STEPTRACKERPHARMACOLOGY + ANESTHESIOLOGY | NEUROLOGY | HIGH-YIELD REVIEW

Anesthetics & Neuromuscular Blockers

General anesthetics switch off consciousness, local anesthetics block nerve conduction, and neuromuscular blockers paralyze — each with rules about potency, speed and reversal.

FOCUS ON
Inhaled anesthetics: potency ∝ lipid solubility (↓ MAC = more potent); speed ∝ low blood solubility (low blood/gas coefficient: N₂O, desflurane fast). Adverse: ↓ BP, respiratory depression, ↑ cerebral flow; malignant hyperthermia (RYR1; with succinylcholine) → dantrolene; halothane hepatitis; N₂O → B12 inactivation. IV: propofol (GABA-A; hypotension, propofol infusion syndrome), ketamine (NMDA; ↑ BP, dissociation, bronchodilation), etomidate (hemodynamically stable; adrenal suppression), midazolam, barbiturates, opioids. Local anesthetics block Na⁺ channels from inside (non-ionized form crosses); esters (procaine, tetracaine, benzocaine — PABA allergy) vs amides (lidocaine, bupivacaine, ropivacaine). Infection (acidic) ↓ effect; epinephrine prolongs. Toxicity: CNS → seizures, cardiovascular (bupivacaine) → lipid emulsion; benzocaine → methemoglobinemia. NM blockers: succinylcholine (depolarizing; hyperkalemia — avoid in burns, crush, denervation; MH; reversal none, phase II block) vs nondepolarizing (rocuronium, vecuronium, cisatracurium — Hofmann elimination) reversed by neostigmine + glycopyrrolate or sugammadex.
DRUG
MECHANISM · PROPERTY
USE
ADVERSE · NOTES
Sevoflurane · desflurane · isoflurane
Halogenated inhaled agents
Maintenance of anesthesia; sevoflurane inhaled induction (children)
Hypotension, MH, ↑ ICP; desflurane airway irritation
Nitrous oxide
Low blood solubility, high MAC (weak)
Adjunct, dental analgesia
Expands gas spaces (pneumothorax), B12 inactivation → myeloneuropathy
Halothane
Older halogenated agent
Rare now
Fulminant hepatitis, arrhythmias with catecholamines
Propofol
Potentiates GABA-A; rapid redistribution
Induction, ICU sedation; antiemetic
Hypotension, apnea, propofol infusion syndrome (acidosis, rhabdo), pain on injection
Ketamine
NMDA antagonist (PCP analog)
Induction in shock/asthma, analgesia; esketamine depression
Emergence hallucinations, ↑ BP, HR, salivation
Etomidate
GABA-A agonist
Induction when unstable
Adrenal suppression (11β-hydroxylase), myoclonus
Midazolam · dexmedetomidine
Benzodiazepine · central α2 agonist
Sedation, amnesia
Respiratory depression (midazolam) · bradycardia (dex)
Ester local anesthetics
procaine, chloroprocaine, tetracaine, benzocaine, cocaine
Na⁺ channel block; metabolized by plasma esterases
Spinal, topical
PABA allergy; benzocaine methemoglobinemia
Amide local anesthetics
lidocaine, bupivacaine, ropivacaine, mepivacaine
Na⁺ channel block; hepatic metabolism
Infiltration, nerve blocks, epidural
Bupivacaine cardiotoxicity; LAST → lipid emulsion
Nerve fiber sensitivity
Small myelinated > small unmyelinated > large myelinated
Order: pain → temperature → touch → pressure → motor
Return in reverse order
Succinylcholine
Depolarizing nicotinic agonist → fasciculation then paralysis (phase I)
Rapid sequence intubation
Hyperkalemia, MH, bradycardia (children), ↑ ICP/IOP; pseudocholinesterase deficiency → prolonged apnea
Rocuronium · vecuronium · cisatracurium
Competitive nicotinic antagonists (nondepolarizing)
Intubation, surgical relaxation
Cisatracurium: Hofmann elimination (organ-independent)
Sugammadex
Encapsulates rocuronium/vecuronium
Rapid reversal
Binds progestins → backup contraception
Dantrolene
Blocks ryanodine receptor Ca²⁺ release
Malignant hyperthermia, NMS
Hepatotoxicity (oral long-term)

Mechanism — malignant hyperthermia

Inhaled agent ± succinylcholine
→
Mutant RYR1 opensUncontrolled SR Ca²⁺ release
→
Rigidity, ↑ CO₂, fever, hyperkalemia, rhabdo
→
Dantrolene + cooling

Inhaled anesthetic rules

PROPERTY
MEANS
EXAMPLE
Low MAC
High potency
Halothane
High MAC
Low potency
N₂O
Low blood/gas
Fast on and off
Desflurane, N₂O
High blood/gas
Slow
Halothane

How it's tested

COMMON CONFUSIONNeostigmine reverses nondepolarizing blockers but deepens phase I succinylcholine block.
THE TRAPSuccinylcholine in a burn, crush, prolonged immobilization or denervation patient (after ~24–72 h) → massive K⁺ release → cardiac arrest.
YOUR APPROACHPotency (MAC) vs speed (solubility). Local anesthetic: ester or amide, pH, vessels. NM block: depolarizing or not, reversal.

If you see… think…

Fever, rigidity, rising end-tidal CO₂ under anesthesia → malignant hyperthermia → dantrolene
Cardiac arrest after bupivacaine → lipid emulsion
Cyanosis after topical throat spray → benzocaine methemoglobinemia
Arrhythmia after succinylcholine in burn patient → hyperkalemia
Prolonged apnea after succinylcholine → pseudocholinesterase deficiency
Induction agent in hypotensive trauma patient → ketamine or etomidate
Adrenal suppression after induction → etomidate
Rapid reversal of rocuronium → sugammadex
Local anesthetic fails in an abscess → acidic tissue keeps it ionized
Subacute combined degeneration after repeated N₂O → B12 inactivation