The Dumping Valve and its Clinical Application
An open reservoir for the collection and evacuation of anaesthetic gases permits leakage to room air. The use of a closed reservoir for the removal of overspill gas from anaesthetic circuits is described. Calibrated gas evacuation is carried out through an ejector flowmeter from the anaesthetic circuit or from a closed reservoir, where the gas is collected via a relief valve. In order to eliminate the risk of high or low pressure in the reservoir employed, a relief valve and a dumping valve is included in the system.
A Simple Method of Monitoring Carbon Dioxide Output in Anaesthetized Patients
The mean CO2 output during anaesthesia in paralyzed patients can be monitored by continuous capnographic analysis of the total exhaled gases, the latter being mechanically integrated by pumice canisters. The gas is evacuated from the Hafnia A circuit via an ejector flowmeter. The results are not influenced by the flow rates employed.
The effects of inflow, overflow and valve placement on economy of the circle system.
Several arrangements of inspiratory and expiratory valves and of overflow location in a circle absorber system were tested to determine which arrangement best conserved fresh gas and preferentially eliminated alveolar gas. The influences of inflow rate, deadspace, tidal volume and alveolar ventilation were also examined. During spontaneous ventilation, the most economical arrangements (most alveolar gas eliminated at a given inflow rate) were those with the overflow close to the patient However, with one exception, when ventilation was controlled, the arrangements with overflow near the patient became least economical. The exception was the arrangement with both inspiratory and expiratory valves close to the patient and the overflow valve immediately downstream from the expiratory valve. This proved to be the most economical of all the arrangements tested. Economy was directly related to inflow rate and indirectly related to alveolar ventilation in all cases. When the overflow valve was distant from the patient, concomitant increases in deadspace and tidal volume (alveolar ventilation unchanged) reduced economy. However, these increases of deadspace and tidal volume had no effect on economy when the overflow was close to the patient.