Funktionsweise des „Anaesthetic Conserving Device“

Abstract

The new anaesthetic conserving device (ACD) allows the use of isoflurane and sevoflurane without classical anaesthesia workstations. Volatile anaesthetic exhaled by the patient is absorbed by a reflector and released to the patient during the next inspiration. Liquid anaesthetic is delivered via a syringe pump. Currently the use of the ACD is spreading among European intensive care units (ICU). This article focuses on the functioning of the device and on particularities which are important to consider. The ACD constantly reflects 90% of the exhaled anaesthetic back to the patient, but if one exhaled breath contains more than 10 ml of anaesthetic vapour (e.g. >1 vol% in 1,000 ml), the capacity of the reflector will be exceeded and relatively more anaesthetic will be lost to the patient. This spill over decreases efficiency but it also contributes to safety as very high concentrations are averted. Compared to classical anaesthesia systems the ACD used in conjunction with ICU ventilators offers advantages in the ICU setting: investment costs are low, carbon dioxide absorbent is not needed, breathing comfort is higher, anaesthetic consumption is low (equal to an anaesthesia circuit with a fresh gas flow of approximately 1 l/min) and anaesthetic concentrations can be controlled very quickly (increased by small boluses and decreased by removal of the ACD). On the other hand, case costs are higher (single patient use) and a dead space of 100 ml is added. There are pitfalls: by a process called auto-pumping, expansion of bubbles inside the syringe may lead to uncontrolled anaesthetic delivery. Auto-pumping is provoked by high positioning of the syringe pump, heat and prior cooling of the liquid anaesthetic. Inherent to the device is an early inspiratory concentration peak and an end-inspiratory dip which may mislead commonly used gas monitors. Workplace concentrations can be minimized by proper handling, a sufficient turnover of room air is important and gas from the expiration port of the ventilator should be scavenged. Inhalational compared to intravenous ICU sedation offers the advantages of better control of the sedation level, online drug monitoring, no accumulation in patients with renal or hepatic insufficiency and bronchodilation. With a lowered opioid dose spontaneous breathing and intestinal motility are well preserved. A clinical algorithm for the care of patients with respiratory insufficiency including inhalational sedation is proposed. Inhalational sedation with isoflurane has been widely used for more than 20 years in many countries and even for periods of up to several weeks. In the German S3 guidelines for the management of analgesia, sedation and delirium in intensive care (Martin et al. 2010), inhalational sedation is mentioned as an alternative sedation method for patients ventilated via an endotracheal tube or a tracheal cannula. Nevertheless, isoflurane is not officially licensed for ICU sedation and its use is under the responsibility of the prescribing physician.

Sevoflurane in combination with esketamine is an effective sedation regimen in COVID-19 patients enabling assisted spontaneous breathing even during prone positioning

“…Mono sedation in these patients with inhalative sevoflurane obviously is difficult. This may be due to technical limitations of the AnaConDa-S device at high RMV [ 15 , 16 ] ( Figure 1 ).…”

“…We used the AnaConDa-S-System (Sedana Medical AB, Danderyd, Sweden) to perform inhaled sedation. At high respiratory minute volumes of more than 7-8 L min -1 , this system reaches its technical limits [14][15][16], and it is more difficult to achieve high Fet% rates. The reflector loses efficiency at high tidal volumes.…”

A novel device for target controlled administration and reflection of desflurane – the Mirus™

“…Therefore, efficiency was calculated as follows: where V liquid (ml) is the consumed volume of liquid desflurane; F BTPS (l.ml) is the factor for calculating vapour volume from liquid volume under body temperature pressure-saturated conditions (F = 0.2373 for desflurane) [ 11 ]; MV i (l.min −1 ) is the minute ventilation volume during time interval i; t i (min) is the length of time interval i; and C i (% volume) is the end-tidal anaesthetic concentration during time interval i.…”