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Surgical sieve
🩵 Low saturations
Is it real, is it new, and is the patient working hard or not working at all? A quiet sleepy desaturation is hypoventilation until proven otherwise — and that is the one people watch rather than treat.
| Upper airway obstruction Must exclude | Stridor, drooling, a voice change, or paradoxical chest movement with no air entry. Saturations fall late.Airway first. Anaesthetics and ENT immediately — do not lie them flat. |
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| Tension pneumothorax Must exclude | Sudden desaturation with absent breath sounds and haemodynamic collapse, classically after a line, a biopsy or ventilation.Decompress before imaging. |
| Acute pulmonary oedema Must exclude | Pink frothy sputum, orthopnoea, bilateral crackles, raised JVP. Often overnight, often after a day of generous fluids.Sit up, high-flow oxygen, IV furosemide, consider CPAP. Check the fluid balance chart. |
| Massive PE Must exclude | Hypoxia with a clear chest and a normal CXR. The mismatch between how hypoxic they are and how normal the chest sounds is the clue.CTPA, or bedside echo if too unstable. |
| Opioid-induced hypoventilation Must exclude | Sleepy, slow respiratory rate, pinpoint pupils — and saturations that look almost normal on oxygen right up until they do not. Commonest after a PCA, an epidural top-up or a dose increase.Naloxone, titrated. RESPIRATORY RATE and SEDATION LEVEL are the early warnings — supplemental oxygen can keep the saturation near-normal while the patient hypoventilates, so do not rely on SpO2 alone. |
| Aspiration Time-sensitive | Abrupt desaturation during or just after eating, vomiting or an NG feed, often with coughing and new right-sided signs.Sit them up, suction, oxygen, CXR. Nil by mouth and a swallow assessment before anything else goes in. |
| Atelectasis / mucus plugging Time-sensitive | Day 1 to 3 after surgery, in a patient who is not breathing deeply because it hurts. Reduced air entry at a base, sometimes tracheal deviation TOWARDS the collapse.Analgesia good enough to cough, sit them up, physiotherapy. This is a treatable cause that gets labelled pneumonia. |
| Pneumonia Time-sensitive | Fever, productive cough, focal crackles and consolidation. After 48 hours in hospital the organisms and the antibiotics change.CXR, cultures, antibiotics. Community or hospital-acquired changes the choice. |
| Infective exacerbation of COPD Time-sensitive | Increased breathlessness, sputum volume or purulence in known COPD. Target saturations are 88–92%.Controlled oxygen via Venturi, nebulisers, steroids, antibiotics if purulent. Gas to check the CO2. |
| Type 2 respiratory failure Time-sensitive | Drowsy, flushed, bounding pulse, flapping tremor, with a rising CO2 on the gas. Can be precipitated by uncontrolled oxygen in a chronic retainer.Blood gas is the test — the saturation probe cannot see CO2. Controlled oxygen and consider NIV. |
| Transfusion reaction Time-sensitive | Desaturation during or within 6 hours of a transfusion. TACO is fluid overload; TRALI is non-cardiogenic oedema with a normal JVP.Stop the transfusion, keep the line, tell the lab. The distinction between TACO and TRALI changes the treatment. |
| Acute severe asthma Time-sensitive | Wheeze, inability to complete sentences, PEFR below 50%. A silent chest and a normalising CO2 are pre-arrest signs.Back-to-back nebulisers, steroids, magnesium. Escalate early. |
| Probe artefact Common | Cold or poorly perfused fingers, nail varnish, shivering, movement, or a trace that does not match the pulse. Check the waveform, not just the number.Warm the hand, move the probe to an ear or a different finger, and correlate with the patient. Then believe it. |
| CO poisoning Consider | Headache, nausea and confusion in more than one person from the same house or a faulty heater. The pulse oximeter reads FALSELY NORMAL because it cannot tell carboxyhaemoglobin from oxyhaemoglobin.Co-oximetry on a blood gas, high-flow oxygen. A normal saturation does not exclude it. |
| Anaemia Consider | Oxygen DELIVERY can be inadequate with a perfectly normal saturation — the probe measures how full the haemoglobin is, not how much there is.FBC. Worth remembering when the numbers look fine and the patient does not. |
15 differentials · 11 open a full pathway in the app.