AnaConDa reflection filter: bench and patient evaluation of safety and volatile anesthetic conservation

The AnaConDa filter permits administration of volatile anesthetic without the use of an anesthesia machine. It is intended for use in the intensive care unit.

We studied the AnaConDa reflection filter on the bench and in anesthetized patients. The bench analysis used a test lung, a gas analyzer, an intensive care ventilator, the AnaConDa filter, and a syringe pump. We studied a range of tidal volume, respiratory rate, and positive end-expiratory pressure values. We simulated errors during syringe refilling and patient transportation. In 15 anesthetized patients, we used the AnaConDa with constant ventilation variables, a constant sevoflurane infusion rate (4-5 mL/h), and two consecutive fresh gas flow levels.

In the bench study, the expired volatile anesthetic fraction decreased linearly with respiratory frequency at constant minute ventilation, and decreased markedly in a hyperbolical manner when tidal volume increased at a constant respiratory rate. Changing the positive end-expiratory pressure level and inspiration/expiration ratio did not modify the AnaConDa's performance. Several safety failures were observed: refilling caused a transient change in AnaConDa output because of a pumping effect, and a standard Luer lock made it possible to connect the halogenate syringe on an IV infusion line. In anesthetized patients, reducing fresh gas flow from 8 to 1 L/min led to a median 40% increase in the expired volatile anesthetic fraction.

This study shows that the device is generally reliable, but that there are several conditions under which it might deliver more anesthetic than intended.