Fate and Toxicity of 2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (Compound A)-derived Mercapturates in Male, Fischer 344 Rats

Background: 2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1 propene (compound A) is formed in the anesthesia circuit by the degradation of sevoflurane. Compound A is nephrotoxic in rats and undergoes metabolism by the mercapturic acid pathway in rats and humans to yield the mercapturates S-[2-(fluoromethoxy) -1,1,3,3,3-pentafluoropropyl]-N-acetyl-L-cysteine (compound 3) and S-[2-(fluoromethoxy)-1,1,3,3,3-tetrafluoro-1-propenyl] -N-acetyl-L-cysteine (compound 5). These experiments were designed to examine the fate and nephrotoxity of compound A-derived mercapturates in rats.

Methods: The deacetylation of compounds 3 and 5 by human and rat kidney cytosol and with purified acylases I and III was measured, and their nephrotoxicity was studied in make Fischer 344 rats. The metabolism of the deuterated analogs of compounds 3 and 5, [acetyl-(2) H3]S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-N-acetyl-L-cysteine (compound 3-d3) and [acetyl-2 H3]S[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-profenyl]-N-acetyl-cysteine (compound 5-d3), respectively, was measured.

Results: Compounds 5, but not compound 3, was hydrolyzed by human and rat kidney cytosols and by acylases I and III.19 F nuclear magnetic resonance spectroscopic analysis showed no urinary metabolites of compound 3, but unchanged compound 5 and its metabolites 2-(fluoromethoxy)-3,3,3-trifluoropropanoic acid and 2-[1-(fluoromethoxy)-2,2,2-trifluoroethyl]-4,5-dihydro-1,3- thiazole-4-carboxylic acid were detected in urine. Compounds 5 (250 [micro sign]M/kg) produced clinical chemical and morphologic evidence of renal injury in two of three animals studied.     

Cysteine Conjugate beta-Lyase-dependent Biotransformation of the Cysteine S-Conjugates of the Sevoflurane Degradation Product Compound A in Human, Nonhuman Primate, and Rat Kidney Cytosol and Mitochondria

Background: 2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A) is a fluorinated alkene formed by the degradation of sevoflurane in the anesthesia circuit. Compound A is toxic to the kidneys in rats and undergoes glutathione-dependent metabolism in vivo. Several nephrotoxic halogenated alkenes also undergo cysteine conjugate beta-lyase-dependent biotransformation. These experiments were designed to test the hypothesis that cysteine S-conjugates of compound A undergo beta-lyase-dependent biotransformation.

Methods: S-[2-(Fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-L-cysteine 4, S-[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-L-cysteine 5, and S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine 11 were incubated with rat, human, and nonhuman primate (cynomolgus, rhesus, and marmoset) kidney cytosol and mitochondria. Beta-Lyase activity was determined by measuring pyruvate formation.

Results: Compound A-derived conjugates 4 and 5 as well as conjugate 11, a positive control, were substrates for cytosolic and mitochondrial beta-lyase from human, nonhuman primate, and rat kidney. For all substrates, beta-lyase activity was highest in the rat and lowest in the human and was higher in cytosol than in mitochondria. Conjugate 11 was a much better substrate than conjugates 4 or 5. The biotransformation of conjugates 4, 5, and 11 was inhibited by the beta-lyase inhibitor (aminooxy)acetic acid and was stimulated by the amino group acceptor 2-keto-4-methylthiolbutyric acid, indicating a role for beta-lyase.     

Compound A Uptake and Metabolism to Mercapturic Acids and 3,3,3-Trifluoro-2-fluoromethoxypropanoic Acid during Low-flow Sevoflurane Anesthesia: Biomarkers for Exposure, Risk Assessment, and Interspecies Comparison

Background: Sevoflurane is degraded during low-flow anesthesia to fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether ("compound A"), which causes renal necrosis in rats but is not known to cause nephrotoxicity in surgical patients. Compound A is metabolized to glutathione S-conjugates and then to cysteine S-conjugates, which are N-acetylated to mercapturic acids (detoxication pathway), or metabolized by renal [beta]-lyase to reactive intermediates (toxification pathway) and excreted as 3,3,3-trifluoro-2-fluoromethoxypropanoic acid. This investigation quantified compound A metabolites in urine after low-flow sevoflurane administration, to assess relative flux via these two pathways.

Methods: Patients (n = 21) with normal renal function underwent low-flow (1 l/min) sevoflurane anesthesia designed to maximize compound A formation. Inspiratory, expiratory, and alveolar compound A concentrations were quantified. Urine mercapturic acids and 3,3,3-trifluoro-2-fluoromethoxypropanoic acid concentrations were measured by gas chromatography and mass spectrometry.

