Neurological emergencies

Pathophysiology of cerebral injury

Most injuries to the brain involve both primary injury (injury directly due to the insult) and secondary injury. Primary injury results in three tissue zones: an area of tissue that is irreversibly injured, an area that is injured but will recover if secondary injury is prevented and an area that is uninjured.

There are multiple mechanisms by which secondary injury may occur but decreased oxygen delivery to the brain is probably the most important. Decreased oxygen delivery may be due to a reduction in systemic oxygen delivery or may be due to a specific reduction in cerebral oxygen delivery. Given that it is not possible to achieve adequate cerebral oxygen delivery without adequate systemic oxygen delivery, it is vital to ensure adequate systemic resuscitation before concentrating specifically on cerebral oxygen delivery. Crystalloids, rather than colloids, are recommended for fluid resuscitation.

Cerebral oxygen delivery is dependent on arterial oxygen content and cerebral blood flow. Cerebral blood flow is, in turn, dependent on cerebral perfusion pressure (cerebral autoregulation is usually impaired in the early stages after cerebral injury). Cerebral perfusion pressure (CPP) is the difference between mean arterial pressure (MAP) and intracranial pressure (ICP):

CPP = MAP - ICP

Hyperglycaemia and electrolyte disturbances may also contribute to secondary injury. Plasma glucose and electrolyte concentrations should be checked regularly and treatment instituted early.

Intracranial pressure

Important because:

• It is a major determinant of cerebral perfusion pressure
• Raised intracranial pressure (ICP) may resu
lt in herniation of brain and irreversible brainstem injury.

A space occupying intracranial lesion results in a rise in ICP if the volume of the lesion exceeds the capacity for compensation. From this point on, further increases in the volume of the intracranial contents results in a marked rise in ICP (figure 1)

Conversely, a reduction in volume of any component of the intracranial contents will result in a significant reduction in intracranial pressure. The four major components are the space occupying lesion itself, the brain, cerebrospinal fluid and circulating blood (figure 2).

The volume of a space occupying lesion can be reduced by surgical evacuation or excision, the volume of an oedematous brain can be reduced by an osmotic diuretic like mannitol, the volume of cerebrospinal fluid can be reduced by intraventricular drainage and the volume of intracranial circulating blood can be reduced by hyperventilation, which causes cerebral vasoconstriction.

Mannitol

Administration of mannitol results in a rapid reduction of intracranial pressure, which starts within minutes. The maximal effect is seen after about 20-40 minutes. The usual dose is 0.25-1 g/kg (1.25-5 mL/kg of 20% mannitol) initially followed by 0.25-0.5 g/kg (1.25-2.5 mL/kg of 20% mannitol) 6 hourly.

The diuresis induced by mannitol may result in hypovolaemia and therefore mannitol should not be given until a volume loss has been replaced. In a patient who urgently requires osmotherapy but is hypovolaemic 150 mL 3% saline can be given instead of mannitol.

In the absence of signs of herniation. mannitol should not be administered to a patient with an intracranial haematoma prior to evacuation of the haematoma.

Hyperventilation

Although hyperventilation reduces intracranial pressure, it does so at the expense of reduced cerebral blood flow. It is, therefore, illogical to use hyperventilation to reduce intracranial pressure if the aim is to improve cerebral perfusion. Furthermore routine hyperventilation has been shown to worsen outcome in patients with traumatic brain injury. If, however, the patient shows signs of herniation then hyperventilation is indicated to prevent irreversible brainstem injury.

Assessment of the comatose patient

As always in critically ill patients, the initial step is to assess and correct any deficiency in airway, breathing or circulation. Subsequently, it is important to distinguish patients with traumatic brain injury from those with non-traumatic brain injury. All comatose patients with traumatic brain injury require CT brain immediately after resuscitation, while not all patients with non-traumatic brain injury require immediate CT scanning. The distinction is made on the basis of the history and external signs of trauma.

Traumatic brain injury

Management

The three main priorities are:

• Resuscitation
• Rapid diagnosis of a brain lesion resulting from head injury
• Prevention of secondary brain insults

Resuscitation to normal physiological values should always be the first priority. Aim for a mean arterial pressure >90 mmHg in an attempt to maintain an adequate cerebral perfusion pressure. Most patients with a severe brain injury (GCS 3-8 [table 1] after restoration of normal physiological end-points) require intubation and ventilation to prevent aspiration and ensure adequate oxygenation and ventilation. In the initial resuscitative phase hyperventilation and osmotic diuretics are not indicated unless the patient shows signs of herniation or progressive neurological deterioration that is not attributable to extracranial causes. In this case hyperventilation to a PaCO₂ of 4-4.5 kPa (30-35 mmHg) should be started and, if the patient has been adequately fluid resuscitated, mannitol 0.25-1 g/kg should be given.

