Safety of the EED - effect on the limbsStopping arterial blood supply to a limb does not cause sustained injury due to limb ischemia if limited to 120 minutes (Klenermann L. The Tourniquet Manual
This practice is used daily in orthopedics (about 16,000 cases/day) by using an Esmarch bandage, pneumatic tourniquet or the HemaClear®. Emergency arterial tourniquets are recommended for stopping blood loss in severe limb injuries and have been recently used succesfully in several hundreds of US soldiers in combat. Time limitsThe effects of ischemia on a tissue vary depending on the oxygen and high energy compounds stores, the level of activity of the tissue which determine the oxygen and metabolites consumption and the treshold for functionality cessation. In addition, the tissue capacity to generate ATP from unaerobic metabolism is important.
There is a large variability in all parameters between tissues. For example, the cardiac muscle has nearly no reserves of energy/oxygen stores. It extracts more oxygen from the blood flowing through the coronary circulation than any other tissue and is in constant high demand for oxygen and metabolites. The brain also lacks storage, and is working hard even when seems idle. The brain has a very low tolerance for low oxygen supply and functionality will decrease or stop very soon after blood supply stops or becomes critically low. Nerves (axons), on the other hand, have little oxygen consumption, particularly when not activated. Muscles, skin, fat and bone tissues, on the other hand are much more resistive to blocking of the blood flow into them. Muscles are used to consuming more energy than is supplied to them. Energy is stored in the form of Creatine Phosphate which can easily transfer a phosphate to an ADP molecule and generate an ATP. In addition, oxygen is stored in the muscle as bound to a Heme component of the Myoglobine which can dissociate and become available when the tissue PO2 falls below 10 or so mm Hg. Also, there are some ATP stores available. Once the muscle PO2 falls sufficiently, glycogen stores are converted to glucose and unaerobic metabolism becomes active. It should be noted that all the enzyme systems that are needed for these metabolic pathways are readily expressed in muscles. They are there to provide energy when the muscles are active and are available to prevent ischemic injury for quite some time. Additional reading on the energy metabolism of muscles can be found in: http://www.nsbri.org/humanphysspace/focus5/ep-energetics.html It is generally accepted that blocking the arterial blood flow into a limb is safe for at least two hours. The abstracts shown on the right are a few of many publications that studied this issue in animals and human experiments. |
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Systemic and local effects of the application of a tourniquet. J Bone Joint Surg Br. 1980 Aug; 62(3):385-8.
KlenermanL, BiswasM, HulandsGH, Rhodes AM. The effect of the application of a tourniquet to a limb and the release of the accumulated metabolites have been investigated with reference to the acid-base level in the blood from the limb and in the right atrium. Investigations have been carried out experimentally in rhesus monkeys and observations have been made on patients undergoing reconstructive operations on the knee. The acidotic blood from the ischaemic limb produces little systemic effect. The limb recovers in approximately 40 minutes after a tourniquet has been in place for four hours. Three hours is recommended as a reasonable upper limit for the safe application of a pneumatic tourniquet. The effect of pneumatic tourniquets on the ultrastructure of skeletal muscleJ Bone Joint Surg Br.
1979 May;61-B(2):178-83. Patterson S, KlenermanL. Experiments have been carried out on rhesus monkeys to determine the effect of the application of a pneumatic tourniquet on the ultrastructure of the muscles of the lower limb. Tourniquets were applied for periods lasting between one and five hours. The changes in the muscle lying immediately under the cuff of the tourniquet were more marked than those observed in muscle distal to the cuff. Three hours appears to be close to the limit of the time that a muscle can resist the sustained compression of a tourniquet. Tourniquet ischaemia. Clinical and biochemical observations.Ann Chir Gynaecol. 1978;67(6):210-3.
SantavirtaS, KausteA, RindellK. The duration of tourniquet ischaemia was recorded in 1000 consecutive operations on extremities under a bloodless field, the average ischaemia time was 74.11 +/-29.52 minutes. The duration of tourniquet ischaemia in meniscectomies was 58.47 +/- 15.91 minutes, in osteosynthesis of malleolar fractures 88.46 +/- 23.33 minutes and in operations for endoprosthetic replacement of the knee joint 131.19 +/- 11.24 minutes. In 85 cases the commonly accepted two hour limit for tourniquet time was exceeded without clinical complications. LDH and CPK levels in venous blood were studied in 15 operations. No significant changes were seen in LDH levels when recorded up to 24 hours following release of the tourniquet. CPK levels increased significantly (p less than 0.05) and highly significantly (p less than 0.005) when measured three hours and 24 hours after the release of the tourniquet, respectively. The results of the study suggest that two hours of ischaemia of the extremities is relatively well tolerated. |
The use of Tourniquet in Emergency MedicineTourniquets have been used in combat and emergency medicine for several hundred years. The indication has always been to stop arterial flow into the limb and by doing so, stop the hemorrhage from a limb injury.
