Effects of Anesthetic Administration on Rat Hypothalamus and Cerebral Cortex Peptidome

Prohormone-derived neuropeptides act as cell-cell signaling molecules to mediate a wide variety of biological processes in the animal brain. Mass spectrometry-based peptidomic experiments are valuable approaches to gain insight into the dynamics of individual peptides under different physiological conditions or experimental treatments. However, the use of anesthetics during animal procedures may confound experimental peptide measurements, especially in the brain, where anesthetics act. Here, we investigated the effects of the commonly used anesthetics isoflurane and sodium pentobarbital on the peptide profile in the rodent hypothalamus and cerebral cortex, as assessed by label-free quantitative peptidomics. Our results showed that neither anesthetic dramatically alters peptide levels, although extended isoflurane exposure did cause changes in a small number of prohormone-derived peptides in the cerebral cortex. Overall, our results demonstrate that acute anesthetic administration can be utilized in peptidomic experiments of the hypothalamus and cerebral cortex without greatly affecting the measured peptide profiles.

Development of an Analytical Method for Detection of Anesthetics and Sedatives in Fish

BACKGROUND

Anesthetics and sedatives are frequently used to prevent abrasions caused by stress and facilitate fish management. However, drug residues may persist and cause changes in fish conditions and induce side effects. In addition, drugs that are not permitted for use in edible fish are sometimes potentially used in fish. The drugs can also be found in wastewater and are likely to be detected in fish.

OBJECTIVE

The purpose of this study was to establish a quantitative analytical method for 10 anesthetic and sedative (azaperone, chlorpromazine, diazepam, estazolam, haloperidol, nitrazepam, nordiazepam, oxazepam, perphenazine, and temazepam) residues in fish sold in Korean markets.

METHODS

Shrimp, flounder, and eel samples were selected as matrices. Acetonitrile (ACN) containing 0.1% formic acid was selected as an extraction solvent for shrimp and 100% ACN for flounder and eel. The QuEChERS method with C18 and PSA was used as the extraction procedure, and the analysis was performed by LC-MS/MS.

RESULTS

Limit of quantitation, recovery, accuracy, and precision were validated, and satisfactory results were obtained for the drugs. All results applied to the real samples were negative.

CONCLUSION

An optimal validation method was studied. Since the results for all samples were negative, it is considered that additional studies are needed by increasing the number of drugs.

HIGHLIGHTS

The most effective QuEChERS pretreatment method and conditions of LC-MS/MS for the analysis of anesthetics and sedatives in fish were established.

Evaluation of benzocaine-based anesthetic gel in anuran skins extracts: A case study using the frog Lithodytes lineatus (Anura: Leptodactylidae)

Extracts made from the skin of dead Lithodytes lineatus frog individuals with the application of the benzocaine-based anesthetic gel, introduced into the oral cavity, were analyzed by ¹H Nuclear Magnetic Resonance to investigate whether the application of this product (oral) can make studies that use extracts from the skins of these animals unfeasible. For comparison, we used skins of another species of anuran following the same death protocol. No trace of the benzocaine substance was found in the ¹H-NMR spectra of the skin extracts from any of the tested anuran species. Still, using the hierarchical clustering model, it was possible to observe the formation of well-defined groups between the skin extracts of anurans and the anesthetic used to kill these animals. Our results suggest that the lethal dose of benzocaine in gel used inside the mouth of frogs may have no influence on potential results regarding the chemical composition or even bioassays using extracts made from the skin of these animals killed under this protocol since there was no detection of this substance for the analyzed samples.

Was Mafeisan an Anesthetic in Ancient China?

According to the Chinese historical books, Records of the Three Kingdoms () and Book of the Later Han (), Hua Tuo (, 140 - 208), a Traditional Chinese medicine (TCM) physician invented Mafeisan, an oral herbal general anesthetic, more than 1800 years ago during Eastern Han Dynasty. However, no written record of ingredients of the original Mafeisan has been found anywhere so far although there have been several similar anesthetic prescriptions published in TCM books later. There has been controversy over the existence of Mafeisan and even Hua Tuo in Chinese literature. We did extensive literature search and analysis, and believe that there indeed was Mafeisan in Hua Tuo's time.

Separation and enhanced detection of anesthetic compounds using solid phase micro-extraction (SPME)-Raman spectroscopy

Polydimethylsiloxane (PDMS)-based solid-phase micro-extraction (SPME) was used along with Raman spectroscopy (RS) to separate and enhance the detection of five anesthetic compounds (halothane, propofol, isoflurane, enflurane, and etomidate) from aqueous and serum phases. Raman signals in the spectral ranges 250-450 cm(-1) and 950-1050 cm(-1) allowed the unique characterization of all five compounds when extracted into the PDMS phase. The SPME-RS detection of clinically relevant concentrations of aqueous propofol (6.5 μM) and halothane (200 μM) is shown. We quantify the partition coefficient for aqueous halothane in PDMS as log K = 1.9 ± 0.2. Solid-phase micro-extraction of the anesthetics makes their detection possible without the strong autofluorescent interference of serum proteins. Because of low solubility and/or weak Raman scattering, we found it challenging to detect enflurane, isoflurane, and etomidate directly from the aqueous phase, but could we do so with SPME enhancement. These studies show the potential of SPME-RS as a method for the direct detection of anesthetics in blood.

Determination of levels of current drugs in hospital and urban wastewater

A rapid, sensitive and highly specific HPLC-MS/MS method with direct on-line preparation was applied for the determination of 20 common pharmaceuticals in hospital and urban wastewater. Median drug concentrations were quite similar in the majority of samples, cerca 1 μg L⁻¹ ranging from 0.06 to 2.67 μg L⁻¹ in both water. Pharmaceutical hospital contribution, below 1 %, was negligible, as compared to the huge amount in the municipal plant flow. Due to only partial elimination in the plant, hundreds of kilograms of harmful waste per year are discharged in the River Seine. Therefore, to reduce potential human and environmental exposure, a topic of major concern, an efficient drug treatment procedure should be used at the municipal plant stage in order to reduce urban wastewater pollution. The HPLC-MS/MS method could be a very useful tool to optimize the pharmaceutical wastewater treatment process.

