Efficacy and Performance of an Automated Pneumatic Tourniquet: A Doppler-Verified Observational Study
An analysis of time-to-occlusion and required pressure relative to limb circumference
Abstract
Background: Rapid and effective hemorrhage control is critical for improving outcomes in trauma. This study evaluates the performance of the AutoTQ®, a novel automated tourniquet, in achieving vascular occlusion.
Methods: An observational study was conducted with 31 healthy volunteers. The AutoTQ® was applied to the upper arm (n=28) and thigh (n=29), covering a wide range of limb circumferences (arm: 8.0-18.0 in; thigh: 17.5-32.5 in). Time to occlusion and final occlusion pressure were recorded, with arterial flow cessation confirmed by a 4MHz Doppler ultrasound.
Results: The AutoTQ® achieved a 100% success rate in occluding arterial blood flow across all 57 applications. The mean time to occlusion was significantly faster for the arm (3.6s) than the thigh (20.6s) (p < 0.001). The mean occlusion pressure was 276 mmHg for the arm and 295 mmHg for the thigh, with no statistically significant difference between the two. A moderate, statistically significant positive correlation was found between limb circumference and both occlusion pressure and time to occlusion for both limbs.
Conclusion: The AutoTQ® is a highly effective device for achieving rapid vascular occlusion across a diverse range of limb sizes at pressures lower than those reported for some windlass-style tourniquets. Its reliability and speed suggest it is a valuable tool for prehospital hemorrhage control.
1. Introduction
Uncontrolled hemorrhage remains a leading cause of preventable death in traumatic injuries, responsible for over 1.5 million deaths annually [1, 2]. The rapid application of a tourniquet is a life-saving intervention for extremity bleeding [3]. However, the efficacy of tourniquets is highly dependent on their design and the pressure they apply. Research has shown that narrow cuffs, such as those on many windlass tourniquets, create high pressure gradients that increase the risk of nerve and tissue damage [4]. Furthermore, studies have documented that windlass tourniquets can be applied with dangerously high pressures, sometimes exceeding 700 mmHg, far above what is necessary for occlusion [5]. The AutoTQ® is a novel automated pneumatic tourniquet designed to simplify application and provide controlled, effective pressure. This study aimed to objectively evaluate the performance of the AutoTQ® by measuring the time and pressure required to achieve complete vascular occlusion, verified by Doppler ultrasound, across a range of participants and limb sizes.
2. Materials and Methods
2.1 Study Design and Participants
A one-time, observational study was conducted in a controlled, non-clinical setting. The protocol (IRB ID: 2025-0372) was reviewed and approved by an independent review board via Expedited Review under 45 CFR 46.110. A total of 31 healthy participants were recruited via word-of-mouth. After providing informed consent, non-identifiable demographic data was collected. Two participants under 18 were evaluated with parental permission and under the supervision of their parents for internal evaluation purposes only and were not part of the formal IRB-approved study protocol.
2.2 Procedures
Limb circumferences were measured for both the upper arm and thigh. The AutoTQ® device was then applied sequentially to the upper arm and thigh. A handheld Huntleigh 4MHz Doppler ultrasound device was used to detect arterial blood flow at the popliteal artery (behind the knee) for thigh applications and the brachial artery (in the elbow pit) for arm applications. Timing began at the moment the device's inflate button was pressed. Initial inflation was limited to 300 mmHg in most cases. If a pulse was still detected, the AutoTQ® pressure was increased until complete occlusion was achieved. Inflation was stopped immediately upon Doppler-confirmed occlusion, and the final pressure and time were recorded.
2.3 Statistical Methods
Descriptive statistics (mean, median, range, standard deviation) were calculated for all demographic and performance variables. Independent samples t-tests were used to compare the mean occlusion pressures and mean times to occlusion between the arm and thigh applications. Pearson correlation coefficients (r) were calculated to assess the strength and direction of the linear relationship between limb circumference and the performance metrics. A one-way analysis of variance (ANOVA) was used to compare means across different age groups. A p-value of < 0.05 was considered statistically significant for all analyses.
3. Results
3.1 Descriptive Statistics
A total of 57 successful occlusions were recorded (28 arm, 29 thigh) from 31 participants. The AutoTQ® achieved a 100% success rate. Key demographic and overall performance data are summarized in the tables below.
| Characteristic | Value |
|---|---|
| Gender Distribution | 20 Male (64.5%), 11 Female (35.5%) |
| Age Range | 8 - 62 years (Mean: 27.4 years) |
| Arm Circumference Range | 8.0 - 18.0 inches (Mean: 13.1 in) |
| Thigh Circumference Range | 17.5 - 32.5 inches (Mean: 23.8 in) |
| Metric | Upper Arm (n=28) | Thigh (n=29) |
|---|---|---|
| Mean Occlusion Pressure (±SD) | 276 (±54.4) mmHg | 295 (±68.7) mmHg |
| Median Occlusion Pressure | 250 mmHg | 300 mmHg |
| Mean Time to Occlusion (±SD) | 3.6 (±4.3) seconds | 20.6 (±15.9) seconds |
| Median Time to Occlusion | 3.0 seconds | 16.0 seconds |
3.2 Inferential Statistics
An independent-samples t-test indicated that the mean time to occlusion for the arm (M=3.6, SD=4.3) was significantly lower than for the thigh (M=20.6, SD=15.9), t(35) = -4.75, p < 0.001. However, there was no significant difference in mean occlusion pressure between the arm (M=276, SD=54.4) and the thigh (M=295, SD=68.7), t(55) = -1.13, p = 0.26.