Results: Sevoflurane exposure was 3.7 +/- 2.0 MAC-h. Inspired compound A maximum was 29 +/- 14 ppm; area under the inspired concentration versus time curve (AUCinsp) was 78 +/- 58 ppm [middle dot] h. Compound A dose, calculated from pulmonary uptake, was 0.39 +/- 0.35 mmol (4.8 +/- 4.0 [mu]mol/kg) and correlated with AUCinsp (r2 = 0.84, P < 0.001). Mercapturic acids excretion was complete after 2 days, whereas 3,3,3-trifluoro-2-fluoromethoxypropanoic acid excretion continued for 3 days in some patients. Total (3-day) mercapturates and fluoromethoxypropanoic acid excretion was 95 +/- 49 and 294 +/- 416 [mu]mol, respectively (1.2 +/- 0.6 and 3.6 +/- 5.0 [mu]mol/kg).     

Compound A uptake and metabolism to mercapturic acids and 3,3,3-trifluoro-2-fluoromethoxypropanoic acid during low-flow sevoflurane anesthesia: biomarkers for exposure, risk assessment, and interspecies comparison.

BACKGROUND: Sevoflurane is degraded during low-flow anesthesia to fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether ("compound A"), which causes renal necrosis in rats but is not known to cause nephrotoxicity in surgical patients. Compound A is metabolized to glutathione S-conjugates and then to cysteine S-conjugates, which are N-acetylated to mercapturic acids (detoxication pathway), or metabolized by renal beta-lyase to reactive intermediates (toxification pathway) and excreted as 3,3,3-trifluoro-2-fluoromethoxypropanoic acid. This investigation quantified compound A metabolites in urine after low-flow sevoflurane administration, to assess relative flux via these two pathways. METHODS: Patients (n = 21) with normal renal function underwent low-flow (11 min) sevoflurane anesthesia designed to maximize compound A formation. Inspiratory, expiratory, and alveolar compound A concentrations were quantified. Urine mercapturic acids and 3,3,3-trifluoro-2-fluoromethoxypropanoic acid concentrations were measured by gas chromatography and mass spectrometry. RESULTS: Sevoflurane exposure was 3.7 +/- 2.0 MAC-h. Inspired compound A maximum was 29 +/- 14 ppm; area under the inspired concentration versus time curve (AUCinsp) was 78 +/- 58 ppm x h. Compound A dose, calculated from pulmonary uptake, was 0.39 +/- 0.35 mmol (4.8 +/- 4.0 micromol/kg) and correlated with AUCinsp (r2 = 0.84, P < 0.001). Mercapturic acids excretion was complete after 2 days, whereas 3,3,3-trifluoro-2-fluoromethoxypropanoic acid excretion continued for 3 days in some patients. Total (3-day) mercapturates and fluoromethoxypropanoic acid excretion was 95 +/- 49 and 294 +/- 416 micromol, respectively (1.2 +/- 0.6 and 3.6 +/- 5.0 micromol/kg). CONCLUSION: Compound A doses during 3.7 MAC-h, low-flow sevoflurane administration in humans are substantially less than the threshold for renal toxicity in rats (200 micromol/kg). Compound A metabolites quantification may provide a biomarker for compound A exposure and relative metabolism via toxification and detoxication pathways. Compared with previous investigations, relative metabolic flux (fluoromethoxypropanoic acid/mercapturates) through the toxification pathway was sixfold greater in rats than in humans. Species differences in dose and metabolism may influence compound A renal effects.     

Role of the Renal Cysteine Conjugate [Greek small letter beta]-Lyase Pathway in Inhaled Compound A Nephrotoxicity in Rats

Background: The sevoflurane degradation product compound A is nephrotoxic in rats and undergoes metabolism to glutathione and cysteine S-conjugates, with further metabolism by renal cysteine conjugate [Greek small letter beta]-lyase to reactive intermediates. Evidence suggests that toxicity is mediated by renal up-take of compound A S-conjugates and metabolism by [Greek small letter beta]-lyase. Previously, inhibitors of the [Greek small letter beta]-lyase pathway (aminooxyacetic acid and probenecid) diminished the nephrotoxicity of intraperitoneal compound A. This investigation determined inhibitor effects on the toxicity of inhaled compound A.

Methods: Fischer 344 rats underwent 3 h of nose-only exposure to compound A (0 - 220 ppm in initial dose - response experiments and 100 - 109 ppm in subsequent inhibitor experiments). The inhibitors (and targets) were probenecid (renal organic anion transport mediating S-conjugate uptake), acivicin ([Greek small letter gamma]-glutamyl transferase), aminooxyacetic acid (renal [Greek small letter beta]-lyase), and aminobenzotriazole (cytochrome P450). Urine was collected for 24 h, and the animals were killed. Nephrotoxicity was assessed by histology and biochemical markers (serum BUN and creatinine; urine volume; and excretion of protein, glucose, and [Greek small letter alpha]-glutathione-S-transferase, a predominantly proximal tubular cell protein).

