Anesthesia 101 Study Notes

Neuromuscular Blockers (NMBs)

Depolarizing vs Non-depolarizing: what this means

• Depolarizing NMBs (phase I block):
  Agonists at the nicotinic ACh receptor (nAChR) that open the channel → transient depolarization (fasciculations) → flaccid paralysis while the endplate stays depolarized and inexcitable.

• Non-depolarizing NMBs:
  Competitive antagonists at nAChR that prevent ACh from opening the channel → no depolarization → paralysis.

Drugs you should know

• Depolarizing

  • Succinylcholine (SCh)

    • Ultra-fast onset (~30–60 s), short duration (5–10 min).

    • Metabolism: plasma pseudocholinesterase (butyrylcholinesterase).

• Non-depolarizing — Aminosteroids

  • Rocuronium (rapid onset at RSI[Rapid Sequence Intubation] doses), Vecuronium, Pancuronium (vagolytic, ↑HR).

• Non-depolarizing — Benzylisoquinoliniums

  • Cisatracurium (Hofmann elimination; good in renal/hepatic failure), Atracurium (histamine, laudanosine), Mivacurium (pseudocholinesterase metabolism; rare).

Succinylcholine: key contraindications & cautions

• Absolute/major:

  • Known/suspected malignant hyperthermia susceptibility.

  • Hyperkalemia or conditions with AChR up-regulation → dangerous K⁺ rise:

    • Burns, crush injuries, prolonged immobilization, denervation/spinal cord injury, stroke with residual paralysis, NM diseases (e.g., ALS, DMD), severe muscle trauma, critical illness myopathy. (Risk begins ~24–72 h after injury and can persist for months.)

  • Pseudocholinesterase deficiency (familial or acquired) → prolonged apnea.

  • Penetrating eye injury / glaucoma (transient ↑IOP).

  • History of severe SCh myalgia/rhabdomyolysis (esp. in myopathies).

• Relative:

  • Sepsis (late), significant metabolic acidosis, potassium-elevating meds.

• What to look for with SCh

  • Pre-existing K⁺ level, high-risk history above, MH cart & dantrolene available.

  • Post-dose: fasciculations, bradycardia (esp. kids/2nd dose—consider atropine), masseter spasm, myalgias, rare anaphylaxis.

  • If prolonged block → consider dibucaine number / pseudochE testing.

Non-depolarizers: pearls

• Rocuronium: RSI dose 1.0–1.2 mg/kg (rapid onset); maintenance 0.1–0.2 mg/kg.

• Vecuronium: hemodynamically neutral; hepatic/renal elimination.

• Cisatracurium: best in organ failure; minimal histamine.

• Interactions: Potentiated by aminoglycosides, magnesium, lithium, local anesthetics, volatile agents; resistance in chronic anticonvulsant use.

• What to look for

  • Train-of-four (TOF) monitoring; aim TOF ratio ≥0.9 for safe extubation.

  • Patient factors (obesity dosing by IBW/AdjBW; organ dysfunction).

  • Residual paralysis risk in PACU.

Reversal Agents

Sugammadex

• MOA: Modified γ-cyclodextrin that encapsulates aminosteroid NMBs (rocuronium > vecuronium ≫ pancuronium), pulling them off the nAChR and inactivating them in plasma.

• Dosing (by depth of block)

  • 2 mg/kg: reappearance of ≥2 TOF twitches.

  • 4 mg/kg: post-tetanic count (PTC) ≥1 but 0 TOF twitches.

  • 16 mg/kg: immediate reversal after RSI-dose rocuronium (can also rescue “can’t intubate/can’t ventilate”).

• Onset: typically ≤3 minutes (faster at higher doses).

• What to look for / safety

  • Bradycardia (rarely severe/asystole): be ready with atropine/epinephrine.

  • Hypersensitivity/anaphylaxis (can be severe).

  • Coagulation: transient ↑PT/INR/aPTT (usually clinically mild).

  • Hormonal contraceptives: binds progestins → advise backup contraception for 7 days.

  • Renal impairment: not recommended if CrCl <30 mL/min or dialysis (drug–complex is renally excreted).

  • Recurarization rare; ensure adequate dosing and observe.

