Abstract: A method and apparatus for monitoring a patient's circulatory status during cardiopulmonary resuscitation is disclosed. The apparatus includes a housing defining a passageway through which the patient's breath passes. The device also includes a carbon dioxide indicator in communication with said passageway for indicating the presence of carbon dioxide in the patient's breath over a temporary period of time wherein the length of the temporary period is a known function of the level of carbon dioxide in the patient's breath. Accordingly, the level or concentration of carbon dioxide in the patient's breath is easily determined by simply measuring the length of the temporary period. The preferred carbon dioxide indicator utilizes a chemical substance that changes color when exposed to carbon dioxide. The chemical substance is preferably disposed in an internal chamber which is in communication with the housing's passageway.