Priming of Anesthesia Circuit with Xenon for Closed Circuit Anesthesia

Abstract: 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 inhalational agent and start xenon. For this transition, we feel it is unacceptable to simply administer xenon at a high flow until the desired endtidal 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 deni-trogenation to closed-circuit xenon anesthesia.     

Massive water infusion into the patient's trachea during the use of cascade type heated humidifier

A case of an inadvertent massive infusion of water via the humidifier module into the trachea during the use of cascade type heated humidifier is described. A Fisher and Paykel anesthetic humidifier was employed in the exhalation side of Jackson Rees type breathing circuit between the anesthesia machine and patient's endotracheal tube. During anesthesia for inguinal hernia, fresh gas flow was 6 liters per minute in the breathing circuit. Humidifier module was inadvertently upside down, and the water in the module was abruptly injected into the patient's trachea and we could not ventilate for a short period of time. This water infusion into the trachea was caused by a large supply of fresh gas flow into the breathing circuit and by narrowing of tube diameter. It is essential, when using heated humidifier, to examine it carefully before anesthesia.     

隔离阀对稳定机械通气、回路内药物浓度和气体量的意义

目的：通过对有新鲜气体隔离阀（FGE valve）的麻醉机与普通麻醉机在不同流量下的机械通气性能的比较;探讨隔离阀对稳定机械通气、回路内药物浓度和气体量的意义。方法：在两种麻醉机上分别设定相同分钟通气量（MV）及安氟醚浓度于不同新鲜气流量下测定MV、气道压力、回路内麻醉气体浓度及贮气囊气体量的变化。结果：在有隔离阀的麻醉回路中,新鲜气体流量对MV、气道压力无明显影响,回路内麻醉气体浓度相对稳定,贮气囊气体量随新鲜气体量和泄漏量变化而改变。结论：隔离阀可稳定机械通气、回路内药物浓度及贮气囊中的贮气量,可适时临测和调节回路中气体量。     

An interchangeable Mapleson A-E breathing system is practical and cost effective

BACKGROUND: In locations where oxygen and anesthesia gas supplies are limited, and where circle systems are not practical, means to reduce fresh gas flow during maintenance of inhalational anesthesia are of potential value. We investigated whether a common transport breathing apparatus could be modified to allow interchange between Mapleson D (Map-D) and Mapleson A (Map A) configurations. METHODS: A common Map-D transport system was converted to a Map-A system by switching positions of the exhaust valve and the elbow connector where fresh gas is delivered; these two breathing systems were compared in this study. The key question was whether rebreathing of CO2 could be eliminated at a lower fresh gas flow rate (FGF) with the Map-A design. A structured protocol was followed. RESULTS: A mean decrease in FGF of 2.8 l/min was seen with the Map-A apparatus when compared with the Map-D (P=0.003). With no significant differences in physiologic or anesthetic variables, FGF/V(E) was significantly lower with the Mapleson A configuration than with the Mapleson D system design (1.1 vs. 1.8; P=0.007). The extent to which FGF could be lowered when switching between Mapleson D and A systems correlated strongly with the patients' respiratory rate while under anesthesia (r=0.45, P<0.01). CONCLUSIONS: Cost and resource savings can be realized through the use of a breathing system modification that achieves appropriate ventilation at lower fresh gas flows.     

Managing fresh gas flow to reduce environmental contamination

Anesthetic drugs have the potential to contribute to global warming. There is some debate about the overall impact of anesthetic drugs relative to carbon dioxide, but there is no question that practice patterns can limit the degree of environmental contamination. In particular, careful attention to managing fresh gas flow can use anesthetic drugs more efficiently--reducing waste while achieving the same effect on the patient. The environmental impact of a single case may be minimal, but when compounded over an entire career, the manner in which fresh gas flow is managed by each individual practitioner can make a significant difference in the volume of anesthetic gases released into the atmosphere. The maintenance phase of anesthesia is the best opportunity to reduce fresh gas flow because circuit gas concentrations are relatively stable and it is often the longest phase of the procedure. There are, however, methods for managing fresh gas flow during induction and emergence that can reduce the amount of wasted anesthetic vapor. This article provides background information and discusses strategies for managing fresh gas flow during each phase of anesthesia with the goal of reducing waste when using a circle anesthesia system. Monitoring oxygen and anesthetic gas concentrations is essential to implementing these strategies safely and effectively. Future technological advances in anesthetic delivery systems are needed to make it less challenging to manage fresh gas flow.     

