What are the recommended doses of Propofol, Fentanyl, Ketamine as an adjunct, and Norepinephrine (Norepi) for a 62-year-old female patient weighing 55 kilograms with potential comorbidities undergoing spine decompression surgery under Total Intravenous Anesthesia (TIVA)?

TIVA Dosing for Spine Decompression Surgery in 62-Year-Old Female (55 kg)

Propofol Dosing

For this 62-year-old patient undergoing spine surgery with neurophysiological monitoring, use propofol induction at 1.0-1.17 mg/kg (55-64 mg total bolus), followed by maintenance infusion at 75-100 μg/kg/min (4.1-5.5 mg/kg/hr). 1, 2

Induction Phase

• Bolus dose: 55-64 mg IV (1.0-1.17 mg/kg based on Indian population data showing lower requirements than Western populations) 1
• Target effect-site concentration (Ce): 2.3-2.4 μg/ml for loss of consciousness 1
• Expected state entropy at induction: 50-52 1

Maintenance Phase

• Infusion rate: 75-100 μg/kg/min (247-330 ml/hr of 1% propofol for 55 kg patient) 1, 2
• For patients >60 years, use the lower end of this range (75-81 μg/kg/min) to avoid excessive depth and hypotension 3, 1
• Target Ce for recovery: approximately 1.0 μg/ml (50% of induction value) 1

Critical Monitoring

• Use processed EEG monitoring (BIS or entropy) targeting BIS 45-50 to avoid burst suppression and reduce postoperative delirium risk in this age group 3
• Avoid BIS <35, which increases delirium risk in patients >60 years 3

Fentanyl Dosing

Administer fentanyl 2-5 μg/kg (110-275 μg) as induction bolus, followed by continuous infusion at 0.5-2 μg/kg/hr during maintenance. 3

Induction

• Bolus: 110-275 μg IV (2-5 μg/kg) 3
• For elderly patients, use lower end: 110-165 μg (2-3 μg/kg)

Maintenance

• Infusion: 0.5-2 μg/kg/hr (27.5-110 μg/hr for 55 kg) 3
• Titrate to minimum effective dose to suppress hemodynamic responses while allowing neurophysiological monitoring 4, 5

Important Caveat

• Reduce fentanyl dose by 20-25% for age >60 years to account for decreased clearance and increased sensitivity 6
• Monitor for chest wall rigidity with rapid bolus administration 3

Ketamine as Adjunct

Use low-dose ketamine 0.25-0.5 mg/kg (14-27.5 mg) bolus at induction, followed by 0.1-0.25 mg/kg/hr infusion, but exercise extreme caution in this 62-year-old patient due to delirium risk. 3, 7

Dosing Protocol

• Induction bolus: 14-27.5 mg IV (0.25-0.5 mg/kg) 7
• Maintenance infusion: 5.5-13.75 mg/hr (0.1-0.25 mg/kg/hr) 3

Critical Age-Related Warning

• The American Geriatrics Society and American College of Cardiology recommend avoiding ketamine in elderly patients (>60 years) due to significant risk of postoperative confusion and delirium 6, 8
• If ketamine is used despite this warning, use only the lowest doses and discontinue early in the procedure 6
• Consider omitting ketamine entirely and using lidocaine infusion instead (see below)

Alternative: Lidocaine Infusion (Preferred for Age >60)

• Lidocaine 1.5 mg/kg bolus (82.5 mg), then 1-2 mg/kg/hr infusion reduces propofol requirements by 14-16% without affecting neurophysiological monitoring 4
• This is a safer adjunct than ketamine for elderly patients undergoing spine surgery 4

Norepinephrine (Vasopressor Support)

Prepare norepinephrine infusion at 0.05-0.15 μg/kg/min (2.75-8.25 μg/min for 55 kg) and titrate to maintain MAP >65 mmHg, as propofol-based TIVA causes significant hypotension in elderly patients. 3

Infusion Preparation

• Starting rate: 0.05-0.1 μg/kg/min (2.75-5.5 μg/min) 3
• Prepare 4 mg norepinephrine in 250 ml (16 μg/ml concentration)
• For 55 kg patient: start at 10-20 ml/hr

Hemodynamic Targets

• Maintain MAP ≥65 mmHg throughout procedure 9
• In patients with cerebrovascular disease or significant cardiovascular comorbidity, maintain higher MAP (70-80 mmHg) 8

Critical Management Points

• Propofol causes greater vasopressor requirements than volatile anesthetics, particularly during induction 3, 7
• Have phenylephrine 100-200 μg boluses available for acute hypotension during induction 9
• Avoid excessive fluid administration in response to propofol-induced hypotension; use vasopressors first 9

Integrated TIVA Protocol Summary

Induction Sequence (for 55 kg, 62-year-old female)

1. Fentanyl 110-165 μg IV (2-3 μg/kg, reduced for age) 3, 6
2. Propofol 55-64 mg IV (1.0-1.17 mg/kg) 1
3. Rocuronium 33-55 mg (0.6-1.0 mg/kg) for intubation 3
4. Consider lidocaine 82.5 mg bolus instead of ketamine for opioid-sparing 4

Maintenance Infusions

• Propofol: 75-100 μg/kg/min (4.1-5.5 mg/kg/hr) 1, 2
• Fentanyl: 0.5-1.5 μg/kg/hr (27.5-82.5 μg/hr, reduced for age) 3
• Lidocaine: 1-2 mg/kg/hr (55-110 mg/hr) if used 4
• Norepinephrine: 0.05-0.15 μg/kg/min titrated to MAP 3

Monitoring Requirements

• BIS/entropy monitoring targeting 45-50, avoiding <35 3
• Quantitative neuromuscular monitoring (train-of-four ≥0.90 before extubation) 3
• Continuous hemodynamic monitoring with MAP goal ≥65 mmHg 9

Age-Specific Adjustments for 62-Year-Old Patient

• Reduce all opioid doses by 20-25% 6
• Use lower propofol infusion rates (75-81 μg/kg/min vs 100-115 μg/kg/min in younger patients) 1
• Avoid ketamine or use minimal doses due to delirium risk 6, 8
• Avoid benzodiazepines entirely (strongly associated with postoperative delirium >60 years) 6