Neostigmine

• MOA: Acetylcholinesterase inhibitor → ↑ACh at NMJ → competes with non-depolarizers. Must give with an antimuscarinic (e.g., glycopyrrolate or atropine) to blunt muscarinic effects.

• Use: Only when some spontaneous recovery is evident (≥2–4 TOF twitches). Ceiling effect—cannot reverse deep block.

• Dose: 0.02–0.07 mg/kg IV (common 0.04–0.05 mg/kg; max ~5 mg) + glycopyrrolate 0.2 mg per 1 mg neostigmine (or atropine 0.4–1 mg).

• Onset/peak/duration: ~5–10 min / ~10 min / 45–60+ min.

• What to look for / safety

  • Bradycardia, bronchospasm, ↑secretions, PONV, cramping/diarrhea, miosis—prevent with antimuscarinic.

  • Avoid if deep block, or with mechanical obstruction of GI/GU, uncontrolled asthma, severe bradyarrhythmias.

  • Monitor TOF to ≥0.9; risk of residual weakness if reversed prematurely.

Inhaled Anesthetics (“Gases”)

Core agents & quick numbers (adults)

• Sevoflurane — MAC ≈ 2.0%; blood/gas ≈ 0.65 (smooth mask, bronchodilation).

• Desflurane — MAC ≈ 6%; blood/gas ≈ 0.42 (very fast on/off; pungent, sympathetic activation).

• Isoflurane — MAC ≈ 1.15%; blood/gas ≈ 1.4 (slow, stable).

• Nitrous oxide (N₂O) — MAC ≈ >100%; blood/gas ≈ 0.47 (analgesic, fast).

System effects (high-yield)

• All volatiles ↓CMRO₂, ↑CBF (dose-dependent), potential ↑ICP; bronchodilation; dose-dependent ↓MAP (SVR drop), variable ↑HR (des > iso > sevo).

• Desflurane: airway irritation, tachycardia/HTN with rapid ↑ in concentration; CO formation with desiccated CO₂ absorbers.

• Sevoflurane: pleasant; Compound A at very low flows/dry absorbers (minimize with adequate flows, fresh absorbents).

• Isoflurane: coronary vasodilation (classic “steal” is mostly theoretical).

• N₂O: diffusion into air-filled spaces (expands them), mild myocardial depression, ↑PONV, inhibits methionine synthase (B₁₂ pathway) with prolonged/high exposure.

Contraindications / cautions

• All volatiles: malignant hyperthermia triggers (avoid in MH patients; ensure dantrolene).

• Raised ICP: use lower MAC, hyperventilate, consider TIVA if needed.

• Sevo: caution severe renal compromise (older concerns about fluoride/Compound A—use modern fresh gas flows and fresh absorbents).

• Des/Iso: avoid abrupt large increases in severe CAD or uncontrolled HTN.

• N₂O — Avoid in:

  • Bowel obstruction, pneumothorax, intracranial air, recent intraocular gas (SF₆/C₃F₈), ear surgery, air embolism risk, severe COPD with bullae.

  • Pregnancy (1st trimester) or B₁₂ deficiency/methylmalonic acidemia concerns; long cases needing strict FiO₂.

• What to look for

  • MH history; availability of non-trigger setup.

  • Procedures with potential air space expansion → no N₂O.

  • CO₂ absorber hydration status (avoid desiccation).

  • Hemodynamics with volatile changes; treat hypotension (vasopressors, fluids).

Cardiac Anesthesia — essentials

Pre/induction goals

• Maintain myocardial oxygen supply–demand balance: avoid tachycardia, hypotension, hypertension, hypoxia, anemia.

• Choose induction tailored to physiology:

  • Etomidate for poor EF/unstable (adrenal suppression with repeats).

  • Propofol great but ↓SVR/↓contractility—titrate.

  • Ketamine supports BP/HR (watch ischemia risk in CAD).

  • High-dose opioids (fentanyl/sufentanil) to blunt sympathetic surges.

  • Volatiles in low doses to avoid hypotension; many cases use balanced anesthesia or TIVA.

Monitoring & access

• A-line (beat-to-beat), large-bore IV, central line ± PA catheter (selected cases), TEE (valves, function, volume status), Foley, temperature, near-infrared cerebral oximetry in high-risk.

