Under Pressure: An Automated Tourniquet Performance Study

Abstract

Background: Rapid extremity hemorrhage control improves trauma outcomes. This study evaluates the performance of the AutoTQ®, an automated pneumatic tourniquet, across various limb sizes and body compositions.

Methods: In a controlled setting, 26 healthy adult participants underwent AutoTQ® application to the upper arm (n=26) and thigh (n=26). Time to occlusion (from inflate-button press) and occlusion pressure were recorded; distal flow was assessed by Doppler ultrasound. This study is novel in its analysis of tourniquet performance stratified by Body Mass Index (BMI).

Results: AutoTQ® achieved occlusion in 52/52 applications (100%). Mean time to occlusion was 5.1 s (arm) vs 19.9 s (thigh). Mean occlusion pressure was 289 mmHg (arm) vs 293 mmHg (thigh). Limb circumference showed moderate positive correlations with both pressure and time. No significant differences in performance were found across BMI categories.

Conclusions: In this controlled volunteer study, AutoTQ® produced rapid, Doppler-verified occlusion across a wide range of limb sizes and body compositions. Findings support further comparative and field evaluations. (Note: timing reflects inflation period only and excludes device placement.)

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 like the Combat Application Tourniquet (CAT), 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 on bench models, 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 with healthy adult volunteers. The protocol (IRB ID: 2025-0372) was reviewed and approved by an independent review board under 45 CFR 46.110. A total of 31 volunteers were recruited, including 4 minors who were excluded from this analysis. Of the 27 adult volunteers, one individual opted out of the procedure, resulting in a final analysis cohort of 26 individuals. After providing informed consent, non-identifiable demographic data were collected.

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 by a single trained operator; the order of application was not randomized. A handheld Doppler ultrasound device was used to detect arterial blood flow. Timing began at the moment the device's inflate button was pressed. Inflation was stopped immediately upon Doppler-confirmed occlusion. No adverse events were reported, and all applications were well-tolerated.

2.3 Statistical Methods

Descriptive statistics (mean, median, range, standard deviation) were calculated. As time data were skewed, medians with interquartile ranges (IQR) are reported. For applications where time was not recorded, the median time for the respective limb type was inferred. Pearson (r) correlation coefficients were calculated to assess relationships with limb circumference. A p-value of < 0.05 was considered statistically significant.

3. Results

3.1 Descriptive Statistics

A total of 52 successful occlusions were recorded from 26 adult participants. The AutoTQ® achieved a 100% success rate; one participant's leg application was considered successful although a distal pulse was not palpable prior to the procedure. Key demographic and performance data are summarized below.

Table 1: Adult Participant Demographics (N=26)

Characteristic	Value
Age Range	21 - 62 years (Mean: 32.5 years)
Arm Circumference Range	9.25 - 16.0 inches (Mean: 13.1 in)
Thigh Circumference Range	19.0 - 32.5 inches (Mean: 24.1 in)
Gender Distribution	19 Male (73%), 7 Female (27%)

Table 2: Participant BMI Distribution (N=26)

BMI Category	N	Percentage
Normal Weight (18.5-24.9)	13	50%
Overweight (25-29.9)	8	31%
Obese (≥30)	5	19%

Table 3: Performance by Limb Type (Adults)

Metric	Upper Arm (n=26)	Thigh (n=26)
Mean Occlusion Pressure (±SD)	289 (±66.0) mmHg	293 (±55.1) mmHg
Median Time to Occlusion (IQR)	3.0 (2.0 - 4.0) s	16.0 (15.5 - 20.0) s

3.2 Visual Analysis

Figure 1: Histograms showing the frequency distribution of occlusion pressures for arm (a) and thigh (b) applications. Figure 2: Histograms displaying the frequency distribution of the time to achieve occlusion for arm (a) and thigh (b) applications. Figure 3: Mean occlusion pressure (a) and time (b) across different BMI categories.

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), Beaven et al. (2018), and Wall et al. (2013) provide relevant data on the Combat Application Tourniquet (CAT).

4.1 Performance Comparison

Table 4: Performance comparison between AutoTQ® and CAT.

Tourniquet	Limb	Occlusion Pressure (mmHg)	Time to Occlusion (s)
AutoTQ® (Mean/Median)	Arm	289 / 280	5.1 / 3.0
AutoTQ® (Mean/Median)	Thigh	293 / 300	19.9 / 16.0
CAT (Median)	Arm	330	31.0
CAT (Mean/Median)	Thigh	410	37.5

CAT thigh pressure data from Gabbitas et al. (2023). CAT thigh time data from Beaven et al. (2018). CAT arm pressure data from Wall et al. (2013). CAT arm time data from Potac et al. (2021). Time metrics are not directly comparable due to different start/end points.

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 52 applications in adults demonstrates an equivalency in hemorrhage control efficacy to properly applied windlass tourniquets. The key difference lies in the pressure required to achieve cessation of distal blood flow; the AutoTQ® accomplished this at significantly lower pressures than those often reported for the CAT.

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]. While not statistically significant in this study, a trend towards higher mean occlusion pressures was observed in participants with higher BMIs, suggesting that body composition may influence the pressure required for occlusion due to increased tissue depth.

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, it is critical to note that our timing metric captured inflation time only and is not directly comparable to studies measuring total application time for manual devices.

Limitations: This study has several limitations. It was conducted in a non-stress, controlled environment with a convenience sample of healthy volunteers; performance in a real-world trauma scenario may differ. The study did not include a head-to-head comparator under identical conditions, and literature comparisons are non-equivalent. The sample size was not based on an a priori power analysis and is sufficient for trend-finding but not definitive conclusions. Finally, the study did not assess hold-time efficacy or self-application.

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. These findings strongly support the AutoTQ® as a reliable and potentially safer tool for prehospital hemorrhage control.

7. References