Toxicity of compound A in rats. Effect of increasing duration of administration

Perioperative management of kidney transplantation in China: A national survey in 2021

Perioperative anaesthesia management has an important significance for kidney transplantation; however, the related consensus remains limited. An electronic survey with 44 questions was developed and sent to the chief anaesthesiologist at 115 non-military medical centres performing kidney transplantation in China through WeChat. A response rate of 81.7% was achieved from 94 of 115 non-military medical centres, where 94.4% of kidney transplants (10404 /11026) were completed in 2021. The result showed an overview of perioperative practice for kidney transplantations in China, identify the heterogeneity, and provide evidence for improving perioperative management of kidney transplantation. Some controversial therapy, such as hydroxyethyl starch, are still widely used, while some recommended methods are not widely available. More efforts on fluid management, hemodynamical monitoring, perioperative anaesthetics, and postoperative pain control are needed to improve the outcomes. Evidence-based guidelines for standardizing clinical practice are needed.

Sevoflurane-Induced Diffuse Alveolar Hemorrhage

Diffuse alveolar hemorrhage (DAH) is a potentially life-threatening pulmonary pathology which results in intra-alveolar hemorrhage secondary to disruption of the alveolar capillary basement membrane. Most commonly, these patients present with hemoptysis, hypoxemia and pulmonary infiltrates. Although rare, sevoflurane, an inhalational anesthetic used as a rapid induction agent for anesthesia may be implicated in the etiology of DAH. We report a case of a 21-year-old otherwise healthy male found to have postoperative diffuse alveolar hemorrhage secondary to sevoflurane inhalation. Thus far, only five documented cases describing sevoflurane induced diffuse alveolar hemorrhage have been described in the literature, with prior cases also showing a clear temporal association between sevoflurane administration and symptom onset. Although uncommon, we must take sevoflurane into consideration as a possible etiology of diffuse alveolar hemorrhage when encountering signs of respiratory distress and hemoptysis in postoperative patients.

Investigation and Possibilities of Reuse of Carbon Dioxide Absorbent Used in Anesthesiology

Absorbents used in closed and semi-closed circuit environments play a key role in preventing carbon dioxide poisoning. Here we present an analysis of one of the most common carbon dioxide absorbents—soda lime. In the first step, we analyzed the composition of fresh and used samples. For this purpose, volumetric and photometric analyses were introduced. Thermal properties and decomposition patterns were also studied using thermogravimetric and X-ray powder diffraction (PXRD) analyses. We also investigated the kinetics of carbon dioxide absorption under conditions imitating a closed-circuit environment.

[Predictive value of plasma cytokines for acute kidney injury following lung resection surgery: prospective observational study]

BACKGROUND AND OBJECTIVES

Patients undergoing lung resection surgery are at risk of developing postoperative acute kidney injury. Determination of cytokine levels allows the detection of an early inflammatory response. We investigated any temporal relationship among perioperative inflammatory status and development of acute kidney injury after lung resection surgery. Furthermore, we evaluated the impact of acute kidney injury on outcome and analyzed the feasibility of cytokines to predict acute kidney injury.

METHODS

We prospectively analyzed 174 patients scheduled for elective lung resection surgery with intra-operative periods of one-lung ventilation. Fiberoptic broncho-alveolar lavage was performed in each lung before and after one-lung ventilation periods for cytokine analysis. As well, cytokine levels were measured from arterial blood samples at five time points. Acute kidney injury was diagnosed within 48h of surgery based estabilished criteria for its diagnosis. We analyzed the association between acute kidney injury and cardiopulmonary complications, length of intensive care unit and hospital stays, intensive care unit re-admission, and short-term and long-term mortality.

RESULTS

The incidence of acute kidney injury in our study was 6.9% (12/174). Acute kidney injury patients showed higher plasma cytokine levels after surgery, but differences in alveolar cytokines were not detected. Although no patient required renal replacement therapy, acute kidney injury patients had higher incidence of cardiopulmonary complications and increased overall mortality. Plasma interleukin-6 at 6h was the most predictive cytokine of acute kidney injury (cut-off point at 4.89pg.mL^-1).

CONCLUSIONS

Increased postoperative plasma cytokine levels are associated with acute kidney injury after lung resection surgery in our study, which worsens the prognosis. Plasma interleukin-6 may be used as an early indicator for patients at risk of developing acute kidney injury after lung resection surgery.

Predictive value of plasma cytokines for acute kidney injury following lung resection surgery: prospective observational study

Background and objectives

Patients undergoing lung resection surgery are at risk of developing postoperative acute kidney injury. Determination of cytokine levels allows the detection of an early inflammatory response. We investigated any temporal relationship among perioperative inflammatory status and development of acute kidney injury after lung resection surgery. Furthermore, we evaluated the impact of acute kidney injury on outcome and analyzed the feasibility of cytokines to predict acute kidney injury.

Methods

We prospectively analyzed 174 patients scheduled for elective lung resection surgery with intra-operative periods of one-lung ventilation periods. Fiberoptic broncho-alveolar lavage was performed in each lung before and after one-lung ventilation periods for cytokine analysis. As well, cytokine levels were measured from arterial blood samples at five time points. acute kidney injury was diagnosed within 48 h of surgery based on acute kidney injury criteria. We analyzed the association between acute kidney injury and cardiopulmonary complications, length of intensive care unit and hospital stays, intensive care unit re-admission, and short-term and long-term mortality.

Results

The incidence of acute kidney injury in our study was 6.9% (12/174). Acute kidney injury patients showed higher plasma cytokine levels after surgery but differences in alveolar cytokines were not detected. Although no patient required renal replacement therapy, acute kidney injury patients had higher incidence of cardiopulmonary complications and increased overall mortality. Plasma interleukin-6 at 6 h was the most predictive cytokine of acute kidney injury (cut-off point at 4.89 pg.mL⁻¹).

Conclusions

Increased postoperative plasma cytokine levels are associated with acute kidney injury after lung resection surgery in our study, which worsens the prognosis. Plasma interleukin-6 may be used as an early indicator for patients at risk of developing acute kidney injury after lung resection surgery.

A Comparison of the Effects of Prolonged (>10 Hour) Low-flow Sevoflurane, High-flow Sevoflurane, and Low-flow Isoflurane Anaesthesia on Hepatorenal Function in Orthopaedic Patients

This study compared the effects of low-flow sevoflurane, high-flow sevoflurane and low-flow isoflurane on hepatorenal function during and after more than 10 hours of anaesthesia. Twenty-five patients scheduled for elective orthopaedic surgery were categorized into three groups; low-flow sevoflurane (fresh gas flow at 1 litre/min, n=9), high-flow sevoflurane (5 l/min, n=7), or low-flow isoflurane (1 l/min, n=9). Inspiratory compound A concentrations were measured. The groups had similar duration of anaesthesia and exposure to anaesthetic agents. The area under the curve of concentration (mean, SD) of compound A in the low-flow sevoflurane group (359.8, 106.1 ppm.h) was greater than that in the high-flow sevoflurane group (61.1, 29.3 ppm.h; P<0.01). All groups showed normal plasma creatinine and creatinine clearance, and transient postoperative increases in plasma alanine aminotrans-ferase and alpha glutathione-S-transferase, as well as urinary glucose and alpha glutathione-S-transferase, with no significant differences between groups. There were no significant relationships between the area under the curve of concentration of compound A and the biomarkers. These findings suggest that prolonged anaesthesia with low-flow sevoflurane has similar effects on hepatorenal function to prolonged anaesthesia with high-flow sevoflurane and low-flow isoflurane.

