Final answer:
The procedure used to estimate the amount of air trapped in the patient's lungs and in the patient circuit is the end-expiratory pause.
Step-by-step explanation:
The procedure used to estimate the amount of air trapped in the patient's lungs and in the patient circuit is the end-expiratory pause. This involves pausing at the end of expiration to measure the pressure and volume in the lungs and circuit. By comparing these measurements to baseline values, healthcare professionals can assess the amount of air trapped and make adjustments to the ventilator settings if needed.