BACKGROUND AND GOAL OF STUDY: HemaClear is the tradename of an elastic, non pneumatic narrow disposable silicone ring tourniquet to achieve both exanguination and oclusion of arterial flow. The actual pressure produced by HemaClear is unknown and uncontrollable by clinical users. In order to know the applied pressure, the manufacturer provides tables of estimated pressure, according to HemaClear size, limb´s circumference and distance position from the fingers.

The purpose of this study is to measure the surface (skin) pressure produced by HemaClear and to compare it with the estimated pressure.

MATERIALS AND METHODS: The lower limb of eight cadavers were used as experimental model. HemaClear Large Brown size was chosen in all cases. The skin pressure was measured by an electronic device made with a micro controller ATMega 328 in a Arduino Nano Card, connected to a resistive force sensor FSR model 402.

In each case we registered gender, limb circumference, distant from fingers, estimated pressure and measured pressure. The variables estimated and measured pressures and it difference were analyzed using statistical software R (R Foundation Vienna, Austria)

RESULTS: The mean Measured Pressure was 473 mmHg (SD 70); The mean Estimated Pressure was 372 mmHg (SD 32); and the mean Pressure Difference was 100 mmHg (SD 55).

CASE GENDER LIMB Q LENGH cm M. PRESS E.PRESS DIFFERENCE

1 M 45 73 482 412 70

2 F 43 73 500 389 121

3 F 43 79 426 389 37

4 F 42 75 527 389 138

5 F 41 80 574 389 185

6 M 37 90 492 354 138

7 M 36 95 320 320 24

8 M 34 77 337 337 105

DISCUSSION: The main complication related to clinical use of pneumatic and non pneumatic tourniquets is nerve injury. It is directly related to the pressure applied, time of compression and volume of compressed tissue.

The mechanism involved is the stretching of the tissue at the edges of the tourniquet and the transverse shear forces transmitted to the underlying nerves. Electronmicroscopy show paranodal mielin rupture. Clinical studies reports a very low incidence of nerve complications related to elastic ring tourniquet: GABRIELY (2010) report 2 cases over 100.000 incidence of not long term paresis, related to use more than 120 minutes; REYENDERS (2012) report 17 cases over 4870 incidence of pain or light paresis; DROSOS (2013) report 0 cases over 536 incidence in orthopaedic surgery.

CONCLUSIONS:

1. In our cadaveric experimental model, the Measured Pressure was always higher than the Estimated Pressure.

2. The clinical implication of this high surface pressure is unknown, but seems to be irrelevant highlighted by clinical studies.

3. The narrow profile of HemaClear could reduce the stretching forces directly related with nerve injury.

03 / Comparison between the measurement of surface pressure produced by HemaClear® surgical tourniquet and the pressure estimated by the manufacturer. Study in human cadavers.