TIVA Drug Preparation (Propofol / Remifentanil, ≤0.5 MAC Sevo‑Des)
Remifentanil syringe
| Remifentanil | 2 mg |
| Diluent volume | 50 mL (NS) |
| Final concentration | 40 mcg/mL |
Maintenance targets
- Propofol infusion @ 50–200 mcg/kg/min
- Remifentanil infusion @ 0.02–0.5 mcg/kg/min
- Sevoflurane/Desflurane @ or below 0.5 MAC (if a volatile adjunct is used)
Source: institutional TIVA/Neuromonitoring reference sheet. Propofol concentration assumed 10 mg/mL (standard 1% formulation) in the calculator below — change it if your pharmacy supplies a different concentration.
Weight‑Based Infusion Rate Calculator
Propofol (mL/hr)
| 50 mcg/kg/min | 100 mcg/kg/min | 150 mcg/kg/min | 200 mcg/kg/min |
|---|---|---|---|
| 21.0 mL/hr | 42.0 mL/hr | 63.0 mL/hr | 84.0 mL/hr |
Remifentanil (mL/hr)
| 0.02 mcg/kg/min | 0.05 mcg/kg/min | 0.1 mcg/kg/min | 0.25 mcg/kg/min | 0.5 mcg/kg/min |
|---|---|---|---|---|
| 2.10 mL/hr | 5.25 mL/hr | 10.50 mL/hr | 26.25 mL/hr | 52.50 mL/hr |
Formula: mL/hr = (rate [mcg/kg/min] × weight [kg] × 60) ÷ concentration [mcg/mL]. Double‑check every pump rate independently before infusing — this calculator is a convenience aid only.
Effect of Anesthetic Agents on Monitoring Modalities
| Modality | Volatile agents >0.5 MAC | N₂O | Propofol (TIVA) | Remifentanil/opioids | Dexmedetomidine | Ketamine | Neuromuscular blockade |
|---|---|---|---|---|---|---|---|
| Transcranial MEP | Avoid dose‑dependent amplitude loss, latency ↑ | Caution synergistic suppression with volatiles | Preferred minimal suppression at steady rate | Minimal effect on amplitude | Caution low‑dose infusion OK; avoid loading bolus/high dose | Neutral–favorable subanesthetic doses may improve amplitude; ≥1 mg/kg suppresses | Blocks response confounds CMAP; avoid maintenance dosing |
| SSEP (cortical) | Suppressed amplitude ↓, latency ↑ | Additive suppression | Preferred | Minimal effect | Minimal at low dose | Minimal / may preserve | No significant effect (sensory cortical response) |
| SSEP (subcortical) | Less affected than cortical | Mild | Minimal | Minimal | Minimal | Minimal | No effect |
| Free‑run / triggered EMG | Usually tolerated (spontaneous EMG less sensitive) | Usually tolerated | Preferred | Minimal | Minimal | Minimal | Abolishes signal — must avoid maintenance NMB |
| BAEP / ABR | Relatively resistant | Minimal | Minimal | Minimal | Minimal | Minimal | No effect |
| EEG | Dose‑dependent burst suppression at high MAC | Mild | Dose‑dependent | Minimal | Sedative pattern changes | Can increase fast activity | No direct effect |
Agent‑by‑Agent Notes
Propofol + Remifentanil (TIVA)
Preferred baseline technique when MEPs and/or EMG are monitored. Steady‑state infusions (avoid boluses right before critical monitoring epochs) give the most stable, reproducible signals. Remifentanil provides analgesia/blunts sympathetic response with negligible effect on evoked potentials, allowing propofol to be titrated to the lowest effective dose.
Volatile agents (sevoflurane/desflurane) & N₂O
Suppress MEP and cortical SSEP amplitude and prolong latency in a dose‑dependent, reversible fashion; effect is most pronounced for MEPs. If a volatile is used as an adjunct, keep at or below ~0.5 MAC and avoid combining with N₂O, which is additive/synergistic with suppression. Desflurane is generally preferred over sevoflurane/isoflurane when a volatile is unavoidable due to faster titration.
