Framework for developing intracerebral haemorrhage recognition scales and technologies for hyperacute prehospital blood pressure lowering

Background Hyperacute prehospital blood pressure (BP)-lowering in randomised trial setting improves outcomes for intracerebral haemorrhage (ICH) but worsens outcomes for acute cerebral ischaemia. Consequently, hyperacute antihypertensive therapy could potentially aid prehospital patients identified as likely having ICH by clinical scales and diagnostic technologies. The required diagnostic performance characteristics needed to yield net benefit have not been well-delineated. Methods We modelled 3-month global disability (modified Rankin Scale, mRS) outcomes using magnitude of beneficial and harmful effects of BP-lowering in the INTERACT 4 trial to develop a two-stage algorithm. In stage 1, positive predictive values (PPVs) are converted to net treatment effect for different ordinal/dichotomised and utility-weighted mRS outcomes. In stage 2, for continuously varied prehospital diagnostic test sensitivity, specificity and disease prevalence, PPVs for ICH are output. Results As PPVs increase, progressively enriching the test-positive population with actual ICH patients, the effect of treating likely ICH patients changes from net harm to neutrality to net benefit for all analysed 3-month outcomes: For the functional independence outcome, treating test-positive likely ICH patients with BP-lowering reached minimal clinically important difference (MCID) desirable for a very simple intervention in mRS 0–2 increase at PPV of 39% and the outcome-specific MCID increase at PPV of 67%. At 67% PPV, among every 1000 patients treated, 130 would have less disabled outcome, including 50 more achieving functional independence. Conclusions This study developed an analytic framework to determine, for all possible combinations of test sensitivity, specificity and ICH prevalence, the effect on global disability outcomes of prehospital BP-lowering among patients identified as likely ICH.