The child with metabolic disease

Author: Dr Yumna Haroon-Mowahed

Introduction

Metabolic diseases are rare but many children with these diseases now survive into adulthood. They represent a significant morbidity and mortality if not recognised and managed appropriately. Many of these disorders are identified through newborn screening but present at all ages with generic symptoms, in keeping with other childhood illnesses.

As clinicians we should understand metabolic disorders in order to manage them appropriately. Hopefully after this section you will have a better understanding of the key considerations in management.

Metabolic diseases

Metabolic diseases form part of a large group of inherited conditions resulting in the body’s metabolic pathways being blocked or defects in transport of substances.

Common metabolic disorders include phenylketonuria (PKU), galactosemia, medium chain acyl-coA dehydrogenase deficiency (MCAD), Prader-Willi syndrome and other disorders of fatty acid utilisation, glycogen storage disorders, mitrochondrial disorders, purine disorders and disruption of the urea cycle.

Eliciting a family history and presenting signs and symptoms can help determine if a child has a metabolic disease.

Family history that may allude to metabolic disease include:

• Parental consanguinity
• Unexplained paediatric death
• Relatives with similar conditions
• Family history with unexplained neurodevelopmental disorders

Acute presentations that may be indicative of metabolic disorders include:

• Confusion without injury
• Poor feeding in the newborn and hypotonia
• Seizures
• Cardiac failure or unexplained shock
• Tachypnoea and breathlessness
• Hypoglycaemia
• Metabolic acidosis or respiratory alkalosis
• Liver dysfunction
• Hepatosplenomegaly

Other important factors in the history include the following:

• Pregnancy and antenatal history including illness in pregnancy, acute fatty liver in pregnancy and HELLP syndrome
• Developmental delay or regression
• Unexplained vomiting
• Recurrent illnesses precipitated by catabolic episodes
• Aversion to certain foods
• Unexplained exercise intolerances and letheragy
• Unexplained neurological symptoms

The main consideration when a child presents with a metabolic syndrome is maintaining normoglycaemia to ensure the child does not undergo a catabolic state due to prolonged fasting. Elective surgery should be undertaken in specialist centres with a multidisciplinary team to optimise their perioperative care.

Investigations include blood and urine samples.

The main principles in management for the unwell child is to treat the underlying or precipitating illness (including treatment of the hypoglycaemia and seizures), maintain hydration, stop triggering factors, prevent catabolism, remove the toxic metabolites by medications or haemofiltration and avoid prolonged fasting.

Management of these patients can be challenging and may need to be individualised. This may involve a multidisciplinary approach to care, in a facility with metabolic expertise and access to PICU/ HDU care post operatively.

Preoperative considerations

• MDT approach
• Management of infections prior to surgery to prevent metabolic decompensation
• Cardiac and respiratory evaluation as they may be affected by disease process
• Full work up with bloods, ECG, blood gas
• Aim to correct metabolic acidosis where possible
• Maintain restrictive diets
• Reduce fasting times and hydrate prior to surgery
• Use sedative premedication with caution where airway compromise may be associated with the disease process or sleep disordered breathing may be present.
• Thorough airway assessment as this also may be affected by the disease process

Intraoperative considerations

• Avoid succinylcholine in myopathic children, high risk of hyperkalaemia
• Use muscle relaxation and opioids with caution in myopathic patients
• Avoid lactate containing fluids
• Avoid hypoxia
• Avoid hypothermia
• Avoid ingestion of blood as constitutes a large protein load and may trigger an acute decompensation in many metabolic disorders
• Avoid prolonged exposure to nitrous oxide

Postoperative considerations

• All patients should be monitored for deterioration
• High dependency units are recommended
• Regular monitoring of electrolytes, acid base balance and ammonia levels
• Reinstitute specialised diet as soon as possible.

Some excellent resources:

• Starship.org.nz guidelines
• RCH guidelines
• BJA education article