Estimating the Impact of Carbon Dioxide Absorbent Performance Differences on Absorbent Cost During Low-Flow Anesthesia.

BACKGROUND: Reducing fresh gas flow when using a circle anesthesia circuit is the most effective strategy for reducing both inhaled anesthetic vapor cost and waste. As fresh gas flow is reduced, the amount of exhaled gas rebreathed increases, but the utilization of carbon dioxide absorbent increases as well. Reducing fresh gas flow may not make economic sense if the increased cost of absorbent utilization exceeds the reduced cost of anesthetic vapor. The primary objective of this study was to determine the minimum fresh gas flow at which absorbent costs do not exceed vapor savings. Another objective is to provide a qualitative insight into the factors that influence absorbent performance as fresh gas flow is reduced. METHODS: A mathematical model was developed to compare the vapor savings with the cost of carbon dioxide absorbent as a function of fresh gas flow. Parameters of the model include patient size, unit cost of vapor and carbon dioxide absorbent, and absorbent capacity and efficiency. Boundaries for fresh gas flow were based on oxygen consumption or a closed-circuit condition at the low end and minute ventilation to approximate an open-circuit condition at the high end. Carbon dioxide production was estimated from oxygen consumption assuming a respiratory quotient of 0.8. RESULTS: For desflurane, the cost of carbon dioxide absorbent did not exceed vapor savings until fresh gas flow was almost equal to closed-circuit conditions. For sevoflurane, as fresh gas flow is reduced, absorbent costs increase more slowly than vapor costs decrease so that total costs are still minimized for a closed circuit. Due to the low cost of isoflurane, even with the most effective absorbent, the rate of absorbent costs increase more rapidly than vapor savings as fresh gas flow is reduced, so that an open circuit is least expensive. The total cost of vapor and absorbent is still lowest for isoflurane when compared with the other agents. CONCLUSIONS: The relative costs of anesthetic vapor and carbon dioxide absorbent as fresh gas flow is reduced are dependent on choice of anesthetic vapor and performance of the carbon dioxide absorbent. Absorbent performance is determined by the product selected and strategy for replacement. Clinicians can maximize the performance of absorbents by replacing them based on the appearance of inspired carbon dioxide rather than the indicator. Even though absorbent costs exceed vapor savings as fresh gas flow is reduced, isoflurane is still the lowest cost choice for the environmentally sound practice of closed-circuit anesthesia.

The environmental impact of the Glostavent® anesthetic machine.

Because anesthetic machines have become more complex and more expensive, they have become less suitable for use in the many isolated hospitals in the poorest countries in the world. In these situations, they are frequently unable to function at all because of interruptions in the supply of oxygen or electricity and the absence of skilled technicians for maintenance and servicing. Despite these disadvantages, these machines are still delivered in large numbers, thereby expending precious resources without any benefit to patients. The Glostavent was introduced primarily to enable an anesthetic service to be delivered in these difficult circumstances. It is smaller and less complex than standard anesthetic machines and much less expensive to produce. It combines a drawover anesthetic system with an oxygen concentrator and a gas-driven ventilator. It greatly reduces the need for the purchase and transport of cylinders of compressed gases, reduces the impact on the environment, and enables considerable savings. Cylinder oxygen is expensive to produce and difficult to transport over long distances on poor roads. Consequently, the supply may run out. However, when using the Glostavent, oxygen is normally produced at a fraction of the cost of cylinders by the oxygen concentrator, which is an integral part of the Glostavent. This enables great savings in the purchase and transport cost of oxygen cylinders. If the electricity fails and the oxygen concentrator ceases to function, oxygen from a reserve cylinder automatically provides the pressure to drive the ventilator and oxygen for the breathing circuit. Consequently, economy is achieved because the ventilator has been designed to minimize the amount of driving gas required to one-seventh of the patient's tidal volume. Additional economies are achieved by completely eliminating spillage of oxygen from the breathing system and by recycling the driving gas into the breathing system to increase the Fraction of Inspired Oxygen (FIO2) at no extra cost. Savings also are accrued when using the drawover breathing system as the need for nitrous oxide, compressed air, and soda lime are eliminated. The Glostavent enables the administration of safe anesthesia to be continued when standard machines are unable to function and can do so with minimal harm to the environment.

