CLASSIFICATION OF GENERAL ANAESTHETICS
1.INHALATIONAL  Gases:  N 2 O,Cyclopropane,Xenon Liquids:  Ether, Halothane, Enflurane, Desflurane,  Isoflurane, Sevoflura...
2.INTRAVENOUS Inducing Agents : Thiopentone sodium,   Methohexitone sodium,   Propofol, Etomidate Dissociative Anaesthesia...
Pharmacokinetics <ul><li>Rapidly diffuse across the alveoli </li></ul><ul><li>Alveoli  blood  brain </li></ul><ul><li>Dept...
Minimum Alveolar Concentration <ul><li>Conc of the inhalational GA that renders 50% of the subjects immobile when exposed ...
<ul><li>0.3 MAC ->mild analgesia </li></ul><ul><li>0.5 MAC->amnesia  </li></ul><ul><li>1.0 MAC->50% patients immobile even...
Minimum Alveolar Concentration limitations <ul><li>Leaves 50% subjects </li></ul><ul><li>At 1.3MAC awareness & recall may ...
Factors affecting pp of anaesthetic in brain <ul><li>PP of anaesthetic in inspired air </li></ul><ul><li>Pulmonary ventila...
1.PP of the anaesthetic in inspired air
PP of the anaesthetic in inspired air <ul><li>Increase in inspired anaesthetic conc increases the rate of induction of ana...
Fick’s Law of Diffusion <ul><li>Flux= diff in conc x A x Permeability </li></ul><ul><li>Thickness of the path </li></ul>
2.PULMONARY VENTILATION
2.Pulmonary Ventilation Rate <ul><li>The rate of rise of anaesthetic gas conc in the arterial blood is directly dependent ...
3.ALVEOLAR EXCHANGE
ALVEOLAR  EXCHANGE <ul><li>GAs diffuse freely across alveoli </li></ul><ul><li>Ventilation Perfusion mismatch delays the a...
4.SOLUBILITY IN BLOOD
SOLUBILITY IN BLOOD <ul><li>One of the most important factor </li></ul><ul><li>Blood:Gas Partition co efficient –index of ...
5.SOLUBILITY IN TISSUES
SOLUBILITY IN TISSUES <ul><li>Relative solubility of the anaesthetic in blood and tissue determines its conc in the tissue...
6.CEREBRAL BLOOD FLOW
CEREBRAL BLOOD FLOW <ul><li>Brain is highly perfused </li></ul><ul><li>GAs are quickly delivered </li></ul><ul><li>CO 2  i...
Second gas effect <ul><li>When certain gases like nitrous oxide are administered in high conc, the other anaesthetic gases...
Concentration effect <ul><li>When an anaesthetic is administered in high conc, its alveolar tension rises more rapidly tha...
e Elimination <ul><li>gradients reversed  </li></ul><ul><li>Through lungs- unchanged,  </li></ul><ul><li>Metabolism-haloth...
Upcoming SlideShare
Loading in …5
×

Classification of general anaesthetics and pharmacokinetics

25,339 views
24,872 views

Published on

Published in: Education, Technology, Business
1 Comment
15 Likes
Statistics
Notes
No Downloads
Views
Total views
25,339
On SlideShare
0
From Embeds
0
Number of Embeds
11
Actions
Shares
0
Downloads
851
Comments
1
Likes
15
Embeds 0
No embeds

