Electrolyte Imbalances in Pediatric Living Related Small Bowel Transplantation Ulf H. Beier, 1 Bruce Kaplan, 2 Suman Setty, 3 Suneeth Samuel, 1 Anna V. Mathew, 1 Jose Oberholzer, 2 Enrico Benedetti, 2 and Eunice John 1,4 Background. Pediatric small bowel transplantations are associated with pronounced electrolyte disturbances in the postoperative period. We investigated the pattern of electrolyte disturbances with regard to enteral malabsorption, renal compensation, and the influence of immunosuppression. Methods. We reviewed 11 small bowel transplantations between October 2002 and February 2007. The data collected included frequent serum, ostomy, and urine electrolyte profiles, renal function parameters, and FK 506 levels in the postoperative period up until either discharge or graft loss. Results. Our results show enteral losses most prominent during the first 4 weeks postoperatively that are only partially compensated by the kidneys. Subsequently, enteral losses improved, although renal function remained challenged, particularly glomerular filtration and phosphorus, magnesium losses, which correlated with high FK 506 levels. Conclusion. Our data reveal several electrolyte imbalances different and unique to postoperative small bowel trans- plants. Although enteral losses improve along with graft villi formation, electrolyte abnormalities continue, to which FK 506-mediated renal toxicity might contribute. Keywords: Tacrolimus, Electrolyte imbalances, Small bowel transplantation. (Transplantation 2008;85: 217–223) R ecipients of small bowel transplantations face enormous immunological and infectious barriers peculiar to the in- testine, as well as high vulnerability to fluid and electrolyte imbalances in the postoperative period (1–3). These barriers are aggravated by numerous factors, including reperfusion injury, graft rejection, dysmotility caused by denervation, infection, malabsorption, and side effects from immune modulatory agents, to name a few (3–7). Unfortunately, the delineation of electrolyte imbalance etiology and thus appropri- ate treatment can be very challenging in the postoperative small bowel transplant patient. However, its management depends on the correct identification of pathophysiology, especially with re- gard to immunosuppressive dosing. FK 506 (tacrolimus) is widely prescribed to achieve immunosuppression in a variety of transplant patients, including renal and small bowel trans- plant recipients (8). Among its numerous side effects, one particularly important is the disturbance of electrolyte ho- meostasis (9). FK 506 has been associated with demineraliza- tion of the bone, which can lead to profound osteoporosis (10 –12). Furthermore, hypomagnesemia is a widely ac- knowledged additional side effect of FK 506 treatment (13). The kidney is crucial for both calcium and magnesium ho- meostasis as it provides the main excretory route for these divalent ions. We investigated electrolyte imbalances in post- operative small bowel transplanted patients and to which de- gree renal FK 506 might be a contributing factor. METHODS Subjects The present study is a retrospective chart review of 11 small bowel transplantation cases from eight patients (54.55% male, mean age 25.5518.04 months, mean weight 10.181.84 kg) hospitalized at the University of Illinois Medical Center, Chicago, IL, from October 2002 un- til February 2007. Informed consent was obtained. Before the implantation, all patients had normal renal function. Patient Demographics Patient characteristics are summarized in Table 1. We reviewed all laboratory data from the postoperative course until either discharge or loss of graft (cumulative observation days 1251; mean 113.7391.21 days). Transplantation Procedure and Nutrition The bowl graft was obtained from the living related donor in form of a 150 cm piece of distal ileum. Postoperative enteral nutrition was initiated at 1–2 weeks after transplan- tation based on 260 mOsm/L unflavored Peptamen Jun- ior® formula (Nestle ´ Nutrition, Glendale, CA). Immunosuppressive Protocol Immunosuppression was achieved as the result of the combination of polyclonal antibodies, corticosteroids, FK 506, and mycophenolate. Thymoglobulin (3 mg/kg) was given one day preoperatively and again at 2 mg/kg on the day of the operation after the completion of the transplant. Addi- tional doses of thymoglobulin were given if the calcineurin inhibitor doses were nontherapeutic. Methylprednisolone Dr. Kaplan received grants from Novartis Pharmaceuticals, Roche Pharma- ceuticals, and Astellas Pharma US, Inc., and is a consultant for Roche Pharmaceuticals and the Bristol-Myers Squibb Company. 1 Division of Pediatric Nephrology, Department of Pediatrics, University of Illinois at Chicago, Chicago, IL. 2 Division of Transplantation, Department of Surgery, University of Illinois at Chicago, Chicago, IL. 3 Department of Pathology, University of Illinois at Chicago, Chicago, IL. 4 Address correspondence to Eunice John, M.D., FAAP, University of Illinois at Chicago, Division of Pediatric Nephrology, Department of Pediatrics, 840 S. Wood Street (MC 856), Chicago, IL. 60612. E-mail: ejohn@uic.edu Received 27 June 2007. Revision requested 16 July 2007. Accepted 17 October 2007. Copyright © 2008 by Lippincott Williams & Wilkins ISSN 0041-1337/08/8502-217 DOI: 10.1097/TP.0b013e31816025b4 Transplantation • Volume 85, Number 2, January 27, 2008 217