# AI calculates IV heparin infusion rate using actual body weight instead of adjusted body weight for an obese patient, causing supratherapeutic aPTT

- **ID:** `medical/iv-pump-rate-miscalculation-obesity`
- **Domain:** medical
- **Category:** medication_error
- **Error Code:** `ANTICOAG-042`
- **Verification:** ai_generated
- **Fix Rate:** 87%

## Root Cause

Heparin dosing for obese patients (BMI >30) should use adjusted body weight (ABW = IBW + 0.4*(actual weight - IBW)) or fixed-dose nomograms; using actual body weight results in supratherapeutic aPTT (>100 sec) and increased bleeding risk (major bleed rate 5-10%).

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| CHEST Antithrombotic Guidelines 2021 | active | — | — |
| Epic Willow v2023 | active | — | — |
| Heparin Nomogram v2.0 (institutional) | active | — | — |

## Workarounds

1. **Calculate adjusted body weight: IBW (males = 50 + 2.3*(height_in_inches - 60); females = 45.5 + 2.3*(height_in_inches - 60)). Then ABW = IBW + 0.4*(actual weight - IBW). Use ABW for heparin bolus (80 units/kg) and infusion (18 units/kg/hr). Verify with nomogram.** (92% success)
   ```
   Calculate adjusted body weight: IBW (males = 50 + 2.3*(height_in_inches - 60); females = 45.5 + 2.3*(height_in_inches - 60)). Then ABW = IBW + 0.4*(actual weight - IBW). Use ABW for heparin bolus (80 units/kg) and infusion (18 units/kg/hr). Verify with nomogram.
   ```
2. **Use electronic health record (EHR) calculator that auto-calculates ABW when BMI >30. Example Epic SmartPhrase: .HEPARINOBESE. Ensure pharmacy verifies before dispensing.** (90% success)
   ```
   Use electronic health record (EHR) calculator that auto-calculates ABW when BMI >30. Example Epic SmartPhrase: .HEPARINOBESE. Ensure pharmacy verifies before dispensing.
   ```
3. **Implement protocol: For BMI >30, use fixed-dose heparin nomogram (e.g., 5000 units bolus + 1000 units/hr infusion) with aPTT monitoring at 6 hours. Adjust per aPTT response.** (85% success)
   ```
   Implement protocol: For BMI >30, use fixed-dose heparin nomogram (e.g., 5000 units bolus + 1000 units/hr infusion) with aPTT monitoring at 6 hours. Adjust per aPTT response.
   ```

## Dead Ends

- **** — IBW underestimates volume of distribution for heparin, leading to subtherapeutic aPTT and increased risk of clot progression. Adjusted body weight is evidence-based. (80% fail)
- **** — Even reduced bolus with actual weight leads to high infusion rates; steady-state levels become toxic. Must use ABW for both bolus and infusion. (75% fail)
- **** — Fixed-dose nomograms are validated for non-obese patients only. For BMI >30, use obesity-specific nomogram (e.g., CHEST guideline). (85% fail)