S. Noordin, J.A. McEwen, J.F. Kragh Jr., A. Eisen, and B.A. Masri reply:
We thank Dr. Gavriely for raising important questions that will serve to stimulate further thinking about current concepts relating to tourniquets in orthopaedics. His question about conflict of interest has been addressed directly with the Editor, and an erratum has been published.
We trust that this will not detract from consideration of some important questions raised by Dr. Gavriely's letter, which include the following:
In our manuscript, we attempted to analyze the pertinent literature relating to each of these questions, among others.
The literature on the mechanism of tourniquet injuries is clear and consistent and well established by many investigators over many years. There is a relationship between higher tourniquet pressures, higher pressure gradients, and a higher probability of injury.
Dr. Gavriely's main assertion is that narrow elastic tourniquet rings are superior to wider cuffs1-6. It appears to us that Dr. Gavriely has misunderstood or misinterpreted aspects of earlier peer-reviewed papers by Ochoa et al.4, Hodgson5, and Crenshaw et al.6. The important findings by Ochoa et al. about the mechanism of tourniquet-related injuries are accurately described in our manuscript (see Figure 3 and page 2959) and do not support Dr. Gavriely's assertion. Hodgson5, in 1993, described an interesting biomechanical model and hypothesized, on the basis of that model, that wider tourniquet cuff designs having a gradual roll-off of pressure near the edges would be optimal in avoiding tourniquet-induced neuropathy; cuffs having such designs subsequently became available. Also, Dr. Gavriely may have misunderstood the importance of the results of Crenshaw et al.6: "The cuff pressure required to eliminate blood flow decreased as cuff width increased… . Thus, wide cuffs transmit a greater percentage of the applied tourniquet pressure to deeper tissues than conventional cuffs; accordingly, lower cuff pressures are required, which may minimize soft-tissue damage during extremity surgery." Dr. Gavriely may not have appreciated that if a lower tourniquet pressure can eliminate blood flow past a specific cuff, then the pressure gradients produced by that cuff will be correspondingly lower. Figure 4 in our study summarizes the relationship between tourniquet cuff width and limb occlusion pressure reported in the literature over many years. Nevertheless, we recognize there are circumstances, particularly certain military applications, when narrow, non-pneumatic tourniquets are appropriate and life-saving.
We find it necessary to correct Dr. Gavriely in his assertion regarding the data presented in Figure 5 in our study: these data were not hypothetical but were based on measurements. Dr. Gavriely suggested that different sizes of an elastic ring tourniquet could be matched to a limb location according to a look-up table able to produce a desired applied pressure. We were not able to find data or evidence of pressure measurements supporting the recommendations of a look-up table and the resultant pressures produced. Further, that suggestion raises safety concerns arising from an inadvertent mismatch between ring and limb size by a user if actual tourniquet pressure is not measured. In the study, we pointed out that the use of non-pneumatic tourniquet devices of current designs precludes accurate pressure measurement, pressure monitoring, and pressure control during use. A direct understanding of some of the relevant safety concerns can be gained by a reader by self-application of any of the tourniquet devices in Figure 5, by operating each as recommended to eliminate blood flow, and by comparing the relative levels of pain experienced. The variation in focal pressure concentration and pain perception is substantial.
We remind Dr. Gavriely of aspects of our brief historical review: narrow rubber bandages were used as tourniquets at the end of the nineteenth century, but their use in surgical, nonmilitary applications was quickly supplanted after Cushing introduced the pneumatic tourniquet in 1904, thereby reducing tourniquet-related injuries by permitting tourniquet pressure to be measured, monitored, and controlled. The safety and effectiveness of wider pneumatic devices is also supported by the military literature, which is analogous to the surgical literature.
In summary, we thank Dr. Gavriely for his thought-provoking comments discussing important current concepts relating to tourniquets in orthopaedics.