Anesthetic Vapor Research Articles

気化器(<特集>全身麻酔器の現況と展望)

気化器は, 揮発性麻酔薬の正確な濃度を規定するための麻酔器の重要なパーツである. 揮発性麻酔薬は室温, 大気圧下で液体であり, これを蒸気(気体)に変えるには密閉した容器でできた気化器が必要となる. 現在(2005年), 本邦で使用されている揮発性麻酔薬にはハロタン, エンフルラン, イソフルラン, セボフルランがあり, それぞれ沸点, 飽和蒸気圧, MAC等の特性は異なっている(表1). 気化器の密閉容器内では液状の麻酔薬とその蒸気とが, ある一定の圧(飽和蒸気圧)で平衡状態になっている. この飽和蒸気圧は先に述べたように揮発性麻酔薬の種類によって異なっているため, それぞれの麻酔薬に対応した気化器が必要となる. また, 飽和蒸気圧は温度に依存しており, 温度が高くなると大きく(気化しやすく), 温度が下がると小さく(気化しにくく)なる. したがって温度の変化は麻酔ガス濃度に直接影響するので, 気化器は比熱の高い金属で作られ, 内部の温度の影響を最小限にするようにされている.

Microelectrode studies of isoflurane and oxygen vapour mixtures in dimethyl sulfoxide

The electrochemical reduction of the inhalation anaesthetic agent isoflurane was investigated at a commercially available Au microelectrode (5 μm) in DMSO solvent, individually, and also as a component of a simple vapour mixture with oxygen using both traditional voltammetric and potential step chronoamperometric techniques. In a binary gas mixture with oxygen, isoflurane is shown to react with the superoxide anion radical, formed from the electro-reduction of oxygen complicating their simultaneous detection. The observed cross-interference reaction is shown to be dependent of the electrode size and the concentration of the anaesthetic agent, isoflurane. Under steady-state conditions, and using small diameter microelectrodes (5 μm) and low isoflurane concentration ([ISO] <0.2% v/v), the superoxide/isoflurane reaction is shown to approach a one-electron process, where the coupled homogeneous reaction kinetics are almost “out-run”. The use of potential step chronoamperometric techniques however, is shown to significantly reduce the deleterious cross-interference reaction between superoxide and isoflurane. In essence, this work provides scope for the development of a rapid, accurate and inexpensive electrochemical gas sensor for measuring anaesthetic vapour mixture under clinically relevant conditions.

Excess delivery of isoflurane liquid from a syringe driver

We would like to report a recent event we experienced using the AnaConDa anaesthetic conservation device (Hudson RCI AB, Upplands, Sweden). This novel apparatus is designed as a recirculating anaesthetic system, but does not utilise traditional valves or a carbon dioxide absorber. Instead, the AnaConDa, which is placed in circuit, has an active carbon layer, which conserves the anaesthetic vapour. The anaesthetic is delivered to the device using a syringe driver. As it is lightweight, cheap and uses only small volumes of volatile agent, the device has the potential to be ideal for field anaesthesia and sedation. We therefore decided to carry out a bench test to assess its compatibility with our current field anaesthesia equipment. An initial rate of 20 ml.h−1 of isoflurane liquid was set to prime the system, and after 1.2 ml of agent had been delivered to the apparatus, isoflurane was detected in the breathing system. The syringe driver was then stopped, and a rate of 10 ml.h−1 set. The concentration of agent was then monitored using a recently calibrated agent monitor (Datex S5, Datex–Engstrom, Finland). Despite reducing the rate of delivery, the concentration of isoflurane in the system continued to rise. Indeed, even with the syringe driver turned off, the measured concentration was more than 5%. At this time we noticed there was a bubble of gas in the syringe, which appeared to be expanding. The average midday temperature in southern Iraq in June is around 60 °C, and the temperature inside our air-conditioned operating theatre was 33 °C. We assume that a small pocket of air had accidentally been left in the syringe. With the relatively high temperatures, the isoflurane had vaporised into this pocket, causing it to expand. Instead of leading to a pressure rise in the syringe, this had the effect of pushing liquid out of the nozzle, independent of the set rate. It would appear therefore that care has to be taken to expel all the air from the syringe containing the volatile agent when using the AnaConDa device in hot climates. Hudson RCI is happy to be able to respond to the findings made by Drs Henning and Bateman. However, since we are not aware of all parameters used in the bench test, we can only comment on the information we have. Isoflurane is a fluoridised ether that, like many other compounds, can dissolve gases (in this case probably oxygen) at a low temperature. The solubility of gases is much lower at higher temperatures and the gas is released, creating a gas bubble in the syringe. This could force some of the isoflurane out of the syringe so that the amount delivered is higher than the pumping rate of the syringe pump. This would create a gas concentration higher than expected. However, our tests, with anaesthetic agent at temperatures of up to 30 °C, did not create any of the effects described above. We strongly advise that the anaesthetic agent is stored at room temperature before use. H. LambertDirector of Research, Hudson RCI (UK) Ltd, Ashby de la Zouch, UK