Sevoflurane

Sevoflurane has been available for clinical practice for about 20 years. Nowadays, its pharmacodynamic and pharmacokinetic properties together with its absence of major adverse side effects on the different organ systems have made this drug accepted worldwide as a safe and reliable anesthetic agent for clinical practice in various settings.

Performance of a new carbon dioxide absorbent, Yabashi lime® as compared to conventional carbon dioxide absorbent during sevoflurane anesthesia in dogs

In the present study, we compare a new carbon dioxide (CO2) absorbent, Yabashi lime(®) with a conventional CO2 absorbent, Sodasorb(®) as a control CO2 absorbent for Compound A (CA) and Carbon monoxide (CO) productions. Four dogs were anesthetized with sevoflurane. Each dog was anesthetized with four preparations, Yabashi lime(®) with high or low-flow rate of oxygen and control CO2 absorbent with high or low-flow rate. CA and CO concentrations in the anesthetic circuit, canister temperature and carbooxyhemoglobin (COHb) concentration in the blood were measured. Yabashi lime(®) did not produce CA. Control CO2 absorbent generated CA, and its concentration was significantly higher in low-flow rate than a high-flow rate. CO was generated only in low-flow rate groups, but there was no significance between Yabashi lime(®) groups and control CO2 absorbent groups. However, the CO concentration in the circuit could not be detected (≤5ppm), and no change was found in COHb level. Canister temperature was significantly higher in low-flow rate groups than high-flow rate groups. Furthermore, in low-flow rate groups, the lower layer of canister temperature in control CO2 absorbent group was significantly higher than Yabashi lime(®) group. CA and CO productions are thought to be related to the composition of CO2 absorbent, flow rate and canister temperature. Though CO concentration is equal, it might be safer to use Yabashi lime(®) with sevoflurane anesthesia in dogs than conventional CO2 absorbent at the point of CA production.

Effect of sevoflurane anesthesia on the severity of renal histopathologic changes in rabbits pretreated with gentamicin: A controlled, investigator-blinded, experimental study

BACKGROUND

Inorganic fluoride and compound A are potential nephrotoxic products of sevoflurane, a halogenated inhalational general-anesthetic drug.

OBJECTIVE

The aim of this study was to microscopically examine the effect of sevoflurane on the severity of renal histopathologic changes in rabbits pretreated with gentamicin.

METHODS

In this controlled, investigator-blinded, experimental study at the Firat University School of Medicine, Elazig, Turkey, male New Zealand white rabbits (age range, 6-8 months; weight range, 2600-3400 g) were randomly divided into 4 groups of equal size. The gentamicin group received IM gentamicin 10 mg/kg · d(-1) for 10 days. Rabbits in the sevoflurane group received pH-balanced saline solution at a volume of 10 mg/kg · d(-1) for 10 days, equivalent to the volume of gentamicin administered to the gentamicin group. On day 11, anesthesia was induced with 8% sevoflurane in 50% oxygen and air using a suitable facemask. When a sufficient depth of anesthesia (loss of eyelash reflex and tolerance to tail-clamp stimuli) was reached (without a muscle relaxant), the rabbits were intubated (3-mm ID) and allowed to breathe spontaneously. End-tidal or end expiratory concentration of sevoflurane was then decreased to 4% and the rabbits were anesthetized at a flow rate of 4 L/min for 4 hours. The rabbits in the gentamicin + sevoflurane group were treated with IM gentamicin at a dosage of 10 mg/kg · d(-1) for 10 days. On day 11, they were exposed to sevoflurane, as described for the sevoflurane group. The control group received IM pH-balanced saline solution for the duration of the study. Twenty-four hours after treatment completion, all rabbits were euthanized and kidney tissue samples were obtained. Histopathologic examinations were then carried out using light microscopy. Changes in renal histopathology were based on the percentage of acute tubular necrosis (ATN) and judged on a scale from none to severe.

RESULTS

Forty male New Zealand white rabbits (mean [SD] age, 7 [0.49] months; mean [SD] weight, 2900 [150] g) were divided into 4 groups of 10 rabbits each. Proximal renal tubule cell injury in the form of ATN (the mean score) was significantly greater in the 3 treatment groups than in the control group (all, P < 0.001), especially at the corticomedullary junction. In the 3 treatment groups, the most severe renal damage observed was rated as mild (10%-25%). More rabbits in the gentamicin + sevoflurane group had mild renal damage (7) than in the gentamicin group (4) or the sevoflurane group (4), but the between-group differences were not statistically significant.

CONCLUSION

In this experimental study of the effects of sevoflurane on the severity of renal histopathologic changes, a higher percentage of rabbits were observed to have greater renal damage in the gentamicin + sevoflurane group than the other groups. However, between-group differences did not reach statistical significance.

Delivery of sevoflurane to dogs using a Stephens anaesthetic machine

OBJECTIVE

To investigate the sevoflurane concentrations produced within the Stephens anaesthetic machine circuit (vaporizer in-circle system) at different fresh gas flow rates (FGFRs), temperatures, vaporizer settings and vaporizer sleeve positions when used to anaesthetize dogs of different body sizes.

STUDY DESIGN

Experimental non-blinded studies.

ANIMALS

Eighteen mixed breed dogs, weights 4-39 kg.

METHODS

Anaesthetic induction with propofol was followed by maintenance with sevoflurane in oxygen via the Stephens anaesthetic machine. In study 1, the vaporizer setting, temperature and circuit FGFRs were altered with the vaporizer sleeve down (n = 3), or in separate experiments, up (n = 3). Delivered (Fi'SEVO) and expired sevoflurane concentrations were recorded. Study 2 determined the vaporizer settings (sleeve up) required to achieve predetermined multiples of minimal alveolar concentration (MAC) of Fi'SEVO when sevoflurane was delivered to dogs (n = 12) of different bodyweights and at different FGFRs.

RESULTS

Delivered concentrations of sevoflurane were sufficient to maintain anaesthesia in all dogs, regardless of bodyweight, FGFR, vaporizer temperature and sleeve position. Fi'SEVO increased with increasing temperature, when the vaporizer sleeve was down, when vaporizer setting was increased and when FGFR was decreased. As the FGFR increased or the dog's bodyweight decreased, higher vaporizer settings were required to produce the same Fi'SEVO. The median Stephens vaporizer settings to achieve an Fi'SEVO of 1.3 MAC ranged from 4.3 to 5.0 for a small dog (1-10 kg), 2.5 to 5.6 for a medium dog (15-25 kg) and 2.5 to 3.5 for a large dog (30-40 kg), depending on the FGFR.