Determination of tricaine residues in fish by liquid chromatography

Tricaine methanesulfonate (MS-222) is approved by the U.S. Food and Drug Administration, Center for Veterinary Medicine (CVM), as an anesthetic drug for select aquaculture species. It was approved for use as a handling aid with a 3 week withdrawal time. The drug is rapidly metabolized and excreted; therefore, CVM approved its use without requiring a regulatory method for drug residues in tissues. However, there are concerns that the drug may be used to sedate fish during transport to slaughter. A regulatory method will enable monitoring for unsafe residues of this drug resulting from extralabel use. We present a quantitative method, using LC at a target level of 0.1 mg/kg (ppm), for three different farmed species: salmon (Salmo salar); tilapia (Oreochromis spp.); and catfish (Ictalurus punctatus). The assay begins with an acetonitrile extraction, followed by filtration and mixed-mode cation-exchange solid-phase extraction cleanup. The extracts are analyzed by reversed-phase LC with UV detection at 320 nm. The method was validated by using fish fillets with incurred residues, control fish fillets, and fish fillets fortified at half the target level, the target level, and twice the target level (0.05, 0.1, and 0.2 ppm, respectively). For all species, accuracy is > or =80% and the RSD is < or =10%. The method complies with CVM performance criteria for the determination of veterinary drug residues.

Evaluation of a method for determining concentrations of isoeugenol, an AQUI-S residue, in fillet tissue from freshwater fish species

AQUI-S is a fish anesthetic/sedative that is approved for use in a number of countries throughout the world and has the potential for use in the United States. The active ingredient in AQUI-S is isoeugenol. A method for determining isoeugenol concentrations in edible fillet tissue is needed for regulatory purposes, including surveillance and potential use in studies fulfilling human food safety data requirements if U.S. Food and Drug Administration approval is pursued. A method was developed and evaluated for determining isoeugenol concentrations in fillet tissue using relatively common procedures and equipment. The method produced accurate and precise results with fillet tissue from 10 freshwater fish species. The percentage of isoeugenol recovered from samples fortified with isoeugenol at nominal concentrations of 1, 50, and 100 microg/g for all species was always >80 and <97%. Within-day precision for samples fortified at those same concentrations was < or =10%, and day-to-day precision was < or =4.0%. Method precision with fillet tissue containing biologically incurred isoeugenol was < or =8.1%. There were no or minimal chromatographic interferences in control fillet tissue extracts from 9 of the 10 species. The method detection limits for all but one species ranged from 0.004 to 0.014 microg/g, and the quantitation limits ranged from 0.012 to 0.048 microg/g.

[Anaesthetics and breast feeding]

Many women undergo anaesthetic procedures related to childbirth or during the period of lactation. Most anaesthetic drugs are lipophilic and are thus excreted into breast milk. This article summarises available knowledge regarding anaesthetics, their excretion into breast milk and possible effects on the suckling infant. The consequences of such an exposure are discussed in terms of whether breast-feeding should be allowed or not after anaesthetic procedures.

Determination of residues of tricaine in fish using liquid chromatography tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the determination of residues of the anaesthetic tricaine mesilate (MS222) in fish tissues is described. Residues were extracted from homogenized tissues with McIllvaine buffer/methanol and purified over a C18 solid-phase extraction column followed by LC-MS/MS analysis. In the multiple-reaction monitoring mode of the mass spectrometer, chromatograms were recorded by monitoring the m/z 166-->m/z 138 and m/z 166-->m/z 94 transitions for quantification and confirmation of the residues in the finfish matrix, respectively. Recoveries were in the range of 67%+/-10% (n=6) for tilapia at 2 microg kg(-1), 95%+/-7% (n=6) at 2 microg kg(-1) in salmon and 92%+/-3% (n=5) for trout at 2.5 microg kg(-1). The limits of detection were 0.5, 0.6 and 0.6 microg kg(-1) in trout, salmon and tilapia, respectively. No residues of tricaine were found in eight sampled aquacultured fish (salmon and trout) bought from the local market.

[A color test for rapid screening of gamma-hydroxybutyric acid (GHB) and gamma-butyrolactone (GBL) in drink and urine]

OBJECTIVE

A rapid color test for screening gamma-hydroxybutyric acid (GHB) and its precursor gamma-butyrolactone(GBL) was investigated in drink and urine samples.

METHODS

In an acidic solution, GHB was converted to GBL, which reacted with hydroxylamine hydrochloride in presence of sodium hydroxide, forming hydroxamate. A purple complex was formed when hydroxamate reacted with ferric chloride in acidic condition.

RESULTS

Detection limit concentrations of GHB in drinks were between 0.5-2 mg/mL, less than the popular abuse concentrations of GHB. This method was usable for urine, with detection limit concentration 0.5 mg/mL. Interferences of common organic solvents and narcotics and depressants were surveyed.

CONCLUSION

This method is simple, safe, and rapid; it facilitates rapid screening of GHB and GBL in clinic and forensic laboratories.

Method development for the enantiomeric purity determination of low concentrations of adrenaline in local anaesthetic solutions by capillary electrophoresis

L-adrenaline is often included in local anaesthetic (LA) solutions for injection to improve the quality of the anaesthetic block. The concentration of the LA is between 2.5 and 20 mg/ml and the concentration of adrenaline is typically < or = 0.1% of the LA concentration. In order to follow the racemization into d-adrenaline, not only is chiral separation needed but also sufficient resolution from the LA and other components of the injection solution. Furthermore, very high sensitivity is needed in order to be able to determine the d-enantiomer at very low concentrations, i.e. down to about 0.1 microg/ml. The development of a chiral capillary electrophoresis method that is able to determine the racemization of adrenaline is described, together with a limited validation. Samples are injected without pretreatment and analysed with a capillary electrophoresis buffer containing 40 mM heptakis(2,6-di-O-methyl)-beta-cyclodextrin, 0.10 M phosphoric acid and 0.05 M triethanolamine. The amounts of d-adrenaline found in the LA products tested were typically < 3% of the l-adrenaline concentration and < 0.003% of the LA concentration.

