TCI Compartment Volumes — Marsh · Schnider

🏺 Volume Tanks Height of each tank is proportional to volume. All three models shown side-by-side per volume.

Marsh

Weight-proportional · Simple scaling

V₁

—

Central
Blood

V₂

—

Fast
Peripheral

V₃

—

Slow
Peripheral

Schnider

Fixed V₁ · Age-adjusted V₂ · Fixed V₃

V₁

—

Central
Blood

V₂

—

Fast
Peripheral

V₃

—

Slow
Peripheral

Eleveld

Allometric scaling · Age + sex + body composition

V₁

—

Central
Blood

V₂

—

Fast
Peripheral

V₃

—

Slow
Peripheral

🫧 Proportional Bubbles Circle area ∝ compartment volume. Instantly see relative sizes.

Marsh

Schnider

Eleveld

📊 Side-by-Side Bar Chart All three models per compartment — easiest for direct comparison.

V₁ — Central Compartment (Blood / Plasma)

Marsh

—

— L/kg

Schnider

—

Fixed

Eleveld

—

— L/kg

V₂ — Fast Peripheral (Muscle / Viscera)

Marsh

—

— L/kg

Schnider

—

Age-adj.

Eleveld

—

— L/kg

V₃ — Slow Peripheral (Fat / Bone / Skin)

Marsh

—

— L/kg

Schnider

—

Fixed

Eleveld

—

Fat-adj.

V₁

Central Compartment

The small-to-medium volume into which propofol is injected. Determines the initial peak concentration after a bolus dose. Marsh: V₁ = 0.228×wt = 15.96 L at 70 kg — scales with weight. Schnider: fixed at 4.27 L regardless of patient weight — this four-fold difference means a Schnider bolus produces ~4× higher peak Cp than Marsh for the same target.

V₂

Fast Peripheral — Muscle & Viscera

Equilibrates with blood within minutes. Acts as a rapid drug reservoir — it absorbs drug after bolus, lowering Cp. When infusion stops, it returns drug to blood, slowing the fall of Cp. Schnider's V₂ decreases with age (less muscle mass), which is clinically important in the elderly.

V₃

Slow Peripheral — Fat, Bone, Skin

The enormous reservoir for lipophilic drugs like propofol. Fills slowly during long infusions and empties even more slowly on stopping — the key driver of context-sensitive half-time. Eleveld adjusts V₃ for fat mass, so obese patients have a larger V₃, explaining prolonged awakening after long TIVA.

⚖️ How Each Model Scales its Volumes The fundamental difference between the three models

🔵 Marsh

V₁0.228 × weight (kg) → 15.96 L at 70 kg

V₂0.463 × weight (kg) → 32.41 L at 70 kg

V₃2.893 × weight (kg) → 202.5 L at 70 kg

Age, sex and height are completely ignored. Every 10 kg increase adds the same increment to every compartment. Source: Marsh et al. BJA 1991;67:41–48.

🟠 Schnider

V₁4.27 L fixed — does NOT scale with weight

V₂18.9 − 0.391 × (age − 53) — decreases with age

V₃238 L fixed — does NOT scale with weight

Only clearances scale (via LBM, age, height). Fixed V₁ is the most important clinical difference vs Marsh.

🟣 Eleveld

V₁Allometric weight + age exponential decay

V₂Allometric weight × age exponential decay

V₃Fat-mass adjusted — increases with obesity

Most physiologically realistic. Handles extremes of age, weight and body composition more accurately than either Marsh or Schnider.