Proximal Middle Cerebral Artery Occlusion Surgery for the Study of Ischemia–Reoxygenation Injury in the Brain

This chapter describes a middle cerebral artery occlusion (MCAO) model in which different issues are addressed through laser Doppler flowmetry (LDF) measurements, pre- and postsurgical heparinization, and telemetric intracranial temperature monitoring. In this model, male Wistar rats weighing between 300 and 350 g are anesthetized in an acrylic induction chamber through administration of halothane or isofluorane until unconscious. The rats continue to receive 1–1.5% halothane delivered via a tabletop anesthesia machine and vaporizer via spontaneous respiration through a nose cone. Halothane is mixed with oxygen-enriched air in order to maintain normal arterial pO 2 and pCO 2 values. A femoral venous line is established for drug delivery. Heparin is infused at the onset of surgery. A femoral arterial line is inserted for continuous blood pressure measurement. Arterial blood samples are taken prior to and during the surgical and recovery periods for the determination of blood gases, pH, and glucose levels. The behavioral assessment is done through different procedures including the ten-point neuro scale, visual placing, forelimb strength, and TTC stain.

Effects of sevoflurane and isoflurane on the efficacy of rewarming from hypothermic cardiopulmonary bypass

Effects of sevoflurane and isoflurane on the efficacy of rewarming from hypothermic cardiopulmonary bypass

Predictive accuracy of a model of volatile anesthetic uptake.

A computer program that models anesthetic uptake and distribution has been in use in our department for 20 yr as a teaching tool. New anesthesia machines that electronically measure fresh gas flow rates and vaporizer settings allowed us to assess the performance of this model during clinical anesthesia. Gas flow, vaporizer settings, and end-tidal concentrations were collected from the anesthesia machine (Datex S/5 ADU) at 10-s intervals during 30 elective anesthetics. These were entered into the uptake model. Expired anesthetic vapor concentrations were calculated and compared with actual values as measured by the patient monitor (Datex AS/3). Sevoflurane was used in 16 patients and isoflurane in 14 patients. For all patients, the median performance error was -0.24%, the median absolute performance error was 13.7%, divergence was 2.3%/h, and wobble was 3.1%. There was no significant difference between sevoflurane and isoflurane. This model predicted expired concentrations well in these patients. These results are similar to those seen when comparing calculated and actual propofol concentrations in propofol infusion systems and meet published guidelines for the accuracy of models used in target-controlled anesthesia systems. This model may be useful for predicting responses to changes in fresh gas and vapor settings. We compared measured inhaled anesthetic concentrations with those predicted by a model. The method used for comparison has been used to study models of propofol administration. Our model predicts expired isoflurane and sevoflurane concentrations at least as well as common propofol models predict arterial propofol concentrations.

The Legacy of Albert Faulconer Jr

The Legacy of Albert Faulconer Jr

With Technology Comes Responsibility: Intraoperative Failure of an Anesthetic Vaporizer

With Technology Comes Responsibility: Intraoperative Failure of an Anesthetic Vaporizer

With Technology Comes Responsibility: Intraoperative Failure of an Anesthetic Vaporizer

Director of Clinical Affairs, Datex-Ohmeda, North America, Madison, Wisconsin. michael.mitton@us.datex-ohmeda.comIn Reply:—Thank you for allowing us to respond to the Letter to the Editor, “With Technology Comes Responsibility: Intraoperative Failure of an Anesthetic Vaporizer.”1Datex-Ohmeda would like to compliment the author for correctly identifying the underlying cause of this particular failure. Indeed, the original design of the D-Tec Plus, with it's improved alarm handling and logging software, does sense differences between the inlet and outlet ports of the vaporizer. This feature was included to prevent any backward flow through the vaporizer, which can significantly alter the function of the vaporizer.The D-Tec Plus is a variant of the Datex-Ohmeda Tec 6 Plus desflurane vaporizer, designed specifically for use with Dräger anesthesia machines. Before the release of the new design, Datex-Ohmeda provided the D-Tec Plus to Dräger Medical so that the vaporizer could be validated on Dräger designed and manufactured anesthesia machines. The effect of the pulsating flows that occur during volume mode ventilation in the Julian design was not recognized during this validation.After notification of the events described in the Letter to the Editor, Datex-Ohmeda, along with Dräger, worked quickly to fully understand the implications of this pulsating fresh gas flow and its impact upon the alarm management of the D-Tec Plus. As a result of this investigation, the D-Tec Plus software has been upgraded. This upgrade has been provided to all the D-Tec Plus vaporizers in use and is currently being used during the manufacture of all new D-Tec Plus vaporizers.

