Tag Archives: speed of onset

Volatile Anesthetics

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In this tutorial we review the modern volatile anesthetic agents used in everyday anesthesia practice: sevoflurane, desflurane and isoflurane. We begin by explaining the key pharmacological concepts that every anesthesia trainee should understand, including blood-gas partition coefficient, oil-gas partition coefficient, tissue-blood partition coefficient, potency, onset of action, emergence, and minimum alveolar concentration (MAC). We also show how MAC is applied in routine clinical practice to achieve and maintain an appropriate depth of anesthesia.

The tutorial then compares the three commonly used volatile agents, highlighting their individual advantages and limitations, including speed of induction and recovery, metabolism, pungency, suitability for inhalational induction, and low-flow anesthesia. Finally, we examine their physiological effects on the brain, spinal cord, respiratory system, cardiovascular system, and other organ systems, explaining why these effects matter during routine anesthesia.

Ions & The pKa – Local Anesthetics, Opioids and Midazolam

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You may think that this whole ionization and pKa stuff is of little relevance to you as a clinician working in ED, Anesthesiology or ICU, but you are mistaken. The pH of blood (whether or not the [H+] exceeds the [OH-] has major impact on the pharmacokinetics of certain drugs. Moreover, some drugs rely on a differential between extracellular and intracellular pH to be effective.

This tutorial looks at the pharmacology of three types of drugs impacted by pH. These drugs are local anesthetics, opioids and the benzodiazepine – midazolam. All of these agents are weak bases whose degree of ionization varies with pH.

  1. Speed of onset is related to the pKa – the lower the pKa of weak bases the more rapid the onset of action
  2. Duration of action is related to protein binding – particularly albumin (there are other proteins). Albumin depletion is common in critical illness, leading to higher bioavailability and shorter duration of action.
  3. Potency is related to lipid solubility. Fentanyl is highly potent because of this.

This tutorial is supplementary to the acid base course. The material is ESSENTIAL for trainees and practitioners in Anesthesiology and Dentistry. @ccmtutorials http://www.ccmtutorials.org