General anesthetics are drugs that induce a reversible loss of consciousness.
They are used during surgical procedures to render the patient unconscious, unresponsive, and incapable of feeling pain.
General anesthetics can be administered intravenously or through inhalation.
Stages of General Anesthesia
General anesthesia is typically described as having four stages, from the onset of anesthesia to complete recovery.
1.Stage 1 (Analgesia or Induction):
This is the period between the initial administration of the anesthetic and the loss of consciousness.
The patient is awake and conversant, but pain threshold increases.
2.Stage 2 (Excitement or Delirium):
This is the period between the loss of consciousness and the onset of automatic breathing.
It is characterized by irregular breathing, increased heart rate, and involuntary movement.
3.Stage 3 (Surgical Anesthesia):
This is the period of surgery where the patient has no reflexes and is unconscious.
Breathing becomes regular, and movements cease.
4.Stage 4 (Overdose):
This is a dangerous and potentially lethal stage characterized by severe brain depression leading to cessation of respiration and potential circulatory failure.
Classification of General Anesthetics:
General anesthetics are classified based on their administration method and their chemical structure.
Here's a classification focused on the method of administration and some examples:
1. Inhalation Anesthetics:
These are gases or volatile liquids that produce anesthesia when inhaled. They are commonly used for their ease of control and pleasant induction characteristics.
Halothane*
Methoxyflurane
Enflurane
Sevoflurane
Isoflurane
Desflurane
2.Intravenous Anesthetics:
These are administered through the bloodstream and are often used for the induction of anesthesia, followed by maintenance with an inhalation agent.
A.Ultra-Short Acting Barbiturates:
These act on the central nervous system to produce unconsciousness rapidly.
Methohexital sodium*
Thiamylal sodium
Thiopental sodium
B.Dissociative Anesthetics:
These provide analgesia and amnesia without complete loss of consciousness.
Ketamine hydrochloride*