CONCLUSION AND CLINICAL RELEVANCE

The Stephens anaesthetic machine can deliver to dogs, weighing 4 kg and above, concentrations of sevoflurane sufficient or in excess of that required to maintain anaesthesia, at temperatures from 10 to 35 °C, FGFRs of 1 to 5 times the patient's estimated metabolic oxygen requirement and at any vaporizer sleeve position.

Sevoflurane has no adverse effects on renal function in cirrhotic patients: a comparison with propofol

BACKGROUND

Cirrhotic patients are prone to developing renal dysfunction after anaesthesia and surgery. However, no consensus has been reached whether sevoflurane could have adverse effects on renal function in cirrhotic patients. We hypothesised that the use of sevoflurane for general anaesthesia would lead to post-operative renal dysfunction in cirrhotic patients undergoing liver resection.

METHODS

A total of 200 patients undergoing liver resection were randomly assigned to a propofol or sevoflurane group. The influence of sevoflurane or propofol on renal function was evaluated by the maximal change, the difference between the pre-operative baseline and the highest values of serum creatinine and blood urea nitrogen measured at day 1, 3 and 6 post-operatively.

RESULTS

The maximal change in serum creatinine after liver resection was -4.52 (5.78) μmol/l and -3.37 (7.34) μmol/l with P = 0.398, and that in blood urea nitrogen was 0.41 (1.49) mmol/l and 0.93 (1.54) mmol/l with P = 0.098 between the sevoflurane group (n = 52) and the propofol group (n = 50), respectively.

CONCLUSIONS

Sevoflurane does not seem to impair post-operative renal function in cirrhotic patients undergoing liver resection.

Comparison of the renal safety between carbon dioxide absorbent products under sevoflurane anesthesia: a pilot study

Background

The chemical reaction of carbon dioxide absorbent and sevoflurane is known to produce compound A. However, carbon dioxide absorbents are not controlled by the Food and Drug Administration, but are treated as industrial products in some nations. Moreover, carbon dioxide absorbents differ in their capacities to produce compound A, because their chemical compositions differ. In this study, we compared the renal safety between carbon dioxide absorbent products in patients under sevoflurane anesthesia.

Methods

Eighty patients with no preexisting renal disease undergoing elective gynecologic surgery were randomly assigned to receive sevoflurane or isoflurane anesthesia with one of four carbon dioxide absorbent products (Sodasorblime®, Sodalyme®, Sodasorb®, Spherasorb®) at the same fresh gas flow of 2 L/min. The renal safety was evaluated by changes of blood urea nitrogen (BUN), creatinine and urine N-acetyl-b-glucoseaminidase (NAG)-creatinine ratio at 24 hours and 72 hours after surgery from preoperative level.

Results

There was no significant difference in the renal safety indicators between carbon dioxide absorbents during sevoflurane anesthesia (P > 0.05). However, the BUN and urine NAG-creatinine ratios at 72 hours after surgery were higher in isoflurane anesthesia in some carbon dioxide absorbent groups (P = 0.03 and 0.04, respectively).

Conclusions

We could not find significant differences of renal safety indicators with carbon dioxide absorbents. Although the adverse effect of carbon dioxide absorbents on renal function was not proved, consideration should be given to their contol by the regulation on their efficacy and safety because carbon dioxide absorbents can produce compound A.

Sofnolime with different water content causes different effects in two sevoflurane inhalational induction techniques with respect to the output of compound-A

OBJECTIVE

During sevoflurane anesthesia with Sofnolime for CO(2) absorption, the factors affecting the production of compound A (a chemical is nepherotoxic) are still not clear. This study is designed to investigate the effects of different fresh gas flow during induction, the vital capacity induction (VCI) vs. the tidal volume breath induction (TBI) on the compound-A production with a fresh Sofnolime or a dehydrated Sofnolime using a simulated lung model.

METHOD

The experiments were randomly divided into four groups: group one, VCIf, vital capacity fresh gas inflow with fresh Sofnolime; group two, TBIf, tidal volume breath fresh gas inflow with fresh Sofnolime; group three, VCId, vital capacity fresh gas inflow with dehydrated Sofnolime, and group four, TBId, tidal volume breath fresh gas inflow with dehydrated Sofnolime. The inspired sevoflurane was maintained at 8%, the concentrations of compound-A were assayed using Gas-spectrum technique, and Sofnolime temperatures were monitored at 1-min intervals throughout the experiment.

RESULTS

The mean and maximum concentrations of compound A were significantly higher in the vital capacity group than the tidal volume breath group (P<0.01). At the beginning of anesthesia maintenance, the compound-A concentration in group VCIf was 36.28±6.13 ppm, which was significantly higher than the 27.32±4.21 ppm observed in group TBIf (P<0.01). However, these values decreased to approximately 2 ppm in the dehydrated Sofnolime groups. Sofnolime temperatures increased rapidly in the dehydrated Sofnolime groups but slowly in the fresh Sofnolime groups.

CONCLUSION

With fresh Sofnolime, vital capacity induction increased compound-A production in the circuit system compared with tidal volume breath induction. However, with dehydrated Sofnolime, the effects of the two inhalation induction techniques on compound-A output were not significantly different.

Direct effects of volatile anesthetics on cardiac functiona

The volatile anesthetics are a class of general anesthetic drugs used by the perfusionist during cardiopulmonary bypass (CPB). These agents are used in low doses in combination with other anesthetics to produce complete anesthesia. During CPB, these agents are capable of safely anesthetizing the paitent. It is well understood that these anesthetics act at the level of the central nervous system. However the intent of this study was to define the effects of isoflurane and sevoflurane on left ventricular function. C57BL/6 female mice were anesthetized with either isoflurane or sevoflurane at concentrations ranging from 0.5 to 5%. The cardiac function was assessed with transthoracic echocardiography (TTE). Sevoflurane caused a reduction of left ventricular function at lower concentrations compared with isoflurane. At concentrations of 2% and greater, sevoflurane significantly reduced cardiac output, ejection fraction, fractional shortening, and increased end-diastolic and end-systolic volumes. Isoflurane-induced reduction of left ventricular function was much less in magnitude when compared with sevoflurane. These data underscore the importance of using lower concentrations of volatile anesthetics during CPB especially during periods of cardiac recovery after aortic cross-clamp removal.

Alterations in the biochemical markers of renal function after sevoflurane anaesthesia

AIM

This study has been carried out to see whether renal function is acutely altered in patients undergoing sevoflurane anaesthesia. For this purpose, the urinary levels of markers of renal tubular function, namely leucine amino peptidase (LAP), gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and beta-2 microglobulin (beta-2M), and urinary albumin as a predictor of renal glomerular function were measured before and after sevoflurane anaesthesia.

METHODS

This study was comprised of 20 patients (11 males and nine females) aged 18-55, who underwent various elective surgical procedures under general anaesthesia. Urine samples of all patients were collected before and 1, 2 and 8 h after the anaesthesia. The levels of LAP, GGT, beta-2M, and albumin were then expressed as factored by urinary creatinine. In all patients, the anaesthesia was maintained with sevoflurane (2% end-tidal) at a high flow-rate (6 L/min).

