Table 3. Volume of distribution and pharmacokinetic half-life of common sedatives used for gastrointestinal procedures according to weight in obese patients.

Sedative	Dose calculation	Volume of distribution	Half-life
Chloral hydrate (67)	Based on TBW	Highly protein bound, hence a low volume of distribution	8–11 h
Fentanyl	Based on LBW* In obese patients, the dose should be adjusted to individual needs because of an increased risk for hypoxia postoperatively	Highly lipophilic 4–6 L/kg	Three compartment model: Phase 1: 6 min Phase 2: 60 min Phase 3: 16 h Mean: 2 to 4 h
Ketamine (68)	Based on IBW†	Highly lipophilic 2 L/Kg	2.5 h
Midazolam (69)	Based on TBW‡	Large volume of distribution and highly lipophilic 1–3 L/kg	1–4 h Half-life is increased in obesity and liver cirrhosis
Propofol (70)	Based on TBW‡	Large volume of distribution and highly lipophilic 5–10 L/kg	Three compartment model: Phase 1: 2–3 min Phase 2: 40 min Phase 3: 300–700 min

BMI = body mass index; IBW = ideal body weight; LBW = lean body weight; TBW = total body weight.

^*LBW is weight devoid of all adipose tissue and is calculated as follows: male, 1.10 × TBW −0.0128 × BMI × TBW; female, 1.07 × TBW − 0.0148 × BMI × TBW.

^†IBW is calculated as follows: male, 49.9 kg + 0.89 × (height in cm − 152.4) kg; female, 45.4 kg + 0.89 × (height in cm − 142.4) kg.

^‡This is applicable if used as a single dose. If used as a continuous infusion, the dose should be based on the IBW.