GENERAL ANAESTHETIC AGENTS / DRUG WHICH INDUCES GENERAL ANAESTHESIA / DIFFERENT STAGES OF ANAESTHESIA
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This document discusses general anesthetics and the stages of anesthesia. It notes that general anesthetics produce reversible loss of sensation and consciousness by irregularly depressing the central nervous system from higher to lower functions. The four stages of anesthesia are then described: stage I involves analgesia and loss of consciousness; stage II involves excitement and delirium; stage III allows for surgery with regular breathing; and stage IV involves medullary paralysis and failure of vital functions. The document also discusses classifications of anesthetics including inhalational and intravenous agents, as well as pre-anesthetic medications that are used to reduce anxiety, provide amnesia and analgesia, decrease secretions, and reduce gastric acid.
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GENERAL ANAESTHETIC AGENTS / DRUG WHICH INDUCES GENERAL ANAESTHESIA / DIFFERENT STAGES OF ANAESTHESIA
- 2. GENERAL ANAESTHETICS “GENERAL ANAESTHETICS ARE DRUGS WHICH PRODUCE REVERSIBLE LOSS OF ALL SENSATION & CONSCIOUSNESS” It renders the patient LOSS OF ALL SENSATION ANALGESIC, SLEEP (UNCONSCIOUSNESS) AMNESIC, UNCONSCIOUSNESS, PROVIDE MUSCLE RELAXATION, IMMOBILITY & SUPRESSION OF UNDESIRABLE REFLEXES General anaesthesia is achieved by using combination of Inhaled & IV Drugs.
- 3. STAGES OF ANAESTHESIA GENERAL ANAESTHETICS: “IRREGULARLY DESCENDING DEPRESSION OF THE CNS” • Higher functions are lost first and progressively lower segments are affected • The vital centre's located in the medulla are paralysed the last as the depth of anaesthesia increases
- 4. GUEDEL (1920) described the four stages of anaesthesia I – STAGE OF ANALGESIA II – STAGE OF DELIRIUM III – SURGICAL ANAESTHESIA IV – MEDULLARY PARALYSIS
- 5. I - STAGES OF ANALGESIA Starts from: Beginning of anaesthetic inhalation lasts up to the loss of consciousness. Pain – Progressively Abolished. Patient remains conscious, can hear & see. At the end of this stage AMNESIA develops. Respiration & Reflexes – normal. Minor operations can be carried out in this stage.
- 6. II – STAGE OF DELIRIUM Stage starts from: Loss of consciousness lasts up to the: Beginning of regular respiration Excitement is produced in this stage Patient may Shout, Struggle, Increase in muscle tone, Jaws are tightly closed. Breathing is jerky Vomiting & involuntary defecation may occur Increase in HR & BP, Pupils are dilated
- 7. III - SURGICAL ANAESTHESIA Stage starts from: Onset of regular respiration lasts up to: Cessation of spontaneous Breathing This stage is divided in to FOUR PLANES PLANE 1: Roving eye balls, when eye balls become fixed this plane ends PLANE 2: Loss of corneal & laryngeal reflexes PLANE 3: Pupil- starts dilating & loss of light reflex PLANE 4: Intercostal muscle paralysis, Shallow abdominal breath, Dilated pupil
- 8. Deep Anesthesia: Muscle tone decreases, BP falls, HR increases, respiration decreases
- 9. IV – MEDULLARY PARALYSIS Stage starts from: Cessation of breathing lasts up to: Failure of circulation & death Pupils widely dilated Muscles tone are totally flabby Pulse – unpredictable BP – very low Medullary paralysis & death.
- 11. CLASSIFICATION INHALATIONAL ANAESTHETICS GAS Nitrous Oxide VOLATILE LIQUIDS Ether Halothane Enflurane Isoflurane Desflurane Sevoflurane
- 12. INTRA VENOUS ANAESTHETICS (iv) INDUCING AGENTS Thiopentone sod Methohexitone sod Propofol Etomidate SLOWER ACTING DRUGS BENZODIAZEPINES Diazepam Lorazepam Midazolam DISSOCIATIVE ANAESTHESIA Ketamine OPIOID ANALGESIA Fentanyl
- 13. INHALATION ANAESTHETICS: NITROUS OXIDE (N20) It is a potent analgesic but a weak anaesthetics Also known as Laughing Gas Unconsciousness cannot be produced in all patients Produced analgesic activity equal to that of morphine It is a poor muscle relaxant Frequently combined with other anesthetics Quick onset of action Smooth mixture of 70% N2O +25 – 30 % O2 + 0.2 – 2% another potent anesthetics is employed for most surgical procedures.
