Blood Vessel Occlusion by the Layperson Audiovisual Assist Tourniquet (LAVA TQ) Compared to the Combat Application Tourniquet: Randomized Controlled Trial

Introduction While windlass-rod style tourniquets stop bleeding in limbs when used by skilled responders, they are less successful in the hands of the untrained or not recently trained public. To improve usability, an academic-industry partnership developed the Layperson Audiovisual Assist Tourniquet (LAVA TQ). The LAVA TQ is novel in design and technology and addresses known challenges in public tourniquet application. A previously published multisite, randomized controlled trial of 147 participants showed that the LAVA TQ is much easier for the lay public to use compared to the Combat Application Tourniquet (CAT). This study evaluates the LAVA TQ’s ability to occlude blood flow in humans compared to the CAT. Methods This study was a prospective, blinded, randomized controlled trial to demonstrate the non-inferiority of the LAVA TQ to occlude blood flow when applied by expert users compared to the CAT. The study team enrolled participants in Bethesda, Maryland, in 2022. The primary outcome was the proportion of blood flow occlusion by each tourniquet. The secondary outcome was surface application pressure for each device. Results The LAVA TQ and CAT occluded blood flow in all limbs (21 LAVA TQ, 100%; 21 CAT, 100%). The LAVA TQ was applied at a mean pressure of 366 millimeters of mercury (mm Hg) (SD 20 mm Hg), and the CAT at a mean pressure of 386 mm Hg (SD 63 mm Hg) (P = 0.14). Conclusion The novel LAVA TQ is non-inferior to the traditional windlass-rod CAT in occluding blood flow in human legs. The application pressure of LAVA TQ is similar to that used in the CAT. The findings of this study, coupled with LAVA TQ’s demonstrated superior usability, make the LAVA TQ an acceptable alternative limb tourniquet.


Background:
Immediate hemorrhage control with a limb tourniquet has been life-saving both on and off the battlefield. 1, 2 The US military estimates that tourniquets saved more than 1,000 lives in Iraq and Afghanistan, and tourniquets are now being used throughout communities and hospitals across the United States. 1 The Stop the Bleed (STB) campaign, launched at the White House in 2015, brings these battlefield medical lessons home by teaching the public to control hemorrhage prior to the arrival of an ambulance. 3,4 Rapid tourniquet application -a core STB principle -is now the first-line treatment for extremity hemorrhage in mainstream public education guidelines. 5 While CAT and other windlass-rod tourniquets can stop bleeding, the public is typically no more than 20% successful at applying them without training. 6 Even with training, the public's ability to apply tourniquets successfully drops rapidly to about 50% mere months after training. 7 While widely available windlass-rod style tourniquets, such as the Combat Application Tourniquet (CAT), can stop bleeding when used by skilled responders, they are not intuitively designed. The non-optimized design makes them difficult for the minimally or untrained public to achieve successful extremity hemorrhage control. Multiple studies have shown poor performance by untrained layperson users, as well as rapid skill loss after training. [6][7][8] windlass rod mechanism found in many standard tourniquets with an intuitive seatbelt design as the tourniquet's strap and a user-friendly knob for tightening. Like a seatbelt in a vehicle, LAVA TQ will tighten to snug against the extremity once the belt is clicked into place. This action removes the initial tightening step required in most standard windlass rod tourniquets, thereby requiring fewer steps to apply. LAVA TQ guides the user to successful application with a series of lights, color cues, pressure application feedback and audio instructions.