Nitrogen accumulation during closed circuit anesthesia depends on the type of surgery

STUDY OBJECTIVE: The aim of this study is to test the hypothesis that the amount of nitrogen that accumulates within the closed breathing system would be greater during open abdominal surgery than during superficial surgery with small wounds. DESIGN: Prospective, comparative study. SETTING: Operating rooms of a university hospital. PATIENTS: Fourteen American Society of Anesthesiologists physical status I and II adult patients scheduled for abdominal surgery (n = 7) or tympanoplasty (n = 7). INTERVENTIONS: After induction of anesthesia and endotracheal intubation, the patients were denitrogenated for 30 minutes using 100% oxygen at a fresh gas flow of 10 L/min. The breathing system was then closed and patients were anesthetized using 60% xenon in oxygen, supplemented with epidural anesthesia in the abdominal surgery group and sevoflurane in the tympanoplasty group. MEASUREMENTS: Nitrogen concentration in the breathing system was determined by gas chromatography immediately before and 2 hours after the breathing system was closed. MAIN RESULTS: The median (range) increase in nitrogen concentration during the 2-hour period of closed circuit anesthesia was greater in the abdominal surgery patients than in the tympanoplasty patients (6.5% [4.0%-10.2%] vs 2.5% [1.4%-8.4%], P = 0.035, Mann-Whitney U test). CONCLUSIONS: The amount of nitrogen accumulation during closed circuit anesthesia is greater during open abdominal surgery than in superficial surgery such as tympanoplasty. We postulate that during open abdominal surgery, nitrogen in the ambient air enters the body across the peritoneum and then diffuses into the alveoli to be exhaled.     

Inside anesthesia breathing circuits: time to reach a set sevoflurane concentration in toddlers and newborns: simulation using a test lung

We measured the time it takes to reach the desired inspired anesthetic concentration using the Primus (Dr?gerwerk, AG, Lübeck, Germany) and the Avance (GE Datex-Ohmeda, Munich, Germany) anesthesia machines with toddler and newborn ventilation settings. The time to reach 95% of inspired target sevoflurane concentration was measured during wash-in from 0 to 6 vol% sevoflurane and during wash-out from 6 to 0 vol% with fresh gas flows equal to 1 and 2 times the minute ventilation. The Avance was faster than the Primus (65 seconds [95% confidence interval (CI): 55 to 78] vs 310 seconds [95% CI: 261 to 359]) at 1.5 L/min fresh gas flow, tidal volume of 50 mL, and 30 breaths/min. Times were shorter by the same magnitude at higher fresh gas flows and higher minute ventilation rates. The effect of doubling fresh gas flow was variable and less than expected. The Primus is slower during newborn than toddler ventilation, whereas the Avance's response time was the same for newborn and toddler ventilation. Our data confirm that the time to reach the target-inspired anesthetic concentration depends on breathing circuit volume, fresh gas flow, and minute ventilation.     

Does fresh gas flow rate affect monitoring requirements?

Opinions vary on the monitoring requirements associated with low flow to closed circuit anesthesia. Fresh gas flow rate affects variables of anesthesia ventilation such as the time constant of the breathing system, the inspired concentrations of O2, N2O and anesthetic vapor and the potential for rebreathing. Furthermore, very low flow rates challenge the performance of rotameters and vaporizers. Consequently, the safe conduct of minimal flow or closed circuit anesthesia mandates oximetry, which should be redundant; the use of anesthetic agent monitors ("anesthetico-meters") is extremely helpful, and so is capnometry. However, none of these safety monitors is beyond the scope of the "essential requirements" proposed for anesthesia workstations by international standard-writing groups, such as CEN or ISO. It may hence be concluded that fresh gas flow rate does affect variables to be monitored, but it does not affect essential monitoring requirements.     

A breathing circuit disconnection detected by anesthetic agent monitoring

PURPOSE: To describe a case involving a spontaneously breathing patient where a circuit disconnection was detected by a change in monitored anesthetic agent parameters. CLINICAL FEATURES: A patient undergoing shoulder surgery was breathing spontaneously from a circle type anesthesia circuit via a laryngeal mask. A disconnection occurred between the heat and moisture exchanger (HME) and the circle system's Y-piece. As the gas sampling port was integrated into the HME a near normal pattern of CO2 continued to be displayed. The disconnection was noted because of a change in the graphical display of the volatile agent concentration. CONCLUSIONS: Anesthetic circuit disconnection can be difficult to detect, especially in the spontaneously breathing patient. Capnometry may not detect a disconnection on the machine side of the gas sampling port. Changes in oxygen and volatile agent concentrations may provide an early indication of these types of disconnection.     

