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Gas gangrene

September 17, 2019


Gas gangrene is a bacterial infection
that produces gas in tissues in gangrene. This deadly form of gangrene
usually is caused by Clostridium perfringens bacteria. It is a medical
emergency. Myonecrosis is a condition of necrotic
damage, specific to muscle tissue. It is often seen in infections with C.
perfringens or any of myriad soil-borne anaerobic bacteria. Bacteria cause
myonecrosis by specific exotoxins. These microorganisms are opportunistic and, in
general, enter the body through significant skin breakage. Gangrenous
infection by soil-borne bacteria was common in the combat injuries of
soldiers well into the 20th century, because of nonsterile field surgery and
the basic nature of care for severe projectile wounds.
Other causes of myonecrosis include envenomation by snakes of the Bothrops
genus, ischemic necrosis, caused by vascular blockage, tumours that block or
hoard blood supply, and disseminated intravascular coagulation or other
thromboses. Features
Gas gangrene can cause myonecrosis, gas production, and sepsis. Progression to
toxemia and shock is often very rapid. It can easily be noticed by the large,
blackened sores that form, as well as a degree of loud and distinctive crepitus
caused by gas escaping the necrotic tissue.
Pathophysiology Gas gangrene is caused by
exotoxin-producing Clostridium species, which are mostly found in soil, but also
found as normal gut flora, and other anaerobes. The exotoxin is commonly
found in C. perfringens type A strain and is known as alpha toxin. This alpha
toxin is a lethal toxin and also known as phospolipase C. It increases vascular
permeability and produces necrotizing activity. These environmental bacteria
may enter the muscle through a wound and go on to proliferate in necrotic tissue
and secrete powerful toxins. These toxins destroy nearby tissue, generating
gas at the same time. Other organisms may occasionally cause
gas gangrene. A gas composition of 5.9% hydrogen, 3.4%
carbon dioxide, 74.5% nitrogen, and 16.1% oxygen was reported in one
clinical case. Myonecrosis differs slightly from other
types of necrosis. While the underlying causes are almost identical, the type of
affected tissue is significantly more important for the patient’s general
health. Superficial necrosis is unsightly and can lead to unattractive
scarring, but otherwise does not affect the patient’s likelihood of survival or
physical capability to the same extent. However, massive myonecrosis will likely
result in the loss of movement of the entire region. If the necrotic damage is
allowed to continue throughout an affected limb, then often that entire
limb is lost permanently. It is often difficult to identify the
extent of muscle damage, as C. perfringens may be at work in deeper
fascial layers below the skin. Unlike other anaerobic infections, discharge in
these infections is often not purulent. Instead, the discharge is often
described as “sweetly putrid” or “dishwater pus” because it is much
thinner than normal pus. This is due to the lysis of neutrophils, a type of
white blood cell, caused by the lecithinases and other toxins released
by Clostridium species. Soil-borne anaerobes are particularly
well-adapted to surviving harsh conditions. Often, a scarcity of
nutrition and competition for resources from numerous other species occurs.
Changes in pH and temperature are often significant, also. Bacteria often
possess the ability to create exotoxins to assist them in competing with other
microbes in their natural environments. When such bacteria are able to enter a
living host, they encounter a vast supply of nutrients, warm conditions,
and an abundance of water. This enables the microbes to rapidly proliferate, far
in excess of the immune system’s capability to defend, as prokaryotic
bacteria possess a far greater capacity for multiplication than the host’s
immune system. The combination of bacterial load and ability to multiply
is the basis for the microbes’ ability to cause massive infection. Alongside
such rapid proliferation is a corresponding mass-production of
exotoxin that causes severe damage to local tissue in the host. One such
exotoxin is produced by C. perfringens and is responsible for the disease
manifestations. This exotoxin is known as alpha toxin.
Massive infection, gross injury, and depletion of the host’s immune
capability result in system-wide sepsis. This is partly due to the burden on the
immune system, its corresponding release of inflammatory cytokines, and the
distribution of bacterial toxins. Massive infection is likely to result in
death from a combination of system-wide septic shock and the unintentionally
damaging effects of the immune response. In animals, disability and distress
caused by all of these factors markedly increase the chance of predation.
Treatment Treatment is usually debridement and
excision, with amputation necessary in many cases. Antibiotics alone are not
effective because they do not penetrate ischaemic muscles sufficiently to be
effective. However, penicillin is given as an adjuvant treatment to surgery. In
addition to surgery and antibiotics, hyperbaric oxygen therapy is used and
acts to inhibit the growth of and kill the anaerobic C. perfringens. The growth
of C. perfrigens is inhibited under pressures above 9.5 kPa, so if started
early, this condition can mostly be cured.
Additional images See also
Blackleg List of cutaneous conditions
References

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