What are the recommended doses of fentanyl (synthetic opioid analgesic) and propofol (hypnotic agent) for a 145kg male?

Dosing of Fentanyl and Propofol for a 145kg Male

For a 145kg male patient, use fentanyl 100-150mcg IV followed by propofol 1-1.5mg/kg based on a dosing weight of approximately 100-108kg (total dose 100-162mg) for induction. 1

Fentanyl Dosing

• Initial IV bolus: 100-150mcg (approximately 1μg/kg based on pharmacokinetic mass rather than total body weight) 2, 1
• Fentanyl should be administered first, as it provides analgesia and reduces the excitatory effects of propofol 3
• Supplemental doses of 25μg can be administered every 2-5 minutes until adequate sedation is achieved 2
• For maintenance, a continuous infusion of 25-300μg/h (0.5-5μg/kg/h based on adjusted weight) can be used if needed for longer procedures 2

Propofol Dosing

• For induction: 1-1.5mg/kg based on pharmacokinetic mass (approximately 100-108kg for a 145kg patient), resulting in a total dose of 100-162mg 4, 1
• Administer slowly over 20 seconds to minimize cardiovascular depression 4, 3
• For maintenance: 50-100μg/kg/min (based on adjusted weight) for general anesthesia 4
• Lower maintenance rates (20-60μg/kg/min) may be appropriate depending on the clinical context 2, 4

Weight Considerations for Obese Patients

• Total body weight significantly overestimates fentanyl dose requirements in obese patients 1
• For patients weighing 140-200kg, a pharmacokinetic mass (dosing weight) of 100-108kg is recommended for fentanyl 1
• Similarly, propofol dosing should be adjusted using this pharmacokinetic mass rather than total body weight to avoid overdosing 4, 1
• The relationship between clearance and total body weight becomes nonlinear above 100kg 1

Important Clinical Considerations

• The combination of propofol and fentanyl produces synergistic effects, allowing for lower doses of each medication 5
• Fentanyl 1μg/kg reduces the required propofol concentration by 31-34% for various stimuli 5
• Monitor closely for respiratory depression, which is the major adverse effect of this combination 2
• Be prepared to manage potential hypotension, as propofol causes vasodilation and may reduce blood pressure, especially in combination with opioids 2, 4
• In large doses, fentanyl may induce chest wall rigidity, which can make ventilation difficult 2
• Elderly patients or those with significant comorbidities would require further dose reduction (not applicable to this case) 4

Monitoring and Safety

• Continuous monitoring of oxygen saturation, blood pressure, and heart rate is essential 2
• Have naloxone readily available for reversal of opioid effects if needed 2
• Be prepared for possible airway management as the combination can cause significant respiratory depression 2
• Titrate to clinical effect rather than administering the full calculated dose at once 4

This approach balances the need for adequate sedation/anesthesia while minimizing the risks of cardiovascular depression and prolonged recovery in this obese patient.