Safety

Safety of the MBV – effect on the limbs

Stopping 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 successfully in several hundreds of US soldiers in combat.

Time limits

The 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 threshold for functionality cessation. In addition, the tissue capacity to generate ATP from anaerobic 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 anaerobic 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.

How is it possible to extend the duration of MBV use beyond the 2 hours limit?

The time limit of 120 minutes for the continuous use of the MBV 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 MBV 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 MBV, 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 MBV from one leg, while applying two child-size MBVs to the arm at about 90 minutes after onset. About 30 minutes later, re-apply an MBV on the free leg, while removing the MBV 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 MBV application for several hours if transport is very long or for other reasons.

Ischemia-Reperfusion and Time Interval between MBV applications.

The time interval from the removal of one MBV 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.

Prehospital tourniquet use in Operation Iraqi Freedom: effect on hemorrhage control and outcomes

J 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. alec.beekley@us.army.mil

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.