Apparent ‘electrocatalytic’ activity of multiwalled carbon nanotubes in the detection of the anaesthetic halothane: occluded copper nanoparticles

The electrocatalytic detection of the anaesthetic halothane on a multiwalled carbon nanotube modified glassy carbon electrode is reported with a low limit of detection of 4.6 microM. A thorough investigation of the underlying cause of this apparent catalytic effect is undertaken by comparing the response of various carbon electrodes including glassy carbon, basal- and edge-plane pyrolytic graphite electrodes (bppg and eppg respectively) to increasing additions of halothane. The reduction of halothane is shifted by 250-300 mV to more negative potentials at an eppg electrode than that observed at the GC-CNT electrode. Therefore the results of this investigation show that, surprisingly, the electrocatalysis is not solely due to the introduction of edge-plane-like defect sites on the carbon nanotubes as is commonly found for many other substrates showing favourable voltammetry at nanotube modified electrodes. Instead, we reveal that in this unusual case the electroactive sites for the reduction of halothane are due to the presence of copper nanoparticles occluded within the carbon nanotubes during their production, which are never completely removed by standard purification techniques such as acid washing. This is only the third known case where apparent electrocatalysis by carbon nanotube modified electrodes is due to occluded metal-related nanoparticles within the nanotube structure, rather than the active sites being the edge-plane-like defect sites on the nanotubes. Furthermore this is the first case where the active sites are nanoparticles of copper metal, rather than metal oxide nanoparticles (namely oxides of iron(II)/(III)) as was found to be the case in the previous examples.

A Rapid HPLC Procedure for Analysis of Analgesic Pharmaceutical Mixtures for Quality Assurance and Drug Diversion Testing

A simple high-performance liquid chromatographic (HPLC) method that allows for the rapid identification and quantification of analgesic and anesthetic solutions typically used in surgical procedures or patient controlled analgesia is presented. The separation of bupivacaine, clonidine, fentanyl, hydromorphone, midazolam, and morphine is complete in less than 20 min. The method allows test solutions to be either directly injected or diluted prior to injection into the HPLC system. The method is useful from the standpoint that pharmaceutical preparations are usually submitted with the known drug of interest and expected concentration. The method is also useful for initial screening of solutions submitted that are either unknown or of questionable identity. The method has been successfully applied as part of hospital-based quality control and quality assurance programs to detect not only errors in the preparation of solutions of scheduled drugs, but also to uncover illegal diversion of drugs of abuse by medical personnel.

Digital sensor chips for agent dosing and metering

Digital sensor chips are providing new possibilities for increased reliability in gas and anaesthesia systems. Operating principles and future use of the technology are outlined here.

Fast Screening of Low Molecular Weight Compounds by Thin-Layer Chromatography and “On-Spot” MALDI-TOF Mass Spectrometry

Fast screening of low-MW compounds is performed by thin-layer chromatography (TLC) followed by direct on-spot matrix-assisted laser desorption/ionization time-of-flight mass spectrometry identification with nearly "matrix-free" mass spectra using an UV-absorbing ionic liquid matrix. Owing to minimal background ions from the proton donor triethylamine/alpha-cyano-4-hydroxycinnamic acid ionic liquid matrix, three arborescidine alkaloids, the anesthesics levobupivacaine and mepivacaine, and the antibiotic tetracycline were readily characterized most frequently by the MS detection of their protonated molecules. The technique is fast and sensitive, requires little sample preparation and manipulation, and is therefore suitable for fast screening with TLC separation and MS identification of low-MW compounds, with potential applications in areas such as phytochemistry, synthetic chemistry, and product manufacturing quality monitoring.

Xenon: elemental anaesthesia in clinical practice

The 'noble' gases have been known to have anaesthetic properties for 50 years yet only recently has their application become a clinical reality. In this review we describe the preclinical and clinical studies that have led to a resurgence of interest in the use of the element xenon as an anaesthetic. Furthermore, we highlight specific areas where xenon demonstrates advantages over other anaesthetics, including safety, beneficial pharmacokinetics, cardiovascular stability, analgesia and neuroprotection.

Validation of capillary electrophoresis--mass spectrometry methods for the analysis of a pharmaceutical formulation

The coupling of capillary electrophoresis (CE) to mass spectrometry (MS) with an electrospray ionization (ESI) technique is generally performed for qualitative applications, and only few quantitative results have been reported. This paper investigates the validation of a CE-ESI-MS method for the analysis of a pharmaceutical formulation containing lidocaine. Some important ESI criteria are discussed including sheath-liquid composition, nebulizing gas pressure and position of the CE capillary outlet. After optimization of these parameters, an intermediate precision of about 5% was achieved. The latter, as well as efficiency and resolution, were compared to those achieved with UV detection. Besides, a multiple injection procedure was developed to reduce analysis time per sample and was successfully applied to both UV and MS detectors. The validation results achieved by multiple injections were identical to those obtained with classical injection, but afforded a gain of time by a factor of 2.5.

Evaluation of the mass spectrometric patterns of volatile liquid anaesthetics to predict the temperature--metal caused decomposition pathway

In this study, prediction of the thermal decomposition pathway of the volatile liquid anaesthetics such as halothane, enflurane and isoflurane in contact with various metal/metal oxides at elevated temperatures has been deduced by evaluating the mass spectrometric fragmentation pattern of each anaesthetic observed in the ionisation process. In the light of the molecular structures and fragmentation components, it was believed that the thermal decomposition pathway of each anaesthetic on metal/metal oxide surface, particularly at higher temperatures, is similar to the ionisation mechanism occurring in the mass spectrometer ionisation process with minor differences for each molecule. The ionisation clusters for each anaesthetic molecule show the most likely fragment and radicals formed in the mass spectrometric ionisation process by considering the isotopic effect. From these clusters, thermal decomposition pathway of the liquid anaesthetics and formation mechanisms of the major halogenated thermal decomposition products have been predicted. It was concluded that the ionisation and thermal decomposition pathway resembles each other, but are not completely similar.

