Laboratory evaluation of the U.S. Army one-handed tourniquet.
It is estimated that 7 out of 100 combat deaths would be preventable with properly applied tourniquets. (1,2) Until recently, the only tourniquets available to the Soldier were the standard strap and buckle tourniquet (NSN 6515-00-383-0565) and the improvised tourniquet (windlass [stick] and cravat). The former has been recognized as ineffective since World War II, and the latter takes excessive tune to apply. (3) The need for a rapidly deployable military tourniquet has been articulated for half a century, and recently it has been recommended that top priority be given to the development of an improved tourniquet capable of reliably stopping arterial bleeding, as well as rapid self-application with one hand. (4,5)
There is a need for an inexpensive, safe, and low volume/ weight tourniquet in the military that is effective in controlling blood loss in extremity wounds. (5,6) Specific design characteristics were developed based on unpublished experimental data and input from user community representatives at the U.S. Army Medical Department and U.S. Special Operations Command. It was recognized that in meeting the desired physical tourniquet characteristics a trade-off may be necessary in that smaller, narrower tourniquets require greater circumferential pressures for arterial occlusion and may be associated with an increased risk of tourniquet related injury. (7,9) As a result, a OHT (NSN 6515-01-504-0827) has been designed, produced, and added to the U.S. Army inventory that meets expense (approx $8 U.S. per unit), volume, and weight criteria (Figure 1). In addition, the nylon and plastic material used to manufacture the OHT provides a long shelf life. This tourniquet system was specifically designed to be self-applied rapidly and easily with one hand in the event of a wound to an upper extremity that left only one hand available for tourniquet application. However, the OHT has not been tested to determine its efficacy in the occlusion of arterial blood flow when applied to either arms or legs of human subjects. Therefore, we conducted a series of experiments designed to test the effectiveness of the OHT in occluding arterial blood flow in both the upper and lower extremities. The purpose of the present investigation was to test the hypotheses that: (1) self application of the OHT to the proximal thigh or proximal arm will stop blood flow to the respective limbs; (2) if one OHT does not stop blood flow, the application of a second OHT will; and (3) when saturated with fluid, reduction in blood flow to the leg with self application of the OHT to the distal thigh will be as effective as the application of a dry OHT.
[FIGURE 1 OMITTED]
Subjects. All procedures and protocols were reviewed and approved by the Institutional Review Board at the Brooke Army Medical Center. After being informed of all procedures and risks, 26 healthy, nonmotensive, nonsmoking men and women (age range: 18-35 years) gave their written consent to serve as subjects in one of two experiments. Eleven subjects (6 males) participated in the initial experiment (Experiment 1), and 15 additional subjects (11 males) participated in second experiment (Experiment 2). Different subjects were used for the two experiments to minimize exposure time and the number of times the OHT was applied to any single subject Prior to each experiment, height, weight thigh and calf circumference, and baseline blood pressure arid heart rate were measured in each subject. Demographic data of the subjects are presented in Table 1. After changing into medical scrubs designed to provide access to the arms and legs and completing an exposure period of 20 min in the supine position, each subjects baseline blood flow (Doppler ultrasound or occlusion plethysmogaphy) was assessed on the limb targeted for OHT application. The OHT was self-applied to maximum tolerable tightness for each evaluation. Immediately after blood flow was reassessed during OHT application, the OHT was loosened to minimize discomfort to the subject.
Experiment 1. While the subjects were supine, the dorsalis pedis, popliteal, and radial arteries were located by auscultation and marked. At these points, Doppler ultrasound was used qualitatively to assess the effectiveness of the OHT in stopping blood flow distal to the tourniquet. Two OHTs were placed 4 cm and 7 cm distal of the inguinal notch. Initially the subject tightened the most proximal OHT on the thigh. The presence or absence of sound (pulsatile blood flow) at the dorsalis pedis and popliteal arteries was determined (Figure 2A). Subsequently, time subject tightened the distal OHT and assessment for presence or absence of sound was repeated. Following the experimental conditions for tourniquet application to the leg, the effectiveness of the OHT in stopping sound at the radial artery was assessed by application of the OHT around the proximal arm 5 mm distal of the deltoid insertion (Figure 2B).