Results: Compound A caused dose-related proximal tubular cell necrosis, diuresis, proteinuria, glucosuria, and increased [Greek small letter alpha]-glutathione-S-transferase excretion. The threshold for toxicity was 98 - 109 ppm (294 - 327 ppm-h). Probenecid diminished (P < 0.05) compound A-induced glucosuria and excretion of [Greek small letter alpha]-glutathione-S-transferase and completely prevented necrosis. Aminooxyacetic acid diminished compound A - dependent proteinuria and glucosuria but did not decrease necrosis. Acivicin increased nephrotoxicity of compound A, and aminobenzotriazole had no consistent effect on nephrotoxicity of compound A.     

Influence of Sevoflurane on the Metabolism and Renal Effects of Compound A in Rats

Background: The sevoflurane degradation product compound A is nephrotoxic in rats. In contrast, patient exposure to compound A during sevoflurane anesthesia has no clinically significant renal effects. The mechanism for this difference is incompletely understood. One possibility is that the metabolism and toxicity of compound A in humans is prevented by sevoflurane. However, the effect of sevoflurane on compound A metabolism and nephrotoxicity is unknown. Thus, the purpose of this investigation was to determine the effect of sevoflurane on the metabolism and renal toxicity of compound A in rats.

Methods: Male rats received 0.25 mmol/kg intraperitoneal compound A, alone and during sevoflurane anesthesia (3%, 1.3 minimum alveolar concentration, for 3 h). Compound A metabolites in urine were quantified, and renal function was evaluated by serum creatinine and urea nitrogen, urine volume, osmolality, protein excretion, and renal tubular histology.

Results: Sevoflurane coadministration with compound A inhibited compound A defluorination while increasing relative metabolism through pathways of sulfoxidation and [beta]-lyase-catalyzed metabolism, which mediate toxicity. Sevoflurane coadministration with compound A increased some (serum creatinine and urea nitrogen, and necrosis) but not other (urine volume, osmolality, and protein excretion) indices of renal toxicity.     

Role of Renal Cysteine Conjugate beta-Lyase in the Mechanism of Compound A Nephrotoxicity in Rats

Background: The sevoflurane degradation product compound A is nephrotoxic in rats, in which it undergoes extensive metabolism to glutathione and cysteine S-conjugates. The mechanism of compound A nephrotoxicity in rats is unknown. Compound A nephrotoxicity has not been observed in humans. The authors tested the hypothesis that renal uptake of compound A S-conjugates and metabolism by renal cysteine conjugate beta-lyase mediate compound A nephrotoxicity in rats.

Methods: Compound A (0-0.3 mmol/kg in initial dose-response experiments and 0.2 mmol/kg in subsequent inhibitor experiments) was administered to Fischer 344 rats by intraperitoneal injection. Inhibitor experiments consisted of three groups: inhibitor (control), compound A, or inhibitor plus compound A. The inhibitors were probenecid (0.5 mmol/kg, repeated 10 h later), an inhibitor of renal organic anion transport and S-conjugate uptake; acivicin (10 mg/kg and 5 mg/kg 10 h later), an inhibitor of gamma-glutamyl transferase, an enzyme that cleaves glutathione conjugates to cysteine conjugates; and aminooxyacetic acid (0.5 mmol/kg and 0.25 mmol/kg 10 h later), an inhibitor of renal cysteine conjugate beta-lyase. Urine was collected for 24 h and then the animals were killed. Nephrotoxicity was assessed by light microscopic examination and biochemical markers (serum urea nitrogen and creatinine concentration, urine volume and urine excretion of protein, glucose, and alpha-glutathione-S-transferase [alpha GST], a marker of tubular necrosis).

Results: Compound A caused dose-related nephrotoxicity, as shown by selective proximal tubular cell necrosis at the corticomedullary junction, diuresis, proteinuria, glucosuria, and increased alpha GST excretion. Probenecid pretreatment significantly (P < 0.05) diminished compound A-induced increases (mean +/- SE) in urine excretion of protein (45.5 +/- 3.8 mg/24 h vs. 25.9 +/- 1.7 mg/24 h), glucose (28.8 +/- 6.2 mg/24 h vs. 10.9 +/- 3.2 mg/24 h), and alpha GST (6.3 +/- 0.8 micro gram/24 h vs. 1.0 +/- 0.2 micro gram/24 h) and completely prevented proximal tubular cell necrosis. Aminooxyacetic acid pretreatment significantly diminished compound A-induced increases in urine volume (19.7 +/- 3.5 ml/24 h vs. 9.8 +/- 0.8 ml/24 h), protein excretion (37.2 +/- 2.7 mg/24 h vs. 22.2 +/- 1.8 mg/24 h), and alpha GST excretion (5.8 +/- 1.5 vs. 2.3 micro gram/24 h +/- 0.8 micro gram/24 h) but did not significantly alter the histologic pattern of injury. In contrast, acivicin pretreatment increased the compound A-induced histologic and biochemical markers of injury. Compound A-related increases in urine fluoride excretion, reflecting compound A metabolism, were not substantially altered by any of the inhibitor treatments.     