The importance of stereoselective determination of drugs in the clinical laboratory

About 56% of the drugs currently in use are chiral compounds, and 88% of these chiral synthetic drugs are used therapeutically as racemates. Only a few of these drugs qualify for a stereospecific determination in a clinical laboratory for therapeutic drug monitoring of patients. If the qualitative and quantitative pharmacokinetic and pharmacodynamic effects are similar, the enantiomers do not need to be separated. However, if the metabolism of the different stereoisomers is handled by different enzymes which are either polymorphic or can be induced or inhibited, and if their pharmacodynamic effects have differences either in strength or in quality, enantiospecific analysis is urgently needed. Unfortunately, there are many racemic drugs where the stereospecificity of the metabolism and/or the pharmacodynamic effects of the enantiomers is not known today. For these drugs, there is a great need for studies concentrating on these differences to improve treatment of the patients.

Use of negatively charged cyclodextrins for the simultaneous enantioseparation of selected anesthetic drugs by capillary electrophoresis-mass spectrometry

The simultaneous enantioseparation of selected anesthetic drugs was studied by capillary electrophoresis (CE) in presence of three different negatively charged cyclodextrins (CDs). Among the chiral selectors tested, namely carboxymethyl, sulfobutyl ether and sulfated-beta-CD, the latter appeared to be the most effective to achieve the enantiomeric resolution of the investigated compounds. Beside CD type, resolution was greatly influenced by the buffer pH, the molecular structure of the anesthetic compounds, CD concentration and temperature. The optimum electrophoretic conditions for the stereoselective analysis of the studied anesthetics were obtained with a poly(vinyl alcohol) coated capillary (48.5 cm total length x 50 microm I.D.), a 50 mM Tris-phosphate buffer at pH 2.5 containing 6 mg ml(-1) of sulfated-beta-CD, an applied voltage of 30 kV and a temperature of 30 degrees C. Under these optimized conditions, four drugs, namely bupivacaine, mepivacaine, ketamine and prilocaine, were simultaneously enantioresolved in less than 12 min. Furthermore, the method was applied to the stereoselective analysis of mepivacaine in a pharmaceutical preparation. Finally, the method was on-line coupled to electrospray ionization mass spectrometry using the counter current partial-filling technique.

Volatile anesthetics give a false-positive reading in chemical agent monitors in the "H" mode

Chemical agent monitors (CAMs) are routinely used by the armed forces and emergency response teams of many countries for the detection of the vesicant sulfur mustard (HD) and the G series of organophosphate nerve agents. Ambient operating room isoflurane levels were found to produce strong positive signals in the "H" mode when the CAM was used to monitor the efficacy of decontamination procedures during routine surgical procedures on HD-poisoned animals requiring up to 8 hours of general anesthesia. Subsequent testing showed that isoflurane, as well as desflurane, sevoflurane, halothane and methoxyflurane, produce two ionization peaks in the CAM response. One of these peaks is interpreted by the CAM processing software as HD, resulting in a CAM "H" mode bar response. No interference was encountered with isoflurane, desflurane, and sevoflurane when the CAM was set to the "G" mode, although extremely high (nonclinical) concentrations of halothane and methoxyflurane yielded a weakly positive bar response. These findings have potentially serious ramifications for the medical management of patients resulting from terrorist, military, or chemical agent decommissioning activity when concomitant chemical injuries are also possible.

A fatality related to the veterinary anesthetic telazol

A 45-year-old male veterinarian was found dead in bed. Police investigation showed no evidence of trauma or other suspicious circumstances. Autopsy was unremarkable except for cardiomegaly and hepatosplenomegaly. Toxicological analysis revealed the presence of Telazol and ketamine. Telazol is a veterinary anesthetic agent that is composed of equal parts of tiletamine and zolazepam. Tiletamine is a disassociative anesthetic similar to ketamine and phencyclidine, and zolazepam is a diazepine derivative tranquilizer used to minimize the muscle hypertonicity and seizures associated with tiletamine. Quantitation of tiletamine and zolazepam was performed using gas chromatography-mass spectrometry in the selected ion monitoring mode following a solid-phase extraction. Postmortem blood, urine, and liver concentrations of tiletamine were 295 ng/mL, 682 ng/mL, and 196 ng/g, respectively, whereas postmortem concentrations of zolazepam for the same tissues were 1.71 microg/mL, 1.33 microg/mL, and 15.5 microg/g, respectively. Blood and urine ketamine levels were 37 ng/mL and 381 ng/mL, respectively. The cause of death was ruled an acute mixed drug intoxication of tiletamine, zolazepam, and ketamine with the manner of death ruled as unclassified.

Determination of embutramide and pentobarbital in meat and bone meal by gas chromatography-mass spectrometry

An analytical procedure, consisting of multiple steps, was developed for the analysis of meat and bone meal for two veterinary drugs, embutramide and pentobarbital, used for euthanasia. After a combined extraction, embutramide was converted to its trimethylsilylether derivative and pentobarbital was methylated. Both analytes were determined by gas chromatography-mass spectrometry in the electron impact or chemical ionisation mode. Limits of determination and identification were between 50 and 100 micrograms kg-1 depending on the compound and the ionisation technique applied. Particular attention was focused on the identification of the analytes.

