The Reflector: a new method for saving anaesthetic vapours

High volatile anaesthetic conservation with a digital in-line vaporizer and a reflector

BACKGROUND

A volatile anaesthetic (VA) reflector can reduce VA consumption (VAC) at the cost of fine control of its delivery and CO₂ accumulation. A digital in-line vaporizer and a second CO₂ absorber circumvent both of these limitations. We hypothesized that the combination of a VA reflector with an in-line vaporizer would yield substantial VA conservation, independent of fresh gas flow (FGF) in a circle circuit, and provide fine control of inspired VA concentrations.

METHOD

Prospective observational study on six Yorkshire pigs. A secondary anaesthetic circuit consisting of a Y-piece with 2 one-way valves, an in-line vaporizer and a CO₂ absorber in the inspiratory limb was connected to the patient's side of the VA reflector. The other side was connected to the Y-piece of a circle anaesthetic circuit. In six pigs, an inspired concentration of sevoflurane of 2.5% was maintained by the in-line vaporizer. We measured VAC at FGF of 1, 4 and 10 l/min.

RESULTS

With the secondary circuit, VAC was 55% less than with the circle system alone at FGF 1 l/min, and independent of FGF over the range of 1-10 l/min. Insertion of a CO₂ absorber in the secondary circuit reduced P_et CO₂ by 1.3-2.0 kpa (10-15 mmHg).

CONCLUSION

A secondary circuit with reflector and in-line vaporizer provides highly efficient anaesthetic delivery, independent of FGF. A second CO₂ absorber was necessary to scavenge the CO₂ reflected by the anaesthetic reflector. This secondary circuit may turn any open circuit ventilator into an anaesthetic delivery unit.

Technology III: in-line vaporizer with reflector

As the clinical advantages of vapor anesthesia (VA) for sedation of patients in ICU become more apparent, the ergonomics, economy and safety issues need to be better addressed. Here we describe the use of a new commercial digital in-line anesthetic vaporizer that can be attached to the inspiratory limb of a ventilator. If used with a simple, and easily assembled secondary circuit and anesthetic reflector, the circuit remains remote from the patient, the VA consumption approaches a physical minimum, VA level is controlled and monitored, and the tidal volume size is not limited.

The New MIRUS System for Short-Term Sedation in Postsurgical ICU Patients

OBJECTIVES

To evaluate the feasibility and safety of the MIRUS system (Pall International, Sarl, Fribourg, Switzerland) for sedation with sevoflurane for postsurgical ICU patients and to evaluate atmospheric pollution during sedation.

DESIGN

Prospective interventional study.

SETTING

Surgical ICU. February 2016 to December 2016.

PATIENTS

Postsurgical patients requiring ICU admission, mechanical ventilation, and sedation.

INTERVENTIONS

Sevoflurane was administered with the MIRUS system targeted to a Richmond Agitation Sedation Scale from -3 to -5 by adaptation of minimum alveolar concentration.

MEASUREMENTS AND MAIN RESULTS

Data collected included Richmond Agitation Sedation Scale, minimum alveolar concentration, inspired and expired sevoflurane fraction, wake-up times, duration of sedation, sevoflurane consumption, respiratory and hemodynamic data, Simplified Acute Physiology Score II, Sepsis-related Organ Failure Assessment, and laboratory data and biomarkers of organ injury. Atmospheric pollution was monitored at different sites: before sevoflurane delivery (baseline) and during sedation with the probe 15 cm up to the MIRUS system (S1) and 15 cm from the filter-Reflector group (S2). Sixty-two patients were enrolled in the study. No technical failure occurred. Median Richmond Agitation Sedation Scale was -4.5 (interquartile range, -5 to -3.6) with sevoflurane delivered at a median minimum alveolar concentration of 0.45% (interquartile range, 0.4-0.53) yielding a mean inspiratory and expiratory concentrations of 0.79% (SD, 0.24) and 0.76% (SD, 0.18), respectively. Median awakening time was 4 minutes (2.2-5 min). Median duration of sevoflurane administration was 3.33 hours (2.33-5.75 hr), range 1-19 hours with a mean consumption of 7.89 mL/hr (SD, 2.99). Hemodynamics remained stable over the study period, and no laboratory data indicated liver or kidney injury or dysfunction. Median sevoflurane room air concentration was 0.10 parts per million (interquartile range, 0.07-0.15), 0.17 parts per million (interquartile range, 0.14-0.27), and 0.15 parts per million (interquartile range, 0.07-0.19) at baseline, S1, and S2, respectively.

