Pharmacology - GENERAL & LOCAL ANESTHETICS (MADE EASY)

Anesthesia is a reversible state induced by anesthetic drugs, leading to reduced or complete loss of pain response and sensations like consciousness during painful procedures. There are two primary types: general anesthesia, which affects the entire body causing loss of feeling and movement; and local anesthesia, which numbs only specific areas. General anesthesia progresses through four stages established in the 1930s but has since benefited from advancements in delivery methods and modern anesthetics that enhance onset speed and safety.

Anesthesia recovery involves four distinct stages. The first stage, induction, transitions the patient from consciousness to unconsciousness. In the second stage, excitement occurs due to CNS inhibition leading to involuntary movements and increased vital signs. The third stage is surgical anesthesia where muscle tone decreases and patients are unresponsive yet stable for surgery. Finally, in the fourth stage of medullary paralysis or overdose, critical respiratory and cardiovascular functions fail.

Mechanisms Behind General Anesthetics' Effects General anesthetics can lead to death if revival is delayed. Their mechanism of action involves multiple sites in the brain, causing reversible loss of consciousness through effects on the thalamus and reticular activating system, amnesia via hippocampus and prefrontal cortex interactions, and immobility from spinal cord influence. General anesthetics are categorized into three groups based on their ability to induce unconsciousness, immobility, or analgesia. The first group includes intravenous agents like Etomidate and Propofol that primarily promote unconsciousness by acting on GABA-A receptors but may cause side effects such as respiratory depression.

Diverse Groups of Anesthetic Agents The second group consists of Ketamine along with inhalation agents like Nitrous Oxide which provide significant analgesia but weaker unconsciousness; they mainly act through NMDA receptor inhibition affecting pain modulation while also influencing potassium channels for sedative effects. Side effects include hypertension from Ketamine or dizziness from Nitrous Oxide. The third group features halogenated volatile anesthetics known for diverse mechanisms producing potent immobility; these affect various ion channels including GABA-A subunits different than those targeted by Group 1 drugs while sharing some similarities with Group 2's NMDA inhibition.

Dexmedetomidine is notable for its ability to provide sedation and analgesia without causing respiratory depression, unlike other general anesthetics. This effect stems from its action on presynaptic alpha-2 adrenergic receptors in the brain and spinal cord, which inhibits norepinephrine release, thereby reducing pain signals while inducing light sedation. Common side effects include bradycardia and hypotension, along with occasional transient hypertension due to weak peripheral vasoconstriction.

Local anesthetics provide a temporary loss of sensation, particularly pain, in specific body areas without inducing unconsciousness. They work by penetrating neuronal membranes and binding to receptors at voltage-gated sodium channels, blocking sodium influx which halts action potential conduction. Common local anesthetics include Bupivacaine, Lidocaine, Mepivacaine, Procaine, Ropivacaine, and Tetracaine. While generally safe when administered correctly, systemic toxicity can lead to symptoms like blurry vision or seizures.