Drugs: Desflurane, Halothane, Enflurane, Isoflurane, Sevoflurane, Methoxyflurane, Nitrous Oxide (N₂O).
| Drug / Class | Mechanism of Action (MOA) | High-Yield Pharmacokinetics | Adverse Effects (AE) & Clinical Notes |
|---|---|---|---|
| Halogenated Anesthetics (Halothane, -fluranes) |
Uncertain. Potentiate GABA_A receptors; increase K+ efflux; inhibit NMDA receptors. | Solubility Principles: 1. Blood/Gas Partition Coefficient: Determines speed of induction/recovery. *(Low solubility = Fast induction).* 2. Oil/Gas Partition Coefficient: Determines potency. *(High lipid solubility = High potency = Low MAC).* MAC (Minimum Alveolar Concentration): % of anesthetic needed to prevent movement in 50% of patients. Potency ∝ 1/MAC. |
Malignant Hyperthermia (MH): Life-threatening muscle rigidity/fever. Mutations in Ryanodine receptor (RyR1). Tx: Dantrolene. Specific Toxicities: • Halothane: Hepatotoxicity (massive hepatic necrosis). • Methoxyflurane: Nephrotoxicity. • Enflurane: Seizures (epileptogenic). General: Myocardial depression, respiratory depression, increased cerebral blood flow (increased ICP). |
| Nitrous Oxide (N₂O) | Primarily NMDA antagonism. | Very Low Blood Solubility: Extremely fast induction and recovery. Low Potency: High MAC (often used as adjunct). |
Diffusional Hypoxia: N₂O floods alveoli upon discontinuation, displacing O₂. Expansion of Trapped Gas: Do NOT use in pneumothorax or bowel obstruction (N₂O diffuses into air pockets faster than N₂ leaves, expanding them). |
| Drug | Mechanism of Action | Clinical Use & "The Nuance" | Adverse Effects (AE) |
|---|---|---|---|
| Thiopental (Barbiturate) |
Facilitates GABA_A (increases duration of Cl- channel opening). | Induction. Effect Termination: Rapid onset due to high lipid solubility; effect ends due to redistribution into tissue/fat (not metabolism). |
Severe respiratory/CV depression. Decreases cerebral blood flow (good for brain surgery). |
| Midazolam (Benzodiazepine) |
Facilitates GABA_A (increases frequency of Cl- channel opening). | Procedural sedation (endoscopy), anesthesia adjunct. Causes anterograde amnesia. |
Respiratory depression. Antidote: Flumazenil. |
| Propofol | Potentiates GABA_A. | Induction & Maintenance. "Milk of Amnesia" (looks milky). Rapid recovery (less "hangover" than thiopental). |
Propofol Infusion Syndrome. Hypotension (vasodilation). Pain on injection. |
| Ketamine | NMDA receptor antagonist. | Dissociative Anesthesia. Patient looks awake but is catatonic/analgesic. Sympathomimetic: Increases HR and Cardiac Output. |
Emergence Reaction: Disorientation, hallucinations, vivid dreams (reduce with benzos). Increases cerebral blood flow (Caution in head trauma). |
| Etomidate | Modulates GABA_A. | Hemodynamically Stable. Use in patients with compromised heart function/hypotension. |
Adrenocortical suppression (inhibits 11β-hydroxylase). |
| Opioids (Fentanyl, Morphine) |
μ-opioid receptor agonist. | Used as adjuncts for analgesia during surgery. | Respiratory depression, chest wall rigidity (Fentanyl), constipation, nausea. |
Mechanism: Block voltage-gated Na+ channels (bind to intracellular portion). Preferentially bind to activated or inactivated channels (use-dependent).
| Class | Drugs | Identification Tip | Clinical Nuances |
|---|---|---|---|
| Esters | Procaine, Tetracaine, Benzocaine, Cocaine. | Have one "i" in name. | Metabolized by plasma cholinesterases (allergy via PABA). Cocaine: Intrinsic vasoconstriction. |
| Amides | Lidocaine, Mepivacaine, Bupivacaine, Ropivacaine. | Have two "i"s in name. | Metabolized by liver P450. Lower allergy risk. |