Anesthesia for Traumatic Brain Injury

TBI Pathophysiology - Brain Under Siege

• Primary Injury:
  • Irreversible mechanical damage occurring at impact (e.g., contusion, laceration, Diffuse Axonal Injury (DAI)).
• Secondary Injury:
  • Develops minutes to days post-injury; a key therapeutic target, as it is potentially preventable or reversible.
  • Exacerbated by:
    • Systemic insults: Hypotension (SBP < 90 mmHg), Hypoxia (PaO2 < 60 mmHg).
    • Intracranial events: Increased Intracranial Pressure (ICP), cerebral edema (vasogenic & cytotoxic), cerebral ischemia.
  • Cellular damage cascade: Excitotoxicity (e.g., glutamate), inflammation, free radical production, apoptosis.
  • 
• Monro-Kellie Doctrine:
  • The skull is a rigid box; the sum of intracranial volumes (brain parenchyma, blood, Cerebrospinal Fluid (CSF)) is constant.
  • An increase in one component must be compensated by a decrease in another, otherwise ICP rises.
• Cerebral Perfusion:
  • Cerebral autoregulation is often impaired in TBI.
  • Cerebral Perfusion Pressure ($CPP = MAP - ICP$); target range is typically 50-70 mmHg.

⭐ Cushing's Triad: Represents a late and ominous sign of critically increased ICP and impending brainstem herniation. It consists of:

• Hypertension (often with a widened pulse pressure)
• Bradycardia
• Irregular respirations (e.g., Cheyne-Stokes breathing)

Preoperative Management - TBI Triage Time

• Airway: Secure early (RSI if GCS ≤8). Avoid hypoxia (SpO₂ >94%) & maintain normocapnia (PaCO₂ 35-45 mmHg).
• Breathing: Optimize oxygenation; mechanical ventilation often needed.
• Circulation:
  • Maintain SBP >100 mmHg (adults), age-adjusted for pediatrics.
  • Aggressive fluid resuscitation (isotonic crystalloids: NS, RL).
  • Target CPP >60-70 mmHg; $CPP = MAP - ICP$.
• Disability: Neurological assessment (GCS, pupils).
  • 
• Exposure/Environment: Prevent hypothermia (target >36°C). Control glucose.

⭐ High-Yield: Indications for ICP monitoring in severe TBI (GCS 3-8 with abnormal CT) OR (GCS 3-8 with normal CT but 2+ of: age >40 yrs, SBP <90 mmHg, or motor posturing).

📌 Mnemonic (ABCDE): Airway, Breathing, Circulation, Disability, Exposure/Environment control for secondary injury prevention during the "Golden Hour".

Intraoperative Anesthesia - Neuro-Protective Shield

• Primary Goals: Maintain CPP (50-70 mmHg), control ICP (<22 mmHg), ensure cerebral oxygenation.
• Induction Agents:
  • Propofol (↓ICP; caution: hypotension).
  • Etomidate (hemodynamic stability).
  • Lidocaine (1.5 mg/kg) IV to blunt intubation response.
• Maintenance Strategy:
  • TIVA (Propofol + Remifentanil): Preferred for ↓CMRO2, ↓CBF, ↓ICP.
  • Volatiles (Isoflurane, Sevoflurane <1 MAC): Use cautiously; dose-dependent ↑CBF/ICP.
• Muscle Relaxants: Non-depolarizing (e.g., Rocuronium). Avoid suxamethonium if ↑ICP suspected.
• Ventilation: Target normocapnia (PaCO2 35-40 mmHg).

  ⭐ The cautious and transient use of hyperventilation to PaCO2 30-35 mmHg for acute ICP rise.

• Fluid Management: Isotonic crystalloids (e.g., Normal Saline). Avoid hypotonic solutions.
• Key Adjuncts:
  • Maintain normothermia (36-37.5°C).
  • Strict glucose control (target 140-180 mg/dL).

Postoperative Care - Recovery & Risks

• ICU Management: Neuro-ICU ideal.
  • Maintain CPP > 60-70 mmHg, ICP < 20-22 mmHg.
  • Normoxia (PaO2 > 100 mmHg), normocapnia (PaCO2 35-40 mmHg).
  • Normothermia, euglycemia.
• Neuromonitoring: Continuous ICP, CPP; serial GCS, pupils.
• Sedation & Analgesia: Titrate carefully (e.g., propofol, opioids).
• Ventilation & Extubation:
  • Lung-protective ventilation.
  • Cautious extubation: assess neuro status, airway reflexes; risk of ICP ↑.
• Key Risks & Management:
  • Cerebral Edema: Mannitol (0.25-1 g/kg), hypertonic saline.
  • Seizures: Prophylaxis (e.g., Phenytoin, Levetiracetam).
  • Infections (VAP, meningitis), DVT prophylaxis.
  • Electrolyte disturbances (SIADH, CSW).

⭐ Prophylactic anticonvulsants (e.g., Phenytoin for 7 days) reduce early post-traumatic seizures (PTS) in high-risk TBI.

High‑Yield Points - ⚡ Biggest Takeaways

• Maintain CPP > 60-70 mmHg and ICP < 20-22 mmHg.
• Avoid hypotension (SBP < 90 mmHg) and hypoxia (PaO2 < 60 mmHg).
• Mild hyperventilation (PaCO2 30-35 mmHg) is temporary for ↑ ICP; avoid prolonged use.
• Mannitol (0.25-1 g/kg) or hypertonic saline (e.g., 3%) reduce ICP.
• Propofol/barbiturates ↓ CMRO2, ICP; risk hypotension, monitor hemodynamics.
• Optimize head position (midline, elevated 30°), avoid neck compression.
• Ketamine: cautiously used if CPP maintained; can ↑ ICP in some patients.