Week #9 as a CRNA Student- Meet Iso, Sevo and Des

by admin

If you are an Anesthesia Provider or want to be one, prepare to earn three new best friends:

Desflurane, Isoflurane and Sevoflurane

Volatile Inhalation Agents

Most of the drugs used in Anesthesia are drugs that you have probably heard of before.  BUT, if you’re like me, you had zero knowledge regarding your “gases.”  These are more professionally referred to as “agents” or “volatiles.”

Our volatile agents are housed and delivered via VaporizersVaporizers are agent-specific, meaning you cannot fill one with Sevo one day and then fill it with Iso the next.  Desflurane (because of its high partial pressure and the fact that it basically evaporates at room temperature) is delivered in a special vaporizer.  They are color coded to help prevent medication errors.  They also utilize a keyed filling system, making it nearly impossible for you to fill an Isoflurane Vaporizer with Sevoflurane.

Most of the volatile agents are similar in action and produce unconsciousness and a little bit of muscle relaxation.  The mechanism of action is unknown but they are believed to act at several different sites in the Central Nervous System (CNS).

Providers frequently choose one over the other based on cost.  Desflurane is the most expensive, followed by Sevoflurane and then Isoflurane.  If anyone knows what these agents actually cost- feel free to comment!  I’ve heard varying numbers…

Desflurane and Isoflurane are also considered respiratory irritants (Des more so than Iso).  On inhalation with these agents, patients will cough and may potentially laryngospasm if their airway reflexes are still intact.  Sevoflurane, on the other hand, has a sweeter odor and is almost always used during a mask induction with pediatric patients who do not really like it so much when you come at them with any type of sharp object.

MAC- Minimum Alveolar Concentration

When you refer to any other drug, you typically use grams/mg/mcg, etc.  With our inhalation agents, we use MAC %.  The definition of MAC is the minimum alveolar concentration that prevents 50% of patients from responding purposefully to noxious stimuli- e.g. when they are cut with a scalpel 50% of people won’t jump off the OR bed.  *(The percent is the percentage of 1 atmosphere)

  • Sevoflurane MAC is 2%
  • Isoflurane MAC is 1.15%
  • Desflurane MAC is 5.8%

Some side notes regarding inhalation agent administration…

Just because the MAC of Sevoflurane is 2% doesn’t mean you always have to give 2%.  There is a synergistic effect with our inhalation agents and other drugs we give (opiods, benzodiazepines, etc.) which means we can give a smaller MAC of our agent.

If your patient is hypotensive, you may need to titrate down your agent.

At the end of the surgical procedure, you turn off your inhalation agent and turn up your oxygen to help flush the agent out of the patient’s lungs and brain.  Emergence (i.e. waking up from anesthesia) is usually fairly rapid depending upon the patient, the length of the case, and other pharmacologic interventions used.

More to come!  Like always, email admin “at” CRNAAcademy.com with questions and comments.

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