CONCLUSIONS

The MIRUS system is a promising and safe alternative for short-term sedation with sevoflurane of ICU patients. Atmospheric pollution is largely below the recommended thresholds (< 5 parts per million). Studies extended to more heterogeneous population of patients undergoing longer duration of sedation are needed to confirm these observations.

Comparing charcoal and zeolite reflection filters for volatile anaesthetics: A laboratory evaluation

BACKGROUND

A modified heat-moisture exchanger that incorporates a reflecting filter for use with partial rebreathing of exhaled volatile anaesthetics has been commercially available since the 1990 s. The main advantages of the device are efficient delivery of inhaled sedation to intensive care patients and reduced anaesthetic consumption during anaesthesia. However, elevated arterial CO2 values have been observed with an anaesthetic conserving device compared with a conventional heat and moisture exchanger, despite compensation for larger apparatus dead space.

OBJECTIVE

The objective of this study is to thoroughly explore the properties of two reflecting materials (charcoal and zeolites).

DESIGN

A controlled, prospective, observational laboratory study.

SETTING

Lund University Hospital, Sweden, from December 2011 to December 2012.

PARTICIPANTS

None.

INTERVENTIONS

Three filters, with identical volumes, were compared using different volatile anaesthetics at different conditions of temperature and moisture. The filtering materials were charcoal or zeolite. Glass spheres were used as an inert control.

MAIN OUTCOME MEASURES

Consumption of volatile anaesthetics using different reflecting materials in filters at different conditions regarding temperature and moisture. CO2 reflection by the filtering materials: glass spheres, charcoal or zeolite.

RESULTS

Isoflurane consumption in an open system was 60.8 g h(-1). The isoflurane consumption in dry, warm air was 39.8 g h(-1) with glass spheres. Changing to charcoal and zeolite had a profound effect on isoflurane consumption, 11.8 and 10.7 g h(-1), respectively. Heating and humidifying the air as well as the addition of N2O created only minor changes in consumption. The percentage of isoflurane conserved by the charcoal filter was independent of the isoflurane concentration (0.5 to 4.5%). Reflection of sevoflurane, desflurane and halothane by the charcoal filter was similar to reflection of isoflurane. Both charcoal and zeolite filters had CO2 reflecting properties and end-tidal CO2 increased by 3 to 3.7% compared with glass spheres. This increase was attenuated to 1 to 1.4% when the air was heated and humidified, and isoflurane was added.

CONCLUSION

Charcoal and zeolite possess gas-reflecting properties, which can be used to conserve volatile anaesthetics. They also reflect CO2. The degree of CO2 reflection was reduced by heating and humidifying the air.

Adsorption of desflurane by the silica gel filters in breathing circuits: an in vitro study

Background

During general anesthesia, a heated breathing circuit (HBC) is used to replace the heat and moisture exchange function of the upper airway. One HBC uses an air dryer filter that employs silica gel (SG) as a desiccant. SG is capable of adsorbing many organic compounds. Therefore, we undertook an in vitro study of the adsorption of desflurane by SG filters.

Methods

An HBC was connected to an anesthesia machine, and a test lung was connected to the circuit. The test lung was mechanically ventilated with 2 or 4 L/min of fresh gas flow, with and without the air dryer filter. Desflurane was administered at a 6 vol% on the vaporizer dial setting. The experiment was repeated 15 times in each group. The end-tidal concentrations were measured during the experiments. The air dryer filter weights were measured before and after the experiments, and the times required to achieve the specific end-tidal desflurane concentrations were determined.

Results

Significant differences in the end-tidal concentrations of desflurane were observed between the control and filter groups (P < 0.001). The filter weights increased significantly after the experiments (P < 0.001). The times required to achieve the same end-tidal desflurane concentrations were different with the application of the air dryer filter (P < 0.001).