Compound A Concentrations during Sevoflurane Anesthesia in Children

Background: Sevoflurane is a new inhalation agent that should be useful for pediatric anesthesia. Sevoflurane undergoes degradation in the presence of carbon dioxide absorbents; however, quantification of the major degradation product (compound A) has not been evaluated during pediatric anesthesia. This study evaluates sevoflurane degradation compound concentrations during sevoflurane anesthesia using a 2-1 fresh gas flow and a circle system with carbon dioxide absorber in children with normal renal and hepatic function.

Methods: The concentrations of compound A were evaluated during sevoflurane anesthesia in children using fresh soda lime as the carbon dioxide absorbent. Nineteen patients aged 3 months-7 yr were anesthetized with sevoflurane (2.8% mean end-tidal concentration) using a total fresh gas flow of 2 l in a circle absorption system. Inspiratory and expiratory limb circuit gas samples were obtained at hourly intervals, and the samples were analyzed using a gas chromatography-flame ionization detection technique. Carbon dioxide absorbent temperatures were measured in the soda lime during anesthesia. Blood samples were obtained before and after anesthesia for hepatic and renal function studies. Venous blood samples were obtained before anesthesia, at the end of anesthesia, and 2 h after anesthesia for plasma inorganic fluoride ion concentration.

Results: The maximum inspiratory concentration of compound A was 5.4 +/-4.4 ppm (mean+/-SD), and the corresponding expiratory concentration was 3.7+/-2.7 ppm (mean+/-SD). The maximum inspiratory compound A concentration in any patient was 15 ppm. Mean concentrations of compound A peaked at intubation and remained stable, declining slightly after 120 min of anesthesia. The duration of anesthesia was 240+/-139 min (mean+/-SD). Maximum soda lime temperature ranged between 23.1 degrees C and 40.9 degrees C. There was a positive correlation between maximum absorbent temperature and maximum compound A concentration (r2 = 0.58), as well as between the child's body surface area and maximum compound A concentration (r2 = 0.59). Peak plasma inorganic fluoride ion concentration was 21.5 +/-6.1 micro mol/l. There were no clinically significant changes in hepatic or renal function studies performed 24 h postanesthesia.     

Influence of sevoflurane on the metabolism and renal effects of compound A in rats

BACKGROUND: The sevoflurane degradation product compound A is nephrotoxic in rats. In contrast, patient exposure to compound A during sevoflurane anesthesia has no clinically significant renal effects. The mechanism for this difference is incompletely understood. One possibility is that the metabolism and toxicity of compound A in humans is prevented by sevoflurane. However, the effect of sevoflurane on compound A metabolism and nephrotoxicity is unknown. Thus, the purpose of this investigation was to determine the effect of sevoflurane on the metabolism and renal toxicity of compound A in rats. METHODS: Male rats received 0.25 mmol/kg intraperitoneal compound A, alone and during sevoflurane anesthesia (3%, 1.3 minimum alveolar concentration, for 3 h). Compound A metabolites in urine were quantified, and renal function was evaluated by serum creatinine and urea nitrogen, urine volume, osmolality, protein excretion, and renal tubular histology. RESULTS: Sevoflurane coadministration with compound A inhibited compound A defluorination while increasing relative metabolism through pathways of sulfoxidation and beta-lyase-catalyzed metabolism, which mediate toxicity. Sevoflurane coadministration with compound A increased some (serum creatinine and urea nitrogen, and necrosis) but not other (urine volume, osmolality, and protein excretion) indices of renal toxicity. CONCLUSIONS: Sevoflurane does not suppress compound A nephrotoxicity in rats in vivo. These results do not suggest that lack of nephrotoxicity in surgical patients exposed to compound A during sevoflurane anesthesia results from an inhibitory effect of sevoflurane on compound A metabolism and toxicity. Rather, these results are consistent with differences between rats and humans in compound A exposure and inherent susceptibility to compound A nephrotoxicity.     

Absence of Biochemical Evidence for Renal and Hepatic Dysfunction after 8 Hours of 1.25 Minimum Alveolar Concentration Sevoflurane Anesthesia in Volunteers

Background: Sevoflurane is degraded by carbon dioxide absorbents to a difluorovinyl ether (compound A) that can cause renal and hepatic injury in rats. The present study applied sensitive markers of renal and hepatic function to determine the safety of prolonged (8 h), high concentration (3% end-tidal) sevoflurane anesthesia in human volunteers.