Delivery of heliox with a semi-closed circuit during spontaneous breathing: a comparative economic theoretical study.

BACKGROUND: Heliox is a mixture of oxygen and helium which reduces airway resistance in patients with airway obstruction. In clinical practice, patients breathing spontaneously receive heliox via an open circuit. Recently, a semi-closed circuit for heliox administration has been proposed which minimizes consumption of heliox and therefore cost of the heliox therapy; although, the semi-closed circuit is associated with additional costs. The aim of the study is to conduct an economical analysis comparing total cost of heliox therapy using an open versus a semi-closed circuit in spontaneously breathing patients with airway obstruction. METHODS: Four different systems for heliox administration were analyzed: an open circuit and three alternatives of a semi-closed circuit involving a custom made semi-closed circuit and two standard anesthesia machines. Total costs of heliox therapy were calculated for all the systems. For calculation of gas consumption, the clinical procedures limiting continuous heliox therapy including the aerosol therapy, personal hygiene and nutrition were taken into account. A sensitivity analysis was conducted for main input variables that may influence the results of the study. RESULTS: Price of gases consumed by a semi-closed system represents less than 20 % of price of gases when a standard open circuit is used. This represents a saving of approximately 540 EUR per patient. The initial cost of the custom-made semi-closed circuit recuperates after treatment of 18 patients. The corresponding number of patients is 32 when a low-cost anesthesia machine is initially acquired and rises to 69 when a highly advanced anesthesia machine is considered. CONCLUSIONS: Heliox therapy in spontaneously breathing patients using a semi-closed circuit becomes more cost-effective compared to the open circuit, currently used in clinical practice, when applied in a sufficient number of cases. The impact of finding a cheaper way of heliox administration on the clinical practice needs to be ascertained.

A closed-circuit neonatal xenon delivery system: a technical and practical neuroprotection feasibility study in newborn pigs.

BACKGROUND: Asphyxia accounts for 23% of the 4 million annual global neonatal deaths. In developed countries, the incidence of death or severe disability after hypoxic-ischemic (HI) encephalopathy is 1-2/1000 infants born at term. Hypothermia (HT) benefits newborns post-HI and is rapidly entering clinical use. Xenon (Xe), a scarce and expensive anesthetic, combined with HT markedly increases neuroprotection in small animal HI models. The low-Xe uptake of the patient favors the use of closed-circuit breathing system for efficiency and economy. We developed a system for delivering Xe to mechanically ventilated neonates, then investigated its technical and practical feasibility in a previously described neonatal pig model approximating the clinical scenario of global HI injury, prolonged Xe delivery with and without HT as a potential therapy, subsequent neonatal intensive care unit management, and tracheal extubation. METHODS: Sixteen newborn pigs underwent a global 45 min HI insult (4%-6% inspired oxygen reducing the electroencephalogram amplitude to <7 microV), then received 16 h 50% inspired Xe during normothermia (39.0 degrees C) or HT (33.5 degrees C). A conventional neonatal ventilator provided breaths of oxygen to a lower chamber compressing a hanging bag within. This bag communicated with the upper closed part of the breathing system containing soda lime, unidirectional valves, Xe/oxygen analyzers, and a tracheal tube connection. At each end-inspiration, this bag emptied fully and a bolus of oxygen, the driving gas, crossed from the lower to upper chamber via an additional valve. This mechanically substituted the gas uptake from the circle during the previous breath cycle (oxygen + small volume of Xe) with an equivalent volume of oxygen creating a slow-rising inspired oxygen concentration. This was offset by manual injection of Xe boluses, infrequently at steady state, due to the low-Xe uptake of the patient. RESULTS: Total mean Xe usage was 0.18 (0.16-0.21) L/h with no differences between Xe-HT and Xe-NT groups, which had weights of 1767 (1657-1877) g and 1818 (1662-1974) g, respectively (95% CI). HT reduced heart rate in the cooled animals; 180 (165-195) vs 148 (142-155) bpm (P < 0.0001) with no differences in arterial blood pressure, oxygen saturation, arterial carbon dioxide tension, or weaning times between these groups. CONCLUSION: We describe a closed-circuit Xe delivery system with automatic mechanical oxygen replenishment, which could be developed as a single use device. Gas exchange was maintained while Xe consumption was minimal (<$2/h at $10/L*). We have shown it is both feasible and cost-efficient to use this Xe delivery method in newborn pigs for up to 16 h with or without concurrent cooling after a severe HI insult.

