General Anesthetics

Definition of General Anesthetics:

• These are central nervous system (CNS) depressants that induce a reversible state of unconsciousness, analgesia, amnesia, muscle relaxation, and loss of reflexes to enable surgical procedures.

Stages of General Anesthesia (Guedel’s Classification for Inhaled Agents)

1. Stage I – Analgesia

   • Patient is conscious but drowsy
   • Perception of pain is reduced

2. Stage II – Excitement

   • Patient becomes unconscious
   • Irregular respiration, increased reflexes, involuntary movements

3. Stage III – Surgical Anesthesia

   • Regular respiration
   • Loss of reflexes, skeletal muscle relaxation
   • Suitable for surgery

4. Stage IV – Medullary Paralysis

   • Overdose stage
   • Severe respiratory and cardiovascular depression
   • Potentially fatal

Classification of General Anesthetics

1. Inhalational Anesthetics

   • Volatile Liquids: Halothane, Isoflurane, Sevoflurane, Desflurane
   • Gases: Nitrous Oxide, Xenon

2. Intravenous Anesthetics

   • Inducing Agents: Propofol, Thiopentone, Etomidate
   • Dissociative Agent: Ketamine
   • Benzodiazepines: Midazolam, Diazepam
   • Opioids: Fentanyl, Morphine

Mechanism of Action

• Although not fully understood, general anesthetics typically work by:
• Enhancing inhibitory neurotransmission (GABA)
• Suppressing excitatory transmission (glutamate)

Main mechanisms include:

• GABA-A receptor potentiation: Propofol, Isoflurane, Thiopental
• NMDA receptor inhibition: Ketamine, Nitrous Oxide
• Hyperpolarization of neurons: Via K⁺ channel activation or Cl⁻ influx → reduces neuronal excitability

Thank you for reading from Firsthope's notes, don't forget to check YouTube videos!