Ch09: Anesthesia I — General Anesthesia（全身麻醉）

Preparatory Mindset

General anesthesia (GA) = a drug-induced reversible state of unconsciousness, amnesia, analgesia, and muscle relaxation (CM exam tested). The lecture (Dr. Wang) covers the definition, the triad of GA, the stages, the drugs (induction, maintenance, muscle relaxants), airway management, and the complications. The prep PDFs add the classic Q&A (麻醉前用药目的, 全麻并发症).

Exam mindset: know the four elements of GA, the triad, the IV induction agents (propofol), the inhaled agents, depolarizing vs non-depolarizing relaxants, and the airway complications (aspiration, laryngospasm, malignant hyperthermia). Know the fasting rules (see perioperative chapter) — the main aspiration-prevention tool.

Core Concepts

1. Definition & elements of GA (MUST KNOW)

1. Unconsciousness (loss of awareness) 2. Analgesia (loss of response to pain) 3. Blunted reflexes (suppression of harmful reflexes) 4. Paralysis (skeletal muscle relaxation)

• General anesthesia: drug-induced reversible state with four elements:
• The triad of GA: analgesia (pain relief) + amnesia (loss of awareness/memory) + muscle relaxation/areflexia — the three components the anesthetist must balance

2. Stages of anesthesia (classic, historical — Guedel)

• Stage I: Analgesia (conscious, pain ↓)
• Stage II: Excitement/delirium (dangerous — avoid; laryngospasm risk)
• Stage III: Surgical anesthesia (4 planes)
• Stage IV: Medullary depression (overdose — respiratory/cardiovascular collapse)
• Modern practice uses rapid induction to skip stage II

3. Anesthetic drugs (MUST KNOW)

IV induction agents:

• Propofol (丙泊酚) — most common; fast onset/offset; hypotension (↓ SVR); respiratory depression
• Thiopental (barbiturate), etomidate (hemodynamically stable — for cardiac/elderly), ketamine (NMDA antagonist — dissociative, preserves airway reflexes & BP; hallucinogenic emergence)
• Benzodiazepines (midazolam) — amnesia, anxiolysis; flumazenil reversal
• Opioids (fentanyl, remifentanil, morphine) — analgesia; respiratory depression; naloxone reversal

Inhaled agents:

• Sevoflurane, desflurane, isoflurane (volatile halogenated) — maintenance; nitrous oxide (N2O) — weak agent, amnesia/analgesia; MAC (minimum alveolar concentration) = potency measure
• Malignant hyperthermia trigger: succinylcholine + volatile agents (esp. halothane)

Muscle relaxants (neuromuscular blockers):

• Depolarizing: succinylcholine (琥珀胆碱) — rapid onset, short duration; used for rapid sequence intubation; side effects: hyperkalemia, malignant hyperthermia trigger, fasciculations, apnea in pseudocholinesterase deficiency
• Non-depolarizing: rocuronium, vecuronium, atracurium, cisatracurium — competitive antagonists; reversed by neostigmine (anticholinesterase) + atropine/glycopyrrolate; sugammadex (rocuronium reversal, encapsulating agent)

4. Conduct of general anesthesia (MUST KNOW)

1. Preoperative: fasting (clear fluids 2 h/light meal 6 h), premedication (benzodiazepine anxiolysis, antacids), ASA classification, consent
2. Induction: IV agent + opioid + relaxant → intubation (direct laryngoscopy, ETT); or LMA (laryngeal mask)
3. Maintenance: inhaled volatile + N2O ± IV (TIVA — total IV anesthesia with propofol); muscle relaxant as needed
4. Emergence/recovery: stop agents, reverse relaxants, extubate when awake with adequate respiration/reflexes

• Monitoring (standard): ECG, SpO2, BP, ETCO2 (capnography — confirms intubation & ventilation), temperature, urine output, neuromuscular monitoring

5. Airway management

• Bag-mask ventilation → oropharyngeal/nasopharyngeal airway → LMA → endotracheal intubation → surgical airway (cricothyroidotomy)
• Rapid sequence induction (RSI): for full stomach (emergency, trauma, pregnancy) — preoxygenation, cricoid pressure (Sellick), fast-acting agents, minimize aspiration risk
• ETCO2 waveform confirms tracheal placement (gold standard)

6. Complications of GA (MUST KNOW)

• Airway: laryngospasm (stage II, secretions, light anesthesia), airway obstruction, aspiration (pneumonitis — Mendelson's), difficult intubation
• Respiratory: hypoventilation, hypoxia, bronchospasm
• Cardiovascular: hypotension (propofol, volatile agents, hypovolemia), arrhythmias, myocardial ischemia
• Drug reactions: anaphylaxis (succinylcholine, antibiotics, latex), malignant hyperthermia (hyperthermia, muscle rigidity, hypercapnia, acidosis, rhabdomyolysis → immediate dantrolene, stop triggers, cool, correct acidosis/electrolytes, ICU) — mortality high if untreated
• Postoperative: nausea & vomiting (PONV), delirium, sore throat, hypothermia, cognitive dysfunction (elderly), awareness (rare)
• Nerve injuries from positioning; corneal abrasion
• Aspiration prevention: fasting rules, RSI with cricoid pressure, antacids

7. Premedication (麻醉前用药) — prep PDF MUST KNOW

• Purpose: eliminate adverse reflex responses to anesthesia/surgery (esp. vagal reflexes), reduce respiratory & digestive secretions (keep airway clear, prevent aspiration), provide sedation/analgesia
• Common choice: sedatives + analgesics + anticholinergics (阿托品 atropine, 东莨菪碱 scopolamine) — reduce secretions & vagal tone

High-Yield Points

• GA elements: unconsciousness + analgesia + blunted reflexes + paralysis; triad = analgesia, amnesia, muscle relaxation
• Induction: propofol (most common); RSI for full stomach (preoxygenation + cricoid pressure)
• Succinylcholine = depolarizing, rapid, malignant hyperthermia trigger; reversed by nothing (spontaneous) — non-depolarizing reversed by neostigmine/sugammadex
• Volatile agents = sevoflurane/desflurane/isoflurane; MAC = potency
• Malignant hyperthermia: dantrolene, stop triggers, cool
• Monitoring: ECG, SpO2, BP, ETCO2 (capnography = intubation confirmation)
• ETCO2 confirms tube placement
• Premedication: sedative + analgesic + anticholinergic (atropine) — reduce secretions & vagal reflexes
• Fasting: clear fluids 2 h / light meal 6 h (aspiration prevention)

Topic Summary

General anesthesia is a reversible state of unconsciousness, analgesia, reflex blunting, and paralysis — the triad of analgesia/amnesia/relaxation. Drugs: IV induction (propofol common; ketamine preserves BP; etomidate for cardiac), inhaled maintenance (sevoflurane/desflurane/N2O; MAC potency), muscle relaxants (succinylcholine depolarizing & fast, triggers malignant hyperthermia; non-depolarizing reversed by neostigmine/sugammadex). Conduct: preop fasting/premedication → induction → intubation (RSI with cricoid pressure for full stomach) → maintenance → emergence. Monitoring: ECG, SpO2, BP, capnography (ETCO2 confirms tube). Complications: laryngospasm, aspiration, hypotension, anaphylaxis, malignant hyperthermia (dantrolene), PONV, hypothermia. Premedication reduces vagal reflexes & secretions (atropine).