To read more about the history and use of combat/emergency tourniquet see: http://www.artofmanliness.com/2012/03/21/how-to-save-lives-like-an-army-medic-using-a-tourniquet-to-control-major-bleeding/
The most recent war in Iraq was associated with a large number of injuries to soldiers. Dr. John Krahg and his associates from the US Army Institute of Surgical Research, Fort Sam Houston, TX diligently followed the outcome of the use of hundreds of tourniquets on hundreds of limbs. The abstracts from their published studies are copied herewith. The clear conclusion is that the use of the tourniquet in combat limb injuries is safe and effective. Most tourniquets did not stay on the limb for more than 2 hours, but some did. Nevertheless, no limbs were lost because of tourniquet use. This recent experience with devices that apply sufficient pressure to occlude arterial flow into the limb is highly relevant to the use of the EED. How is it possible to extend the duration of EED use beyond the 2 hours limit?The time limit of 120 minutes for the continuous use of the EED is based on the standard practice in orthopedic surgery and with the use of emergency/combat tourniquet. In most instances this should be sufficient time to evacuate the patient to definitive care in a medically controlled environment, to establish the other measures needed to stabilize the patient (Diagnostic tests, Surgical intervention if needed, IV fluids, blood, vasoactive drugs, antibiotics, steroids and the like) and to stabilize the patient's hemodynamics. However, sometimes 120 minutes are not enough, due to a variety of clinical and/or logistical reasons. In addiition, the requirement that the EED be removed from the patient gradually in small steps while monitoring his/her blood pressure and other indicators of hemodynamics, will sometimes require more time. The question of "buying" additional time becomes crucial.
Extending the tourniquet time is discouraged. Although the literature, including recommendations by authorities such as Mr. Leslie Klenerman from the UK, indicates that the use of a tourniquet for more than 2 hours (up to three hours) is not associated with irreversible injury to the limb, we do not recommend doing so, unless it is a clear case of "Life vs. Limb" condition with an explicit decision made by a competent physician. The alternative, proposed by Dr. David Tank, a pioneer in the use of the EED, is to apply a "rotating tourniquet" approach. Not unlike the old rotating (venous) tourniquet used in cases of sever CHF before positive pressure ventilation became widely available, Dr. Tang proposed to remove the EED from one leg, while applying two child-size EEDs to the arm at about 90 minutes after onset. About 30 minutes later, re-apply an EED on the free leg, while removing the EED from the second leg and from one or both arms. This process can be repeated while maintaining a very careful log of the duration of each limb blood flow occlusion. The Tang Method can extend the duration of EED application for several hours if transport is very long or for other reasons. Ischemia-Reperfusion and Time Interval between EED applications. The time interval from the removal of one EED and the application of another depends on the duration of the ischemia prior to the interval. Studies in experimental animals show that after one hour of ischemia, 20 minutes are sufficient for recovery of standard bicarbonate, potassium and Hydrogen Ion levels in the tissues. (Klenerman L. et Al. Systemic and local effects of application of a tourniquet. Journal of Bone and Joint Surgery 1980; 62B: 385-388. [Also on page 31 of the Tourniquet Manual by Klenerman]. If the tourniquet is kept on the limb for 2 hours, the data in this study shows that 40 minutes are needed to fully recover HCO3-, K+ and H+ levels. By extrapolation, one may deduce that 30 minutes of recovery are required after 1.5 hours of blood flow occlusion. Combining these data render the Tang method reasonable, although prospective validation is indicated. |
Practical use of emergency tourniquets to stop bleeding in major limb traumaJ Trauma. 2008 Feb;64(2 Suppl):S38-49; discussion S49-50.
