What is a suitable anesthetic approach for spine surgery with intraoperative neuromonitoring (IONM) using Target-Controlled Infusion (TCI) for Total Intravenous Anesthesia (TIVA) with propofol and fentanyl, without neuromuscular blockade?

TIVA with TCI for Spine Surgery with IONM: Anesthetic Protocol

For spine surgery with intraoperative neuromonitoring (IONM), use propofol TCI at effect-site concentration 0.5-1 mcg/mL combined with remifentanil infusion 0.05-0.3 mcg/kg/min (or fentanyl boluses 0.5-1 mcg/kg as needed), avoiding neuromuscular blockade after intubation to preserve motor evoked potential monitoring. 1, 2

Induction Protocol

Intubation and Initial Muscle Relaxation:

• Administer rocuronium 0.9-1.2 mg/kg for rapid sequence intubation (or succinylcholine 1-2 mg/kg as alternative) 1, 2
• Critical: Do not administer additional neuromuscular blocking agents after intubation - this is essential for motor evoked potential (MEP) monitoring during spine surgery 3
• Establish invasive arterial blood pressure monitoring before induction when feasible, with vasopressors immediately available (ephedrine or metaraminol) 1, 4

Propofol Induction:

• Use slow induction with propofol 20 mg every 10 seconds until loss of consciousness (total 0.5-1.5 mg/kg) 5
• Avoid rapid bolus dosing - this causes significant hypotension, especially in elderly or hemodynamically compromised patients 5
• In elderly patients, reduce induction dose due to higher peak plasma concentrations and increased sensitivity to cardiovascular effects 5, 2

Maintenance Protocol

Propofol TCI Settings:

• Target effect-site concentration of 0.5-1 mcg/mL for propofol TCI maintenance 1, 2
• Avoid bolus dosing during maintenance to prevent hemodynamic instability 2
• Do not exceed 1.5 mcg/mL - doses above this carry significant risk of over-sedation and hypoventilation, especially with concomitant opioid use 2

Opioid Management:

• Primary option: Remifentanil infusion at 0.05-0.3 mcg/kg/min, avoiding bolus dosing to prevent respiratory depression 1, 4, 2
• Alternative: Fentanyl boluses 0.5-1 mcg/kg as needed for surgical stimulation 1, 2
• The combination of propofol TCI with remifentanil reduces propofol requirements by approximately 30% 1

Why No Neuromuscular Blockade After Intubation:

• Motor evoked potentials (MEPs) require intact neuromuscular transmission for accurate monitoring 3
• Neuromuscular blockade abolishes MEP responses, making it impossible to detect spinal cord injury intraoperatively 6, 7
• Both somatosensory evoked potentials (SSEPs) and EMG are recommended when the surgeon desires immediate feedback regarding potential neurological injury 3

Essential Monitoring Requirements

Processed EEG Monitoring:

• Maintain BIS between 40-60 throughout the procedure to prevent awareness while avoiding excessive depth that could impair neuromonitoring 3, 1, 4
• When TIVA is administered without neuromuscular blockade, processed EEG monitoring should still be used to confirm adequate anesthetic depth 3
• Avoid BIS values below 35 in elderly patients (>60 years) to reduce postoperative delirium risk 2

Neuromuscular Monitoring:

• If any muscle relaxant was used for intubation, use quantitative neuromuscular monitoring to document complete recovery 3, 4
• Document train-of-four ratio ≥0.90 before extubation to ensure complete reversal 1, 4, 2

Standard Monitoring:

• Continuous pulse oximetry and waveform capnography 3, 4
• ECG and non-invasive blood pressure measured at least every 5 minutes 3, 4
• Core temperature monitoring 3, 4
• Invasive arterial blood pressure with transducer at tragus level when feasible 4

IONM-Specific Anesthetic Considerations

Drugs That Preserve IONM Signals:

• Propofol and remifentanil TIVA provides stable IONM comparable to other techniques 8, 9
• Recent evidence shows remimazolam with remifentanil also yields stable IONM comparable to propofol 8
• Avoid inhalational agents if possible - while 3% desflurane (0.5 MAC) may be used in some adult patients, TIVA is preferred for optimal IONM 9

Drugs That Impair IONM:

• Avoid boluses of sufentanil - these cause significant amplitude decreases (30% reduction) in MEP responses 7
• Avoid nitrous oxide as it may interfere with neuromonitoring 4
• Propofol, remifentanil, and sufentanil continuous infusions cause minimal amplitude changes (13-26%) compared to bolus dosing 7

Facilitating Techniques:

• Ketamine boluses dramatically increase MEP amplitude (730% increase) and may be considered if MEP signals are inadequate 7
• Consider increasing stimulus intensity if MEP responses are suboptimal 7

Adjunctive Medications

Anti-inflammatory:

• Administer dexamethasone 0.15-0.25 mg/kg (maximum 0.5 mg/kg) at induction to reduce postoperative swelling and inflammation 1

Hemodynamic Support:

• Have vasopressors immediately available (ephedrine or metaraminol) 1, 4
• Propofol increases vasopressor requirements in hemodynamically challenged patients 2
• The combination of propofol with opioids can cause significant hypotension 1

Emergence and Extubation

Reversal and Recovery:

• Ensure complete return of airway reflexes and adequate tidal volumes before extubation, with the patient fully awake 1, 4, 2
• Propofol has rapid clearance with predictable emergence and fast return of airway reflexes 4, 2
• Extubate in sitting position when feasible 4, 2

Postoperative Analgesia:

• For breakthrough pain in PACU, titrate fentanyl 0.5-1.0 mcg/kg to effect 1
• Alternatives include morphine 25-100 mcg/kg or ketamine 0.25-0.5 mg/kg 1
• Transition to multimodal oral analgesia as soon as possible with scheduled acetaminophen 10-15 mg/kg every 6 hours and scheduled NSAIDs if not contraindicated 1

Critical Pitfalls to Avoid

Anesthetic Management:

• Never administer neuromuscular blockade after intubation - this abolishes MEP monitoring 3, 6
• Never use rapid bolus induction with propofol - use slow titration (20 mg every 10 seconds) 5
• Avoid propofol boluses during maintenance - use continuous TCI infusion only 2
• Do not use sufentanil boluses - these significantly impair MEP amplitude 7

Monitoring:

• Do not rely solely on BIS index values - develop understanding of EEG waveforms and power spectral analysis 3
• Never extubate without confirming adequate neuromuscular recovery if muscle relaxants were used 1, 4, 2

Patient-Specific:

• In elderly patients, reduce propofol doses and avoid excessive depth (BIS <35) to reduce postoperative delirium risk 2, 5
• Do not use propofol in patients with egg, soy, or sulfite allergies (propofol contains 10% soybean oil and 1.2% purified egg phosphatide) 4

Rationale for This Approach

The combination of propofol TCI with opioid infusion (remifentanil preferred) or intermittent fentanyl boluses provides optimal conditions for IONM while maintaining adequate anesthesia 1, 8, 9. This technique allows reliable monitoring of both somatosensory and motor evoked potentials, which is essential for detecting potential neurological injury during spine surgery 3. The avoidance of neuromuscular blockade after intubation is non-negotiable for MEP monitoring, as these agents abolish the motor responses needed to detect spinal cord compromise 6, 7.