Chapter 11 – Anesthetics

Overview

  • Anesthetics: Drugs that reduce or eliminate pain by depressing CNS/PNS nerve function.

  • Anesthesia = state of reduced neurologic function.

    • General anesthesia:

      • Complete loss of consciousness & reflexes.

      • Respiratory muscles paralyzed → requires ventilatory support.

    • Local anesthesia:

      • No paralysis of respiration.

      • Blocks pain sensation in innervated tissues.

    • Monitored Anesthesia Care (MAC):

      • Local + sedation + analgesia.

      • Patient remains responsive, protects airway, and can be discharged soon after.

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General Anesthetics

  • Indications:

    • Surgical procedures, ECT therapy.

  • Administration:

    • Inhalational: volatile liquids/gases (e.g., sevoflurane, nitrous oxide).

    • Parenteral: IV (e.g., propofol, ketamine, etomidate).

    • Adjunct drugs: “helper drugs” (opioids, benzodiazepines, anticholinergics, antiemetics, NMBDs).

  • Balanced anesthesia = combination of drugs for better effect and fewer adverse reactions.

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Mechanism of Action

  • Overton-Meyer theory:

    • Potency ∝ lipid solubility.

    • Lipid-soluble anesthetics cross BBB easily → CNS depression.

  • Effects: Progressive reduction in sensory & motor CNS function.

    • Loss of sight, touch, taste, smell, hearing → unconsciousness.

    • Cardiac/pulmonary functions last to be affected.

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Contraindications

  • Known allergy.

  • Drug-specific: pregnancy, narrow-angle glaucoma, acute porphyria.

  • History/susceptibility to malignant hyperthermia.

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Adverse Effects

  • General: Myocardial depression, hypotension, respiratory depression, hepatic/renal effects.

  • Malignant Hyperthermia:

    • Triggered by inhaled anesthetics + succinylcholine.

    • Signs: ↑ temperature (>104°F), tachycardia, tachypnea, rigidity.

    • Treatment: dantrolene + supportive care.

  • Postoperative nausea & vomiting (PONV): common complication.

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Toxicity & Overdose

  • Risk: Cardiac/respiratory arrest.

  • Rare in practice (controlled settings, fast metabolism).

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Drug Interactions

  • Antihypertensives → ↑ hypotension.

  • Beta blockers → ↑ myocardial depression.

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Key Drug Profiles

  • Dexmedetomidine (Precedex):

    • Alpha2 agonist, sedation without respiratory depression.

    • Used in ICU, short surgeries, alcohol withdrawal.

  • Ketamine:

    • Dissociative anesthesia, NMDA antagonist.

    • Good for asthma (bronchodilator).

    • Can cause hallucinations (↓ with benzodiazepines).

  • Nitrous Oxide:

    • Only inhaled gas used.

    • Weak; mostly dental/minor procedures.

  • Propofol (Diprivan):

    • IV general anesthetic.

    • Used for induction/maintenance, ICU sedation, moderate sedation.

    • Monitor triglycerides (lipid-based).

  • Sevoflurane (Ultane):

    • Widely used inhaled volatile anesthetic.

    • Rapid onset & elimination.

    • Non-irritating, useful in pediatrics.

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Moderate Sedation

  • AKA conscious/procedural sedation.

  • Combines benzodiazepine (midazolam) or propofol + opioid (fentanyl, morphine).

  • Patient relaxed, some amnesia, maintains airway & response to commands.

  • Used for diagnostic & minor surgical procedures.

  • Safer profile, rapid recovery.

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Local Anesthetics

  • Mechanism: Block nerve conduction in specific body regions.

  • Forms:

    • Topical (creams, drops).

    • Parenteral (nerve block, infiltration, epidural, spinal).

  • Drug examples: lidocaine (most common), bupivacaine, ropivacaine.

  • Adverse effects:

    • Rare, but may occur with inadvertent IV injection, overdose, allergy.

    • “Spinal headache” with spinal anesthesia.

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Neuromuscular Blocking Drugs (NMBDs)

  • Purpose: Paralyze skeletal muscles (including diaphragm → requires ventilation).

  • Types:

    • Depolarizing: succinylcholine (causes flaccid paralysis).

    • Nondepolarizing: rocuronium, vecuronium, pancuronium.

  • Effects:

    • Sequence: fingers/eyes → limbs → trunk → respiratory muscles.

    • Recovery in reverse.

  • Contraindications/adverse effects: malignant hyperthermia, respiratory paralysis.

  • Antidotes: anticholinesterase drugs (neostigmine, pyridostigmine, edrophonium).

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Nursing Implications

  • Assessment: History (anesthesia reactions, allergies, meds, alcohol/illicit use). Baseline VS, labs, ECG, O₂ sat.

  • Intraoperative: Monitor VS, ABCs, malignant hyperthermia signs.

  • Recovery: Monitor for CV/respiratory depression, reorient, implement safety.

  • Teaching: Turning, coughing, deep breathing post-op