Intravenous (IV) induction is the rapid administration of anesthetic drugs via a vein to achieve unconsciousness and facilitate airway management (e.g., endotracheal intubation). It is the most common method for inducing general anesthesia in adults and children.
Why IV Induction?
- Speed & Predictability:
- Unconsciousness occurs in 15–60 seconds (vs. 2–5 minutes with inhalational agents).
- Allows precise titration to effect (e.g., loss of eyelash reflex, apnea).
- Patient Comfort:
- Avoids the pungent smell and airway irritation of inhalational agents (e.g., sevoflurane).
- Ideal for anxious patients or those with difficult IV access (use inhaled induction if needed).
- Hemodynamic Control:
- Enables rapid intervention if hypotension or adverse effects occur.
Key Principles
- Pharmacokinetics:
- High Lipid Solubility: Agents cross the blood-brain barrier rapidly (e.g., propofol, thiopental).
- Redistribution: Initial effect ends as drug redistributes to muscle/fat (explains short duration).
- Metabolism: Hepatic (propofol) or plasma esterases (remimazolam) terminate effects.
- Dosing:
- Weight-based (e.g., propofol 1–2.5 mg/kg; etomidate 0.2–0.3 mg/kg).
- Adjust for age, comorbidities, and concurrent medications (e.g., reduce dose in elderly).
- Hemodynamic Impact:
Clinical Workflow
- Pre-Induction:
- Confirm IV access, monitoring (ECG, SpO₂, BP), and pre-oxygenation.
- Prepare emergency drugs (e.g., vasopressors for hypotension).
- Induction:
- Administer IV agent slowly (e.g., propofol over 20–30 seconds).
- Add adjuncts:
- Opioid (fentanyl/remifentanil) to blunt sympathetic response.
- Muscle relaxant (rocuronium/succinylcholine) for paralysis.
- Airway Management:
- Intubate once full paralysis/loss of consciousness is achieved.
- Confirm placement with capnography.
Indications vs. Contraindications
Advantages Over Inhalational Induction
Challenges & Complications
- Hypotension: Most common with propofol/thiopental (mitigate with fluid bolus/vasopress
ors). - Pain on Injection: Propofol (30–70% incidence; reduce with lidocaine).
- Myoclonus: Etomidate (up to 50%; pre-treat with fentanyl/benzodiazepine).
- Adrenal Suppression: Etomidate (single dose safe; avoid in sepsis).
- Anaphylaxis: Rare but life-threatening (e.g., propofol, rocuronium).
Future Directions
- Ultra-Short-Acting Agents: ABP-700 (etomidate analog) aims to avoid adrenal suppression
. - Target-Controlled Infusion (TCI): Computerized systems to optimize dosing (e.g., propofol TCI for induction).
- Microemulsion Formulations: Reduce injection pain (e.g., propofol alternatives).
Key Takeaway
IV induction is the cornerstone of modern anesthesia, balancing speed, control, and safety. Mastery requires understanding pharmacology, patient physiology, and contingency planning. Always tailor the agent to the patient’s comorbidities and surgical context.
Further Reading: