Objectives <p>Hypotension and shock are potential modifiable contributors to adverse outcome. Inhospital, invasive blood pressure (IBP) monitoring is standard, while prehospital care mainly uses non-invasive blood pressure measurement. This study tested whether prehospital IBP monitoring improves shock index (SI) at hospital admission.</p> Methods <p>This prospective interventional study included patients requiring prehospital intubation, catecholamines, or fluid resuscitation. Patients were assigned to prehospital IBP or Non-IBP group – according to the directives of the emergency physician. Primary endpoint was the SI at hospital admission. Secondary endpoints included catecholamines doses, fluid volume and arterial blood gas parameters (pH, lactate, base excess) at admission. Multiple regression analysis assessed whether IBP independently influenced SI at hospital admission.</p> Results <p>392 patients were enrolled, and 19.6% (n = 77) had prehospital IBP. The IBP group had a significantly lower shock index at hospital admission (mean ± SD: 0.77 ± 0.4 with IBP vs. 0.93 ± 0.5 with NIBP; p = 0.002). Multiple regression analysis showed that IBP was independently associated with a lower shock index. IBP patients received more catecholamine boluses (2.1 ± 2.5 vs. 1.2 ± 1.8; p &lt; 0.001), had more frequent use of continuous catecholamines (35.1% vs. 21.6%; p = 0.017), higher pH (7.34 ± 0.13 vs. 7.25 ± 0.16; p &lt; 0.001) and less negative base excess (-3,8 ± 5.2 vs. -6.0 ± 7.8; p = 0.004) while lactate levels were lower (3.6 ± 3.2 vs. 4.4 ± 4.2; p = 0.047).</p> Conclusions <p>Prehospital IBP monitoring significantly was associated with a decreased shock index at hospital admission in critically ill patients, likely due to earlier detection of hypotension and targeted hemodynamic therapy. IBP should be considered in patients receiving catecholamines.</p> Graphical Abstract <p></p>