Methods: Thirteen healthy male volunteers provided informed consent to undergo 8 h of 1.25 minimum alveolar concentration sevoflurane anesthesia delivered with a fresh gas flow of 2 l/min. Glucose, protein, albumin, N-acetyl-beta-D-glucosaminidase (NAG), and alpha- and pi-glutathione-S-transferase (GST) levels were analyzed in urine collected at 24 h before and for 3 days after sevoflurane anesthesia. Daily blood samples were analyzed for creatinine, blood urea nitrogen (BUN), alanine aminotransferase, alkaline phosphatase, and bilirubin concentrations. Circuit compound A and plasma fluoride concentrations were measured.

Results: During anesthesia, average and maximum inspired compound A concentrations were 27 +/- 7 and 34 +/- 7 6 (mean +/- SD) and median mean blood pressure, esophageal temperature, and end-tidal carbon dioxide levels were 63 mmHg, 36.8 [degree sign] Celsius, and 32 mmHg, respectively. The average serum inorganic fluoride concentration 2 h after anesthesia was 66.2 +/- 14.7 micro Meter. Results of tests of hepatic function and renal function (BUN, creatinine concentration) were unchanged after anesthesia. Glucose, protein, albumin, and NAG excretion were not significantly increased after anesthesia. Urine concentrations of alpha-GST and pi-GST were increased on day 1 after anesthesia and alpha-GST was increased on day 2 after anesthesia but returned to normal afterward.     

Immunochemical Evidence against the Involvement of Cysteine Conjugate [small beta, Greek]-lyase in Compound A Nephrotoxicity in Rats

Background: Compound A, a degradation product of sevoflurane, causes renal corticomedullary necrosis in rats. Although the toxicity of this compound was originally hypothesized to result from the biotransformation of its cysteine conjugates into toxic thionoacyl halide metabolites by renal cysteine conjugate [small beta, Greek]-lyase, recent evidence suggests that alternative mechanisms may be responsible for compound A nephrotoxicity. The aim of this study was to evaluate these issues by determining whether mercapturates and glutathione conjugates of compound A could produce renal corticomedullary necrosis in rats, similar to compound A, and whether renal covalent adducts of the thionacyl halide metabolite of compound A could be detected immunochemically.

Methods: Male Wistar rats were administered, intraperitoneally, N-acetylcysteine conjugates (mercapturates) of compound A (90 or 180 [micro sign]mol/kg) or glutathione conjugates of compound A (180 [micro sign]mol/kg) with or without intraperitoneal pretreatments with aminooxyacetic acid (500 [micro sign]mol/kg) or acivicin (250 [micro sign]mol/kg). Rats were killed after 24 h, and kidney tissues were analyzed for toxicity by histologic examination or for protein adducts by immunoblotting or immunohistochemical analysis, using antisera raised against the covalently bound thionoacyl halide metabolite of compound A.

Results: Mercapturates and glutathione conjugates of compound A both produced renal corticomedullary necrosis similar to that caused by compound A. Aminooxyacetic acid, an inhibitor of renal cysteine conjugate [small beta, Greek]-lyase, did not inhibit the toxicity of the mercapturates, whereas acivicin, an inhibitor of [small gamma, Greek]-glutamyltranspeptidase, potentiated the toxicity of both classes of conjugates. No immunochemical evidence for renal protein adducts of the thionacyl halide metabolite was found in rats 24 h after the administration of the mercapturates of compound A or in the kidneys of rats, obtained from a previous study, 5 and 24 h after the administration of compound A.     

Compound A: Toxikologie und klinische Relevanz

Sevoflurane, like all currently used volatile anaesthetics, is degraded by carbon dioxide absorbents. The most significant degradant is a haloalkene known trivially as ”compound A”. Compound A is nephrotoxic in rats and, at higher doses, in nonhuman primates, causing proximal tubular necrosis. There has been much interest in the potential for compound A toxicity in humans. Inhaled compound A concentrations are greatest at low flow rates, high sevoflurane concentrations, warmer absorbent, barium hydroxide vs soda lime, and drier absorbent. Typical inspired compound A concentrations during low-flow and closed-circuit sevoflurane anaesthesia in humans are 8–24 and 20–32 ppm with soda lime and barium hydroxide lime, respectively. Renal effects of compound A production during sevoflurane anesthesia have been examined in surgical patients and volunteers, using standard (creatinine clearance, serum BUN and creatinine) and experimental (urine excretion of protein, glucose, NAG, GST, AAP) markers of renal function. Investigations to date in surgical patients show similar renal effects of low-flow sevoflurane, low-flow isoflurane or high-flow sevoflurane. There have been no case reports of compound A-associated renal injury in humans. In volunteers, one study found changes in experimental but not conventional renal markers, while other investigations show no significant changes in either standard or experimental markers. The mechanism of compound A nephrotoxicity in rats appears to involve metabolism to glutathione and cysteine conjugates, and their subsequent renal uptake and metabolism by pathways that are different in rats and humans.     

