Absence of renal and hepatic toxicity after four hours of 1.25 minimum alveolar anesthetic concentration sevoflurane anesthesia in volunteers

Cost analysis of three techniques of administering sevoflurane

Background. This study aimed to evaluate and compare total cost of sevoflurane and propofol for 1.0 MAC-hour of anaesthesia, employing three anaesthetic techniques. Methods. Adult patients scheduled for surgical procedures under general anaesthesia anticipated to last approximately an hour were randomized into three groups (n = 15 each), to receive anaesthesia using one of the following techniques: low flow technique involving induction with propofol, followed by sevoflurane delivered using initial fresh gas flows of 6 L/min till MAC reached 1.0 and then reduced to 0.5 L/min; alternate method of low flow entailing only a difference in fresh gas flow rates being maintained at 1 L/min throughout; the third technique involving use of sevoflurane for both induction and maintenance of anaesthesia. Results. Cost of sevoflurane to maintain 1 MAC-hour of anaesthesia was clinically least with low flow anaesthesia, though statistically similar amongst the three techniques. Once the cost of propofol used for induction in two of the three groups was added to that of sevoflurane, cost incurred was least with the technique using sevoflurane both for induction and maintenance of anaesthesia, as compared to low flow and alternative low flow techniques, a 26% and 32% cost saving, respectively (P < 0.05).

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.

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.

Inhalational anaesthesia

Sevoflurane and desflurane have important advantages over isoflurane and halothane. Disadvantages, which the clinician should keep in mind, include the degradation of both agents by soda lime under certain circumstances during closed circuit anaesthesia. As a result compound A and carbon monoxide (CO) may be generated in soda lime canisters and may be inhaled by patients. The extent to which this constitutes a significant problem during routine anaesthesia in humans is not clear. Recent developments in absorbent technology have the potential to reduce any hazard to negligible proportions. Other undesirable properties of the newer inhalation agents include agitation with sevoflurane in children and cardiovascular and airway effects with desflurane.

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 role of new anesthetic agents

The three anesthetic drugs introduced most recently to the market are sevoflurane, desflurane, and ropivacaine. Sevoflurane and desflurane are both inhalational anesthetic agents and ropivacaine is a local anesthetic agent. Sevoflurane provides a rapid onset and offset of action; it is well tolerated with little airway irritation. It is hemodynamically stable, with low potential for toxicity. Concerns about its interaction with soda lime during low-flow anesthesia with the production of Compound A have not proved to be a clinical problem. While desflurane also provides rapid onset and recovery from anesthesia, it is not as hemodynamically stable as sevoflurane, and also causes airway irritation. Ropivacaine is a unique local anesthetic in that it is supplied as the pure S-enantiomer. It is at least as effective as bupivacaine, with lower toxicity and less motor block for the same degree of sensory block.

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.