Background: Prehospital thrombolysis in a mobile stroke unit (MSU, CT ambulance) reduces onset to treatment times compared with conventional ED delivery of IV tPA. Studies to determine if MSU thrombolysis improves final functional outcome have been underpowered, but can provide preliminary estimates of benefit magnitude.
Methods: We analyzed group outcome data from the PHANTOM-S Observational Registry Study (Kunz et al, 2016). For all possible dichotomizations of the modified Rankin Scale (mRS) of global disability (mRS), net benefit per thousand (BPT) treated patients were derived by multiplying absolute risk differences by 1000 and number needed to treat (NNT) by taking the inverse of absolute risk difference. For benefit in shifting patients to any lower disability level across all 6 functional transitions on the mRS, BPT and NNT were derived using the algorithmic joint outcome table method.
Results: Group data were available for 305 patients treated with IV tPA in an MSU and 353 patients treated conventionally in the ED. Of the 6 cutpoints on the mRS, 5 showed more favorable outcomes with MSU care and 1 more favorable outcome with conventional care. The Table shows resulting Benefit per Thousand and NNT values. For the 6 possible dichotomizations of the mRS, the benefit per thousand patients ranged from -21 to 93, with the greatest benefit seen at 0-3, and a BPT of 58 for the study primary outcome of freedom from disability (mRS 0-1). For benefit of improving by 1 or more mRS levels across all 6 transitions of the mRS, the BPT was 182 and NNT 5.5.
Conclusions: This preliminary estimate indicates that, out of every 1000 patients treated with prehospital, MSU thrombolysis rather than conventional ED thrombolysis, care, 182 will have a less disabled final outcome, including 58 more who would be free from disability. If confirmed in larger controlled clinical trials, these findings suggest that MSU-based thrombolysis would have a substantial clinical benefit.