Thiopentone Dosage for Induction of Anesthesia
The recommended dosage of thiopentone for induction of anesthesia is 3-5 mg/kg intravenously, with 4 mg/kg being the standard effective dose for most adult patients. 1
Dosage Considerations by Patient Population
Adults
- Standard dose: 4-5 mg/kg IV 1
- Elderly patients: 3-4 mg/kg IV (reduced dose due to altered pharmacokinetics) 2
- Patients with complete spinal cord injuries: 3.9 mg/kg IV (reduced requirements compared to non-SCI patients) 3
Special Circumstances
- Obstetric patients: 5 mg/kg IV for rapid sequence induction during cesarean section 1
- When combined with opioids: Reduced dosage required
- With fentanyl 5 μg/kg: Reduce thiopentone to 2.2 mg/kg 4
- With other opioid pretreatment: Consider 25-40% dose reduction
Pediatric Patients
- Rabbits: 30 mg/kg (single IV injection) 1
- Children: Dosing similar to adults, with careful titration based on response
Administration Technique
Method of Administration
- Administer as a 2.5% solution (25 mg/ml) 5
- Inject at a rate of approximately 50 mg/15 seconds (or 4 ml/15 seconds of 2.5% solution) 3
- For rapid sequence induction, administer as a single bolus 5
Monitoring During Administration
- Titrate to clinical effect (loss of eyelash reflex) 3
- Monitor for:
- Loss of consciousness
- Hemodynamic changes (particularly hypotension)
- Respiratory depression
Precautions and Contraindications
Cardiovascular Effects
- May cause hypotension, particularly in:
- Elderly patients
- Hypovolemic patients
- Patients with cardiovascular disease
- Monitor blood pressure closely during induction
Respiratory Effects
- Causes respiratory depression
- Be prepared to provide respiratory support
- Ensure proper pre-oxygenation before administration
Drug Interactions
- Reduced dosage required when combined with:
- Opioids (fentanyl, remifentanil)
- Benzodiazepines
- Other CNS depressants
Alternatives to Thiopentone
Other Induction Agents
- Propofol: 2-2.5 mg/kg IV (causes more hypotension than thiopentone) 6
- Etomidate: 0.3 mg/kg IV (better cardiovascular stability) 6
- Ketamine: 1-2 mg/kg IV (useful for hemodynamically unstable patients) 1
Special Considerations
Breastfeeding
- Thiopentone is compatible with breastfeeding
- No waiting period required before resuming breastfeeding after a single dose 1
Rapid Sequence Induction
- When used for rapid sequence induction:
- Ensure adequate dose (4-5 mg/kg)
- Follow immediately with neuromuscular blocking agent
- Apply cricoid pressure (10 N initially, increasing to 30 N after loss of consciousness) 1
Common Pitfalls
- Underdosing: Doses less than 4 mg/kg may lead to awareness during induction 1
- Extravasation: Can cause tissue necrosis; ensure proper IV access
- Arteriovenous concentration differences: Blood levels vary between arterial and venous samples, particularly in elderly patients 2
- Failure to adjust for patient factors: Age, cardiovascular status, and concurrent medications significantly affect dose requirements
Remember that while these dosage guidelines provide a framework, the ultimate goal is to achieve adequate anesthesia depth while maintaining hemodynamic stability. Always have resuscitation equipment readily available when administering thiopentone.