KraghJF Jr, Walters TJ, Baer DG, Fox CJ, Wade CE, Salinas J, Holcomb JB. Source: US Army Institute of Surgical Research, Fort Sam Houston, TX 78234-6315, USA. [email protected] BACKGROUND: Previously we showed that tourniquets were lifesaving devices in the current war. Few studies, however, describe their actual morbidity in combat casualties. The purpose of this study was to measure tourniquet use and complications. METHODS: A prospective survey of casualties who required tourniquets was performed at a combat support hospital in Baghdad during 7 months in 2006. Patients were evaluated for tourniquet use, limb outcome, and morbidity. We identified potential morbidities from the literature and looked for them prospectively. The protocol was approved by the institutional review board. RESULTS: The 232 patients had 428 tourniquets applied on 309 injured limbs. The most effective tourniquets were the Emergency Medical Tourniquet (92%) and the Combat Application Tourniquet (79%). Four patients (1.7%) sustained transient nerve palsy at the level of the tourniquet, whereas six had palsies at the wound level. No association was seen between tourniquet time and morbidity. There was no apparent association of total tourniquet time and morbidity (clots, myonecrosis, rigor, pain, palsies, renal failure, amputation, and fasciotomy). No amputations resulted solely from tourniquet use. However, six (2.6%) casualties with eight preexisting traumatic amputation injuries then had completion surgical amputations and also had tourniquets on for >2 hours. The rate of limbs with fasciotomies with tourniquet time <or=2 hours was 28% (75 of 272) and >2 hours was 36% (9 of 25, p = 0.4). CONCLUSIONS: Morbidity risk was low, and there was a positive risk benefit ratio in light of the survival benefit. No limbs were lost because of tourniquet use, and tourniquet duration was not associated with increased morbidity. Education for early military tourniquet use should continue. Prehospital tourniquet use in Operation Iraqi Freedom: effect on hemorrhage control and outcomesJ Trauma. 2008 Feb; 64(2 Suppl):S28-37; discussion S37.
BeekleyAC, SebestaJA, BlackbourneLH, Herbert GS, KauvarDS, Baer DG, Walters TJ, MullenixPS, Holcomb JB; 31st Combat Support Hospital Research Group. Source Department of General Surgery, Madigan Army Medical Center, Fort Lewis, WA 98431-1100, USA. [email protected] BACKGROUND: Up to 9% of casualties killed in action during the Vietnam War died from exsanguination from extremity injuries. Retrospective reviews of prehospital tourniquet use in World War II and by the Israeli Defense Forces revealed improvements in extremity hemorrhage control and very few adverse limb outcomes when tourniquet times are less than 6 hours. HYPOTHESIS: We hypothesized that prehospital tourniquet use decreased hemorrhage from extremity injuries and saved lives, and was not associated with a substantial increase in adverse limb outcomes. METHODS: This was an institutional review board-approved, retrospective review of the 31st combat support hospital for 1 year during Operation Iraqi Freedom. Inclusion criteria were any patient with a traumatic amputation, major extremity vascular injury, or documented prehospital tourniquet. RESULTS: Among 3,444 total admissions, 165 patients met inclusion criteria. Sixty-seven patients had prehospital tourniquets (TK); 98 patients had severe extremity injuries but no prehospital tourniquet (No TK). Extremity Acute Injury Scores were the same (3.5 TK vs. 3.4 No TK) in both groups. Differences (p < 0.05) were noted in the numbers of patients with arm injuries (16.2% TK vs. 30.6% No TK), injuries requiring vascular reconstruction (29.9% TK vs. 52.5% No TK), traumatic amputations (41.8% TK vs. 26.3% No TK), and in those patients with adequate bleeding control on arrival (83% TK vs. 60% No TK). Secondary amputation rates (4 (6.0%) TK vs. 9 (9.1%) No TK); and mortality (3 (4.4%) TK vs. 4 (4.1%) No TK) did not differ. Tourniquet use was not deemed responsible for subsequent amputation in severely mangled extremities. Analysis revealed that four of seven deaths were potentially preventable with functional prehospital tourniquet placement. CONCLUSIONS: Prehospital tourniquet use was associated with improved hemorrhage control, particularly in the worse injured (Injury Severity Score >15) subset of patients. Fifty-seven percent of the deaths might have been prevented by earlier tourniquet use. There were no early adverse outcomes related to tourniquet use. Survival with emergency tourniquet use to stop bleeding in major limb trauma.Ann Surg. 2009 Jan;249(1):1-7.
