Normocapnia, Ventilation and CO2

Take a deep breath…8). It will do you a world of good and it will feed the plants.

Increasing alveolar ventilation while maintaining normocapnia(Increasing airflow into lungs while maintaining CO2 levels in the blood). -Content Source

Historically, the advances in treatment of CO poisoning were also linked to the fabrication of devices required to implement them. Henderson and Haggard in New York devised their H-H Infusor to administer carbogen. built the first fixed and then portable hyperbaric chambers in the Aberdeen Royal Infirmary, in Scotland. Recently, researchers in our laboratory described a method that passively maintains normocapnia regardless of minute ventilation and pattern of breathing. In that circuit, a constant O2 flow is provided to a standard self-inflating bag, and the inspiratory relief valve of the self-inflating bag is attached to a demand regulator supplying 6% CO2 in O2. Any increase in minute ventilation above the O2 flow is therefore supplied by the demand regulator (6% CO2 in O2). The O2 flow is adjusted to match the patient’s metabolic CO2 production and controls the alveolar ventilation for CO2. Arterial PCO2 is therefore unchanged by any increase in ventilation, because any ventilation exceeding the O2 flow is composed of 6% CO2 in O2, a mixture that does not contribute to a CO2 diffusion gradient between capillary blood and the alveoli, However, it is the combined flow of O2 and 6% CO2 in O2 that serves to wash out CO from the lungs, thereby clearing it from the blood.

We believe we have now come full circle in the treatment of CO poisoning. At the beginning of the 20th century, carbogen proved to be an effective means of treating CO poisoning. Only relatively recently was it realized that it was not the CO2 in carbogen but the increase in alveolar ventilation induced by the CO2 that accelerated the clearance of CO. By then, however, rapid advances in the technology of positive-pressure ventilation and hyperbaric chambers overshadowed the old-fashioned approach using carbogen. Despite the initial enthusiasm for hyperbaric O2 as the treatment for CO poisoning, the fact remains that hyperbaric O2 facilities are expensive and their distribution around the world is poorly matched to the incidence and prevalence of CO poisoning. Even in wealthier urban areas, the inherent delays to initiate treatment make them clinically ineffective. The technical barriers to safely enable lung clearance of CO are low, making it feasible to provide for widespread availability of the means for early and rapid CO elimination. In any case, early pulmonary CO clearance does not delay or preclude any other treatment, including subsequent treatment with hyperbaric O2.