What is the recommended protocol for propofol infusion in neurosurgery?

Propofol Infusion Protocol for Neurosurgery

Induction Dosing

For neurosurgical patients, use slower induction with boluses of 20 mg every 10 seconds, titrated to clinical response, which typically results in reduced total induction requirements of 1-2 mg/kg 1. This approach minimizes the risk of hypotension and decreased cerebral perfusion pressure that can occur with rapid bolus administration 1.

Standard Adult Patients (ASA I-II, <55 years)

• Administer 20 mg boluses every 10 seconds until loss of consciousness 1
• Total induction dose typically 1-2 mg/kg (lower than the 2-2.5 mg/kg used in general surgery) 1
• Avoid rapid bolus administration as this increases cardiorespiratory depression 1

Elderly, Debilitated, or ASA III-IV Patients

• Further reduce to approximately 1-1.5 mg/kg total induction dose 1
• Maintain the 20 mg every 10 seconds bolus approach 1
• Never use rapid bolus technique in these patients as it significantly increases risk of hypotension, apnea, airway obstruction, and oxygen desaturation 1

Maintenance Infusion

Maintenance rates for neurosurgery should be 50-100 mcg/kg/min (3-6 mg/kg/h) in adults to optimize recovery times while maintaining adequate anesthesia 1.

Initial Maintenance Phase

• Start at 100-200 mcg/kg/min immediately following induction 1
• Higher rates (150-200 mcg/kg/min) are typically needed for the first 10-15 minutes 1
• Reduce infusion rate by 30-50% after the first 30 minutes 1

Ongoing Maintenance

• Target 50-100 mcg/kg/min for optimal recovery 1
• Titrate downward in absence of clinical signs of light anesthesia 1
• Supplement with analgesic agents (opioids reduce propofol requirements by approximately 30-50%) 1

Critical Neurosurgical Considerations

When increased intracranial pressure (ICP) is suspected, hyperventilation and hypocarbia must accompany propofol administration 1. Propofol decreases cerebral metabolic rate (CMRO2) and cerebral blood flow (CBF), making it advantageous for neurosurgery 2.

Managing Cerebral Perfusion Pressure

• Avoid significant decreases in mean arterial pressure to prevent decreased cerebral perfusion pressure 1
• Use slow infusion or 20 mg boluses every 10 seconds rather than rapid administration 1
• Correct fluid deficits prior to propofol administration 1
• Consider vasopressor support if additional fluid therapy is contraindicated 1

Advantages for Neurosurgery

• Decreases CMRO2 and acts as cerebral vasoconstrictor 2
• Maintains cerebral autoregulation and CO2 responsiveness 2
• Provides brain relaxation through decreased CBF 2
• Rapid, predictable recovery allows early postoperative neurological assessment 2, 3

Monitoring Requirements

Continuous monitoring of heart rate, blood pressure, and oxygen saturation is mandatory during propofol administration 4, 5.

• Monitor for hypotension (occurs in 5-7% of patients with transient desaturation <90%) 6
• Propofol causes dose-dependent decreases in cardiac output, systemic vascular resistance, and arterial pressure 7, 5
• Consider prophylactic anticholinergic agents in patients with bradycardia risk factors 4
• For significant bradycardia, administer IV atropine or glycopyrrolate 4

Special Populations and Contraindications

Patients with Cardiovascular Instability

• Avoid bolus loading doses entirely in hemodynamically unstable patients 6, 1
• If loading dose necessary, use only 5 mcg/kg/min over 5 minutes in patients where hypotension unlikely 6
• Administer in small incremental doses with sufficient time between doses to assess peak effect 5, 1

Patients with Pulmonary Hypertension

• Use extreme caution due to risk of decreased cardiac output and worsened right ventricular function 5
• Propofol's negative cardiac inotropy particularly problematic in this population 5
• Be prepared for rapid intervention including immediate discontinuation, IV fluids, and vasopressors 5

Combination with Other Agents

Opioid premedication (morphine 0.15 mg/kg) with nitrous oxide 67% decreases necessary propofol maintenance rates and therapeutic blood concentrations compared to non-narcotic premedication 1.

• Benzodiazepines and opioids reduce propofol induction requirements 1
• When opioid used as primary agent, propofol maintenance should not be less than 50 mcg/kg/min 1
• When propofol is primary agent, maintenance should not be less than 100 mcg/kg/min with supplemental opioid analgesia 1

Recovery and Emergence

Propofol's rapid clearance (elimination half-life 3-12 hours) allows for better control of sedation level and facilitates early neurological assessment 6.

• Recovery time significantly shorter than with benzodiazepines or barbiturates 6
• Target-controlled infusion using Marsh model in effect site mode shows positive bias of 27.6% with greatest bias in early maintenance phase (15-30 minutes) 8
• Obesity (BMI >30) contributes significantly to increased bias in pharmacokinetic performance 8

Common Pitfalls to Avoid

• Never use rapid bolus in elderly, debilitated, or hemodynamically unstable patients 1
• Do not use propofol as sole agent without adequate analgesia for painful procedures 7
• Avoid high-dose opioid technique with propofol as primary anesthetic (increases hypotension risk) 1
• Account for propofol's 1.1 kcal/mL lipid content when calculating nutritional requirements 6
• Monitor for propofol infusion syndrome (PRIS) with doses >70 mcg/kg/min or prolonged infusions 6