Background: Last known well time (LKWT) is increasingly used by EMS systems to identify acute stroke patients appropriate for direct routing to Stroke Centers. However, determining LKWT in the field is challenging, as patients may be aphasic, witnesses may not be available on scene, and rapid departure from the scene is desirable.
Objective: To characterize the concordance and degree of discordance between prehospital-determined LKWT and final LKWT documented at the hospital.
Methods: This is a retrospective analysis of consecutive patients with positive prehospital stroke screens transported to an approved stroke center in a large metropolitan system from January 2011 to December 2014. Data was abstracted from the regional EMS Agency stroke database. Patients with missing prehospital or hospital documentation of LKWT were excluded. The percent concordance and the median difference were calculated for prehospital versus final hospital documented LKWT. The effect of patient characteristics on discordance was also explored via multivariate regression analysis.
Result: Among the 9,810 patients transported for suspected stroke, the median age was 75 (Interquartile range [IQR] 62-85) years, 53% were women, 67% White, 11% Asian, 9% Black and 27% Hispanic. The median NIHSS was 11 (IQR 4 to 20). 83% had a cerebrovascular final diagnosis, ischemic stroke (IS) being the most common (n=5160, 53%), whereas 17% had a non-stroke-related diagnosis. There were 6873 patients missing either prehospital or hospital documentation of LKWT leaving 9810 patients for the analysis. Prehospital and hospital documented LKWTs were exactly equal in 42% of patients (36% for IS), within 15 minutes in 53% (48% for IS), within 1 hour in 66% (63% in IS) and within 2 hours in 70% (68% in IS). The median difference in LKWT between documented prehospital and hospital values was 0 minutes (IQR -6 to 18). The degree of discordance in LKWT did not vary with patient sex, race, or Hispanic ethnicity.
Conclusions: Paramedic-documented LKWT was within 15 minutes of the final hospital documented LKWT in just over half of acute stroke EMS transports and within 1 hour in two-thirds.. As accurate LKWT determination in the field is challenging, time of symptom onset should be confirmed after hospital arrival.