Final answer:
Capnography is the correct method for estimating arterial CO₂ levels, as it specifically measures the concentration or partial pressure of carbon dioxide in respiratory gases.
Step-by-step explanation:
An estimation of the arterial levels of CO₂ is determined with the use of capnography. Capnography is a non-invasive monitoring technique that allows fast and reliable insight into the patient's respiratory status by measuring the concentration or partial pressure of carbon dioxide (CO₂) in respiratory gases. While a pulse oximeter is used to measure the percentage of oxygen saturation in the blood, it does not provide CO₂ levels. A sphygmomanometer is utilized to measure blood pressure and does not provide any information regarding gas levels. A spirometer is used to measure the volume of air inhaled and exhaled by the lungs and does not measure blood gas levels either.