Determination of oxygen dosage effects on cytochrome oxidase after anoxia in brain.

Recent evidence reports that high doses of O(2) administered via hyperbaric oxygen therapy (HBOT) improve the return of spontaneous circulation (ROSC), and the outcome of damage to the heart following a 25 min normothermic cardiac arrest. However, excessive O(2) during HBOT can be toxic. Near infrared absorbance spectroscopy (NIRS) measures and determines when cytochrome oxidase (aa(3)), the O(2) end user, changes from reduced to oxidized, signifying adequate dosage. Present NIRS monitoring methods do not account for change in scattering expected in severe anoxia. Given this limitation, we simultaneously measured changes in intensity and scattering that occurred over time after 830 nm light traveled 4.25 cm through brain tissue during both normoxia and anoxia. Results indicated increased intensity and scattering during anoxia with correlation between the two, demonstrating that scattering does not remain constant and is associated with intensity. With this additional insight in concurrent scattering and intensity change during anoxia, we believe improvements can be made to our aa(3) measuring technique resulting in a method to ascertain adequate O(2) dosage during HBOT.

Hyperbaric oxygen improves rate of return of spontaneous circulation after prolonged normothermic porcine cardiopulmonary arrest.

AIM: This controlled, prospective, randomized porcine study tests the hypothesis that high-dose hyperbaric oxygen (HDHBO2) compared with normobaric oxygen (NBO2) or standard-dose hyperbaric oxygen (SDHBO2), improves return of sustained spontaneous circulation (ROSC) after a normothermic, normobaric, 25-min, non-intervened-upon cardiopulmonary arrest. The study incorporated a direct mechanical ventricular assist device (DMVAD) for open chest continuous cardiac compressions (OCCC) to assist advanced cardiac life support (ACLS). The experiment demonstrates a dose response to oxygen concentration in the breathing mix used in resuscitative ventilation. MATERIALS AND METHODS: Male pigs (average 30kg weight) underwent a 25-min, normothermic, non-intervened-upon cardiopulmonary arrest. Following arrest all animals were ventilated with 100% oxygen and were subjected to OCCC, incorporating DMVAD-aided ACLS. The animals so treated were randomized to be in one of three groups, with six animals in each group. The NBO2 group remained at 1.0 atmosphere absolute (ATA), while the SDHBO2 and HDHBO2 groups were initially placed at 1.9 and 4.0ATA, respectively. Uniform, but not American Heart Association (AHA) protocol, ACLS was maintained as needed over the ensuing 2h for all animals in all groups. At the end of 2h, the animals were euthanized. RESULTS: Continuously sustained ROSC (mean arterial pressure > or =50mmHg at all times), without the need of the pump assist over the 2-h resuscitation attempt that followed the 25-min arrest, occurred in four out of six animals in the HDHBO2 group, and in none of the animals in the NBO2 or SBHBO2 groups (p< or =0.001). CONCLUSIONS: Our results show significantly sustained ROSC using HDHBO2 to resuscitate swine after a 25-min, non-intervened-upon, normothermic cardiopulmonary arrest. These results could not be achieved using NBO2 or SDHBO2.