- 14. MECHANISM OF ACTION: GENERAL ANAESTHETICS INCREASE THE SENSITIVITY OF GABA-A RECEPTORS TO THE NEUROTRANSMITTER GABA MORE ENTRY OF CHLORIDE IONS IN TO THE NEURON HYPER POLARIZATION OF CELL & DIFFICULT TO DEPOLARIZE DECREASED NEURAL EXCITABILITY INDUCTION OF GENERAL ANAESTHESIA
- 15. PHARMOKINETICS: Non toxic to liver , kidney & brain Metabolism of N2O does not occur Removed from body by lungs Cheap & commonly used ADR: Arrhythmia Hypotension Hepatotoxicity
- 16. INTRAVENOUS ANAESTHETICS “INTRAVENOUS ANAESTHETICS ON IV INJECTION PRODUCE LOSS OF CONSCIOUSNESS IN ONE ARM BRAIN CIRCULATION TIME ( 11 SECONDS)” Generally used for the induction of anaesthesia because of rapidity of onset of action Induced anaesthesia is maintained by inhalation anaesthetic agent, It is supplemented with analgesics and muscle relaxants
- 17. THIOPENTONE SODIUM: Ultra short acting thiobarbiturate Highly soluble in water Must be prepared freshly before injection IV injection of 2.5% solution produces unconsciousness in 15-20 sec Highly lipid soluble drug so enters the brain immediately Consciousness retained in 6-10 min It is a poor analgesic Weak muscle relaxant BP falls immediatly after injection
- 18. PHARMACOKINETICS: Given through IV injection Undergo hepatic metabolism t ½ - 7-12 hrs ADR: Shivering Delirium Restlessness Nausea, Vomiting
- 20. PRE ANAESTHETIC MEDICATION “USE OF DRUGS BEFORE ANAESTHESIA TO MAKE IT MORE PLEASANT AND SAFE” AIMS OF PRE ANAESTHETIC MEDICATIONS: • Relief of anxiety & apprehension (anxiety or fear that something bad or unpleasant will happen) • Amnesia • Supplement analgesic action of anaesthetic agent, which facilitates the anaesthetic dose reduction • Decrease secretions and vagal stimulation caused by anaesthetics • Decrease the volume of gastric juice
- 21. SEDATIVE & ANTI ANXIETY DRUGS: Diazepam 5-10 mg oral (or) Lorazepam 2mg i.m Used to produce smooth induction of anaesthesia Midazolam: It is a good amnesic with potent and short lasting action It is also better suited for i.v injection OPIOIDS Morphine 10 mg, Pethidine 50-100mg i.m. Produce pre and post operative analgesia Reduce the dose of anesthetics required
- 22. ANTI CHOLINERGICS: Atropine / Hyoscine 0.6mg i.m./ i.v Used reduce salivary & bronchial secretion Now used to prevent vagal bradycardia and hypotension and prophylaxis of laryngospasm Glycopyrrolate (0.1-0.3mg i.m.) is a long acting atropine substitute also used now NEUROLEPTICS: Chlorpromazine 25 mg, Haloperidol 2-4 mg i.m. are frequently used They allay anxiety, have anti emetic action
- 23. H2 BLOCKERS: Ranitidine 150mg / Famotidine 20mg Given night before and in the morning Patients undergoing prolonged operations, caesarian section this H2 blockers were used It raises the gastric PH, reduce its volume and prevent the chance of regurgitation Prevention of stress ulcer They are now routinely used before prolonged surgery
- 25. ANTI EMETICS: Metoclopranide 10-20 mg i.m. / Domperidone / Ondansetron 4-8 mg. i.v. Effective in reducing post operative vomiting Combined use of metoclopramide and H2 blockers is more effective
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