What are the appropriate total intravenous anesthesia (TIVA) doses of propofol, fentanyl, and remifentanil for a 110‑kg adult undergoing a spine procedure?

TIVA Dosing for 110 kg Patient Undergoing Spine Surgery

For a 110 kg adult undergoing spine surgery, use propofol target-controlled infusion (effect-site concentration 0.5-1 mcg/mL), remifentanil infusion (0.05-0.3 mcg/kg/min), and maintain BIS monitoring at 40-60 throughout the procedure. 1, 2

Pre-Induction Preparation

• Establish invasive arterial blood pressure monitoring before induction with transducer at tragus level 1, 2
• Have vasopressors immediately available (ephedrine or metaraminol) to treat propofol-induced hypotension 1, 2
• Ensure quantitative neuromuscular monitoring equipment is ready 1, 2

Induction Protocol

Opioid Selection and Dosing

Choose either fentanyl OR remifentanil for induction:

Fentanyl option:

• Administer fentanyl 5 mcg/kg IV (550 mcg for 110 kg patient) over 2-3 minutes 1
• Give 3-5 minutes before propofol to allow peak effect during laryngoscopy 3

Remifentanil option (preferred for spine surgery):

• Start remifentanil infusion at 0.5 mcg/kg/min (55 mcg/min for 110 kg patient) for 5 minutes before propofol 2, 4
• This reduces propofol requirements by approximately 29% and provides faster induction 4

Hypnotic Induction

• Administer propofol 2 mg/kg IV bolus (220 mg for 110 kg patient) for rapid onset 1
• Avoid excessive bolus dosing to prevent hemodynamic instability 5, 1
• Critical caveat: Expect mean arterial pressure to decrease by 26% with propofol-remifentanil combination 4

Muscle Relaxation

• Administer rocuronium 0.9-1.2 mg/kg (99-132 mg for 110 kg patient) for intubation 5, 2
• Alternative: succinylcholine 1-2 mg/kg (110-220 mg) if rocuronium unavailable 5
• Give neuromuscular blocking agent immediately after loss of consciousness to prevent fentanyl-induced rigidity 3

Maintenance Protocol

Propofol Maintenance

• Use propofol target-controlled infusion with effect-site concentration of 0.5-1 mcg/mL 1, 2
• Never exceed 1.5 mcg/mL as this significantly increases risk of over-sedation and hypoventilation 5, 1
• Avoid bolus dosing during maintenance 5, 1
• Expected infusion rate: approximately 81 mcg/kg/min (8,910 mcg/min or 534 mg/hour for 110 kg patient) 6

Opioid Maintenance

Remifentanil maintenance (preferred for spine surgery):

• Reduce remifentanil to 0.05-0.3 mcg/kg/min (5.5-33 mcg/min for 110 kg patient) after intubation 2, 7
• Titrate within this range to control intraoperative responses while allowing rapid emergence 7
• Key advantage: Context-sensitive half-time of 3 minutes allows rapid recovery regardless of infusion duration 7

Fentanyl maintenance (if used for induction):

• Give supplemental boluses of 2 mcg/kg (220 mcg for 110 kg patient) as needed for inadequate analgesia 1
• Important limitation: Fentanyl has longer duration requiring careful timing before emergence 3

Optional Adjuncts for Enhanced Recovery

• Consider ketamine 0.5 mg/kg bolus (55 mg) followed by 0.1-0.2 mg/kg/h infusion (11-22 mg/hour) to reduce opioid requirements 1, 2
• Consider dexmedetomidine 0.5-1 mcg/kg bolus (55-110 mcg) then 0.2-0.7 mcg/kg/h (22-77 mcg/hour) to minimize postoperative pain 2

Intraoperative Monitoring Requirements

• Use BIS monitoring targeting 40-60 throughout procedure 1, 2
• Avoid BIS values below 35 in patients over 60 years to reduce postoperative delirium risk 5, 1, 2
• Use quantitative neuromuscular monitoring when muscle relaxants administered 1, 2
• Monitor standard ASA parameters including pulse oximetry, capnography, ECG, invasive arterial blood pressure 1
• Monitor core temperature routinely 1

Emergence Protocol

• Discontinue propofol and opioid infusions 5-10 minutes before anticipated end of surgery 1, 2
• With remifentanil: Expect recovery within 3-7 minutes regardless of case duration 7
• With fentanyl: Recovery may be delayed; respiratory depression may persist postoperatively in approximately 10% of patients 3
• Document train-of-four ratio ≥0.90 with quantitative monitoring before extubation 1, 2
• Ensure return of airway reflexes and adequate tidal volumes before extubation 1, 2

Critical Dosing Considerations for 110 kg Patient

Weight-based calculations:

• Consider using lean body weight for propofol dosing in obese patients to avoid overdosing 5, 1
• For 110 kg patient, if BMI >30, calculate lean body weight and adjust propofol accordingly 5
• Opioid dosing typically uses total body weight 3

Hemodynamic management:

• Propofol increases vasopressor requirements, especially in hemodynamically challenged patients 5
• Remifentanil causes greater blood pressure reduction than fentanyl during induction (mean arterial pressure decrease of 26% vs 18% with thiopental) 4
• Have vasopressors drawn up and ready before induction 1, 2

Common Pitfalls to Avoid

• Do not use bolus dosing of propofol during maintenance - this causes hemodynamic instability 5, 1
• Do not exceed propofol effect-site concentration of 1.5 mcg/mL - significantly increases over-sedation risk 5, 1
• Do not give fentanyl immediately before propofol - allow 3-5 minutes for peak effect 3
• Do not forget neuromuscular monitoring - mandatory when using muscle relaxants 1, 2
• Do not allow BIS <35 in elderly patients - increases postoperative delirium risk 5, 1, 2