Although hyperbaric oxygen (HBO) is as effective as cephalothin against osteomyelitis due to Staphylococcus aureus in the rabbit, the effect is not by directing killing. To investigate the mechanism, argon washouts (perfusion) and oxygen tensions were measured by intramedullary probes placed in the metaphyses of infected and uninfected tibias. In vitro phagocytic killing activity for S. aureus was determined at oxygen tensions found in these bones under ambient and HBO conditions. Mean tibial oxygen tensions (mm Hg) under ambient conditions were 21 (infected) and 45 (uninfected); under HBO conditions, 104 (infected) and 321 (uninfected). Perfusion was decreased in osteomyelitic bone and was not acutely increased by HBO in either normal or infected bone. Phagocytic killing of S. aureus was markedly decreased at 23 mm Hg of O2, significantly improved at 45 and 109 mm Hg, and most effective at 150 mm Hg. Thus, in osteomyelitic bone, HBO increased intramedullary oxygen to tensions consistent with normal phagocytic function.

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Hyperbaric oxygen (HBO) is used as adjunctive therapy of chronic osteomyelitis, but its efficacy remains controversial. A recently developed rabbit model for osteomyelitis due to Staphylococcus aureus was used to compare the results of treatment with HBO, cephalothin, a combination of both, or no treatment. Cultures of bone were positive in 10 (91%) of 11 control animals (untreated), five (36%) of 14 animals treated with HBO, eight (47%) of 17 treated with cephalothin, and six (40%) of 15 treated with HBO plus cephalothin. All three treatment groups differed significantly from untreated controls in the number of positive cultures obtained (P less than 0.01), but there were no significant differences among treatment groups. In vitro growth and killing curves (1.0 microgram of cephalothin/ml) constructed after exposure to HBO revealed no change from parallel control studies in ambient air. These data demonstrate that therapy with HBO is at least as effective as antibiotic therapy. The therapeutic effectiveness of HBO does not appear to be related to antibacterial activity.

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