# PERC Rule and Calculating Risk

by Sharon Bord, MD
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00:01 So following back up with our patient, so do we think she has a pulmonary embolus? She has normal vital signs and a normal physical exam.

00:08 She denies any risk factors for blood clots.

00:11 So let’s move on to the next step for her.

00:13 So let’s think about the PERC rule for pulmonary embolus.

00:17 So this was derived from a study that was done and we basically use this only for patients who are low risk by Well’s criteria.

00:24 We’ll be talking about Well’s criteria in a moment.

00:27 When we’re thinking about the PERC rule we think about if the patient has any of the following: Are they over 50 years of age? Is their heart rate over a hundred? Is their oxygen saturation on room air less than 95%? Do they have exogenous estrogen use? And generally, in here, I also include endogenous estrogen when I’m thinking about this.

00:48 So exogenous estrogen are those birth control pills, endogenous estrogen is the pregnancy state.

00:54 Do they have any history of DVT or PE? Any recent trauma or surgery? Any hemoptysis? So what that means is that they cough or is there any blood in their sputum? And do they have any unilateral leg swelling? Now we use to determine the ED is the patient PERC negative.

01:10 So if a patient is negative, that means they have none of these things that can be checked off.

01:14 That means they don’t have any of those criteria that we talked about.

01:17 And if that’s the situation, the risk of pulmonary embolus is less than 2% and we say actually that no further work up is indicated for those patients.

01:26 So we wanna figure out if our patient is PERC negative.

01:29 Now, if someone ticks off even one of these boxes, so if you’re 51 years old, if your heart rate is 105, anything here you automatically are PERC positive.

01:42 So when you’re PERC positive you’re put out of this negative category and then we have to use the Well’s criteria so think about what the next steps are.

01:50 So the Well’s criteria is our next way that we think about calculating risk.

01:55 So again, if our patient is PERC negative, work for the most part done.

01:58 If the patient is positive, they’ve ticked off one of those boxes, we can go ahead and think about Well’s criteria.

02:04 So do they have any clinical signs and symptoms of a DVT? Do they have swelling in their leg? Do they have pain in their leg? Is PE the number one diagnosis or equally likely? And this give you points so you could see the points over here.

02:19 Clinical signs and symptoms of DVT give you 3 points.

02:22 PE being the number 1 diagnosis or equally likely also gives you 3 points.

02:26 Now this is what people say as one of the issues with this decision rule, this is a subject of thing, right? So one person might say I think PE is the most likely thing, but another person might say I don’t think PE is the most likely thing.

02:40 So that could make this decision rule a little bit tricky and 3 points is actually a lot of points to be awarded for this little check box.

02:48 Is the heart rate greater than a hundred? 1.5 points.

02:52 And mobilization of 3 days or surgery within the last 4 weeks, 1.5 points.

02:57 Previously, objectively diagnosed PE or DVT, 1.5 points.

03:03 Hemoptysis, again, that’s when you see blood in your sputum when you cough.

03:07 And then malignancy with treatment in the 6 months or undergoing palliative care, 1 point.

03:13 So when we’re thinking about our Well’s criteria, we add up the number of points that our patient has and we divided them into different categories.

03:20 So for the most parts, someone who has a score of greater than 3 those are patients who are in a lower risk category or someone who has a score between 3 and 4.5 those are in the moderate risk category and over 4.5 is in a high risk category.

The lecture PERC Rule and Calculating Risk by Sharon Bord, MD is from the course Respiratory Emergencies.

### Included Quiz Questions

1. PERC positive means having at least two of the evaluated parameters in the PERC rule
2. The following are evaluated using PERC rule: age, heart rate, oxygen saturation, estrogen use, history of DVT, recent trauma/surgery, hemoptysis, or unilateral leg swelling
3. If the risk of embolus is < 2 %, no further work up is indicated
4. If a patient fulfills the 8 PERC criteria, the risk of pulmonary embolus is < 2%
5. It should be used only in patients who are low risk by Well’s criteria
1. Hemoptysis is equal to 2 points
2. A score of 2 is considered low risk
3. A score of 4 is considered moderate risk
4. A score of greater than 4.5 is considered high risk
5. Clinical signs and symptoms of DVT is equal to 3 points

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