5.4 Traumatic Brain Injury & Spinal Cord Emergencies

5.4 Traumatic Brain Injury & Spinal Cord Emergencies

Neurotrauma represents a major source of critical morbidity and mortality encountered in the emergency department. Traumatic neurovascular injuries require rapid physiological resuscitation centered on preventing secondary cellular damage. In severe traumatic brain injury (TBI) and acute spinal cord injury (SCI), the primary mechanical insult (contusion, hemorrhage, parenchymal laceration) occurs instantaneously at the moment of impact and cannot be reversed pharmacologically. Clinical emergency medicine pharmacotherapy focuses entirely on mitigating secondary insults—including systemic hypotension, arterial hypoxemia, cerebral hypoperfusion, intracranial hypertension, and post-traumatic seizures.

---

Severe Traumatic Brain Injury (TBI, GCS $\le 8$): Secondary Insult Mitigation

The Brain Trauma Foundation (BTF) Guidelines (4th Edition) establish evidence-based parameters designed to protect the vulnerable, ischemic penumbra following severe head injury:

1. Hemodynamic Targets: Blood Pressure & Hypoxia

Secondary physiological insults dramatically escalate mortality in severe TBI:

• Hypotension: Even a single documented episode of systemic systolic blood pressure $<90\text{ mmHg}$ doubles mortality in severe TBI. Current BTF guidelines define specific, age-adjusted systolic thresholds:
  • Age 50 to 69 years: Maintain SBP $\ge 100\text{ mmHg}$.
  • Age 15 to 49 years OR $\ge 70$ years: Maintain SBP $\ge 110\text{ mmHg}$.
• Hypoxia: Maintain $PaO_2 \ge 60\text{ mmHg}$ or $SpO_2 \ge 90\%$. Avoid hyperoxia ($PaO_2 >300\text{ mmHg}$), which triggers reactive oxygen species production and cerebral vasoconstriction.
• The Lethal Combination: The co-occurrence of both systemic hypotension and arterial hypoxia quadruples mortality in severe neurotrauma patients.

2. Cerebral Perfusion Pressure (CPP) & Intracranial Pressure (ICP)

Cerebral perfusion pressure represents the net pressure gradient driving oxygenated blood delivery across cerebral vascular beds:

$CPP = MAP - ICP$

• Target CPP Threshold: Maintain CPP between 60 and 70 mmHg.
  • Avoid CPP $<60\text{ mmHg}$: Insufficient perfusion triggers severe microvascular cerebral ischemia and accelerates infarction of the contused penumbra.
  • Avoid CPP $>70\text{ mmHg}$: Aggressive fluid loading and high-dose vasopressor titration to push CPP above 70 mmHg significantly elevates pulmonary capillary hydrostatic pressure, increasing the incidence of acute respiratory distress syndrome (ARDS) and acute lung injury five-fold without conferring any neurological benefit.
• ICP Monitoring Indications: An indwelling intracranial pressure monitor (external ventricular drain [EVD] or intraparenchymal fiberoptic probe) is indicated in all salvageable severe TBI patients (GCS 3 to 8 after cardiopulmonary resuscitation) who exhibit an abnormal admission head CT (hematoma, contusions, swelling, compressed basal cisterns). It is also indicated in severe TBI patients with a normal head CT if two or more of the following criteria are met upon admission: age $>40$ years, unilateral or bilateral motor posturing, or SBP $<90\text{ mmHg}$.
• ICP Treatment Threshold: Initiate active osmotherapy and neurocritical interventions when sustained ICP exceeds $22\text{ mmHg}$.

3. Ventilation Management & The Dangers of Hyperventilation

Cerebral arterioles are exquisitely sensitive to alterations in arterial carbon dioxide tension ($PaCO_2$):

• Normocarbia Standard: Maintain arterial $PaCO_2$ between 35 and 45 mmHg.
• The Danger of Hyperventilation: Prophylactic hyperventilation ($PaCO_2 <35\text{ mmHg}$) is strongly contraindicated during the first 24 to 48 hours post-injury. Hypocapnia induces severe cerebral vasoconstriction, drastically reducing cerebral blood flow ($CBF$) at a time when cerebral perfusion is already reduced by 50% compared to baseline, causing profound secondary ischemic infarction.
• The Sole Exception: Brief, mild hyperventilation ($PaCO_2\text{ 30 to 35 mmHg}$) is reserved exclusively as a temporary rescue temporizing maneuver during acute, life-threatening uncal herniation (pupillary asymmetry, extensor posturing, sudden GCS drop) while hypertonic saline or mannitol is rapidly infused.