Isoflurane and whole body leucine, glucose, and fatty acid metabolism in dogs

Following 4 h of general anesthesia with halothane [1.5 minimum alveolar concentration (MAC)]-nitrous oxide (50% in oxygen), whole body protein synthesis is decreased and the rate of leucine oxidation is increased in dogs. To evaluate the effects of general anesthesia with isoflurane on whole body fuel metabolism and the effects of duration of anesthesia on these processes, eight dogs were studied, once in the conscious state (over 9 h) and again prior to and during isoflurane anesthesia (1.5 MAC) for 3.5 h (n = 8). Three additional dogs were studied in the conscious state and over 5 h of anesthesia. Changes in protein, fatty acid, and glucose metabolism were estimated using isotope dilution techniques, employing simultaneous infusions of L-[1-14C]leucine, [6-3H]glucose and [9,10-3H]palmitate. Ten minutes after the beginning of the administration of isoflurane, total leucine carbon flux, leucine oxidation, and leucine incorporation into proteins decreased (P less than 0.05), resulting in a slight decrease in the ratio of leucine oxidation to nonoxidative leucine disappearance (LOX/NOLD, P less than 0.05), an indicator of leucine catabolism. Throughout the 5 h of anesthesia, whole body protein synthesis remained decreased (P less than 0.01), whereas leucine flux and oxidation increased progressively throughout the remainder of the study, resulting in a more than 80% increase in the ratio of LOX/NOLD. After 10 min of isoflurane anesthesia, both plasma free fatty acid concentrations and palmitate turnover had decreased by more than 70% (P less than 0.001) and remained suppressed (P less than 0.001) throughout the remainder of the anesthesia, consistent with decreased lipolysis. Glucose production was increased 10 min (P less than 0.05) following induction of anesthesia and peripheral glucose utilization was decreased following 3.5 h of isoflurane anesthesia (P less than 0.05). These data strongly suggest a widespread and immediate metabolic effect of isoflurane anesthesia, which includes peripheral insulin resistance to glucose disposal, decreased lipolysis, and a progressive increase in protein wasting with increasing duration of anesthesia.     

In Vitro Compound A Formation in a Computer-controlled Closed-circuit Anesthetic Apparatus: Comparison with a Classical Valve Circuit

Background: Few data exist on compound A during sevoflurane anesthesia when using closed-circuit conditions and sodalime with modern computer-controlled liquid injection.

Methods: A PhysioFlex apparatus (Drager, Lubeck, Germany) was connected to an artificial test lung (inflow [almost equal to] 160 ml/min carbon dioxide, outflow [almost equal to] 200 ml/min, simulating oxygen consumption). Ventilation was set to obtain an end-tidal carbon dioxide partial pressure (Petco2) [almost equal to] 40 mmHg. Canister inflow (T[degrees]in) and outflow (T[degrees]out) temperatures were measured. Fresh sodalime and charcoal were used. After baseline analysis, sevoflurane concentration was set at 2.1% end-tidal for 120 min. At baseline and at regular intervals thereafter, Petco2, end-tidal sevoflurane, T[degrees]in, and T[degrees]out were measured. For inspiratory and expiratory compound A determination, samples of 2-ml gas were taken. These data were compared with those of a classical valve-containing closed-circuit machine. Ten runs were performed in each set-up.

Results: Inspired compound A concentrations increased from undetectable to peak at 6.0 (SD 1.3) and 14.3 (SD 2.5) ppm (P < 0.05), and maximal temperature in the upper outflow part of the absorbent canister was 24.3[degrees]C (SD 3.6) and 39.8[degrees]C (SD 1.2) (P < 0.05) in the PhysioFlex and valve circuit machines, respectively. Differences between the two machines in compound A concentrations and absorbent canister temperature at the inflow and outflow regions were significantly different (P < 0.05) at all times after 5 min.     

Renal Responses to Low-flow Desflurane, Sevoflurane, and Propofol in Patients

Background: The contributing factors that result in significant, postoperative proteinuria and glucosuria after low-flow isoflurane and sevoflurane anesthesia are unknown. The present study compared renal responses after anesthesia with desflurane (negligible metabolism), sevoflurane, or intravenous propofol.