Neuromuscular blocking agents
Any maintenance NMB abolishes free‑run/triggered EMG and confounds the muscle (CMAP) component of transcranial MEP. Typical approach: use a short‑acting agent only to facilitate intubation, then allow full spontaneous recovery (train‑of‑four 4/4, no fade) before baseline signals are acquired; avoid re‑dosing for the remainder of a case that relies on EMG/MEP. Confirm the plan with the surgeon and neurophysiologist, since some centers tolerate a partial, monitored block for specific modalities.
Dexmedetomidine
Useful adjunct for hemodynamic stability and opioid/propofol sparing. Low‑dose infusions without a loading bolus appear to have minimal impact on SSEP/MEP, but bolus dosing or higher infusion rates have been associated with reduced MEP amplitude — avoid bolus loading and titrate cautiously when signals are borderline.
Ketamine
Subanesthetic bolus/infusion doses can preserve or even increase MEP amplitude and are used as an opioid‑sparing adjunct; higher doses (roughly ≥1 mg/kg) have been associated with MEP suppression. Consider low‑dose ketamine as an adjunct rather than a primary agent when monitoring is critical.
Physiologic factors
Signal quality is also affected by non‑drug factors: hypotension/reduced spinal cord perfusion, hypothermia, hypocapnia, anemia, and hypoxia can all degrade SSEP/MEP independent of the anesthetic. Maintain normothermia, adequate MAP (per baseline/surgeon target), and stable ventilation.
Practical Checklist
- Default to TIVA (propofol/remifentanil) as the primary technique for cases monitoring MEP and/or EMG.
- If a volatile agent is used at all, keep it ≤0.5 MAC and avoid nitrous oxide.
- Use a short‑acting NMB only for intubation; confirm TOF 4/4 recovery before the neurophysiologist records baseline signals, and avoid maintenance dosing for EMG/MEP cases unless explicitly agreed with the surgical/neuromonitoring team.
- Keep infusion rates steady through critical monitoring epochs; avoid large propofol/remifentanil boluses immediately before a check.
- If adding dexmedetomidine or ketamine, avoid loading boluses and start at the low end of the dose range, especially early in the case before baselines are established.
- Maintain MAP within the patient's baseline range (or the specific target set by the surgical team), and maintain normothermia, normocapnia, and adequate oxygenation/hemoglobin.
- Communicate any planned anesthetic change (agent, bolus, major rate change) to the neurophysiologist before making it, and re‑check baseline signals after any change or repositioning.
- Record baseline SSEP/MEP/EMG signals after induction and before surgical positioning or incision, and again promptly after any position change.
Selected References
- Reysner M, et al. "The Influence of Anesthesia on Neuromonitoring During Scoliosis Surgery: A Systematic Review." NeuroSci. 2024;5(4):693–712.
- Kawaguchi M, et al. "A Practical Guide for Anesthetic Management during Intraoperative Motor Evoked Potential Monitoring" (JSA MEP Monitoring Guideline Working Group). J Anesth. 2020;34:5–28.
- Walker CT, et al. "Neuroanesthesia Guidelines for Optimizing Transcranial Motor Evoked Potential Neuromonitoring During Deformity and Complex Spinal Surgery: A Delphi Consensus Study." Spine. 2020;45:310–610.
- Rao S, Kurfess J, Treggiari MM. "Basics of Neuromonitoring and Anesthetic Considerations." Anesthesiol Clin. 2021;39:195–209.
- Ma K, Bebawy JF, Hemmer LB. "Multimodal Analgesia and Intraoperative Neuromonitoring." J Neurosurg Anesthesiol. 2023;35:172–176.
This page paraphrases general conclusions from the above peer‑reviewed sources; consult the original articles and your institutional guidelines for full detail and specific dosing decisions.