[Usefulness of a simple expiratory gas monitor during sedation under spinal anesthesia]

We introduce a simple expiratory gas monitor during sedation under spinal anesthesia. A small extension tube for infusion used as a gas sampling line is placed in the nasal vestibule. It is necessary to make it sure that the point of the tube should not contact with the mucous membrane of the nose. Our method needs no special equipments such as Capnoxygen or Nazorcap, but a cheap extension tube available in any operating room. Therefore this is a simple method. Expiratory gas monitor can detect apnea early, airway obstruction and stenosis and predict PaCO2 during sedation. The change of fractional concentration of oxygen in inspired gas predicts the change of tidal volume. Increase in the former reflects a decrease in the latter under the administration of oxygen. It is possible to evaluate whether sedation became steady with analysis of respiratory pattern. However, nasal discharge may interrupt monitoring expiratory gas. Our simple method to monitor expiratory gas is useful during sedation under regional anesthesia.