INTRODUCTION

Feeding intolerance is common among neonates following surgery for congenital abnormalities of the intestine, such as small bowel atresia or gastroschisis.¹ Feeding intolerance in these patients is likely multifactorial, but we recently reported that one reason involves congenital maldevelopment of the small bowel villi.² Specifically, we measured villus height, area, and length, and cypt depth of proximal bowel of 11 normal fetuses and compared these with surgical specimens of 16 neonates who had various congenital anomalies of the GI tract. Each congenital anomaly had different degrees of dysmorphic mucosa, but all lacked normal histological architecture with blunted villi and with disorganized and shallow crypts.²

When a fetus has duodenal or jejunal atresia, swallowing of amniotic fluid is impaired. Amniotic fluid contains intestinal growth factors that, when swallowed by the fetus, bind to receptors on the luminal surface of villous enterocytes.^3,4 We postulated that it is the lack of such binding that results in the dysmorphic mucosa we observed² and that a limitation in amniotic fluid swallowing could constitute at least part of the explanation for postoperative feeding intolerance.

We previously sought to reduce feeding intolerance among preterm infants by enterally administering a sterile, isotonic, growth factor containing solution patterned after human amniotic fluid.^5,6 The preparation contains albumin and two of the enterocyte growth factors present in human amniotic fluid; erythropoietin and granulocyte colony-stimulating factor. We reported that this solution is stable,⁷ that the growth factors are remarkably resistant to digestion,⁸ that the cognate receptors are expressed on the luminal surface of the neonate's intestinal villi,⁹ and that the ingested growth factors are not absorbed into the circulation but have a topical action in the intestine.^10,11 We completed two Phase I clinical trials where this solution was administered to 60 neonates for periods of 72 hours preparatory to beginning enteral feedings.^5,6

The two previous Phase I studies with this solution involved only a 3-day period of administration. However, among neonates with congenital surgical abnormalities of the intestine, we reasoned that their abnormal villi might require a longer period of administration if any salutary effect could be expected. Thus, before designing a trial to assess the risks and benefits of administering this experimental solution to neonates following surgery for congenital bowel abnormalities, we first conducted a pilot trial to assess tolerance when given to these patients for longer periods. Specifically, we used a dose of 20 ml/kg/day, divided into eight equal aliquots (2.5 ml/kg every 3 hours), because this was the largest dose tested in the previous Phase I studies.^5,6 We planned to begin the enteral administration of the experimental solution before any "trophic" milk feedings were started and to continue the administration until the patient had achieved 100 ml/kg/day of milk feedings.

METHODS

Patients

Patients were eligible for this pilot trial if they were admitted to the neonatal intensive care unit at the Hospital General Dr. Ignacio Morones Prieto in San Luis Potosi, Mexico, and had undergone surgery for esophageal or bowel atresia, gastroschisis, omphalocele, congenital diaphragmatic hernia, or volvulus. Patients had to be deemed by their attending neonatologist and surgeon as likely to survive at least 28 days, and as likely to be NPO for at least the first 48 hours after the test solution was to be started. Neonates were ineligible if they had proven or suspected chromosomal trisomy 13 or 18 or if they were judged as being too ill to be acceptable study candidates; this criterion was set as receiving mechanical ventilation with an FIO₂ >0.50 at the time of study entry. We arbitrarily elected to limit this pilot study to 10 patients. The Institutional Review Board of the Hospital General Dr. Ignacio Morones Prieto approved the study and informed consent was obtained from parents of all enrolled subjects.

Study procedures

The hospital pharmacist made the solution using sterile technique and the parenteral nutrition equipment in the manner previously reported.⁷ The solution contained 115 meq/l sodium chloride, 17 meq/l sodium acetate, 4 meq/l potassium chloride, 225 ng/ml Neupogen (Filgrastim, Amgen Inc., Thousand Oaks, CA), and 4400 mU/ml Epoetin alfa (Epogen, Amgen). Human serum albumin (5%) (Baxter Healthcare Corp., Hyland Division, Glendale, CA) was added to the infusion bag prior to adding the cytokines (the final concentration of albumin was 0.05%).