An unexplained death: Hannah Greener and chloroform.

An unexplained death: Hannah Greener and chloroform.

Diffusion Hypoxia

ABSTRACTThe aim of this study was to see if we could improve our practice in theatres for the benefit of the patient thus preventing diffusion hypoxia. When a patient continues to breathe from an anaesthetic circuit at the end of anaesthesia, there is a risk of delayed recovery, both by rebreathing and by the presence of anaesthetic vapour emerging from the tubes and other components of the anaesthetic equipment. It has been recommended that nitrous oxide be discontinued early in the recovery period, to monitor the patient during the first elimination phase. As hyperventilation does not influence the elimination of nitrous oxide largely, but increases the risk of subsequent hypoventilation during transport to the recovery room, hyperventilation should be avoided. It is also recommended that oxygen therapy should be used, during transport from theatre to the recovery room, regardless of the duration of nitrous oxide anaesthesia. There has proven to be a risk of Diffusion Hypoxia for at least 30 minutes after discontinuation of nitrous oxide administration in the presence of hypoventilation. The practitioner should always be cautious with heavy smokers, as they present a much greater risk of respiratory problems, and careful observation is needed for the first 5 minutes of breathing room air. Diffusion Hypoxia has proven to be avoided by administration of oxygen for 10 minutes from cessation of nitrous oxide anaesthesia.

A Comparison of the Incidence of the Oculocardiac and Oculorespiratory Reflexes During Sevoflurane or Halothane Anesthesia for Strabismus Surgery in Children

We examined changes in the cardiorespiratory system of small children during surgical correction of strabismus with a laryngeal mask airway and spontaneous respiration with sevoflurane or halothane inhaled anesthesia. Fifty-one children, 1–7 yr old, having outpatient strabismus correction were randomized to sevoflurane (S) or halothane (H) in 66% nitrous oxide at 1.3 minimum alveolar concentration. Children breathed spontaneously through a laryngeal mask airway and were not pretreated with anticholinergics. The oculocardiac reflex (OCR), defined as a 20% decrease in heart rate (HR) from baseline, dysrhythmias, or sinoatrial arrest concomitant with ocular muscle traction occurred less frequently with sevoflurane than with halothane (S 38%, H79%, P = 0.009). The baseline HR was higher with sevoflurane (S 114 ± 13 bpm, H 101 ± 15 bpm, P = 0.002). The lowest HR occurred with halothane (S 95 ± 22 bpm, H 73 ± 19 bpm, P = 0.001). The incidence of dysrhythmias was higher in the halothane group (S 4%, H 42%, P = 0.004). Reductions in minute ventilation and PETCO2 accompanied OCRs. Airway irritability was present with halothane only (S 0, H 3). Eleven children, of whom the majority had received halothane, required measures to correct SpO2 < 95% or PETCO2 > 60 mm Hg during maintenance anesthesia (S 11%, H 32%). Sevoflurane may be a more suitable anesthetic than halothane for operations involving traction on the ocular muscles with spontaneous respiration in children because of reduced incidence of OCR, airway irritability, and ventilatory disturbances. Implications Some children experience a sudden slowing of the heart and impaired breathing when the surgeon pulls on the eye muscles during squint operations under anesthesia. Sevoflurane, a recently developed anesthetic vapor, may reduce this problem when compared with the established vapor halothane.

The impact of drugs used in anaesthesia on bacteria

The impact of drugs used in anaesthesia on bacteria

Vaporizer Level Obstruction Detected by Anesthetic Vapor Analysis

Vaporizer Level Obstruction Detected by Anesthetic Vapor Analysis

A simple strategy for faster induction and more cost-effective use of anesthetic vapor.

