Post-operative respiratory compromise is breathlessness, desaturation or a rising respiratory rate after surgery, and the four causes a CST candidate must separate are atelectasis, pneumonia, pulmonary embolism and fluid overload. The answer is oxygen to a BTS target of 94 to 98%, a blood gas and chest X-ray, a two-level Wells score for pulmonary embolism under NICE NG158, and treatment of the cause you find.

Key takeaways

  • According to the BTS guideline for oxygen use in adults (2017), the target saturation for most acutely ill adults is 94 to 98%, and 88 to 92% for those at risk of hypercapnic respiratory failure until a blood gas is available.
  • The BTS guideline starts critically ill patients on a reservoir mask at 15 L/min and does not give oxygen to patients who are not hypoxaemic.
  • The two-level PE Wells score in NICE NG158 gives 1.5 points for immobilisation over 3 days or surgery in the previous 4 weeks, and a score of more than 4 points means PE is likely.
  • NG158 says offer a CTPA immediately when PE is likely, with interim therapeutic anticoagulation if the scan cannot be done immediately, and a D-dimer within 4 hours when PE is unlikely.
  • NG158 offers apixaban or rivaroxaban first for confirmed PE, and for PE with haemodynamic instability a continuous unfractionated heparin infusion with thrombolysis considered.
  • Timing helps: atelectasis in the first two days, pneumonia after, and a pulmonary embolus at any point but typically once the patient is mobilising.

How do I recognise post-operative respiratory compromise?

Recognise it from the respiratory rate, which rises before the saturation falls, and from the NEWS2 trend rather than one set of observations. A patient on day two after a laparotomy with a respiratory rate of 26, saturations of 91% on air and a temperature of 38 is the standard scenario.

What are the differentials, and how does timing separate them?

  • Atelectasis: the first 48 hours, low-grade fever, reduced basal breath sounds, worse with poor analgesia and an upper abdominal wound
  • Pneumonia: after day two, productive cough, focal signs, consolidation on the chest X-ray, a raised CRP and white cell count
  • Pulmonary embolism: sudden breathlessness, pleuritic pain, tachycardia out of proportion, a clear chest X-ray, often in a patient who has just started mobilising
  • Fluid overload: a positive fluid balance, raised jugular venous pressure, bilateral crackles and a cardiac history
  • Less common: opioid-induced hypoventilation, aspiration, pneumothorax after a central line, or an anastomotic leak presenting as splinting and tachypnoea

In practice the panel is checking that you consider the surgical cause. A patient who is breathless because a leak is irritating the diaphragm will not be fixed by a chest physiotherapist.

What is the immediate management from A to E?

Immediate management is ABCDE with breathing as the focus: sit the patient up, give oxygen to the BTS target, take a blood gas, and examine the chest and the calves before the chest X-ray arrives.

  • Airway: patent; secretions suctioned; conscious level noted, because a drowsy patient may be hypercapnic
  • Breathing: respiratory rate, saturations, work of breathing, tracheal position, percussion and auscultation; oxygen to 94 to 98%, or 88 to 92% if at risk of hypercapnia, starting with a reservoir mask at 15 L/min if critically ill
  • Circulation: pulse, blood pressure, capillary refill, jugular venous pressure, fluid balance and an ECG
  • Disability: AVPU or GCS, pupils and the opioid chart
  • Exposure: temperature, the wound, the calves for a deep vein thrombosis, and the abdomen

According to the BTS guideline, oxygen is a treatment for hypoxaemia, not for breathlessness, and should not be given to patients who are not hypoxaemic. Say the target range you are aiming for and that you will reassess with a repeat gas.

Which investigations separate the causes?

The decisive investigations are the arterial or venous blood gas, the chest X-ray and, when the Wells score is likely, a CTPA. The gas tells you whether this is type 1 or type 2 respiratory failure; the X-ray tells you whether there is collapse, consolidation, effusion or oedema; a clear film with hypoxaemia points to embolism.

How do I use the two-level PE Wells score?

