Pulmonary Embolism

investigation

We know from experience that few patients (around 10%) present with the textbook triad of pleuritic chest pain, dyspnoea and haemoptysis. Pulmonary embolism can be difficult to diagnose as it can present with virtually any cardiorespiratory symptom/sign depending on its location and size.

So which features make pulmonary embolism more likely?

The PIOPED study in 2007 looked at the frequency of different symptoms and signs in patients who were diagnosed with pulmonary embolism.

The relative frequency of common clinical signs is shown below:

• Tachypnea (respiratory rate >20/min) - 96% → ABG shows respiratory alkalosis
• Crackles - 58%
• Tachycardia (heart rate >100/min) - 44%
• Fever (temperature >37.8°C) - 43%

It is interesting to note that the Well's criteria for diagnosing a PE use tachycardia rather than tachypnoea.

All patients with symptoms or signs suggestive of a PE should have a history taken, examination performed and a chest x-ray to exclude other pathology.

Pulmonary embolism rule-out criteria (PERC)

NICE updated their guidelines on the investigation and management of venous thromboembolism (VTE) in 2020. One of the key changes was the use of the pulmonary embolism rule-out criteria (the PERC rule)

• a copy of criteria can be found in the image below
• all the criteria must be absent to have negative PERC result, i.e. rule-out PE
• this should be done when you think there is a low pre-test probability of PE, but want more reassurance that it isn't the diagnosis
  • this low probability is defined as < 15%, although it is clearly difficult to quantify such judgements
• a negative PERC reduces the probability of PE to < 2%