Preparation of Datex-Ohmeda Aestiva® and Aisys® anaesthetic machines for use in malignant hyperthermia susceptible patients

Abstract

Preparation of anaesthesia machines for use by malignant hyperthermia susceptible patients requires purging the machines of halogenated anaesthetic agents. The endpoint of this process is to reach a gas concentration of 5 ppm or less, which has been arbitrarily chosen as the safe limit of exposure to avoid triggering a malignant hyperthermia event. We examined the washout characteristics of sevoflurane and desflurane from the Datex-Ohmeda Aestiva ® Anaesthesia System and Aisys ® Anaesthesia Carestation ® anaesthetic machines. The machines were contaminated for two hours using either sevoflurane 2 vol% or desflurane 6 vol%. At the end of the priming period, the patient breathing circuit and reservoir bag, carbon dioxide absorbent, sampling line and test lung were replaced with uncontaminated components. During the test period, machines were purged using oxygen flows of 10 l/minute. The average time to reach 5 ppm with the Aestiva machines was 51 minutes with sevoflurane and 71 minutes with desflurane. The average time to reach 5 ppm for the Aisys machines was 55 minutes with sevoflurane and 69 minutes with desflurane. All configurations of machines and anaesthetic gases demonstrated a rebound effect in agent concentration above 5 ppm when the fresh gas flow was subsequently reduced from 10 to 2 l/minute. Aestiva and Aisys anaesthetic machines require a prolonged period to adequately purge them of halogenated volatile anaesthetic agent. The rebound effect poses a serious concern, suggesting that after the purging period, fresh gas flows of 10 l/minute should be maintained for the duration of anaesthesia care of the malignant hyperthermia susceptible patient.

Washout times of desflurane, sevoflurane and isoflurane from the GE healthcare Aisys® and Avance® Carestation® and Aestiva® Anesthesia System

“…Also, the Aestiva exhibited a more gradual biphasic decrease in concentration because of a breathing system equivalent to twice the volume of the ABS, predisposing to a greater degree of incomplete mixing . Prior studies have suggested the breathing system may contribute to incomplete mixing and pockets of trapped gas . Also, similar washout times were recorded using an autoclaved ABS and no ABS confirming the ABS as a source of anesthetic gases.…”

“…This study utilized the maximum flow rate of 15 lpm, and one machine representing each model to standardize testing conditions. Reduction of high flow rates to demonstrate the rebound phenomenon was not performed, because this has been well documented . The washout times for the Avance and Aisys were within the MHAUS recommendations.…”

“…The second set of experiments focused on the external circuitry. Washout of anesthetic gases from the Avance and Aisys exhibited a biphasic elimination process reflecting the initial purging of anesthetic gas within the passageways followed by a slower outgasing from exposed surfaces and delayed washout from stagnant areas of the internal breathing system (1)(2)(3)(4)(5)(6)(12)(13)(14). The ABS has a volume of 2.7 l, a large Figure 3 The washout of desflurane 7 vol%, isoflurane 1.2 vol% and sevoflurane 2.5% over time from the Aestiva â Anesthesia System (GE Healthcare, Madison, WI, USA).…”

Malignant hyperthermia: a review

“…Silicone products incorporated into these machines absorb inhalational anesthetics and result in prolonged release of the agent. Flushing of these machines can take longer that 60 min to achieve a safe level of agent [ 168 ]. A vapor-free anesthetic machine would eliminate this problem but it is likely that most anesthetic departments do not have such a machine available.…”

Consideraciones anestésicas en el síndrome de Moebius: a propósito de un caso

“…Se debe priorizar evitar los fármacos desencadenantes (anestésicos halogenados y relajantes neuromusculares). Para evitar que ninguna partícula de gas halogenado pase al paciente en riesgo de sufrir una HM, es preciso dejar ciclando la máquina de anestesia un tiempo que depende del tipo de máquina (13) , nosotros empleamos una Datex-Ohmeda Aestiva, motivo por el cual dejamos ciclando la máquina a altos flujos más de 90 minutos (13) .…”