[FIGURE 2 OMITTED]
Experiment 2. Venous occlusion plethysmography was used to assess the effectiveness of the OHT in reducing or stopping blood flow to the leg and arm. The use of a Whitney strain gauge for quantitative blood flow measurements in limbs is a well-documented procedure. (10-12) A ducal loop mercury-in-silastic strain gauge was placed around the calf or forearm at the point of maximum circumference (Figure 3). Venous outflow from the distal limb was prevented by the placement of a cuff around the thigh or arm just above the knee or elbow using an occlusion pressure of 60 mmHg. An ankle or wrist cuff was inflated to a pressure of 250 mmHg for 1 min prior to the occlusion of venous outflow in order to isolate the circulation from the foot and hand, respectively. Venous occlusion was initiated for 10 s followed by the cuff's release for 10 s for 6 sequential occlusions. The relative change in strain gauge length over 10 s was quantified as a volume of blood per unit time. The use of the thigh or arm cuff was not needed to occlude venous blood flow when the tourniquet was applied. Blood flow was determined by the change in leg or forearm volume per unit time during the initial minute after the application of the tourniquet (Figure 4).
[FIGURES 3-4 OMITTED]
To test the effectiveness of the OHT in reducing blood flow to the limbs under varying conditions, the OHT was placed on the distal thigh (dry and saturated with water), proximal thigh (one and two OHTs applied), and proximal arm. The order in which OHT condition (wet or dry) and number of OHTs applied (one or two) was counterbalanced. The OHT was positioned 6 cm proximal of the patella, 4 and 7 cm distal of the inguinal notch, and 5 mm distal of the deltoid insertion for the distal thigh, proximal thigh, and proximal arm positions, respectively.
Data Analysis. Paired t-tests were used to compare limb blood flow values. Bonferroni correction was used to adjust the alpha level of 0.05 because of multiple comparisons. No statistical analysis was performed on the Doppler data because. of the lack of variance (100% success or failure rates).
Subjects. As a group, the subjects were normotensive active military personnel. Their demographic data are presented in Table 1. The circumference of location for placement of the OHT on the proximal thigh was approximately twice the circumference of location for placement of the OHT on the arm.
Experiment 1. The number of trials per application of the OHT that restated in the absence of Doppler sound (blood flow) at the radial, dorsalis pedis, and pophliteal arteries is presented in Table 2. The OHT was successful in stopping Doppler sound at the radial artery in all 11 subjects when applied to the proximal aria. In contrast, the OHT failed to eliminate Doppler sound at the popliteal or dorsalis pedis arteries in any of the 11 subjects when either one or two OHTs were applied to the proximal thigh.
Experiment 2. The relative (%[DELTA]) reductions in blood flow resulting from OHT application to the leg and arm are presented in Figures 5 and 6. When applied to the proximal arm, the OHT reduced blood flow from 2.9 [+ or -] 0.2 ml.[dl.sup.-1].[min.sup.-1] at baseline to 0.6 [+ or -] 0.1 ml.[dl.sup.-1].[min.sup.-1] following OHT application (t = 10.69, P<0.0001). When applied to the proximal thigh, the OHT reduced blood flow from 2.2 [+ or -] 0.2 ml.[dl.sup.-1].min-1] at baseline to 0.9 [+ or -] 0.1 ml.[dl.sup.-1].min-' following application of either one or two OHT (t>5.73, P<0.0001). Finally, baseline blood flow was reduced from 2.1 [+ or-] 0.2 ml.[dl.sup.-1].[min.sup.-1] at baseline to 0.9 [+ or -] 0.1 ml.[dl.sup.-1].[min.sup.-1] (t=5.87, P<0.0001) when a dry OHT was applied to the distal thigh compared to 1.0 [+ or -] 0.1 ml.[dl.sup.-1].[min.sup.-1] (t=4.72, P<0.0003) when a wet OHT was applied to the distal thigh.
[FIGURES 5-6 OMITTED]
Relationships Between Limb Circumference and Blood Flow Occlusion. In general, smaller average limb circumference of the upper extremity, was related to a greater relative reduction in blood flow during application of the OHT as indicated by average blood flow reductions of 79% in the arm and 49%-55% in the leg. This corresponded to average arm and proximal thigh circumferences of 32.5 and 59.8 cm, respectively. However, correlation coefficients ([r.sup.2]) calculated from individual limb circumferences and relative (%[DELTA]) reductions in blood flow were 0.064 for the arm and 0.218 for the leg.
