General anesthetics

Generic and Brand Names

Inhalational volatile agents

• Sevoflurane — Ultane, Sevorane

• Desflurane — Suprane

• Isoflurane — Forane

• Halothane — Fluothane legacy

• Enflurane — Ethrane legacy

Inhalational non-volatile gases

• Nitrous oxide — generic

• Xenon — regional research and limited clinical use

Intravenous induction and maintenance agents

• Propofol — Diprivan many generics

• Etomidate — Amidate

• Ketamine — Ketalar

• Thiopental sodium — Pentothal legacy

• Methohexital — Brevital legacy ECT use

• Midazolam — Versed adjunct anesthetic induction in select settings

• Remimazolam — Byfavo regional approvals mainly procedural sedation

Analgesic adjuncts during general anesthesia

• Fentanyl sufentanil remifentanil alfentanil generics

• Morphine hydromorphone generics

Class

• Agents that produce reversible loss of consciousness, amnesia, analgesia, and immobility for surgery and procedures.

• Two main modalities

  • Inhalational anesthesia volatile or gaseous

  • Total intravenous anesthesia TIVA using IV hypnotic plus opioid and neuromuscular blocker as needed

Mechanism of Action

• Volatile agents sevoflurane desflurane isoflurane primarily potentiate inhibitory GABA A currents and two-pore domain potassium channels; reduce excitatory transmission NMDA and nicotinic to varying degrees.

• Nitrous oxide xenon predominantly antagonize NMDA receptors; minimal GABA A potentiation.

• Propofol and etomidate are GABA A positive allosteric modulators producing hypnosis.

• Ketamine is a non-competitive NMDA receptor antagonist producing dissociative anesthesia with analgesia.

• Barbiturates thiopental methohexital enhance GABA A and inhibit AMPA kainate.

• Benzodiazepines midazolam remimazolam increase frequency of GABA A channel opening; strong amnesia, modest hypnosis.

Indications

• Induction and maintenance of general anesthesia for surgical and diagnostic procedures.

• Rapid-sequence induction for aspiration-risk cases selected IV agents.

• ICU sedation and status epilepticus refractory propofol barbiturates as specialist use.

• Electroconvulsive therapy methohexital or propofol.

• Procedural sedation and analgesia ketamine propofol midazolam per local policy.

• Pediatric mask induction sevoflurane.

Dosage and Administration

Inhalational maintenance typical end-tidal targets depend on age and surgery

• Sevoflurane 1 to 3 percent end-tidal adjust to MAC fraction.

• Desflurane 3 to 8 percent end-tidal.

• Isoflurane 0.5 to 1.5 percent end-tidal.

• Nitrous oxide 30 to 70 percent mixed with oxygen and or volatile.

• Fresh-gas flow and vaporizer settings tailored to physiology and equipment.

Intravenous induction common adult doses

• Propofol 1.5 to 2.5 mg per kg IV reduce in elderly hypovolemia; maintenance TIVA 50 to 200 micrograms per kg per min.

• Etomidate 0.2 to 0.3 mg per kg IV single induction dose.

• Ketamine 1 to 2 mg per kg IV or 4 to 6 mg per kg IM; analgesic infusion 0.1 to 0.3 mg per kg per h.

• Thiopental 3 to 5 mg per kg IV; methohexital 1 to 1.5 mg per kg IV.

• Midazolam 0.02 to 0.1 mg per kg IV adjunct; remimazolam dosing per regional label.

Opioid adjuncts typical

• Fentanyl 1 to 5 micrograms per kg IV; remifentanil 0.05 to 2 micrograms per kg per min infusion; sufentanil 0.1 to 1 microgram per kg IV.

Monitoring

• Adhere to standards of care ECG noninvasive blood pressure pulse oximetry capnography temperature.

• Ventilation oxygenation and anesthetic depth end-tidal agent concentration processed EEG where used.

• Neuromuscular monitoring with paralytics.

• Invasive arterial central venous or cardiac output monitoring in selected high-risk cases.

Contraindications

• Known malignant hyperthermia susceptibility avoid all volatile anesthetics and succinylcholine; use TIVA.

• Propofol hypersensitivity to components per label clinical allergy to egg lecithin or soy is not an absolute contraindication but evaluate history.

• Etomidate relative caution in septic shock or adrenal suppression concerns.

• Barbiturates absolute contraindication acute intermittent porphyria.

• Nitrous oxide avoid in conditions with trapped gas pneumothorax intracranial air intraocular gas bowel obstruction inner ear surgery and in B12 deficiency.

• Ketamine caution in uncontrolled hypertension ischemic heart disease elevated intracranial pressure risk scenarios when ventilation not controlled.

Precautions

• Airway management plan including backup devices and difficult-airway algorithms.

• Malignant hyperthermia preparedness dantrolene supply rapid recognition protocol.

• Hemodynamic effects volatile agents and propofol can cause hypotension; titrate carefully in hypovolemia elderly cardiac disease.

• Postoperative nausea and vomiting risk assessment and prophylaxis volatile agents and nitrous oxide increase PONV; propofol reduces PONV.

• Sevoflurane low fresh-gas flows use approved flow limits to mitigate Compound A formation machine and absorbent dependent.

• Desflurane airway irritation tachycardia at high concentrations; avoid for inhalational induction and in reactive airways.

• Ketamine emergence reactions hallucinations minimize with benzodiazepine co-administration; increases secretions consider anticholinergic.

• Etomidate myoclonus give small opioid or benzodiazepine pretreatment.

Adverse Effects

• Hypotension bradycardia or tachycardia dose and agent dependent.

• Respiratory depression apnea with IV induction agents.

• Airway irritation cough laryngospasm desflurane isoflurane; smooth with sevoflurane.