Conclusions

The adsorption of desflurane with the use of an air dryer filter was verified in this in vitro study. Careful attention is needed when using air dryer gel filters during general anesthesia.

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

The intensive care unit (ICU) environment is often perceived to be hostile and frightening by patients due to unfamiliar surroundings coupled with presence of numerous personnel, monitors and other equipments as well as a loss of perception of time. Mechanical ventilation and multiple painful procedures that often need to be carried out in these critically ill patients add to their overall anxiety. Sedation is therefore required not only to allay the stress and anxiety, but also to allow for mechanical ventilation and other invasive therapeutic and diagnostic procedures to be performed. The conventional intravenous sedative agents used in ICUs suffer from problems of over sedation, tachyphylaxis, drug accumulation, organ specific elimination and often lead to patient agitation on withdrawal. All this tend to prolong the ventilatory as well as ICU and hospital discharge time, which increase the risk for infection and add to the overall increase in morbidity, mortality and hospital costs. In 2005, the anaesthetic conserving device (AnaConDa(®)) was marketed for ICU sedation with volatile anaesthetic agents. A number of trials have shown the effectiveness of using volatile anaesthetic agents for ICU sedation with the AnaConDa device. Compared with intravenous sedatives, use of volatile anaesthetic agents have resulted in shorter wake up and extubation time, lesser duration of mechanical ventilation and faster discharge from hospitals. This review shall focus on the benefits, technical pre-requisites and status of sedation with volatile anaesthetic agents in ICUs with the AnaConDa(®) device.

Efficiency and safety of inhalative sedation with sevoflurane in comparison to an intravenous sedation concept with propofol in intensive care patients: study protocol for a randomized controlled trial

Background

State of the art sedation concepts on intensive care units (ICU) favor propofol for a time period of up to 72 h and midazolam for long-term sedation. However, intravenous sedation is associated with complications such as development of tolerance, insufficient sedation quality, gastrointestinal paralysis, and withdrawal symptoms including cognitive deficits. Therefore, we aimed to investigate whether sevoflurane as a volatile anesthetic technically implemented by the anesthetic-conserving device (ACD) may provide advantages regarding ‘weaning time’, efficiency, and patient’s safety when compared to standard intravenous sedation employing propofol.

Method/Design

This currently ongoing trial is designed as a two-armed, monocentric, randomized prospective phase II study including intubated intensive care patients with an expected necessity for sedation exceeding 48 h. Patients are randomly assigned to either receive intravenous sedation with propofol or sevoflurane employing the ACD. Primary endpoint is the comparison of the ‘weaning time’ defined as the time required from discontinuation of the sedating agent until sufficient spontaneous breathing occurs. Moreover, sedation depth evaluated by Richmond Agitation Sedation Scale and parameters of patient’s safety (that is, vital signs, laboratory monitoring of organ function) as well as the duration of mechanical ventilation and overall stay on the ICU are analyzed and compared. An intention-to-treat analysis will be carried out with all patients for whom it will be possible to define a wake-up time. In addition, a per-protocol analysis is envisaged. Completion of patient recruitment is expected by the end of 2012.

Discussion

This clinical study is designed to evaluate the impact of sevoflurane during long-term sedation of critically ill patients on ‘weaning time’, efficiency, and patient’s safety compared to the standard intravenous sedation concept employing propofol.

Trial registration

EudraCT2007-006087-30; ISCRTN90609144

Carbon dioxide rebreathing with the anaesthetic conserving device, AnaConDa®

BACKGROUND

The anaesthetic conserving device (ACD) AnaConDa(®) was developed to allow the reduced use of inhaled agents by conserving exhaled agent and allowing rebreathing. Elevated has been observed in patients when using this ACD, despite tidal volume compensation for the larger apparatus dead space. The aim of the present study was to determine whether CO(2), like inhaled anaesthetics, adsorbs to the ACD during expiration and returns to a test lung during the following inspiration.

METHODS

The ACD was attached to an experimental test lung. Apparent dead space by the single-breath test for CO(2) and the amount of CO(2) adsorbed to the carbon filter of the ACD was measured with infrared spectrometry.