Exposure of postoperative nurses to exhaled anesthetic gases

The National Institute of Occupational Safety and Health (NIOSH) has established recommended exposure limits of 25 parts per million (ppm) as a time-weighted average for nitrous oxide and a ceiling of 2 ppm for volatile anesthetics. We quantified exposure of postanesthetic nurses to exhaled anesthetic gases. This study was conducted in the postanesthesia care unit (PACU) of a medium-sized hospital. PACU air exchanges averaged 8 vol/h; however, much of this air was recirculated. We evaluated 50 adults anesthetized with either isoflurane (n = 19) or desflurane (n = 31). Roughly half the patients were tracheally extubated in the operating room, whereas the others were extubated just after admission to the PACU. Exhaled anesthetic gases were sampled through a 20-m hose attached to the participating nurses' shoulders (breathing zone). We also evaluated nursing exposure to exhaled anesthetic gases during recovery of 15 patients who had been anesthetized with nitrous oxide. Exposure was quantified with lapel dosimeters. Anesthetic and recovery durations were each approximately 1 h, with most patients being tracheally extubated in the PACU. Breathing-zone anesthetic concentrations in the patients given isoflurane exceeded NIOSH recommendations in 37% of the patients, representing 12% of recovery time. Breathing-zone anesthetic concentrations in the patients given desflurane, however, exceeded NIOSH limits in 87% of the patients, representing 49% of recovery time. Altogether, noncompliant episodes were detected in 68% of these patients, representing 35% of the entire recovery duration. Breathing-zone anesthetic concentrations in the patients given nitrous oxide exceeded NIOSH limits in 53% of the patients. Our data suggest that postoperative nurses' exposure to exhaled anesthetic gases exceeds NIOSH limits under some circumstances.

IMPLICATIONS

Some epidemiological evidence suggests that exposure to waste anesthetic gases may be associated with reproductive toxicity. Accordingly, the National Institute of Occupational Safety and Health has established recommended exposure limits for nitrous oxide and volatile anesthetics. Our data suggest that exposure of healthcare personnel may exceed recommended levels in poorly ventilated postanesthesia care units.

Electrochemical analysis of clinical blood-gases, gases and vapours

This tutorial review charts the development of electrochemical sensors for the analysis of blood-gases, gases and vapours in clinical medicine over the past four decades. The development of each sensor is set in its historical and clinical context, and the first part of the review concentrates on aqueous electrolyte electrochemistry and on those sensors which have made a major impact on the clinical measurement of the partial pressures of oxygen and carbon dioxide in the blood. The electrochemical interference effects of anaesthetic agents on these measurements are also described. Those electrochemical sensors which have failed, in the past, to make a clear impact in this area are not considered, but the few attempts to devise aqueous electrolyte electrochemical sensors for anaesthetic agent measurement are reviewed. The second part of the review describes the chequered history of the development of non-aqueous solvent electrochemical sensors to measure the partial pressures of oxygen and carbon dioxide, in both the presence and absence of each other, in the gas phase. The last part of the review examines various attempts, using non-aqueous solvent electrochemistry, to measure the concentration of inhalational anaesthetic vapours in the gas phase. These sensors have yet to make an impact on clinical practice. Throughout this tutorial review, theoretical models of membrane-covered electrochemical sensors are described where appropriate. This review represents a personal view of the development of electrochemical sensors for clinical measurement, and it is therefore necessarily selective in its approach and emphasis.

The use of high-resolution solid-state NMR spectroscopy and differential scanning calorimetry to study interactions of anaesthetic steroids with membrane

We have used a combination of high-resolution solid-state 13C-NMR and DSC (differential scanning calorimetry) to study the distinctively different thermotropic and dynamic properties of the anaesthetic steroid alphaxalone and its inactive congener delta16-alphaxalone in dipalmitoylphosphatidylcholine (DPPC) model membranes. In the solid-state 13C-NMR, the techniques included cross polarization (CP) and/or magic angle spinning (MAS). The observed data revealed the following important results. (a) DSC as a bulk method showed that the active steroid lowers the main phase transition temperature and broadens the pretransition more significantly than the inactive congener. The 13C-CP/MAS experiments allowed us to detect the pretransition temperature in the alphaxalone-containing preparation, which was not discernible in DSC. (b) The chemical shift values varied with temperature, indicating different degrees of trans-gauche isomerization in the lipid acyl chains when the bilayer is in the liquid crystalline phase. (c) Only specific additional peaks appeared in the 13C-CP/MAS spectra when each of the steroids was present in the preparation. delta16-alphaxalone gives rise to more additional peaks than alphaxalone, indicating a different mobility of the corresponding molecular moiety in the phospholipid bilayer environment. (d) The relative intensities of these peaks also confirmed that alphaxalone is fully incorporated in the bilayer, whereas delta16-alphaxalone is only partially so. These results suggest that the differential effects of these two analogues in the membrane may, at least in part, explain the reason for their different biological activities.

Gas chromatography in anaesthesia. I. A brief review of analytical methods and gas chromatographic detector and column systems

Practical applications and relevant studies involving the anaesthetic gases, have been extensively described in the literature. Many eminent analytical methods have already been developed for medical practice where routine analysis of anaesthetics is frequently needed, particularly during anaesthesia, and in related and respiratory research programmes. The determination of halothane, isoflurane, enflurane and nitrous oxide concentrations from vaporizers, in exhaled and inhaled gas mixtures, in body fluids and tissues is necessary to control anaesthetic concentrations, and thus, the relevant and adverse effects successfully. Therefore, a literature review, with particular emphasis on gas chromatography would provide important information for investigators in the search for a suitable analytical method for the analysis of multi-component mixtures of anaesthetic gases.

