General Anesthetics
General anesthesia is a medically induced state of unconsciousness and insensitivity to pain, achieved through the administration of anesthetics. These drugs suppress the central nervous system (CNS), ensuring loss of awareness, memory, and pain sensation during surgical procedures.
Classification
- Parenteral (Intravenous) Anesthetics:
- Induction agents: Propofol, Etomidate, Thiopental, Methohexital
- Benzodiazepines: Midazolam, Diazepam
- Opioids: Fentanyl, Morphine
- Inhaled Anesthetics:
- Volatile agents: Sevoflurane, Isoflurane, Desflurane, Halothane
- Gaseous agent: Nitrous Oxide
Pharmacodynamics
- Parenteral Anesthetics:
- Induction agents (e.g., propofol, etomidate, thiopental, methohexital) act primarily by enhancing GABA at its receptors.
- Increased chloride ion influx → Neuronal hyperpolarization → Sedation and hypnosis.
- Benzodiazepines (e.g., midazolam, diazepam) also enhance GABAergic activity, leading to sedation and anxiolysis.
- Opioids (e.g., fentanyl, morphine) act on mu-opioid receptors, providing analgesia and mild sedation.
- Potential side effects: Respiratory depression, cardiovascular suppression.
- Inhaled Anesthetics:
- Work through multiple mechanisms:
- Potentiation of GABA and glycine receptors → CNS depression.
- Inhibition of NMDA receptors → Reduced excitatory neurotransmission.
- Disruption of synaptic transmission → Unconsciousness, amnesia, and immobility.
- Can cause vasodilation, myocardial depression, and respiratory suppression.