CT scanning is the most useful investigation in demonstrating treatable pathology following traumatic brain injury. All patients with a severe head injury should have a CT scan of the brain once they have been stabilized.

Patients should be referred to a neurosurgeon and the Intensive Care Unit at an early stage

Non-traumatic coma

Aetiology

Ask two questions to determine the likely diagnosis (figure 3):

• Are there focal, brainstem or localizing signs?
• Is there meningism?

Further clues to the aetiology can obtained from the history and from examination. A CT scan will be necessary in most cases but the urgency will depend on the likely diagnosis. For example CT should usually follow blood cultures and administration of antibiotics in suspected meningitis but should be performed as a matter of urgency in patients with suspected cerebral haemorrhage.

History

• Speed of onset: sudden loss of consciousness is suggestive of intracranial haemorrhage or brainstem infarction
• Headaches are characteristic of cerebral, cerebellar and subarachnoid haemorrhage
• Disturbance of higher functions eg memory loss, hallucinations etc may precede unconsciousness in epilepsy
• The brain is more susceptible to ischaemic injury than hypoxaemic injury

Examination

Nervous system

Note that examination of the central nervous system in the patient with decreased consciousness is not just assessment of the Glasgow Coma Scale and deep tendon reflexes.

• Note position and posture of patient and any spontaneous movements
• Glasgow Coma Scale. This should be assessed from highest score to lowest (ie check if the patient obeys commands before applying a painful stimulus and determine whether he/she localizes before checking for withdrawal

• Important points:
  • Minimum GCS is 3/15
  • Before performing a neurological assessment on a patient, check for barriers to performing an accurate assessment, such as language barriers, hearing and vision impairments, presence of a tracheostomy, spinal injury, limb paralysis, etc. These barriers should be overcome if possible, i.e. with the use of family members, interpreters, communication aids, hearing aids etc.
  • Sedative drugs may need to be paused to perform an accurate patient assessment.
  • Observe patient for signs of speech disturbances, such as dysarthria, dysphasia and aphasia that may affect the GCS.
• Painful stimulus:
  • Painful stimuli are meant to be painful. An insufficiently strong stimulus will result in an underestimate of the level of consciousness.
  • If the patient does not open his or her eyes to speech or doesn’t obey commands, apply central pain using a trapezius squeeze (Figure 4), sternal rub (Figure 5) or supraorbital pressure (Figure 6)

• If the patient makes a purposeful movement towards painful stimulus when central pain is applied, then he or she is localising to pain (Figure 7).

• If the patient does not make a purposeful movement to remove the painful stimuli, apply a painful stimulus to each limb. If he or she attempts to withdraw from the painful stimulus the score is 4 (Figure 8).

• If the patient flexes his or her elbows rigidly the score is 3 (Figure 9).

• If the patient extends his or her arms against the trunk of the body with fists rotated outwards the score is 2 (Figure 10).

• Meningism:
  • It’s important to distinguish neck stiffness due to meningeal irritation from neck stiffness due to coning. Theformer is associated with positive Kernig's and Brudzinski's signs (flexing the neck causes flexion of the hips, figure 11)
  • Check for the possibility of trauma before testing neck stiffness

• Fundi. Look for:
  • Papilloedema suggestive of long standing (>1 week) intracranial hypertension
  • Haemorrhage suggestive of subarachnoid haemorrhage
  • Emboli suggestive of embolic stroke
  • Hypertensive or diabetic retinopathy
• Pupillary reflexes (figure 12):

• Corneal reflex: usually retained until coma is very deep except in drug-induced coma. Loss of corneal reflex is a sign of poor prognosis if not due to drugs
• Oculocephalic reflex. Lost in patients with pontine depression.
• Gag
• Motor function: tone, response to pain and reflexes. Look for:
  • Asymmetry
  • Tremors (most often seen in metabolic, hypercapnic and drug induced coma)
  • Myoclonus (most commonly seen in anoxic brain injury
  • Flap
  • Rigidity: metabolic, temperature disturbance, amphetamine or phenothiazine poisoning

Respiratory system

Pattern of breathing gives important clues

• Periodic breathing
  • Common in patients with metabolic encephalopathy. Occasionally Cheyne-Stokes seen in this group
  • Also seen in brainstem lesions
• Central neurogenic hyperventilation implies a lesion at the level of the upper pons

Cardiovascular system

Hypotension unresponsive to volume expansion in the context of metabolic/drug induced coma suggests intoxication with barbiturates or opiates, myxoedema, Addisonian crisis. Occult sepsis must be excluded.

