INHALATION ANESTHETICS

1. INHALATION ANESTHETICS Dr. Rupak Bhattarai

2. INTRODUCTION • Nitrous oxide, Chloroform and Ether were the first universally accepted general anesthetics. • Ethyl chloride, Ethylene and Cyclopropane were also used , but the toxicity and flammability led to their withdrawal from the market. • Mainly 5 inhalation anesthetics agents are used in clinical practice these days: • 1. Nitrous oxide • 2.Halothane • 3.Isoflurane • 4.Desflurane • 5. Sevoflurane

3. MINIMUM ALVEOLAR CONCENTRATION (MAC) DEF: The minimum alveolar concentration of an inhaled anesthetics is the alveolar concentration that prevents movement in 50% of patient in response to a standardized stimulus (e.g. Surgical Incision)

4. MAC VALUE OF INHALATION ANESTHETICS AGENTS • Nitrous oxide: 105% • Halothane: 0.75% • Isoflurane : 1.2% • Desflurane: 6% • Sevoflurane: 2%

5. NITROUS OXIDE Physical properties: • It is a laughing gas. • It is only inorganic anesthetic gas in clinical use. • Colorless and odorless • Non Explosive and Non Infammable • Gas at room temperature and can be kept as a liquid under pressure. • It is relatively inexpensive.

6. Effects of Nitrous Oxide on Organ System 1. CARDIOVASCULAR SYSTEM • Stimulate sympathetic nervous system. • Directly depresses myocardial contractility. • Arterial blood pressure ,heart rate and cardiac output are slightly increased. 2. RESPIRATORY SYSTEM: • Increases respiratory rate with decreases tidal volume. • Minimal change in minute ventilation.

7. 3. CEREBRAL: • Increases CBF thus increasing intracranial pressure. 4. RENAL SYSTEM: • It decreases renal blood flow thus leads to drop in glomerular filtration rate and urinary output. 5. HEPATIC SYSTEM: • Decreases the Hepatic blood flow but to a lesser extent than other inhalation agents. 6. GASTROINTESTINAL: • It causes post operative Nausea and Vomiting.

8. CONTRAINDICATION OF N2O • Air embolism • Pneumothorax • Acute Intestinal Obstruction • Tension Pneumocephalus • Tympanic membrane grafting

9. HALOTHANE • Physical Properties: • It is halogenated alkene. • Non Inflammable and Non explosive. • Least expensive .

10. EFFECTS ON ORGAN SYSTEM • CARDIOVASCULAR: • Dose dependent reduction of arterial blood pressure by direct myocardial depression. • It is a coronary artery vasodilator. • It causes slowing of SA node conduction resulting in bradycardia. 2. RESPIRATORY SYSTEM: • Causes rapid ,shallow breathing. • Decrease in alveolar ventilation and Paco2 elevated. • Potent dronchodilator.

11. 3. CEREBRAL: • It increases cerebral blood flow. 4. NEUROMUSCULAR: • Relaxes skelatal muscle and potentiates Non depolarizing neuro-muscular blocking agents. 5.RENAL: • Reduces renal blood flow, glomerular filtration rate and urinary output. 6. HEPATIC: • Decreases hepatic blood flow.

12. CONTRAINDICATION • Unexplained liver dysfunction. • Intra-cranial mass lesions. • Hypo-volemic patient with severe cardiac diseases.

13. ISOFLURANE • It is non flammable volatile with a pungent smell. EFFECTS ON ORGAN SYSTEM: • CARDIOVASCULAR: • Causes minimal cardiac depression. • Rapid increase in MAC lead to increase in HR and BP.( Coronary Steal) • Dilates coronary arteries. 2. RESPIRATORY SYSTEM: • Respiratory depression . • Acts as a good bronchodilator.

14. 3. CEREBRAL: If con> 1 MAC causes increase in CBF and Intracranial pressure. 4. NEUROMUSCULAR: Relaxes skeletal muscles. 5. RENAL: Decreases renal blood flow , glomerular filtration rate and urinary output. 6. HEAPTIC: Reduces hepatic blood flow. INDICATIONS- For Cardiac and Neuro- Surgery

15. CONTRAINDICATION • No such contraindication. • Patient with severe hypovolemia may not tolorate its vasodilating effects.

