What is the recommended Total Intravenous Anesthesia (TIVA) protocol for an elderly patient, weighing 55 kg, on losartan (Angiotensin II receptor antagonist) maintenance, undergoing spine decompression T6-L1 with Intraoperative Neurophysiological Monitoring (IONM), without a Bispectral Index (BIS) monitor available?

TIVA Protocol for Elderly Patient Undergoing Spine Decompression with IONM

For this 55 kg elderly patient undergoing T6-L1 spine decompression with IONM and no BIS monitor available, use age-adjusted propofol dosing with strict clinical vigilance: induction with 1-1.5 mg/kg propofol (55-82.5 mg total) administered slowly at 20 mg every 10 seconds, maintenance at 50-100 mcg/kg/min (2.75-5.5 mg/min), supplemented with low-dose fentanyl boluses and ketamine as adjunct, while maintaining systolic blood pressure within 10% of baseline. 1, 2

Critical Considerations for Elderly Patients

Elderly patients require 30-50% dose reduction of propofol compared to younger adults due to decreased clearance and altered pharmacodynamics. 1, 2 The Association of Anaesthetists explicitly warns that failure to adjust doses commonly results in relative overdose and prolonged, significant hypotension, which is associated with higher mortality. 1

Without BIS monitoring, you must rely on age-adjusted dosing algorithms and meticulous clinical assessment. 1 The guidelines state that age-adjustment algorithms are routinely used for TIVA and should be employed when depth-of-anaesthesia monitors are unavailable. 1

Induction Protocol

Propofol Dosing

• Administer 1-1.5 mg/kg propofol (55-82.5 mg total for this 55 kg patient) slowly at approximately 20 mg every 10 seconds. 2
• Never use rapid bolus technique in elderly patients—this significantly increases risk of hypotension, apnea, airway obstruction, and oxygen desaturation. 2
• Titrate against clinical response until loss of consciousness occurs. 2

Fentanyl Dosing

• Administer 1-2 mcg/kg fentanyl (55-110 mcg total) during induction. 2
• Opioid premedication decreases necessary propofol maintenance rates by reducing therapeutic blood concentrations. 2

Ketamine Adjunct

• Consider 0.25-0.5 mg/kg ketamine (13.75-27.5 mg) as adjunct during induction to provide additional analgesia and reduce propofol requirements.
• Ketamine does not significantly interfere with IONM when used at sub-anesthetic doses.

Maintenance Protocol

Propofol Infusion

• Start maintenance immediately after induction at 100-150 mcg/kg/min (5.5-8.25 mg/min) for the first 10-15 minutes. 2
• After initial period, decrease to 50-100 mcg/kg/min (2.75-5.5 mg/min) to optimize recovery while maintaining adequate anesthesia. 2
• For elderly patients, target the lower end of this range (50-75 mcg/kg/min or 2.75-4.125 mg/min). 1, 2
• Research demonstrates that propofol-based TIVA may reduce postoperative cognitive dysfunction in elderly patients compared to inhalational agents. 3

Fentanyl Supplementation

• Administer 25-50 mcg boluses of fentanyl in response to hemodynamic signs of inadequate analgesia (tachycardia, hypertension, patient movement). 2
• For elderly patients with potential renal dysfunction (common with losartan use), reduce both dose and frequency of opioid boluses by 50%. 1
• Monitor for signs of opioid accumulation throughout the case.

Ketamine Infusion

• Maintain ketamine infusion at 0.1-0.3 mg/kg/hr (5.5-16.5 mg/hr or 0.09-0.275 mg/min) as adjunct.
• This provides additional analgesia, reduces propofol requirements, and has minimal impact on IONM signals at these doses.

IONM-Specific Considerations

Propofol-based TIVA is the preferred anesthetic technique for procedures requiring IONM because it has less suppressive effects on motor evoked potentials compared to volatile anesthetics. 4, 5, 6

• Avoid neuromuscular blocking agents after intubation—use only for induction. 5 IONM requires intact neuromuscular transmission for accurate motor evoked potential monitoring.
• Maintain consistent propofol infusion rates during critical monitoring periods. 4 Sudden changes in anesthetic depth can alter IONM signals.
• If adding low-dose volatile anesthetic becomes necessary, do not exceed 0.2 MAC sevoflurane equivalent, as 0.5 MAC reduces motor evoked potential amplitude to less than 150 µV, making monitoring unreliable. 6
• Research shows multimodal IONM in spine surgery has 99.1% sensitivity and 100% specificity for detecting intraoperative neurological events. 5

Monitoring Without BIS

Essential Clinical Parameters

• Maintain arterial line for continuous blood pressure monitoring—this is mandatory in elderly patients undergoing major spine surgery. 1, 7
• Keep systolic blood pressure within 10% of baseline to reduce risk of postoperative delirium and cognitive dysfunction. 1
• Monitor for clinical signs of anesthetic depth: heart rate, blood pressure, lacrimation, pupil size, and absence of movement. 1

Hemodynamic Targets

• Avoid the "triple low" state (low blood pressure, low heart rate, low anesthetic requirement) as this is associated with higher mortality and prolonged hospital stay. 1
• Administer fluids in small divided boluses (250 mL aliquots) to assess response, as elderly patients have reduced homeostatic compensation. 1

Losartan Considerations

Patients on chronic angiotensin II receptor antagonists like losartan are at increased risk of intraoperative hypotension. 7

• Prepare vasopressors (phenylephrine 100-200 mcg boluses or norepinephrine infusion) before induction. 7
• Consider continuing losartan on the morning of surgery for cardiovascular stability, but be prepared for exaggerated hypotensive response to anesthetic induction. 7
• Maintain intravascular volume with goal-directed fluid therapy using arterial line waveform analysis. 1

Additional Safety Measures

Peripheral Nerve Monitoring

• Use peripheral nerve stimulator to monitor for residual neuromuscular blockade, as elderly patients experience unpredictably prolonged blockade. 1
• Ensure train-of-four ratio >0.9 before extubation.

Temperature Management

• Actively warm patient throughout procedure—elderly patients are highly susceptible to hypothermia during prolonged spine surgery. 1
• Maintain core temperature >36°C using forced-air warming and warmed intravenous fluids.

Positioning and Pressure Care

• Meticulously pad all pressure points before prone positioning—elderly patients have thin skin and are at high risk for pressure injuries and peripheral nerve damage. 1
• Document pre-existing pressure sores before surgery. 1

Emergence and Recovery

• Titrate propofol downward 30-45 minutes before anticipated end of surgery to facilitate smooth emergence. 2
• Ensure adequate reversal of any residual neuromuscular blockade with neostigmine/glycopyrrolate or sugammadex. 1
• Avoid rapid boluses of opioids during emergence—use multimodal analgesia with scheduled acetaminophen as first-line. 7
• Monitor closely for postoperative delirium in the first 24-72 hours, as elderly patients undergoing spine surgery are at high risk. 1, 7