Investigation

• Hypoglycaemia should be excluded as a priority
• Electrolytes, renal and liver function tests, arterial blood gases
• CT brain
• Other investigations based on differential diagnosis in individual patient:
  • Toxicology, particularly paracetamol and salicylate concentrations
  • Lumbar puncture
  • EEG. Major use is in diagnosis of subclinical status epilepticus, particularly in patients with acute structural brain lesions, or complex partial seizures. May also be useful in diagnosis of feigned coma

Management

The immediate management and role of CT in diagnosis are outlined in figure 13. Obviously other investigations should be carried out as appropriate.

Patients who are comatose (Glasgow Coma Scale <9) and not expected to make a rapid recovery will need tracheal intubation to prevent macro-aspiration. In the meantime they should be placed in the recovery position (figure 14), once cervical trauma has been excluded).

Signs of herniation are an indication for urgent treatment with mannitol and hyperventilation.

Generalized status epilepticus

This should be urgently treated as electrical seizure activity causes neuronal damage (whether accompanied by motor manifestations or not) and convulsions become progressively harder to stop the longer they continue.

Diagnosis

Generalized status epilepticus is defined as recurrent generalized tonic and/or clonic convulsive seizures without full recovery of consciousness before the next seizure begins, or more-or-less continuous generalized clinical and/or electrical seizure activity lasting for more than 30 min.

In differentiating patients with generalized convulsions from those with partial seizures it is important to recognize that there is a wide range of presentations of generalized seizures. These range from repeated, overt generalized seizures to very subtle focal twitches of a localised part of the body (eg rhythmic nystagmoid eye jerks, twitching of an eyelid). Although the latter may superficially appear to be a form of focal epilepsy, they can be clearly distinguished from focal epilepsy by the fact that the patient has profound impairment of conscious level and bilateral EEG changes. In addition, if a patient with generalized tonic-clonic convulsions is inadequately treated, the motor manifestations may stop, despite continued ictal EEG discharges.

Fixed dilated pupils are a feature of generalized convulsions and do not indicate herniation in patients who are fitting or are immediately post ictal.

Investigations

Investigations to consider are listed in table 3.

• If hypoglycaemic or if blood glucose estimation not available, give glucose. In adults give 100 mg thiamine first then 50 mL 50% glucose IV bolus; in children give glucose 25% 2 mL/kg.
• Lorazepam 0.1 mg/kg at 2 mg/min IV if IV access available. Otherwise give midazolam 10 mg IM. Diazepam IV 0.2 mg/kg at 5 mg/min is a less preferable alternative. If diazepam is given, phenytoin should also be given to prevent recurrence:
  • Give 15-20 mg/kg of phenytoin IV at a rate < 50 mg/min in adults and 1 mg/kg/min in children. Monitor ECG and BP during infusion. If hypotension or arrhythmias develop slow the rate of infusion.

Acute ischaemic stroke

Diagnosis

Consider the diagnosis of an acute stroke in all patients with a sudden onset of a neurological deficit. Onset time of neurological deficit is particularly important as these patients may benefit from urgent thrombolysis if treated within 4.5 hours of symptom onset.

Investigation

An immediate CT is required to exclude intracerebral haemorrhage. Note that there will not be overt signs of infarction on the CT at this stage.
Blood test, particularly glucose level, platelet count and clotting profile, should be performed urgently.

Management

Oxygen supplement should be provided if oxygen saturation <94%.
Source of hyperthermia (temperature >38 degree) should be identified and antipyretics (e.g paracetamol) should be prescribed to control hyperthermia.

These patients must be assessed urgently and referred to a stroke team as soon as possible for consideration of thrombolysis.

Aspirin should be prescribed within 24 to 48 hours after symptoms onset (usually delayed until 24hours later if thrombolytics prescribed)