Post-op Hypoxia & Opioid Toxicity

The commonest thing you will actually be bleeped about from this list. Work through the causes by timing: immediate (residual anaesthetic, neuromuscular blockade, airway obstruction), hours (opioids, atelectasis, aspiration, fluid overload), days…

Post-operative Desaturation

The pathway

1 · Oxygen and sit up

15L non-rebreathe initially, titrate to target
Sitting upright alone improves FRC substantially after abdominal or thoracic surgery
Full A–E assessment

2 · Look for opioid toxicity specifically

Respiratory rate <8–10, pinpoint pupils, increasing sedation
Sedation score rises before the respiratory rate falls — a drowsy post-op patient is a warning, not a comfortable one
Check the PCA history, epidural, and every route they may be receiving opioid by

3 · Stop the opioid

Stop the PCA, epidural or infusion before reaching for an antidote
Many patients need nothing more than this plus oxygen and stimulation

4 · Naloxone — titrated, not full reversal

Dilute 400 microgram in 10 ml saline = 40 microgram/ml
Give 20–100 microgram IV every 2 minutes, titrated to respiratory rate
Aim for RR >8 and rousable — NOT full reversal. Full reversal causes severe pain, agitation, hypertension, arrhythmia and rarely pulmonary oedema
Half-life is ~20 minutes, shorter than morphine — the patient can re-sedate. Observe, and consider an infusion
Extra caution in chronic opioid users and palliative patients: use the smallest increments

5 · Think beyond opioids

Atelectasis — commonest cause of post-op hypoxia. Sit up, deep breathing, physiotherapy, incentive spirometry
Aspiration — new infiltrate, fever, recent vomiting or obtunded airway
Fluid overload / pulmonary oedema — review the operative and post-op fluid balance
Pneumothorax — after central line, brachial plexus block, thoracic or laparoscopic surgery
PE — from day 1 onwards, especially pelvic or orthopaedic surgery
Residual neuromuscular blockade in recovery — weak, flailing, unable to sustain head lift

6 · Investigate

ABG — type 1 vs type 2 failure changes the whole differential
CXR, ECG, FBC, CRP
A rising CO₂ with a low RR points back at opioids or residual blockade

7 · Escalate and plan the level of care

Persistent hypoxia despite oxygen, or rising CO₂, needs critical care review
A patient needing repeated naloxone needs continuous monitoring, not a ward bed

Drugs

Drug	Dose	Route	Notes
Naloxone	20–100 microgram IV, repeated every 2 min	IV	Dilute 400 mcg in 10 ml. Titrate to respiratory rate, not consciousness. Half-life shorter than morphine — re-sedation is common and an infusion may be needed.
Oxygen	15L then titrate	NRB / Venturi	Target SpO₂ 94–98%, or 88–92% if known CO₂ retention.
Furosemide	20–40mg	IV	Only where fluid overload is the demonstrated cause. Review the operative fluid balance first.

When to escalate

RR <8 or requiring repeated naloxone,SpO₂ <92% despite 15L oxygen,Rising CO₂ or falling GCS,Suspected aspiration, PE or pneumothorax,Residual neuromuscular blockade in recovery — anaesthetist immediately

Reference: Association of Anaesthetists / RCoA post-operative care guidance; BNF naloxone

This page is the reference half

The app adds what a web page cannot: a VINDICATE differential builder, worked on-call scenarios with full A–E findings, recall practice, and all of it offline.