Types of Anesthesia

There are four main categories of anesthesia used for medical procedures:

• General Anesthesia: A state of controlled, reversible unconsciousness with loss of protective reflexes. The goals are amnesia (memory loss), analgesia (pain relief), unconsciousness, and muscle relaxation. It's used for major operations like cardiac or abdominal surgery.
• Regional Anesthesia: Blocks sensation to a large area of the body (e.g., a limb, or the lower half of the body). The patient can remain conscious.
  • Neuraxial Blocks: Injections near the spinal cord.
    • Spinal: Anesthetic injected directly into the cerebrospinal fluid (CSF) in the subarachnoid space. Provides a rapid, dense block.
    • Epidural: Anesthetic injected into the epidural space (outside the dura). Slower onset; a catheter can be left in place for continuous analgesia (e.g., during labor or post-op).
  • Peripheral Nerve Blocks: Anesthetic injected near a specific nerve or group of nerves (e.g., brachial plexus block for arm surgery).
• Monitored Anesthesia Care (MAC) / Sedation: Often called "twilight sleep." Induces a state of relaxation and sleepiness. The level can range from minimal (patient is awake but relaxed) to deep (patient is asleep but can breathe independently). Often combined with local or regional anesthesia.
• Local Anesthesia: Numbs a small, specific area by injecting an anesthetic (e.g., lidocaine) directly into the tissue. Used for minor procedures like suturing a cut or dental work.

Phases & Stages of General Anesthesia

1. Pre-operative Preparation:

   • Goal: Anxiolysis, amnesia, analgesia.
   • Agents: Benzodiazepines (Midazolam), Opioids (Fentanyl).

2. Induction:

   • Goal: Smooth transition from consciousness to unconsciousness.
   • IV Agents (most common):
     • Propofol: Standard, rapid onset.
     • Etomidate: For hemodynamically unstable patients (cardiovascular stability).
     • Ketamine: For hypotensive or bronchospastic patients.
   • Inhalation Agents: Primarily for pediatric induction (e.g., Sevoflurane).

3. Maintenance:

   • Goal: Maintain unconsciousness, analgesia, and muscle relaxation during surgery.
   • Agents:
     • Volatile Anesthetics: Sevoflurane, Isoflurane, Desflurane.
     • IV Anesthetics: Propofol infusion (Total Intravenous Anesthesia - TIVA).
     • Adjuncts:
       • Opioids (e.g., Fentanyl, Hydromorphone) for analgesia.
       • Neuromuscular Blocking Agents (NMBAs) (e.g., Rocuronium, Vecuronium) for muscle relaxation.

4. Emergence (Recovery):

   • Goal: Smooth return to consciousness and spontaneous breathing.
   • Process:
     • Discontinue maintenance anesthetics.
     • Reverse NMBAs if needed (Neostigmine + Glycopyrrolate; or Sugammadex for Rocuronium/Vecuronium).
     • Manage post-op pain (opioids) and nausea/vomiting (e.g., Ondansetron).