Technical Performance and Reflection Capacity of the Anaesthetic Conserving Device—A Bench Study with Isoflurane and Sevoflurane

Abstract

ABSTRACT. Objective. The anaesthetic conserving device (AnaConDa Ò , Sedana Medical, Sundbyberg, Sweden) facilitates administration of isoflurane or sevoflurane by liquid infusion. An anaesthetic reflector inside the device conserves exhaled anaesthetic and re-supplies it during inspiration. In this bench study, we examined the influence of infusion rates and ventilatory settings on the resulting anaesthetic concentrations on patient (C pat ) and ventilator side of the reflector (C loss ) to describe its technical performance. Methods. A Puritan Bennett 840 ICU ventilator (Pleasanton, US), AnaConDa Ò , and a test lung (3 l-chloroprene-bag) were assembled. Infusion rates (IR, 0.2-50 ml h -1 ), respiratory rates (RR, 5-40 breaths min -1 ), and tidal volumes (V T , 0.3, 0.5, and 1.0 l) were varied. C pat was measured via a thin catheter in the middle of the 3 l-bag in steady state (online data storage and averaging over >10 min). C loss was calculated from IR (to yield the volume of vapour per unit of time), and expired minute volume (in which the vapour is diluted) on the assumption that, in the steady state, input by liquid infusion equals output through the reflector. Results. At lower concentrations (C pat < 1 vol%) the ratio C loss /C pat was constant (R C = 0.096 ± 0.012) for all combinations of IR, RR and V T , both for isoflurane and sevoflurane. The device could efficiently reflect up to 10 ml vapour per breath (e.g. 2 vol% in 0.5 l). When exceeding this capacity, surplus vapour ''spilled over'' and R C markedly increased indicating decreased performance. Conclusions. The triple product minute volume times R C times C pat describes anaesthetic losses through the reflector. It can easily be calculated as long as the 10 ml reflection capacity is not exceeded and thus R C is constant. Increased minute ventilation necessitates increasing the IR to keep C pat constant. When using large V T and high C pat ''spill over'' occurs. This effect offers some protection against an inadvertent overdose.

A review of the practice of sedation with inhalational anaesthetics in the intensive care unit with the AnaConDa® device

“…Second, ICU ventilators are high-fidelity performers with a number of ventilatory modes which include both spontaneous as well as controlled ventilation, and therefore the delivered anaesthetic concentration will depend not only on the flow, but also on the minute ventilation. [14] Third, the bulky anaesthesia machine is not only ill designed for ICU ventilation, but also lack of familiarity with the machine and limited alarms prevent it from being a standalone machine in the ICU. Finally, the main challenges with the use of volatile anaesthetic agents for ICU sedation are to conserve the anaesthetic gases using an open system and simultaneously avoid workplace contamination.…”

“…% in 500 mL, etc.). [14] Therefore, the infusion rates of the volatile anaesthetic agents need to be increased with increases in minute ventilation in order to keep the end-tidal anaesthetic concentrations constant. Resistance to gas flows at 60 L/min is 2.5 cm H 2 O/L/s, which is comparable to the standard HME filters.…”

Funktionsweise des „Anaesthetic Conserving Device“

“…Unabhän-gig von den Beatmungsparametern Atemfrequenz, Tidalvolumen und Atemminutenvolumen wurde der Quotient der respiratorseitigen Konzentration zur Patientenkonzentration konstant als 0,096 bestimmt. Hierbei fand sich kein Unterschied zwischen Isofluran und Sevofluran [11].…”

“…Ab diesem Dampfvolumen steigt die respiratorseitige Konzentration relativ zur Patientenkonzentration deutlich an. Dieser Effekt wurde als "spill over" beschrieben (wörtlich: über-schwappen; [11]). …”

“…Mittlerweile gibt es 2 klinische Studien, die belegen, dass durch einfache Dosierungsmodelle die endtidalen Konzentrationen weitaus genauer vorhergesagt werden können als die Serumkonzentrationen bei klassischen weit verbreiteten Dosierungsalgorithmen der "target controlled infusion" etwa für Propofol oder Remifentanil [17,18] [11,17]. Um das Abfluten der Anästhetika zu beschleunigen, empfiehlt es sich, das ACD aus dem Schlauchsystem zu entfernen und ggf.…”