Most surgeons seem to employ inflation pressure as follows: they use modifications in certain scenarios, for example, adjustments for age, blood pressure, weight, and extremity shape and size, or they apply a set pressure of 50–150
mmHg above SBP [1
The most distinctive feature of the new tourniquet system used in this study is that it automatically regulates the effective pressure to supply a bloodless surgical field synchronized with SBP. It responds to a sharp rise or a drop of SBP to supply an adequate pressure; we did not need to deflate and re-inflate to employ different pressures during any procedure. This contributes not only to saved time but also to safety and accuracy by preventing futile oozing and edema in the surgical field. It also prevents excessive pressure and avoids severe neurologic complication, post-operative edema, and subsequent joint contracture. For example, SBP above 200
mmHg exceeds 300
mmHg of inflation pressure, that is thought to be border value in the safely use, in the situation additional pressure is set on 100
mmHg. With patients under general anaesthesia, the anaesthesiologist monitors vital signs and manages excessive high SBP with anaesthetic changes. Ishii et al. [7
] used this tourniquet for 100 consecutive foot and ankle surgeries. They reported all cases maintained an excellent operative field without measurable bleeding and there were no postoperative complications.
There are two main physiological effects in the application of a tourniquet to a limb: ischemia and local pressure on the tissue beneath the cuff. Tourniquet paralysis is now thought to arise not only from ischemia of nerve tissue distal to the compression level but also from a combined effect with mechanical nerve compression beneath the tourniquet [1
]. Ochoa et al. [9
] used a primate model to demonstrate mechanical deformation of nerve fibers with displacement of the nodes of Ranvier and distortion of the paranodal myelin relating to the direction and magnitude of externally applied pressure, away from the site of compression towards uncompressed tissue. Lundborg [8
] showed that ischemia alone must occur for 8 to 10 hours for the walls of endoneural vessels to be injured sufficiently to produce extravascular leakage of albumin. In the compressed nerve segment, a prominent leakage of albumin from endoneural vessels occurred after four hours of cuff compression. Their study suggested that localized compression of the nerve segment is also a principal factor in the pathogenesis of tourniquet paralysis.
In many reported cases of neurologic complications caused by pneumatic tourniquet, the pressure was too high, or applied for too long [2
]. A survey of 151 members of the Australian Orthopaedic Association [3
] reported the incidence of nerve palsy in the upper limb after the use of a tourniquet to be 1:5000. These nerve palsies occurred both with the use of the pressure-retained pneumatic cuff and the outmoded use of Esmarch rubber bandage as a tourniquet. A Norwegian study [2
] reported two cases of major complication with tourniquet inflating duration of 130 and 180 minutes and with acceptable pressures of 250 and 300
mmHg (resulting in an incidence of three neurologic complications in 18,465 upper extremity procedures).
The inflation pressure of a pneumatic cuff may not represent the actual pressure in the soft tissues under the cuff, and pressures vary widely from the applied pressures [6
]. It is difficult to measure actual perineural pressures in the midst of surgery. Several studies applied various techniques to lower cuff pressures sufficient to produce a bloodless surgical field [7
]. Many authors recommend a wide tourniquet cuff to reduce the actual pressure in the tissue under the tourniquet [14
], and attention should be paid to recognize the incongruities between the shape of the limb and the tourniquet resulting in pressure concentrations [12
]. Controlled hypotension to bring down SBP can also be used to decrease direct cuff pressure against the tissue [18
]. An alternating double tourniquet technique, to change the point of compression, is another method to improve [19
Traditional recommendations suggest parameters for maximum pressure and time limits rather than the minimal effective pressure to achieve a bloodless field. The recommended maximum safe pressure for the upper limb in standard surgical texts is 250–300
mmHg for adults [4
]. Little or no consensus has been reached regarding optimum tourniquet pressure [1
Van Roekel et al. [22
] reported 200
mmHg to be adequate minimum tourniquet pressure to produce a bloodless surgical field for upper limb surgery; similarly, 250
mmHg was reported to be adequate for lower limb surgery in an average sized, normotensive patient. Levy et al. [23
] studied the correlations between several potential influencing parameters and the minimal tourniquet pressure in the upper limb using Doppler stethoscope, and blood pressure showed significant correlation; their formula is tourniquet pressure
mean arterial pressure)
mmHg. They reported mean calculated minimal effective tourniquet pressures to be predicted were well below 250-300
mmHg previously recommended. However, their studies presupposed that tourniquet pressures were constant during the operation. It is nearly impossible for patient’s blood pressure to remain constant. Sharp rises in SBP might allow blood to ooze into the operative field. On the other hand, relatively high tourniquet pressures with low SBPs produces unnecessary pressure on tissues. In our study, although seven cases showed a sharp rise in SBP (over 30
mmHg) during a 2.5-minute interval, the system was able to respond automatically and produce an excellent surgical field. Twenty-seven cases exhibited a maximum change in SBP greater than 40
mmHg; an excellent surgical field was maintained in all cases. Additionally, the system could also respond automatically to decreasing changes in SBP; 22 cases showed lower SBP during the surgery than initial pressure with no problems with the surgical fields. Based on these results, we recommend the application tourniquet pressure at 100
mmHg above SBP at the upper arm.
Skin disorders are another possible complication with the tourniquet used in this study, because repeated inflation of different pressures might cause skin and subcutaneous tissue distortion. We had no case of skin complications, although this could occur despite appropriate use of the tourniquet [1
]. Padding beneath the tourniquet is important to decrease sheer stress at the skin surface, particularly in elderly patients with delicate skin [24
This study has some limitations. First, we are not comparing the new tourniquet system to a standard one. Our rating system for the bloodless field also might be biased as not blinded because we used single tourniquet. It is desirable to review the merit of this system relatively in the study using several tourniquets with large number of cases. Second, we did not try the additional pressure lower than 100
mmHg on SBP, which might be sufficient to supply excellent bloodless field. A continuous effort should be made to apply lower pressure as possible.