General anesthetics

Anaesthetics

1. GENERAL ANESTHETICS BY P.PAVITHRA M.Pharm I Year Dept. Of Pharmacology

2. GENERAL ANESTHETICS General Anaesthetics are drugs which produce Reversible loss of sensation and consciousness.

3. STAGES OF GENERAL ANESTHESIA : STAGE OF ANALGESIA: Starts from beginning of anesthetic inhalation and lasts up to loss of consciousness. Patient remains conscious , can hear and see. Amnesia develops at the end of this stage. Reflexes and Respiration is normal. STAGE OF DELIRIUM: From loss of consciousness to beginning of regular Respiration. Patient may shout ,struggle. Heart rate and BP increases.

4. SURGICAL ANAESTHESIA: Extends from onset of regular respiration t o cessation of Breathing. It may be distinguished into 4 planes PLANE 1 :Roving eye balls.This plane ends when eyes become fixed. PLANE 2 :Loss of corneal and laryngeal reflexes. PLANE 3 :Pupil starts dilating and light reflex is lost. PLANE 4 :Intercostal paralysis ,shallow abdominal respiration , dilated pupil. MEDULLARY PARALYSIS: Cessation of breathing to failure of circulation and death.

5. CLASSIFICATION OF GENERAL ANESTHETICS

6. inhalational anesthetics: 1.)volatile liquids: ETHER:(Diethyl ether) It is a highly volatile liquid, produces irritating vapours and are inflammable and explosive. Advantages: It can be used without any complicated apparatus. Potent anaesthetic and good analgesic. Disadvantages: Slow induction and recovery. Cardiac arrest and convulsion in children. Cross placental barrier.

7. HALOTHANE: Flourinated volatile liquid with sweet odour . supplied in amber coloured bottle Advantages: Potent anaesthetic Non-inflammable and non-irritant Rapid induction and recovery Disadvantages: Requires special apparatus Hypotension and arrhythmia Poor analgesic and muscle relaxation.

8. ENFLURANE: Non-inflammable with mild sweet odour Similar to halothane in action Disadvantages: Induces Seizures in deep anaesthesia and therefore not used now. Renal toxicity. ISOFLURANE: Isomer of enflurane and have similar properties but slightly more potent

9. 2.)GAS: NITROUS OXIDE: LAUGHING GAS Colourless odourless inorganic gas with sweet taste Advantages: Non-irritating and non-inflammable Rapid induction and recovery Very potent analgesic No nausea and vomiting Non-toxic to liver,kidney and brain Disadvantages: Not potent alone(supplementation) Hypoxia

10. INTRAVENOUS ANAESTHETICS: 1.)INDUCING AGENTS : THIOPENTONE SODIUM Ultra short acting barbiturate Highly soluble in water yielding a very alkaline solution ,which must be freshly prepared before injection. Advantages: Induction and recovery is rapid Disadvantages: Poor analgesic ,Weak muscle relaxant Uses: Thiopentone sodium is commonly used inducing agent. It can be employed as the sole anesthetic for short operations that are not painful.

11. PROPOFOL : Oily liquid employed as 1% emulsion. Advantages: Induction and recovery is rapid Lacks airway irritancy Disadvantages: Fall in BP,Bradycardia It is not approved for use in children; prolonged sedation,severe metabolic effects and heart failure even in adults. Uses: It is the drug of choice for sedating intubating patients in ICU. Patient acceptability is good.

12. Benzodiazepines: Diazepam : In addition to preanaesthetic medication ,BZD are now frequently used for inducing , maintaining and supplementing anesthesia as well as for conscious sedation . Relatively large doses are injected i.v produce sedation , amnesia and then unconscious in 5-10 min .

13. 2.) SLOWER ACTING DRUGS: DISSOCIATIVE ANAESTHESIA: KETAMINE: Is a Dissociative Anaesthetic as it produces a cataleptic state in which the patient appear to be awake but is detached from the environment and is unresponsive to pain. Unique drug ,because, it has Hypnotic, Analgesic and Amnesic efects No other drug has these 3 features. Advantages: Respiration is not depressed. Disadvantages: Heart rate , BP,Cardiac output increases. Uses: Used for operations on the head and neck.

14. OPIOID ANALGESIC: FENTANYL: High Potent opioid analgesic(mu receptor agonist) Short duration of action Rapid onset of action Disadvantages: Respiratory depression Uses: Used as supplement anaesthetics in Balanced Anaesthesia . Ideal for children and un-cooperative patients.

15. ALPHA -2 AGONIST : DEXMEDETOMIDINE and CLONIDINE: Action of central alpha-2 adrenergic receptor has been known to cause sedation and analgesia Clonidine causes anaesthesia Disadvantages: Respiratory depression. Hypotension ,dry mouth,bradycardia Uses: Critically ill/ventilated patients in ICU.