Accelerating the washout of inhalational anesthetics from the Dräger Primus anesthetic workstation: effect of exchangeable internal components

BACKGROUND: To establish guidelines for the preparation of the Primus anesthetic workstation (Dr?ger, 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.     

回路内麻醉气体吸附器的临床应用

目的在吸入麻醉术后恢复阶段,观察回路内麻醉气体吸附器是否可缩短吸入麻醉的苏醒时间。方法在固定潮气量、每分通气量和新鲜气体流量的条件下,术毕关闭挥发罐后,比较使用回路内麻醉气体吸附装置对回路内麻醉气体浓度变化的影响。结果使用吸附器后,回路内麻醉气体浓度降至MAC0．3所需时间,异氟醚由20．0±0．3分钟降至3．3±0．5分钟(P＜0．01)。安氟醚由25．0±0．1分钟降至3．5±0．5分钟(P＜0．01)。结论应用回路内麻醉气体吸附器可显著缩短病人苏醒时间,并减少气源浪费和环境污染。     

Drawover anesthesia. A review of equipment, capabilities, and utility under austere conditions

Anesthesia care may be required under austere conditions during military operations and natural disasters. Drawover anesthesia devices that provide inhalational anesthetic agents in air or an air/oxygen mixture are useful in these circumstances. This equipment must be portable, rugged, lightweight, and capable of functioning with an absolute requirement for compressed gas supplies. The historical experience, available equipment and literature on this subject are reviewed.     

Clinical applications of low flow and closed circuit anesthesia

Minimal Flow Anesthesia, an extreme technique of semiclosed use of rebreathing systems performed with a fresh gas flow of 0.5 l/min, can be managed with already available anesthesia machines. As a standardized fresh gas volume with fixed composition is used, due to the exponential decrease of the patient's gas uptake, the gas composition within the breathing system may change markedly during the time course of anaesthesia. Nevertheless, by this degree of fresh gas flow reduction, being very close to the patient's gas uptake, the advantages of the rebreathing technique can be achieved nearly extensively. Closed System Anesthesia, however, the anesthetic technique by which just these volumes of oxygen, nitrous oxide, and volatile anesthetics are applied, which are taken up by the patient at the particular time, can't be performed satisfactorily even if highly sophisticated equipment is used. The need for continuous adjustment of the fresh gas controls, the insufficient accuracy of the dosaging systems and the impossibility to calculate precisely the uptake figures in the individual case are essential obstacles for the routine use of this method. An account of the clinical realization of both techniques is given and the specific advantages and disadvantages are considered: although modern anesthesia machines are designed especially for the use of even lowest fresh gas flow rates, quantitative Closed System Anesthesia will not become a technique for routine clinical practice until apparatus with computer-aided closed loop feedback control of the fresh gas supply will be available.     

Desflurane Enhances Reactivity during the Use of the Laryngeal Mask Airway

Background: Desflurane and sevoflurane have markedly different pungencies. The tested hypothesis was that patients breathing equivalent concentrations of desflurane or sevoflurane through a laryngeal mask airway (LMA) would have similar responses.

Methods: After institutional review board approval and informed consent were obtained, 60 patients were enrolled and given intravenous midazolam (14 [mu]g/kg) and fentanyl (1 [mu]g/kg) 5 min before induction of anesthesia. The LMA was inserted at loss of consciousness after 2 mg/kg propofol. When spontaneous breathing returned, a randomly assigned volatile anesthetic was started at an inspired concentration of either 1.8% sevoflurane or 6% desflurane at a fresh gas flow of 6 l/min in air:oxygen (50:50). After 5 min, a controlled movement of the LMA took place. Three minutes later, the inspiratory anesthetic concentration was changed to either 3.6% sevoflurane or 12% desflurane for 3 min. A blinded observer recorded movements and airway events during the start of anesthetic, LMA movement, deepening of the anesthetic, and emergence before LMA removal.

Results: There were no differences at anesthetic start and LMA movement. Desflurane titration to 12% increased heart rate, increased mean arterial blood pressure, and initiated frequent coughing (53% vs. 0% sevoflurane) and body movements (47% vs. 0% sevoflurane). During emergence, there was a twofold greater incidence of coughing and a fivefold increase in breath holding in the desflurane group.     

