]) and the mean duration of PT was 80 hours (range, 18-139 hours).

The study was devised to include 2 separate groups: 1 group of 19 preterm infants (48.7%) received CPT (group 1), while the second group of 20 preterm infants (51.3%) received FO-PT (group 2). The patients were selected to enter either of the 2 groups randomly by means of the sealed envelope technique. Infants were studied on the day when PT was to be discontinued (day 4; range, 2-7 days). In each group the following parameters were studied, during PT, before and 30 minutes after feeding: SMA mean velocity (MV = the area under the curve), SMA end-diastolic velocity (EDV), heart rate, mean arterial pressure, skin temperature, and cardiac output. The mean arterial blood pressure/MV ratio was calculated as an estimate of SMA relative vascular resistance (RVR). The same preprandial and postprandial measurements were repeated 3 to 4 hours after PT discontinuation at the time of the next meal. Infants with 34 weeks' gestational age or more were breastfed or bottle-fed after PT; during PT all infants were bottle-fed. Infants <34 weeks' gestational age were fed by gavage. All infants were fed with pumped mother's milk and with a feeding interval of 3.5 hours. In all infants the approximate duration of feeding was ~15 minutes. The amount of milk, both during and after PT, averaged 37.7 mL (range, 8-50 mL). In the 2 groups, infants did not receive extra amounts of fluid during PT.

A Photo grph - Therapie 800 Heraeus unit (Drager, Lübeck, Germany) was used for CPT, incorporating a metal vapor discharge blue lamp with 2 filters: a KG1 Schott (Lübeck, Germany) infrared cut-off filter and a plexiglas sheet ultraviolet cut-off filter. The spectral distribution of the lamp demonstrates the absence of ultraviolet radiation. The infrared radiation intensity is ~1 mW/cm², measured by thermopile OPHIR with an interposed Schott RG 1000 filter to remove visible light. A Biliblanket PT system (Ohmeda, Louisville, KY) was used for FO-PT; this unit incorporates a 140-W quartz halogen lamp containing a built-in dichroic reflector with a low infrared and ultraviolet radiation reflectivity; before entering the fiber bundle, the light is filtered to cut off all wavelengths falling outside the 400 to 550 nm spectral range;¹⁵ in this way the ultraviolet and infrared emission from the pad is practically absent. The emission spectra of this fiber-optic device have been published previously.¹⁵

Examinations of mesenteric BFV were performed using a real-time computed ultrasound scanner (Toshiba Sonolayer SSH 140A, Nasu, Japan) with a microconvex 7-MHz transducer. MV and EDV were automatically calculated by the instrument software from 5 sequential cardiac cycles of optimal quality. The newborns were examined by the same investigator, blinded to the group assignment of the infant, in the incubators or in the beds with the transducer positioned on the mid-abdomen just above the umbilicus in the sagittal plane; infants were at rest in the supine position. The sample volume of the Doppler system was set a few millimeters distal to the origin of the SMA, with an angle of insonation <15 degrees. The measurement of cardiac output was recorded by studying the ascending aorta from a right upper parasternal long-axis view; the aortic flow velocity was obtained by placing the sample volume at the level of the aortic orifice; the aortic diameter was measured in systole when the leaflets were maximally separated. By entering the diameter of the aortic orifice after the aortic velocity curve was traced, cardiac output was automatically calculated by the Toshiba instrument software. Cardiac output was corrected for body weight and expressed in milliliters per minute per kilogram.

Mean arterial pressure was measured by the standard oscillometric method (Escort 300A MDE, Arleta, CA) at the end of each mesenteric blood flow study. At the same time the heart rate was recorded.

To document whether the 2 groups of infants presented clinical differences regarding gastrointestinal symptoms, abdominal distention and increased passage of loose watery stools were studied.

Informed consent was obtained from the parents and the study was approved by our institutional review board.

Statistical analysis was performed by using SPSS for Windows version 6.0 (Redmond, WA). Data are expressed as mean ± SD and paired and independent Student's t test was used. A P value of <.05 was considered to be statistically significant.

	RESULTS

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At the time of study (age, 2 to 7 days; mean, 4.9 days) all neonates were stable. All infants were hyperbilirubinemic and preterm, with appropriate size for gestational age. Mean gestational age was 34.5 ± 1.6 SD in the 19 preterm infants treated with CPT (group 1) and 34.5 ± 1.8 SD in the 20 preterm infants treated with FO-PT (group 2) (P = .863). Mean birth weight was 2095 ± 339 g SD in group 1 and 2107 ± 355 g SD in group 2 (P = .917). No statistically significant differences were found in regards to feeding volume (P = .909) between group 1 (37.5 ± 10.8 mL SD) and group 2 (37.9 ± 9.2 mL SD) and day of initiation of PT (P = .575) in group 1 (4.89 ± 0.8 SD) and group 2 (4.75 ± 0.7 SD). Intestinal disturbances (increased passage of loose watery stools and abdominal distension) were greater in group 1, but were not statistically significant.

No significant differences in mean serum bilirubin concentration were noted between the 2 groups on initiation of PT (P = .204), after 24 hours of PT (P = .862), and at the end of PT (P = .723).

