Obesity dosing goes wrong most often when one weight is used for everything. The useful habit is to decide, drug by drug, which body compartment the dose is chasing.
Induction agents are chasing an initial concentration in a well-perfused central compartment that does not scale with fat mass, so lean or ideal body weight is the anchor. Maintenance is chasing clearance, which rises with size but not in proportion, so adjusted body weight fits. Drugs distributing into fat, and those titrated to a measured endpoint rather than a calculation, follow their own rules.
Write the weight you used on the chart next to the dose, not just the dose. The commonest cause of an unexplained deep or light patient in a bariatric list is a colleague reading a milligram figure and assuming a different denominator from the one you used.
- Record which weight — total, lean, ideal or adjusted — was used for each calculated dose, on the chart
- Lean or ideal body weight for induction boluses; adjusted body weight for maintenance infusions
- Titrate to a measured endpoint where one exists rather than trusting the arithmetic alone
- Recalculate at handover rather than continuing an infusion rate whose basis you did not set
- Agree one adjusted body weight formula across the department so figures are comparable between anaesthetists
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for anaesthesiology, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free