A 32-year-old male presents with bilateral fractures of the tibia following a road traffic accident. He undergoes operative management and is reviewed the following day on the ward round. On examination, he is unable to speak in full sentences and is visibly short of breath. There are equal breath sounds bilaterally on chest auscultation and his trachea is central. He has a petechial rash across his body. His vital signs are: HR 120bpm, oxygen saturations 90% on room air, RR of 33, BP 95/43, and temperature 36.5.

Which of the following is the most likely diagnosis?

Options:
explanation: A pulmonary embolism is an important differential for post operative hypoxia, especially in the context of orthopaedic patients where mobility may be dramatically reduced. However, pulmonary emboli usually present later in the post-operative period, with the highest risk being 1-5 weeks after an operation. This is since it takes time for the deep vein thrombus to form. Furthermore, pulmonary emboli are not associated with petechial rashes.
name: Pulmonary embolism
label: b
answer: no
explanation: Atelectasis post operatively may result in lung collapse and respiratory distress. It is a good differential diagnosis, but the presence of equal breath sounds, a central trachea (which may be deviated in a collapse), and a petechial rash, make this less likely.
name: Atelectasis
label: e
answer: no
explanation: Compartment syndrome presents with pain out of proportion to any clinical signs and passive stretch in the early stages. Progression leads to pallor, pulselessness, and paraesthaesia as the bloody supply to the limb is compromised. The pain typically does not responding to any analgesia. This can occur after limb trauma because muscle swelling and inflammation increases the pressure in the muscle compartment. This is an orthopaedic emergency which must be diagnosed and treated immediately as it can potentially result in loss of blood supply to the limbs if untreated. Patients with compartment syndrome would not present primarily with respiratory distress as in this case.
name: Compartment syndrome
label: c
answer: no
explanation: A pneumothorax is an important differential to exclude in this context, especially after trauma. It is likely this patient would have had a trauma series CT scan performed on presentation, which would image the thorax, and he would also likely get repeat chest imaging after being observed to be more short of breath during the ward round to rule this out. However, given the equal breath sounds on clinical examination and the presence of a petechial rash, this is unlikely. A tension pneumothorax may present with haemodynamic instability and shock, and warrants immediate needle decompression without delay. This patient has a central trachea, making this unlikely.
name: Pneumothorax
label: d
answer: no
explanation: A fat embolism is a potential complication of long bone fractures. Patients present with respiratory distress, a petechial rash, and haemodynamic instability. It may occur 24-72 hours after the initial injury. Management is supportive.
name: Fat embolism
label: a
answer: yes

Correct answer: a


Learning point: Fat embolism syndrome can occur after long bone fractures, presenting with respiratory distress, petechial rash, and haemodynamic instability within 24-72 hours post-injury.