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Secondary brain injury and neuroprotective measures

Summary

Secondary brain injury is an indirect injury caused by physiological changes that are triggered by an acute CNS insult (e.g., traumatic brain injury, stroke, cerebral hypoxia secondary to cardiac arrest) and/or the management of the primary insult. Unlike primary brain injury, which refers to the direct, immediate, and potentially irreversible neuronal damage from an acute CNS insult, secondary brain injury is preventable or can be minimized with the early administration of neuroprotective measures. Neuroprotective measures involve the early and aggressive control of factors that are implicated in the etiology of secondary brain injury. Such measures include optimization of oxygenation, ventilation, blood pressure, blood sugar, body temperature, intracranial pressure, and electrolyte levels. In addition, seizure prophylaxis and treatment, nutritional support, and patient positioning are important aspects of neuroprotective measures.

Definition

  • Secondary brain injury: indirect brain injury that results from physiological changes triggered by acute CNS insults and/or treatment measures for acute CNS insults that affect ICP, oxygenation, blood pressure, etc.
  • Neuroprotective measures: measures to prevent and/or minimize secondary brain injury in the immediate management of patients who have sustained an acute CNS insult

Pathophysiology

An acute CNS insult can trigger any of the following, resulting in secondary brain injury. [1][2][3]

Secondary brain injury is preventable. Neuroprotective measures to prevent or minimize secondary brain injury should be initiated as early as possible in all patients with acute CNS insults.

Oxygenation and ventilation

Avoid hypoxia, hyperoxia, hypocapnia, and hypercapnia in patients with acute CNS insult. [2]

Control of PaO2 (oxygenation)

Hypoxia and hyperoxia can worsen neurological outcome and should be avoided.

Routine use of supplemental oxygen in nonhypoxic patients is of no clinical benefit in the prevention of secondary brain injury. [7]

Control of PaCO2 (ventilation)

Hypercapnia (including permissive hypercapnia) and long-term hypocapnia worsen neurological outcome in patients with acute CNS insults and should be avoided. [2]

Hypocapnia should only be used as a temporizing measure for patients with signs of cerebral herniation syndromes while simultaneously initiating definitive management for ↑ ICP. [6]

Blood pressure and cerebral perfusion pressure

Blood pressure control after acute CNS insult is complex and the optimal treatment goals are yet to be established. The main aim is to maintain cerebral perfusion pressure (CPP) between 60–70 mm Hg by maintaining mean arterial pressure (MAP) between 65–100 mm Hg [2][9][3]

Avoid hypovolemia and hypervolemia when resuscitating a patient with an acute CNS insult. Hypovolemia decreases cerebral perfusion, worsens cerebral ischemia, and may potentiate thromboses in the injured tissue. Hypervolemia worsens cerebral edema. [4]

Hypotensive patients

Hypotension should be avoided in all patients with depressed consciousness as it decreases CBF, thus worsening neurological outcomes and increasing the mortality risk. [2][10][11]

Hypertensive patients

The SBP threshold at which to administer antihypertensives and target SBP differ according to the etiology of the acute CNS insult. [17][18][19]

Ischemic stroke

Intracranial hemorrhage (including TBI)

  • Target SBP: 140–180 mm Hg [17][20][21]
  • Timing: Initiate treatment as soon as possible in patients with SBP > 180 mm Hg [18][22][11][19]
  • Commonly used antihypertensive agents [18][11]

Blood sugar

Blood glucose should be checked at presentation and serially monitored. Strict blood glucose control is recommended as hypoglycemia or hyperglycemia worsen the neurological outcome after an acute CNS insult.

Avoid dextrose-containing solutions in the resuscitation of nonhypoglycemic patients with an acute CNS insult. [4]

Seizure prophylaxis and treatment

Because seizures may be clinically inapparent in comatose patients or those on neuromuscular blockers, continuous EEG monitoring is recommended in this group of patients.

Electrolyte abnormalities

Sodium disorders and hypokalemia are the most common electrolyte abnormalities seen after an acute CNS insult. [30][31]

Disorders of sodium balance [32]

  • General considerations
    • Identify and treat the underlying cause.
    • Sodium disturbances are often self-limiting in patients with brain injury.
  • Hyponatremia [32]
    • Acutely symptomatic patients: prompt treatment with gradual correction (see “Treatment” in hyponatremia and SIADH)
    • Asymptomatic patients: Supportive treatment strategy is usually appropriate.
  • Hypernatremia [33]
    • Severe elevation (> 160 mEq/L): gradual correction (see “Treatment” section in hypernatremia)
    • Mild–moderate elevation (up to 160 mEq/L): consider gradual correction

Symptomatic hypernatremia should be corrected gradually to minimize the risk of cerebral and pulmonary edema. Symptomatic hyponatremia should be corrected gradually to minimize the risk of central pontine myelinolysis. [32]

Disorders of potassium balance

Neurogenic fever and targeted temperature management

Neurogenic fever (central hyperthermia) [34][35]

In patients with acute CNS insults, fever should be aggressively treated as it is associated with a poor neurological outcome and increased risk of mortality.

Targeted temperature management (TTM)

  • Definition: controlled maintenance of a target body temperature aimed to prevent secondary brain injury after an acute CNS insult
  • Target body temperature: differs according to the inciting event
  • Measures to achieve TTM [42]

Other

Intracranial pressure (ICP)

  • Target: Maintain ICP below 20–22 mm Hg [2][12][3]
  • Treatment: See ICP management.

Patient positioning

Transfusion

Nutrition [50][51]

  • Neurological insult typically leads to a hypermetabolic state. [52]
  • Early (ideally within 24 hours) nutritional support (enteral and parenteral) improves neurological outcomes compared to delayed nutritional support.
  • Enteral nutrition is preferred if possible; patients with low GCS or dysphagia may require a nasogastric or nasojejunal tube.

Acute management checklist

  • Identify and treat hypoxia.
  • Maintain normocapnia (consider short-term hypocapnia in patients with signs of ↑ICP or cerebral herniation syndromes).
  • Blood pressure management
  • Normoglycemia
  • Consider seizure prophylaxis and/or seizure management (if appropriate)
  • Identify and treat electrolyte abnormalities.
  • Identify and treat hyperthermia.
  • ICP management.
  • Patient positioning
  • Support nutritional needs.
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last updated 09/22/2020
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