Pearson correlation analysis revealed a moderate, positive correlation between limb circumference and occlusion pressure for both the arm (r=0.59, R²=0.35, p < 0.05) and the thigh (r=0.41, R²=0.17, p < 0.05). A similar correlation was found between limb circumference and time to occlusion for the arm (r=0.48, R²=0.23, p < 0.05) and thigh (r=0.45, R²=0.20, p < 0.05).
Figure 1. Pressure vs. Limb Circumference
Figure 2. Time to Occlusion vs. Limb Circumference
Figure 3. Mean Occlusion Pressure by Age Group
Figure 4. Mean Time to Occlusion by Age Group
A one-way ANOVA was conducted to determine if there were significant differences in occlusion pressure and time to occlusion between age groups (0-9, 10-19, 20-29, 30-39, 40-49, 50+). For occlusion pressure, there was no statistically significant difference between the groups, F(5, 51) = 0.75, p = 0.59. Similarly, for time to occlusion, there was no statistically significant difference between the age groups, F(5, 30) = 1.08, p = 0.39. This suggests that participant age was not a significant factor in the AutoTQ's performance in this study. This is a critical finding, as age and limb size are significant limiting factors for many windlass tourniquets, which are often too large to be used effectively on pediatric limbs [6]. As children are also susceptible to major hemorrhage, the AutoTQ's consistent performance across a wide age and size spectrum suggests it provides a viable solution for this vulnerable population.
4. Comparative Analysis
To contextualize the performance of the AutoTQ®, we compared our findings with published data on other commercially available tourniquets. Studies by Gabbitas et al. (2023) and Beaven et al. (2018) provide relevant data on the Combat Application Tourniquet (CAT).
4.1 Performance Comparison
| Tourniquet | Limb | Occlusion Pressure (mmHg) | Time to Occlusion (s) |
|---|---|---|---|
| AutoTQ® (Mean) | Arm | 276 | 3.6 |
| AutoTQ® (Mean) | Thigh | 295 | 20.6 |
| CAT (Mean/Median) | Thigh | 713 | 37.5 |
CAT pressure data from Gabbitas et al. (2023) on a simulated limb. CAT time data from Beaven et al. (2018).
The AutoTQ® demonstrated mean occlusion pressures significantly lower than those reported for the CAT. Furthermore, the AutoTQ® achieved occlusion on both the upper arm and thigh substantially faster than the CAT. This suggests that the AutoTQ® can achieve effective hemorrhage control with potentially less pressure and in less time, which may reduce the risk of iatrogenic injury and improve outcomes.
5. Discussion
The results of this observational study strongly indicate that the AutoTQ® is a highly effective and reliable device for achieving vascular occlusion. The 100% success rate across all 57 applications is a critical finding, particularly when compared to the high failure rates reported for other tourniquets in layperson hands. The automated inflation mechanism appears to remove significant user error associated with manual tightening.
The statistical analysis confirms a direct and significant relationship between limb circumference and required occlusion pressure, which aligns with physiological principles. The device's ability to achieve occlusion at pressures significantly lower than those reported for the CAT is a key advantage, potentially reducing the risk of compression-related nerve and tissue damage [4, 6].
The significantly faster time-to-occlusion for the arm compared to the thigh is an expected outcome due to the difference in limb volume and the corresponding cuff sizes. However, even on the thigh, the AutoTQ® achieved occlusion faster than reported median times for the CAT, highlighting its efficiency in critical situations.
Limitations: This study was conducted in a non-stress, controlled environment with healthy volunteers. Performance in a real-world trauma scenario may differ. The sample size (N=31) is sufficient for identifying trends but larger studies would be beneficial to confirm these findings.
6. Conclusion
This study provides objective, Doppler-verified evidence that the AutoTQ® is a highly effective and efficient device for achieving rapid vascular occlusion. It demonstrated a 100% success rate on both upper and lower extremities across a diverse participant pool, achieving occlusion at lower pressures and in less time than reported for the CAT. The data confirms a predictable, positive correlation between limb circumference and performance metrics, providing valuable data for refining training protocols. As children are also susceptible to major hemorrhage, and windlass tourniquets are often too large for pediatric limbs, the AutoTQ's consistent performance across a wide age and size spectrum suggests it provides a viable solution for this vulnerable population. These findings strongly support the AutoTQ® as a reliable and potentially safer tool for prehospital hemorrhage control.
7. References
[1] Alexander BT et al. The Public Access Bleeding Control (PABC) trial. Resuscitation. 2023;188:109747. doi:10.1016/j.resuscitation.2023.109747
[2] Latif, R. K., et al. (2023). Traumatic hemorrhage and chain of survival. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, 31, 25. https://doi.org/10.1186/s13049-023-01088-8
[3] Nyberger, K., et al. (2023). A systematic review of hemorrhage and vascular injuries in civilian public mass shootings. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, 31, 30. https://doi.org/10.1186/s13049-023-01075-8
[4] McEwen, J. A., & Casey, V. (2006). Measurement of hazardous pressure levels and gradients produced on human limbs by non-pneumatic tourniquets. Proceedings of the 28th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 510-513.
[5] Gabbitas, J. et al. (2023). Smart Tactical Application Tourniquet Versus Combat Application Tourniquet: Comparing Layperson Applications for Arterial Occlusion After a Video Demonstration. Cureus, 15(7), e42615.
[6] Beaven, A., et al. (2018). The Combat Application Tourniquet Versus the Tactical Mechanical Tourniquet. Journal of Special Operations Medicine, 18(3), 95-98.