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Maintenance — TIVA, Balanced, MAC

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Intraop I · 9 min read

Three maintenance strategies for three patient profiles. Each has the cases where it's clearly correct.

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Choose volatile, TIVA, or balanced maintenance for a given case.
Calculate MAC adjusted for age and the additive effect of opioids/N₂O.
Recognize when context-sensitive half-time becomes clinically important.
Plan emergence + reversal accordingly.

Balanced volatile + opioid

KeyDefault maintenance for most cases.

Volatile (sevoflurane, desflurane, isoflurane) at MAC 0.7-1.0 + opioid (fentanyl or remifentanil infusion).

MAC-reducing benefit of opioid means lower volatile concentration, less hemodynamic depression.

NMB titrated to surgical need.

Cost-effective, reliable, forgiving.

Standard practice for routine inpatient + outpatient surgery.

Minimum alveolar concentration (MAC): defined as alveolar concentration preventing movement in 50% of patients to surgical stimulus. Standard MAC values: sevo 2.0, iso 1.2, des 6.0, N2O 104. Decreases with age, hypothermia, opioids, alpha-2 agonists.

TIVA — propofol + remi

KeyPropofol 75-150 mcg/kg/min + remifentanil 0.1-0.3 mcg/kg/min.

Indications

MH-susceptible (no volatile)
severe PONV history (propofol anti-emetic)
motor evoked potentials (volatile suppresses)
rapid emergence needed (cardiac surgery, neuro)
environmental concerns (high-volatile-cost institutions)

Cost higher than volatile + opioid.

BIS or processed EEG often added (no end-tidal to monitor depth).

Total intravenous anesthesia (TIVA) overview: indications (MH risk, neuromonitoring, severe PONV, airway laser), agents (propofol, remifentanil, dexmedetomidine, ketamine), TCI vs manual infusion, depth monitoring with BIS.

MAC sedation

KeyMonitored anesthesia care — anesthesia provider continuously present, titrated sedation, prepared to convert to GA.

Agents

propofol infusion
dexmedetomidine
low-dose remifentanil
ketofol mix

ASA 2011 standard: continuous ventilation monitoring (capnography or equivalent) REQUIRED — sedation-related apnea deaths drove this.

Indications

minor procedures tolerable with local + sedation
awake fiberoptic
cataract surgery

Low-flow vs high-flow tradeoffs

KeyLow-flow (≤1 L/min FGF): agent + cost savings, environmental responsibility, humidification preservation.

Requires real-time agent + FiO₂ monitoring.

Compound A concern for sevo at low flow (Amsorb absorbent removes concern).

High-flow during induction (denitrogenation) + emergence (wash-out); maintenance at low flow.

Standard modern practice.

Depth monitoring

KeyEnd-tidal volatile concentration ≥0.7 MAC = standard depth signal.

BIS adds value for TIVA (no end-tidal) + when MAC must be lower (severe cardiac).

BAG-RECALL trial: equivalent awareness rates between BIS-guided and end-tidal-guided when properly used.

Burst suppression on EEG in elderly correlates with postop delirium — avoid prolonged BIS <20.

Evoked potentials and raw EEG patterns: SSEP, MEP, BAEP can be affected by volatile anesthetics; minimize agent doses, use TIVA when monitoring evoked potentials.

SedLine (PSI) waveform shows multichannel frontal EEG with PSI 25-50 target for general anesthesia; provides raw EEG, density spectral array, and processed index for depth monitoring. — Evoked potentials and raw EEG patterns: SSEP, MEP, BAEP can be affected by volatile anesthetics; minimize agent doses, use TIVA when monitoring evoked potentials.

Emergence planning

KeyReverse NMB to TOF ≥0.9 (quantitative).

Turn off volatile/TIVA at appropriate timing — sevo wash-out 5-10 min, des 3-5 min, propofol context-sensitive half-time depends on infusion duration (after 4 hr propofol infusion, CSHT ~30 min vs ~10 min after 1 hr).

Awake extubation in most cases — sitting up, suction OG, intact gag, follows commands.

Deep extubation for selected cases (eye, neuro, hernia) where cough = harm.

Adequate analgesia before emergence — multimodal works best.

Context-sensitive half-time (CSHT): time for plasma concentration to fall by 50% after stopping a constant infusion; varies with infusion duration and drug (e.g., remifentanil ~3 min vs fentanyl/propofol rises with time).

TCI (target-controlled infusion) + context-sensitive half-time

KeyTarget-controlled infusion (TCI) — propofol pump algorithms (Schnider, Marsh, Eleveld models) target a desired plasma or effect-site concentration rather than mg/kg/hr rate.

