A capnography is usually used in Intensive Care to monitor ventilation, mainly in neurologic patients. Car- bon dioxide levels are frequently monitored during car-diopulmonary resuscitation to aid in determining the proper placement of an endotracheal tube and to assess the effectiveness of resuscitation efforts. Although pulse oximetry is useful in the assessment of oxygenation, capnography provides more direct information on the ventilatory status of a patient. This is particularly true when patients are receiving supplemental oxygen, during which oxygen saturation may be normal despite the presence of marked hypoventilation. Conversely, capno- graphy does not monitor oxygenation; hypoxemia may be present even when a capnography tracing is normal. There are two types of capnographs. Mainstream capno- graphs use sensors that are placed directly into the breathing circuit of a ventilator. Sidestream capnographs draw a sample of gas away from the breathing circuit to a separate gas sensor (The response of a sidestream device to changes in carbon dioxide concentration is delayed by a few seconds, since the gas must travel through the sampling line before it can be analyzed. However, side-stream capnographs can be used conveniently in a patient who is not intubated if the patient is fitted with a face mask or nasal cannula to monitor respiration. Nasal can-nulas and face masks that feature integrated carbon di-oxide sampling lines are commercially available. You can modify standard face masks by attaching the sampling line directly to the orifice of a mask or by securing the sampling line inside the mask. A normal capnogram shows a regular, nearly square waveform that oscillates at the same frequency as the patient’s respiratory rate. During inspiration, the capnogram should be at zero as the patient breathes in fresh gas. When the patient starts to exhale, the first gas exhaled will be from the anatomi-cal dead space and will contain little or no carbon diox-ide. However, the concentration of carbon dioxide in the exhaled gas will rise rapidly and plateau as the alveoli begin to empty. As exhalation proceeds, the concentra-tion of carbon dioxide remains high and increases sligh- tly. The peak concentration reached at the end of exhala-tion is the ETCO2. As the patient begins to inhale again, the capnogram falls rapidly to zero, indicating the ab-sence of carbon dioxide in the inspired gas.