Changing patterns in anesthetic fresh gas flow rates over 5 years in a teaching hospital.

BACKGROUND: Reducing anesthetic fresh gas flows can reduce volatile anesthetic consumption without affecting drug delivery to the patient. Delivery systems with electronic flow transducers permit the simple and accurate collection of fresh gas flow information. In a 2001 audit of fresh gas flow, we found little response to interventions designed to foster more efficient use of fresh gas. We compared current practice with our earlier results. METHODS: Flow data were collected in areas with a mix of general and acute surgery in March and November 2001, and again during 2006, by recording directly from the Datex ADU to a computer every 10 s. We extracted the distribution of flow rates when a volatile anesthetic was being administered. Data collection in March 2001 and 2006 was not advertised. RESULTS: In 2001, the mean flow rates were 1.95 and 2.1 L/min with a median flow of 1.5 L/min. In 2006, the mean was 1.27 and the median in the range 0.5-1.0 L/min. Isoflurane use decreased from 47% in 2001 to 4% in 2006. CONCLUSIONS: Fresh gas flows used in our department have decreased by 35% over 4 years. Although the absolute change in flow rate is not large, this represents potential annual savings of more than $US130,000. This occurred without specific initiatives, suggesting an evolution in practice towards lower fresh gas flow. Improvements in equipment and monitoring, including a locally developed system, which displays forward predictions of end-tidal and effect-site vapor concentrations, may be factors in this change.

[Use of isoflurane in a closed-circuit. Economic advantages]. / Utilisation de l'isoflurane en circuit fermé. Avantages économiques.

The present study was designed to assess whether isoflurane requirement was significantly affected by fresh gas flow in a closed-circuit system. Sixty patients scheduled for orthopaedic procedures were randomly assigned into three groups. In group A (n = 20), anaesthesia was conducted with a fresh gas flow of 482.5 +/- 186.6 ml X min-1, corresponding to the patient's metabolic demand. In group B (n = 20), the fresh gas flow was 2000 ml X min-1. In group C (n = 20), it was adjusted to the ventilation minute, i.e. 7145 +/- 986 ml X min-1. Artificial ventilation was conducted using a tidal volume of 10 ml X kg-1 and a rate of 10 to 12 c X min-1. Anaesthesia was induced after 10 min denitrogenation with fentanyl (4 micrograms X kg-1), thiopentone (4 mg X kg-1) and vecuronium (0.1 mg X kg-1). FIO2 was then brought to 0.5 in nitrous oxide and was monitored continuously using a polarographic oxymeter. Liquid isoflurane was injected in the expiratory limb of the circuit using an electrical syringe driver. Alveolar concentration of isoflurane was set at 0.92 vol. % according to Lowe and Ernst. Statistical analysis was carried out using Student's test for means. Anaesthesia lasted 138 +/- 88.3 min in group A, 125.5 +/- 45.1 min in group B and 146.5 +/- 50 min in group C, no difference being significant.(ABSTRACT TRUNCATED AT 250 WORDS)

[Closed anesthetic systems]. / Lukkede anaestesisystemer.

