Comparison of HemaShock & PASG/MAST

We developed the HemaShock®, an Auto-Transfusion tourniquet, which is an elastic torus with a long sleeve wrapped around it that, when applied to a limb, squeezes the blood away from the limb into the central circulation and blocks the re-entry of blood into it.

Below is an outline of the differences and similarities between our new approach to external counter-pressure and the current pneumatic anti-shock garments (PASG) including the MAST:

a. Auto-transfusion – in more than 150 journal papers that we collected and read on the PASG there was NOT even ONE study that demonstrated sustained auto-transfusion that was induced by the device. The HemaShock®, on the other hand, induced more than 1000 ml of auto-transfusion from the legs to the central circulation in our study, which is attached herein. This difference is due to the mode of pressure application sequence of the two devices: the HemaShock® applies the pressure from distal to proximal, while the PASG applies it to the lower body.

b. HemaShock® acts on the legs alone and does not interfere with blood flow to the abdominal organs, as does the PASG. As such, it does not cause ischemia of the gut and/or liver and does not impede their normal activity. We believe that the reason for the slight drop in lactic acid and CPK levels found in our study during HemaShock® application is actually due to elevated hepatic blood flow induced by the auto-transfusion.

c. Unlike the PASG, HemaShock® can be removed stepwise while monitoring the patient’s condition. It can easily be rolled down from thigh to knee level, each leg at a time and then down to the ankle. Any attempt to remove the PASG by slow deflation is bound to cause trapping of blood distal to the partially inflated abdominal compartment with pooling of venous blood. This venous occlusion effect of the partially inflated MAST actually removes blood from the central circulation. In addition, the pooled blood quickly becomes rich in Potassium, acids, and other toxic by-products of ischemia. When the pressure is completely released the blood outpours into the central circulation with negative effects on the heart and other essential organs. We believe that distal blood trapping is a major flaw in the design of the PASG, which is responsible, in large part, to the overall poor outcome of the PASG use. This problem is overcome by the HemaShock® design.

d. The effect of the HemaShock® can be titrated to maintain a desired BP of 90-100 mm Hg. This is done by selecting the number of limbs (1 – 4, including the arms) and the level of the elastic ring position on the limb. The ring can easily be rolled up and down to meet the needs of the patient’s treatment if so desired. This cannot be done with the PASG. Deflation of the PASG to less than the maximum pressure of 104 mm Hg in a patient whose systolic BP is higher than the PASG pressure causes arterial blood to escape beyond the proximal (abdominal) compartment. This blood gets trapped due to the venous occlusion effect of the partially inflated PASG. Re-inflation of the PASG pressure does not induce re-infusion of the trapped blood, particularly the blood pooled in the body segments not directly under the effect of the MAST cuffs (the genitals, the pelvis, etc.).

e. The HemaShock® is not different in essence from the method used in orthopedic surgery to maintain ‘bloodless’ surgical field. The extremity is tightly wrapped with an elastic strip followed by inflation of a pneumatic cuff at the proximal end of the limb. The cuff is typically inflated to 250 mm Hg. The current teaching is to keep the cuff inflated for not more than 2 hours, but there are animal studies that show that this period can be extended if the limb is hypothermic. This method is routinely used in almost every elective orthopedic procedure with a rate of complications reported to be one per 5000-8000, mostly transient paresis due to direct mechanical compression of the nerves beneath the occluding cuff. The HemaShock® pressure inside the limb is lower (130 mm Hg). The literature on clinical and animal studies with the orthopedic tourniquet does not mention any severe systemic effects during its use and/or after its removal. A detailed description and discussion of the orthopedic tourniquet method may be found in Canale TS. Campbell’s Operative Orthopaedics. 9th ed. St. Louis, Mosby 1998:30-31. Additional references will be provided upon request.

f. There are several technological differences between the PASG and the HemaShock®:

HemaShock® is much smaller (320 g per set of two vs. 4.5 kg) and occupies much less space.

HemaShock® is intended for single use, while the PASG is not.

Once HemaShock® is applied, the sleeve may be cut away to permit access to a wound if that is necessary. This is not possible with the PASG.

HemaShock® is not a pneumatic device. As such it is not affected by changes in ambient atmospheric pressure and/or temperature.

The HemaShock® cannot be removed inadvertently as was reported with the Velcro fasteners of some versions of the PASG.

Applying HemaShock® by one person is feasible, even during transport. Using the PASG usually requires a team of at least two men.
It takes 6-12 seconds to apply the HemaShock® to each limb. A trained team of medics can put the PASG on a patient within one minute, but then it takes 2-4 additional minutes to inflate it. A large study of MAST use showed an average of 5 minutes longer transport time in patients who were treated with MAST.

Training: use of the HemaShock® is simple, requires minimal training and can be applied by persons with no medical background. Safe application of the MAST requires several hours of training.

Cost:: HemaShock® cost is lower than that of the PASG.

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