21 - 25 Pharmacology SBAs for the Primary FRCA
Question 21
You are performing rapid sequence induction for a fifty-three year old man weighing 165kg undergoing a laparoscopic cholecystectomy.
Which of the following is true?
- Alfentanil should be dosed to lean body weight
- Suxamethonium should be dosed to total body weight
- Rocuronium should be dosed to total body weight
- Propofol should be dosed to adjusted body weight
- Fentanyl should be dosed to total body weight
Answer
- Suxamethonium should be dosed to total body weight
There are three weights to be aware of:
- Total body weight
- Adjusted body weight
- Lean body weight
Adjusted body weight takes into account the fact that obese patients have increased lean body mass as well as adipose tissue.
Most water soluble drugs (including rocuronium) should be dosed based on lean body weight as they generally remain in the central vascular compartment.
Suxamethonium is a strange exception to this rule and should be dosed on total body weight.
Other examples
- Propofol = lean body weight for induction, adjusted body weight for maintenance
- Antibiotics = adjusted BW
- Alfentanil = adjusted BW
- Fentanyl = lean BW
- Paracetamol = lean BW