A 65 year old male with a past history of ischaemic heart disease is admitted to the ICU after a motorcycle  crash having sustained  long bone fractures  of the lower limbs. He has no head, chest or abdominal injuries. Prior to surgery, his GCS was 15 and SpO2 was 98% on 4l oxygen via Hudson mask with a normal chest X-Ray.


He required prolonged operative fixation of his fractures and that was complicated by significant blood loss. Intra-operatively, he also developed increasing oxygen requirement.  On arrival in ICU, his most recent arterial blood gas on an FiO2 of 0.7 shows a PaO2 55 mmHg.

28.1.   List the differential diagnoses for his respiratory failure.

28.2.   What  assessment  and  investigations  would  you  perform  to  help  establish  the diagnosis?

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College Answer

28.1.   List the differential diagnoses for his respiratory failure.

•  Iatrogenic fluid volume overload due to blood product/resuscitation fluid
•  Atelectasis/Collapse/sputum  plugging
•  Unrecognised pulmonary contusions
•  Unrecognised pneumothorax – Mech vent, line insertion
•  Aspiration at time of MBA or at intubation
•  Endobronchial intubation
•  Transfusion related acute lung injury (TRALI)
•  Cardiogenic pulmonary oedema/myocardial event
•  Fat embolism syndrome
•  Anaphylaxis 
•   PE

28.2.   What  assessment  and  investigations  would  you  perform  to  help  establish  the diagnosis?

Clinical examination –          Ensure adequate tertiary survey Detailed respiratory examination Review fluid balance and urine output
Evidence of generalised allergic reaction
FBE – Hb, WCC, eosinophilia
Coags – ongoing coagulaopathy,
CXRay  –  infiltrates,  ETT  position,  hardware,  PTx,  pleural effusions
Cardiac enzymes – TnI
ECG – ischaemic changes, arrhythmia, R heart strain
Echo cardiogram – if suspect cardiogenic component, assess
LVF, or RVF for PE
CTPA – early for PE but possible if pt delayed in ED

Bronchoscopy -   if   evidence    of     localised collapse or unexplained infiltrates

Discussion

The list of differentials for post-operative hypoxia can be a long one.

Approached systematically, a list would resemble the following:

  • Vascular/embolic causes:
    • Fat embolism
    • Pulmonary thromboembolism
    • Pulmonary oedema due to MI
  • Infectious causes:
    • Aspiration pneumonia
  • Drug-associated causes:
    • Opiate-associated respiratory depression
  • Iatrogenic causes:
    • ETT maplosition
    • TRALI
    • Atelectasis
    • Resuscitation-associated fluid overload
  • Autoimmune causes
    • Anaphylaxis
  • Traumatic causes
    • Pneumothorax
    • Cardiac tamponade
    • Pulmonary contusions

Assessment and investigations would thus follow a systematic A-B-C algorithm:

  • Assess ETT position with auscultation
  • Examine for rash of anaphylaxis and petechii of fat embolism
  • Perfrom ECG and cardiac enzymes to exclude MI
  • Perform bedside TTE to rule out tamponade, and to grossly assess cardiac filling and contractility
  • Perform CXR to exclude pneumothorax, TRALI and aspiration
  • Perform CTPA for exclude PE

References

Sellery, G. R. "A review of the causes of postoperative hypoxia." Canadian Anaesthetists’ Society Journal 15.2 (1968): 142-151.