Capnograms

A capnogram is a graphical representation of the concentration of carbon dioxide (CO2) in exhaled air over time. It is used primarily in medical settings to monitor ventilation and assess patients' respiratory status. The shape of a capnogram reflects the physiological and anatomical characteristics of the respiratory system, making it a valuable tool for diagnosing and managing respiratory conditions.

Typically, a capnogram consists of four phases. Phase I represents the baseline, which shows virtually no CO2 as it corresponds to the exhalation of dead space air lacking CO2. Phase II, or the expiratory upstroke, shows a rapid rise as alveolar air with high CO2 mixes with dead space air. Phase III, the alveolar plateau, indicates the exhalation of alveolar air with relatively consistent CO2 levels. During the transition to inhalation, the CO2 level drops sharply back to baseline.

Capnograms are used in various clinical scenarios, including anesthesia, emergency medicine, and intensive care. They help confirm endotracheal tube placement, assess the effectiveness of ventilation, and detect conditions such as hypoventilation, airway obstruction, or cardiac arrest. Deviations in the shape or values of a capnogram can indicate specific problems—for example, a "shark fin" pattern suggests airway obstruction, while an absent waveform may signify apnea or disconnection.

Advances in capnography technology have improved its portability and ease of use, allowing continuous monitoring in diverse settings. Overall, capnograms provide real-time, non-invasive insights into respiratory function, facilitating prompt decision-making and intervention in critical care.