What is the target controlled infusion (TCI) concentration of propofol for Total Intravenous Anesthesia (TIVA) maintenance in a 62-year-old female patient with hypertension, on losartan (Angiotensin II receptor antagonist) therapy, undergoing spinal decompression from T6 to L1 with Intraoperative Neurophysiological Monitoring (IONM) without a Bispectral Index (BIS) monitor?

Target Propofol Concentration for TCI-TIVA in Spine Surgery with IONM

BIS monitoring is strongly recommended when administering TIVA with neuromuscular blockade for procedures requiring IONM, and proceeding without it requires extreme caution with conservative dosing strategies. 1

Critical Safety Concern: Absence of BIS Monitoring

The Association of Anaesthetists explicitly recommends using processed EEG monitoring when administering TIVA with neuromuscular blockade to prevent intraoperative awareness and ensure patient safety 1. Without BIS monitoring in this case:

• You cannot reliably titrate anesthetic depth since clinical signs are unreliable in paralyzed patients 1
• Risk of awareness increases during the prolonged multilevel spinal decompression procedure 1
• Risk of excessive depth increases, particularly concerning in a 62-year-old patient where BIS <35 significantly increases postoperative delirium risk 2

Recommended TCI Approach Without BIS

Effect-Site Concentration Targets

For maintenance without BIS monitoring, use conservative propofol effect-site concentrations of 3.0-4.0 mcg/mL combined with adequate opioid analgesia 3. This approach prioritizes:

• Avoiding awareness by maintaining higher concentrations than the typical BIS-guided range of 2.5-3.5 mcg/mL 1
• Avoiding excessive depth that could increase delirium risk in this 62-year-old patient 2
• Maintaining adequate IONM signals since propofol-based TIVA is compatible with motor and somatosensory evoked potential monitoring 4, 5, 6

Induction Protocol

• Effect-site concentration: 4.0-5.0 mcg/mL for induction 3
• Avoid rapid bolus administration in this 62-year-old patient on losartan, as rapid boluses cause pronounced hypotension in elderly patients 3
• Slow induction at approximately 20 mg every 10 seconds (0.5-1.5 mg/kg total) minimizes cardiovascular depression 3

Maintenance Strategy

Propofol effect-site target: 3.0-4.0 mcg/mL 3

Remifentanil infusion: 0.15-0.25 mcg/kg/min 3, 4

The FDA label specifies that when propofol is the primary agent, maintenance infusion rates should not be less than 100 mcg/kg/min and must be supplemented with analgesic levels of continuous opioid 3. However, TCI models automatically calculate these rates based on effect-site targets.

Special Considerations for This Patient

Age-Related Dosing (62 years old)

• Elderly patients require 30-50% dose reduction due to decreased volume of distribution and intercompartmental clearance 3
• Higher peak plasma concentrations occur with standard dosing, predisposing to hypotension, apnea, and oxygen desaturation 3
• Avoid BIS <35 if monitoring were available to reduce postoperative delirium risk 2

Losartan Interaction Considerations

• This patient is on chronic antihypertensive therapy, which increases risk of intraoperative hypotension 7
• Maintain arterial pressure at higher levels in hypertensive patients to prevent end-organ ischemia 7
• Avoid excessive blood pressure reduction during this prolonged multilevel spine surgery, as hypotension combined with prone positioning and blood loss increases perioperative visual loss risk 7
• Resume losartan postoperatively as soon as feasible, as delaying ACE inhibitor/ARB resumption increases 30-day mortality 8

IONM Compatibility

Propofol-based TIVA is fully compatible with IONM for this T6-L1 decompression 4, 5, 6. Research demonstrates:

• Baseline IONM recordings are obtainable in all patients with propofol-remifentanil TIVA 4
• No significant differences in SSEP cortical amplitudes or tcMEP amplitudes occur with propofol infusion rates of 99-148 mcg/kg/min 4, 5
• Avoid volatile anesthetics >0.2 MAC as sevoflurane 0.5 MAC decreases tcMEP amplitude to <150 µV, making monitoring unreliable 9

Hemodynamic Management Algorithm

Blood Pressure Targets

Maintain MAP within 10% of baseline throughout the procedure 8. For this hypertensive patient on losartan:

1. Obtain preoperative baseline blood pressure to establish individualized targets 7
2. Continuously monitor arterial pressure via arterial line given the high-risk nature of multilevel spine surgery 7
3. Treat prolonged significant decreases immediately with vasopressors rather than reducing propofol, as adequate anesthetic depth must be maintained without BIS guidance 7
4. Avoid deliberate hypotension in this high-risk patient, as the combination of prone positioning, prolonged duration, and potential blood loss increases perioperative visual loss risk 7

Fluid Management

• Correct fluid deficits before propofol administration 3
• Monitor for blood loss and hematocrit changes during this multilevel decompression, as substantial blood loss increases visual loss risk 7
• Consider colloid administration if significant blood loss occurs, as higher colloid percentage reduces ischemic optic neuropathy risk 7

Critical Pitfalls to Avoid

Relying on clinical signs alone: Movement, tachycardia, or hypertension are unreliable indicators of awareness in paralyzed patients 1. Without BIS, you must maintain conservative propofol concentrations throughout.

Excessive dose reduction for age: While elderly patients require lower doses, reducing propofol below 3.0 mcg/mL effect-site concentration without BIS monitoring risks awareness during this prolonged procedure 1, 3.

Inadequate opioid supplementation: The FDA label explicitly states propofol as primary agent requires analgesic levels of continuous opioid administration 3. Remifentanil 0.15-0.25 mcg/kg/min provides this coverage while maintaining IONM signal quality 4.

Ignoring hypotension: This 62-year-old on losartan is at high risk for intraoperative hypotension 7. Treat hypotension aggressively with vasopressors rather than reducing anesthetic depth, as awareness risk is unacceptably high without depth monitoring 1.

Rapid emergence: Continue propofol infusion until 10-15 minutes before extubation to prevent rapid awakening with agitation 3. Abrupt discontinuation causes anxiety and resistance to mechanical ventilation 3.