Let's Talk Sevoflurane

-

Physical Properties

SEVOFLURANE is halogenated with fluorine. 
SEVOFLURANE’s blood/gas partition coefficient is 0.65 . 
It's non-pungency & rapid increase in alveolar concentration make SEVOFLURANE an excellent choice for smooth & rapid inhalation inductions in peds & adult patients. 
In fact, you can achieve inhalation induction w/ 4% to 8% SEVOFLURANE in a 50% mixture of NITROUS OXIDE & O2 within 1 min. 
It has a low blood solubility thus a rapid decrease in alveolar concentration upon discontinuation & quicker emergence compared w/ ISOFLURANE (although not an earlier discharge from the PACU). 
SEVOFLURANE’s modest vapor P permits the use of a conventional variable bypass vaporizer.

Effects on Organ Systems

Cardiovascular

  • SEVOFLURANE mildly ↓ myocardial contractility.
  • SVR & BP decrease slightly less than w/ ISOFLURANE or DESFLURANE.
  • Because SEVOFLURANE causes little if any increase in HR, CO is not maintained as well as with ISOFLURANE or DESFLURANE.
  • SEVOFLURANE may prolong QT interval, the clinical significance of which is unknown. QT prolongation maybe manifests 60 min following anesthetic emergence in infants.

Respiratory

  • SEVOFLURANE decreases respiration & reverses bronchospasm to an extent similar to that of ISOFLURANE.

Cerebral

 

  • Similar to ISOFLURANE & DESFLURANE, SEVOFLURANE causes slight ↑in CBF & ICP at normocarbia, although some studies show a ↓in CBF. 
  • High[SEVOFLURANE] (>1.5 MAC) may impair autoregulation of CBF, thus allowing a ↓ in CBF during hemorrhagic hypotension. This effect on CBF autoregulation seems to be less pronounced than w/ ISOFLURANE.
  • Decreases CMRO2 .
  • Seizure activity has not been reported.

Neuromuscular

  • SEVOFLURANE produces adequate muscle relaxation for intubation of children following an inhalation induction.

Renal

  • SEVOFLURANE slightly decreases RBF. 
  • Its metabolism to substances associated with impaired renal tubule fxn (eg, ↓ concentrating ability).

Hepatic

  • SEVOFLURANE ↓ portal vein BF, but increases hepatic artery blood flow thus maintaining total hepatic BF & O2 delivery.
  • It is generally not associated with immune-mediated anesthetic hepatotoxicity.

Biotransformation & Toxicity

The liver microsomal enzyme P-450 (specifically the 2E1 isoform) metabolizes SEVOFLURANE at a rate 1/4 that of HALOTHANE (5% versus 20%), but 10 to 25 x that of ISOFLURANE  or DESFLURANE & may be induced with ethanol or phenobarbital pre-treatment.

The potential nephrotoxicity of the resulting increase in [F- ] > 50 μmol/L in ~ 7% of pts who receive SEVOFLURANE, yet clinically significant renal dysfunction has not been associated with SEVOFLURANE anesthesia. Nonetheless, there has been no association with peak F- levels following SEVOFLURANE & any renal concentrating abnormality.

Alkali such as barium hydroxide lime or soda lime (but not CaOH) can degrade SEVOFLURANE, producing another proven (at least in rats) nephrotoxic end product (compound A, fluoromethyl- 2,2-difluoro-1-[trifluoromethyl] vinyl ether) thus Accumulation of compound A increases with increasing respiratory gas T°, decreasing flow anesthesia, dry barium hydroxide absorbent (Baralyme), increasing [SEVOFLURANE] & anesthetics of long duration.

Most studies have not associated SEVOFLURANE with any detectable postop impairment of renal function that would indicate toxicity or injury. Nonetheless, some clinicians recommend that FGF be at least 2 L/min for anesthetics lasting more than a few hours & that SEVOFLURANE not be used in patients with preexisting renal dysfunction.

SEVOFLURANE can also be degraded into hydrogen fluoride by metal & environmental impurities present in manufacturing equipment, glass bottle packaging, & anesthesia equipment which can produce an acid burn on contact w/ respiratory mucosa. The risk of patient injury has been substantially decreased by inhibition of the degradation process by adding water to SEVOFLURANE during the manufacturing process and packaging it in a special plastic container with a  “Dear Provider” letter warning of isolated incidents of fire in the respiratory circuits of anesthesia machines with desiccated CO2 absorbent when SEVOFLURANE was used.

Contraindications

  •           Severe hypovolemia
  •           Susceptibility to malignant hyperthermia
  •           IC HTN


Comments

Post a Comment