Inducing general anesthesia often involves mask ventilation using high fresh gas flow (FGF) to administer anesthetic vapor prior to endotracheal intubation. A common practice is to turn the vaporizer off when the mask is removed from the patient's face to avoid room contamination (VAPOff). An alternative approach is to leave the vaporizer on and turn the FGF to minimum to reduce the amount of vapor laden gas that can enter the room (FGFOff). The objective of this study is to compare the relative induction times and vapor costs associated with each induction strategy. Each induction method was simulated using Gasman (MedMan Simulations, Chestnut Hill, MA) for Windows assuming a 70 kg patient. To simulate a period of mask ventilation with anesthetic vapor prior to intubation, the FGF was set to 6 l/min and the isoflurane vapor concentration to 1.2% (1 MAC) for three minutes with an alveolar ventilation of 5 l/min and cardiac output of 5 l/min. For the first simulation of the intubation period (FGFOff), FGF was turned to 150 ml/min, minute ventilation was set to zero and the vaporizer setting unchanged for one minute. Initial settings were then restored and the rate of change of anesthetic vapor concentration in the circuit (Vckt) and alveolus (Valv) followed for 10 minutes along with the cost of delivered vapor (V(S)). For the second simulation (VAPOff), after the initial three minutes of vapor delivery, the vaporizer was set to zero, minute ventilation was set to zero and the FGF left unchanged for one minute. The initial settings were then restored and Vckt, Valv and V(S) followed for ten minutes. The cost calculation was based upon a 100 ml bottle of Isoflurane at $72/bottle. Actual gas flow was measured at the y-piece of a circle system for fresh gas flows from 0.15 to 6 l/min. At the end of the simulated intubation period (minute 4), Vckt was unchanged with the FGFOff method whereas it had fallen by more than half with the VAPOff method. Using VAPOff, it took until the 6-minute mark for Vckt to return to the same concentration that existed prior to intubation at minute three. Throughout the 10 minute simulated induction, Valv using FGFOff exceeded Valv using VAPOff although the difference became small at the end of the period. V(S) was essentially identical at all time points. No flow into the room was measured at the minimum fresh gas flow whereas higher fresh gas flows resulted in a significant portion of the fresh gas flowing into the, room. The strategy of turning the FGF to minimum and leaving the vaporizer on during intubation does not contaminate the room and speeds induction by fostering a greater alveolar concentration than the VAPOff method. Cost savings are derived using FGFOff since a higher alveolar concentration is achieved at the same vapor cost. Additional cost savings are demonstrated since a low flow technique is possible immediately after intubation when using FGFOff. The practice of turning off the vaporizer during endotracheal intubation while FGF remains high should be abandoned.

Phencyclidine- and diazepam-like discriminative stimulus effects of inhalants in mice.

It has been shown that abused solvents, such as 1,1,1-trichloroethane (TCE) and toluene, share certain pharmacological properties with central nervous system depressants, such as alcohol and anesthetic vapors. Several vapors were tested for diazepam (DZ)- and phencyclidine (PCP)-like discriminative stimulus effects to further explore their pharmacological specificity. In DZ-trained mice, methoxyflurane fully substituted, and TCE produced partial substitution. Fluorothyl and toluene produced no appreciable DZ-lever responding at any concentration tested. On the other hand, toluene produced concentration-related partial substitution for PCP, whereas methoxyflurane, TCE, and fluorothyl did not substitute. The substitution of some these vapors for DZ or PCP suggests that, like ethanol, the discriminative stimulus effects of abused solvents partially overlap those of N-methyl-D-aspartate antagonists as well as those of gamma amino butyric acid agonists.

A system for the delivery of general anesthetics and other volatile agents to the fruit-fly Drosophila melanogaster

The system described here provides a simple method of delivering anesthetic vapor to the fruit-fly Drosophila melanogaster. This system delivers known concentrations of volatile anesthetic vapor obtained from liquid anesthetics in a continuous gas stream of pure humidified air. It controls for evaporation, and absorption of volatile agents, whilst allowing for extracellular electrophysiological recordings. Recordings were made from the fly's escape muscles, the jump tergotrochanter muscle (TTM) and the flight dorsal longitudinal muscle (DLM). The system minimizes the quantity of anesthetic used, making the use of more expensive and more conventional anesthetics cost effective and practicable. It also permits monitoring the fly's movements during anesthesia.

