Examqo › Examqo library › Anesthesiology › Special populations · IMLE
Anaesthesia in obesity and obstructive sleep apnoea (OSA)
In an obese patient the FRC is small and oxygen consumption high, so the patient desaturates faster and is harder to ventilate — prepare a ramped position, preoxygenate with PEEP, and calculate each drug by the type of weight that suits it.
Why it matters in the exam
The exam asks about detecting OSA before surgery (the STOP-BANG questionnaire), the ramped position for intubation, which weight each drug is calculated by (propofol for induction by lean weight, succinylcholine by total weight, rocuronium by ideal weight), the tidal volume by predicted weight, and postoperative care: CPAP, few opioids and continuous monitoring.
The STOP-BANG questionnaire covers snoring, tiredness, observed apnoeas, high blood pressure, BMI above 35, age above 50, neck circumference above 40 cm and male sex; 3 or more positive answers raise suspicion, and 5 or more indicate high risk. Obesity also brings more reflux, more venous thrombosis, and sometimes obesity hypoventilation syndrome (BMI of 30 or more with a daytime PaCO2 above 45 mmHg) and pulmonary hypertension. The aspiration risk rises with GLP-1 drugs, which slow gastric emptying.
In exam questions watch for two dangerous moments: induction, when saturation falls very fast and the airway is harder, and the hours after surgery, when opioids and sedatives worsen obstruction during sleep. Preparation therefore includes planning where the patient will be observed after surgery, not only the position and the equipment. A patient who uses CPAP at home is asked to bring the device to hospital, and it is important to ask about weight-loss drugs that slow gastric emptying.
Key points
- STOP-BANG: 3 or more — suspicion; 5 or more — high risk.
- Ramped position, head-up and preoxygenation with PEEP.
- Propofol and fentanyl by lean weight; rocuronium by ideal; succinylcholine by total.
- Ventilation by predicted weight with PEEP.
- After surgery: CPAP, few opioids, continuous monitoring.
Summary table
| Drug or issue | By which weight | Explanation |
|---|---|---|
| Propofol for induction, fentanyl | Lean weight | A dose by total weight causes severe hypotension |
| Succinylcholine | Total weight | Higher pseudocholinesterase activity and extracellular fluid |
| Rocuronium, vecuronium | Ideal weight | A dose by total weight prolongs paralysis |
| Tidal volume | 6–8 mL/kg of predicted weight + PEEP | Not by actual weight |
| Cefazolin prophylaxis | 2 g; 3 g from a weight of 120 kg | Total weight is used for the threshold |
A free exam question
במטופלים עם Morbid obesity , לאיזו תרופה יש לחשב מינון לפי המשקל האמיתי של המטופל ( Total Body Weight ) ? (the question as examined, in Hebrew)
- א. Rocuronium
- ב. Remifentanil
- ג. Dexmedetomidine
- ד. Fentanyl
In the full version for subscribers
- A simple algorithm
- Memory aid
- Exam traps
- 5 review cards
- Enough for IMLE
The full version is open to subscribers of: Anesthesiology, General surgery, Internal medicine, Medical licensing exam (IMLE).
Subscriber? Read the full topic Plans and prices 25 free questions
Sources
- Society of Anesthesia and Sleep Medicine guidelines on preoperative screening and assessment of adult patients with obstructive sleep apnea, 2016 — Screening and preparation
- ASA Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea, 2014 — Postoperative management
- Miller's Anesthesia, 9th edition (2020) — Anesthesia for Bariatric Surgery
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.