Untangling Misconceptions about Narrow Cuffs and Safety
It has been well established in medical literature that the probability of tourniquet-related injuries increases as tourniquet pressure increases, and as the pressure gradient near the edges of tourniquet cuffs increase, e.g. [1-7]. Unnecessarily high tourniquet pressure gradients represent a serious and recognized hazard associated with unnecessarily high probabilities of patient injuries, specifically nerve injuries. Hazardously high pressure gradients can be minimized by the design of improved pneumatic tourniquet cuffs and by the design of improved pneumatic tourniquet instruments.
Over the last few decades, the safety and effectiveness of surgical tourniquets have increased greatly as a result of clinical studies, peer-reviewed publications, and innovations in both the tourniquet instrument and the tourniquet cuff. Some of the major advances that resulted in increased safety and effectiveness are listed below:
- Microcomputer-based tourniquet instruments allowing more accurate and automatic pressure regulation and control, and many important safety features not possible in early pneumatic tourniquet systems [7, 8].
- Tourniquet instruments with the capability to recommend a safe and effective tourniquet pressure based on the patient’s Limb Occlusion Pressure (LOP). LOP can be defined as the minimum pressure required, at a specific time in a specific tourniquet cuff applied to a specific patient’s limb at a specific location, to stop the flow of arterial blood into the limb distal to the cuff. The use of LOP to set tourniquet pressure for individual patients is an important factor that allows tourniquet pressures and pressure gradients to be reduced [8-12].
- Wider tourniquet cuffs that have been shown to reduce the pressures required to stop arterial blood flow [11, 13, 14].
- Variable-contour tourniquet cuffs that can be adjusted to the shape of the limb, providing personalized fit, and resulting in lower pressure and pressure gradients [11, 13, 14].
- Limb protection sleeves matched to the tourniquet cuffs help protect the soft tissues underneath the cuffs by reducing wrinkling, pinching, and mechanical shearing of the tissues [14-16].
Even though hazards of high pressures and high pressure gradients are well established in the surgical realm and supported by decades of clinical studies, they are often not well-understood in developing fields.
In recent years, there has been a new and exciting development in improving rehabilitation of injured patients through of use of Blood Flow Restriction (BFR). BFR rehabilitation involves low-load exercise while restricting arterial inflow into the muscle, and occluding venous return from the muscle [17]. Typically, a person needs to lift weights at around 70% of their one repetition maximum (1RM) to have noticeable increase in muscular strength and size [18]. However, heavy resistance training has risk of injuries and may not be used for many at risk population such as the elderly, and patients undergoing rehabilitation. Studies have shown that BFR training at low resistance (20%-30% of 1RM) can increase both muscle mass and strength, and is beneficial for the recovery of injured athletes and patients requiring muscle gain [18-21].
Although BFR has been shown to be successful in the rehabilitation of injured patients, many people in this field do not understand or follow the results from decades of literature on surgical tourniquet safety and effectiveness. As a result, inconsistencies in methodology and equipment have made it difficult to apply a safe and consistent BFR stimulus to patients, preventing a controlled comparison of different BFR protocols, and thus limiting the identification and delivery of optimal patient outcomes. The following is a list of common misconceptions in BFR rehabilitation:
Misconception 1: Setting BFR pressure as a function of blood pressure or at a fixed pressure is safe and effective
Limb Occlusion Pressure (LOP) is the minimum pressure required, at a specific time in a specific tourniquet cuff applied to a specific patient’s limb at a specific location, to stop the flow of arterial blood into the limb distal to the cuff. Loenneke et al. [22,23] demonstrated that setting BFR pressure as a function of blood pressure or at a fixed pressure does not provide a consistent stimulus across patients because these methods of setting pressure neglect important factors that affect LOP, including limb circumference and cuff width, Figure 1. This confirms what has been well established in the surgical tourniquet literature on LOP [7]. Fatela et al. [24] analyzed the effect of relative BFR pressure on the acute neuromuscular response to BFR resistance exercise and showed that muscular activation and neuromuscular fatigue varies as a function of relative blood flow restriction. Consequently, Fatela et al. [24] concluded that it is crucial to determine individual levels of vascular restriction, by quantifying the resting LOP, before engaging in BFR exercise and rehabilitation.