• Injection pain propofol treat with lidocaine and large-bore antecubital vein.

• PONV higher with volatiles and nitrous oxide; lower with propofol TIVA.

• Etomidate adrenal suppression transient inhibition of 11 beta hydroxylase; myoclonus.

• Ketamine psychomimetic emergence sympathetic stimulation hypersalivation rare laryngospasm.

• Nitrous oxide megaloblastic anemia neuropathy with chronic exposure; diffusion hypoxia if stopped abruptly without oxygen washout.

• Volatile agents rare hepatic dysfunction older halothane hepatitis phenomenon not seen with modern agents.

Drug Interactions

• Additive CNS and respiratory depression with opioids benzodiazepines alcohol sedatives.

• Volatile agents and non-depolarizing neuromuscular blockers synergistic neuromuscular blockade reduce NMB dose.

• Enzyme inducers barbiturates chronic phenytoin carbamazepine may increase anesthetic dose requirements.

• MAOIs tricyclics SSRIs can alter hemodynamic response to indirect sympathomimetics; manage vasopressor choice accordingly.

• Nitrous oxide inactivates vitamin B12 dependent methionine synthase prolonged exposure risk in deficiency.

Overdose

• Airway control 100 percent oxygen mechanical ventilation.

• Hemodynamic support fluids vasopressors inotropes.

• Discontinue anesthetic agent and treat specific toxicities malignant hyperthermia protocol dantrolene active cooling.

Patient Counselling

• Preoperative fasting instructions per institutional guideline.

• Medication optimization continue or hold per anesthesia clinic guidance especially anticoagulants antihypertensives diabetes medications.

• Postanesthesia driving and decision-making restrictions for at least twenty four hours after general anesthesia; arrange escort home.

• Expect sore throat hoarseness nausea or fatigue; report severe pain chest symptoms neurologic change or persistent vomiting.

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Comparison Table 1 — Inhalational General Anesthetics

Attribute	Sevoflurane	Desflurane	Isoflurane	Nitrous oxide
MAC adults percent	≈2.0	≈6.0	≈1.15	≈105
Blood gas partition lower faster	≈0.65	≈0.42	≈1.4	≈0.47
Onset offset	Rapid	Very rapid	Moderate	Rapid but weak anesthetic alone
Airway irritation	Minimal smooth mask induction	Prominent pungent avoid inhalational induction	Pungent cough	Minimal
Hemodynamics	Mild to moderate vasodilation hypotension	Sympathetic activation tachycardia at high doses	Vasodilation hypotension	Mild myocardial depressant; increases PVR slightly
Bronchodilation	Yes useful in asthma	Limited	Yes	Neutral
Metabolism percent	~3 to 5	~0.02	~0.2	~0.004
Special cautions	Compound A at very low flows heed machine and absorbent recommendations	Tachycardia airway reactivity; avoid in severe asthma	Coronary steal theoretical rarely clinically relevant	Expands closed gas spaces B12 enzyme inhibition; high PONV

Comparison Table 2 — Intravenous Induction Agents

Attribute	Propofol	Etomidate	Ketamine	Thiopental Methohexital
Onset seconds	30 to 45	30 to 60	30 to 60 IV	20 to 30
Duration minutes single dose	5 to 10	5 to 10	10 to 20	5 to 10
Hemodynamic profile	Marked hypotension vasodilation myocardial depression	Cardiovascular stability minimal BP change	↑ HR BP CO sympathetic stimulation	Hypotension less than propofol but possible
Respiratory effects	Apnea common	Apnea possible less than propofol	Preserves airway reflexes relative bronchodilation	Apnea common
CNS ICP CBF	↓ ICP and CBF neuroprotective properties	Neutral to ↓ ICP minimal effect	Traditionally ↑ ICP; with controlled ventilation generally acceptable	↓ ICP and CBF
Analgesia	None intrinsic antiemetic	None	Yes strong	None
Notable adverse	Injection pain hypotension bradycardia PRIS with prolonged high-dose ICU infusion	Transient adrenal suppression myoclonus PONV	Emergence reactions hypersalivation laryngospasm rare	Porphyria trigger hangover effect
Preferred scenarios	PONV risk neuro cases outpatient smooth wakeups	Hemodynamic instability induction	Asthma hypotension analgesia burn dressing pediatric mask adjunct	ECT methohexital status epilepticus thiopental

Comparison Table 3 — Choosing an Agent by Clinical Context

Clinical scenario	Preferred options	Avoid or use with caution
Hemodynamic instability hypovolemia	Etomidate ketamine low-dose opioid sequence	Propofol large bolus volatile overpressurization
Reactive airways asthma	Sevoflurane ketamine propofol	Desflurane airway irritant
High PONV risk	Propofol TIVA minimize N2O volatile dose	Nitrous oxide high volatile concentrations
Intracranial pathology elevated ICP	Propofol thiopental controlled ventilation	Ketamine if ventilation not controlled hypercarbia volatile hyperventilation mismanagement
Pediatric inhalational induction	Sevoflurane	Desflurane isoflurane pungency
Malignant hyperthermia susceptible	Propofol ketamine etomidate opioid TIVA	All potent volatile agents and succinylcholine

Comparison Table 4 — Environmental and Operational Considerations

Attribute	Sevoflurane	Desflurane	Isoflurane	Nitrous oxide	TIVA propofol
Equipment needs	Standard vaporizers circle systems	Heated vaporizer special	Standard vaporizer	Pipeline or cylinder scavenging	Infusion pumps lines
Recovery profile	Fast smooth	Fast but airway irritant	Moderate	Rapid adjunct only	Fast smooth low PONV
Greenhouse impact relative	Lower than desflurane	High	Moderate	Moderate	Minimal waste gas