A clinical evaluation of an operational postanesthesia care unit source control system

Various air safety hazards in the PACU and a number of attempts to cope with the hazards have been addressed (see J Peri Anesth Nurs 11:207, 1996). This article presents a clinical evaluation of an operational source control system developed specifically for use in the PACU. The criterion for evaluation was the degree to which the source control system could reduce the concentration of waste anesthetic gases released into the environment by the patient. The N2O molecule is a thousand times smaller than droplet nuclei that carry infectious respiratory disease. Thus, containment of waste gases may also indicate containment of pathogens. Twenty-two postsurgical patients were studied. The control group was given routine care with supplemental oxygen by nasal prong. The experimental group was given supplemental oxygen and had exhalent scavenged via the source-control system. Waste gas concentrations were monitored, and a criterion was applied to the data to determine the effectiveness of the source control group when compared to nasal prong group. The nasal prong group exceeded the compliance criterion 58% of the time. The source control group exceeded the compliance criterion at no time during the study. From these results, the source control system is effective at reducing concentrations of waste anesthetic gases allowed into the atmosphere of a room. Application of the source control to the PACU environment could prove valuable in addressing air safety hazards.

[The temperature-humidity profile of the PhysioFlex. Studies on a model]

Closed-system anaesthesia provides the best prerequisites for optimal warming and humidification of anaesthetic gases. The PhysioFlex anaesthesia machine fascilitates quantitative closed-system anaesthesia. Furthermore, its design may improve the climatization of the anaesthetic gases by revolving the system volume at 70 l/min, using a small soda-lime canister to allow optimal usage of the heat and moisture generated by CO2 absorption and by integrating all system components in thermally isolating housing. To determine the capacity of the PhysioFlex to climatize anaesthetic gases, we evaluated the heat and humidity profile at four characteristic places in the anaesthetic circuit under standardised conditions in a model.

MATERIALS AND METHODS

In an air-conditioned room at 19-20 degrees C ambient temperature, the PhysioFlex was operated with a fresh gas flow of less than 500 ml/min, similar to quantitative closed-system anaesthesia in adults. With a respiratory rate of 10/min and a tidal volume of 600 ml, a humidifier was ventilated, that delivered humidity-saturated gas at 33-34 degrees C; 200 ml/min CO2 were added to the system at the humidifier to mimic the heat, moisture, and CO2 input of a patient into the anaesthetic circuit. A total of six series were performed, each starting with a cold and dry anaesthetic circuit. For 2 h the time-courses of temperature and humidity of the anaesthetic gases were measured at four distinct places: (1) in the soda-lime canister (M1); (2) at the outlet of the anaesthesia machine (M2); (3) at the inlet of the anaesthesia machine (M3); and (4) in the inspiratory limb close to the Y-piece (M4). Capacitive humidity sensors (VAISALA Type HMM 30 D without a protective cap) and very small thermocouples were used to measure relative humidity (rH) and temperature. The data were recorded at 5 min intervals. Due to the continuous gas stream in the system, the response time of the sensors, which is in the range of a few seconds, did not affect the accuracy of the measurement. With the temperature-dependent humidity content of 100% rH obtained from equation 1, absolute humidity was calculated.

RESULTS

The time courses of temperature and humidity at the different measuring points are depicted in Figs. 2 and 3, respectively. The steepest increase in temperature and humidity was observed at M1. Within 10 min 100% rH was achieved at all measuring points. Initially, there was a considerable temperature gradient between M1 and M2; this became gradually smaller, indicating system components with high heat capacities. There was only a small gradient between M2 and M4, indicating that there was only a small heat loss compared to the heat input. The recommended minimal climatization of the anaesthetic gases of 20 mg H2O/l [20] was obtained within 10 min at M4. During the whole measuring period heat and humidity increased in the system, reaching a maximum at M4 after 120 min with average values of more than 28 degrees C and 27 mg H2O/l, respectively.

CONCLUSION

With the PhysioFlex anaesthesia machine employing closed-system conditions, minimal climatization of anaesthetic gases was reached within 10 min. After a period of 120 min, the anaesthetic gases were nearly climatized to the extent recommended for long-term respiratory therapy. To date, no comparable temperature and humidity level has been reported with conventional anaesthesia machines. The time course of the gradient between M1 and M2 may give an opportunity for further optimising the system in reducing heat loss after the soda-lime canister, the active heat and moisture source in the circuit. At about 32 degrees C, the temperature in the soda-lime canister is 10-15 degrees C less than in conventional anaesthesia machines. Thus, the use of thermally instable volatile anaesthetics in the PhysioFlex under closed-system conditions may be less critical than in conventional anaesthesia machines under minimal-flow conditions.

Source-control strategies and efficacy

We have presented a source-control technology that addresses all three areas of concern. Using waste anesthesia gases as a marker for the efficacy with which the source-control system could control the dissemination of respiratory and bloodborne pathogens, the system reduced exposure to virtually undetectable levels. We thus conclude that source-control is a cost-effective method of markedly reducing the risk of infectious disease transmission in the perioperative setting for both patients and personnel.

Interference of volatile anaesthetics with infrared analysis of carbon dioxide and nitrous oxide tested in the Dräger Cicero EM using sevoflurane

In theory, setting an infrared multi-gas analyser to measure a volatile anaesthetic different from that in the sampled gas mixture may cause interference with carbon dioxide and nitrous oxide readings. The theory was investigated during evaluation of the Dräger Cicero EM anaesthetic workstation for the Medical Devices Agency. Interference occurred as predicted, and was most pronounced when the vapour analyser of the Cicero EM was deliberately and erroneously set to measure isoflurane, but with sevoflurane present in the gas mixture. With 6% sevoflurane in the gas mixture, the carbon dioxide reading decreased from 5% to 3.6%, and the nitrous oxide reading increased from 0% to 8% although, as the apparent isoflurane reading was 9%, the Cicero EM would alert the operator to the problem. However, operators are encouraged to ensure that, when using gas analysers such as that incorporated into the Cicero EM, the analyser is set to measure the correct volatile anaesthetic (the Cicero EM does this automatically when a Vapor vaporizer is attached) and the breathing system does not contain any other volatile anaesthetic agents.