KraghJF Jr, Walters TJ, Baer DG, Fox CJ, Wade CE, Salinas J, Holcomb JB. Source: US Army Institute of Surgical Research, Fort Sam Houston, TX, USA. OBJECTIVE: The purpose of this study was to determine if emergency tourniquet use saved lives. BACKGROUND DATA: Tourniquets have been proposed as lifesaving devices in the current war and are now issued to all soldiers. Few studies, however, describe their actual use in combat casualties. METHODS: A prospective survey of injured who required tourniquets was performed over 7 months in 2006 (NCT00517166 at ClinicalTrials.gov). Follow-up averaged 28 days. The study was at a combat support hospital in Baghdad. Among 2,838 injured and admitted civilian and military casualties with major limb trauma, 232 (8%) had 428 tourniquets applied on 309 injured limbs. We looked at emergency tourniquet use, and casualties were evaluated for shock (weak or absent radial pulse) and prehospital versus emergency department (ED) tourniquet use. We also looked at those casualties indicated for tourniquets but had none used. We assessed survival rates and limb outcome. RESULTS: There were 31 deaths (13%). Tourniquet use when shock was absent was strongly associated with survival (90% vs. 10%; P < 0.001). Prehospital tourniquets were applied in 194 patients of which 22 died (11% mortality), whereas 38 patients had ED application of which 9 died (24% mortality; P = 0.05). The 5 casualties indicated for tourniquets but had none used had a survival rate of 0% versus 87% for those casualties with tourniquets used (P < 0.001). Four patients (1.7%) sustained transient nerve palsy at the level of the tourniquet. No amputations resulted solely from tourniquet use. CONCLUSIONS: Tourniquet use when shock was absent was strongly associated with saved lives, and prehospital use was also strongly associated with lifesaving. No limbs were lost due to tourniquet use. Education and fielding of prehospital tourniquets in the military environment should continue. |
General information about the regulatory status of the EED
The EED is intended for use in patients whose systolic blood pressure is pathologically low (i.e. less than 80 mm Hg in adults) due to Hemodynamic Shock or Circulatory (Cardiac) Arrest. The EED shares technology with the Surgical Exsanguination Tourniquet manufactured by OHK as HemaClear (www.HemaClear.com) which has been cleared for use in many countries around the world. The following is information on the regulatory status of the device in various countries. Should you have any questions, please contact [email protected] .
Europe
The Surgical Exsanguination Tourniquet has the CE Mark as a sterile device used in orthopedic limb surgery to remove the blood from a limb to create a bleeding-free surgical field. The EED clearance by CE is in process.
The Surgical Exsanguination Tourniquet has the CE Mark as a sterile device used in orthopedic limb surgery to remove the blood from a limb to create a bleeding-free surgical field. The EED clearance by CE is in process.
USA
The Surgical Exsanguination Tourniquet was cleared by the FDA in 2002. The EED is currently being reviewed by the FDA.
The Surgical Exsanguination Tourniquet was cleared by the FDA in 2002. The EED is currently being reviewed by the FDA.
The Pneumatic Anti-Shock Garment (PASG), also called Medical (Military) Anti-Shock Trousers (MAST). It is shown ready for use with the two leg compartments (on right) and the abdominal wrap (on left). The air bladders are connected to the foot pump (black circular element) and a gauge with a relief valve which limits the pressure to 104 mm Hg above ambient pressure.
The pressure during pumping up is distributed evenly and does not act from proximal to distal as required for displacing blood into the central circulation.
The pressure during pumping up is distributed evenly and does not act from proximal to distal as required for displacing blood into the central circulation.
Is MAST a Must?
Noam Gavriely MD, DSc
State regulations in Illinois required until recently that every ambulance be equipped with a pneumatic anti-shock garment (PASG) or as it is often called, medical (military) anti-shock trousers (MAST). In the following paragraphs I shall review the physical and physiological rationale behind the MAST, some of the pitfalls associated with its use and the current clinical indications for its application (1,3).
PASG apply external positive pressure of up to 104 mm Hg to the legs and abdomen. Like with the cuff of a sphygmomanometer, the pressure inside the inflated air bladders of the device compresses the tissues beneath them and diminishes the transmural pressure (i.e. the pressure inside the vessel minus the pressure outside) acting on the walls of all the blood vessels in the tissue. The theoretical result is marked
reduction in vascular volume, and if the transmural pressure falls to zero or below (i.e. the pressure outside is equal to or greater than the blood pressure within), the blood vessels completely collapse and blood flow stops.
Shock continues to be a common cause of death in trauma and non-trauma (medical) patients. Inappropriate proportion between blood volume and vascular volume reduces blood flow and perfusion pressure to the essential organs (brain, heart, gut and kidneys) and reduces the supply of oxygen and metabolic substrates, which rapidly results in loss of function, cell destruction and death. This volume-volume discrepancy (VVD) is caused by either diminution of blood volume due to hemorrhage or dehydration or by inappropriate expansion of the blood
vessels due to anaphylaxis, sepsis or toxins. Substrate reserves and compensatory mechanisms provide a period of time the “Golden Window” in which adequate treatment aimed at restoring normal or near normal VVD and tissue perfusion can save the life of the shock victim. The presumed ability of PASG to reverse VVD, by reducing the vascular volume is the underlying rationale of its use in hope for extending the "Golden Window". It should be noted that cardiogenic shock is an exception as it is caused by pump failure and the PASG was never shown to be beneficial in this condition (7).