Anaesthesia with closed anaesthetic systems demands knowledge of the physiology of the patients and of how the various anaesthetic gases behave in the organism as only the gases which the patients produces and absorbs are eliminated and replaced. The system is educational as it provides knowledge of the genuine absorption of oxygen and anaesthetic gases. The method is favourable to the environment as only the gases which are used are supplied and it is thus economical in use although investment in monitoring equipment is necessary. In practice, induction and waking of the patient are complicated with this system and it requires an anaesthetist who constantly adjusts the gases in the circuit.

[Low-flow anesthesia systems]. / Lav-flow-anaestesisystemer.

At present, when economy and environment receive high priority, the ideal anaesthesia system with inhalation anaesthetics is a closed circle system in which only the gases which the patient consumes or produces are replaced or eliminated. Low-flow (LF) anaesthesia in which the fresh gas flow which is employed in a closed system, provides a stable system compares with closed anaesthesia systems. Compared with open systems and circler systems with considerable fresh gas flow, the LF system provides advantages as regards economy, environment and exposure of staff to inhalation anaesthetics. The special conditions involved in LF anaesthesia are described in detail with the hope that the method will obtain more widespread distribution than is the case in Denmark today. If greater safety under anaesthesia is desired, eg by monitoring the concentrations of CO2, O2 and inhalation anaesthetics which the patients inspire and expire, this monitoring equipment can be financed by introduction of LF anaesthesia.

Cost-effectiveness of basal flow sevoflurane anaesthesia using the Komesaroff vaporizer inside the circle system.

After ethics committee approval, 51 consenting ASA physical status 1 or 2 adult patients were given basal flow sevoflurane anaesthesia using fresh gas flows of 150 to 300 ml x min(-1) oxygen. A Komesaroff vaporizer was placed on the inspiratory limb of the circle system. Basal flows were introduced immediately following intravenous induction of anaesthesia. The vaporizer was set to deliver the maximum concentration until the inspired sevoflurane concentration (FSI) reached 3%. The dial was then adjusted to maintain the FSI at 3%. After every 60 minutes, the circuit was washed out with 100% oxygen at a flow rate of 10 l x min(-1) for one minute. The FSI reached 3% after an average of 8.5 (3.8) [mean (SD)] minutes. The trends in FSI and the expired sevoflurane concentrations were significantly different (P<0.05) between the mechanically ventilated patients (n=21) and the spontaneously ventilating patients (n =30) and demonstrated a more gradual build-up in the former group. The consumption of sevoflurane was found to be 9.2 (2.8) ml x h(-1). This represented a 52.5% cost saving over the clinical application of the Mapleson's ideal fresh gas flow sequence for low-flow anaesthesia.

[Closed circuit inhalation anesthesia. Consumption and cost]. / Anestesia inalatoria in circuito chiuso. Consumi e costi.

Closed circuit anaesthesia (CCA) and minimal flow anaesthesia diminish inhalatory anaesthetic consumption. Consumption of inhalatory anaesthesia was calculated using two different techniques: CCA and "non rebreathing" system. Costs were compared on the basis of the official list price. The CCA allowed for reduced consumption at lower costs. The resulting annual savings are equal to one third of the total price of the whole apparatus with its complementary monitoring and control systems.

Economic analysis and pharmaceutical policy: a consideration of the economics of the use of desflurane.

