Shock, Sepsis & Multisystem · Topic 11 of 14

Severe Obesity in Acute Care

Special populations · severe obesity

Severe Obesity in Acute Care

Small lungs in a big body: ramp and preoxygenate with NIV, ventilate by predicted weight, and dose drugs on lean or adjusted weight.

Key numbers

Tidal volume by predicted body weight6–8 mL/kg PBW

Dose on lean or adjusted weightAdjBW = IBW + 0.4 × excess

BMI ≥ 40: enoxaparin 40 mg twice dailyBMI ≥ 40 → 40 mg q12h

01 · DoRamp, NIV preoxygenation, video laryngoscopy

Preoxygenate head-up (ramped, reverse Trendelenburg or sitting) with noninvasive positive-pressure ventilation, give positive-pressure breaths between induction and laryngoscopy, and use video laryngoscopy to maximize first-attempt success.

02 · CalculateTidal volume by predicted body weight

Set tidal volume from predicted (ideal) body weight, 6–8 mL/kg PBW, never actual weight — lung size does not scale with body mass, and actual-weight volumes are injurious.

03 · The ruleDose on lean or adjusted weight

Total-body-weight dosing is rarely appropriate and risks overdose: dose most sedatives, opioids and anesthetic drugs on lean, ideal or adjusted body weight (IBW + 0.4 × [actual − IBW]), then titrate.

The rules

Know these

Obesity does not preclude prone positioningUse prone positioning for standard ARDS indications in patients with obesity, with adequate staff and extra attention to pressure-injury prevention; obesity alone is not a reason to withhold it.

What it is

Core idea

Obesity often needs higher PEEPHigh pleural pressure from chest-wall and abdominal fat collapses dependent lung, so patients with obesity often need higher PEEP; airway plateau pressure overestimates true lung stress — esophageal pressure can guide titration.

Causes & risk factors

Why it happens

Expect rapid desaturation during intubation must knowSevere obesity lowers functional residual capacity and raises oxygen consumption, so safe apnea time is short: plan every intubation as a high-risk airway, with hypoxemia the most common complication.

Continue home CPAP and minimize opioidsSevere OSA affects 10–20% of patients with BMI > 35 and is often undiagnosed; it heightens sensitivity to opioid respiratory depression — continue home CPAP and use opioid-sparing analgesia.

Diagnosis & monitoring

Work-up

Ideal body weight formulaIdeal body weight = 50 kg (men) or 45.5 kg (women) + 2.3 kg for each inch of height over 60 inches; adjusted body weight = IBW + 0.4 × (actual − IBW).

Do right now

In this order

First moves

Ramp, NIV preoxygenation, video laryngoscopy

→

Tidal volume by predicted body weight6–8 mL/kg PBW

→

BMI ≥ 40: enoxaparin 40 mg twice dailyBMI ≥ 40 → 40 mg q12h

Why each step

Ramp, NIV preoxygenation, video laryngoscopyPreoxygenate head-up (ramped, reverse Trendelenburg or sitting) with noninvasive positive-pressure ventilation, give positive-pressure breaths between induction and laryngoscopy, and use video laryngoscopy to maximize first-attempt success.

Tidal volume by predicted body weightSet tidal volume from predicted (ideal) body weight, 6–8 mL/kg PBW, never actual weight — lung size does not scale with body mass, and actual-weight volumes are injurious.

BMI ≥ 40: enoxaparin 40 mg twice dailyFixed enoxaparin 40 mg daily underdoses severe obesity: for BMI ≥ 40 give enoxaparin 40 mg subcutaneously twice daily for prophylaxis, considering higher doses at BMI ≥ 50.

Management

Orders

Succinylcholine on total, rocuronium on lean weightDose succinylcholine on total body weight (plasma cholinesterase activity is higher) and rocuronium on lean body weight — total-weight rocuronium does not speed onset but markedly prolongs paralysis.

Propofol and dexmedetomidine on ideal or adjusted weightCalculate propofol and dexmedetomidine infusions on ideal or adjusted body weight: actual-weight dosing gives supratherapeutic levels, and obesity more than doubles the risk of propofol-induced hypotension.

