Healthy Adults Aged 18-55, Three Ukrainian Windlass Tourniquets (SICH, DNIPRO GEN 2, PULS) Compared With CAT Gen 7, and Complete Limb Arterial Occlusion Confirmed by Doppler.

Background Heavy bleeding from an injured arm or leg is one of the main causes of preventable death among people wounded in combat and in serious civilian accidents. A limb tourniquet is a strap placed around the limb above the wound. It is tightened by turning a rigid rod (the "windlass") until blood flow below it stops. International guidelines for combat casualty care (TCCC) recommend applying a windlass tourniquet immediately as the first step to control life-threatening limb bleeding. Wide use of such tourniquets, together with training, has saved many lives.

In Ukraine, several windlass tourniquets are manufactured locally, including SICH, DNIPRO GEN 2 and PULS. They are already widely used by the Armed Forces of Ukraine, alongside internationally recognized devices such as the Combat Application Tourniquet (CAT Gen 7). CAT is the reference tourniquet recommended by the U.S. Committee on Tactical Combat Casualty Care and has the largest body of evidence. Laboratory testing has shown that the Ukrainian tourniquets can stop arterial blood flow. However, they have never been compared directly with CAT in a randomized clinical study with blinded assessment of the result.

This study is therefore designed to:

provide independent, standardized clinical data to support a National Standard of Ukraine for windlass tourniquets.

Study design TORQUE is a prospective, randomized, controlled, open-label clinical investigation with a blinded outcome assessor. It takes place at a single site in Kyiv, Ukraine: the National Institute of Traumatology and Orthopedics of the National Academy of Medical Sciences of Ukraine. It is conducted according to with the principles of the Declaration of Helsinki, ISO 14155:2026 (Good Clinical Practice for medical device studies), and the applicable Ukrainian regulations. It is a non-commercial study. This study is funded by the UK Government through the Foreign, Commonwealth \& Development Office (FCDO), with project implementation support provided by Alinea International Limited in Ukraine. The Acting Sponsor is a Ukrainian public organization "FUND FOR EXPERT SUPPORT OF GOVERNANCE AND ECONOMIC DEVELOPMENT" (EDGE). No medical device manufacturer is involved in the funding, conduct, management, or analysis of the study.

About 120 healthy adult volunteers will take part. They will be randomly assigned in equal numbers (40 each) to one of three device pairs:

CAT Gen 7 and SICH CAT Gen 7 and DNIPRO GEN 2 CAT Gen 7 and PULS

Each participant receives both devices in their pair, one at a time, on two different study days at least 24 hours apart. One device is placed on the upper arm and the other on the thigh, on the same side of the body. The order of the two devices, and which device goes on the arm or the thigh, is also chosen at random. Comparing both devices in the same person reduces the effect of differences between people.

All tourniquets are applied by trained and certified study staff, never by the participants themselves. A thin, standardized protective layer of gauze is placed under each tourniquet to protect the skin. Each application lasts no more than 120 seconds. The tourniquet is released immediately once blood flow is confirmed to be stopped, once 120 seconds have passed, or at any moment the participant asks.

The devices look different, so staff and participants know which device is used. To keep the main result objective, the doctor who checks blood flow with Doppler ultrasound does not know which device is being tested. This doctor sits behind a screen and wears noise-cancelling headphones during application.

What is being measured The main outcome is whether each tourniquet completely stops arterial blood flow below it within 120 seconds of the first turn of the windlass. Complete occlusion means no blood flow signal in the artery of the wrist or foot for at least 10 seconds, confirmed by several Doppler ultrasound methods. The study tests whether each Ukrainian device is not meaningfully worse than CAT Gen 7, defined as no more than 10 percentage points lower in success rate.

Other outcomes include:

• time needed to stop blood flow;
• pain, rated on a 0-10 cm visual analogue scale, and comfort, rated on a 1-5 scale, at four time points;
• return of normal blood flow 1 and 30 minutes after removal;
• skin temperature around and below the tourniquet, measured with an infrared thermometer, as an indicator of even pressure and recovery of circulation;
• how reliably each device can be applied, including number of attempts, loss of tension and slipping;
• any device faults;
• side effects such as numbness, tingling, bruising or pain lasting more than 24 hours.

A structured record of device faults will be shared with the manufacturers to help improve technical specifications.

What participants will do Screening visit: consent, vital signs,medical history, physical examination, ECG, blood, urine tests, and a pregnancy test for women, tests for hepatitis B (HBsAg) and hepatitis C (anti-HCV) on the blood sample, and a rapid HIV test using a mouth swabblood.

Day 1 and Day 3: a tourniquet is applied once on each day, with ultrasound checks before, during and after application. Participants rate their pain and comfort and stay at the site until normal circulation is confirmed.

Follow-up phone calls: on Day 2, Day 4 and Day 6. An extra clinic visit is arranged only if a side effect is reported.

Total time in the study is about 10 days, from screening to the last phone call.

Safety

Brief tourniquet use in healthy people commonly causes temporary pain, skin marks, redness or numbness. These usually go away quickly. Serious harm is very unlikely with an application time of 120 seconds or less. Measures that reduce risk include:

• strict eligibility criteria that exclude people with vascular, nerve, blood-clotting or other relevant conditions;
• trained staff and continuous medical supervision;
• the 120-second time limit and the protective gauze layer;
• a rest period between applications; follow-up phone calls.

An independent Data and Safety Monitoring Committee will review safety data, including any serious adverse event. Participants may leave the study at any time without giving a reason.

Who can take part Healthy civilian men and women aged 18 to 55 years with a body mass index of 18.5-29.9 kg/m² can take part. Military personnel, pregnant or breastfeeding women, and people in dependent relationships with the study organizers are not included. This ensures that participation is fully voluntary.

Expected use of results Results will be reported for each device separately. They are intended to be published in a peer-reviewed journal, with no participant identifiable.