In a morbidly obese patient with BMI approximately 42 kg/m², how accurate is the Eleveld target‑controlled infusion (TCI) model for propofol compared with the Marsh and Schnider models?

Eleveld Model Shows Superior Accuracy in Morbidly Obese Patients with BMI 42 kg/m²

For a morbidly obese patient with BMI 42 kg/m², the Eleveld model is more accurate than both Marsh and Schnider models when using total body weight (TBW) as input, though using adjusted body weight (ABW) with Marsh or Schnider can achieve comparable performance.

Critical Context for Your Patient

Your patient with BMI 42 kg/m² falls precisely at the upper limit where Schnider becomes unreliable - commercial pumps restrict Schnider model use to BMI ≤42 kg/m² (male) or ≤35 kg/m² (female) 1. The Marsh model becomes unreliable above 140-150 kg total body weight 1.

Performance Data in Morbidly Obese Patients

When Using Total Body Weight:

The most relevant study directly addressing your question examined 20 morbidly obese patients (mean BMI 41.4 kg/m², range 35-52 kg/m²) - essentially your exact patient population 2. Key findings:

• Eleveld allometric model: MDPE = 18.2%, MDAPE = 27.5% (best performance, P < 0.0001)
• All five tested models showed a tendency to underestimate propofol concentrations when using TBW
• The Eleveld model's superiority stems from its allometric scaling and broader population development

The Adjusted Body Weight Solution:

If you must use Marsh or Schnider (due to pump availability), calculate adjusted body weight and use this as your weight input 2:

ABW (kg) = IBW (kg) + 0.4 × (TBW (kg) - IBW (kg))

This adjustment dramatically improved performance:

• MDPE <10% and MDAPE <25% for both models (P < 0.0001)
• Achieved the lowest predictive errors of all tested approaches 2

Clinical Algorithm for Your Patient

Step 1: Determine Available TCI System

• If Eleveld model available → Use with TBW input
• If only Marsh/Schnider available → Calculate ABW and proceed to Step 2

Step 2: Calculate Adjusted Body Weight

• Calculate IBW: Height (cm) - 100 (males) or -105 (females) 1
• Apply ABW formula above
• Input ABW as "weight" in pump

Step 3: Target Effect-Site Concentrations

• For moderate-deep sedation: 2.0-2.5 μg/mL 3
• For general anesthesia: 3.2 μg/mL (in presence of remifentanil) 2
• Elderly/high-risk: Start closer to 2.0 μg/mL 3

Step 4: Mandatory Safety Measure Given the significant risk of accidental awareness in obese patients using TCI (NAP5 audit showed disproportionate representation) 1, depth of anesthesia monitoring is strongly recommended 1.

Important Caveats

The Awareness Risk

The NAP5 audit revealed that obese patients had disproportionate AAGA incidents when using TCI, with 93% involving neuromuscular blocking drugs 1. The mechanism: rapid redistribution into larger fat mass causes faster wake-up after bolus dosing, and inadequate maintenance dosing leads to awareness 1.

Mitigation strategy: Ensure maintenance infusion immediately follows induction without gap 1.

Model Limitations Persist

Even the Eleveld model showed 27.5% median absolute performance error in morbidly obese patients 2. Recent 2025 systematic review confirms that no single model consistently outperforms across all populations 4. The Eleveld model improved drug clearance estimation in obese patients but inconsistencies remain in predicting brain concentrations 4.

Recent Comparative Data

A 2025 study comparing Schnider vs. Eleveld for sedation showed Eleveld achieved target sedation faster (6.1 vs 9.8 minutes) and required significantly lower effect-site concentrations (2.1 vs 3.3 μg/mL) 5. This suggests Eleveld may be more efficient, though both were safe.

Practical Recommendation

Primary approach: Use Eleveld model with TBW if available on your pump, targeting 2.0-3.2 μg/mL depending on procedure depth.

Alternative approach: If limited to Marsh/Schnider, calculate ABW and use this as weight input - this achieves comparable accuracy to Eleveld 2.

Universal requirement: Use processed EEG monitoring (BIS/entropy) given the established awareness risk in this population 1.

The 2024 study developing a new propofol PK model specifically included 21 patients with BMI >50 kg/m² and found that incorporating multiple weight descriptors (TBW for clearance, lean body weight for distribution volumes) improved accuracy 6, supporting the rationale for ABW adjustments with traditional models.