Pharmacokinetics · TCI Education

Three-Compartment Model

Target-Controlled Infusion — Interactive Simulation (Propofol · Marsh Parameters)

Target Cp 3.0 µg/mL
TCI 3.0 µg/mL INFUSION PUMP (TCI) Infusion C₁ CENTRAL COMPARTMENT Blood & Plasma • Drug injected directly here • V₁ = 0.228×wt → 15.96 L • Rapid mixing with blood • TCI targets this as Cp Cp = 0.00 µg/mL Ce Effect-site 0.00 µg/mL ke0 C₂ FAST PERIPHERAL Well-perfused tissues • Muscle, liver, viscera • V₂ = 0.463×wt → 32.4 L 0.00 µg/mL C₃ SLOW PERIPHERAL Poorly-perfused tissues • Fat, skin, bone • V₃ = 2.893×wt → 202.5 L 0.00 µg/mL k₁₂ → ← k₂₁ k₁₃ → ← k₃₁ k₁₀ Elimination (Liver)
Infusion Rate 0.00 mg/min 0.0 mg/kg/hr 0.0 mL/hr (1% propofol)
🎯 Target Plasma Concentration
3.0 µg/mL
Range: 0.5 – 8.0 µg/mL  ·  Step: 0.5
Live Concentrations
C₁ Central (Cp) 0.00 µg/mL
C₂ Fast Peripheral 0.00 µg/mL
C₃ Slow Peripheral 0.00 µg/mL
Ce Effect-Site 0.00 µg/mL

🩸 C₁ — Central Compartment

Drug delivered directly into blood. TCI targets this as plasma concentration (Cp). Marsh V₁ = 0.228 × weight → 15.96 L at 70 kg. Larger than Schnider's fixed 4.27 L, so bolus doses are proportionally higher.

💪 C₂ — Fast Peripheral

Well-perfused tissues (muscle, liver). Marsh V₂ = 0.463 × weight → 32.41 L at 70 kg. Equilibrates within minutes. Acts as a reversible reservoir — drug returns to blood as Cp falls.

🧈 C₃ — Slow Peripheral

Fat & poorly-perfused tissues. Marsh V₃ = 2.893 × weight → 202.5 L at 70 kg. Slow uptake and slow release — explains prolonged effects after long infusions (context-sensitive half-time).

🔥 k₁₀ — Elimination

Drug exits only from C₁ via hepatic metabolism. TCI pump continuously recalculates rate to compensate for this ongoing clearance.

Rate Constants
k₁₂ C₁→C₂
k₂₁ C₂→C₁
k₁₃ C₁→C₃
k₃₁ C₃→C₁
k₁₀ Elim.
ke0 Effect