Body Weight, Dosing Scalars & Ventilation

Derived weights

BMI— kg/m²

Set weight and height above

WHO Technical Report Series 894, 2000 — underweight <18.5 · normal 18.5–24.9 · overweight 25.0–29.9 · obese I 30.0–34.9 · II 35.0–39.9 · III ≥40.0 kg/m².

Body surface area · Mosteller— m²

Set weight and height above

Mosteller, N Engl J Med 1987;317:1098.

Ideal body weight · Devine— kg

Set height and sex above

Devine, Drug Intell Clin Pharm 1974;8:650 — not validated below 152.4 cm.

Lean body weight · Janmahasatian— kg

Set weight, height and sex above

Janmahasatian et al, Clin Pharmacokinet 2005;44:1051.

Adjusted body weight— kg

Set weight, height and sex above

AAGBI / SOBA: Nightingale et al, Anaesthesia 2015;70:859, Table 2.

Which weight for which drug

The weight to multiply your usual mg/kg by — not a dose. Two figures where guidance differs.

Propofol · induction—

Ingrande, Brodsky & Lemmens, Anesth Analg 2011;113:57 (LBW) · Nightingale et al, Anaesthesia 2015 (LBW or ABW) · Friesen, Br J Anaesth 2016;116:730.

Propofol · infusion—

Ingrande & Lemmens, Br J Anaesth 2010;105(S1):i16 (TBW) · Nightingale et al, Anaesthesia 2015, Table 3 (ABW). Marsh and Schnider TCI models are unreliable above 140–150 kg.

Suxamethonium—

Lemmens & Brodsky, Anesth Analg 2006;102:438 (TBW).

Rocuronium—

Leykin et al, Anesth Analg 2004;99:1086 (IBW) · Nightingale et al, Anaesthesia 2015, Table 3 (LBW).

Vecuronium—

Schwartz et al, Anesth Analg 1992;74:515 (IBW) · Nightingale et al, Anaesthesia 2015, Table 3 (LBW).

Fentanyl—

Shibutani et al, Br J Anaesth 2005;95:377 · Ingrande & Lemmens, Br J Anaesth 2010 · Nightingale et al, Anaesthesia 2015 — all LBW.

Remifentanil—

Egan et al, Anesthesiology 1998;89:562 (LBW or IBW).

Paracetamol—

BNF · NHS Specialist Pharmacy Service, Prescribing and administering intravenous paracetamol safely · Nightingale et al, Anaesthesia 2015, Table 3 (LBW in obesity). Confirm against your product label.

Local anaesthetics—

Rosenberg, Veering & Urmey, Reg Anesth Pain Med 2004;29:564 · Nightingale et al, Anaesthesia 2015, Table 3 (LBW). A scalar, not a permitted dose.

Cross-checked against Nightingale et al, Anaesthesia 2015, Table 3 and Ingrande & Lemmens, Br J Anaesth 2010. Where the two differ, both are shown.

Starting ventilation

Predicted body weight ignores actual weight by design — lung size follows height and sex.

Predicted body weight— kg

Set height and sex above

ARDS Network, N Engl J Med 2000;342:1301.

Tidal volume · 6 ml/kg PBW— ml

Set height and sex above

Tidal volume · 8 ml/kg PBW— ml

Set height and sex above

Young et al, Br J Anaesth 2019;123:898 — start 6–8 ml/kg PBW · in ARDS 6 ml/kg with plateau ≤30 cmH₂O (ARDS Network 2000) · Futier et al, N Engl J Med 2013;369:428.

Respiratory rate12–16 /min

Titrate to end-tidal CO₂ 35–45 mmHg (4.7–6.0 kPa); the ARDS Network protocol permits up to 35 /min.

PEEP5 cmH₂O

Young et al, Br J Anaesth 2019 — 5 cmH₂O, then individualised · Futier et al 2013 used 6–8 · PROVHILO, Lancet 2014;384:495 — 12 cmH₂O gave no benefit.

I:E ratio1:2

Protective-ventilation protocols use 1:1.5 to 1:2; lengthen expiration if there is gas trapping.