The Pulmonary Embolism Rule-out Criteria (PERC) is a clinical prediction rule used to exclude pulmonary embolism (PE) as a diagnosis in patients with low pretest probability. It is specifically designed for use in adult patients who are suspected of having a PE but are deemed to be at low risk based on clinical judgment. 

The PERC rule is a useful tool in the emergency department setting, as it helps to avoid unnecessary diagnostic testing, such as D-dimer testing or computed tomography pulmonary angiography (CTPA), in patients who are unlikely to have a PE. 

The PERC rule should not be used in patients with a high pretest probability of PE, or in patients with signs of right ventricular strain or hypoxia. It is also not applicable to pregnant women or patients under the age of 18.

Pulmonary embolism rule-out criteria (PERC)

# Criteria
 A. Age >= 50 (+1)
B. Heart rate >= 100 (+1)
C. SpO2 < 94% (+1)
D. Unilateral leg swelling (+1)
E. Hemoptysis (+1)
F. Recent surgery (<= 4 weeks) (+1)
G. Prior pulmonary embolism or deep venous thrombosis (+1)
H. Oral hormone use (+1)

# Conditions
- score == 0
- score >= 1