Which monitor among the five basic monitors provides information about ventilation by measuring end-tidal CO2?

• A. EtCO2
• B. SpO2
• C. ECG
• D. Temperature probe

Answer: (A)

End-tidal CO2 monitoring directly reflects ventilation by measuring the CO2 concentration at the end of expiration. This is captured as a capnography waveform plus a numeric value (EtCO2), showing how effectively CO2 is being eliminated by the lungs on each breath. It’s sensitive to changes in ventilation, can help detect hypoventilation or apnea, and is routinely used to verify airway placement and ongoing adequacy of ventilation during anesthesia. Normal EtCO2 is typically around 35–45 mmHg, though it can be slightly lower than arterial CO2 depending on ventilation-perfusion relationships. The other monitors here assess different things: SpO2 gauges oxygenation, ECG tracks heart electrical activity, and a temperature probe measures body temperature; none measure ventilation directly.