The physiological logic behind the introduction of PASG to widespread clinical use for treatment of shock in the mid 1970s was based on
the following four arguments:
1. Compression of blood vessels causes shifting of blood from the less essential tissues of the extremities to the central circulation – the ‘auto-transfusion’ effect. Unfortunately, this phenomenon was never confirmed in any of the studies that sought to document it.
2. Inflation of the PASG to the maximum level (104-mm Hg) completely collapses the arteries in the lower body, increases cardiac afterload and redirects the cardiac output to the essential organs. However, the benefit of this effect is limited and temporary; once the patient’s systolic blood pressure rises above 104-mm Hg, or the PASG pressure falls (or is reduced) to lower levels, quantities of blood escape under the most proximal bladders in each heart beat and are trapped distally as if the PASG was a large venous tourniquet. This is most noticeable in the perineal area that is not covered by the PASG. This phenomenon eventually deteriorates the VVD of the essential organs and worsens the patient’s condition.
3. External counter-pressure reduces bleeding from severed blood vessels beneath it. This confirmed beneficial effect of PASG is most apparent when the bleeding is due to blunt or penetrating abdominal injury (5). Direct manual pressure is probably as effective in tamponading hemorrhage from the groin area down, but PASG is probably superior when the bleeding is in the abdomen and retroperitoneal area.
4. PASG can be used to support and stabilize compound femoral fractures and fractures of the pelvis with or without shock. It reduces blood loss and provides temporary splinting of the bones during transport (4).
Pitfalls
Contrary to these potential advantages of PASG, several concerns were presented regarding its use:
1. Delay in transport. The application of PASG was shown to extend the time of transport by approximately 5 minutes when used by well-trained paramedics. This delay may be justified in situations where PASG use extends the ‘Golden Window’ by more than 5 minutes (9) and when transport of the victim to advanced care facility is expected to be longer than 30 minutes.
2. When PASG is applied to patients with chest trauma, especially when there is bleeding into the pleural space, multiple rib fractures, cardiac tamponade etc. it may actually increase blood loss, it interferes with breathing and may reduce cardiac output due to afterload hike (6).
3. Use of PASG during air transport, where ambient air pressures change significantly, is not desired (8). While ascending, the ambient air pressure falls and the air bladders become hyperinflated, loosing air through the pressure-regulating valve. Then, when descending, increased ambient pressure compresses the air in the bladders and their tension diminishes. This inadvertent fall in PASG pressure may cause the venous tourniquet effect mentioned above and a rapid deterioration in the patient’s condition.
4. Sudden removal of the PASG or loss of bladder pressure is associated with deterioration of the patient’s condition. There are several causes for this including the change in afterload distribution and the sudden flooding of the central circulation with lactic acid-rich blood from the lower
extremities.
5. PASG application limits the access to the lower body of the patient. It must be removed before diagnostic and/or surgical procedures are performed on the abdomen, groin area (e.g. femoral vein access) and the legs. This may be in conflict with the limitations outlined in paragraph 4 above.
6. There are now data showing that optimal blood pressure in a trauma victim prior to definitive hemorrhage control is approximately 80-100 mm Hg, not higher. Maintaining this blood pressure reduces bleeding and help prevent dislodging of early soft clots that were formed at the injury site. The PASG does not readily permit titration of its effect to achieve the desired blood pressure. Any reduction of PASG pressure under the patient’s systolic blood pressure that results in lowering BP is due to distal trapping of blood (the venous tourniquet effect), an undesired side effect of the PASG.
Clinical experience
Studies conducted in the mid- to late- 1980s evaluated the outcome of shock victims when PASG was used or avoided. The studies were design so that PASG is used on alternate days on all hypotensive (BP<90 mm Hg) patients and is not used on the other days. Over 900 patients were enrolled in one of the studies (2). The data showed no advantage of PASG use in terms of overall survival. This study included patients with chest trauma and intrathoracic hemorrhage, a condition in which PASG was known to be detrimental from early on (6). Indeed this group had worse results when PASG was used which influenced the overall statistics. Another study where PASG was used for victims of abdominal trauma with profound shock (BP<70 mm Hg) showed that use of PASG had a tendency to improve the outcome (9).