RESULTS

Urinary beta-2M and LAP levels after anaesthesia were unchanged (P > 0.05). While urinary GGT and ALP levels were found elevated in the first hour, LDH levels were higher in the second hour (P < 0.05). They returned to normal levels in the later periods after the anaesthesia. Urinary albumin excretion (UAE) was significantly elevated in the second hour after the anaesthesia (P < 0.001). Although UAE was decreased in the eighth hour after the anaesthesia, it still remained higher than the pre-anaesthesia level (P < 0.001).

CONCLUSIONS

These results suggest that a 2% end-tidal concentration of sevoflurane at a high flow-rate (6 L/min) acutely alters renal glomerular function but does not have a significant acute effect on biochemical markers of renal tubular damage.

Formation and toxicity of anesthetic degradation products

Toxic degradation products are formed from a range of old and modern anesthetic agents. The common element in the formation of degradation products is the reaction of the anesthetic agent with the bases in the carbon dioxide absorbents in the anesthesia circuit. This reaction results in the conversion of trichloroethylene to dichloroacetylene, halothane to 2-bromo-2-chloro-1,1-difluoroethylene, sevoflurane to 2-(fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (Compound A), and desflurane, isoflurane, and enflurane to carbon monoxide. Dichloroacetylene, 2-bromo-2-chloro-1,1-difluoroethylene, and Compound A form glutathione S-conjugates that undergo hydrolysis to cysteine S-conjugates and bioactivation of the cysteine S-conjugates by renal cysteine conjugate beta-lyase to give nephrotoxic metabolites. The elucidation of the mechanisms of formation and bioactivation of degradation products has allowed for the safe use of anesthetics that may undergo degradation in the anesthesia circuit.

Acivicin-induced alterations in renal and hepatic glutathione concentrations and in γ-glutamyltransferase activities

gamma-Glutamyltransferase (gamma-GT) catalyzes the hydrolysis of glutathione, glutathione S-conjugates, and gamma-substituted l-glutamate derivatives. Acivicin is an irreversible inhibitor of gamma-GT that has been used to study the role of gamma-GT in glutathione homeostasis and glutathione-dependent bioactivation reactions. The present studies were undertaken because of reported conflicting effects of acivicin on the nephrotoxicity of some haloalkenes that undergo glutathione-dependent bioactivation. The objective of this study was to test the hypothesis that acivicin may alter renal glutathione concentrations; acivicin-induced changes in renal glutathione concentrations may alter the susceptibility of the kidney to the nephrotoxic effects of haloalkenes. Hence, diurnal and acivicin-induced changes in renal and hepatic glutathione concentrations along with renal and hepatic gamma-GT activities were investigated. The previously observed diurnal variations in hepatic glutathione concentrations in fed rats were confirmed, but no diurnal variations were observed in renal glutathione concentrations or in renal or hepatic gamma-GT activities. Renal and hepatic glutathione concentrations and gamma-GT activities were measured in tissue homogenates from rats given 0, 0.1, or 0.2 mmol acivicin/kg (i.p.) and killed 0, 2, 4, 8, 12, or 24 hr later. Renal glutathione concentrations were increased above control values in acivicin-treated rats, whereas acivicin had no effect on hepatic glutathione concentrations. Renal gamma-GT activities decreased within 2 hr after giving acivicin and remained decreased for 24 hr. Acivicin had no effect on hepatic gamma-GT activities, except at 24 hr after treatment when values in acivicin-treated rats were elevated compared with controls. Although the present studies do not afford an explanation of the mechanism whereby acivicin increases the nephrotoxicity of some haloalkenes, they do indicate that acivicin is not a reliable probe to investigate the role of gamma-GT in haloalkene-induced nephrotoxicity.

Sevoflurane degradation by carbon dioxide absorbents may produce more than one nephrotoxic compound in rats

PURPOSE

Degradation of sevoflurane by carbon dioxide absorbents produces compound A, a vinyl ether. In rats, compound A can produce renal corticomedullary necrosis. We tested whether other compounds produced by sevoflurane degradation also could produce corticomedullary necrosis.

METHODS

Two groups of rats were exposed for four hours to sevoflurane 2.5% delivered through a container filled with fresh Sodasorb and heated to 30 degrees C or to 50 degrees C, respectively. Compound A was added to produce an average concentration of 120 ppm in both groups. A third (control) group received 2.5% sevoflurane that did not pass through absorbent, and no compound A was added.

RESULTS

As determined by gas chromatography, the higher temperature produced more volatile breakdown products, including compound A. Median necrosis of the corticomedullary junction in the 50 degrees C group [10% (quartiles 1.0%-7.8%); n = 20] exceeded that in the 30 degrees C group [5% (6.5%-15%); n = 18; P < 0.02], and both exceeded the median necrosis in the control group [0% (0.0%-0.2%); n = 10; P < 0.02]. The respective mean +/- SD values for these three studies were: 12.8 +/- 16.7%, 5.3 +/- 4.4%, and 0.3 +/- 0.5%.

CONCLUSION

Degradation products of sevoflurane other than compound A can cause or augment the renal injury in rats produced by compound A.

Compound A concentration in the circle absorber system during low-flow sevoflurane anesthesia: comparison of Drägersorb Free, Amsorb, and Sodasorb II

STUDY OBJECTIVE

To determine compound A concentrations in a low-flow circuit containing Drägersorb Free (Dräger, Lübeck, Germany), Amsorb (Armstrong, Coleraine, Northern Ireland), and Sodasorb II (W. R. Grace, Lexington, MA).

DESIGN

Randomized study.

SETTING

Hamamatsu University Hospital.

PATIENTS

24 ASA physical status I and II patients scheduled for general anesthesia greater than 3 hours' duration.

INTERVENTIONS

Patients were allocated to three groups of eight patients each to receive either using either Drägersorb Free, Amsorb, or Sodasorb II. Immediately before anesthesia induction, 1 kg of fresh absorbent was placed in the anesthesia canister. Anesthesia was maintained with sevoflurane (end-tidal concentration 1% to 3%) in oxygen and nitrous oxide (FIO(2) > 0.3) at a total flow of 1 L/min.

MEASUREMENTS

Inspiratory compound A concentration in the circuit was measured once every hour.

MAIN RESULTS

Maximum compound A concentrations for Drägersorb Free, Amsorb, and Sodasorb II were 2.4 +/- 0.8 (mean +/- SD) ppm, 3.1 +/- 0.5 ppm, and 28.0 +/- 10.0 ppm (p < 0.01 vs. Drägersorb Free and Amsorb). Concentrations with Drägersorb Free and Amsorb remained at less than 4 ppm throughout the study.

CONCLUSIONS

Because compound A concentrations in the circuit with Drägersorb Free and Amsorb were negligible, sevoflurane can be used at a fresh gas flow of 1 L/min with these two absorbents.

