Download A Scientific Explanation of Automatic Tourniquet System

A Scientific Explanation of Automatic Tourniquet System
A tourniquet is a constricting or compressing device used to control venous and
arterial circulation to an extremity for a period of time. Pressure is applied
circumferentially upon the skin and underlying tissues of a limb; this pressure is
transferred to the walls of vessels, causing them to become temporarily occluded. It is
generally used as a tool for a medical professional in applications such as cannulation
or to stem the flow of traumatic bleeding, especially by military medics
Surgical tourniquets prevent blood flow to a limb and enable surgeons to work in a
bloodless operative field. This allows surgical procedures to be performed with
improved precision, safety and speed. Tourniquets are widely used in orthopedic and
plastic surgery, as well as in intravenous regional anesthesia (Bier block anesthesia)
where they serve the additional function of preventing local anesthetic in the limb
from entering general circulation
Surgical tourniquets enable surgeons to work in a bloodless operative field by
preventing blood flow to a limb. This allows surgical procedures to be performed with
improved precision, safety and speed. Tourniquets are widely used in orthopedic and
plastic surgery, as well as in intravenous regional anesthesia (Bier block anesthesia)
where they serve the additional function of preventing local anesthetic in the limb
from entering general circulation.
In the early 1980s, microprocessor-controlled pneumatic tourniquets were invented by
Dr James McEwen, PhD [1][2]. Automatic tourniquets based on this invention are
now standard equipment in operating rooms worldwide, and these systems have
significantly improved the safety and convenience of tourniquet use.
Despite many advances in tourniquet technology, tourniquet-related injuries continue
to be of concern. High pressures under a tourniquet cuff can cause nerve, muscle and
skin injury. Minimizing tourniquet pressure, reducing inflation time and using a
microprocessor-controlled pneumatic tourniquet, which allows pressure to be
accurately monitored and controlled, reduce the risk of tourniquet-related injury
An emergency tourniquet is a tightly tied band applied around a body part (an arm or
a leg) sometimes used in an attempt to stop severe traumatic bleeding.[1] Tourniquets
are also used during venipuncture and other medical procedures. Severe bleeding
means the loss of more than 1,000 ml (1 liter) of blood. This flow of blood can soak a
paper or cloth handkerchief in a few seconds. In such a situation, the bleeding will
cause the death of the casualty in seconds to minutes.
In most applications, a tourniquet is a last resort method of bleeding control as all
blood flow below the application of an emergency tourniquet is stopped, and can
subsequently kill the tissue, leading to eventual loss of the limb below
application.[1][2][3]
Even in cases of amputation, most bleeding can be controlled through alternative
methods such as direct pressure. The rare exception is when a limb is shattered by
massive trauma or when a major blood vessel is torn along its length. Even in these
cases, the use of a pressure point above the wound (i.e. proximal to the wound), or
application by a doctor of a hemostat to clamp the blood vessel above the tear can be
used.
However, using of tourniquets is widespread in military applications, and has the
potential to save lives during major limb trauma. Analysis has shown that in cases of
major limb trauma, there is no apparent link between tourniquet application and
morbidity of the limb.
Current technology
In recent years there have been significant advancements in tourniquets. These
advancements have vastly improved tourniquet safety.
Limb occlusion pressure
Limb occlusion pressure (LOP) is the minimum tourniquet pressure required to
occlude blood flow to a specific patient's limb at a specific time and accounts for a
patient’s limb and vessel characteristics, and the type and fit of the cuff. LOP can be
determined by gradually increasing tourniquet pressure until distal arterial pulses
cease, as indicated by a device sensing blood flow, such as a Doppler stethoscope.
Studies have shown that cuff pressure based on LOP measured immediately prior to
surgery is generally lower than commonly used cuff pressures and is sufficient to
maintain a satisfactory surgical field.
Automatic systems
Automatic tourniquet systems are capable of providing safety features that are not
possible in older mechanical tourniquets. These systems can monitor the cuff inflation
time as well as regulate the cuff pressure to a known pressure throughout the surgical
procedure. Some microprocessor controlled tourniquets are capable of calculating
LOP in about 30 seconds. This assists the operating room staff in deciding what the
tourniquet pressure should be set at on a per-patient basis.
Contoured and wide cuffs
Studies have shown that tourniquet cuff pressure can be substantially reduced by
using wide, contoured cuffs. A wider and contoured cuff has more contact with the
limb's surface area and disperses the cuff's force. This concept is emerging from the
surgical field into the emergency field with wider emergency tourniquets.
Integrated tourniquet cuff testing
The Association of preoperative Registered Nurses (AORN) recommends that the
tourniquet cuff, tubing, connectors, gauges, and pressure source should be kept clean
and in working order. Some modern tourniquet systems are capable of testing these
items in 30 seconds.
Bier block anesthesia is an intravenous regional anesthesia technique in which an
extremity (generally an arm) is made numb for surgery by injecting a local anesthetic
solution into a vein after the blood has been squeezed out of the extremity and a
tourniquet has been placed on it. The tourniquet prevents the local from leaving the
extremity and blood from entering it, giving the patient a numb (anesthetic) extremity
and the surgeon a bloodless field to work in.
The advantages of the technique is that it is simple to perform, and provides a
bloodless field that is easy to work in and minimizes blood loss. The disadvantages
are that there is a practical time limit on its use (1 - 2 hours) due to the tourniquet
restricting blood flow to the extremity. Thus, the tissues of the extremity are not
getting oxygen. The extremity could eventually be damaged, and large doses of local
anesthetic are required intravenously to produce the numbness. If the tourniquet is
released before a large amount of the local anesthetic is metabolized or chemically
bound, there is a possibility of a toxic blood level with the attendant problems
Tourniquet test
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For Tourniquet, see that article
A tourniquet test (also known as a Rumpel-Leede Capillary-Fragility Test or simply a
capillary fragility test) determines capillary fragility. It is a clinical diagnostic method
to determine a patient's hemorrhagic tendency. It assesses fragility of capillary walls
and is used to identify thrombocytopenia (a reduced platelet count).
The test is defined by the WHO as one of the necessary requisites for diagnosis of
Dengue fever. A blood pressure cuff is applied and inflated to a point between the
systolic and diastolic blood pressures for five minutes. The test is positive if there are
more than 20 petechia per square inch (a petechia is a small red or purple spot on the
body, caused by a minor hemorrhage).
This test does not have high specificity. Interfering factors with this test are women
who are premenstrual, postmenstrual and not taking hormones, or those with sun