Vancomycin load on actual weight, max 3 gFor serious infection in obesity, a vancomycin loading dose of 20–25 mg/kg actual body weight (maximum 3000 mg) may be given; base maintenance on AUC monitoring — empiric doses rarely exceed 4500 mg/day.

Extubate awake and sitting onto prophylactic NIVExtubate the patient awake and sitting up, with airway reflexes and good tidal volumes, and start prophylactic noninvasive ventilation immediately after extubation to reduce reintubation.

Bariatric surface and scheduled turns prevent pressure injuryStart pressure-injury prevention on ICU admission: structured risk assessment and skin inspection, a sufficiently wide bariatric support surface with microclimate control, and regular repositioning with enough staff.

Red flags & don'ts

Avoid harm

Inspect skin folds for candidal intertrigo complicationMoisture, heat and friction in skin folds cause intertrigo, often secondarily infected with Candida (satellite lesions); keep folds dry and treat candidal intertrigo with a topical antifungal twice daily.

More detail

Reference

Show 8 reference facts

Rhabdomyolysis is a rare but serious complication in obesity after long procedures, hypotension or immobility; check creatine kinase promptly for deep tissue pain, classically in the buttocks.

Opioids, ketamine and midazolam are dosed on ideal or adjusted body weight in severe obesity; midazolam clearance does not rise with weight, so actual-weight infusions accumulate.

Functional residual capacity falls an estimated 5–15% for every 5 kg/m² rise in BMI, which explains the short safe apnea time.

Lean body weight plateaus as BMI rises and rarely exceeds 100 kg in men or 70 kg in women, whatever the total body weight.

In the PREOXI trial, NIV preoxygenation lowered peri-intubation hypoxemia in patients with obesity from 26.4% to 9.0% — a benefit more than three times that seen in patients without obesity.

Cardiovascular collapse complicates about 1 in 5 emergency intubations in critically ill patients with obesity — a rate similar to patients without obesity; propofol induction predicts it, and ketamine or etomidate are both acceptable.

Intermittent pneumatic compression devices may not fit or work properly in some patients with obesity, which limits mechanical prophylaxis.

Turning safely needs a wide enough surface: more than 91 cm for BMI > 35 and more than 127 cm for BMI > 45; check equipment weight limits before use.

Pearl

The lungs and the lean mass do not grow with the body: tidal volume follows predicted weight, and most drug doses follow lean or adjusted weight.

Sources · Russotto V, Casey JD, Myatra SN, Semler MW et al. Airway management in critically ill patients with obesity. Intensive Care Med 2026;52:1256–1268 · Nightingale CE et al. Peri-operative management of the obese surgical patient 2015 (AAGBI / Society for Obesity and Bariatric Anaesthesia). Anaesthesia 2015;70:859–876 · Kitisin N, Caroli A, Serpa Neto A et al. Mechanical ventilation for ICU patient with obesity: current best practices and future directions. Intensive Care Med 2026 · Erstad BL, Barletta JF. Drug dosing in the critically ill obese patient — a focus on sedation, analgesia, and delirium. Crit Care 2020;24:315 · Sebaaly J, Covert K. Enoxaparin dosing at extremes of weight: literature review and dosing recommendations. Ann Pharmacother 2018;52(9):898–909 · Rybak MJ et al. Therapeutic monitoring of vancomycin for serious MRSA infections: revised consensus guideline (ASHP/IDSA/PIDS/SIDP). Am J Health-Syst Pharm 2020;77(11):835–864 · DoseMe — Vancomycin dosing guidelines essentials (quotes the 2020 consensus: obese loading 20–25 mg/kg actual weight, max 3000 mg; maintenance ≤ 4500 mg/day) · Key principles for rehabilitation of critically ill patients with obesity. Intensive Care Med 2026 · Kalra MG, Higgins KE, Kinney BS. Intertrigo and secondary skin infections. Am Fam Physician 2014;89(7):569–573 · Merck Manual Professional — Deep Venous Thrombosis (DVT) Prevention · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).