To The Editor:
In a recent article, "Surgical Tourniquets in Orthopaedics" (2009;91:2958-67), by Noordin et al., the authors expressed highly critical opinions on the use of "a non-pneumatic elastic ring designed to combine exsanguination and tourniquet functions." The only commercial device that is currently available on the market and fits this description is the S-MART/HemaClear (www.hemaclear.com; www.ohkmed.com) manufactured by OHK Medical Devices (Newark, New Jersey). The authors confidently predict that "uncritical use and acceptance of non-pneumatic tourniquets for extended periods … may increase the incidence of tourniquet-related adverse events, exposing patients and surgical staff in civilian settings to unnecessary risks." Clearly, if these presumed facts are substantiated, it is imperative that the use of the HemaClear is discontinued immediately and indefinitely. However, the excellent safety track record of the S-MART/HemaClear, as outlined below, is far from supporting the allegations by Noordin et al. As the developers, manufacturers, and distributors of HemaClear, we find it necessary to set the record clear on scientific as well as procedural levels.
Before getting into the physics and physiology of the subject matter, it is important to clarify the status of the authors and the motives that they may have had in publishing this supposedly objective scientific manuscript. It is unfortunate that the ethics rules of full disclosure have not been followed by at least one of the authors. Their disclosure statement says: "The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity." This statement is in fact false and misleading: The intensive commercial conflicts of interest of Dr. J.A. McEwen, the founder, inventor, and officer of several commercial entities in the field of pneumatic tourniquets (e.g., www.tourniquet.org), were withheld from The Journal and its readers. Clearly, since the S-MART/HemaClear has been gaining rapid popularity among leading orthopaedic surgeons in the United States and elsewhere, there potentially exists a commercial and financial interest in displacing such competition from the market.
It is within this context that we now wish to address some of the scientific aspects of this paper.
First, we address the safety track records of wide pneumatic tourniquets compared with the narrow elastic exsanguination-arterial blocker ring. In a recent paper referenced by the authors, Odinsson and Finsen1 described the rate of complications using tourniquets in orthopaedic surgery in Norway. The authors found fifteen cases of neurological deficit in more than 60,000 applications of a tourniquet (a prevalence of approximately 24/100,000), the majority of which were in the lower extremity. This prevalence was no better than that reported twenty-five years earlier in Australia (Middleton and Varian2) and, in fact, was somewhat worse, despite the use of modern tourniquets (wide tourniquets with controlled pressure and monitoring) and use (i.e., with the pressure adjusted at approximately 100 mm Hg above systolic blood pressure) by the majority of the Norwegian surgeons. It is interesting to note that none of the neurological complications occurred among the 14% of the survey responders who routinely use an Esmarch bandage to control blood flow. Clearly, the one parameter that changed from Australia in 1974 to Norway in 1999 is the cuff width, which may have gotten bigger and may have been a contributing factor to the worsening of the data.
These numbers, while not high in and by themselves, are substantially higher than the data on possible nerve involvement available to OHK Medical Devices on the use of its S-MART/HemaClear in more than 150,000 cases worldwide (three cases of nerve involvement for a prevalence of 2/100,000, and all three occurred when the device was used beyond the recommended 120-minute time limit). This is despite the fact that the S-MART/HemaClear elastic ring is much narrower than the wide pneumatic tourniquet promoted by Dr. McEwen and his companies over the last twenty-five years (references related to the Noordin et al. study3-13). This obviously superior track record for safety is supported by a number of independent scientific studies that clearly provide the physical and physiological explanation to the observed difference in incidence. Examples include the following:
Thus, there is a strong and well-documented body of evidence that is independent from any commercial interests to show that narrow tourniquets are actually better than wide pneumatic tourniquet cuffs. In fact, the evidence in support of using a wide cuff, outside of Dr. McEwen's own publications, is scant or nonexistent.
Second, we address the question: What is happening inside the limb when a tourniquet is applied? Pressure. It is rather regrettable that the authors failed to comprehend the fundamental aspects of the mechanics of tissue compression beneath surgical tourniquets (pneumatic or elastic ring). The first key parameter in preventing damage to the tissues inside the limb (e.g., nerves and blood vessels) is the pressure inside the limb rather than at the skin surface, as described by Noordin et al. in their Figure 5. In fact, in order to stop the arterial blood flow into a limb, all that is needed is to compress the artery over a few millimeters of its length by a pressure applied just outside the artery that is a few millimeters of mercury higher than the highest fluctuation of systolic blood pressure, e.g., 150 mm Hg if the patient's mean systolic blood pressure is 130 mm Hg.
