Clinical diagnosis

The classic triad of respiratory distress, petechial rash, and neurological dysfunction is notable ( Table !). The onset of these symptoms and signs usually occurs 12 to 72 h after injury. The key to making the diagnosis is to have a high index of suspicion. In centers where arterial blood gas analysis is routine for patients suffering from long-bone fractures, 30 per cent show evidence of hypoxia which is usually self-limiting but may progress to respiratory failure.

Table 1 Signs and symptoms of fat embolism syndrome

Respiratory dysfunction characterized by a low PO2 (< 8.0 kPa (60 mmHg)) in a patient at risk should arouse suspicion that fat embolism syndrome may be present. Initially, compensatory mechanisms lead to hypocapnia and a mild respiratory alkalosis. If the condition progresses, a mixed metabolic and respiratory acidosis supervenes. In patients with multiple injuries, respiratory distress and hypoxia may be compounded by associated chest trauma and underlying lung injury. Further diagnostic difficulties may arise as multiple rib fractures alone may precipitate fat embolism syndrome.

Although fat embolism syndrome may develop at any time from 12 h to 7 days after injury, the risk is greatest in the first 48 h. Therefore any significantly injured patient should be repeatedly assessed, bearing fat embolism syndrome in mind. Pulse oximetry is useful in a well-perfused patient.

Neurological dysfunction ranges from mild restlessness and agitation to convulsions and coma. The signs may be related to hypoxia of pulmonary origin, fat embolization of the brain, or a combination of both. Further confusion may arise if there is an altered mental state related to head injury or inadequate resuscitation in the face of multiple system injury. Careful systemic assessment and investigation are required.

The hallmark sign in a patient at risk is the petechial rash ( Fig 1). It should be sought for specifically and is most commonly found on the trunk, conjunctiva, sclera, and buccal mucosa. Petechias appear in crops but are of short duration, usually fading after 48 h. They are associated with capillary fragility, not direct skin embolization. Profound thrombocytopenia and massive blood transfusion can also give rise to petechias and should be clinically considered.

Fig. 1 Typical distribution of the petechial rash. (Reproduced with permission from Peltier ...(.19.70.).)

Fat embolism syndrome is usually accompanied by fever (> 38 °C) and tachycardia (100-120 beats/min). In the absence of sepsis, fat embolism syndrome should be strongly considered. Fundoscopy should be performed in all cases, as fat may be seen in the retinal arterioles. Fat embolization in the eye may also provoke non-specific retinal exudate and hemorrhage.

In conclusion, a high index of suspicion is needed for patients at risk. Early and repeated arterial blood gas analysis is the most important single investigation.

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