anesthsia general

Undesirable Reflex Suppression

  • Describes the functions related to consciousness and loss of consciousness.

  • Notable components include:

    • Thalamus

    • Cortex

  • Amnesia affects conscious awareness; primarily associated with:

    • Prefrontal cortex

    • Hippocampus

    • Medial amygdala (mentioned by some researchers)

  • Analgesia achieved through blocking spinal cord pain pathways.

Stages of General Anesthesia

  • General anesthesia is divided into four main stages:

    1. Induction:

    • Patient transitions to unconsciousness.

    1. Excitement (historically):

    • Not commonly seen in modern anesthesia; previous practice experienced a state of involuntary muscle movement due to inhibition depression.

    • Example: Reflexive movements akin to a decapitated chicken.

    1. Surgical Anesthesia:

    • Characterized by reduced muscle tone and reflexes.

    • Important to manage subdivisions within this stage for surgical needs.

    • Sub-stages require orchestration during larger operations.

  • Sleep and Anesthesia Similarities:

    • Analgesics might induce a relaxed state but lack consciousness.

Compounds Used in General Anesthesia

Main Groups of Anesthetic Compounds

  1. GABA Receptor Modulators:

    • Example: Propofol

    • GABA A receptor: GABA-gated chloride channel

    • Induces hyperpolarization via inhibitory post-synaptic potentials (IPSPs).

    • Function: Reduces neuron firing and connectivity between brain areas, causing unconsciousness.

    • Propofol:

      • Appearance: Milky substance.

      • Induces unconsciousness in less than a minute due to its lipophilicity.

      • Fast brain absorption; redistribution occurs to fat tissue later, causing a temporary effect.

      • Mechanism:

      • Allosteric potentiator (does not directly bind to GABA; modifies receptor actions).

      • Mixed effects include increasing potency and efficacy of GABA, can even activate channels independently at high doses.

  2. Benzodiazepines and Barbiturates:

    • Work synergistically with GABA but no longer popular for induction; benzodiazepines are safer with clear antidotes available.

    • Barbiturates increase GABA efficacy, making binding more effective.

    • Benzodiazepines enhance GABA potency even at low concentrations.

  3. NMDA Receptor Inhibitors:

    • Example: Ketamine

    • Effect: Works as an antagonist on NMDA receptors, influencing analgesia.

    • Additional targets likely due to varying pharmacological behaviors across drugs and effects on potassium channels, enhancing resting potential.

    • Adverse effects: Can cause hypertension and tachycardia.

Anesthesia Practical Considerations

Propofol Indication

  • Adverse effects: Does not provide analgesia; often supplemented with opioids (such as fentanyl).

  • Distribution phases include:

    • Phase Distribution: Distinct pharmacokinetics due to fat tissue absorption.

    • Elimination Half-Life: Redistribution phase (2-8 minutes); later, liver metabolism and kidney excretion (around an hour).

  • Utilized effectively for quick procedures and prolonged ICU sedation using constant drip.

Volatile Anesthetics

  • Commonly used for maintaining anesthesia post-induction.

  • Examples: Halothane, Nitro oxide, Xenon

  • Mechanism of action: Effects on various targets, interactions with GABA, NMDA receptors, and unknown channels.

  • Monitoring: Must be precise, with emphasis on minimal alveolar concentration (MAC), determining human response efficacy.

  • Importance of blood solubility analyzed to explain the rate of induction and recovery.

Comparison of Anesthetic Techniques

General Anesthesia Advantages

  • High success rate (nearly 100%).

  • No need for patient cooperation, ideal for unresponsive patients.

  • Rapid onset.

  • Excellent control of anesthesia depth.

General Anesthesia Disadvantages

  • Risk factors associated with hemodynamic stability.

  • Necessitates an anesthetic team for administration.

Conclusive Notes on Anesthetic Profiles

  • Malignant Hyperthermia:

    • Genetic predisposition causing calcium release; notable in operations using halothane.

    • Symptoms: Elevated body temperature due to intensive muscle activity.

    • Treatment: Directly involves agent-induced suppression or cooling strategies.

Additional Anesthetic Considerations

  • Reversal Agents: Used to counteract effects of opioids, benzodiazepines, etc., introducing rapid responsiveness.

  • Monitoring Vital Signs: Critical given overarching depressant effects of anesthetics on the cardiovascular system.

Summary of Anesthetic Drug Properties

  • Comparison across anesthetics according to solubility, MAC values, and pharmacodynamics to ensure contextual appropriate usage in diverse clinical settings.

  • Choose drugs tailored to specific patient needs and procedure requirements to optimize outcomes.

  • Consider additional adjuncts for optimal sedation and response control.