Summary: A restriction pressure level set for each individual patient, based on a percentage of LOP measured at rest, is crucial before engaging in BFR exercise and rehabilitation. Setting BFR pressure as a function of blood pressure or at a fixed pressure will not apply a safe and consistent BFR stimulus to patients. It may result in full occlusion on some patients, and lack of arterial restriction for others.
Figure 1: Limb Occlusion Pressure (LOP) versus the ratio of tourniquet cuff width to limb circumference. For any given limb circumference, the tourniquet pressure required to stop arterial bloodflow decreases as the width of the tourniquet cuff increases. Adapted from Graham et al. [16].
Misconception 2: Setting pressures based on pain level or intensity level is safe and effective
Some BFR systems recommend setting “individualized” BFR pressures based on the patient’s pain level or intensity level. Typically, they recommend tightening a non-pneumatic belt or increasing pressure in a pneumatic bladder applied to a limb until a 7/10 pain level or intensity level is felt. While this allows some input from the patient in determining the BFR level, this method is highly subjective and will not provide a controlled and consistent BFR stimulus to the patient.
Summary: A restriction pressure level set for each individual patient, based on a percentage of LOP measured at rest, is crucial before engaging in BFR exercise and rehabilitation. Setting BFR pressure based on subjective pain level or intensity level will not apply a safe and consistent BFR stimulus to patients. It may result in full occlusion on some patients, and lack of arterial restriction for others.
Misconception 3: Narrow, non-pneumatic belts and narrow, pneumatic tourniquets are safe
Many BFR devices in the market utilize narrow, non-pneumatic belts or narrow, pneumatic tourniquets to provide BFR stimulus. Most of these devices recommend setting BFR pressures as a function of the patient’s systolic blood pressure, at fixed pressures or based on the patient’s pain level or intensity level which will not apply a safe and consistent BFR stimulus to patients (see misconception 1 and misconception 2). Some devices recommend setting BFR pressures based on LOP which is safer and more effective. However, it has been shown in literature that narrow tourniquet widths result in higher LOPs. Therefore, inherently, narrow non-pneumatic belts and narrow pneumatic tourniquets require and apply higher pressures and pressure gradients resulting in greater risk of patient injury, see Figure 1 [1-7,16].
Summary: Narrow, non-pneumatic belts and narrow, pneumatic tourniquets require higher pressures and higher pressure gradients than wide tourniquets to achieve the same level of BFR stimulus. It has been shown in literature that higher pressures and pressure gradients increase the risk of patient injury. Therefore, use should select and apply a wide tourniquet cuff to reduce the risk of patient injury.
Misconception 4: Blood pressure cuffs are as safe and effective as tourniquet cuffs when used for BFR rehabilitation
Some BFR devices use blood pressure (BP) cuffs to restrict arterial blood flow for BFR rehabilitation. However, BP cuffs do not have inflatable bladders that fully surround the limb, resulting in (1) non-uniform applied pressure, (2) high pressure gradients between the inflatable and non-inflatable regions, and (3) higher risk of tissue displacement and injury under the blood pressure cuff when pressurized at a high level for a sustained period of time. This is because BP cuffs are designed to momentarily restrict and occlude blood flow (1-2 minutes). BP cuffs are not designed to provide sustained pressures. For optimal safety and effectiveness, users should use surgical-grade tourniquet cuffs as they are designed to apply uniform pressures around the limb circumference for sustained and repeated applications.
Summary: Blood pressure cuffs are designed to measure blood pressure. They are not intended to be used for BFR rehabilitation. BP cuffs do not apply uniform pressure to the limb for sustained and repeated applications, resulting in increased risk of nerve and soft tissue injury to the patient. For optimal safety and effectiveness, users should use surgical-grade tourniquet cuffs as they are designed to apply uniform pressures for sustained and repeated applications.
