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in the cerebellum present with combinations of ataxia, vertigo, nausea, occipital
headache, and resistance to neck flexion. Coma is an unusual early sign of
infarction of cerebral structures but becomes more common as lower anatomic
centers are affected. Occlusion of the basilar artery may result in upper brainstem
infarction, resulting in rapid onset of coma, as does hemorrhage or infarction of
the pons. Posterior reversible encephalopathy syndrome (PRES, a.k.a. reversible
posterior leukoencephalopathy syndrome [RPLS]) causing ALOC is associated
with autoimmune disease, sepsis, nephrotic syndrome, or immunosuppressive
agents.
Cerebrospinal Fluid Shunt Problems
Children with congenital or acquired hydrocephalus as a result of prematurityrelated hemorrhage, neoplasm, or trauma depend on the continued function of an
intraventricular shunt to drain CSF and maintain normal ICP (see Chapter 122
Neurosurgical Emergencies ). The most common shunt type is
ventriculoperitoneal (VP), draining CSF from a lateral cerebral ventricle through
a small skull burr hole and valve with an attached reservoir into the peritoneum
via subcutaneous tubing running through neck, chest, and abdomen. CSF shunts
may malfunction for many reasons, including shunt infection, tubing blockage,
rupture, disconnection, or valve malfunction. The risk of failure is greatest during
the first 6 months after shunt placement or revision.

Systemic Abnormalities
The second major category of disorders causing coma listed in Table 17.2 arise in
organs other than the CNS and affect the brain diffusely. These abnormalities
alter neuronal activity by a variety of mechanisms, including decreasing
metabolic substrates required for normal function (e.g., hypoxia, hypotension,
hypoglycemia, other electrolyte abnormalities), altering the rate of intracellular
chemical reactions (e.g., hypothermia, hyperthermia), and introducing extraneous
toxins into the CNS. Children with autoimmune disease such as systemic lupus
erythematosus, Behỗet disease, multiple sclerosis, and acute disseminated
encephalomyelitis (ADEM, a.k.a. postinfectious encephalitis) may present with
ALOC due to inflammation of brain parenchyma.

Hypoxia
Oxygen delivery to the brain may be adversely affected by disorders that
compromise a patient’s airway, breathing, or circulation. Neurons are the cells
most sensitive to oxygen deprivation, and they will cease to function within
seconds after being deprived of adequate levels of oxygen. Hypoxic coma may