What are the guidelines for using thiopental for induction of anesthesia?

Thiopental for Anesthesia Induction

Standard Dosing

The recommended induction dose of thiopental for adult patients is 4-5 mg/kg IV, prepared as a 2.5% solution (25 mg/mL). 1

• Doses below 4 mg/kg are associated with increased risk of intraoperative awareness and should be avoided 1
• For pediatric patients or when precise dosing is required, thiopental can be further diluted to a 1% solution (10 mg/mL) 1
• The solution must be prepared fresh immediately before use, as alkaline solutions will precipitate thiopental 1

Clinical Context and Limitations

Thiopental should be used with significant caution in specific patient populations due to its cardiovascular effects:

Patients with Cardiovascular Compromise

• In hemodynamically unstable patients, thiopental causes direct myocardial depression and peripheral vasodilation, which can be hazardous 2
• These effects are particularly pronounced in hypovolemic trauma patients or those with excessive fluid losses 2
• Etomidate is a safer alternative in traumatized or hemodynamically compromised patients due to its superior cardiovascular stability 2

Patients with Cardiac Hypertrophy

• In patients with significant myocardial hypertrophy (such as Pompe disease), thiopental should be reserved only for those with less severe hypertrophy 2
• The drug's afterload reduction and lower diastolic pressure can predispose these patients to myocardial ischemia 2
• Ketamine or etomidate are preferred alternatives as they maintain systemic vascular resistance and coronary perfusion pressure 2

Patients with Septic Shock

• Thiopental carries significant risk in pediatric septic shock due to direct myocardial depression and vasodilation 2
• Ketamine with atropine premedication is the preferred agent for intubation in septic shock, as it maintains cardiovascular stability and blocks inflammatory mediators 2

Respiratory Considerations

• In patients with pre-existing asthma or in the presence of cholinergic stimulation, thiopental may lead to severe bronchoconstriction 2
• Ketamine is preferred in patients with asthma or chronic obstructive pulmonary disease due to its bronchodilatory effects 2

Practical Administration

• Have additional doses readily available in case intubation proves difficult 1
• Consider gentle bag-mask ventilation (pressure <20 cmH₂O) after induction to prevent oxygen desaturation 1
• Avoid mixing thiopental with acidic drugs, as the alkaline solution will precipitate 1

Current Practice Trends

Propofol has largely replaced thiopental in many clinical settings due to better suppression of airway reflexes, fewer drug errors, greater clinician familiarity, and easier preparation 1. However, thiopental remains a viable option when propofol is contraindicated or unavailable, particularly in patients without significant cardiovascular compromise.