Managing the uncontrolled PKU patient who cannot feed.

Background:

The principal components in the management of Phenylketonuria (PKU) diagnosed by newborn screening include early restriction of dietary phenylalanine (phe) and commencement of phe-free formula to provide energy and essential and non-essential amino acids to reduce phe levels to a neurologically safe level (< 360µmol/l).

Case Report

This case describes a newly diagnosed 1-week old infant with classical PKU (phe 1500 µmol/l), who presented acutely unwell and unable to receive adequate enteral feeds of phe-free formula due to relatively poor gut perfusion in the setting of a coarctation of the aorta. In the absence of phe-free parenteral nutrition (PN), we describe our attempt to effectively lower blood phe. Initial introduction of ‘trophic feeding’ was attempted twice preoperatively but this resulted in elevated lactate levels, clinical concerns around necrotising enterocolitis and required subsequent instigation of high calories with intravenous dextrose and lipid solutions and insulin.

Results

Phe levels were initially lowered, and remained at 1100-1200 µmol/l however branched-chain and other essential amino acids fell below reference ranges. Complications from instigating these measures both pre and post-operatively included insulin resistance leading to poor glycaemic control and hypertriglyceridaemia. Early attempts to enterally feed post operatively were complicated by haemodynamic instability and opiate induced ileus.

Discussion

The challenge of managing uncontrolled PKU in an infant who cannot feed raised the following questions: What is a safe and effective method of providing nutrition to reduce phe levels? In the absence of bespoke ‘low Phe’ PN, what is the role of standard paediatric PN to provide essential amino acids when phe-free protein cannot be provided enterally?