Methods in Medicine
SEVOFLURANE A NEW ERA IN INHALATION ANAESTHESIA
T
he search for new volatile inhalational anaesthetic agents still continues in quest of the "ideal inhalation anaesthetic" which should fulfill the criteria of non-inflammability, non-irritant, rapid in induction and emergence, lack of effects on vital functions, absence of organ toxicity and should be cost effective. Sevoflurane is the recently introduced volatile anaesthetic agent. The pharmacokinetics and pharmacodynamics of sevoflurane translate into several advantages over other inhalational anaesthetic agents being currently used in clinical practice. Sevoflurane is halogenated by fluoride ions exclusively, resulting in very low blood gas solubility and a favourable blood gas solubility coefficient and a pleasant odour. This property determines that in both adults and paediatric age group of patients, induction of anaesthesia is very rapid and smooth, alteration of depth of anaesthesia can be achieved very rapidly and emergence and recovery is much faster as compared to halothane or isoflurane, and is much less dependent on the duration of the anaesthesia. The patients are more alert in the early recovery period with sevotlurane than they are with either halothane or isoflurane. The vapour pressure and physical properties of sevoflurane permit the use of standard vaporizer technology. MAC value is 3.3% in neonates and reduces to 2.05% in adults and so high concentration of oxygen can be administered. Sevoflurane has been found to be cardio-stable, maintaining the cardiac output and lesser coronary dilatation than isoflurane. Its action on the central nervous system, renal and splanchnic vascular systems and hepatic function, compare well with those of isoflurane. Although it is a respiratory depressant, rapid elimination of sevoflurane results in less postoperative depression than halothane. It also relaxes bronchioles constricted by histamine and acetylcholine. It is neither teratogenic nor mutagenic. However, it's benefit to the mother and fetus is not yet fully established. Hence, the use of sevoflurane in pregnancy is not recommended till further evaluation.
Sevoflurane undergoes biotransformation in humans to less than 5% and the remaining compound is excreted unchanged by the lung. Inorganic fluorides. the primary product of biotransformation, undergo rapid urinary excretion. Various studies have failed to demonstrate renal injury with sevoflurane. It is associated with a very low incidence of side effects which are mild and transient. Advantages of sevoflurane over the other volatiles are. rapid and pleasant induction making it especially attractive for paediatric patients. It also results in faster recovery, time to emergence and response to commands. It potentiates the effects of sedatives. narcotics and non-depolarizing muscle relaxants. The dose of these agents may have to be reduced when used with sevoflurane. Cost factor - 250 ml bottle costs Rs.7100/- approximately. If used with low flows of upto llImin, the consumption is 11 ml per hour, which goes upto 33 ml per hour with a flow rate of 4Vmin. It does not appear to be cost effective despite several clinical advantages over others. However. by bringing new agents more can be learnt about older agents. A little compromise can be made for better safety of patients, as we still do not have the perfect anaesthetic for every patient. References 1. Wallin RF. Regan 8M. Napoli MD. Stem U. Sevoflurane. a
new inhalational anesthetic agent. Anesth Analg 1975;54: 758-66. 2. Smith I. Ding Y. White PF. Comparison of induction. Maintenance and recovery characteristics of Sevoflurane-Nilrous Oxide and Propofol-Sevoflurane-Nitrous Oxide and Propofol-Isoflurane-Nitrous Oxide. Anesth Analg 1992;74:253-9. 3. Eger EI II. New inhaled anesthetics. Anesthesiology. 1994; 80:906-22.
Contributed by Col PK ROY·, Surg Lt Cdr (Mrs) S GARG+ •Associate Professor. "Clinical Tutor. Department of Anaesthesiology and Critical Care Medicine. Armed Forces Medical College. Pune - 411 040.
SEVOFLURANE A NEW ERA IN INHALATION ANAESTHESIA
T
he search for new volatile inhalational anaesthetic agents still continues in quest of the "ideal inhalation anaesthetic" which should fulfill the criteria of non-inflammability, non-irritant, rapid in induction and emergence, lack of effects on vital functions, absence of organ toxicity and should be cost effective. Sevoflurane is the recently introduced volatile anaesthetic agent. The pharmacokinetics and pharmacodynamics of sevoflurane translate into several advantages over other inhalational anaesthetic agents being currently used in clinical practice. Sevoflurane is halogenated by fluoride ions exclusively, resulting in very low blood gas solubility and a favourable blood gas solubility coefficient and a pleasant odour. This property determines that in both adults and paediatric age group of patients, induction of anaesthesia is very rapid and smooth, alteration of depth of anaesthesia can be achieved very rapidly and emergence and recovery is much faster as compared to halothane or isoflurane, and is much less dependent on the duration of the anaesthesia. The patients are more alert in the early recovery period with sevotlurane than they are with either halothane or isoflurane. The vapour pressure and physical properties of sevoflurane permit the use of standard vaporizer technology. MAC value is 3.3% in neonates and reduces to 2.05% in adults and so high concentration of oxygen can be administered. Sevoflurane has been found to be cardio-stable, maintaining the cardiac output and lesser coronary dilatation than isoflurane. Its action on the central nervous system, renal and splanchnic vascular systems and hepatic function, compare well with those of isoflurane. Although it is a respiratory depressant, rapid elimination of sevoflurane results in less postoperative depression than halothane. It also relaxes bronchioles constricted by histamine and acetylcholine. It is neither teratogenic nor mutagenic. However, it's benefit to the mother and fetus is not yet fully established. Hence, the use of sevoflurane in pregnancy is not recommended till further evaluation.
Sevoflurane undergoes biotransformation in humans to less than 5% and the remaining compound is excreted unchanged by the lung. Inorganic fluorides. the primary product of biotransformation, undergo rapid urinary excretion. Various studies have failed to demonstrate renal injury with sevoflurane. It is associated with a very low incidence of side effects which are mild and transient. Advantages of sevoflurane over the other volatiles are. rapid and pleasant induction making it especially attractive for paediatric patients. It also results in faster recovery, time to emergence and response to commands. It potentiates the effects of sedatives. narcotics and non-depolarizing muscle relaxants. The dose of these agents may have to be reduced when used with sevoflurane. Cost factor - 250 ml bottle costs Rs.7100/- approximately. If used with low flows of upto llImin, the consumption is 11 ml per hour, which goes upto 33 ml per hour with a flow rate of 4Vmin. It does not appear to be cost effective despite several clinical advantages over others. However. by bringing new agents more can be learnt about older agents. A little compromise can be made for better safety of patients, as we still do not have the perfect anaesthetic for every patient. References 1. Wallin RF. Regan 8M. Napoli MD. Stem U. Sevoflurane. a
new inhalational anesthetic agent. Anesth Analg 1975;54: 758-66. 2. Smith I. Ding Y. White PF. Comparison of induction. Maintenance and recovery characteristics of Sevoflurane-Nilrous Oxide and Propofol-Sevoflurane-Nitrous Oxide and Propofol-Isoflurane-Nitrous Oxide. Anesth Analg 1992;74:253-9. 3. Eger EI II. New inhaled anesthetics. Anesthesiology. 1994; 80:906-22.
Contributed by Col PK ROY·, Surg Lt Cdr (Mrs) S GARG+ •Associate Professor. "Clinical Tutor. Department of Anaesthesiology and Critical Care Medicine. Armed Forces Medical College. Pune - 411 040.
