GA

General Anesthesia

G A
Drug induced absence of perception of all sensation allowing surgery or other painful procedure to be carried out

Triad of General anaesthesia

Hypnosis
Analgesia
Muscle relaxation

Mechanism of action of general anesthesia 

1- old theory the anesthetic agent bind with lipid matrix of the nerve membrane , this lead to secondary changes in ion flux and interaction with membrane of the ligand – gated ion channel . 2- facilitation GABA receptor function. 3- Antagonise the action of the excitatory neurotransmitter glutamic acid on the N-methyl-aspartate (NMDA) receptor.

4- causes membrane hyper polarization (inhibitory action) by their activation of potassium channel. 5- anesthetic decease the duration of opening nicotinic receptor – an action that decrease the excitatory effect of acetylcholine synapse

Classic Stages of Anesthesia*

Stage 1: Analgesia decreased awareness of pain, amnesia ,without loss of consciousness excitation:Stage 2 delirium & excitation, enhanced reflexes, retching, incontinence, irregular respiration Stage 3: Surgical Anesthesia unconscious, no pain reflexes, regular respiration, BP is maintained Stage 4: Medullary Depression respiratory & CV depression requiring ventilation & pharmacologic support.
* Seen mainly with Ether. Not all stages are observed with modern GAs.

Pre-anesthetic medication

:It is the use of drugs prior to anesthesia to make it more safe and pleasant.To relieve anxiety – benzodiazepines.To prevent allergic reactions – antihistaminics.To prevent nausea and vomiting – antiemetics.To provide analgesia – opioids.To prevent Bradycardia and secretion – atropine.

Phases of Anesthesia

Induction: putting the patient to sleep Maintenance: keeping the patient asleep Recovery: waking the patient up

Anesthesiology

There are two types of anesthetics : Inhalational --- for maintenance Intravenous --- for induction and short procedures .

Gas
Volatile liquids*
Barbiturates
Opioids
Benzodiazepines
(nitrous oxide)
(halothaneisoflurane,desflurane, sevoflurane) Enflurane
(thiopental)
(midazolam)
(fentanyl)
(etomidate, propofol)
General Anesthetics
Inhalational
Parenteral
ketamin

Inhaled Anesthetics

Easily vaporized liquid halogenated hydrocarbons Administered as gases
(gas)

Properties of Inhaled anesthetics

Nitrous Oxide(N2O) laughing gas Good analgesia Weak anesthesia Less effect on respiratory and cardiovascular system. Rapid onset & recover Used along w/ other anesthetic; fast induction & recovery

Properties of Inhaled anesthetics

Enflurane Rapid induction and recovery Used for maintenance of anesthesia Less potent than halothen -good muscle relaxation less sanitization to the myocardium Metabolize into fluoride ion Decrease BP

Parenteral Anesthetics (IV)

Most commonly used drugs to induce anesthesia Barbiturates (Thiopental* & Methohexital) Benzodiazepines (Midazolam) Opioids (Morphine & Fentanyl) Propofol* Etomidate Ketamin

Ketamine

A “dissociative anesthetic”Characterized by: analgesia, amnesia, eyes open, involuntary limb movement,.(unconscious appear to be awake)Rapid onset and last for5-10 min.(short acting)

Mechanism of action

It is bind to NMDA (N-methyl-D-aspartate receptor ) and also stimulate the central sympathetic outflow which cause heart stimulation, increased blood pressure and cardiac output.

Ketamine

Used in children & young adults for short procedures Side Effects: 1-salivation, 2-hallucinations 3- & vivid dreams(adult) 4- stimulation of sympathetic nervous system cause tachycardia, increase blood pressure 5- reach to stage two of anesthesia only

Xylazine

It is used in veterinary medicine for many diagnostic and surgical procedures.It is α2 sympathomimetic agent, it act by activation of central α2 receptors which will cause reduction or depression in release of dopamine and norepinphrine.

Pharmacological effects

CNS depression and sedation (30-90 min). Analgesia which last (15-30 min). Muscle relaxation. Emesis Hypotension and brady cardia Decreased respiratory rate. recovery from effect usually takes 2-4 hr.

Methodology

recovery
Duration of anesthesia
Duration of analgesia
onset
agents
Ketamine only
Ketamine& xylazine



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