PASG has been shown to be of some benefit in patients with VVD due to anaphylaxis or sepsis. Few anecdotal reports indicate that PASG
application should be considered as an added temporary measure in these conditions (10).
Summary
The theoretical physiological basis of using external counter-pressure in the treatment of shock is valid. Measures to improve VVD are clearly desired. However, it is obvious that the existing designs of PASG are sub-optimal. It is probably prudent to use PASG when abdominal trauma is
associated with significant shock and when pelvis or femoral fractures are suspected. PASG should definitely not be used in chest trauma patients and when transport to definite care is expected to be quick. Clinical judgement, based on clear understanding of the PASG physiological effects, should be used whenever shock is threatening the patient survival.
Additional reading
1. Robert E. O’Connor, MD, MPH; Robert Domeier, MD Use of the Pneumatic AntiShock Garment (PASG) Prehospital Emergency Care, January/March 1997, (Approved by the NAEMSP Board of Directors in 1996).
2. Mattox KL, Bickell W, Pepe PE, Burch J& Feliciano D: Prospective MAST study in 911 patients. J Trauma. 1989;29:1104-1112.
3. McSwain NE Pneumatic anti-shock garment: State of the art. 1988. Ann. Emerg. Med.,
17:506-525. [A review with good insight into the physics and physiology of PASG]
4. Moreno C, Moore EE, Rosenberger A& Cleveland HC: Hemorrhage associated with major pelvic fracture: a multispecialty challenge. J
Trauma. 1986;26:987-994. [Supports use of PASG in pelvic fructure]
5. Hibbard LT: Spontaneous rupture of the liver in pregnancy: a report of eight cases. Am J Obstet Gynecol. 1976;126:334-338. [The two women who survived were treated with PASG]
6. Honigman B, Lowenstein SR, Moore EE, Roweder K& Pons P: The role of the pneumatic antishock garment in penetrating cardiac wounds. JAMA. 1991;266:2398-2401. [Bad outcome]
7. Jabbour I, Savino JA, Agarwal N& Byrne D: Pneumatic antishock garments detrimental in elderly with diminished myocardial reserve. Curr Surg. 1986;43:498-501. [Do not use in pump failure]
8. Sanders AB, Meislin HW: Effect of altitude change on MAST suit pressure. Ann Emerg Med. 1983;12:140-144. [Basic physics]
9. Cayten CG, Berendt BM, Byrne DW, Murphy JG& Moy FH: A study of pneumatic antishock garments in severely hypotensive trauma patients. J Trauma. 1993;34:728-735. [Improved outcome in profound shock and abdominal injury in an urban setting]
10. Oertel T, Loehr MM: Bee-sting anaphylaxis: the use of medical antishock trousers. Ann Emerg Med. 1984;13:459-461. [Case of patient on beta-blocker, who improved only after PASG was applied]
`
State regulations in Illinois required until recently that every ambulance be equipped with a pneumatic anti-shock garment (PASG) or as it is often called, medical (military) anti-shock trousers (MAST). In the following paragraphs I shall review the physical and physiological rationale behind the MAST, some of the pitfalls associated with its use and the current clinical indications for its application (1,3).
PASG apply external positive pressure of up to 104 mm Hg to the legs and abdomen. Like with the cuff of a sphygmomanometer, the pressure inside the inflated air bladders of the device compresses the tissues beneath them and diminishes the transmural pressure (i.e. the pressure inside the vessel minus the pressure outside) acting on the walls of all the blood vessels in the tissue. The theoretical result is marked
reduction in vascular volume, and if the transmural pressure falls to zero or below (i.e. the pressure outside is equal to or greater than the blood pressure within), the blood vessels completely collapse and blood flow stops.
Shock continues to be a common cause of death in trauma and non-trauma (medical) patients. Inappropriate proportion between blood volume and vascular volume reduces blood flow and perfusion pressure to the essential organs (brain, heart, gut and kidneys) and reduces the supply of oxygen and metabolic substrates, which rapidly results in loss of function, cell destruction and death. This volume-volume discrepancy (VVD) is caused by either diminution of blood volume due to hemorrhage or dehydration or by inappropriate expansion of the blood
vessels due to anaphylaxis, sepsis or toxins. Substrate reserves and compensatory mechanisms provide a period of time the “Golden Window” in which adequate treatment aimed at restoring normal or near normal VVD and tissue perfusion can save the life of the shock victim. The presumed ability of PASG to reverse VVD, by reducing the vascular volume is the underlying rationale of its use in hope for extending the "Golden Window". It should be noted that cardiogenic shock is an exception as it is caused by pump failure and the PASG was never shown to be beneficial in this condition (7).