Carbon monoxide production from sevoflurane breakdown: modeling of exposures under clinical conditions

Isoflurane, enflurane, sevoflurane, and especially desflurane produce carbon monoxide (CO) during reaction with desiccated absorbents. Of these, sevoflurane is the least studied. We investigated the dependence of CO production from sevoflurane on absorbent temperature, minute ventilation (VE), and fresh gas flow rates. We measured absorbent temperature and in vitro CO concentrations when desiccated Baralyme reacted with 1 minimum alveolar anesthetic concentration of (2.1%) sevoflurane at 2.3-, 5.0-, and 10.0-L VE. Mathematical modeling of carboxyhemoglobin concentrations was performed using an existing iterative method. Rapid breakdown of sevoflurane prevented the attainment of 1 minimum alveolar anesthetic concentration with low fresh gas flow rates. CO concentrations increased with VE and with absorbent temperatures exceeding 80 degrees C, but concentrations decreased with higher fresh gas flow rates. Average CO concentrations were 150 and 600 ppm at 2.3- and 5.0-L VE; however, at 10 L, over 11,000 ppm of CO were produced followed by an explosion and fire. Methanol and formaldehyde were present and may have contributed to the flammable mixture but were not quantitated. Mathematical modeling of exposures indicates that in average cases, only patients < or =25 kg, or severely anemic patients, are at risk of carboxyhemoglobin concentrations >10% during the first 60 min of anesthesia. IMPLICATIONS: Sevoflurane breakdown in desiccated absorbents is expected to result in only mild carbon monoxide (CO) exposure. Completely dry absorbent and high minute ventilation rates may degrade sevoflurane to extremely large CO concentrations. Serious CO poisoning or spontaneous ignition of flammable gases within the breathing circuit are possible in extreme circumstances.     

Low flow anesthesia at a fresh gas flow of 10 ml.kg-1.min-1 for hours using time-cycled ventilator]

Low flow anesthesia (LFA) at a fresh gas flow (FGF) level of 10 ml.kg-1.min-1 with oxygen flow set at 0.5 ml.kg-1.min-1: 0.5 ml.kg-1.min-1 nitrous oxide and 3% isoflurane was performed using time-cycled ventilator on 10 patients of ASA class I or II, with age of 55 +/- 13 (mean +/- SD) years and body weight of 55 +/- 10 kg for 5 h. Excessive anesthetic gases from the anesthesia gas monitor were led to an expiratory breathing tube. After rapid induction and tracheal intubation, denitrogenation was performed for about 5 min using a 100% oxygen flow of 6 l.min-1 before LFA. The inspired/expired oxygen concentration decreased gradually from 96 +/- 2%/90 +/- 2% at beginning of LFA to 42 +/- 3%/37 +/- 4% at 5 h. The operation was started after 29 +/- 10 min of beginning of LFA. The nitrous oxide concentration reached 37 +/- 4%/35 +/- 4% at the beginning of operation and further increased to 55 +/- 3%/53 +/- 3% at 5 h. The isoflurane concentration reached 1.0 +/- 0.1%/0.8 +/- 0.1% at the beginning of operation and further increased to 1.2 +/- 0.1%/1.0 +/- 0.1% at 5 h. The anesthetic potency was 1.2 +/- 0.1 MAC/1.0 +/- 0.2 MAC at the beginning of operation. The isoflurane vaporizer setting was changed only once in two cases from 3% to 2% exceeding 1.5% in inspired concentration. There was no need to change the flow of oxygen and nitrous oxide for 5 hrs. No SpO2 lower than 95% was observed during this study. This method is a clinically safe, easily applicable anesthesia method and used the smallest FGF reported in LFA without occurrence of low FIO2.     