OHT Application to the Arm. The primary objective of any tourniquet is to occlude arterial blood flow. Previous evaluation of possible tourniquets for combat far-forward settings established the criteria that a tourniquet must occlude detectable (Doppler) blood flow in at least 75% of the subjects in order for the device to be considered successful. (6) The specific requirement for a tourniquet that can be self-applied with one hand may be important for application to an upper extremity wound when the hand of the injured limb is not functional. From this standpoint, OHT application to the upper extremity appears to meet the criteria for a relatively effective approach of excluding blood flow in the arm. This notion was supported by the results from our study that demonstrated that 100% of our subject were able to arrest detectable blood flow with OHT application to the proximal arm as determined by Doppler auscultation. The absence of Doppler sound with OHT application to the proximal arm corresponded to ~80% reduction in average forearm blood flow. This 80% reduction in blood flow to the distal arm could be of great significance in the event of an upper extremity injury. Since a 50% loss of a total blood volume of ~6 liters (~3 liters) is acutely life-threatening, we could expect a Soldier that has an arterial arm injury that loses 100 ml of blood per minute to "bleed out" in ~30 min in the absence of tourniquet application. (13) It the normal blood loss from such a wound could be reduced by 80% as indicated by the results of the present investigation, the amount of time required to reach a 50% blood volume loss (bleed out) would be increased by 120 min. Thus, OHT application to a major arterial wound to the arm could be expected to "buy" as much as two additional hours for the Soldier to receive the definitive care that could save his or her life. This could be the worst-case scenario because the reduced blood flow might allow spontaneous coagulation or effective control with hemostatic dressings to stop blood loss completely.
OHT Application to the Leg. In contrast to the arm, OHT application to the leg failed to stop detectable blood flow (Doppler auscultation) when applied to the thigh in any of the subjects. The presence of Doppler sound with OHT application to the thigh corresponded to a reduction in average leg blood flow of only, ~50%. Although the blood flow to one leg is approximately 0.3 L/min at rest, bleeding from a severe would can be exacerbated in a Soldier engaged in combat (during mild physical activity) when blood flow in the leg can be increased by 5- to 10-fold (14) Therefore, depending on the physical activity required during combat conditions, a wounded Soldier with a severe hemorrhage wound and blood flow of 1.0 to 1.5 liters/ min in the leg may "bleed out" (lose 3 liters of blood) in as few as 2 minutes. The results of this investigation indicate that immediate application of the OHT may perhaps double this time. Under this scenario, it is unlikely that the additional 2 minutes would result in a lifesaving measure.
A recent panel of experts has questioned the specific requirement for a tourniquet that can be self-applied to a bleeding arm wound with the uninjured hand. (15) The panel was concerned that the design requirement for one-handed operation may be incompatible technically with the ability to occlude arterial flow in the lower limb adequately. This is because the pressure required to occlude blood flow in a limb increases exponentially with the circumference of that limb (7,9,16) Thus, the lower limb requires much greater tourniquet pressure to occlude blood flow than does the upper limb. However, the vast majority of the battlefield wounds requiring tourniquet application occur in the lower limb where both hands should be available for tourniquet application. (17) Inasmuch, it is much more important that a battlefield tourniquet is first able to occlude arterial flow in the lower extremity. (3) In an earlier survey, Calkins et al identified two strap-type tourniquets that did provide satisfactory arterial occlusion, both employed a ratchet device with a 1.75" strap. (6) However, neither was compatible with one-handed operation.
It is likely that the relatively narrow width (1") of the OHT was a primary contributor to its inability to stop leg blood flow effectively. Previous investigators have demonstrated clearly an inverse relationship between tourniquet width and minimum pressure required to occlude arterial blood flow. (7-9) That is, as the width of the tourniquet decreases, the pressure required to occlude arterial blood flow, increases exponentially. Furthermore, as introduced previously, the pressure required to occlude blood flow in a limb increases exponentially with the circumference of that limb. (7,9,16) Thus it was not unexpected that the OHT was more effective in occluding blood flow in the arm, which is approximately half the circumference of the leg. However, there existed great variability in blood flow occlusion within the same limb (for example, arm) across subjects, suggesting that factors other than limb circumference per se contributed (for example, subject strength, subject intolerance to discomfort, and tissue composition).
Based on the relationship between tourniquet width and occlusion pressure, described above, it might seem that the ineffectiveness of the OHT could be addressed by increasing the width of the strap. However, wider straps cause more friction through the D-rings and, consequently, prohibit pressure development in the tourniquet (unpublished observation). Also, as width increases, so does the amount of tissue that must be compressed increases, greatly increasing the effort required to produce tension. (18) Taken together, these two factors likely would further reduce the effectiveness of the OHT. It is theoretically possible to attain adequate occlusion pressure using a one inch wide tourniquet augmented with a mechanism that provides a mechanical advantage, such as a ratchet system. However, such a system could produce significant tissue damage. A wider tourniquet employing a mechanism other than that used in the OHT should be pursued in future development of an improved tourniquet for combat use.
