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?
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.