EMS & LKNs in Wake-up Stroke

This study regarding EMS determining last known normal is set to be published this month in ‘Stroke’.

In the abstract the authors compared the Last Known Normal time of stroke patients as determined by EMS to the Last Known Normal time as determined by a neurologist. In 91% of cases the EMS-determined time was within 15 minutes of the neurologist-determined time. However when looking at types of stroke, EMS struggled with determining the LKN time in wake-up strokes. (A ‘wake-up stroke’ is a phrase referring to strokes which occur overnight and are discovered when the patient or the patient’a family awakens)

The mean difference between the neurologist-determined time and the EMS-determined time was 208 minutes.We reached out to the authors of the study to provide commentary and thoughts as to this result. The principle investigator, Dr. David Curfman of Washington University, graciously provided the following:

“Our paper did not look at the specifics of each EMS interaction, so I can’t really say how/why the EMS providers came to a specific time. We thought possibilities included asking when they noticed the symptoms and not clarifying when the patient was last well or the lack of witnesses to corroborate a time, so they assumed time of onset was when call was placed, but these are just guesses. Overall, it is good that when EMS are unsure of the LKN, they assume the more recent time as it is better to evaluate for tPA than to miss potential tPA eligible patients. 

Anectdotally, there are patients that when asked “when did this start” will state the time they woke up, but if you ask when they were last normal, state a time prior to going to bed.
I do not have a specific line of questioning to recommend but generally the best way to obtain LKN is to ask “when did you last feel normal” or something similar. With wake up strokes in particular, not only is it important to find out bedtime/time last feeling well, but also it is important to ask about any night time awakenings and if they felt normal during that time as well because sometimes people will not think of waking up to go to the bathroom at 2 AM, for example, until they are pushed to recall it.
I also hope that awareness that wake-up strokes are prone inaccuracy in LKN will in itself help improve times as providers are aware they need to be more conscious of the history taking for these patients.”
Dr. Curfman makes a number of excellent points, especially in his closing sentence. It bears repeating:“[EMS providers] need to be more conscious of the history taking for these patients.”While time is a precious commodity during a ‘Code Stroke’, it’s a good reminder that EMS has a pivotal role in acquiring vital patient information. Taking a history is a skill just as any other. Be sure to employ a thorough line of questioning!

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