[Measurement of expired alcohol concentrations with a new electrochemical sensor. A model investigation to determine interference with volatile anesthetics and clinical application]

Absorption of irrigating fluid in transurethral prostatic resection (TURP) and percutaneous nephrolitholapaxy (PNL) into veins or delayed absorption due to fluid extravasation may result in a TURP syndrome. The measurement of end-tidal breath alcohol concentration (et AC) as a monitor of absorption of irrigating fluid labelled with 2% ethanol is limited by the disturbance of infrared sensors by volatile anaesthetics and nitrous oxide (N2O) (Fig. 2). An electrochemical sensor is acceptable for this method. The aim of the present study was the evaluation of breath alcohol measurements using an electrochemical sensor device (Alcomed 3010, Envitec). The stability of the sensor in the presence of volatile anaesthetics was examined using a lung model. In a clinical investigation, the device was then applied to spontaneously breathing or mechanically ventilated patients inhaling volatile anaesthetics during endoscopic urological surgery.

METHOD

A two-chamber lung model filled with water for performing noninvasive measurements at the mouth of a patient has already been introduced by Brunner et al. (Fig. 1). With the addition of different amounts of ethanol to the temperature-controlled water, a constant ethanol concentration is achievable in the air above the water that is dependent on adjustments of the ventilator. Increasing concentrations of volatile anaesthetics (isoflurane, enflurane, halothane, and sevoflurane) were added to the fresh gas flow (2 l O2/3 l N2O) and etACs were measured using the manually triggered self-absorbent electrochemical sensor. First, regression equations were established between breath alcohol concentrations and increased volatile anaesthetic concentrations. Regression equations were then established between end-tidal anaesthetic gas concentrations and vaporizer adjustments in order to rule out an influence of ethanol on the anaesthetic gas monitor Ultima V (Datex). In the clinical investigation, 53 intubated and ventilated patients (33 undergoing PNL, 20 undergoing TURP) and 48 patients breathing spontaneously (32 with inhalation anaesthesia, 16 with spinal anaesthesia) were investigated. The etAC was measured with the Alcomed 3010 and compared with gas-chromatographically registered blood alcohol concentrations (BAC). The study had previously been approved by the Ethical Committee of the Medical University of Luebeck. Patients with liver disease and a history of toxic abuse were excluded. Only one value per patient (maximum BAC) was included in the statistics in order to avoid a cluster effect.

RESULTS

The lung model experiments demonstrated that the measurement of etAC with an electrochemical sensor is free of interference by volatile anaesthetics (Table 1). The slope of the regression between the measured alcohol concentration and increased concentrations of anaesthetics did not differ significantly from baseline values. The measurement of end-tidal anaesthetic concentrations was not significantly different from vaporizer adjustments in the presence of increased alcohol concentrations (Table 2). During the clinical investigation, a regression between etAC and BAC was determined for both groups. For the group of patients breathing spontaneously, the correlation coefficient was 0.961 and the regression equation revealed etAC = 0.5677*BAC-0.1303 (Fig. 5). However, in the group of ventilated patients a biphasic course was shown that was dependent on BAC (Fig. 6). At BAC < 0.4%, a similar correlation (r = 0.856) to the spontaneously breathing group could be seen (regression equation: etAC = 0.617*BAC-0.020). Above 0.4% BAC there was no acceptable correlation (r = 0.444, regression equation: etAC = 0.202*BAC+0.104).

CONCLUSIONS

The tested electrochemical sensor does not interfere with volatile anaesthetics and N2O as demonstrated by a lung model. There is a good correlation between etAC and BAC measurements in patients breathing spontaneously with special regard to the slope of the regression (s = 0.57).

[Exposure to anesthetic gases]

In recent years there has been a growing awareness of possible hazards caused by anaesthetic gases in operating theatres. Our study monitored ambient nitrous oxide (N2O) levels in the operating theatres and recovery rooms at the University Hospital in Tromsø. The results show that exposure to waste anaesthetic gases occurs because of leaks in the anaesthetic equipment. The three major sources of leaks are masks, high pressure fittings and exhalation valves. Prevention of leakage from equipment is very important, and a leakage testing programme should be an essential part of the daily control strategy. Good working practices and tracheal intubation results in low exposure to nitrous oxide in the breathing zone of the anesthetic personnel. During mask anaesthesia we have observed nitrous oxide concentrations above 1500 ppm, owing to mask leakage. A closely fitting scavenging mask and good working practices lead to in lower nitrous oxide concentrations. Nitrous oxide exhalation from the patient in the recovery room is only a minor problem.

The use of a portable refractometer to measure desflurane

The measurement of volatile anaesthetic agents by infrared absorption is liable to interference by other gases which absorb infrared light. In particular, nitrous oxide may, in principle, interfere with the measurement of desflurane. On the other hand, the refractometer should be immune to such effects. We demonstrated that interactions may occur between desflurane and nitrous oxide with some gas analysers and that the refractometer remains a useful instrument.

Analysis of sevoflurane degradation products in vapor phase samples

Sevoflurane degradation products were measured by GC-flame ionization detection in vapor phase samples using manual and automated injection methods. Sample handling techniques allowed the transfer and storage of samples for up to 72 h. Compound A, fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether, was the major vapor phase degradation product formed in simulated clinical conditions. Recoveries of 4-32 ppm (v/v) compound A concentrations using the manual method were in the range of 88-117% (n = 12, mean = 102%, R.S.D. = 9%).

Erroneous mass spectrometer readings caused by desflurane and sevoflurane

OBJECTIVE

Medical mass spectrometers are configured to detect and measure specific respiratory and anesthetic gases. Unrecognized gases entering these systems may cause erroneous readings. We determined how the Advantage 1100 (Perkin-Elmer, now Marquette Gas Systems, Milwaukee, WI) and PPG-SARA (PPG Biomedical Systems, Lenexa, KS) systems that were not configured to measure desflurane or sevoflurane respond to increasing concentrations of these new potent volatile anesthetic agents.