Methods: Informed consent was obtained from 52 patients with American Society of Anesthesiologists physical status I-III (aged 36-81 yr). Patients with diabetes or renal insufficiency were excluded. Desflurane (n = 20) or sevoflurane (n = 22), without nitrous oxide, was given at 1 l/min fresh gas flow for elective surgical procedures lasting more than 2 h; 10 patients received propofol without nitrous oxide as the primary anesthetic. Blood and urine chemistries were obtained before surgery. Blood and 24-h urine collections were obtained for 3 days after surgery and were analyzed for liver and renal indices.

Results: Length of surgery averaged ~ 300 min (range, 136-750 min), minimum alveolar concentration-hour averaged 4.3 (range, 1.2-11.0), and infusion rates of propofol were 99-168 [mu]g [middle dot] kg-1 [middle dot] min-1. Plasma creatinine concentration did not change, plasma blood urea nitrogen decreased significantly, and significant increases in urine glucose, protein, and albumin occurred similarly in all groups. Mean (+/- SD) postoperative urine glucose values for day 1 after desflurane, sevoflurane, and propofol were 1.4 +/- 3.0, 1.1 +/- 2.1, and 1.9 +/- 2.6 g/d (normal, < 0.5 g/d). The average daily protein/creatinine ratios for postoperative days 2-3 after desflurane, sevoflurane, and propofol were 240 +/- 187, 272 +/- 234, and 344 +/- 243 (normal,< 150 mg/g). Regardless of anesthetic, there were significantly greater urine protein concentrations after surgical procedures in central versus peripheral regions.     

低流量七氟烷吸入麻醉时不同二氧化碳吸收剂环路中化合物A浓度的比较及其对患者肝肾功能的影响

Objective To investigate the influence of different carbon dioxide (CO2) absorbents (Dr(a)gersorb 800 plus , Sodasorb,Sodasorb LF) on the production of compound A during low-flow sevoflurane anesthesia.Methods Twenty-seven ASA Ⅰ or Ⅱ patients aged 20-64 years were randomly assigned to three groups according to different CO2 absorbents: Dr(a)gersorb 800 plus' group (group D, n = 10), Sodasorb group (group S, n = 10) and Sodasorb LF group (group LF, n = 7). Anesthesia was maintained with low-flow (500 ml/min) sevoflurane inhalation (with the end-tidal sevoflurane concentration of approximately 2% ). At 2 h after low-flow sevoflurane anesthesia, gas samples were taken from the expiratory limb of the circuit. Compound A was detected by gas chromatography. Serum alanine transaminase (ALT), aspartate aminotransferase (AST), bilirubin (BR), urea nitrogen (BUN) and creatinine (Cr) levels were measured before (T0 ) and 24 h after operation (T1).Results The three groups were comparable with respect to age, body weight and height. After 2 h of low-flow sevoflurane anesthesia, compound A concentrations in the expiratory limb of the circuit were 11.6 ± 5.8 (group D), 2.1 ± 1.9 (group S)and ＜ 0.1 ppm (group LF), respectively. There were no significant changes in the serum ALT, AST, BR, BUN and Cr levels at 24 h after operation as compared with the preoperative baseline values in the three groups.Conclusion After 2 h of low-flow (500 ml/min) sevoflurane anesthesia, compound A concentrations within the circuit with different CO2 absorbents ( Dr(a)gersorb 800 plus' , Sodasorb, Sodasorb LF) are less than 50 ppm, with the lowest in Sodasorb LF.However, they have no significant effects on hepatic or renal function.     

The Role of Human Lungs in the Biotransformation of Propofol

Background: The metabolism of propofol is very rapid, and its transformation takes place mainly in the liver. There are reports indicating extrahepatic metabolism of the drug, and the alimentary canal, kidneys, and lungs are mentioned as the most probable places where the process occurs. The aim of this study was to determine whether the human lungs really take part in the process of propofol biotransformation.

Methods: Blood samples were taken from 55 patients of American Society of Anesthesiologists grade 1-3 scheduled for elective intracranial procedures (n = 47) or for pulmonectomy (n = 8). All patients were premedicated with diazepam (10 mg) administered orally 2 h before anesthesia. Propofol total intravenous anesthesia was performed at the following infusion rates: 12 mg [middle dot] kg-1 [middle dot] h-1, 9 mg [middle dot] kg-1 [middle dot] h-1, and 6 mg [middle dot] kg-1 [middle dot] h-1. Fentanyl and pancuronium bromide were also administered intermittently. After tracheal intubation, the lungs were ventilated to normocapnia with an oxygen-air mixture (fraction of inspired oxygen = 0.33). Blood samples for propofol and 2,6-diisopropyl-1,4-quinol analysis were taken simultaneously from the right atrium and the radial artery, or the pulmonary artery and the radial artery. The concentration of both substances were measured with high-performance liquid chromatography and gas chromatography-mass spectroscopy.

