Anesthesia for Spine Surgery

Preoperative Evaluation - Spine Ready Risks

• Airway: Critical, esp. cervical spine.
  • Assess Mallampati, thyromental distance, neck ROM.
  • Anticipate difficult airway if C-spine instability (e.g., RA, ankylosing spondylitis).
• Respiratory:
  • Optimize: smoking cessation (>4-8 wks), treat infections.
  • PFTs for severe disease.
• Cardiovascular:
  • ASA status, functional capacity (METS >4).
  • Manage HTN, IHD.
• Neurological:
  • Document baseline deficits (motor, sensory).
  • Consider neuromonitoring (SSEP, MEP).
• Hematological:
  • CBC, Coags. Type & Screen/Crossmatch (major surgery).
  • Stop anticoagulants/antiplatelets as per guidelines.
• Positioning Risks: Prone (POVL, pressure sores, nerve injury), lateral.

⭐ Major risk in prone position: Postoperative Visual Loss (POVL), especially with prolonged surgery (>6 hrs), significant blood loss (>1L), or hypotension.

Intraoperative Positioning & Monitoring - Prone Vigilance

Prone Positioning: Risks & Mitigation

• Ocular Injury (POVL): ION/CRAO. Risks: Surgery >6h, blood loss >1L, MAP <65 mmHg, Hct <30%. Prevent: Head neutral, no eye pressure, maintain perfusion.
• Pressure Sores: Eyes, chin, chest, iliacs, knees. Pad well; check often.
• Airway: Secure ETT; re-verify post-turn.
• Ventilation: ↓FRC, ↓Compliance. Abdomen free (bolsters/Wilson frame) → ↓IVC compression, ↓bleeding.
• Nerve Injury: Brachial plexus (arm <90° abd.), ulnar. Pad pressure points.
• VAE: Monitor EtCO2 (sudden ↓), Doppler.

Key Monitoring:

• Std ASA + A-line (transducer @ tragus).
• Neuromonitoring: SSEP, MEP (TIVA for MEPs). Alert: MEP loss, SSEP ↓ >50% or latency ↑ >10%.
• Temp, UOP.

⭐ ION is main POVL cause in prone spine cases. Aim MAP >65 mmHg, Hct >30%.

Anesthetic Techniques & Hemostasis - Smooth Spine Sailing

• Goals: Hemodynamic stability, optimal neuromonitoring, smooth emergence, good analgesia.
• Techniques:
  • General Anesthesia (GA): Standard.
    • Induction: Propofol; Etomidate (if unstable).
    • Maintenance: Inhalational (Sevoflurane) vs. TIVA (Propofol + Remifentanil).
  • Regional: Epidural/paravertebral for adjunct analgesia.
• Hemostasis Strategies (📌 "TRACk Blood Loss"):
  • Tranexamic Acid (TXA): Load 10-15 mg/kg, then 1-2 mg/kg/hr.
  • Reduced MAP (Controlled Hypotension): Target 60-70 mmHg.
  • Autologous Blood (Cell Salvage): If EBL >1L.
  • Careful Fluid Management: Goal-directed.

⭐ TIVA (Propofol-Remifentanil) minimally affects Somatosensory Evoked Potentials (SSEP)/Motor Evoked Potentials (MEP), ideal for neuromonitored spine surgery.

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Perioperative Complications & Emergence - Spine Alert Wake-Up

• Key Complications:
  • Neurological Deficit: New/worsening, cord ischemia, epidural hematoma.
  • POVL (Postoperative Visual Loss): Ischemic Optic Neuropathy (ION) > Central Retinal Artery Occlusion (CRAO). Risks: prone position, long duration, ↓BP, significant blood loss/anemia. *
  • Venous Thromboembolism (VTE), airway edema (esp. anterior cervical), positioning injuries (nerve palsies, pressure sores).
• Spine Alert Wake-Up Test:
  • Purpose: Early detection of iatrogenic motor deficit.
  • Procedure: Post-instrumentation → Lighten anesthesia → Command patient to move feet/hands.
  • If Deficit: ⚠️ Alert surgeon STAT! Investigate (imaging, reposition), optimize Mean Arterial Pressure (MAP).
  • Smooth emergence critical to prevent graft/implant issues.

⭐ The intraoperative wake-up test (e.g., Stagnara test) is crucial for early detection of new neurological deficits after spinal correction/instrumentation, allowing for potential immediate corrective actions.

High‑Yield Points - ⚡ Biggest Takeaways

• Prone positioning risks: Postoperative Visual Loss (POVL) and pressure sores.
• Intraoperative Neuromonitoring (IONM) (SSEP, MEP) is vital; Total Intravenous Anesthesia (TIVA) is often preferred.
• Anticipate significant blood loss; ensure large-bore IV access and transfusion readiness.
• High risk of Venous Air Embolism (VAE), especially in prone/sitting positions; monitor ETCO2, Doppler.
• Employ controlled hypotension cautiously, ensuring adequate Spinal Cord Perfusion Pressure (SCPP).
• The wake-up test allows direct intraoperative assessment of motor function.