Anticoagulation & hemostasis

• Heparin before CPB; target ACT ≥ 400–480 s.

• Protamine reversal (give slowly; watch hypotension, anaphylactoid rxn, pulmonary HTN).

• Antifibrinolytics (tranexamic acid) to reduce bleeding (beware seizures at very high doses).

Bypass & myocardial protection

• Cardioplegia (blood or crystalloid; antegrade/retrograde).

• Manage temperature, hematocrit, pump flows, acid–base.

• Post-bypass: expect vasoplegia, myocardial stunning → need vasopressors (phenylephrine, norepi, vasopressin) and inotropes (epinephrine, dobutamine, milrinone).

Arrhythmias

• A-fib common post-op → rate control (β-blocker, amio), anticoagulation strategy per team.

• Ventricular arrhythmias → treat electrolytes, ischemia, amio/lidocaine, defib if unstable.

What to look for (checklist)

• Preop: EF, valve lesions (stenosis vs regurg), coronary anatomy, pulmonary HTN, conduction disease, antiplatelet/anticoag regimen.

• Induction: anticipate lability—vasopressor ready, gentle laryngoscopy.

• Bypass: ACT targets; line separation checks; air management on separation.

• Post-bypass: echo for function/valves; vasoplegia vs low-output differentiation; pacing wires plan.

• Post-op: bleeding/coagulopathy, temperature, electrolytes (K⁺, Mg²⁺), analgesia, early extubation criteria.

Airway: Intubating Patients With or Without Teeth

Universal steps & “look-fors”

• Preoxygenate 3–5 min; plan A/B/C (video scope available).

• Position: sniffing or ramped for obese; ear-to-sternal-notch alignment.

• Induction: choose RSI vs modified vs awake based on aspiration risk and airway eval (Mallampati, mouth opening, thyromental, neck mobility).

• Protect the teeth (and gums) and never lever on incisors; sweep tongue; gentle controlled force.

• Suction ready; confirm EtCO₂ + bilateral chest rise; secure tube; document teeth status pre/post.

With teeth (dentate)

• Risks: dental trauma (especially prominent/fragile incisors), loose teeth/bridges.

• Tips

  • Document loose teeth; remove unstable dental work if possible.

  • Use video laryngoscopy to minimize force; consider a molar approach if anterior larynx.

  • Bite block/oral airway after intubation to protect ETT and teeth during emergence.

Without teeth (edentulous)

• Mask ventilation challenge: poor facial seal, tongue/posterior airway collapse.

  • Keep dentures in for preoxygenation/mask if safe, then remove before laryngoscopy.

  • Use two-hand mask, place oral airway, pack wet gauze/rolls in the buccal sulci to improve seal (remove before intubation).

• Laryngoscopy: more mouth space but fragile gums—pad blade, be gentle.

• Post-intubation: ensure dentures/partials are accounted for and stored; use soft bite block to protect gums with tube in place.

Fast “what to look for” summaries

Before giving NMBs

• K⁺, renal/hepatic function, burns/denervation/immobilization/myopathy history.

• MH history; availability of non-trigger technique if needed.

• TOF baseline; plan for reversal (sugammadex available?).

When reversing

• TOF ratio ≥0.9 target.

• Sugammadex: dose to depth; watch bradycardia/anaphylaxis; renal function; contraception counseling.

• Neostigmine: only with twitches; give with glycopyrrolate/atropine; watch secretions/bronchospasm/bradycardia.

With volatiles

• Procedure type (air-space risks → avoid N₂O).

• Hemodynamics (des/iso swings), airway reactivity (prefer sevo for reactive airways).

• ICP/neuromonitoring needs; CO₂ absorber status.

One-liners to memorize

• Succinylcholine: fastest, but MH + hyperkalemia risks.

• Rocuronium + Sugammadex: modern RSI pair; dose sugammadex to block depth.

• Neostigmine needs twitches and an antimuscarinic; has a ceiling.

• Des: fastest volatile, pungent, watch HR/BP. Sevo: smooth; N₂O expands air spaces.

• For airways: protect teeth/gums, position well, and never lever.