DIFFUSE CEREBRAL SWELLING

Diffuse brain swelling in the absence of oedema is a frequent early finding in paediatric brain injury, and is due to generalised cerebral vasodilatation. It often resolves in 1–2 days if there is no other significant brain injury. With more severe primary traumatic injury, diffuse cerebral swelling may be accompanied by areas of contusion, multifocal petechial haemorrhage and vasogenic oedema that progress over several days.

CEREBRAL BLOOD FLOW AND METABOLISM

The cerebral perfusion pressure (CPP) represents the difference between mean arterial pressure (MAP) and intracranial pressure (ICP).

If autoregulation is disturbed as part of the illness, CPP becomes the major determinant of cerebral blood flow, particularly in areas with more severe damage. The ideal CPP in childhood is not known. The normal range of MAP varies with age from 40 mmHg in a term neonate to 90 mmHg in an adult. The target CPP is usually adjusted with age, taking into consideration the normal blood pressure for age. For example, for an adolescent patient, therapy may be directed at maintaining a CPP of 70 mmHg, while for a child aged 5 years, the aim may be to maintain a CPP of 50 mmHg.

In conditions where vasogenic oedema occurs, arterial hypertension may increase vascular shift of fluid and worsen brain swelling. However, treatment aimed at lowering arterial pressure (e.g. with vasodilators) may interfere with homeostatic mechanisms and should be used cautiously.

The brain comprises up to 12% of body weight in infancy compared with 2–3% in adulthood. Cerebral oxygen and glucose consumption is therefore proportionately greater in childhood while glycogen stores are readily depleted. As hypoglycaemia occurs commonly in severe illnesses such as sepsis, blood glucose should be monitored regularly.

HYPOVOLAEMIA

Children have small blood volumes and commonly develop hypovolaemia from scalp bleeding or intracranial haemorrhage. For example, hypovolaemia will develop in a 5-kg infant (blood volume 400 ml) following blood loss of only 100 ml. Hypovolaemia should be treated aggressively with fluid boluses of 20 ml/kg to ensure adequate cerebral perfusion.

RELATIVE GROWTH

The child’s short stature and proportionately large head confer a number of risks. The toddler’s head is at the level of the front of a motor vehicle and isolated head injury is subsequently common following pedestrian injury in this age group. The neck muscles are relatively weak in infancy and they support a large head. This renders the brain prone to deceleration injury in motor vehicle crashes and in cases of domestic violence. Injury inflicted by shaking an infant by the shoulders snaps the head to and fro, leading to compression of brain tissue and rupture of delicate bridging veins.

BONE DEVELOPMENT

The skull bones in the first year of life are thin with open sutures and open fontanelles. Beyond 2 years, the skull sutures close and the cranial vault thickens. In young children there tends to be less bony protection from high impact trauma, while the non-rigid skull may expand to partially decompress expanding lesions.¹

INITIAL MANAGEMENT

Management should always begin with rapid assessment of the adequacy of airway, ventilation and circulation. If inadequacies are detected, interventions aimed at correcting them should occur immediately. Once venous access is obtained, blood should be drawn for routine tests including immediate measurement of blood glucose. If hypoglycaemia is demonstrated 2 ml/kg of 25% glucose or 5 ml/kg of 10% glucose should be given intravenously as the neurological sequelae of unrecognised hypoglycaemia can be profound.

Concurrent with the initial assessment and resuscitation, relevant details of the present and past history should be obtained. A detailed neurological and general physical examination should be performed. It is important to document accurately the conscious state so that changes over time, particularly deterioration, can be easily recognised. The Glasgow Coma Scale (GCS) is appropriate for this purpose. The responses of children change with development and therefore the GCS requires modification for paediatric use (Table 102.2). After completing the clinical assessment, the likely diagnosis is often apparent and appropriate investigation and treatment can commence. Multiple factors may compound to produce coma. For example, a child with severe gastroenteritis may have hyperthermia, hyponatraemic dehydration, metabolic acidosis and hypovolaemic shock.

CONTROLLED VENTILATION

Indications for ventilating a comatose child are:

Once ventilation is initiated the stomach should be drained with a gastric tube and blood pressure checked every 5 minutes. Raised ICP should be considered in any case of rapidly progressive coma. Intracranial hypertension should be managed with moderate hyperventilation and intravenous mannitol (0.25 g/kg). Hypertonic saline given as 0.5 ml/kg of 20% solution (3.4 mmol/ml) can also rapidly reduce ICP.² Once stability is achieved, adequate sedation and analgesia is required. Muscle relaxants may be necessary to facilitate ventilation and prevent straining; however, their use precludes further neurological assessment and therefore, if long-acting muscle relaxants are continued, ICP monitoring is advisable. Hyperventilation is a short-term manoeuvre and following the early resuscitation phase, gradual return to a low-normal PaCO₂ should be the aim. This is best achieved with end tidal CO₂ and ICP monitoring. Particular attention should be paid to restoring intravascular volume and maintaining an adequate CPP.

CRANIAL COMPUTED TOMOGRAPHY (CT)

A CT scan is required in comatose children with localising signs and in those in whom the diagnosis is not clear. A CT should also be performed if the conscious state is abnormal and there is a history of trauma. Even if the general condition does not warrant controlled ventilation, a CT is often best performed under general anaesthesia. Unwanted movement will cause poor-quality images and sedation alone may place the child at risk of hypoventilation or aspiration.

LUMBAR PUNCTURE

Lumbar puncture (LP) should be performed when there is reasonable suspicion of meningitis or encephalitis. The risks and contraindications to LP are discussed under bacterial meningitis.

