Lesson 14: Pharmacokinetics & Pharmacodynamics in Anesthesia

Key Physiologic Differences in Anesthesia

  • Cardiac Output: Higher in neonates (200 mL/kg/min).

  • Volume of Distribution: Larger for water-soluble drugs due to higher total body water.

  • Plasma Protein Concentration: Lower; higher free drug concentrations increase toxicity risk.

  • Hepatic Function: Immature; drug metabolism reaches adult values around 1 year.

  • Renal Function: Immature; normal GFR by 8-24 months, tubular function by 2 years.

  • Blood-Brain Barrier: Immature; increased drug penetration results in heightened sensitivity.

  • Minimum Alveolar Concentration (MAC): Varies with age:

    • Neonates have lower MAC than infants.

    • MAC peaks in infants 2-3 months, then decreases but remains higher than adults (Sevoflurane: 6 months-12 years MAC is 2.5%).

Neonatal Responses in Pharmacokinetics

  • Increased free fraction of highly protein-bound drugs.

  • Faster circulation time.

  • Larger volume of distribution for water-soluble drugs.

  • Longer duration of action for lipid-soluble drugs due to lower fat content.

Summary of Key Points

  • Prioritize Monitoring in neonates due to immature physiological functions impacting drug efficacy and safety.