Serum fluoride concentrations, biochemical and histopathological changes associated with prolonged sevoflurane anaesthesia in horses

The volatile anaesthetic sevoflurane is degraded to fluoride (F-) and a vinyl ether (Compound A), which have the potential to harm kidney and liver. Whether renal and hepatic injuries can occur in horses is unknown. Cardiopulmonary, biochemical and histopathological changes were studied in six healthy thoroughbred horses undergoing 18 h of low-flow sevoflurane anaesthesia. Serum F- concentrations were measured and clinical laboratory tests performed to assess hepatic and renal function before and during anaesthesia. Necropsy specimens of kidney and liver were harvested for microscopic examination and compared to pre-experimental needle biopsies. Cardiopulmonary parameters were maintained at clinically acceptable levels throughout anaesthesia. Immediately after initiation of sevoflurane inhalation, serum F- levels began to rise, reaching an ongoing 38-45 micromol 1(-1) plateau at 8 h of anaesthesia. Serum biochemical analysis revealed only mild increases in glucose and creatinine kinase and a decrease in total calcium. Beyond 10 h of anaesthesia mild, time-related changes in urine included increased volume, glucosuria and enzymuria. Histological examination revealed mild microscopic changes in the kidney involving mainly the distal tubule, but no remarkable alterations in liver tissue. These results indicate that horses can be maintained in a systemically healthy state during unusually prolonged sevoflurane anaesthesia with minimal risk of hepatocellular damage from this anaesthetic. Furthermore, changes in renal function and morphology observed after sevoflurane inhalation are judged minimal and appear to be clinically irrelevant; they may be the result of anaesthetic duration, physiological stressors, sevoflurane (or its degradation products) or other unkown factors associated with these animals and study conditions.

Sevoflurane low-flow anaesthesia: best strategy to reduce Compound A concentration

BACKGROUND

To define the best strategy to reduce Compound A production in Sevoflurane low-flow anaesthesia by experiments in vitro and in vivo of different absorbers and different anaesthesia machines.

METHODS

In vitro Compound A has been measured at 45 degrees C in vitro following Sevoflurane interactions with potassium hydroxide, sodium hydroxide, soda lime, Dragersorb 800 Plus and Amsorb, a new absorber that does not contain sodium or potassium hydroxide. In vivo Compound A concentration in the anaesthesia circuit (inspiratory branch) has been measured using an indirect sampling method through absorber vials (SKC) with active coal granules, during low flows (500 ml/min) general anaesthesia using soda lime, Dragersorb 800 Plus or Amsorb as absorber. Compound A was also measured during low flows (500 ml/min) general anaesthesia using as carbon dioxide absorber soda lime with different anaesthesia machines.

RESULTS

In vitro at 45 degrees C Compound A concentration with soda lime and Dragersorb 800 Plus was about 10 times higher than with Amsorb. In vivo the Compound A concentrations in the inspiratory branch of the circuit were lower in the group with Amsorb.

CONCLUSION

The Compound A production is minimal with Amsorb as carbon dioxide absorber.

Toxic, halogenated cysteine S-conjugates and targeting of mitochondrial enzymes of energy metabolism

Several haloalkenes are metabolized in part to nephrotoxic cysteine S-conjugates; for example, trichloroethylene and tetrafluoroethylene are converted to S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFEC), respectively. Although DCVC-induced toxicity has been investigated since the 1950s, the toxicity of TFEC and other haloalkene-derived cysteine S-conjugates has been studied more recently. Some segments of the US population are exposed to haloalkenes either through drinking water or in the workplace. Therefore, it is important to define the toxicological consequences of such exposures. Most halogenated cysteine S-conjugates are metabolized by cysteine S-conjugate beta-lyases to pyruvate, ammonia, and an alpha-chloroenethiolate (with DCVC) or an alpha-difluoroalkylthiolate (with TFEC) that may eliminate halide to give a thioacyl halide, which reacts with epsilon-amino groups of lysine residues in proteins. Nine mammalian pyridoxal 5'-phosphate (PLP)-containing enzymes catalyze cysteine S-conjugate beta-lyase reactions, including mitochondrial aspartate aminotransferase (mitAspAT), and mitochondrial branched-chain amino acid aminotransferase (BCAT(m)). Most of the cysteine S-conjugate beta-lyases are syncatalytically inactivated. TFEC-induced toxicity is associated with covalent modification of several mitochondrial enzymes of energy metabolism. Interestingly, the alpha-ketoglutarate- and branched-chain alpha-keto acid dehydrogenase complexes (KGDHC and BCDHC), but not the pyruvate dehydrogenase complex (PDHC), are susceptible to inactivation. mitAspAT and BCAT(m) may form metabolons with KGDHC and BCDHC, respectively, but no PLP enzyme is known to associate with PDHC. Consequently, we hypothesize that not only do these metabolons facilitate substrate channeling, but they also facilitate toxicant channeling, thereby promoting the inactivation of proximate mitochondrial enzymes and the induction of mitochondrial dysfunction.

Recent advances in inhalation anesthesia

Both desflurane and sevoflurane offer theoretical and practical advantages over other inhalation anesthetics for horses. The lower solubility of both agents provides improved control of delivery and helps to counteract the confounding influence of the voluminous patient breathing circuit commonly used for anesthetizing horses. The lower solubility should account for faster rates of recovery compared with the older agents; whether or not the quality of recovery differs remains to be objectively evaluated in a broad range of circumstances. The pharmacodynamic effects are, in large part, similar to those of isoflurane (e.g., low arrhythmogenicity) but with some differences. For example, desflurane may be overall more sparing to cardiovascular function (especially during controlled ventilation) compared with isoflurane and sevoflurane, which are roughly similar. Respiratory depression with both new agents is equal to or more depressing than isoflurane, suggesting the use of mechanical ventilation, especially in circumstances of prolonged management (i.e., hours of anesthesia). Both new anesthetics, not surprisingly, are expensive. From this point there are some agent-unique considerations. The anesthetic potency of both agents is less than that of isoflurane, which influences the cost of anesthesia, but also places an upper limit on inspired oxygen concentration (of particular concern with desflurane). Both agents require new vaporizers, but because of the high boiling point and steep vapor-pressure curve of desflurane, new technology was required. This translates into more costly equipment, adding to the cost of desflurane use. In addition, electricity is necessary for the new desflurane vaporizer to function, which limits its portability and adds additional practical considerations in its clinical use. On the other hand, desflurane strongly resists degradation both in vitro and in vivo, but in vitro degradation of sevoflurane by CO2 absorbents may produce renal injury. This may be true especially in association with low fresh-gas inflow rates (used to reduce the cost of using the new agent), and university based practices, where prolonged anesthesia is common.

Renal toxicity with sevoflurane: a storm in a teacup?