Aliquots of the solution were frozen until use. Separate aliquots (10 ml) were frozen and labeled "Priming". Solution in the "Priming" syringe was pushed through the orogastric tube prior to insertion into the patient in order to reduce binding of recombinant erythropoietin to the plastic tubing. Upon enrollment of a subject, a full day's dose and a priming syringe were thawed. The full day's dose was then divided into eight equal amounts, to be administered by the bedside nurse every 3 hours. Each aliquot was allowed to warm to room temperature before it was administered, and was recorded in the medical record as both a medication and an enteral fluid.

We planned that when enteral feedings of human milk were initiated they would be mixed with the experimental solution. Once the enteral intake of milk reached 100 ml/kg/day, the experimental solution was discontinued and the milk feedings advanced as deemed appropriate by the Neonatologist and Surgeon.

Measurements of intolerance and safety

We previously showed that rEpo and rG-CSF in this solution are not absorbed into the circulation, but have only a local action in the intestine.^10,11 On this basis, we speculated that the most likely adverse effects would be emesis, increased gastric residuals, increased abdominal girth, or diarrhea. Thus we specifically sought these from the nursing records. In addition, we sought adverse effects by specifically looking for the presence of a new skin rash and for any change in blood pressure (hypotension or hypertension) using the bedside nursing records. Additional data collected from the bedside nursing records included length of time between starting each patient on the experimental solution and that patient receiving 20, 50, 100, and 120 ml/kg/day of milk feedings. The days of hospitalization were also recorded.

RESULTS

The characteristics of the 10 study participants are given in Table 1. Demographic information includes the surgical condition, birth weight, gestational age, and day of life the surgery was performed. The feeding advancement of each subject is shown in Table 2. The experimental solution was begun 4 to 32 days after surgery and was administered for 3 to 14 days. All 10 subjects achieved 100 ml/kg of milk feedings by 14 or fewer days after the experimental solution was begun (mean, 11.1 days; range, 3 to 14). All of the subjects received exclusively human milk feedings because this is the standard of care in this neonatal intensive care center. The surgical procedure in the patient with imperforate anus was a colostomy, with definitive surgery to be scheduled subsequently.

Table 1 - Features of the 10 Study Subjects.

Full table

Table 2 - Feeding Advances of 10 Study Subjects, Treated with 20 ml/kg/day of an Enteral Amniotic Fluid-like Solution. The Test Solution was Started before "Trophic" Feedings were Begun and Continued Concomitantly with the Feedings Until 100 ml of Milk Feedings/kg/day was Tolerated.

Full table

No cases of skin rash or hypotension or hypertension were observed. No cases of postoperative NEC or perforation were observed and no deaths occurred. No patients were taken off study for emesis, increased abdominal girth, or diarrhea. The length of hospital stay was 20.2 days (range, 8 to 42) from starting the experimental solution.

DISCUSSION

Advancing from hyperalimentation to full enteral feedings can be a challenging and frustrating part of caring for neonates with certain congenital bowel anomalies such as small bowel atresia, gastroschisis, or omphalocele.¹ Feeding intolerance in these patients is common and can be manifested as emesis, bloating, large gastric residuals, or diarrhea. The underlying mechanism responsible for this feeding intolerance is probably multifactorial. One likely contributing factor is congenitally dystrophic villi related to the fetuses' inability to swallow normal amounts of amniotic fluid in utero.^2,12 Another probable contributor is the intestinal disuse atrophy that occurs when patients are NPO for days, or sometimes weeks, after surgery.¹³ Indeed, feeding intolerance in the neonatal intensive care unit is not unique to surgical patients, but is common among VLBW and ELBW neonates, particularly those NPO for long periods of time, and contributes to the extrauterine growth restriction common in those populations.^14,15

The human fetus normally swallows over 200 ml of amniotic fluid per kilogram body weight each day and such swallowing is essential for normal small bowel development. It was once thought that the critical factor was the volume of liquid swallowed, but experimentation showed that it is the growth factors in amniotic fluid that are critical to small bowel villous development.^4,12 Amniotic fluid contains multiple intestinal growth factors that have cognate receptors on the luminal surface of developing villous enterocytes.^3,4,12 The precise action of each factor remains to be defined. Erythropoietin and granulocyte colony-stimulating factor are two such facors that have the practical advantage of being available as sterile human recombinant factors in quantities sufficient to use in clinical trials.⁴

Obviously, large multicentered, randomized trials are needed to test the approach of enterally providing growth factors to neonates after bowel surgery in order to restore villous structure and function and thereby reduce feeding intolerance. However, before any such trials can be designed, basic information is needed regarding whether neonates following intestinal surgery can even tolerate such a solution for the period preceding and during the time milk feedings are introduced and advanced. From our small pilot trial reported here, we suspect that these neonates are indeed likely to tolerate this approach. Certainly not all patients with bowel surgery require an approach like this, as some have little or no feeding intolerance. Our patient with imperforate anus is an example. Like many who are not NPO for a prolonged period of time, that patient probably had normal small bowel mucosa and had no need for a new approach to diminish feeding intolerance.

