Time from arrival on-scene until initial CCT in this study was 79 min in patients receiving prehospital invasive blood pressure measurement and 73 min in those who had it initiated in the resuscitation room, revealing no significant difference. However, the on-scene time of the physician response units (45 min vs. 36 min) was prolonged in those with prehospital invasive blood pressure measurement.

Data of on-scene times for prehospital induction of emergency anesthesia in similar systems varies. In a retrospective study from Finland evaluating 4496 patients with both traumatic and non-traumatic indications for prehospital intubation, median on-scene time was 33 (23–45) minutes in case of first pass success and 40 (29–52) minutes if two or more intubation attempts were required [16]. Two Australian studies showed markedly longer on-scene times. In an investigation of patients with stroke (both ischemic and hemorrhagic) and advanced airway management, mean time from arrival on-scene to transport was 58 min [17]. In a more heterogenous group of patients with non-traumatic brain injury, median time on-scene was 77 min [18].

The nominal difference of six minutes in the time from arrival on-scene to CCT is slightly longer compared to previously published data. In a previous study in our system by Wildner et al., prehospital arterial cannulation required a median of two minutes and preparation of the invasive blood pressure set, which is usually carried out simultaneously, a median of three minutes [15]. Furthermore, time between arrival on-scene and initial CCT did not differ in patients with isolated traumatic brain injury and on-scene times were prolonged only by a median of three minutes in the prehospital invasive blood pressure measurement cohort [19].

Reasons for this difference remain speculative and the following aspects might play a role in this:

In this study patients suffering from stroke were investigated. Compared to trauma victims, these patients are frequently older and may have pre-existing cardiovascular disease, for example arteriosclerosis. These comorbidities can make arterial cannulation difficult and time-consuming. In addition, a lot of emphasis by emergency medical systems is put on achieving short on-scene times—ideally within one hour—in trauma patients. This focus might be less pronounced in the care of non-traumatic patients.

Interestingly, in the exploratory analysis of the admission blood pressure, no difference between the two groups was found. Improved hemodynamic management due to invasive blood pressure measurement was previously shown in the in-hospital setting: improved hypotension detection and substantial decrease of hypotension during anesthetic induction led to the recommendation to establish invasive monitoring prior to induction in high-risk hospitalized patients [20, 21]. The observed discrepancy may be explained by our study’s methodology, which restricted blood pressure assessment to a single time point during handover in the resuscitation room. At handover, situations with a high risk of hemodynamic disturbances, such as anesthetic induction, have already been performed, and a steady state is commonly achieved. Further, blood pressure measured non-invasively could possibly underestimates the incidence of hypotension [22,23,24].

The question remains whether prehospital arterial cannulation for invasive blood pressure measurement, despite its association with a prolonged on-scene time in this study, provides sufficient clinical benefit to justify its out-of-hospital use. To fully answer this question, a large prospective randomized trial is necessary. However, the following aspects may potentially support it:

In the study by Fouche et al., longer on-scene times were associated with a higher probability of survival in patients with hemorrhagic stroke and prehospital rapid sequence intubation [25]. In contrast, the probability of survival decreased with longer on-scene times in patients with traumatic brain injury. Of course, an association of prolonged on-scene time and improved survival generally seems unplausible and the referenced study has a high risk of bias. However, this could still potentially indicate that there is some room and time for additional advanced prehospital interventions in patients with stroke and airway management providing a benefit despite slight on-scene time prolongation. Invasive blood pressure measurement is the in-hospital gold standard for these patients. This is primarily due to its capacity for rapid interventions facilitated by beat-to-beat analysis and the inherent advantages it offers in measurement accuracy compared to non-invasive methods. The authors of a retrospective study from a HEMS service in the United Kingdom, which concurrently measured invasive and non-invasive blood pressure values, concluded that non-invasive values are frequently inaccurate, particularly in patients with hemodynamic instability, and direct measurement should be considered [22]. A similar conclusion was reported in a study comparing invasive and non-invasive measurements in in-hospital patients with stroke. Patients with systolic blood pressures above 180 mmHg had a mean non-invasive value 19.8 mmHg (95% confidence interval 12.2–27.4) below the invasive measurement [26]. This is, especially in patients having hemorrhagic stroke, of high relevance. In these patients, close blood pressure monitoring with narrow limits is recommended in guidelines [9, 27].

A recent randomized trial evaluated prehospital blood pressure management in patients with stroke and provided neutral outcomes. However, in the subgroup of patients with hemorrhagic stroke, a lower odds ratio for poor functional outcome was shown if strict blood pressure management (aiming at a systolic blood pressure of 140 mmHg) was performed in the prehospital phase compared to usual care (treatment only of systolic blood pressure was above 220 mmHg) [28]. In a retrospective study conducted in Australia, the intracranial blood volume measured in the admission CCT was positively correlated with the prehospital systolic blood pressure in patients with intracranial hemorrhage [29]. At the same time, it has been shown that critical blood pressure drops, which frequently happen during induction of anesthesia, are associated with worse outcomes in patients with ischemic stroke injury [30, 31].

There are several limitations to this study. Due to the retrospective nature and hence absence of randomization, causal inference cannot be drawn and an indication bias might be present. To address this, stringent propensity score matching was performed to mitigate potential biases and strengthen the reliability of the findings. Prehospital systems vary worldwide and therefore, these findings may not be directly translatable to countries with different out-of-hospital structures. Moreover, because only patients with documented arterial access were included, patients with failed cannulation could not be identified, introducing potential bias that could not be accounted for. However, in two studies evaluating arterial access in a prehospital population, unsuccessful cannulation was rare [15, 32]. Hemodynamic parameters obtained in the prehospital setting would be of great interest and offer additional valuable insights. Nevertheless, a direct comparison of prehospital blood pressure measurements was not possible, as not all prehospital records provided the necessary detail and precision required for scientific analysis. Furthermore, the sample size is limited, which has to be accounted for when interpreting the results.