Hyperventilation with and without maintenance of isocapnia: a comparison of selected gasometric and respiratory parameters.

The aims of this study were to examine selected respiratory and gasometric parameters during hyperventilation with and without isocapnia and to identify the possible mechanism by which isocapnic hyperventilation might be useful in the elimination of volatile substances, including CO. Ten healthy non-smoking volunteers were studied, and each underwent two procedures. During one session, CO2 was added to the respiratory circuit, and during the other session, only 100% O2 was used. The volunteers were coached to hyperventilate until the appearance of side effects. Isocapnic hyperventilation significantly increased alveolar minute ventilation and partial pressure of oxygen in arterialized capillary blood (paO2); to the best of our knowledge, these findings have not previously been reported. Isocapnic hyperventilation was associated with only mild side effects, such as dyspnea, increased respiratory effort and headache, in 30% of subjects. Side effects, including vertigo, paresthesias and muscle tremor, were present in 70% of the volunteers during hyperventilation with 100% O2, and these side effects forced them to limit their respiratory rates and tidal volumes. These increases in alveolar ventilation and the partial pressure of oxygen in the blood may play crucial roles in decreasing the half-time of carboxyhemoglobin, which is the primary goal of the treatment of CO poisoning.