Accelerating the washout of inhalational anesthetics from the Dräger Primus anesthetic workstation: effect of exchangeable internal components.
Department of Anesthesia, The Hospital for ick Children, University of Toronto, Canada. Anesthesiology
(Impact Factor: 5.88).
To establish guidelines for the preparation of the Primus anesthetic workstation (Dräger, Lübeck, Germany) for malignant hyperthermia-susceptible patients, the authors evaluated the effect of replacing the workstation's exchangeable internal components on the washout of isoflurane.
Primus workstations were exposed to isoflurane, and contaminated internal components were replaced as follows: group 1, no replacement; group 2, new ventilator diaphragm; group 3, autoclaved ventilator diaphragm; group 4, autoclaved integrated breathing system; group 5, flushed integrated breathing system; group 6, autoclaved ventilator diaphragm and integrated breathing system. The fresh gas flow was set at 10 l/min, and subsequently reduced to 3 l/min when a concentration of 5 ppm was achieved. Isoflurane concentration was measured in the inspiratory limb of the circle circuit every minute.
Washout times for isoflurane decreased in the following order: group 1 (67 +/- 6.5 min) > groups 2 and 3 (50 +/- 4.1 and 50 +/- 5.7 min, respectively) > group 5 (43 +/- 9.5 min) > group 4 (12 +/- 1.5 min) > group 6 (3.2 +/- 0.4 min). Isoflurane concentration increased approximately threefold when the fresh gas flow was reduced to 3 l/min.
Washout of isoflurane increased 20-fold with the use of an autoclaved ventilator diaphragm and integrated breathing system. To prepare the Primus for malignant hyperthermia-susceptible patients, the authors recommend replacing the ventilator diaphragm and integrated breathing system with autoclaved components, flushing the workstation for 5 min at a fresh gas flow of 10 l/min, and maintaining this flow for the duration of anesthesia.
Available from: anesthesia-analgesia.org
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ABSTRACT: Anesthesia machines must be flushed of halogenated anesthetics before use in patients susceptible to malignant hyperthermia. We studied the kinetics of sevoflurane clearance in the Dräger Fabius anesthesia machine and compared them to a conventional anesthesia machine (Dräger Narkomed GS).
Before each trial, the anesthesia machine was contaminated for 2 h with 3% sevoflurane and then prepared by changing the CO(2) absorbent, removing the vaporizer(s), and mounting a clean circuit and artificial lung. The basic flush procedure consisted of oxygen 10 L/min with the ventilator set to a tidal volume of 600 mL at a rate of 10/min. Residual sevoflurane in the inspiratory limb of the circuit was measured using an ambient air analyzer capable of measuring sevoflurane to < 1 ppm. Results were analyzed using log-linear regression of residual concentration as a function of time. This model was used to estimate the time required to achieve a desired residual anesthetic concentration.
Times to achieve 10 and 5 ppm in the Dräger Narkomed GS were 11 and 18 min, respectively. For the Dräger Fabius anesthesia machine, times to 10 and 5 ppm were 75 and 104 min, respectively. Several maneuvers to accelerate clearance of residual sevoflurane from the Dräger Fabius resulted in only modest reductions in these times (10 and 5 ppm times 40-50 min and 60-80 min, respectively). Insertion of an activated charcoal filter (QED, Anecare Laboratories, Salt Lake City, UT) into the inspiratory limb of the Dräger Fabius circuit reduced the residual anesthetic concentration to <5 ppm within 10 min; this concentration was maintained for > 6 h despite a fresh gas flow of only 2 L/min after the first 15 min.
Preparation of the Dräger Fabius anesthesia machine using conventional flushing techniques required almost 10 times as long as an older, conventional anesthesia machine. If a prolonged flush is impractical or impossible, we describe a procedure using an activated charcoal filter inserted on the inspiratory limb of the breathing circuit which can effectively scrub residual sevoflurane to a concentration < 5 ppm within 10 min. This procedure includes an initial 5 min flush without the activated charcoal filter followed by a 5 min flush with the charcoal filter, after which the machine is ready for use in the malignant hyperthermia-susceptible patient. The charcoal filter must remain on the machine for the remainder of the anesthetic, and the fresh gas flow should be maintained > or = 10 L/min for the first 5 min, and > or = 2 L/min thereafter.
Available from: Carolyne Pehora
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ABSTRACT: In order to establish guidelines for the preparation of the Dräger Fabius GS premium anesthetic workstation for malignant hyperthermia-susceptible patients, the authors evaluated the effect of the workstation's exchangeable and autoclavable components on the washout of isoflurane.
A Dräger Fabius GS workstation was primed with 1.5% isoflurane, and exchangeable components were replaced as follows: Group 1: no replacement (control); Group 2: autoclaved ventilator diaphragm and ventilator hose; Group 3: flushed ventilator diaphragm and ventilator hose; Group 4: autoclaved compact breathing system. The fresh gas flow (FGF) was set at 10 L . min(-1), and the concentration of isoflurane in the inspiratory limb of the circle breathing circuit was recorded every minute until an endpoint of 5.0 parts per million (ppm) was achieved, at which time the FGF was reduced to 3 L . min(-1). Six experiments were conducted in each of the four groups.
The time to achieve an isoflurane concentration of 5.0 ppm decreased in the following order: Group 1 (151 +/- 17 min) > Group 3 (137 +/- 7 min) > Group 4 (122 +/- 11 min) > Group 2 (42 +/- 6 min) (P < 0.01 vs control). Isoflurane concentration increased approximately fivefold when the FGF was reduced to 3 L . min(-1).
Anesthetic washout from the Dräger Fabius GS is relatively slow. Although washout was accelerated when the Dräger Fabius GS was equipped with autoclaved components, the reduction in washout time may be less than that required for this technique to be accepted into clinical practice. A dedicated vapor-free workstation may be preferable for rapid turnover between cases.
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ABSTRACT: Malignant hyperthermia-susceptible patients have an increased risk during anaesthesia. The aim of this review is to present current knowledge about pathophysiology and triggers of malignant hyperthermia as well as concepts for safe anaesthesiological management of these patients.
Trigger substances and mechanisms have been well defined to date. Anaesthesia can be safely performed with i.v. anaesthetics, nitrous oxide, nondepolarizing muscle relaxants, local anaesthetics as well as xenon. Attention must be directed to the preparation of the anaesthetic machine because modern workstations need longer cleansing times than their predecessors. Alternatively, activated charcoal might be beneficial for elimination of volatile anaesthetics. Day case surgery can be performed in malignant hyperthermia-susceptible patients, if all safety aspects are regarded. Whether there is an association between malignant hyperthermia susceptibility and other disorders is still a matter of debate.
The incidence of malignant hyperthermia is low, but the prevalence can be estimated as up to 1: 3000. Because malignant hyperthermia is potentially lethal, it is relevant to establish management concepts for perioperative care in susceptible patients. This includes preoperative genetic and in-vitro contracture testing, preparation of the anaesthetic workstation, use of nontriggering anaesthetics, adequate monitoring, availability of sufficient quantities of dantrolene and appropriate postoperative care. Taking these items into account, anaesthesia can be safely performed in susceptible patients.
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