L17.Anesthetics

Step 16: Anesthetics

  • Historical Context

    • General anesthesia was discovered in the mid-19th century.

    • Prior to anesthesia, surgeries were performed with no pain relief, causing extreme suffering and risk.

    • In 1846, dentist William Morton discovered the effects of sulfuric ether when inhaled.

    • Morton performed a public demonstration of anesthesia at Massachusetts General Hospital, successfully anesthetizing a patient for tumor removal, showcasing the efficacy of anesthesia.

  • Definition of Anesthesia

    • Anesthetic: Substance causing lack of feeling or awareness, essential for pain relief during surgeries.

    • Anesthesia: Condition of reversible unconsciousness or lack of sensation, induced by anesthetics.

    • Key effects:

      • Unconsciousness

      • Analgesia: Loss of pain sensation

      • Immobility

      • Amnesia: Loss of memory of the procedure

      • Maintains cardiovascular and respiratory functions.

  • Types of Anesthesia

    • Local Anesthesia:

      • Acts on nerve membranes for brief sensation loss without affecting consciousness.

    • General Anesthesia:

      • Affects the entire body, leading to complete unconsciousness.

      • Commonly administered via inhalation, though some are delivered intravenously (IV).

  • Stages of General Anesthesia

    1. Analgesia: Begins with agent administration, lasting until loss of consciousness.

    2. Delirium: Post-loss of consciousness, may feature excitement and irregular breathing; risk of hypertension and tachycardia.

    3. Surgical Anesthesia: Ongoing loss of consciousness with no natural respiration; divided into four planes monitored closely (pupil size, reflexes, etc.).

    4. Medullary Depression: Deepest stage, where brain function declines, and respiration/circulation cease; pupils are fixed and dilated.

  • Preanesthetic Medications

    • Administered to prepare the patient, typically from half an hour prior to surgery to the night before.

    • Advantages:

      • Reduces anxiety and pain

      • Promotes amnesia

      • Reduces secretions

    • Common preanesthetics include:

      • Benzodiazepines (e.g., diazepam, lorazepam)

      • Opioid analgesics (e.g., morphine)

  • Induction Anesthesia

    • Following preanesthetic medication, induction anesthesia induces a medically-induced coma.