Misconception 5: The patient is safe as long as a BFR device does not occlude arterial blood flow
Some BFR product manufacturers proudly proclaim their systems are inherently safe because the devices physically cannot occlude arterial blood flow. There are videos circulating on the web showing their BFR system applying pressures as high as 500 mmHg to the subject’s limb without occluding arterial blood flow. While it is true arterial blood flow remained non-occluded, the BFR system allows the application of high pressure (500 mmHg), and high pressure gradient over a small surface area (narrow pneumatic belt) resulting in increased risk of patient injury, specifically nerve injuries.
Summary: Narrow BFR tourniquet cuffs apply high pressures and high pressure gradients which increase the risk of patient injury. For safest and optimal BFR stimulus, (1) use wide, variable contour cuffs that provide a personalized fit to the patient resulting in the lowest LOP and restriction pressures, (2) use a tourniquet system that measures the patient’s personalized BFR pressure, based on LOP.
Misconception 6: Any device that applies pressure to a limb is all that is required for a consistent and safe BFR stimulus
Some BFR devices apply pressures to a limb without a microcomputer-based instrument for pressure regulation. This has a negative impact on the safety and effectiveness of the BFR rehabilitation for the following reasons:
- As the patient exercises, the cuff pressure will deviate from the original set pressure. Without an instrument to regulate the pressure near the set pressure, the cuff may apply occlusive pressure (arterial and venous occlusion) for the entire or majority of the BFR exercise resulting in decreased safety and effectiveness. Beware of narrow cuffs without pressure regulation. The cuff pressure in these devices can change drastically during exercise due to their smaller bladder volume.
- Without pressure regulation, the belt or tourniquet cuff may shift on the patient’s limb during use, resulting in inconsistent cuff pressure and BFR stimulus.
- During exercise, the belt may loosen or the tourniquet cuff may leak, resulting in reduced applied pressure and decreased BFR stimulus. Performing BFR with an instrument that provides pressure regulation allows consistent applied pressure and BFR stimulus.
Summary: In order to provide consistent, safe and effective BFR stimulus to the patient, it is important to use a BFR device with the ability to regulate the cuff pressure. For optimal results, users should look for BFR devices utilizing surgical-grade tourniquet cuffs and instruments. Surgical-grade tourniquet cuffs can minimize the risk of cuff movement during use while surgical-grade tourniquet instruments can maintain cuff pressure near the set pressure during exercise. Both surgical-grade tourniquet cuffs and instruments have gone through regulated quality systems ensuring their effectiveness and function.
Conclusion:
Although BFR has been gaining a lot attention in recent years and is shown to be a promising rehabilitation method, users should be aware of the common misconceptions listed above. For optimal BFR stimulus, it is recommended to use personalized restriction pressure based on a relative percentage of LOP, determined automatically on a rest patient by a surgical-grade tourniquet instrument, and applied safely and consistently by a surgical-grade tourniquet cuff.
The use of such tourniquet instruments and cuffs are based on decades of experience in surgical settings, and assures the safe, accurate, and reliable application of pressure to a patient’s limb [7]. Setting and regulating the pressure as a predetermined percentage of the individualized LOP can help avoid adverse events that may result from inadvertently applying pressures that result in complete arterial occlusion [25]. The application of a consistent level of restriction pressure limits variability in BFR intensity for individual patients, since muscular activation, as well as neuromuscular fatigue, varies as a function of relative BFR intensity [24]. Accurately applying a consistent level of restriction pressure enables the outcomes and results of a full range of BFR studies to be compared on a meaningful basis so that optimal protocols can be identified and applied [26,27].
Sources:
[19] Bell, Stephanie. “New method may benefit athletes.” ESPN. ESPN Internet Ventures, 11 Nov 2014. Web. 26 Nov 2014. <http://espn.go.com/nfl/story/_/id/11858977/tourniquet-training-change-way-athletes-recover-injuries>.