Results: The concentration of propofol in the central venous system (right atrium or pulmonary artery) is greater than in the radial artery, whereas the opposite is observed for propofol's metabolite, 2,6-diisopropyl-1,4-quinol. Higher propofol concentrations are found in blood taken from the pulmonary artery than in the blood collected from the radial artery.     

Compound A concentration is decreased by cooling anaesthetic circuit during low-flow sevoflurane anaesthesia

PURPOSE: In the presence of carbon dioxide absorbents, sevoflurane is degraded to CF2 = C(CF3)OCH2F, an olefin compound A. There remains some concern of the hepatic and renal toxicity that compound A poses when using low-flow anaesthetic techniques. We investigated a device to decrease the concentration of compound A products by decreasing the temperature of exhaled air and soda lime in semi-closed low-flow anaesthesia technique in surgical patients. METHODS: Ten patients, ASA 1 or 2, were studied. Five received anaesthesia using a cooling circuit, that consisting of an anaesthetic circuit and an intercooler device interposed in the expiratory tube. The intercooler was dipped in an iced water tank. Anaesthesia was given through this circuit from induction to emergence. Another five patients received anaesthesia without cooling. Anaesthesia was maintained with sevoflurane and O2 50%/N2O during four to six hours of operation. A fixed concentration of sevoflurane 2% at a total flow of 1 L.min-1 was administered. Gas samples were taken every hour and compound A was quantitated by gas chromatography. The temperatures of canister, circuit and body were measured every hour. RESULTS: The device effectively lowered the temperatures [24 +/- 3.4 to 5 +/- 1.3 degrees C] and the concentrations of compound A [27.1 +/- 3.8 ppm to 16.3 +/- 2.08 ppm, P < 0.05] in the circuit. The body temperatures were not lowered. CONCLUSION: Compound A concentrations were reduced by cooling the anaesthetic circuit in clinical settings.     

A randomized controlled trial of the anticatabolic effect of epidural analgesia and hypocaloric glucose

BACKGROUND AND OBJECTIVES: The goal of the present study was to investigate whether epidural analgesia exerts a protein-sparing effect after colorectal surgery in the presence of hypocaloric glucose supply initiated with surgical skin incision. METHODS: We randomly allocated 10 patients to receive general anesthesia combined with epidural anesthesia with bupivacaine, followed by epidural analgesia using bupivacaine/fentanyl, and 10 patients to receive general anesthesia, followed by patient-controlled analgesia with intravenous morphine. All patients received a 48-hour infusion of glucose 10% from surgical skin incision until the second day after surgery. The glucose infusion rate provided 50% of the patient's resting energy expenditure. Kinetics of protein and glucose metabolism were assessed by a stable-isotope tracer technique (L-[1-(13)C]leucine and [6,6-(2)H(2)]glucose). RESULTS: The rate of appearance of leucine increased in the intravenous-analgesia group (112 +/- 29 to 130 +/- 25 micromol/kg/h) 2 days after surgery, and this increase was more pronounced than in the epidural analgesia group (preoperative 120 +/- 24, postoperative 123 +/- 22 micromol/kg/h, P < .05). Leucine oxidation rate increased in the intravenous analgesia group from 17 +/- 8 to 23 +/- 8 micromol/kg/h and in the epidural group from 17 +/- 6 to 19 +/- 7 micromol/kg/h without the difference between the groups reaching statistical significance (P = .067). Nonoxidative leucine disposal remained unaltered in both groups. No differences in glucose metabolism were seen between the groups. CONCLUSIONS: Epidural analgesia inhibits the increase in whole-body protein breakdown in patients receiving perioperative hypocaloric glucose infusion initiated with surgical skin incision. However, oxidative protein loss, protein synthesis, and glucose metabolism are not affected by epidural analgesia.     

Compound A Induces Sister Chromatid Exchanges in Chinese Hamster Ovary Cells

Background: Compound A [CF2 = C(CF3)OCH2 F], a degradation product of sevoflurane [(CF3)2 CHOCH2 F], is a vinyl ether and may be an alkylating agent. Thus it is a potential genotoxin.

Methods: The capacity of compound A to produce sister chromatid exchanges was measured in Chinese hamster ovary cells with and without metabolic activation. Concentrations of 11 to 468 ppm compound A were applied for 2 h, the Chinese hamster ovary cells were incubated for a further 34 h in the presence of bromodeoxyuridine, and then colcemid was added to produce arrest in metaphase. Coded slides of cells were examined blindly, and 50 chromosome spreads were counted for each test concentration.

Results: The lowest concentration of compound A applied without metabolic activator (27 ppm) significantly increased (P < 0.001) sister chromatid exchanges, and increasing concentrations of compound A increased the incidence of exchanges. Metabolic activation did not increase the incidence of exchanges.