When a wide tourniquet is used, the pressures outside the artery and the nerve are the same as those at the skin surface (i.e., approximately 100 mm Hg higher than the systolic blood pressure). This has to do with the fact that the pressure field (distribution) beneath a wide cuff is uniform, except toward the margins of the cuff. When applying the narrow cuff or the HemaClear elastic ring, the skin surface pressure dissipates when transmitted through the soft tissues (skin, fat layer, and muscle) to the level of the artery and the nerve (i.e., radial pressure gradient), so that even if the skin-surface pressure is high, the pressure at the nerve level is quite low. Actually, in most patients, the skin pressure is around 250 mm Hg when the HemaClear 40 is used on the arm and 300 to 350 mm Hg when the HemaClear 60 and HemaClear-90-Black and White are applied to the thigh (see HemaClear pressure charts at www.hemaclear.com) and not as illustrated in Figure 5 in Noordin et al.
Third, we address the pressure gradient. The second most important parameter with respect to nerve damage is the axial pressure gradients at the edges of the tourniquet. There is an across-the-board agreement that the higher this axial gradient at the level of the nerve, the higher the risk for shear stress and telescoping injury to the axons as documented by Ochoa et al.17. However, the notion that narrower cuffs and rings exert higher axial gradients than wide cuffs (as alluded to in the hypothetical graph shown in Figure 5 of Noordin et al.) is simply not true. In fact, the experimental data to date have shown exactly the opposite. The figure shown here from the landmark 1988 study by Crenshaw et al.19 clearly demonstrates it (Fig. 3). The graphs show the intralimb axial pressures at four radial locations with narrow (Fig. 3, a and c) and wide (Fig. 3, b and d) tourniquet cuffs inflated to 400 mm Hg. It is readily seen that the gradients with the narrow cuff (red lines in Fig. 3, c) are much less steep than with the wide cuff (blue lines in Fig. 3, d). Similar experimental data as well as computational models confirm this observation. The graphs also show that the actual pressure internally is lower with the narrow cuff.
Thus, with pressures at the nerve level that are lower with the narrow cuff and with gradients that are much less steep, it is not surprising that the incidence of nerve injury is higher with the wide cuff.
Fourth, we address the question: Is the higher pressure at the skin level with narrow cuffs or an elastic ring a cause for concern? The pressure exerted on the skin by the S-MART/HemaClear depends only on the limb circumference and the distance of the placed ring from the toes or fingers. This pressure is factory calibrated and cannot be exceeded. With pneumatic tourniquets, while the pressure used in the majority of patients is not more than 300 to 350 mm Hg, it is possible that if bleeding starts into the surgical field because of a sudden surge in arterial blood pressure, the surgeon will instruct to increase the pressure on the controller. Pneumatic tourniquet controllers can be dialed up to 475 mm Hg in the cuff, with a 700 mm Hg reservoir (e.g., ATS 2000; Zimmer, Warsaw, Indiana20). It is, however, more important to note the overall skin safety record of wide pneumatic tourniquets compared with the S-MART/HemaClear. The recent study by Din and Geddes21 on skin complications following the use of a wide pneumatic tourniquet indicated a prevalence of 6%, even when adequate padding was used. This is far beyond the very few cases known to us from among the >150,000 patients managed with the HemaClear. This is attributed to the round contour of the ring-skin interface and the many layers of stockinette left around the elastic ring. Figures 4-A and 4-B show examples of skin conditions with a wide pneumatic tourniquet and the S-MART/HemaClear.
In summary, the data described above clearly document the superior safety track record of the elastic exsanguination tourniquet (S-MART/HemaClear) over the wide tourniquet promoted by Dr. McEwen and materially refute his unsubstantiated allegations. The smaller pressure inside the limb at the nerve level and the less steep internal axial pressure gradients are the underlying mechanisms of this improved patient outcome. The fact that the patient's skin tolerates the S-MART/HemaClear better than the wide tourniquet cuff has to do with specific design details. These features are accompanied by other advantages: the overall lower volume of tissue that is under compression conditions, the time needed for preparation and application, the fact that the S-MART/HemaClear exsanguination is superior, with an excellent surgical field and larger room for wider exposure because of the smaller footprint of the occluding ring, its usefulness both on the upper part of the limbs (arm and thigh) as well as on the tapered parts of the limb (calf and forearm), and its sterility all contribute to the popularity that this product is gaining.