In the 19 preterm infants treated with CPT (group 1) the postprandial increase in SMA MV was significant both during PT and after discontinuation of PT, although the postprandial increase was much more evident when the infants were not receiving PT (Table 1). Postprandial SMA EDV significantly increased both during and after PT, but after PT the increase was much greater (Table 1). Postprandial SMA RVR decreased significantly both during PT and when they were not receiving PT, but the postprandial decrease was greater when the infants were not receiving PT (Table 1). There were no significant differences between preprandial and postprandial mean arterial pressure, heart rate, and cardiac output both during PT and when the infants were not receiving PT (Table 2). During PT, mean values of skin temperature (36.8 ± 0.49) were found to be significantly higher (P < .001) than those found after PT (36.5 ± 0.34).

In group 2 (20 preterm infants treated with FO-PT) feeding induced a significant increase of SMA MV both during and after PT; there were no significant differences between the postprandial increase of SMA MV during and after PT. Furthermore, the postprandial increase of MV was significantly higher during FO-PT than during CPT (Table 1). The postprandial SMA EDV increased significantly in the infants both during PT and when they were not receiving PT. As for MV, the postprandial increase of EDV was significantly higher during FO-PT than during CPT (Table 1). Feeding induced a significant reduction of SMA RVR both during and after PT. Postprandial reduction was significantly higher during FO-PT than during CPT (Table 1). No significant differences were found between preprandial and postprandial mean arterial pressure, heart rate, and cardiac output both during PT and when the infants were not receiving PT (Table 2). Furthermore, there were no significant differences in mean arterial pressure, heart rate, and cardiac output between patients of group 1 and patients of group 2 (Table 2). No statistically significant differences (P = .871) were found in skin temperature during and after PT in group 2.

	DISCUSSION

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Our data show that in preterm infants the postprandial increase in mesenteric blood flow, indicated qualitatively by changes in SMA MV and SMA EDV, is significantly reduced during PT with a conventional apparatus. Our data are in agreement with the results obtained by Yao et al¹⁴ in full-term neonates. These authors supposed that PT induces an increase in peripheral blood flow because of photorelaxation of the peripheral vasculature that could compete with SMA vasodilation during digestion by diverting blood flow to the skin. This conclusion is supported by the postprandial decrease in SMA RVR.

As a consequence of the high dose of infrared rays, CPT induces changes in body temperature, peripheral blood flow, intestinal blood perfusion, electrolyte and water balance, and insensible water loss.^13,16 FO-PT, on the contrary, incorporates a quartz halogen lamp containing a built-in dichroic reflector with a low infrared and ultraviolet radiation reflectivity.¹⁵ Therefore FO-PT should not induce peripheral vasodilation with consequent relative reduction of mesenteric blood flow. In the group treated with FO-PT we demonstrated that the postprandial increase in intestinal blood flow was not attenuated while FO-PT was being given, and that such postprandial increase was significantly greater compared with infants receiving CPT. Cardiac output, mean arterial pressure, and heart rate did not significantly change during either CPT or FO-PT nor when the infants were not receiving PT; these data suggest that the reduction or nonreduction of the postprandial increase in SMA blood flow is mainly a consequence of PT. During and after FO-PT a significant reduction of postprandial SMA RVR was found. During FO-PT such reduction was significantly greater than during CPT, proving that greater mesenteric vasodilation is induced on feeding by FO-PT in respect to CPT. Such difference is because of the fact that during CPT skin vasodilation is greater than during FO-PT, as demonstrated by the increase of skin temperature and the smaller reduction in SMA RVR.

In the last few years, several clinical trials have compared the efficacy of CPT versus FO-PT in reducing bilirubin levels in preterm and term infants with jaundice.^17-29 In some studies the efficacy of the FO systems was similar to that of CPT, in others it was less effective. In our study we did not find significant differences between the effectiveness of the 2 devices of PT. FO-PT is better tolerated than CPT¹⁶ and, owing to its intrinsic simplicity, may be effectively used for the therapy of jaundice of the preterm infant.

	CONCLUSION

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This study shows that, contrarily to CPT, FO-PT does not reduce the postprandial increase in SMA blood flow. In summary, we conclude that FO-PT is preferable to CPT for the therapy of hyperbilirubinemia in preterm neonates because it does not affect the physiologic postprandial redistribution of blood flow from the periphery to the gastrointestinal system as does CPT.

	ACKNOWLEDGMENT

We thank Dr Franco Fusi from the Department of Clinical Physiopathology of the University of Florence for his help with the physiopathologic data.

	FOOTNOTES

Received for publication Mar 16, 1999; accepted Jun 11, 1999.

Address correspondence to Marco Pezzati, MD, Division of Neonatology, Careggi University Hospital, Viale Morgagni 85-50134, Firenze, Italy. E-mail: pezzati{at}cesit1.unifi.it

	ABBREVIATIONS

SMA, superior mesenteric artery; BFV, blood flow velocity; PT, phototherapy; FO-PT, fiber-optic phototherapy; CPT, conventional phototherapy; EDV, end-diastolic velocity; MV, mean velocity; RVR, relative vascular resistance.

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