Microcirculation in Prehospital Medicine

Emergencies

Microcirculation, prehospital care, risk stratification

Diagnostic and risk stratification are limited in emergencies. The measurement of microcirculation might identify patients with poor perfusion but compensated macrocirculation such as in beginning shock. This proof-of-concept study will examine whether sublingual prehospital sidestream dark field microscopy is feasible. This prospective observational study will include patients receiving medical aid by an emergency ambulance who had a spontaneous circulation and offer access to the sublingual mucosa. Sublingual measurement of microcirculation will be performed using a sidestream dark field camera. Video-quality will be evaluated with MIQS (microcirculation image quality score). AVA 4.3C software will calculate microcirculatory parameters.

Risk stratification is a key element in emergency medicine and there is great interest to identify and validate novel tools and parameters. These tools must be are easy to handle even in the emergency setting by emergency physicians and paramedics. The main challenge for these tools is to identify critically ill patients, but usually, an ambulance disposes on clinical examination and basic hemodynamic values. Therefore, diagnostic tools are limited to the assessment of macrocirculatory values, which are not very reliable and might not necessarily reflect factual organ perfusion. Focusing only on macrocirculation might mask already ongoing impaired organ perfusion as tissue hypoxia is crucial and microcirculatory collapse or at least dysregulation occurs very early. Reduced microcirculation might result in attenuated cellular nutrient and oxygen supply that might result in severe cell damage. In fact, impaired microcirculation is ubiquitous in shock and can be found even in the setting of hemodynamic compensation. An impaired microcirculation is often the very first sign of alarm for deteriorating critically ill patients. A promising way to identify patients with impaired microcirculation is the use of sublingual IDF- and SDF-measurement (IDF: incident dark-field; SDF: sidestream dark field) devices as sublingual microcirculation is a suitable target because it reliably reflects organ perfusion. Measuring sublingual microcirculation has already been used to identify high-risk patients in many intra-hospital or experimental settings. These measurement tools are easy to use hand-held devices. The newest generation of SDF offers the great improvement of automatic software which independently calculates various microcirculatory parameters. Therefore, there is no need for the treating physician to interpret the videos by himself. This investigation will take place in the ambulance emergency service of the metropolitan area around Düsseldorf, Germany. To participate in the study, patients must meet the following criteria: 1) the call for an acute emergency outside the hospital with the indication for sending out an emergency doctor, 2) a spontaneous circulation without previous resuscitation, 3) informed consent, 4) the sublingual mucosa must be accessible. The following data will be collected: age, sex, cause for emergency alarm (cardiac reason, respiratory reason, gastroenterological, oncological, general internal medicine, renal, neurological, psychiatric, paediatric, traumatic), and the National Advisory Committee on Aeronautics' (NACA), that ranges from 0 = no injury, 7 = lethal injury severity score. Vital parameters (heart rate, non-invasive blood pressure, peripheral oxygen saturation) will be measured using a standard out-of-hospital monitoring device (Corpuls3 (GS Elektromedizinische Geräte G. Stemple GmbH, Kaufering, Germany)). Mean arterial pressure (MAP) will be calculated as follows: (2 \* diastolic pressure + systolic pressure) /3. The capillary refill was evaluated in a standardized manner as described by Hernandez et al. Only sufficiently trained investigators will perform measurements. The microcirculation will be assessed by the implementation of the sidestream darkfield microscope (MicroScan® device, Microvision Medical, Amsterdam, The Netherlands). At the tip of the device, a highly sensitive camera digitally records the sublingual capillary network. The software analysis can directly be performed and visualized on a tablet screen. Additionally, the videos will be saved for later analysis. A suitable tablet computer will be used (Microsoft Surface Pro 4, (Redmond, Washington, USA). After acquisition of the videos, a validated automatic algorithm-software (AVA, Version 4.3 C) will perform the analyses. According to the second consensus on the assessment of sublingual microcirculation in critically ill patients (European Society of Intensive Care Medicine), the following parameters of microcirculation will be assessed both for all and for small vessels: PPV (Percentage of Perfused Vessels), NC (Number of Crossings), PNC (Perfused Number of crossings), TVD (Total Vessel Density), PVD (Perfused Vessel Density). The study plans to include at least 25 patients.

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