RESULTS

Apparent dead space was 230 ml larger using the ACD compared with a conventional heat and moisture exchanger (internal volumes 100 and 50 ml, respectively). Varying CO(2) flux to the test lung (85-375 ml min(-1)) did not change the measured dead space nor did varying respiratory rate (12-24 bpm). The ACD contained 3.3 times more CO(2) than the predicted amount present in its internal volume of 100 ml.

CONCLUSIONS

Our measurements show a CO(2) reservoir effect of 180 ml in excess of the ACD internal volume. This is due to adsorption of CO(2) in the ACD during expiration and return of CO(2) during the following inspiration.

[Anesthetic conserving device (AnaConDa) used after cardiac surgery: experience in a postoperative recovery unit]

OBJECTIVE

To assess the safety and efficacy of using the Anesthetic Conserving Device (AnaConDa) when maintaining sedation after cardiac surgery.

MATERIAL AND METHODS

Descriptive study of 46 consecutive patients in the postoperative recovery unit after cardiac surgery between January and April 2009. The patients were under sevoflurane sedation administered with the AnaConDa placed in the inhalation tube. No exclusion criteria were established before enrollment. The sevoflurane dose was set using the manufacturer's normogram and was later adjusted to give an end-tidal concentration of sevoflurane between 0.5% and 0.7% on the basis of data from a gas analyzer. Remifentanil was administered to all patients; a fast-track extubation protocol was used. The only criterion for excluding a patient's data from analysis was prolonged sedation (> 5 hours).

RESULTS

The mean (SD) time patients were under sedation with the AnaConDa in place was 2588 (12.32) minutes. The end-tidal concentration of sevoflurane never exceeded 1%. Scores on the Richmond agitation-sedation scale were -5 at 60 minutes in all cases; there was some score variability at 120 minutes. Deeper sedation was desired for the first 60 minutes to avoid awakening related to rewarming. The mean time until awakening was 6.17 minutes (range, 1-30 minutes). The mean time until extubation was 43 (6.69) minutes. The most common adverse effect was arterial hypotension (12 cases). Hypotension was related to bleeding in 3 patients and to low cardiac output in 4 patients.

CONCLUSION

Administering sevoflurane through the AnaConDa can be a safe, valid, and reliable method for sedating patients after cardiac surgery. With this device, it is possible to monitor the concentration administered.

Influence of two different ventilation modes on the function of an anaesthetic conserving device in sevoflurane anaesthetized piglets

OBJECTIVE

To investigate the influence of two ventilation modes on the performance of an anaesthetic conserving device (AnaConDa) in piglets.

STUDY DESIGN

Prospective randomized experimental trial.

ANIMALS

Eight female piglets weighing 24.7 +/- 2.2 kg.

METHODS

Anaesthesia was maintained with sevoflurane (in 60% oxygen) delivered from the AnaConDa placed between endotracheal tube (ETT) and Y-piece. Anaesthetic depth was guided using standard clinical parameters. Ventilation mode was volume controlled (VC) during the first and pressure support (PS) during the second period of anaesthesia in four piglets (group 1); the order was reversed in group 2. Anaesthetic gases were sampled before (at the proximal end of the ETT) and after the AnaConDa (Y-piece). Data were analysed using a model I anova, with treatment and group as fixed categorical effects. Using a paired t-test, partial pressures of carbon dioxide (Pe'CO(2)) on both sides of the device were compared.

RESULTS

Although the mean administration rate of sevoflurane was comparable in both groups (3.8 +/- 1.8 mL hour(-1)), E'Sevo was higher in group 1, more specifically during the first period (p = 0.035). Less sevoflurane escaped during VC (14.0 +/- 3.4%) compared with PS ventilation (17.2 +/- 5.7%) (p = 0.001). Pe'CO(2) was lower at the Y-piece (6.4 +/- 0.8 kPa, 48 +/- 6 mmHg) compared with the ETT (9.3 +/- 1.4 kPa, 70 +/- 11 mmHg) in both groups and ventilation modes. On average, inspiratory CO(2) tension was 2.0 +/-1.0 kPa (15 +/- 8 mmHg). Respiration rate was comparable in all piglets while tidal volume () and peak inspiratory pressure were lower during VC compared with PS (p < 0.001, p = 0.015 respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

The observed differences in E'Sevo concentration and sevoflurane breakthrough were probably related to differences in . The observed high FiCO(2) indicated an excessive dead space with the AnaConDa for these piglets.