The inhaled anaesthetic sevoflurane is metabolised into two products that have the potential to produce renal injury. Fluoride ions are produced by oxidative defluorination of sevoflurane by the cytochrome P450 system in the liver. Until recently, inorganic fluoride has been thought to be the aetiological agent responsible for fluorinated anaesthetic nephrotoxicity, with a toxic concentration threshold of 50 micromol/L in serum. However, studies of sevoflurane administration in animals and humans have not shown evidence of fluoride-induced nephrotoxicity, despite serum fluoride concentrations in this range. Compound A (fluoromethyl-2,2-difluoro-1-[trifluoromethyl] vinyl ether) is a breakdown product of sevoflurane produced by its interaction with carbon dioxide absorbents in the anaesthesia machine. The patient then inhales compound A. Compound A produces evidence of transient renal injury in rats. The mechanism of compound A renal toxicity is controversial, with the debate focused on the role of the renal cysteine conjugate beta-lyase pathway in the biotransformation of compound A. The significance of this debate centres on the fact that the beta-lyase pathway is 10- to 30-fold less active in humans than in rats. Therefore, if biotransformation by this pathway is responsible for the production of nephrotoxic metabolites of compound A, humans may be less susceptible to compound A renal toxicity than are rats. In three studies in human volunteers and one in surgical patients, prolonged (8-hour) sevoflurane exposures and low fresh gas flow rates resulted in significant exposures to compound A. Transient abnormalities were found in biochemical markers of renal injury measured in urine. These studies suggested that sevoflurane can result in renal toxicity, mediated by compound A, under specific circumstances. However, other studies using prolonged sevoflurane administration at low flow rates did not find evidence of renal injury. Finally, there are substantial data to document the safety of sevoflurane administered for shorter durations or at higher fresh gas flow rates. Therefore, the United States Food and Drug Administration recommends the use of sevoflurane with fresh gas flow rates at least 1 L/min for exposures up to 1 hour and at least 2 L/min for exposures greater than 1 hour. We believe this is a rational, cautious approach based on available data. However, it is important to note that other countries have not recommended such limitations on the clinical use of sevoflurane and problems have not been noted.

Glutathione S-conjugation of the sevoflurane degradation product, fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether (compound A) in human liver, kidney, and blood in vitro

Fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether (FDVE) is a fluorinated alkene formed by degradation of the volatile anesthetic sevoflurane in anesthesia machines. FDVE is nephrotoxic in rats and undergoes glutathione-dependent conjugation to form two alkane (G1, G2) and two alkene glutathione S-conjugates (G3, G4), cleavage to cysteine S-conjugates, and beta-lyase-catalyzed metabolism to reactive thionoacyl fluorides, which may react with cellular macromolecules to cause nephrotoxicity. Although similar metabolites have been identified in human urine in vivo, little is known about sites and mechanisms of GSH conjugation in humans. This investigation quantified FDVE-GSH conjugates formed by human hepatic and renal microsomal and cytosolic fractions and blood in vitro. LC-MS/MS analysis identified all four GSH conjugates (G1-G4) formed in all human subcellular fractions. Quantitative analysis indicated that the relative order of formation was G2 > G1 > G4 > G3 with human liver and kidney subfractions. In blood, the order was G1 > G4 > G2 > G3. These results demostrate that FDVE undergoes GSH-dependent conjugation in human liver and kidney microsomes and cytosol as well as blood, which may account for the detection of corresponding mercapturic acids in the urine of patients exposed to FDVE.

Long-duration low-flow sevoflurane and isoflurane effects on postoperative renal and hepatic function

Sevoflurane degradation by carbon dioxide absorbents during low-flow anesthesia forms the haloalkene Compound A, which causes nephrotoxicity in rats. Numerous studies have shown no effects of Compound A formation on postoperative renal function after moderate-duration (3-4 h) low-flow sevoflurane; however, effects of longer exposures remain unresolved. We compared renal function after long-duration low-flow (<1 L/min) sevoflurane and isoflurane anesthesia in consenting surgical patients with normal renal function. To maximize degradant exposure, Baralyme was used, and anesthetic concentrations were maximized (no nitrous oxide and minimal opioids). Inspired and expired Compound A concentrations were quantified. Blood and urine were obtained for laboratory evaluation. Sevoflurane (n = 28) and isoflurane (n = 27) groups were similar with respect to age, sex, weight, ASA status, and anesthetic duration (9.1 +/- 3.0 and 8.2 +/- 3.0 h, mean +/- SD) and exposure (9.2 +/- 3.6 and 9.1 +/- 3.7 minimum alveolar anesthetic concentration hours). Maximum inspired Compound A was 25 +/- 9 ppm (range, 6-49 ppm), and exposure (area under the concentration-time curve) was 165 +/- 95 (35-428) ppm. h. There was no significant difference between anesthetic groups in 24- or 72-h serum creatinine, blood urea nitrogen, creatinine clearance, or 0- to 24-h or 48- to 72-h urinary protein or glucose excretion. Proteinuria and glucosuria were common in both groups. There was no correlation between Compound A exposure and any renal function measure. There was no difference between anesthetic groups in 24- or 72-h aspartate aminotransferase or alanine aminotransferase. These results show that the renal and hepatic effects of long-duration low-flow sevoflurane and isoflurane were similar. No evidence for low-flow sevoflurane nephrotoxicity was observed, even at high Compound A exposures as long as 17 h. Proteinuria and glucosuria were common and nonspecific postoperative findings. Long-duration low-flow sevoflurane seems as safe as long-duration low-flow isoflurane anesthesia.

IMPLICATIONS

Postoperative renal function after long-duration low-flow sevoflurane (with Compound A exposures greater than those typically reported) and isoflurane anesthesia were not different, as assessed by serum creatinine, blood urea nitrogen, and urinary excretion of protein and glucose. This suggests that low-flow sevoflurane is as safe as low-flow isoflurane, even at long exposures.

Comparison of genotoxicity of sevoflurane and isoflurane in human lymphocytes studied in vivo using the comet assay

In the present paper, we report data on the possible genotoxic properties of two inhalation anaesthetics--sevoflurane (SVF) and isoflurane (ISF) - in peripheral blood lymphocytes of patients before, during and after anaesthesia as compared to an unexposed control group. Both anaesthetics were evaluated for genotoxic activity using the comet assay. The exposed groups consisted of 24 ASA grades 1-2 unpremedicated patients (aged 20-66 years, anaesthetized 115-162 min for elective lower abdominal surgery), while the control group consisted of 12 healthy individuals. After induction of anaesthesia (thiopenthone sodium 5-7 mg/kg, fentanyl citrate 0.1mg and vecuronium bromide 0.1mg/kg), anaesthesia was maintained with inhalation of SVF 1-1.5% (n=12) or ISF 1-1.5% (n=12) in oxygen-air mixture. Venous blood samples were obtained before the induction of anaesthesia, at 60 and 120 min of anaesthesia and on the first, third and fifth days following anaesthesia. The comet assay detects DNA damage which includes strand breaks and alkaline labile sites induced directly by genotoxic agents as well as DNA degradation due to cell death. One hundred cells from each sample were examined and graded as no tailed, short and long tailed nuclei. The mean comet response was not different between controls and patients before anaesthesia. However, similar significant increases were observed in the mean comet response in blood sampled from patients at 60 (36.5+/-11.2, 37.8+/-12.1), or 120 min (53.1+/-17.1, 50.0+/-12.2) of anaesthesia and on the first day (37.8+/-15.1, 35.2+/-15.7) after anaesthesia in SVF and ISF treated groups, respectively. Removal of the DNA damage was observed after the third day of anaesthesia and the repair was completed within 5 days. The DNA damage detected in lymphocytes of patients during anaesthesia with SVF or ISF showed similar results as demonstrated by an increased mean comet migration at 120 min of anaesthesia and the cells were able to repair the induced DNA damage completely on the fifth postoperative day.