Several factors have to be considered in determining the cost of applying a new inhalational anaesthetic such as desflurane into clinical practice. Factors beyond the immediate control of the anaesthetic practitioner include the price set by the manufacturer (although this may be influenced by economic and political pressures), and the physical-pharmacological properties of the anaesthetic (e.g. vaporization, potency, solubility). The anaesthetic practitioner can minimise cost by applying lower inflow rates. Lower solubility (and hence lower uptake) provides a greater economy at lower inflow rates than does higher solubility. Furthermore, lower solubility permits the use of lower inflow rates with greater precision to the control of anaesthesia, and greater ease of application. At present unit prices, the cost of desflurane approximately equals that of isoflurane when a 1 l.min-1 inflow rate is used. The use of lower inflow rates presupposes that such rates do not allow the production of toxic compounds in recirculating gases. Modern equipment makes low-flow anaesthesia reliable and easy to control, and as desflurane is not degraded by the standard carbon dioxide absorbents, its use in low-flow systems is effective and economical. These cost considerations do not take into account the savings that may result from a more rapid recovery from anaesthesia, nor do they take into account the increased expense of capital equipment needed to apply a new anaesthetic.

[Minimal-flow anesthesia in the dog]. / Minimal-Flow-Narkose beim Hund.

Many veterinary practices possess an anesthetic machine with a rebreathing system, and therefore the facility to induce anesthesia under more cost-effective reduced fresh gas flow conditions in a semi-closed system. However, as the fresh gas flow is frequently far too high, the rebreathing element is used rarely or not at all, making the anesthesia unnecessarily expensive. The relationships between the fresh gas setting and the final concentrations of expired air are discussed, and experience in 53 dogs with minimal flow anesthesia (500 ml/min), an extreme variant of anesthesia induction using a semi-closed system with minimal excess gas volume and a high proportion of rebreathed gas, is described.

An audit of anaesthetic fresh-gas flow rates and volatile anaesthetic use in a teaching hospital.

AIM: The large number of anaesthetics administered means that the total cost to a hospital of inhalational anaesthetic agent such as isoflurane or sevoflurane can be considerable. The total anaesthetic gas flow is a major determinant of the use of these agents. Modern anaesthetic machines and monitoring facilitate reduced gas flows, which can significantly reduce wastage of these anaesthetic agents. The purpose of this study was to audit gas flow rates and volatile anaesthetic use. METHODS: We audited gas flows and choice of anaesthetic agent over two one-month periods in one theatre at Christchurch Hospital. Data were collected directly from the anaesthetic machine using a computer. The second study period was clearly advised and followed widespread discussion of results from the first study period. RESULTS: Average fresh-gas flow was approximately 2 l/min (Month 1 = 2.0 l/min, Month 2 = 2.1 l/min). Use of the more expensive agent, sevoflurane, increased but gas flows with this agent decreased. CONCLUSIONS: Given the low flows used, the small difference between study periods was not surprising. The gas flows recorded represent responsible use of anaesthetic agents and are at least as good as flows achieved in previous studies that employed various methods to encourage their reduction.

[Anesthesia with low fresh gas flow in clinical routine use]. / Anästhesie mit niedrigem Frischgasfluss in der klinischen Routine.

Anaesthesia in low-flow techniques gains increasing interest. The possibility of cost reduction, widespread use of highly developed anaesthesia machines and monitors, and introduction of two new fluorinated inhalational anaesthetics with low solubility in human tissues encourage the use of low-flow anaesthesia techniques. Further advantages are improved climatisation of breathing gas and estimation or even measurement of the important parameter "oxygen consumption". The anaesthesia machines and inhalational anaesthetics currently available allow a safe use of low-flow techniques if safety requirements are complied with (tight circle system, monitoring of: inspired oxygen concentration, minute ventilation, airway pressure, transcutaneous oxygen saturation). Low-flow anaesthesia techniques using a fresh gas flow rate of 1 l/min can be performed with almost every anaesthesia machine. However, the use of multigas monitors, analyzing most parts of the breathing gas, facilitates the use of low-flow techniques. Multigas monitors and anaesthesia machines equipped with intermittent fresh gas delivery are recommended for the use of fresh gas flow rates close to the metabolic rate. Because of its physicochemical properties the new inhalational anaesthetic desflurane offers advantages for the use in low-flow anaesthesia techniques.

Priming of anesthesia circuit with xenon for closed circuit anesthesia.

