The “Tiny Tips” series aims to provide helpful memory aids for remembering difficult to recall exam material for emergency medicine. You can get all of them compiled in an easy-to-review way by downloading the Tiny Tips deck of Boring Cards. This post outlines a mnemonic to help remember the PERC rule (Pulmonary Embolism Rule-out Criteria).
PERC is a useful clinical decision rule to help rule-out pulmonary embolism in patients a clinician’s gestalt suggests are low risk. It was developed by Kline in 2004 and validated by him in a prospective, multicenter trial in 2008. As outlined by very well by Chris Nickson on Life in the Fast Lane in much greater depth, a very low risk patient (estimated at <15%) that is PERC(-) is as likely to be harmed by the work-up (think cancer, contrast nephropathy, anaphylaxis) as they are to have a PE in the first place (they are below the test threshold). Knowing this rule is helpful both clinically and for exam purposes (although I’d highly recommend using a smartphone checklist when applying the rule in clinical practice). I remember it using the (aptly named) HAD CLOTS mnemonic that I have added to the Boring Cards deck.
- H – Hormone (estrogen) use
- A – Age > 50
- D – DVT or PE history (have they HAD CLOTS?)
- C – Coughing blood
- L – Leg swelling disparity
- O – O2 sats < 95%
- T – Tachycardia (>100bpm)
- S – Surgery or Trauma (recent)
The subtleties of this clinical decision tool are discussed well elsewhere (also see the unfortunately unFOAMy but still awesome 2013 update on EM:RAP), but it is important to apply it with the gestalt criteria for use (it is bolded, italicized and colored above) and remember that it is only is an all-or-none proposition used to RULE OUT PE (it’s not for risk-stratification!). While a low-scoring patient may be a low risk patient, if any of the criteria are positive they are not PERC(-) and an appropriate combination of Wells/Geneva/DDimer/CTPA should be used to rule out this diagnosis.
This mnemonic may not be new to many of you, but it is one of the ones I use most frequently and I wanted to get it into the deck so I would quit forgetting what the damn C stands for!