EndtidalKohlendioxid

EndtidalKohlendioxid refers to the end-tidal carbon dioxide, the concentration or partial pressure of CO2 in the airway gas at the end of an exhalation. It is typically measured by capnography, which produces a capnogram waveform and reports a numerical ETCO2 value. ETCO2 reflects the balance between CO2 production, pulmonary ventilation, and the efficiency of gas exchange, and it is influenced by ventilation–perfusion matching and lung function. In healthy ventilation, ETCO2 values are usually in the range of 35–45 mmHg, and the end-tidal value is often slightly lower than the arterial CO2 (PaCO2).

Measurement methods include mainstream sensors, placed directly in the breathing circuit, and sidestream systems, which draw a small sample of gas to a separate sensor. ETCO2 can be reported as a partial pressure (mmHg) or as a percentage of CO2 concentration. Clinically, endtidal CO2 is used to monitor ventilation during anesthesia and procedure-related sedation, in emergency and critical care settings, and to assess the effectiveness of resuscitation.

Interpreting ETCO2 involves recognizing trends and waveform morphology. A rising ETCO2 can indicate increased CO2 production or reduced ventilation, while a falling ETCO2 may reflect hyperventilation, low cardiac output, or airway problems. A sudden drop can signal disconnection, apnea, or severe airway obstruction. The capnogram waveform provides additional information about the phase of exhalation and airway status.

Limitations include sampling errors, dead space ventilation, rebreathing, high inspired oxygen, or poor perfusion, which can distort ETCO2 readings. ETCO2 is a trend and surrogate marker for PaCO2, not a direct measurement of arterial CO2, and its interpretation must consider clinical context.