Production of compound A under low-flow anesthesia is affected by type of anesthetic machine

PURPOSE

The purpose was to compare the concentrations of compound A in inspired gas breathed by patients produced by different types of anesthetic machines under prolonged sevoflurane low-flow anesthesia.

METHODS

The anesthetic machines tested were Excel 210 SE (Datex-Ohmeda, Louisville, CO), Cicero (Dräger, Lübeck, Germany), and AS/3 ADU (Datex-Ohmeda, Louisville, CO). Anesthesia expected to last more than four hours was maintained with 2.0% sevoflurane and nitrous oxide (0.5 L x min(-1))/oxygen (0.5 L x min(-1)). The concentrations of compound A, obtained from the inspiratory limb of the circle system, were measured using a gas chromatograph.

RESULTS

When Excel and Cicero were used, concentrations of compound A increased steadily from the baseline values to 28 and 29 (mean) ppm, respectively, at two hours after exposure to sevoflurane and became constant. There was no significant difference between the concentrations of compound A produced by these anesthetic machines. In contrast, the new anesthetic machine AS/3 was associated with lower concentrations of compound A (6 ppm at one hour, P <0.05 compared with Excel and Cicero), and the concentration did not change significantly thereafter.

CONCLUSION

In spite of the use of a conventional carbon dioxide (CO2) absorbent with strong bases, the anesthetic machine AS/3 with a small volume of canister/soda lime (900 ml/700 ml) produced lower concentrations of compound A than those produced by the other machines.

Primate anesthesia

This article provides an update on some of the recent advances in primate anesthesia. It focuses in particular on some of the newest information available regarding the effects of opioids and alpha-2 agonists in primates, and how these effects are different from what we might expect in other companion animals. It reviews the important properties of the latest induction and inhalation agents, and stresses the need for continuous monitoring of the anesthetized patient.

Sevoflurance: approaching the ideal inhalational anesthetic. a pharmacologic, pharmacoeconomic, and clinical review

Sevoflurane is a safe and versatile inhalational anesthetic compared with currently available agents. Sevoflurane is useful in adults and children for both induction and maintenance of anesthesia in inpatient and outpatient surgery. Of all currently used anesthetics, the physical, pharmacodynamic, and pharmacokinetic properties of sevoflurane come closest to that of the ideal anesthetic (200). These characteristics include inherent stability, low flammability, non-pungent odor, lack of irritation to airway passages, low blood:gas solubility allowing rapid induction of and emergence from anesthesia, minimal cardiovascular and respiratory side effects, minimal end-organ effects, minimal effect on cerebral blood flow, low reactivity with other drugs, and a vapor pressure and boiling point that enables delivery using standard vaporization techniques. As a result, sevoflurane has become one of the most widely used agents in its class.

The effects of prolonged low-flow sevoflurane anesthesia on renal and hepatic function

We assessed the effects of prolonged low-flow sevoflurane anesthesia on renal and hepatic functions by comparing high-flow sevoflurane with low-flow isoflurane anesthesia. Thirty patients scheduled for surgery of > or =10 h in duration randomly received either low-flow (1 L/min) sevoflurane anesthesia (n = 10), high-flow (6-10 L/min) sevoflurane anesthesia (n = 10), or low-flow (1 L/min) isoflurane anesthesia (n = 10). We measured the circuit concentrations of Compound A and serum fluoride. Renal function was assessed by blood urea nitrogen, serum creatinine, creatinine clearance, and urinary excretion of glucose, albumin, protein, and N:-acetyl-beta-D-glucosaminidase. The hepatic function was assessed by serum aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alkaline phosphatase, and total bilirubin. Compound A exposure was 277 +/- 120 (135-478) ppm-h (mean +/- SD [range]) in the low-flow sevoflurane anesthesia. The maximum concentration of serum fluoride was 53.6 +/- 5.3 (43.4-59.3) micromol/L for the low-flow sevoflurane anesthesia, 47.1 +/- 21.2 (21.4-82.3) micromol/L for the high-flow sevoflurane anesthesia, and 7.4 +/- 3.2 (3.2-14.0) micromol/L for the low-flow isoflurane anesthesia. Blood urea nitrogen and serum creatinine were within the normal range, and creatinine clearance did not decrease throughout the study period in any group. Urinary excretion of glucose, albumin, protein, and N:-acetyl-beta-D-glucosaminidase increased after anesthesia in all groups, but no significant differences were seen among the three groups at any time point after anesthesia. Lactate dehydrogenase and alkaline phosphatase on postanesthesia Day 1 were higher in the high-flow sevoflurane group than in the low-flow sevoflurane group. However, there were no significant differences in any other hepatic function tests among the groups. We conclude that prolonged low-flow sevoflurane anesthesia has the same effect on renal and hepatic functions as high-flow sevoflurane and low-flow isoflurane anesthesia.

IMPLICATIONS

During low-flow sevoflurane anesthesia, intake of Compound A reached 277 +/- 120 ppm-h, but the effect on the kidney and the liver was the same in high-flow sevoflurane and low-flow isoflurane anesthesia.

Separation and absolute configuration of the enantiomers of a degradation product of the new inhalation anesthetic sevoflurane

In a rebreathing anesthesia circuit, the inhaled anesthetic sevoflurane degrades into at least two products, termed "compound A" and "compound B." The enantiomer separation of the chiral compound B (1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane ) by capillary gas chromatography (cGC) using heptakis (2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin as chiral selector was studied. With this cyclodextrin derivative diluted in the polysiloxane PS 86, an unprecedented high separation factor alpha of 4.1 (at 30 degrees C) was found. Consequently, the enantiomers of compound B were isolated by preparative GC and their specific rotations were measured. In addition, their absolute configurations were determined by X-ray crystallography. To collect the X-ray data, single crystals of both enantiomers were grown in situ on the diffractometer. The levorotatory enantiomer B(-) has the R-configuration while the dextrorotatory enantiomer B(+) has the S-configuration. The elution order of the compound B enantiomers on heptakis (2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin is R before S.

The effects of sevoflurane on serum creatinine and blood urea nitrogen concentrations: a retrospective, twenty-two-center, comparative evaluation of renal function in adult surgical patients

Despite mounting clinical evidence that supports its safety, the question of the potential adverse effects of sevoflurane on renal function continues to generate some controversy. This study retrospectively evaluated pooled renal laboratory data from 22 different clinical trials that compared sevoflurane with three widely used anesthetics. The trials examined postoperative changes in serum creatinine and blood urea nitrogen levels from a total of 3, 436 ASA physical status I-IV adult surgical patients administered either sevoflurane (n = 1941) or a control drug (isoflurane, enflurane, or propofol; n = 1495) as the maintenance anesthetic. The incidences of increased serum creatinine and blood urea nitrogen concentrations were similar among patients administered sevoflurane and those administered control drugs. Additionally, no trends specific to sevoflurane were observed with respect to postoperative serum creatinine concentration and fresh gas flow rate, concurrent treatment with nephrotoxic antibiotics, or type of carbon dioxide absorbent.