Relationship Between Doppler Sounds and Blood Flow
The use of presence of sound obtained from Doppler ultrasound placed on arteries is a common method used by physicians to determine blood flow in extremities. With the use of occlusion plethysmography, a more sensitive technique, we demonstrated that a minimum of ~20% of baseline blood flow can be present in the absence of Doppler sound. Since the presence of sound obtained from Doppler auscultation relies on the presence of pulses, our results may reflect a pressure generated by OHT application that eliminates pulsatile blood flow but allows nonpulsatile flow. Our observations provide evidence that Doppler auscultation may overestimate the effectiveness of a clinical procedure designed to occlude blood flow (for example, a tourniquet) and underestimate the actual amount of blood flow present.
A recent panel of experts has questioned the specific requirement for a tourniquet that can be self-applied to a bleeding arm wound with the uninjured hand. (15) The panel was concerned that the design requirement for one-handed operation may be incompatible technically with the ability to occlude arterial flow in the lower limb adequately. The lower limb requires much greater tourniquet pressure to occlude blood flow than does the upper limb due to differences in limb circumference. However, the vast majority of the battlefield wounds requiring tourniquet application occur in the lower limb where both hands should be available for tourniquet applications (17) Inasmuch, it is much more important that a battlefield tourniquet is first able to occlude arterial flow in the lower extremity. (3) In an earlier survey, Calkins et al identified two strap-type tourniquets that provided satisfactory arterial occlusion when self applied by subjects provided with distal pulse feedback; both employed a ratchet device with a 1.50" strap. (6) However, neither was compatible with one-handed operation.
There is an urgent need for an effective tactical tourniquet that can be rapidly self- or buddy-applied by the Soldier under fire. The current Army OHT represents a step towards satisfying that need. Although effective when applied to the arm, the inability of the OHT to occlude arterial blood flow in the lower extremity, when tightened to a pain threshold, emphasizes the need for continued development of tourniquet systems that can meet weight and cube requirements without sacrificing effectiveness and safety. We suggest that the need for one-handed application, while desirable, be secondary to effective arterial occlusion. Future designs for battlefield tourniquets mint balance the need to meet size and weight requirements with established principles of tourniquet design.
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Joseph C. Wenke, PhD ([dagger])
Thomas J. Walters, PhD ([double dagger])
SFC Dominique J. Greydanus, ([dagger])([dagger])([dagger])
Anthony E. Pusateri, PhD ([dagger])([dagger])([dagger])([dagger])
Victor A. Convertino, PhD ([dagger]) ([dagger]) ([dagger])([dagger])([dagger])
The following, authors are all assigned to the U.S. Army Institute of Surgical Research, Fort Sam Houston, TX:
([dagger]) Doctor Wenke, Research Assistant.
([double dagger]) Doctor Walters, Laboratory Division.
([dagger])([dagger])([dagger]) Sergeant First Class Greydanus, Pre-hopstial Research NCOIC.
([dagger])([dagger])([dagger])([dagger]) Doctor Pusateri, Chief, Department of Biochemistry.
([dagger])([dagger])([dagger])([dagger])([dagger]) Doctor Convertino, Chief, Human Physiology Research Laboratory.
Table 1 Experiment 1 Experiment 2 (N=11) (N=15) Age, yr 22 [+ or -] 1 23 [+ or -]1 Height, cm 174 [+ or -] 3 176 [+ or -] 2 Weight, kg 74.4 [+ or -] 3.1 82.5 [+ or -] 2.8 Blood Pressure, mmHg Systolic 112 [+ or -] 4 117 [+ or -] 3 Diastolic 61 [+ or -] 3 64 [+ or -] 3 Mean 78 [+ or -] 3 82 [+ or -] 3 Heart Rate, bpm 68 [+ or -] 2 67 [+ or -] 3 Circumference,cm Arm 30.5 [+ or -] 0.9 32.5 [+ or -] 0.6 Distal Thigh N/A 45.8 [+ or -] 0.8 Proximal Thigh 60.2 [+ or -] 1.4 59.8 [+ or -] 1.0 Table 2. OHT Success Rate Using Doppler Auscultation at Different Arterial Locations Dormalis Pedis Popliteal Radia 1 OHT Proximal Thigh 0/11 0/11 N/A 2 OHT Distal Thigh 0/11 0/11 N/A OHT Arm N/A N/A 11/11
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|Author:||Wenke, Joseph C.; Walters, Thomas J.; Greydanus, Dominique J.; Pusateri, Anthony E.; Convertino, Vic|
|Publication:||U.S. Army Medical Department Journal|
|Date:||Apr 1, 2005|
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