  • Clinical signs and symptoms of DVT: 3 points
  • An alternative diagnosis is less likely than PE: 3 points
  • Heart rate more than 100 beats per minute: 1.5 points
  • Immobilisation for more than 3 days or surgery in the previous 4 weeks: 1.5 points
  • Previous DVT or PE: 1.5 points
  • Haemoptysis: 1 point
  • Malignancy on treatment, treated in the last 6 months or palliative: 1 point
  • More than 4 points: PE likely. 4 points or less: PE unlikely

According to NICE NG158, a likely score means a CTPA immediately if possible, or interim therapeutic anticoagulation if it cannot be done immediately. An unlikely score means a D-dimer with the result within 4 hours, with interim anticoagulation if the result will take longer. A post-operative patient scores 1.5 before you have examined them, so the threshold is close.

Add a full blood count, urea and electrolytes, CRP, blood cultures if febrile, and sputum culture. A bedside echocardiogram is for the hypotensive patient in whom you suspect a massive embolus.

What is the definitive management of each cause?

Definitive management is specific to the cause: physiotherapy and analgesia for atelectasis, antibiotics for pneumonia, anticoagulation for embolism, and diuresis for overload. The common thread is that each is also a decision about the level of care.

Atelectasis

Chest physiotherapy, deep breathing and incentive spirometry, sitting out of bed, and analgesia good enough to allow a deep breath and a cough. An epidural or a rectus sheath catheter that is not working is a respiratory problem.

Pneumonia

Hospital-acquired pneumonia is treated with antibiotics from the local formulary after cultures, oxygen to target, and chest physiotherapy. If the NEWS2 reaches the NG253 sepsis bands, the sepsis pathway takes over with antibiotics within 1 hour.

Pulmonary embolism

NG158 says offer apixaban or rivaroxaban for confirmed PE, which in a fresh post-operative patient is a conversation with the operating surgeon about bleeding risk before the first dose. For PE with haemodynamic instability, NG158 says offer a continuous unfractionated heparin infusion and consider thrombolysis, which means critical care.

When do I escalate, and who do I call?

Escalate to the registrar for any patient who needs more than a few litres of oxygen to stay in range, and to critical care for anyone who is tiring, hypercapnic or needing a reservoir mask. Respiratory failure that is not responding is a level 2 or 3 decision, not a ward one.

  • Rising carbon dioxide on the gas, or a falling conscious level: critical care, for ventilatory support
  • Saturations not reaching target on a reservoir mask: critical care outreach now
  • Suspected massive PE with hypotension: the registrar, critical care and the medical registrar for thrombolysis
  • Any new anticoagulation in the first days after surgery: the operating consultant before the first dose

How do I prevent it in the next patient?

Prevention is analgesia that allows breathing, early mobilisation, chest physiotherapy after upper abdominal surgery, and thromboprophylaxis prescribed and actually given. Ask on the ward round whether the stockings are on and whether the low molecular weight heparin was signed for last night.

What is the interviewer listening for?

  • The BTS targets said as numbers, and oxygen treated as a drug with a target range
  • The four differentials separated by timing and examination, with the surgical cause included
  • The Wells score used correctly, with the surgery point recognised and the NG158 pathway that follows each result
  • Anticoagulation discussed with the surgeon rather than started reflexively
  • Early critical care involvement for the patient who is tiring

What are the common mistakes?

  • Oxygen without a target, or 15 L/min left running on a stable patient with COPD
  • Calling desaturation on day one 'atelectasis' without examining the calves or the abdomen
  • Sending a D-dimer in a patient who is already Wells-likely, which NG158 does not ask for
  • Starting a DOAC without telling the surgeon
  • Forgetting that opioid toxicity is a respiratory diagnosis

How this comes up at the CST interview

The CST management and clinical station scores a structured approach, knowledge, prioritisation and communication. A breathless post-operative patient tests whether your ABCDE has a target in it, whether your differential includes the surgical cause, and whether you know the NG158 pathway well enough to say it under pressure.

coresurgeryinterview's 299-question bank, with AI-marked spoken practice, includes a day-three desaturation scenario that is marked on exactly this sequence: oxygen to target, gas and film, Wells score, cause-specific treatment, escalation.