IMPLICATIONS

Our data for changes in serum creatinine and blood urea nitrogen indicate that, for exposures of less than 4 minimum alveolar anesthetic concentration/h, sevoflurane is not associated with an increased risk of renal toxicity compared with other commonly used anesthetics. For clinical purposes, the pre- to postoperative changes in serum creatinine and blood urea nitrogen are appropriate measures of renal function in surgical patients.

Dose-dependent metabolism of fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether (compound A), an anesthetic degradation product, to mercapturic acids and 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid in rats

The volatile anesthetic sevoflurane is degraded in anesthesia machines to fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether (FDVE), to which humans are exposed. FDVE is metabolized in rats and humans to two alkane and two alkene glutathione S-conjugates that are hydrolyzed to the corresponding cysteine S-conjugates. The latter are N-acetylated to mercapturic acids, or bioactivated by renal cysteine conjugate beta-lyase to metabolites which may react with cellular macromolecules or hydrolyze to 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid. FDVE causes nephrotoxicity in rats, which evidence suggests is mediated by renal uptake of FDVE S-conjugates and metabolism by beta-lyase. Although pathways of FDVE metabolism have been described qualitatively, the purpose of this investigation was to quantify FDVE metabolism via mercapturic acid and beta-lyase pathways. Fischer 344 rats underwent 3-h nose-only exposure to FDVE (0 +/- 0, 46 +/- 19, 98 +/- 7, 150 +/- 29, and 220 +/- 40 ppm), and urine was collected for 24 h. Urine concentrations of the mercapturates, N-acetyl-S-(1,1,3,3, 3-pentafluoro-2-fluoromethoxypropyl)-L-cysteine and N-acetyl-S-(1-fluoro-2-fluoromethoxy-2-(trifluoromethyl)vinyl)-L- cysteine, the beta-lyase-dependent metabolite 3,3, 3-trifluoro-2-(fluoromethoxy)propanoic acid, and its degradation product trifluorolactic acid, were determined by GC/MS. There was dose-dependent urinary excretion of the alkane mercapturate N-acetyl-S-(1,1,3,3,3-pentafluoro-2-fluoromethoxypropyl)-L- cysteine and 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid, while excretion of the alkene mercapturate N-acetyl-S-(1-fluoro-2-fluoromethoxy-2-(trifluoromethyl)vinyl)-L- cysteine plateaued at higher FDVE exposures. The alkane:alkene mercapturic acid excretion ratio was between 2:1 and 4:1. Trifluorolactic acid was only rarely observed. Urine excretion of the beta-lyase-dependent metabolite 3,3, 3-trifluoro-2-(fluoromethoxy)propanoic acid was 10-fold greater than that of the combined mercapturates. Results show that FDVE cysteine S-conjugates undergo facile metabolism via renal beta-lyase, particularly in comparison with detoxication by mercapturic acid formation. The quantitative assay developed herein may provide a biomarker for FDVE exposure and relative metabolism via toxification and detoxifying pathways, applicable to animal and human investigations.

Carbon dioxide absorption: toxicity from sevoflurane and desflurane

The degradation of volatile anaesthetics by desiccated carbon dioxide absorbents can result in adverse outcomes. Desiccated carbon dioxide absorbent reacting with desflurane can cause potentially life-threatening intraoperative carbon monoxide exposure; the reaction with sevoflurane can cause the formation of several toxic breakdown products, e.g. compound A. Compound A-related renal toxicity in humans is still a matter of controversy.

Comparison of renal function following anesthesia with low-flow sevoflurane and isoflurane

STUDY OBJECTIVE

To evaluate postoperative renal function after patients were administered sevoflurane under conditions designed to generate high concentrations of compound A.

STUDY DESIGN AND SETTING

A multicenter (11 sites), multinational, open-label, randomized, comparative study of perioperative renal function in patients who have received low-flow (< or = 1 L/min) sevoflurane or isoflurane.

PATIENTS

254 ASA physical status I, II and III patients requiring endotracheal intubation for elective surgery lasting more than 2 hours.

INTERVENTIONS

After induction, low-flow anesthesia was initiated at a flow rate < or = 1 L/min. Blood and urine samples were studied to assess postoperative renal function.

MEASUREMENTS AND MAIN RESULTS

Measurements of serum BUN and creatinine, and urine glucose, protein, pH, and specific gravity were used to assess renal function preoperatively and up to 3 days postoperatively. Serum inorganic fluoride ion concentration was measured at preinduction, emergence, and 2, 24 and 72 hours postoperatively. Compound A concentrations were measured at two sites for those patients receiving sevoflurane. Adverse experience data were analyzed. One hundred eighty-eight patients were considered evaluable (98 sevoflurane and 90 isoflurane). Peak serum fluoride concentrations were significantly higher after sevoflurane (40 +/- 16 microM) than after isoflurane (3 +/- 2 microM). Serum creatinine and BUN decreased in both groups postoperatively; glucosuria and proteinuria occurred in 15% to 25% of patients. There were no clinically significant differences in BUN, creatinine, glucosuria, and proteinuria between the low-flow sevoflurane and low-flow isoflurane patients.

CONCLUSIONS

There were no statistically significant differences in the renal effects of sevoflurane or isoflurane in surgical patients undergoing low-flow anesthesia for up to 8 hours. Low-flow sevoflurane anesthesia under clinical conditions expected to produce high levels of compound A appears as safe as low-flow isoflurane anesthesia.

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.

Humidification during low-flow anesthesia in children

PURPOSE

The aim of this study was to compare the effect of low-flow anesthesia with or without a heat and moisture exchanger with high-flow anesthesia on airway gas humidification in children.

METHODS

One hundred twenty children were randomly assigned to one of three groups: low-flow anesthesia with 0.5l·min^-1 of total gas flow (LFA,n=40), low-flow anesthesia with 0.5l·min^-1 using a heat and moisture exchanger (HME,n=40), and high-flow anesthesia with 6l·min^-1 (HFA,n=40). The temperature and relative humidity of the inspired gas were measured throughout anesthesia.

RESULTS

The relative humidity of the inspired gas in the HME group was increased compared with that of the LFA and HFA groups 20 min after induction (p<0.05). The airway humidification in the LFA group was higher than that in the HFA group 10 min after induction (p<0.05). The temperature of the inspired gas in the HME group was increased compared with that in the LFA and HFA groups after 70 min (P<0.05).

CONCLUSION

Low-flow anesthesia is less effective in providing adequate humidification of inspired gas than low-flow anesthesia with a heat and moisture exchanger, but significantly better than high-flow anesthesia in children.