METHODS

Desflurane 0% to 18% in 3% increments or sevoflurane 0% to 7% in 1% increments in 5-L/min oxygen was delivered to the Advantage and PPG-SARA mass spectrometry systems. For each concentration of each agent, the displayed gas analysis readings and uncompensated collector plate voltages were recorded.

RESULTS

The Advantage 1100 system read both desflurane and sevoflurane mainly as enflurane and, to a lesser extent, as carbon dioxide and isoflurane. For enflurane(E) readings < 9.9%, the approximate relationships are: %Desflurane = 1.6E; %Sevoflurane = 0.3E. These formulas do not apply if E > 9.9% because of saturation of the summation bus. PPG-SARA read desflurane mainly as isoflurane(I) and, to a lesser extent, as nitrous oxide. PPG-SARA read sevoflurane mainly as enflurane(E) and, to a lesser extent, as nitrous oxide and halothane. The approximate relationships are: %Desflurane = 1.11 (for I < 9%); %Sevoflurane = 2.1E.

CONCLUSIONS

Advantage 1100 and PPG-SARA systems not configured for desflurane or sevoflurane display erroneous anesthetic agent readings when these new agents are sampled. Advantage 1100 also displays falsely elevated carbon dioxide readings when desflurane is sampled.

Refractive indices for volatile anesthetic gases: equipment and method for calibrating vaporizers and monitors

OBJECTIVE

The objective of our study was to establish the refractive indices and the virial coefficients of the volatile anesthetic vapors. These indices and coefficients will allow refractometry to be used by manufacturers to produce accurate calibration, without requiring expensive high-precision calibration gases.

METHODS

We used a precision refractometer to measure the refractive indices for five volatile anesthetic vapors. We prepared our calibration gases by mixing a gravimetrically calibrated amount of liquid agent with a constant gas flow.

RESULTS

The refractive indices for the volatile anesthetic vapors are 1,603.2 for halothane, 1,540.4 for enflurane, 1,563.3 for isoflurane, 1,538.3 for sevoflurane, and 1,211.7 for desflurane. The maximum theoretical error in our measurements, due to all sensors and all uncertainty in our measurement of apparatus and physical constants, is +/- 0.56% of the reading (+/- 0.70% for desflurane).

CONCLUSIONS

If refractometry replaced calibration gases in cylinders, as a calibration standard, manufacturers might avoid errors that now occur because calibration gases manufactured by numerous companies seem to differ. We propose that our values serve as an interim database.

Determination of embutramide in biological matrices by gas chromatography with nitrogen-phosphorus detection

Embutramide is a general anesthetic having a strong narcotic effect on the central nervous system where it paralyzes the brain center that controls respiration. It is a constituent of T61, a veterinary euthanasia drug. This paper describes a gas chromatographic procedure using nitrogen-phosphorus detection for the determination of embutramide in biological matrices. The drug and the internal standard (ambucetamide) are extracted with dichloromethane under alkaline conditions. The method is linear from 100 to 3000 ng/ml. The within-day and day-to-day coefficients of variation range from 5.1 to 5.7% and from 9.1 to 10.0%, respectively. The recovery is above 80% while the minimum detectable level under the conditions described is 40 ng/ml analyzing a 1-ml or a 1-g aliquot of a sample (blood or tissue). The method is also applied to different samples from dogs euthanized with T61.

Effects of end-tidal gas monitoring and flow rates on hemodynamic stability and recovery profiles

This study was designed to evaluate the impact of routine end-tidal anesthetic gas monitoring on the intraoperative hemodynamic stability and early recovery profile in 253 consenting ASA physical status I-III patients undergoing elective otolaryngologic procedures with isoflurane or enflurane anesthesia. Patients were randomly assigned to one of six treatment groups: Group I, monitored high-flow isoflurane; Group II, unmonitored high-flow isoflurane; Group III, monitored low-flow isoflurane; Group IV, unmonitored low-flow isoflurane; Group V, monitored low-flow enflurane; or Group VI, unmonitored low-flow enflurane. After a standardized induction sequence, anesthesia was maintained by administering variable concentrations of isoflurane or enflurane in an air/oxygen mixture at two different total gas flow rates (0.7 L/min or 3.5 L/min, respectively). Mean arterial pressure (MAP), heart rate (HR), and end-tidal (ET) anesthetic concentrations were recorded by a computer throughout the operation. The resident anesthesiologist was instructed to maintain an adequate "depth of anesthesia" by varying the administration of isoflurane (Groups I-IV) or enflurane (Groups V and VI) with or without end-tidal gas monitoring. Intraoperative hemodynamic stability was assessed in each patient and reported as the average error from the preincisional (baseline) MAP, average absolute error from the baseline MAP, coefficients of variation for HR, systolic, diastolic, and MAP values, and ET anesthetic concentrations. Recovery times from discontinuation of the volatile drug until awakening, following commands, and postanesthesia care unit (PACU) discharge were recorded. The six study groups had similar intraoperative MAP and HR values, coefficients of variation, and numbers of episodes of hypertension, hypotension, tachycardia, and bradycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pollution of operating room air by anesthetic gases in relation to the air conditioning method and anesthesia techniques]

Volatile anesthetics are suspected to cause various health risks even in subnarcotic concentrations (hepatotoxicity, mutagenicity, teratogenicity). Yet only for halothane a limit (MAK-value = 5 ppm) has been established for the entire FRG. In addition, in 1991 Hamburg and Schleswig-Holstein defined preliminary limits for isoflurane, enflurane and nitrous oxide. We analysed the pollution of operating-room air by narcotic gases in 20 hospitals of Niedersachsen. In several cases limits have been exceeded evidently. Reasons for high concentrations were: insufficient room ventilation, defective air-conditioning plants, technical defects (leakage) and high gas emission due to special techniques in anesthesia (bronchoscopy). In order to take care of personnel-health air concentration of anesthetic gases should be kept as low as possible by the help of sufficient room ventilation avoiding unnecessary emissions.