---

Post-Traumatic Seizure (PTS) Prophylaxis: The 7-Day Rule

Post-traumatic seizures are categorized temporally into early PTS (occurring within 7 days of injury) and late PTS (occurring $>7$ days post-injury, representing true post-traumatic epilepsy). Early seizures occur in 4% to 25% of severe TBI patients and drastically increase cerebral metabolic oxygen consumption ($CMRO_2$), intracranial pressure, and secondary brain injury.

Loading diagram...

Clinical Practice Guidelines for PTS Prophylaxis

• Guideline Recommendation: Antiseizure prophylaxis is recommended to decrease the incidence of early post-traumatic seizures for the first 7 days post-injury in high-risk patients (GCS $\le 8$, cortical contusions, depressed skull fracture, subdural/epidural/intracerebral hematoma, penetrating brain injury, or acute seizure at presentation).
• The 7-Day Limit: Prophylactic antiseizure medication beyond 7 days is not recommended. Large randomized controlled trials have demonstrated that continuing anticonvulsants beyond 7 days does NOT decrease the incidence of late post-traumatic epilepsy or improve long-term functional recovery, while exposing patients to adverse drug reactions, hepatic toxicity, and drug interactions.

Pharmacotherapeutic Options: Levetiracetam vs. Phenytoin

1. Levetiracetam (Keppra):
   • Dosing: 1000 mg IV every 12 hours (some centers initiate with a loading dose of 20 to 30 mg/kg IV).
   • Clinical Pearls: Preferred in clinical neurotrauma practice over phenytoin due to lack of therapeutic drug monitoring, absence of hepatic cytochrome P450 enzyme induction, fewer adverse drug events, and zero risk of cardiac dysrhythmias or purple glove syndrome. Requires dosage adjustment in renal impairment.
2. Phenytoin / Fosphenytoin:
   • Dosing: Loading dose of 15 to 20 mg/kg IV (or fosphenytoin 15 to 20 mg PE/kg IV); maintenance dose 100 mg IV/PO every 8 hours (4 to 6 mg/kg/day).
   • Therapeutic Target: Total serum phenytoin level 10 to 20 mcg/mL (free phenytoin level 1 to 2 mcg/mL).
   • Winter's-Tozer Albumin Correction: In trauma and critical illness, hypoalbuminemia causes total phenytoin levels to appear falsely depressed due to decreased plasma protein binding, while the pharmacologically active unbound (free) fraction remains normal or elevated. Adjust total concentration using the Winter's-Tozer equation:

$Phenytoin_{adjusted} = \frac{Phenytoin_{measured}}{(0.2 \times \text{Serum Albumin [g/dL]}) + 0.1}$

---

Acute Spinal Cord Injury (SCI): Deconstructing the NASCIS Steroid Paradigm

For decades, high-dose methylprednisolone was routinely administered in acute traumatic spinal cord injury based on the National Acute Spinal Cord Injury Studies (NASCIS II and III) protocols (30 mg/kg IV bolus over 15 minutes, followed 45 minutes later by a continuous infusion of 5.4 mg/kg/h for 23 to 47 hours).

Contemporary Guideline Consensus (AANS / CNS Guidelines)

• Recommendation: The 2013 AANS/CNS guideline does not recommend high-dose methylprednisolone for acute spinal cord injury. The 2017 AO Spine guideline is more permissive, suggesting that a 24-hour infusion started within 8 hours of injury may be offered to selected adults, so practice varies; prolonged 48-hour courses are not supported.
• Evidence Summary: Rigorous re-analysis of the NASCIS trials and multiple subsequent systematic reviews demonstrated that high-dose corticosteroids provide no consistent, clinically meaningful improvement in long-term neurological or functional recovery. Conversely, high-dose corticosteroid infusions produce a statistically significant increase in severe, life-threatening complications, including severe pneumonia, hospital-acquired infections, bacteremia/sepsis, gastrointestinal ulceration/hemorrhage, acute myopathy, and overall mortality.