Standard outside US (TCI pumps not FDA-approved for adult propofol in US).

Allows precise titration + faster wake-up.

CONTEXT-SENSITIVE HALF-TIME (CSHT) is the time for plasma concentration to fall by 50% after STOPPING infusion — depends on duration of infusion: short infusion = short CSHT (drug is mostly in central compartment), long infusion = longer CSHT (drug accumulated in peripheral compartments).

Remifentanil has nearly flat CSHT (~3 min regardless of duration) — uniquely useful.

Fentanyl + sufentanil + alfentanil all accumulate with long infusions.

Context-sensitive half-time of common infusion drugs: remifentanil constant ~4 min; propofol rises moderately; fentanyl and sufentanil increase markedly with longer infusion; alfentanil intermediate.

Maintenance choice by case

KeyMAJORITY ADULT INPATIENT/OUTPATIENT: balanced volatile + opioid is the default — cheap, reliable, forgiving.

CARDIAC SURGERYTIVA increasingly common (cardio-protection theories + cleaner emergence) — propofol + remi + low-dose ketamine.

NEUROSURGERY (craniotomy): TIVA preferred for tight brain + smooth emergence + MEP/SSEP-friendly; balanced acceptable if no neuromonitoring.

SPINE WITH MEPSTIVA mandatory (volatile suppresses MEPs).

MH-SUSCEPTIBLETIVA + trigger-free machine setup.

SEVERE PONV HISTORY (Apfel 4): TIVA propofol-based + multimodal anti-emetics.

AMBULATORY

shortest-acting agents (sevo or des; remi or fentanyl)

avoid long-acting opioids day of surgery

multimodal opioid-sparing

ELDERLYlower MAC + reduced opioid + avoid benzo + processed-EEG to avoid burst suppression.

Anesthetic management for craniotomy: smooth induction, avoid coughing/HTN, maintain CPP, mild hyperventilation (PaCO2 30-35) only briefly, mannitol/hypertonic saline for ICP, avoid N2O with pneumocephalus.

Adjunct infusions in modern multimodal

DEXMEDETOMIDINE 0.2-0.7 mcg/kg/hr — sympatholytic + sedative + opioid-sparing

slows HR + BP

useful in cardiac, ENT, awake fiberoptic, neuro for smooth emergence

KETAMINE 0.15-0.3 mg/kg/hr — NMDA antagonist + analgesic + anti-hyperalgesia; useful in opioid-tolerant + chronic pain + major spine.

LIDOCAINE 1.5-2 mg/kg/hr — analgesic + anti-inflammatory + GI motility; major abdominal surgery.

MAGNESIUM 1-2 g IV bolus + 10 mg/kg/hr — NMDA + opioid-sparing.

ESMOLOL infusion — opioid-sparing in some studies, blunts sympathetic surges.

METHADONE single dose 0.1-0.3 mg/kg at induction — long-acting analgesia for major surgery (NMDA + mu activity); QT caution.

Opioid-induced hyperalgesia (OIH): paradoxical sensitization with chronic or high-dose opioid exposure via NMDA activation and central sensitization. Management: opioid rotation, ketamine, dexmedetomidine, multimodal analgesia.

⚠ Common pitfalls

Running TIVA without BIS in a paralyzed patient — awareness risk is real.
Forgetting that MAC drops ~6%/decade after 40 — over-MAC in the elderly causes hypotension.
Using remi at a single rate for hours — context-sensitive half-time is short, but the opioid debt is real.
Crossing over volatile + propofol at high doses — synergistic hypotension can be steep.

💎 Clinical pearls

TIVA wins for MH risk, severe PONV, thoracic + neuro cases (MEPs), and short ambulatory cases.
Balanced (low MAC volatile + remi) gives fast emergence with PONV reduction.
Sevoflurane below 1 L FGF for >2 hr raises Compound A — use Amsorb absorber or higher FGF.
Wake-up testing for spinal MEP cases: TIVA-only is the rule; volatile suppresses MEPs >0.5 MAC.

Recap

TIVA wins for MH risk, severe PONV, thoracic + neuro cases (MEPs), and short ambulatory cases.
Balanced (low MAC volatile + remi) gives fast emergence with PONV reduction.
Sevoflurane below 1 L FGF for >2 hr raises Compound A — use Amsorb absorber or higher FGF.
Wake-up testing for spinal MEP cases: TIVA-only is the rule; volatile suppresses MEPs >0.5 MAC.

Mark each section done to complete the module.