Acute Infections
Anaerobic bacteria are especially sensitive to increased tissue
PO2
, as mentioned previously, probably
because of the lack of antioxidant defenses such as superoxide dismutase in these
bacteria. Inhibition of exotoxin production, especially the α-toxin of Clostridium
species, by high O2
tension has been demonstrated.[135]
Because the systemic manifestations of clostridial infection are largely attributable
to the production of toxin, the clear beneficial effects of HBO in this type of infection
are often attributed to this mechanism. A large clinical series of clostridial myonecrosis
has been published by Bakker and van de Kleij,[25]
[26]
and it appears that early treatment of disease
with HBO, in addition to antibiotics and appropriate surgical débridement,
can be limb saving and probably lifesaving. An immediate clinical response to HBO
may often be seen in these patients, including a reduction in tissue crepitus, heart
rate, cardiac output, and other signs of sepsis. Hyperbaric treatment should not
be delayed and may be used beneficially before surgery to preserve viable infected
tissue and allow better demarcation for surgical débridement.[25]
[26]
Typical treatment schedules for clostridial myonecrosis are up
to 3.06 ATA for 90 minutes while the patient breathes 100% O2
. Commonly,
three HBO treatments are administered within the first 24 hours, five times within
the first 48 hours, and then twice daily for a total of seven to nine treatments,
by which time the clinical course of the infection is usually evident.
Initially, it may be difficult to differentiate clostridial from
nonclostridial infections, and evidence has shown that patients with either infection
benefit from HBO in a manner similar to that of documented clostridial infection.
HBO also appears to offer a significant reduction in morbidity and mortality in
nonclostridial necrotizing infections, as documented in a controlled trial.[29]
[30]
A meta-analysis of 554 published cases indicated
a mortality of 44% in patients not treated with HBO versus 20% in HBO-treated patients.
[136]
Because many nonclostridial infections are
indolent, treatment beyond the first 3 or 4 days may be beneficial.
The traditional rationale for the treatment of anaerobic soft
tissue necrotizing infections with high oxygen pressure is that high tissue PO2
will directly inhibit the growth of anaerobic bacteria or reverse hypoxia-induced
neutrophil function.[31]
[137]
[138]
However, there is evidence for other mechanisms.
In experimental animals, HBO has been demonstrated to reduce lung, liver, and intestinal
injury after the administration of zymosan.[139]
[140]
In a model of chemical-induced colitis, HBO
administration reduced inflammation as assessed by colonic weight, myeloperoxidase
and NO synthase activity, and the generation of prostaglandin E2
and leukotriene
B4
.[141]