---

Neurogenic Shock vs. Spinal Shock: Critical Hemodynamic Differentiation

Emergency clinicians frequently confuse neurogenic shock and spinal shock, yet their underlying pathophysiology and therapeutic management differ fundamentally.

1. Neurogenic Shock

• Pathophysiology: A severe form of distributive shock resulting from the disruption of descending sympathetic autonomic pathways in cervical and high thoracic spinal cord injuries (typically at or above T6).
• Mechanistic Profile:
  • Loss of Sympathetic Vasomotor Tone: Severe, unopposed arteriolar and venous dilation causes massive pooling of blood in peripheral capacitive beds $\rightarrow$ profound systemic hypotension.
  • Loss of Cardiac Accelerator Fibers (T1 to T4): Leaves cardiac sinoatrial and atrioventricular nodal pacing under unopposed parasympathetic (vagal) tone $\rightarrow$ relative or absolute bradycardia.
  • Poikilothermia / Hypothermia: Vasodilation causes heat loss; extremities are initially warm, dry, and well-perfused (unlike the cold, clammy extremities seen in hemorrhagic or cardiogenic shock).
• The Classic Triad: Hypotension, bradycardia, and hypothermia / poikilothermia.

2. Spinal Shock

• Pathophysiology: A transient, localized neurophysiologic phenomenon characterized by the complete temporary loss or depression of all sensorimotor and spinal reflex activity below the level of the injury.
• Clinical Presentation: Flaccid muscle paralysis, absent deep tendon reflexes, loss of bowel and bladder sphincter tone, and loss of the bulbocavernosus reflex. It is not a hemodynamic state of circulatory failure.
• Resolution: Reflex activity gradually returns over days to weeks, typically transitioning into long-term spasticity and hyperreflexia.

---

Perfusion Targets & Vasopressor Management in Acute SCI

Because the injured spinal cord exhibits disrupted local microvascular autoregulation, spinal cord blood flow becomes directly dependent on systemic perfusion pressure. Systemic hypotension worsens secondary cord ischemia, converting an incomplete spinal injury into a permanent complete deficit.

Perfusion Target

• Guideline Goal: The 2013 AANS/CNS guideline suggests a Mean Arterial Pressure (MAP) of 85 to 90 mmHg for the first 7 days after injury. The 2024 AO Spine/Praxis hemodynamic guideline is less aggressive, suggesting a MAP of at least 75 to 80 mmHg as the lower limit and no more than 90 to 95 mmHg as the upper limit, for 3 to 7 days. Know both; many centers now use the newer range.

Vasopressor Selection Architecture

Because neurogenic shock produces both profound vasodilation and bradycardia, optimal vasopressor pharmacotherapy requires agents that provide both alpha-1 (vasoconstriction) and beta-1 (inotropy/chronotropy) adrenergic receptor stimulation:

1. Norepinephrine (First-Line):
   • Receptor Profile: Potent alpha-1 agonist with moderate beta-1 adrenergic activity.
   • Clinical Rationale: Effectively restores systemic vascular resistance while beta-1 activity supports heart rate and cardiac output against unopposed vagal tone. Drug of choice for cervical and high-thoracic neurogenic shock.
2. Epinephrine (Alternative First-Line):
   • Receptor Profile: Potent non-selective alpha and beta agonist.
   • Clinical Rationale: Excellent alternative, particularly when severe, symptomatic bradycardia predominates and does not respond adequately to norepinephrine.
3. Phenylephrine Warning:
   • Receptor Profile: Pure, selective alpha-1 adrenergic agonist without beta activity.
   • Critical Hazard: Increases systemic vascular resistance, but the resulting afterload spike stimulates carotid baroreceptors, triggering reflex bradycardia. In a patient who has already lost cardiac sympathetic tone, phenylephrine can precipitate catastrophic bradyasystole and cardiovascular collapse. Avoid in cervical and high-thoracic SCI (may be considered only for low-thoracic or lumbar injuries where cardiac sympathetic innervation [T1-T4] is intact).
4. Dopamine Limitations:
   • While historically used, dopamine is associated with significantly higher rates of tachyarrhythmias, excessive tachycardia, and failure to consistently achieve MAP targets compared to norepinephrine.

---

Neurotrauma Resuscitation Reference Matrix