HBO in experimental models of infections

A certain number of experimental studies have been based on these mechanical effects. The earliest, carried out by Brummelkamp86, Holland87, and Demello88, showed the usefulness - in a decreasing order - of antibiotic therapy, surgical drainage, and HBO for treating Clostridium infections.

The early work proved the effectiveness of HBO in experimental models of soft-tissue anaerobic infections. In a study performed by Hill89, a standardized inoculum of C. perfringens and adrenaline was injected in the paws of mice to trigger ischemic infection. The animals were sorted into 2 groups which were subjected to repeated sessions of HBO at 2 or 3 ata of pure oxygen, and a 3rd group was kept as a control group. A significant difference in mortality was shown in favour of the higher pressure of oxygen.

Further work in this field was carried out by Demello88 who assessed the effectiveness of antibiotic therapy, surgical drainage and HBO in a model of gas gangrene with C. perfringens in dogs (Table 2.2.4-4).

No survivals were obtained by surgery (extensive incision, drainage and rising with antiseptic solutions), HBO, or a combination of both. There was some improvement in survival after antibiotic therapy combining penicillin and another antibiotic with an effect on aerobic germs such as tetracycline.

But mostly, the best survival percentages were obtained by combining the 3 forms of therapy88.

Table 2.2.4-4. Comparative study of different treatments against experimental gas gangrene in dogs (from Demello et al.88)._

Therapy_Survival (%)

Surgery 0

HBO 0

HBO + surgery 0

Antibiotic therapy 50

Antibiotics + surgery 70

Antibiotics + surgery + HBO 95

These early data have been confirmed by more recent data: Hirn found a significantly more favourable effect on the survival of rats which had been injected with Clostridium perfringens to trigger experimental gangrene, in the group treated by a combination of surgery and HBO as in the group where surgery only was provided90. In a model of intra-peritoneal poly-microbial infection, Thom identified a significantly favourable effect on mortality in the group treated by HBO as compared to the control group91.

Lastly, the usefulness of HBO was studied in a model of muscle infection involving Streptococci as a result of the general interest taken in soft-tissue Streptococci infections (these were described in the English press as "flesh eating bacterial disease")92. Conclusions were similar to those reached previously in other experimental models involving other bacteria: when used alone, HBO changes neither mortality nor bacterial proliferation; antibiotic therapy (in this case penicillin was used) is effective on both criteria; and combining antibiotic and HBO therapies was significantly more effective on both criteria than antibiotic therapy alone.

To conclude, animal models have proved that although pressures of oxygen play a part in the development of soft-tissue infections, a hierarchy exists regarding effectiveness of the different therapies available. HBO cannot be used on its own, and the best results are obtained when it is combined with antibiotic therapy and surgery.

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