活性炭可有效吸附麻醉机内的吸入麻醉药

目的如果一个恶性高热易感者需要进行麻醉，就要求对先前使用过吸入麻醉药的麻醉机以高流量新鲜气流进行冲洗。关于冲洗时间，既往的研究结果各异，从10—104分钟不等。在先前提出的替代净化技术中，有研究者提出在呼吸回路吸气端安装活性炭过滤器。方法本研究中，我们将活性炭过滤器安置于几种分别受异氟烷、七氟烷和地氟烷污染的麻醉机呼吸回路的吸气和呼气两端，测出为使上述3种麻醉药浓度降至5ppm，用新鲜气流冲洗麻醉机所需要的时间。接下来我们还模拟了临床上麻醉诱导90分钟后被诊断为恶性高热的患者，评估用活性炭过滤器减少麻醉药接触的有效性。结果活性炭过滤器放置于呼吸回路的吸气端和呼气端后，使挥发性麻醉药浓度降低至低于5ppm所需要的时间小于2分钟。麻醉药的浓度可保持远低于5ppm至少60分钟。麻醉诱导后，一旦患者确诊为恶性高热，由于活性炭过滤器的存在，在吸入麻醉药浓度超过5ppm前，可使用同一麻醉机至少67分钟。结论用新鲜气流冲洗的方法清洗用过吸入麻醉药的麻醉机通常需要10—104分钟，安装活性炭过滤器给我们提供了一种取而代之的新方法。     

Faulty anesthesia circuits: a source of environmental pollution in the operating room

Commonly used disposable anesthesia circuits were studied for leak and gas spillage. Trace anesthetic gas concentrations produced by these circuits in the anesthesiologist's breathing zone were analyzed by a Hewlett-Packard Gas Chromatograph. These measurements demonstrated ambient halothane (3.29 +/- 0.1 ppm) and N2O (333.5 +/- 2.31 ppm) concentrations well above target levels, when swivel-type disposable anesthesia circuits were used, despite the presence of standard gas-scavenging devices and appropriate operating room fresh air exchange rates. Lower ambient concentration levels (0.38 +/- 0.03 ppm halothane and 31.3 +/- 1.49 ppm N2O) were measured when Y-type disposable anesthesia circuits were used.     

Desflurane enhances reactivity during the use of the laryngeal mask airway

BACKGROUND: Desflurane and sevoflurane have markedly different pungencies. The tested hypothesis was that patients breathing equivalent concentrations of desflurane or sevoflurane through a laryngeal mask airway (LMA) would have similar responses. METHODS: After institutional review board approval and informed consent were obtained, 60 patients were enrolled and given intravenous midazolam (14 microg/kg) and fentanyl (1 microg/kg) 5 min before induction of anesthesia. The LMA was inserted at loss of consciousness after 2 mg/kg propofol. When spontaneous breathing returned, a randomly assigned volatile anesthetic was started at an inspired concentration of either 1.8% sevoflurane or 6% desflurane at a fresh gas flow of 6 l/min in air:oxygen (50:50). After 5 min, a controlled movement of the LMA took place. Three minutes later, the inspiratory anesthetic concentration was changed to either 3.6% sevoflurane or 12% desflurane for 3 min. A blinded observer recorded movements and airway events during the start of anesthetic, LMA movement, deepening of the anesthetic, and emergence before LMA removal. RESULTS: There were no differences at anesthetic start and LMA movement. Desflurane titration to 12% increased heart rate, increased mean arterial blood pressure, and initiated frequent coughing (53% vs. 0% sevoflurane) and body movements (47% vs. 0% sevoflurane). During emergence, there was a twofold greater incidence of coughing and a fivefold increase in breath holding in the desflurane group. CONCLUSIONS: When airway responses to sevoflurane and desflurane were compared in elective surgical patients breathing through an LMA, there were significantly more adverse responses with desflurane at 12% concentrations and during emergence.     

Model for the administration of low-flow anaesthesia

A general (multiple-gas) three-compartment mass-balance model of the circle-absorber breathing circuit with intermittent positive-pressure ventilation has been developed. We propose it as a tool to determine flowmeter and vapourizer settings for inhalation anaesthesia by low- flow methods (less than 1 litre min-1 total fresh gas flow). This model reproduces the results of various previously-published mass-balance models, but it appears to underestimate slightly the delivery of fresh gases to the inspired limb of the breathing circuit when tested with clinical data from surgical cases. Low-flow dosing schedules for 35% inspired oxygen and 1% inspired halothane were computed with the model and tested in vitro with a circle-absorber breathing circuit and an active gas-exchange lung at nine values of simulated patient gas exchanges. The mean inspired oxygen concentration over all trials was 32.8% (SD = 1.9%), while the mean inspired halothane concentration was 1.2% (SD = 0.3%). The flow meter and vapourizer settings calculated from the model appear to have sufficient accuracy to be useful in the clinical setting in conjunction with active oxygen and anaesthetic agent monitoring.