Methods:
This study is a prospective, blinded, randomized controlled trial to assess non-inferiority of the novel LAVA TQ (experimental arm) to occlude blood flow in human volunteers when compared to the CAT (control arm). The Uniformed Services University's (USU) Institutional Review Board reviewed and approved this study (USUHS.2020-060), and it is registered on the National Library of Medicine's Clinical Trials website (clinicaltrials.gov, NCT05504733).
We performed an a priori power calculation for a parallel group non-inferiority trial. We assumed that all tourniquet applications, in both the control (CAT) and experimental (LAVA TQ) study arms, would occlude blood flow. We then calculated a minimum sample size of 13 applications with each device (26 total) to have 80% power to detect a 10% difference (noninferiority limit) in performance between the two devices. With IRB permission, we enrolled a total of 21 participants to undergo 42 applications (one device on each leg) by medical professionals. The primary outcome is the proportion of CAT applications compared to LAVA TQ applications that occluded blood flow in human volunteers. The secondary outcome is the surface pressure of an applied CAT tourniquet compared to an applied LAVA TQ tourniquet in human volunteers. We recruited healthy participants to undergo application of tourniquets to both of their legs. The exclusion criteria were: age less than 18 or greater than 65 years old, hypertension, prior vascular surgery, peripheral vascular disease, diabetes, prior lower extremity surgery, active lower extremity infection, any hypercoagulable condition, pregnancy, or any condition in which participants felt they may suffer harm from brief tourniquet application. Participants were recruited via email messages sent to members of the USU community, as well as word of mouth.
Participants were not compensated. Studies involving military members and students at USU are reviewed and approved by a series of offices, including the Office of Student Affairs and military chain of command to prevent coercion of participants. This study protocol obtained all the routine approvals prior to execution.
The study team collected all data on May 9 th , 2022 on the USU campus in Bethesda, Maryland.
Twenty-one participants arrived at a pre-scheduled time, and then completed a screening questionnaire to verify eligibility (Table 1, Figure 2).   was not linked to the participant, and no personally identifying data was collected as part of the study. The randomization occurred in blocks with the first 10 participants assigned to begin the study with CAT application, and the next 11 participants were assigned to begin the study with the LAVA TQ application. Study observers evaluating blood flow were blinded to the participants randomization. Participants completed a pre-study questionnaire consisting of basic demographic information, height, and weight. Then study team members measured and recorded their resting brachial blood pressure and calf circumferences 10 cm distal to the tibial plateau.
Following the enrollment procedures, participants underwent the first part of the study. The participant removed shoes and socks from both feet and removed or moved any clothing distal to their knees. A trained observer, then entered the study room, and used a handheld Doppler ultrasound to detect the participant's dorsalis pedis pulse in each foot. The observer used a surgical marker to place an "X" at the location of the detected pulse on the participant's foot, and then left the room. One of two trained medical professionals, both with military medical experience and a history of numerous CAT applications, applied either a CAT or LAVA TQ, as determined by randomization, to one of the participant's legs. The medical professionals were trained to use LAVA TQ prior to the study. Neither medical professional was involved in LAVA TQ's development or had financial or intellectual property interest in the device. The medical professionals also did not assist with study design. The medical professionals applied the tourniquet at a standardized location on all participants: 10 cm distal to the tibial plateau. The medical professionals applied the tourniquet until they thought it was tight enough to stop blood flow. As soon as the tourniquet was applied, the medical professional covered the tourniquet and

Results:
The 21 study participants had a mean age of 28 years old (range 22-51 years old), a mean weight of 81 kg (range 50-132 kg), and 26% of them were female (Table 1). For the study's primary outcome, the medical professionals occluded blood flow in all participants in both the experimental LAVA TQ arm (n=21, 100%), and the control CAT arm (n=21, 100%) ( Table 2).
For the study's secondary outcome of tourniquet application pressure, the LAVA TQ was applied at a mean pressure of 366 mm Hg (SD 20 mm Hg), and the CAT was applied at a mean pressure of 386 mm Hg (SD 63 mm Hg) ( Table 2). The difference in application pressures was not statistically significant (P = 0.14). Table 2 Blood Tourniquets are now widely recommended for use by the public as the first-line treatment for life-threatening extremity hemorrhage. 5,12 While existing standard tourniquets can occlude blood flow, there are multiple studies that show the public has difficulty applying them if they have never been trained to apply a tourniquet, if they have not been trained within the past several weeks, or if they do not have adjunctive aids to assist them. 6,13-15 Since many Americans will not receive ongoing or refresher STB training, finding alternative methods or devices to assist tourniquet application at the point of injury is essential. In fact, utilizing audiovisual instructions to assist tourniquet application was one of the five original goals of the Stop the Bleed campaign. 4 The LAVA TQ is the first device to bring this goal to reality, and this study public who may use the LAVA TQ eventually. We used professionals to ensure that we could attribute an inability of either device to occlude blood flow to device design, rather than human application error. The neonatal blood pressure cuff measuring system has been described previously but has limitations. 16 The use of air in the measurement cuffs, rather than an incompressible liquid, could cause some variation from the actual pressures applied due to cuff deformation or air leakage. We anticipate that any errors due to cuff performance would affect LAVA TQ and CAT equally, but this is not certain.
Tourniquet application is a painful procedure. We did not survey the participants specifically about application pain of the two tourniquets. However, multiple participants remarked spontaneously to the study team that the LAVA TQ was less painful than the CAT. This is likely due to the wider strap on LAVA TQ compared to CAT, and it could be a useful area for future investigation.

Conclusion:
The novel LAVA TQ is non-inferior to a traditional windlass-rod CAT in occluding blood flow in human legs when applied by a trained medical professional. The surface application pressure of LAVA TQ is similar to CAT in healthy volunteer study subjects. The findings of this study confirm LAVA TQ as an acceptable alternative limb tourniquet for occluding blood flow. Study of LAVA TQ's performance in real-world bleeding situations is warranted.