ADDITIONAL INVESTIGATIONS

Additional investigations include arterial blood gas analysis, serum electrolytes, glucose, urea and creatinine, liver function tests, serum ammonia, serum and CSF lactate and pyruvate, and urine analysis. Appropriate screening of blood and urine will exclude common poisons and drug intoxications.

SPECIFIC TREATMENT

The clinical signs and results of investigations generally guide treatment. If hypoglycaemia occurs, after initial correction, care should be taken to ensure that it does not recur by the administration of appropriate glucose containing i.v. fluid and regular blood glucose monitoring. Herpes simplex encephalitis can present in many ways and is not excluded by the absence of CSF pleocytosis. Aciclovir therapy should therefore be considered in any patient in whom herpes cannot be confidently excluded.

PATHOPHYSIOLOGY

Many physiological changes occur during prolonged seizures. There is an initial phase of compensation lasting less than 30 minutes. Following a period of transition there is a phase of decompensation commencing between 30 and 60 minutes and evolving over hours. Physiological changes during the compensated phase include tachycardia, hypertension, increased catecholamine release and increased cardiac output. Changes within the brain include increased cerebral blood flow and increased cerebral utilisation of glucose and oxygen. After 30–60 minutes the mechanisms for homeostatic compensation fail. During the decompensated phase there may be falling blood pressure and cardiac output, hypoglycaemia, hypoxia, acidosis, electrolyte disturbance and rhabdomyolysis. The cerebral physiology is characterised by failing autoregulation and reduced cerebral blood flow and oxygen and glucose utilisation. Over hours a deficit in brain energy develops and this is associated with the development of brain damage.⁴

MANAGEMENT

The initial management is as for other neurological emergencies with attention to airway and oxygenation. Most seizures in childhood cease spontaneously in a short time, but if they persist for 5 minutes or continue after presentation to an emergency department, they should be stopped to avoid metabolic and ischaemic neuronal damage. Hypoglycaemia should be excluded or detected early. If intravenous access cannot be obtained rapidly, drugs can be administered intramuscularly, intranasally, rectally or via the intraosseous (i.o.) route. If benzodiazepines are administered within 20 minutes of a seizure commencing, the rate of seizure control is higher than if they are administered after 30 minutes.⁶ This justifies early prehospital administration of benzodiazepines to children with active seizures at the time of ambulance arrival.⁷ Specific drug treatment includes the following.

OUTCOME

The outcome of CSE is dependent on the aetiology. Neurologically normal children in whom CSE is precipitated by fever are considered to have a good prognosis with mortality reported between 0 and 2%.¹⁹ The incidence of neurological deficits or cognitive impairment in this group is also very low.⁵ In acute symptomatic CSE (where CSE is a symptom of an acute neurological process such as infection or trauma), mortality is 12–16% and the incidence of new neurological dysfunction is more than 20%.¹⁹ In this setting, however, it is very difficult to tease out the extent to which prolonged seizures contribute to neurological sequelae.

PATHOPHYSIOLOGY

Bacterial meningitis (BM) usually occurs following haematogenous spread of organisms carried in the nasopharynx. In childhood the common bacteria causing BM are Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae type b (Hib). Group B Streptococcus, Escherichia coli and Listeria monocytogenes are the most common causative organisms of neonatal BM. Occasionally, meningitis occurs as a complication of other pathology such as base of skull fracture, chronic middle ear infection or infection of a congenital dermoid sinus.

In the early stages of the disease cerebral hyperaemia occurs. This can be followed by cerebral ischaemia, which may occur by several different mechanisms. Local vasculitis of vessels transversing the subarachnoid space can progress to arterial thrombosis and focal infarction. Other vascular abnormalities including vasospasm and sagittal sinus thrombosis can also occur. Cerebral oedema is relatively common in meningitis and is caused by a combination of vasogenic, cytotoxic and hydrostatic factors. If cerebral oedema is severe, raised ICP and impaired cerebral perfusion can occur, leading to global cerebral ischaemia.

CLINICAL FEATURES

In children the typical features of BM are fever, headache, photophobia, neck stiffness and vomiting. The history may extend over several days; however, in fulminant cases the time from first symptom to coma and death may only be a few hours. Neonates and young infants do not present with the typical localised symptoms and signs. Instead, they present with generalised signs of illness including lethargy, poor feeding and pallor. Generalised or focal convulsions or apnoea may be present at presentation. Tuberculous meningitis usually presents with a more insidious onset of symptoms and may be associated with focal neurological signs.

Complications occur commonly in BM. During the early phase, meningitis may be associated with septic shock and disseminated intravascular coagulation (DIC). Fluid and electrolyte abnormalities are relatively common, particularly hyponatraemia and hypoglycaemia. Focal and generalised convulsions are relatively common and may progress to status epilepticus. During the recovery phase subdural effusions or hydrocephalus may occur.

INVESTIGATIONS

Lumbar puncture for CSF microscopy, culture and bacterial antigen testing is required for definitive diagnosis of BM and to guide antibiotic therapy. While an LP can be performed safely in the majority of children with BM, LP may precipitate brainstem herniation if raised ICP is present.²⁰ Identifying children at risk of this complication is difficult, so it is generally recommended that empiric antibiotic therapy be commenced and LP deferred if any of the following clinical features are present:

A normal CT scan does not exclude the possibility of elevated ICP.²⁰ Therefore, the decision to defer an LP should be based on clinical rather than radiological signs. In addition to signs of increased ICP, other indications for deferring the LP include cardiorespiratory instability and severe coagulopathy.

If LP is deferred, alternative methods of establishing a bacterial diagnosis include blood culture and bacterial antigen testing in urine and polymerase chain reaction (PCR) testing of blood.^21,22

MANAGEMENT