16. DESFLURANE • Structure much similar to that of isoflurane. • Recovery time are approximately 50 % less than those of Isoflurane. Pungent Smell • TEC 6 EFFECTS ON ORGAN SYSTEM: • CARDIOVASCULAR SYSTEM: • Similar to Isoflurane( Increases HR and BP when increased MAC rapidly) • Dilates coronary arteries.

17. 2. RESPIRATORY SYSTEM: • Causes decrease in tidal volume and increase in resp rate. • Pungency and airway irritation so causes coughing and sometime bronchospasm. 3. CEREBRAL: • Increases CBF and Intracranial pressure. 4. NEUROMUSCULAR: • Relaxes skeletal muscle. 5. RENAL AND HEPATIC SYSTEM: • No any evidence has been documented. INDICATION- For Hepatic and Renal Surgery

18. CONTRAINDICATION • Severe hypo-volemia. • Intracranial hypertension. • Malignant hyperthermia.

19. SEVOFLURANE • It is Non pungency. EFFECTS ON ORGANS: • CARDIOVASCULAR SYSTEM: • Mildly depresses myocardial contractility. • May prolong QT interval, but no significance. 2. RESPIRATORY SYSTEM: • Depresses respiratory rate. • It reverses broncho-spasm

20. 3. CEREBRAL: • Increases CBF and intra-cranial pressure. 4. RENAL SYSTEM: • Slightly decreases renal blood flow. Higher Conc Causes Nephro-toxicity 5. HEPATIC: • Decreases portal vein blood flow but increases hepatic artery blood flow thus maintaining total hepatic blood flow. 6.NEUROMUSCULAR: • Adequate muscle relaxation.

21. CONTRAINDICATION • Severe hypo-volemia. • Intracranial hypertension. • Malignant hyperthermia.

22. ETHER • W.T.G Morton on 16th Oct 1846 used for removal of jaw tumor. PHYSICAL PROPERTIES: • Pungent smelling liquid, decomposes in presence of light, air, heat. • Highly inflammable and explosive. • Highly irritant vapour. • Very Cheap. • Also called as Complete Anesthetic agents. • Can be used by less experience hands.

23. Induction very slow, pungent smells and may causes laryngeal spasm • Very good analgesic. • Very good muscle relaxants.

24. Cardiovascular: Does-not depresses myocardium, but stimulates sympathetic system. • Respiratory system: Does-not depresses respiration. It is a potent bronchodilator. Tracheo-bronchial secretions is markedly increased. • GIT: Nausea and vomiting. • Hepatic and renal: Well preserved. • Cerebral: Increases intracranial pressure. • May causes Hyperglycemia.

25. STAGES OF ETHER ANESTHESIA • STAGE I: (Stage of analgesia) (From analgesia to loss of consciousness) • Respiration is regular with small tidal volume. • Pupil is normal in size. • STAGE II : (Stage of Excitement): ( From loss of consciousness to rhythmic respiration) • Respiration is irregular. • Pupil is Mid dilated. • Eyelashes reflex absent.

26. STAGE III : ( Stage of Anesthesia): • Plane I: ( From rhythmic resp to cessation of eye movement)Respiration is regular with large volume. Pupil is normal in size. Eyelashes reflex absent, Pharyngeal and vomiting reflex lost. • Plane II: (From cessation of eye movement to resp paresis)Respiration is regular with large volume , Pupil is mid dilated with corneal reflexes lost. • Plane III: ( Resp paresis to Paralysis)From Respiration is regular with small volume, Pupil is moderate dilated with laryngeal reflexes absent. • Plane IV: (Diaphragmatic Paralysis)Respiration is irregular with small volume, Pupil dilated and centrally placed.

27. Stage IV: (Stage of overdose) (Medullary Paralysis) • Apnea • Pupil dilated and non reacting to light. NOTE: Withdrawal of anesthetic agents and administration of 100% oxygen lightens anesthesia with recovery.