Sevoflurane
Physical properties :
- Sevoflurane was first synthesized in 1968
- Clinical used reported in 1971
- First used in a volunteer 1981
- Due to problem in biotransformation and stability with soda lime work was delayed
- The drug has been available for general clinical use since 1990
Uptake and distribution :
- Colorless, sweet smelling, non-irritating, non-flammable
- Oil/gas solubility coeff. = 47
- Blood/gas solubility coeff. = 0.69
- MAC = in adult 1.7-2%with oxygen
- MAC in nitrous oxide is 0.66
- MAC in children 2.6 in oxygen 2% in nitrous oxide
- Fastest induction & recovery
- It is stable and stored in amber colored bottle
- In the presence of water undergoes some hydrolysis this reaction also occur with soda lime
Action on respiratory system :
- Sevoflurane has low blood/gas partition coefficient the induction is faster than halothane and Isoflurane
- The rate of recovery is faster than halothane and Isoflurane but lesser than Desflurane
- Approximately 5% of the absorbed dose is metabolized in the liver to two main metabolites
- Hexafluroisoproanol and inorganic fluoride molecules which is excreted in the urine
- The fluoride molecules potentially nephrotoxic
Action on cardiovascular system :
- Non irritant to airway
- Dose dependent respiratory depression
- Reduce respiratory drive to hypoxemia and Hypercarbia
- The ventilatory depression associated with Sevoflurane may result from medullary respiratory center and depression of diaphragmatic function and contractility
- It relaxes bronchial smooth muscle but less than halothane
- Good in asthmatic and COPD
- Properties similar to Isoflurane
- Smaller effect on heart rate than Isoflurane
- Decrease peripheral vascular resistance but cardiac out put is well maintained
- Decrease oxygen consumption of myocardium because of mild depression of myocardial contractility, Less coronary vasodilator
- Little sensitization of myocardium to catecholamine
Action on CNS:
Action on Hepatic :
- CNS effect are similar to those of isoflurane and Desflurane
- Intracranial pressure increase in high inspired concentration but this effect is minimal over the 0.5-1.0 MAC
- Decrease cerebral vascular resistance and cerebral metabolic rate
- Renal effect
- Renal blood flow is well preserved with Sevoflurane
- Serum fluoride concentration has been reported greater than 50umol/L but renal toxicity is not reported
- Sevoflurane decrease portal vain blood flow but increase hepatic artery blood flow thus maintaining tootle hepatic blood flow and oxygen delivery
Musculoskeletal system :
Advantages:
- Sevoflurane potentiate NDMR to similar extent to isoflurane
- May trigger malignant hyperthermia in suspectible patient
- There is limited data on the use use of sevoflurane in the obstetric population
Disadvantages:
- Well tolerated (non-irritant, sweet odor), even at high concentrations, making this the agent of choice for inhalational induction
- Rapid induction and recovery (low blood:gas coefficient.
- Does not sensitize the myocardium to catecholamine as much as halothane
- Does not result in carbon monoxide production with dry soda lime
Contraindication :
- Less potent than similar halogenated agents.
- Interacts with CO2 absorbers. In the presence of soda lime (and more with baralyme lime) compound A (a vinyl ether) is produced which is toxic to the brain, liver, and kidneys
- About 5% is metabolized and elevation of serum fluoride levels has led to concerns about the risk of renal toxicity
- Postoperative agitation may be more common in children then seen with halothane
- Relative expensive
- Hypovolemic patient
- Malignant hyperthermia
- Intracranial hypertension
