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Pediatric toxic ingestions are often unwitnessed and are usually complicated by
the young patient’s inability to provide information on the quantity or identity of
the substance ingested (see Chapter 102 Toxicologic Emergencies ). Table 17.2
lists many drug classes that cause coma with overdose. Exogenous toxins may
impair neuronal function directly or by causing hypoxia, acidosis, enzyme
inhibition, hypoglycemia, or seizures. ALOC can occur after direct intrathecal
injection of medication such as baclofen resulting from intrathecal pump
malfunction.
Metabolic Alterations
Abnormal serum concentrations of any substrate or product involved in neuronal
metabolism can produce ALOC leading to coma. Hypoglycemia is the most
common disorder in this category, especially in infants and young children,
whose capacity for hepatic gluconeogenesis is limited. Disorders known to
produce hypoglycemia include serious bacterial infections, sepsis, dehydration,
and toxic ingestions (especially ethanol, beta blockers, and oral hypoglycemics).
Diabetes mellitus, especially of new onset, may present with profoundly
depressed consciousness from the combination of hyperosmolarity, dehydration,
hypotension, and metabolic acidosis. Patients under treatment for diabetic
ketoacidosis may also develop cerebral edema and ALOC. Patients with type 2
diabetes may have coma as part of hyperglycemic hyperosmolar nonketotic
syndrome, which can be complicated by malignant hyperthermia.
Metabolic acidosis or alkalosis of sufficient degree produces ALOC. The most
common disorder of this type in children is severe dehydration leading to
metabolic acidosis. Abnormal concentrations of any serum electrolyte, including
sodium, calcium, magnesium, and phosphorus, can also produce altered mental
status. Hyponatremia, from either dehydration or dilution from excess water, and
hypernatremic dehydration, are among the most common causes of ALOC in
infants. The degree of resulting neurologic compromise will be affected by the
duration and severity of the electrolyte disturbance and concurrent disorders.
Severe dehydration alone may also produce profound lethargy in infants and
children, even in the absence of significant electrolyte abnormalities.

Other causes of metabolic coma in the pediatric age group include kidney or
hepatic failure, both of which may result in progressive apathy, confusion, and
lethargy. Urea cycle defects may present with ALOC and hyperammonemia in
young infants (see Chapter 95 Metabolic Emergencies ). Acute toxic
encephalopathy (Reye syndrome) is a rare but devastating illness caused by
mitochondrial injury of unknown origin that affects all organs of the body,