General anathesia (1).pptx

general anathesia

1. General Anesthesia Dr. Amany Mohamed Dr. Engy Reda Dr. Rana Hassan Doaa Mahmoud Othman Id 201817210

2. GENERAL ANESTHESIA : - Is a state characterized by unconsciousness, analgesia, amnesia, skeletal muscle relaxation, and loss of reflexes - Drugs used as general anesthetics are CNS depressants with actions that can be induced and terminated more rapidly than those of conventional sedative-hypnotics

3. Triad of General anesthesia

4.   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- F acilitation GABA receptor function . 3- Antagonize the action of the excitatory neurotransmitter glutamic acid on the N-methyl-aspartate (NMDA) receptor . 4- Causes membrane hyperpolarization (inhibitory action) by their activation of potassium channel . 5- A nesthetic decease the duration of opening nicotinic receptor – an action that decrease the excitatory effect of acetylcholine synapse

5.   Classic Stages of Anesthesia Stage 1: Analgesia decreased awareness of pain, amnesia ,without loss of consciousness Stage 2 : excitation 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.

6. Pre-anesthetic medication General anesthesia usually involves the administration of different drugs for premedication, induction of anesthesia and maintenance of anesthesia Premedication has two main aims : 1- The prevention of the parasympathomimetic effect of anesthesia ( bradicardia , brochial secretion ) 2- The reduction of anxiety or pain

7. 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 . The aim is to relieve apprehension and facilitate smooth induction . To supplement analgesic, amnesic action of anesthetics.To prevent bradycardia and secretion.

8. Phases of Anesthesia 1) Induction : putting the patient to sleep 2) Maintenance : keeping the patient asleep 3) Recovery : waking the patient up

9. C lassification of general anaesthesia

10. Inhaled Anesthetics Easily vaporized liquid halogenated hydrocarbons Administered as gases .

11. 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

12. 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

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

14. 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)

15. 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. Mechanism of action

16. 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 Ketamine

17. 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 . Xylazine

18. 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. Pharmacological effects

19. The speed of induction of anesthetic effects depends on several factors 1. Solubility The more rapidly a drug equilibrates with the blood, the more quickly the drug passes into the brain to produce anesthetic eflects 2.Inspired gas partial pressure 3.Ventilation rate 4. Pulmonary blood flow 5. Arteriovenous concentration gradient A high partial pressure of the gas in the lungs results in more rapid achievement of anesthetic levels in the blood. The greater the ventilation, the, more rapid is the rise in alveolar and blood partial presure of the agent and the onset of anesthesia At high pulmonary blood flows, the gas partial pressure rises at a slower rate, thus, the speed of onset of anesthesia is reduced. At low flow rates, onset is faster.