LOW FLOW ANESTHESIA FOR AMBULATORY SURGERY

S10 For low flow anesthesia (LFA) techniques an initial high flow phase of 15-20 min is required, thus limiting the effectiveness in saving anesthetic vapors in short duration anesthesia. Anesthetic gas monitoring offers the opportunity to reduce the duration of the inital wash-in phase down to 1-2 min. This renders LFA practicable for brief surgical procedures. The aim of the study was to evaluate LFA for brief surgical procedures. METHODS: After IRB approval and written informed consent the anesthetic procedure shown in Figure 1 was employed in an ambulatory surgery unit. After premedication with nordiazepam, anesthesia was induced with propofol (1-2mg/kg body weight) and alfentanil (1mg) and maintained with nitrous oxide in oxygen and isoflurane or enflurane. The patient's age, surgical procedure, duration of anesthesia and post-anesthetic care unit time spent were recorded. The consumption of anesthetic vapors per patient was calculated from the overall consumption.Figure 1: Course of modified low flow anesthesia: T0: preoxygenation, intravenous induction, endotracheal intubation, controlled ventilation: T1: wash in phase - fresh gas flow at 9 L/min for 1-2 min, vaporizer setting 5Vol% isoflurane (Iso) or enflurane (Enf) until the desired endtidal anesthetic gas concentration is reached: T2: low-flow phase - fresh gas flow reduction to 1 L/min, adaptation of the vaporizer setting: T3: discontinuation of Isoflurane/N2 O, patient breathing spontaneously, O2 flow at 9 Lmin: T4: extubationRESULTS: 3185 consecutive patients were included in the study. The age of the patients ranged from 5 months to 94 years with a median of 31 years, duration of anesthesia from 15 min to 4 h with a median of 46 min. 29% of the patients were discharged from the post-anesthetic care unit within 2 h, 56% after 2-4 h and 15% after more than 4 h. On the average 24 l N2 O, 7.1 ml enflurane or 3.7 ml isoflurane (liquid) per patient were needed. CONCLUSION: LFA proved to be a useful, practicable and cost-effective anesthetic technique for brief surgical procedures in ambulatory patients. The extremely short wash-in phase as compared to previously described LFA techniques can be achieved by using anesthetic gas monitoring.

Review of Chemical, Medication, and Anesthesia Toxicity in the OR

A host of toxic substances exist in the OR. The toxicity of prep solutions, cleaning chemicals, common medications, and trace anesthetic gases varies greatly. Nurses use, direct others in the use of, or administer potential toxins while breathing air that may be contaminated to some degree with anesthetic vapors. Often, the OR nurse is the neighborhood resource when questions about the toxicity of common chemicals and drugs arise. A general knowledge of the toxicity of these substances improves the nurse's ability to assess the risk from trace anesthetic gases, prevent injury to patients, provide first aid when potentially dangerous exposure occurs, and direct others in the safe use of OR chemicals.

THE EFFECT OF VOLATILE ANESTHETICS UPON THE FLAMMABILITY OF ENDOTRACHEAL TUBES

S201 Operating room fires continue to occur, the most serious of which are airway fires. Work has been done examining the oxygen index of flammability of various endotracheal tube (ETT) materials in an oxygen and nitrous oxide enriched atmosphere [1]. Our goal was to determine the effect that volatile anesthetics have upon the oxygen index of polyvinylchloride (PVC) and red rubber (RR), two common ETT materials. We postulate that due to the similar chemical structures of halogenated anesthetics and halogenated fire extinguishing agents (halons), volatile anesthetics might reduce the flammability of ETT materials. METHODS: The measurement of oxygen index was based upon the American Society for Testing and Materials (ASTM) standards for determining the minimum oxygen concentration to support candle-like combustion of plastics. Nitrogen and oxygen gases were obtained from commercial cylinders and were of medical grade. The gases were routed through flowmeters then to an agent specific anesthetic vaporizer. From the vaporizer, the gases entered a mixing chamber and then flowed upward through a cylindrical test chamber. Midway in the test chamber was a clamp in which the ETT material was placed. The atmosphere within the test chamber was then controlled by varying the oxygen and nitrogen flows and adjusting the agent specific vaporizer. Steady state concentrations were confirmed with an Ohmeda RGM multigas analyzer and an oxygen analyzer. The material was then ignited with a methane pilot flame. While maintaining a constant anesthetic agent concentration the oxygen concentration was adjusted to determine the minimum O2 concentration which would support sustained combustion. Halothane, isoflurane, and desflurane were each studied at four different concentrations ranging from low to maximum vaporizer output. RESULTS: Our results, represented below, indicate that the O2 indices of both PVC and RR are increased in the presence of halogenated anesthetics. Halothane, structurally most similar to halon fire extinguishing agents, has the most pronounced effect upon the O2 index but when compared on and equi-MAC basis is similar to Desflurane. Isoflurane appears to be least effective when examined within its clinical range. (Figure 1)Figure 1It appears from our data that the use of halogenated anesthetics may be instrumental in minimizing the risk of airway fire since they increase the oxygen concentration necessary to support the combustion of the most common ETT materials. However, in spite of this data, it is premature to recommend their use clinically since the toxicity of the pyrolysis and combustion products of these agents is yet to be determined.