What are the computed ml/hr for intraoperative maintenance of propofol (anesthetic agent) and fentanyl (opioid analgesic) for a 55kg patient undergoing spine endoscopic surgery?

Intraoperative Maintenance Infusion Rates for 55kg Patient

For a 55kg patient undergoing spine endoscopic surgery, use propofol at 5.5-11 ml/hr (assuming 10mg/ml concentration) and fentanyl supplemental boluses of 110 mcg as needed rather than continuous infusion. 1

Propofol Maintenance Dosing

The recommended propofol maintenance rate is 100-200 mcg/kg/min for general surgery, which translates to 5.5-11 mg/min or 330-660 mg/hr for this 55kg patient. 2

Concentration-Based Calculations:

• If using 10mg/ml propofol concentration: 33-66 ml/hr 2
• If using 20mg/ml propofol concentration: 16.5-33 ml/hr 2

Specific Guidance for Spine Surgery:

• For endoscopic spine procedures specifically, use target-controlled infusion with effect-site concentration of 0.5-1 mcg/ml, avoiding bolus dosing during maintenance to prevent hemodynamic instability. 1
• Never exceed 1.5 mcg/ml effect-site concentration as this significantly increases risk of over-sedation and hypoventilation. 1

Initial vs. Maintenance Rates:

• During the first 10-15 minutes after induction, higher rates of 150-200 mcg/kg/min (8.25-11 mg/min = 495-660 mg/hr) are generally required. 2
• After the first 30 minutes, decrease infusion rates by 30-50%, targeting 50-100 mcg/kg/min (2.75-5.5 mg/min = 165-330 mg/hr) to optimize recovery. 2

Fentanyl Dosing Strategy

Fentanyl should be administered as supplemental boluses of 2 mcg/kg (110 mcg for 55kg patient) as needed for inadequate analgesia, rather than continuous infusion. 1

Loading Dose:

• Administer fentanyl 5 mcg/kg (275 mcg for 55kg patient) IV bolus over 2-3 minutes during induction. 1

Maintenance Strategy:

• Use intermittent boluses of 2 mcg/kg (110 mcg) when signs of inadequate analgesia appear (tachycardia, hypertension, movement). 1
• The intraoperative dose range is typically 1-2 mcg/kg per bolus. 3

Why Not Continuous Infusion:

• The guideline for endoscopic spine surgery specifically recommends bolus dosing rather than continuous infusion for fentanyl, reserving continuous infusions for remifentanil when ultra-short-acting opioid is desired. 1

Synergistic Effects and Dose Reduction

When propofol and fentanyl are combined, fentanyl reduces the required propofol concentration by 31-34% at 1 ng/ml fentanyl plasma level and by 50-55% at 3 ng/ml fentanyl level. 4

• A fentanyl concentration of 1 ng/ml reduces the propofol requirement for skin incision by 63%, and 3 ng/ml reduces it by 89%. 5
• This synergistic effect allows for lower propofol maintenance rates when adequate fentanyl is administered, improving hemodynamic stability. 4, 5

Critical Monitoring Requirements

Maintain BIS monitoring at 40-60 throughout the procedure, avoiding values below 35 in patients over 60 years to reduce postoperative delirium risk. 1

• Use quantitative neuromuscular monitoring, documenting train-of-four ratio ≥0.90 before extubation. 1
• Monitor invasive arterial blood pressure continuously with transducer at tragus level. 1
• Have vasopressors immediately available (ephedrine or metaraminol) to treat propofol-induced hypotension. 1

Common Pitfalls to Avoid

Avoid bolus dosing during maintenance as this causes hemodynamic instability—use continuous infusion only. 1

• Do not use propofol maintenance rates below 100 mcg/kg/min when propofol is the primary agent, as this risks inadequate anesthesia. 2
• Propofol provides zero analgesic properties, so adequate fentanyl supplementation is essential for surgical stimulation. 1, 6
• In elderly or ASA III-IV patients, reduce initial rates and avoid rapid boluses to prevent severe hypotension and respiratory depression. 2

Adjunct Considerations

Consider adding ketamine 0.5 mg/kg bolus followed by 0.1-0.2 mg/kg/h infusion (5.5-11 mg/hr for 55kg patient) as co-analgesic to reduce opioid requirements. 1

• Ketamine infusion at 0.1-0.2 mg/kg/h provides additional analgesia and reduces propofol requirements. 3, 1
• This multimodal approach improves postoperative pain control and may reduce total opioid consumption. 1