Chapter 14  ·  Module 5  ·  Visual Summary

Intravenous Anesthetic Agents and Total Intravenous Anesthesia

Mechanisms, key advantages, critical adverse effects, and total intravenous anesthesia indications

Comparative Intravenous Agent Profiles

All Major Agents

Mechanism, Key Advantage, and Critical Adverse Effect

Agent Mechanism Key Advantage Critical Adverse Effect / Limitation
Propofol Gamma-aminobutyric acid type A potentiation Antiemetic; smooth emergence; favorable for neuroanesthesia; total intravenous anesthesia maintenance Propofol infusion syndrome (high dose, prolonged); hypotension; apnea; contraindicated for pediatric intensive care unit sedation
Etomidate Gamma-aminobutyric acid type A potentiation Hemodynamic stability — preferred in cardiovascular compromise (cardiogenic shock, severe aortic stenosis, tamponade) Adrenocortical suppression (11-beta-hydroxylase inhibition) — 6 to 24 hours after single dose; avoid in septic shock; myoclonus
Ketamine N-methyl-D-aspartate receptor antagonism → dissociative anesthesia Increases blood pressure and heart rate (sympathomimetic) — hemodynamically unstable patients; bronchodilator; subanesthetic analgesia Increases intracranial pressure; emergence reactions (hallucinations, dysphoria) — prevent with midazolam premedication
Thiopental Gamma-aminobutyric acid type A potentiation (barbiturate) Cerebral metabolic suppression; burst suppression for neuroprotection; rapid induction Contraindicated in porphyria; slow elimination — unsuitable for maintenance; severe tissue necrosis with intraarterial injection
Midazolam Gamma-aminobutyric acid type A (benzodiazepine site) — increases channel opening frequency Anxiolysis, anterograde amnesia; prevents ketamine emergence reactions; co-induction (reduces propofol dose) Cannot produce surgical anesthesia alone; renal failure prolongs 1-hydroxymidazolam metabolite
Dexmedetomidine Alpha-2 adrenergic agonist (locus coeruleus, spinal cord, peripheral) Arousable sedation without respiratory depression; analgesia; reduces opioid requirements; awake intubation; intensive care unit delirium reduction Bradycardia and hypotension; biphasic blood pressure with loading; not for bolus administration
Flumazenil Competitive benzodiazepine receptor antagonist Reverses benzodiazepine sedation within 1 to 2 minutes Duration shorter than most benzodiazepines — resedation risk; can precipitate withdrawal seizures in physically dependent patients

Total Intravenous Anesthesia — When It Is Preferred

Absolute

Malignant Hyperthermia Susceptibility

  • All volatile halogenated agents are triggers — contraindicated
  • Total intravenous anesthesia obligatory: propofol + opioids + nondepolarizing agents
  • Nitrous oxide permitted

Strong

High Postoperative Nausea and Vomiting Risk (Apfel 3–4)

  • Propofol reduces postoperative nausea and vomiting ~25–30% vs volatile maintenance
  • Propofol antiemetic mechanism: serotonin type 3 antagonism + dopaminergic inhibition
  • Combined with multimodal antiemetic prophylaxis

Strong

Motor Evoked Potential Monitoring

  • Volatile agents suppress motor evoked potentials prohibitively at clinical doses
  • Propofol-remifentanil total intravenous anesthesia required for spine, cerebrovascular, and eloquent cortex surgery

Strong

One-Lung Ventilation (Thoracic Surgery)

  • Propofol does NOT inhibit hypoxic pulmonary vasoconstriction
  • Volatile agents inhibit hypoxic pulmonary vasoconstriction — worsen shunt and oxygenation during lung isolation

Remifentanil pharmacokinetics: ester hydrolysis by nonspecific plasma esterases → context-sensitive half-time of 3 to 5 minutes regardless of infusion duration (8 hours or 30 minutes — same offset). No residual postoperative analgesia — transition analgesia must be planned before emergence.