Xenon is an inert gas with a practical anesthetic potency (1 MAC = 71%). Because it is very expensive, the use of closed circuit anesthesia technique is ideal for the conduction of xenon anesthesia. Here we describe our methods of starting closed circuit anesthesia without excessive waste of xenon gas. We induce anesthesia with intravenous agents, and after endotracheal intubation, denitrogenate the patient for approximately 30 min with a high flow of oxygen. This is done to minimize accumulation of nitrogen in the anesthesia circuit during the subsequent closed-circuit anesthesia with xenon. Anesthesia is maintained with an inhalational anesthetic during this period. Then, we discontinue the inhalation agent and start xenon. For this transition, we feel it is unacceptable to simply administer xenon at a high flow until the desired end-tidal concentration is reached because it is too costly. Instead we set up another machine with its circuit filled in advance (i.e., primed) with at least 60% xenon in oxygen and switch the patient to this machine. To prime the circuit, we push xenon using a large syringe into a circuit, which was prefilled with oxygen. Oxygen inside the circuit is pushed out before it is mixed with xenon, and xenon waste will thus be minimized. In this way, we can achieve close to 1 MAC from the beginning of xenon anesthesia, and thereby minimize the risk of light anesthesia and awareness during transition from denitrogenation to closed-circuit xenon anesthesia.

[Soda lime--service life, consumption and costs in relation to fresh gas flow]. / Atemkalk--nutzungsdauer, Verbrauch und Kosten in Abhängigkeit vom Frischgasfluss.

The utilisation time of carbon dioxide absorbers in anaesthesia textbooks is nearly identically specified to last about 5 hours. Therefore in most departments the soda lime of the absorbers is changed routinely on a daily schedule. As rebreathing volume increases considerably with fresh gas flow reduction, the question arises as to whether the soda lime should be changed at even shorter intervals--if low-flow anaesthesia is performed routinely--to to guarantee carbon dioxide absorption safely. In three anaesthesia machines with different technical properties the carbon dioxide absorbers were only changed when the inspiratory carbon dioxide concentration increased to 1 vol. %, indicating definite exhaustion of the soda lime. If a fresh gas flow of 4.4 l/min was used exclusively, utilisation times of 42.7 and 62.3 hours were measured using absorbers filled with 1 l of soda lime pellets, whereas a utilisation time of 98.7 hours was noted with a 1.5 l absorber, all values being surprisingly higher than the above-mentioned figure. If, however, minimal flow anaesthesia is performed routinely in clinical practice, the percentage of time in which the fresh gas flow can really be reduced to 0.5 l/min does not exceed 50 to 80%. Under these conditions the utilisation time of the absorbers decreases to between one half (1/2) and one quarter (1/4) of the utilisation time which can be gained if a flow of 4.4 l/min is used. Thus, the performance of minimal-flow anaesthesia increases the consumption of soda lime two- to fourfold.(ABSTRACT TRUNCATED AT 250 WORDS)

[Anesthetic gas consumption and costs in a closed system with the PhysioFlex anesthesia equipment]. / Anästhesiegasverbrauch und -kosten im geschlossenen System mit dem PhysioFlex-Narkosegerät.