[Sedation concepts with volatile anaesthetics in intensive care: practical use and current experiences with the AnaConDa system]

The use of volatile anaesthetics in intensive care medicine has so far been limited by the lack of equipment suitable for daily routine use and the need for an anaesthetic machine. The new Anaesthetic Conserving Device (AnaConDa) enables the routine use of volatile anaesthetics for long-term sedation via intensive care ventilators. The Anaesthetic Conserving Device replaces the common heat and moisture exchanger in the ventilation circuit. The volatile anaesthetic is continuously applied in liquid status via a syringe pump to a form of mini-vaporiser where the anaesthetic agent is vaporised. The expired anaesthetic gas is stored in the carbon filter and approximately 90% of the gas is resupplied into the breathing cycle. The current experiences suggest that volatile anaesthetics present an alternative for long-term sedation in intensive care units, providing optimised pathways, from a medical as well as from an economical point of view. It must, however, be emphasized that the use of volatile anaesthetics for longer periods of time is an off-label use and should only undertaken by medical professionals at their own risk.

The anesthetic conserving device compared with conventional circle system used under different flow conditions for inhaled anesthesia

The Anesthetic Conserving Device (ACD) is a high-flow anesthesia system closed to volatile anesthetics only. We compared the ACD with a circle system under different fresh gas flow (FGF) conditions. Eighty-one patients undergoing major surgery were randomly allocated to receive sevoflurane from a circle circuit combined either with the ACD placed at the Y-piece (n = 41) or with a vaporizer (n = 40). The FGF was set to 8 L/min in the ACD system, where the circle circuit served as a nonrebreather. In the conventional circle system without ACD, the vaporizer was supplied with 1-, 1.5-, 3-, and 6-L/min FGFs. We compared the ACD with the circle system under the four FGFs in terms of sevoflurane dosing, sevoflurane consumption, humidification efficiency, and environmental pollution. The ACD and the low-flow circle system (1.5- and 1-L/min FGFs) resulted in the smallest sevoflurane consumption. The increase in inspired sevoflurane concentration was faster with the circle system than with the ACD only with FGFs > or =3 L/min. The removal of ACD from the circuit allowed the fastest washout of sevoflurane. Respiratory gas humidification was always adequate. Sevoflurane ambient concentration with the ACD was 1-70 ppb. The ACD is a valid and simple alternative to low-flow systems.

IMPLICATIONS

The Anesthetic Conserving Device (ACD) is a new device for anesthetic vapor delivery. We demonstrated that the ACD reduces anesthetic consumption and environmental pollution similarly to a low-flow circle system, offering advantages such as simplicity, no toxicity from compounds produced in the absorber, and potential cost savings.

Interaction of inhalational anaesthetics with CO2 absorbents

We review the currently available carbon dioxide absorbents: sodium hydroxide lime (=soda lime), barium hydroxide lime, potassium-hydroxide-free soda lime, calcium hydroxide lime and non-caustic lime. In general, all of these carbon dioxide absorbents are liable to react with inhalational anaesthetics. However, there is a decreasing reactivity of the different absorbents with inhalational anaesthetics: barium hydroxide lime >> soda lime > potassium-hydroxide-free soda lime > calcium hydroxide lime and non-caustic lime. Gaseous compounds generated by the reaction of the anaesthetics with desiccated absorbents are those that threaten patients. All measures are comprehensively described to--as far as possible--prevent any accidental drying out of the absorbent. Whether or not compound A, a gaseous compound formed by the reaction of sevoflurane with normally hydrated absorbents, is still a matter of concern is discussed. Even after very high loading with this compound, during long-lasting low-flow sevoflurane anaesthesias, no clinical or laboratory signs of renal impairment were observed in any of the surgical patients. Finally, guidelines for the judicious use of different absorbents are given.