No notes for slide

Classification of general anaesthetics and pharmacokinetics

  1. 1. CLASSIFICATION OF GENERAL ANAESTHETICS
  2. 2. 1.INHALATIONAL Gases: N 2 O,Cyclopropane,Xenon Liquids: Ether, Halothane, Enflurane, Desflurane, Isoflurane, Sevoflurane, Methoxyflurane
  3. 3. 2.INTRAVENOUS Inducing Agents : Thiopentone sodium, Methohexitone sodium, Propofol, Etomidate Dissociative Anaesthesia: Ketamine Neuroleptanalgesia: Fentanyl+Droperidol (Analgesic)(Neuroleptic) BZDs: Diazepam,Lorazepam,Midazolam
  4. 4. Pharmacokinetics <ul><li>Rapidly diffuse across the alveoli </li></ul><ul><li>Alveoli blood brain </li></ul><ul><li>Depth of anaesthesia-potency & pp </li></ul><ul><li>Induction & Recovery-rate of change of pp </li></ul>
  5. 5. Minimum Alveolar Concentration <ul><li>Conc of the inhalational GA that renders 50% of the subjects immobile when exposed to a strong noxious stimulus </li></ul>Halothane 0.75% Ether 1.9% Enflurane 1.68% Isoflurane 1.2% Desflurane 6% Sevoflurane 2% Nitrous oxide 105%
  6. 6. <ul><li>0.3 MAC ->mild analgesia </li></ul><ul><li>0.5 MAC->amnesia </li></ul><ul><li>1.0 MAC->50% patients immobile even after stimulation </li></ul><ul><li>1.3 MAC->sympathetically mediated response blunted </li></ul><ul><li>2.0 MAC->potentially lethal </li></ul><ul><li>MAC α 1 / Potency </li></ul>
  7. 7. Minimum Alveolar Concentration limitations <ul><li>Leaves 50% subjects </li></ul><ul><li>At 1.3MAC awareness & recall may still exist </li></ul><ul><li>Large no. of patients receive muscle relaxants </li></ul><ul><li>Other indicators of awareness-highly suggestive when present but not definitive when absent </li></ul><ul><li>A patient who moves with incision is not necessarily awake &one who does not move is not necessarily unconscious </li></ul>
  8. 8. Factors affecting pp of anaesthetic in brain <ul><li>PP of anaesthetic in inspired air </li></ul><ul><li>Pulmonary ventilation rate </li></ul><ul><li>Alveolar exchange </li></ul><ul><li>Solubility of anaesthetic in blood </li></ul><ul><li>Solubility of anaesthetic in tissues </li></ul><ul><li>Cerebral blood flow </li></ul>
  9. 9. 1.PP of the anaesthetic in inspired air
  10. 10. PP of the anaesthetic in inspired air <ul><li>Increase in inspired anaesthetic conc increases the rate of induction of anaesthesia by increasing the rate of transfer into blood according to Fick’s Law </li></ul><ul><li>Used for mod soluble-halothane- 3-4% ->1-2% </li></ul>
  11. 11. Fick’s Law of Diffusion <ul><li>Flux= diff in conc x A x Permeability </li></ul><ul><li>Thickness of the path </li></ul>
  12. 12. 2.PULMONARY VENTILATION
  13. 13. 2.Pulmonary Ventilation Rate <ul><li>The rate of rise of anaesthetic gas conc in the arterial blood is directly dependent on both rate & depth of ventilation </li></ul><ul><li>Effects- solubility </li></ul><ul><li>4x ↑ In VR 2x T of halothane bt only 15% ↑ in T of nitrous oxide </li></ul>
  14. 14. 3.ALVEOLAR EXCHANGE
  15. 15. ALVEOLAR EXCHANGE <ul><li>GAs diffuse freely across alveoli </li></ul><ul><li>Ventilation Perfusion mismatch delays the attainment of equilibrium between blood and alveoli </li></ul>
  16. 16. 4.SOLUBILITY IN BLOOD
  17. 17. SOLUBILITY IN BLOOD <ul><li>One of the most important factor </li></ul><ul><li>Blood:Gas Partition co efficient –index of solubility </li></ul><ul><li>When an anaesthetic with low solubility diffuses from alveoli into arterial blood, relatively few molecules are required to raise its partial pressure and therefore its arterial tension rises rapidly </li></ul>
  18. 18. 5.SOLUBILITY IN TISSUES
  19. 19. SOLUBILITY IN TISSUES <ul><li>Relative solubility of the anaesthetic in blood and tissue determines its conc in the tissue at equilibrium </li></ul><ul><li>expressed as tissue : blood pc </li></ul><ul><li>=ly soluble in lean tissue & blood. More soluble in fat </li></ul><ul><li>Conc ↑ in white than in grey matter </li></ul>
  20. 20. 6.CEREBRAL BLOOD FLOW
  21. 21. CEREBRAL BLOOD FLOW <ul><li>Brain is highly perfused </li></ul><ul><li>GAs are quickly delivered </li></ul><ul><li>CO 2 inhalation </li></ul>
  22. 22. Second gas effect <ul><li>When certain gases like nitrous oxide are administered in high conc, the other anaesthetic gases are also pulled in and their alveolar tension rises more rapidly </li></ul><ul><li>Eg: halothane when given with N 2 O, delivered at same rate </li></ul>
  23. 23. Concentration effect <ul><li>When an anaesthetic is administered in high conc, its alveolar tension rises more rapidly than when the same gas is inhaled in lower conc. </li></ul>
  24. 24. e Elimination <ul><li>gradients reversed </li></ul><ul><li>Through lungs- unchanged, </li></ul><ul><li>Metabolism-halothane>20% in liver </li></ul><ul><li>Lipid soluble anaesthetic-delayed recovery </li></ul>

×