Anesthetic Induction: The First Five Minutes
Pharmacology I · 8 min read
What happens minute-by-minute from pre-oxygenation through ETT confirmation. The order matters; the doses matter; the watch-fors matter.
Minute -3 to 0: Pre-oxygenation
Tight-fitting mask, 100% O₂, three minutes of normal breathing or eight vital-capacity breaths. Goal: replace the patient's nitrogen-filled FRC with O₂ — buys you 6+ minutes of safe apnea in a healthy adult, ~2-3 minutes in obese patients. Sit the obese/OSA patient in ramped position (ear-to-sternal-notch alignment); apply CPAP 10 cmH₂O during preoxygenation if denitrogenation needs help. Capnography on the mask confirms ventilation.
Minute 0: Induction agents
Most common pattern (healthy adult, no aspiration risk): fentanyl 1-3 mcg/kg → wait 90 seconds → propofol 1.5-2.5 mg/kg → wait for LOC + apnea → rocuronium 0.6 mg/kg (or sux 1-1.5 mg/kg if RSI). Watch the BP: induction-related drop is universal but should be modest in young healthy. Older / cardiac / volume-depleted patients: reduce propofol 30-50%, consider etomidate 0.2 mg/kg. Always have phenylephrine 100 mcg drawn + ready.
Induction agents reference →Minute 1-2: Mask ventilation + intubation
Once asleep + apneic, two-handed mask ventilation while NMB takes effect. Verify chest rise + ETCO₂ + clear breath sounds. Time to peak NMB block: roc 0.6 mg/kg ≈ 90 sec; sux ≈ 60 sec. Direct laryngoscopy or video — confirm Cormack-Lehane grade. Insert tube to depth 21-22 cm at lip in average adult. Cuff inflation to minimum-occlusive volume (or pilot pressure < 25 cmH₂O via manometer).
Minute 2-3: ETT confirmation
Three confirmation methods, NOT one: (1) capnography — sustained CO₂ wave for 6+ breaths; (2) bilateral breath sounds + gastric absence; (3) tube fogging. Capnography is the gold standard — esophageal intubation will show no CO₂. If unsure, pull + remask. After confirmation, secure tube, transition to anesthesia circuit, document tube depth + ETCO₂.
Minute 3-5: Settle in
Maintenance starts: volatile titrated to MAC 0.7-1.0 (or TIVA propofol 100-150 mcg/kg/min). Ventilator settings TV 6-8 mL/kg IBW, RR for ETCO₂ 35-40, PEEP 5. BP starts to recover; if it doesn't, reach for phenylephrine. Document everything. Now you have your patient.
References
- · Miller's Anesthesia 9e Ch 23 (Induction Agents)
- · Stoelting Pharmacology 6e Ch 5
- · Hagberg Difficult Airway 4e