Comparison of plasma inorganic fluoride concentration with sevoflurane-N2O and enflurane-N2O anesthesia

Halogenated inhalational anaesthetics

The halogenated inhalational anaesthetics halothane, enflurane, isoflurane and desflurane can produce metabolic hepatocellular injury in humans to a variable extent. During metabolism of these anaesthetics, tissue acetylation occurs due to the formation of reactive intermediates. Proteins modified by acetylation may constitute neo-antigens with a potential for triggering an antibody-mediated immune response. The likelihood of suffering post-operative immune hepatitis depends on the amount of the anaesthetic metabolized and is thereby considerably less with enflurane, isoflurane or desflurane compared with halothane. Plasma inorganic fluoride concentrations are regularly increased after sevoflurane. Elevated inorganic fluoride concentrations have been associated with nephrotoxicity following methoxyflurane anaesthesia but not after sevoflurane. Another source of concern is the products of degradation from reactions with carbon dioxide absorbents. Most important is compound A, which has been shown to exhibit nephrotoxicity in rodents. However, no significant changes in renal function parameters have been reported in surgical patients.

Inhalational anesthetics: desflurane and sevoflurane

This article reviews the physico-chemical properties and performance characteristics of the two new potent inhaled anesthetics, desflurane and sevoflurane. Both drugs provide a greater degree of control of anesthetic depth and a more rapid immediate recovery from anesthesia than is currently available with other inhaled agents because of their decreased solubility. Desflurane is currently in widespread clinical use in the United States and parts of Europe. Compared with sevoflurane, it has the additional advantage of being extremely resistant to degradation and biotransformation. However, its pungent odor and tendency to irritate the respiratory tract make it unsuitable for inhalational inductions, and it has been linked to CO production in CO2 absorbents. The sympathetic nervous system activation that occurs with desflurane limits its use in patients with cardiac disease. Otherwise, its hemodynamic and physiologic effects are similar to those seen with isoflurane. Studies of the economics of using desflurane are mixed, although it may offer the advantage of shorter postoperative recovery time. Sevoflurane is currently in widespread clinical use in Japan and parts of South America. The FDA Advisory Panel has recently recommended approval of sevoflurane in the United States, and we can expect the drug to be clinically available in the United States in the second quarter of 1995. Compared with desflurane, sevoflurane has the additional advantage of being nonirritating to the airway; inhalational induction of anesthesia with sevoflurane is achieved rapidly and easily. The instability of sevoflurane with CO2 absorbents and its in vivo biotransformation produce potentially toxic byproducts. These byproducts, including Compound A and fluoride, have been extensively studied, and although the possibility for iatrogenic sequelae from sevoflurane exists, the likelihood of long-term toxicity appears quite low. Phase IV studies are indicated to determine the safety of administering sevoflurane (1) to renally impaired patients and (2) to any patient with fresh gas flows less than 2 L/min. Sevoflurane is otherwise very well tolerated and appears to offer the advantage of rapid and smooth induction and emergence from general anesthesia.