The physiological logic behind the introduction of PASG to widespread clinical use for treatment of shock in the mid 1970s was based on
the following four arguments:
1. Compression of blood vessels causes shifting of blood from the less essential tissues of the extremities to the central circulation – the ‘auto-transfusion’ effect. Unfortunately, this phenomenon was never confirmed in any of the studies that sought to document it.
2. Inflation of the PASG to the maximum level (104-mm Hg) completely collapses the arteries in the lower body, increases cardiac afterload and redirects the cardiac output to the essential organs. However, the benefit of this effect is limited and temporary; once the patient’s systolic blood pressure rises above 104-mm Hg, or the PASG pressure falls (or is reduced) to lower levels, quantities of blood escape under the most proximal bladders in each heart beat and are trapped distally as if the PASG was a large venous tourniquet. This is most noticeable in the perineal area that is not covered by the PASG. This phenomenon eventually deteriorates the VVD of the essential organs and worsens the patient’s condition.
3. External counter-pressure reduces bleeding from severed blood vessels beneath it. This confirmed beneficial effect of PASG is most apparent when the bleeding is due to blunt or penetrating abdominal injury (5). Direct manual pressure is probably as effective in tamponading hemorrhage from the groin area down, but PASG is probably superior when the bleeding is in the abdomen and retroperitoneal area.
4. PASG can be used to support and stabilize compound femoral fractures and fractures of the pelvis with or without shock. It reduces blood loss and provides temporary splinting of the bones during transport (4).
Pitfalls
Contrary to these potential advantages of PASG, several concerns were presented regarding its use:
1. Delay in transport. The application of PASG was shown to extend the time of transport by approximately 5 minutes when used by well-trained paramedics. This delay may be justified in situations where PASG use extends the ‘Golden Window’ by more than 5 minutes (9) and when transport of the victim to advanced care facility is expected to be longer than 30 minutes.
2. When PASG is applied to patients with chest trauma, especially when there is bleeding into the pleural space, multiple rib fractures, cardiac tamponade etc. it may actually increase blood loss, it interferes with breathing and may reduce cardiac output due to afterload hike (6).
3. Use of PASG during air transport, where ambient air pressures change significantly, is not desired (8). While ascending, the ambient air pressure falls and the air bladders become hyperinflated, loosing air through the pressure-regulating valve. Then, when descending, increased ambient pressure compresses the air in the bladders and their tension diminishes. This inadvertent fall in PASG pressure may cause the venous tourniquet effect mentioned above and a rapid deterioration in the patient’s condition.
4. Sudden removal of the PASG or loss of bladder pressure is associated with deterioration of the patient’s condition. There are several causes for this including the change in afterload distribution and the sudden flooding of the central circulation with lactic acid-rich blood from the lower
extremities.
5. PASG application limits the access to the lower body of the patient. It must be removed before diagnostic and/or surgical procedures are performed on the abdomen, groin area (e.g. femoral vein access) and the legs. This may be in conflict with the limitations outlined in paragraph 4 above.
6. There are now data showing that optimal blood pressure in a trauma victim prior to definitive hemorrhage control is approximately 80-100 mm Hg, not higher. Maintaining this blood pressure reduces bleeding and help prevent dislodging of early soft clots that were formed at the injury site. The PASG does not readily permit titration of its effect to achieve the desired blood pressure. Any reduction of PASG pressure under the patient’s systolic blood pressure that results in lowering BP is due to distal trapping of blood (the venous tourniquet effect), an undesired side effect of the PASG.
Clinical experience
Studies conducted in the mid- to late- 1980s evaluated the outcome of shock victims when PASG was used or avoided. The studies were design so that PASG is used on alternate days on all hypotensive (BP<90 mm Hg) patients and is not used on the other days. Over 900 patients were enrolled in one of the studies (2). The data showed no advantage of PASG use in terms of overall survival. This study included patients with chest trauma and intrathoracic hemorrhage, a condition in which PASG was known to be detrimental from early on (6). Indeed this group had worse results when PASG was used which influenced the overall statistics. Another study where PASG was used for victims of abdominal trauma with profound shock (BP<70 mm Hg) showed that use of PASG had a tendency to improve the outcome (9).
PASG has been shown to be of some benefit in patients with VVD due to anaphylaxis or sepsis. Few anecdotal reports indicate that PASG
application should be considered as an added temporary measure in these conditions (10).
