Can a patient undergoing spine surgery with intraoperative neuromonitoring (IONM) and no neuromuscular blockade use target-controlled infusion (TCI) for total intravenous anesthesia (TIVA) with propofol and fentanyl, without a bispectral index (BIS) monitor?

TCI-Based TIVA for Spine Surgery with IONM: Feasible Without BIS

Yes, you can safely use TCI for TIVA with propofol and fentanyl during spine surgery with IONM without BIS monitoring, but you must implement specific safeguards to prevent awareness and maintain optimal neuromonitoring conditions. 1

Core TCI Regimen for IONM Cases

Target propofol effect-site concentration of 0.5-1 mcg/mL combined with fentanyl boluses of 3-5 mcg/kg at induction, followed by intermittent 0.5-1 mcg/kg boluses as needed for maintenance. 1, 2 This combination provides adequate depth while preserving motor evoked potentials.

• The propofol Cp50 for skin incision alone is 15.2 mcg/mL, but fentanyl 1 ng/mL reduces this by 63%, and 3 ng/mL reduces it by 89% 3
• For maintenance during spine surgery, propofol effect-site targets of 0.5-1 mcg/mL combined with adequate fentanyl provide sufficient depth without excessive suppression of neuromonitoring 1, 4
• Never exceed propofol effect-site concentration of 1.5 mcg/mL, as this significantly increases risk of over-sedation and could impair neuromonitoring 4

Critical Modifications Without BIS Monitoring

Since BIS is unavailable, you must rely on clinical signs and hemodynamic parameters more heavily:

• Monitor for clinical signs of inadequate depth continuously: lacrimation, sweating, pupil dilation, hypertension, tachycardia, or movement 2
• Establish invasive arterial blood pressure monitoring before induction to detect hemodynamic responses to surgical stimulation in real-time 1, 4
• Have vasopressors immediately available (ephedrine or metaraminol) as propofol causes dose-dependent cardiovascular depression 5, 6
• Consider starting at the higher end of the propofol target range (closer to 1 mcg/mL) initially, then titrate down based on clinical response 4

Neuromuscular Blockade Management

Administer rocuronium 0.9-1.2 mg/kg for intubation only, then avoid any additional neuromuscular blocking agents throughout the case. 1

• Use quantitative neuromuscular monitoring to document complete recovery before allowing MEP monitoring to begin 1, 4
• Never give additional muscle relaxant after intubation, as this abolishes motor evoked potential monitoring 1
• Document train-of-four ratio ≥0.90 before extubation 1, 4

Induction Protocol

Follow this sequence to minimize hemodynamic instability and ensure adequate depth:

1. Pre-oxygenate thoroughly and establish arterial line if time permits 1, 4
2. Administer high-dose fentanyl 3-5 mcg/kg (reduces propofol requirements by 50-55%) 1, 2
3. Start propofol TCI at effect-site target 3-4 mcg/mL for induction 4
4. Give rocuronium 0.9-1.2 mg/kg once loss of consciousness confirmed 1
5. Avoid propofol boluses during maintenance—use continuous TCI infusion only 4
6. After intubation, reduce propofol target to 0.5-1 mcg/mL for maintenance 1, 4

Maintenance Strategy Without BIS

Titrate propofol effect-site concentration between 0.5-1 mcg/mL based on hemodynamic responses and clinical signs, supplementing with fentanyl 0.5-1 mcg/kg boluses for inadequate analgesia. 1, 2

• Propofol concentrations in this range combined with adequate fentanyl suppress both somatic and hemodynamic responses to noxious stimuli 2, 3
• Watch for hypertension or tachycardia (>20% increase from baseline) as indicators of inadequate depth—respond with fentanyl bolus first, then consider increasing propofol target 2
• Fentanyl 1-3 ng/mL plasma concentration provides optimal synergy with propofol for surgical stimulation 2, 3
• The combination of propofol and fentanyl attenuates systolic blood pressure increases to noxious stimuli in a dose-dependent fashion 2

Awareness Prevention Without BIS

Multiple safeguards compensate for absent BIS monitoring:

• Maintain propofol effect-site concentration ≥0.5 mcg/mL at all times during surgery 1, 4
• Ensure adequate fentanyl dosing (plasma concentration 1-3 ng/mL) which markedly reduces propofol requirements and deepens anesthesia 2, 3
• Monitor end-tidal CO2 waveform for sudden increases suggesting inadequate depth 5
• Watch for autonomic signs: sudden hypertension, tachycardia, lacrimation, or sweating indicate inadequate depth 2
• Document all drug doses and infusion rates meticulously for medicolegal protection 4

Hemodynamic Management

Propofol causes predictable cardiovascular depression that requires proactive management:

• Propofol decreases cardiac output, systemic vascular resistance, and arterial pressure in a dose-dependent manner 6
• Have vasopressors drawn up and immediately available before induction 5, 1
• Target mean arterial pressure >65 mmHg to maintain spinal cord perfusion 5
• If hypotension occurs, treat with vasopressors first rather than increasing fluids, as brain-injured patients do not tolerate hypovolemia well 5

Emergence and Extubation

Ensure complete recovery before extubation:

• Stop propofol infusion at skin closure to allow rapid emergence 4
• Ensure return of airway reflexes and adequate tidal volumes before extubation 1, 4
• Verify train-of-four ratio ≥0.90 if any muscle relaxant was used 1, 4
• Extubate fully awake with patient able to follow commands 1
• Transition to multimodal oral analgesia immediately with scheduled acetaminophen and NSAIDs if not contraindicated 1

Critical Pitfalls to Avoid

• Never use propofol boluses during maintenance—this causes hemodynamic instability and unpredictable depth 4
• Never give neuromuscular blockade after intubation—this abolishes MEP monitoring 1
• Never allow propofol effect-site concentration to drop below 0.5 mcg/mL during surgery without BIS monitoring 1, 4
• Avoid excessive propofol depth (would be BIS <35 if monitored) as this increases postoperative delirium risk, especially in elderly patients 1
• Do not rely on hemodynamic stability alone as evidence of adequate depth—propofol suppresses hemodynamic responses even at inadequate anesthetic concentrations 2

Alternative Consideration

If you remain concerned about awareness risk without BIS, consider using remifentanil infusion 0.05-0.3 mcg/kg/min instead of intermittent fentanyl boluses, as this provides more stable plasma concentrations and better synergy with propofol TCI 1. However, fentanyl boluses are acceptable and widely used for IONM cases 1, 2.