Whether the specific solution we tested will have any significant trophic effects on the intestine, reduce feeding intolerance, facilitate the transition from hyperalimentation to full enteral nutrition, and reduce extrauterine growth restriction are not known, but can now be assessed in randomized trials.

References

1. Flake AF, Rychman RC. Selected anomalies and intestinal obstruction. In Fanaroff AA, Martin RJ, editors, Neonatal-Perinatal Medicine, Diseases of the Fetus and Infant. 5th edn, St. Louis: Mosby Year Book; 1992. p. 1038–1062.
2. Condino AA, Barleycorn AA, Lu W, Maheshwari A, Christensen RD, Calhoun DA. Abnormal intestinal histology in neonates with congenital anomalies of the gastrointestinal tract. Biol Neonate 2004;85(3):145–150. | Article | PubMed |
3. Hirai C, Ichiba H, Saito M, Shintaku H, Yamano T, Kusuda S. Trophic effect of multiple growth factors in amniotic fluid or human milk on cultured human fetal small intestinal cells. J Pediatr Gastroenterol Nutr 2002;34(5):524–528. | Article | PubMed |
4. Calhoun DA. Enteral administration of hematopoietic growth factors in the neonatal intensive care unit. Acta Paediatr Suppl 2002;91(438):43–53. | Article | PubMed |
5. Sullivan SE, Calhoun DA, Maheshwari A, et al. Tolerance of simulated amniotic fluid in premature neonates. Ann Pharmacother 2002;36(10):1518–1524. | Article | PubMed |
6. Lima-Rogel V, Calhoun DA, Maheshwari A, et al. Tolerance of a sterile isotonic electrolyte solution containing select recombinant growth factors in neonates recovering from necrotizing enterocolitis. J Perinatol 2003;23(3):200–204. | Article | PubMed | ChemPort |
7. Calhoun DA, Juul SE, McBryde EV, Veerman MW, Christensen RD. Stability of filgrastim and epoetin alfa in a system designed for enteral administration in neonates. Ann Pharmacother 2000;34(11):1257–1261. | Article | PubMed | ChemPort |
8. Calhoun DA, Richards BE, Gersting JA, Sullivan SE, Christensen RD. G-CSF and Epo stability in amniotic fluid during simulated in vitro digestion conditions. J Pharm Technol 2002;18:310–315.
9. Calhoun DA, Christensen RD. Human developmental biology of granulocyte colony-stimulating factor. Clin Perinatol 2000;27(3):559–576. | PubMed |
10. Calhoun DA, Maheshwari A, Christensen RD. Recombinant granulocyte colony-stimulating factor administered enterally to neonates is not absorbed. Pediatrics 2003;112(2):421–423. | Article | PubMed |
11. Juul SE, Christensen RD. Absorption of enteral recombinant human erythropoietin by neonates. Ann Pharmacother 2003;37(6):782–786. | Article | PubMed | ChemPort |
12. Mulvihill SJ, Stone MM, Fonkalsrud EW, Debas HT. Trophic effect of amniotic fluid on fetal gastrointestinal development. J Surg Res 1986;40(4):291–296. | Article | PubMed | ChemPort |
13. Hernandez G, Velasco N, Wainstein C, et al. Gut mucosal atrophy after a short enteral fasting period in critically ill patients. J Crit Care 1999;14:73–77. | Article | PubMed | ChemPort |
14. Ehrenkranz RA, Younes N, Lemons JA, et al. Longitudinal growth of hospitalized very low birth weight infants. Pediatrics 1999;104:280–289. | Article | PubMed | ISI | ChemPort |
15. Clark RH, Wagner CL, Merrit RJ, et al. Nutrition in the neonatal intensive care unit: how do we reduce the incidence of extrauterine growth restriction? J Perinatol 2003;23:337–344. | Article | PubMed |