Summary
The theoretical physiological basis of using external counter-pressure in the treatment of shock is valid. Measures to improve VVD are clearly desired. However, it is obvious that the existing designs of PASG are sub-optimal. It is probably prudent to use PASG when abdominal trauma is
associated with significant shock and when pelvis or femoral fractures are suspected. PASG should definitely not be used in chest trauma patients and when transport to definite care is expected to be quick. Clinical judgement, based on clear understanding of the PASG physiological effects, should be used whenever shock is threatening the patient survival.
Additional reading
1. Robert E. O’Connor, MD, MPH; Robert Domeier, MD Use of the Pneumatic AntiShock Garment (PASG) Prehospital Emergency Care, January/March 1997, (Approved by the NAEMSP Board of Directors in 1996).
2. Mattox KL, Bickell W, Pepe PE, Burch J& Feliciano D: Prospective MAST study in 911 patients. J Trauma. 1989;29:1104-1112.
3. McSwain NE Pneumatic anti-shock garment: State of the art. 1988. Ann. Emerg. Med.,
17:506-525. [A review with good insight into the physics and physiology of PASG]
4. Moreno C, Moore EE, Rosenberger A& Cleveland HC: Hemorrhage associated with major pelvic fracture: a multispecialty challenge. J
Trauma. 1986;26:987-994. [Supports use of PASG in pelvic fructure]
5. Hibbard LT: Spontaneous rupture of the liver in pregnancy: a report of eight cases. Am J Obstet Gynecol. 1976;126:334-338. [The two women who survived were treated with PASG]
6. Honigman B, Lowenstein SR, Moore EE, Roweder K& Pons P: The role of the pneumatic antishock garment in penetrating cardiac wounds. JAMA. 1991;266:2398-2401. [Bad outcome]
7. Jabbour I, Savino JA, Agarwal N& Byrne D: Pneumatic antishock garments detrimental in elderly with diminished myocardial reserve. Curr Surg. 1986;43:498-501. [Do not use in pump failure]
8. Sanders AB, Meislin HW: Effect of altitude change on MAST suit pressure. Ann Emerg Med. 1983;12:140-144. [Basic physics]
9. Cayten CG, Berendt BM, Byrne DW, Murphy JG& Moy FH: A study of pneumatic antishock garments in severely hypotensive trauma patients. J Trauma. 1993;34:728-735. [Improved outcome in profound shock and abdominal injury in an urban setting]
10. Oertel T, Loehr MM: Bee-sting anaphylaxis: the use of medical antishock trousers. Ann Emerg Med. 1984;13:459-461. [Case of patient on beta-blocker, who improved only after PASG was applied]
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Comparison of the EED and PASG/MAST
We developed the "Extremity Exsanguination Device" (EED), 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 EED, 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 EED applies the pressure from distal to proximal, while the PASG applie it to the lower body en bloc.
b. The EED 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 EED application is actually due to elevated hepatic blood flow induced by the auto-transfusion.
c. Unlike the PASG, the EED 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 EED design.
d. The effect of the EED 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 EED 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 EED 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 EED:
The EED is much smaller (320 g per set of two vs. 4.5 kg) and occupies much less space.
The EED is intended for single use, while the PASG is not.
Once the EED 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.
The EED is not a pneumatic device. As such it is not affected by changes in ambient atmospheric pressure and/or temperature.
The EED cannot be removed inadvertently as was reported with the Velcro fasteners of some versions of the PASG.
Applying the EED 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 EED 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 average of 5 minutes longer transport time in patients who were treated with MAST.
Training: use of the EED 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: the EED cost is a small fraction of that of the PASG.
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 EED, 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 EED applies the pressure from distal to proximal, while the PASG applie it to the lower body en bloc.
b. The EED 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 EED application is actually due to elevated hepatic blood flow induced by the auto-transfusion.
c. Unlike the PASG, the EED 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 EED design.
d. The effect of the EED 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 EED 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 EED 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 EED:
The EED is much smaller (320 g per set of two vs. 4.5 kg) and occupies much less space.
The EED is intended for single use, while the PASG is not.
Once the EED 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.
The EED is not a pneumatic device. As such it is not affected by changes in ambient atmospheric pressure and/or temperature.
The EED cannot be removed inadvertently as was reported with the Velcro fasteners of some versions of the PASG.
Applying the EED 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 EED 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 average of 5 minutes longer transport time in patients who were treated with MAST.
Training: use of the EED 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: the EED cost is a small fraction of that of the PASG.
