A temporal analysis of the effects of pressurized oxygen (HBO) on the pH of amputated muscle tissue

The effect of hyperbaric oxygen (HBO) on ischemic muscle tissue pH was evaluated continuously. The hind limbs of male Sprague-Dawley rats (N = 11, both groups) were amputated and stored in room air (20.1% oxygen [O₂], 1.0 ATM, 24°C) or in HBO (100% O₂, 2.9 ATM, 24°C) for 240 minutes. Rat muscle tissue pH was continuously monitored with a micro-pH electrode following amputation. There was no significant difference between the average starting tissue pH of control and treated limbs (p = 0.45). At 240 minutes of ischemia the control group tissue pH decreased 0.80 pH units whereas the treatment group decreased 0.68 pH units (p < 0.05). The tissue pH of control limbs declined 30.7 times faster than treated limbs during the first 36 minutes of ischemia (p < 0.05). From 36 to 240 minutes the rates of acidosis were similar and did not differ significantly (p = 0.46). In a separate study, male Sprague-Dawley rats were anesthetized with pentobarbital and ketamine. Aortic arterial blood gases were obtained at 5 minutes (N = 8) and 15 minutes (N = 8) postanesthesia. The average serum pH, carbon dioxide, oxygen, and bicarbonate levels remained within normal limits in both groups and did not differ significantly (p > 0.05 for all parameters). Anesthesia produced no serum respiratory or metabolic acidosis and did not contribute to the initial ischemic tissue pH. These results suggest that HBO delays the progression of metabolic acidosis in this amputated limb model. This is further supporting evidence for the tissue-preserving effect of oxygen when delivered in hyperbaric conditions. However, the clinical application of this technique may be limited due to the difference in the volume of tissue presented for major limb replantation and the short window of beneficial effects.