A marked decrease in both personal and environmental pollution with anaesthetic gases as well as in costs is possible with anaesthesia machines which can be run with a low fresh gas flow (FGF) [9]. Low-flow anaesthesia can be performed with appropriately equipped circle systems, although strongly reduced FGF minimises the control of depth of anaesthesia and gas concentrations. Microprocessor-controlled feedback systems allow the utilisation of closed-circuit systems throughout the whole duration of anaesthesia, maintaining full anaesthetic control [3,5]. The aim of this investigation was to determine the costs resulting from gas consumption and clinical suitability of the recently marketed PhysioFlex anaesthesia machine. METHODS. We used a PhysioFlex (Physio, Hoofdorpp, Netherlands) in a series of 15 routine otorhinolaryngological interventions. After induction with thiopentone and suxamethonium, general anaesthesia was maintained with nitrous oxide in 30% oxygen and isoflurane and supplemented with fentanyl and atracurium. The expenditure of anaesthetic gases was recorded during a total of 61 h and 27 min and differentiated into its components. Anaesthetic gas uptake and costs were compared with different breathing systems (low-flow anaesthesia, semiclosed system and non-rebreathing system) under similar clinical conditions. RESULTS. The average minute volume was 6.84 (+/- 1.17) l and the expiratory isoflurane concentration was 0.91% (+/- 0.14%) (Table 1). These settings resulted in an oxygen expenditure of 27.9 (+/- 8.46) l/h with total costs of SFr. 0.04, nitrous oxide 11.9 (+/- 5.4) l/h and 0.27, isoflurane 3.9 ml/h and SFr. 5.42. In contrast, other breathing systems in analogous settings resulted in greater costs by a factor of 0.77 for low-flow anaesthesia (FGF 1 l/min), 2.47 for a semiclosed system (FGF 3 l/min) and 5.63 for a valve-controlled non-rebreathing system (FGF 6.84 l/min) (Table 2). DISCUSSION. The emission of anaesthetic gases can be lowered by measures that avoid unintended gas fallout, the application of filters, scavenging systems and efficient air circulation in operation and recovery rooms [8]. Above all, the use of the lowest possible FGF is advantageous for the patient insofar as better conditioned breathing gases are available, and economic and environmental effects are more significant (Table 3). With the method of quantitative anaesthesia as performed by the PhysioFlex, it is now possible to reduce gas expenditure according to the requirements of the patient as well as maintaining full control of anaesthesia depth. Simultaneously, multiple secured feedback control systems guarantee adequate monitoring and storage of respiratory and metabolic parameters. The duration of nitrous oxide wash-out can be a problem, in particular, when a changeover to O2/air is required.

An alternative strategy for infection control of anesthesia breathing circuits: a laboratory assessment of the Pall HME Filter.

Contaminated breathing systems have been responsible for nosocomial upper respiratory tract and pulmonary infections in patients undergoing general anesthesia. The current infection control guidelines for anesthesia breathing circuits require single-patient use or high-level disinfection of breathing tubes, y-connector, and reservoir bag. An alternative infection control strategy has been suggested that incorporates placement of a microbial filter downstream from the y-connector between the circuit and the patient. This laboratory study assessed the capacity of the Pall HME Filter as a bidirectional barrier to transmission of bacteria between the y-connector of an anesthesia circle breathing system and a test lung. The investigators modified a sterile circle system to allow aerosolization of a suspension of 10(9) Micrococcus luteus over 5 h into the inspiratory limb proximal to the y-connector or downstream from the filter into the test lung. Cultures indicated that the Pall HME Filter placed between the y-connector and the test lung completely prevented transmission of bacteria in both directions. The results of this study suggest that the Pall HME Filter could be used as an effective microbial barrier between the anesthesia circle breathing system and the patient as part of an alternative strategy for infection control.

Measuring the costs of inhaled anaesthetics.

The cost of inhalation anaesthesia has received considerable study and is undoubtedly reduced by the use of low fresh gas flows. However, comparison between anaesthetics of the economies achievable has only been made by computer modelling. We have computed anaesthetic usage for MAC-equivalent anaesthesia with isoflurane, desflurane, and sevoflurane in closed and open breathing systems. We have compared these data with those derived during clinical anaesthesia administered using a computer-controlled closed system that measures anaesthetic usage and inspired concentrations. The inspired concentrations allow the usage that would have occurred in an open system to be calculated. Our computed predictions lie within the 95% confidence intervals of the measured data. Using prices current in our institution, sevoflurane and desflurane would cost approximately twice as much as isoflurane in open systems but only about 50% more than isoflurane in closed systems. Thus computer predictions have been validated by patient measurements and the cost saving achieved by reducing the fresh gas flow is greater with less soluble anaesthetics.