Distal volume monitoring

A system that enables the accurate monitoring of tidal volume of a patient when using a Bain, Mapleson D or similar type of patient breathing circuit (48) in an anesthesia system. The system allows the use of flow sensors (62, 60) positioned at the machine or distal end of the patient breathing circuit (48) and not at the less desirable patient or proximal end of the patient breathing circuit. Thus, the flow sensors can be positioned out of the way of the patient (16) and will provide a measurement of the tidal volume of the patient. A CPU (43) is used to take into account, the additional fresh gas provided to the patient breathing circuit during the expiration cycle to correct the flow monitored in the main breathing tube (50) that supplies the gas to the patient from a ventilator or breathing bag (12, 18).