Anesthetic Dosing During Surgery: Key Adjustment Principles

Guiding Principles for Intraoperative Anesthetic Titration

Anesthetic depth is continuously adjusted based on multimodal monitoring. No fixed formula—individualized to patient and surgical stimulus.

Core Determinants

1. Patient factors: Age, weight, BMI, comorbidities (cardiac, pulmonary, renal, hepatic), frailty, pharmacogenomics (e.g., CYP2B6, BChE variants).
2. Baseline dose: Age- and weight-based MAC (minimum alveolar concentration) for volatiles; target-controlled infusion (TCI) models for IV (propofol, remifentanil).
3. Surgical stimulus intensity: Incision, laparoscopy, bone work, laparotomy – each demands deeper plane.
4. Anesthetic site of action: Volatiles (CNS), opioids (spinal/supraspinal), NMBAs (neuromuscular junction) – distinct monitoring.
5. Procedure duration: Context-sensitive half-time (remifentanil unique); accumulation of volatiles/IV agents.

Monitoring-Guided Adjustments

• Hemodynamics: HR, BP (arterial line) – surrogate for sympathetic response to nociception.
• Processed EEG (BIS, PSI, Entropy): Target 40–60 for general anesthesia.
• Neuromuscular monitoring (TOF): Guide NMBA dosing/reversal.
• End-tidal agent concentration (EtAA): Confirm inspired/delivered match.
• Clinical signs: Lacrimation, sweating, movement, pupil size.

Individual Variability & Recovery

• Elderly, obese, cardiac patients need 20–50% dose reduction.
• Redheads may require more volatile anesthetic.
• Emergence: Taper agents, ensure reversal, normothermia, normocapnia, adequate analgesia.