Classification of general anaesthetics and pharmacokinetics
-
Upload
bhavyalatha -
Category
Education
-
view
18.240 -
download
2
Transcript of Classification of general anaesthetics and pharmacokinetics
![Page 1: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/1.jpg)
CLASSIFICATION OF CLASSIFICATION OF GENERAL ANAESTHETICSGENERAL ANAESTHETICS
![Page 2: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/2.jpg)
1.INHALATIONAL
Gases: N2O,Cyclopropane,Xenon
Liquids: Ether, Halothane,
Enflurane, Desflurane,
Isoflurane, Sevoflurane,
Methoxyflurane
![Page 3: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/3.jpg)
2.INTRAVENOUS
Inducing Agents: Thiopentone sodium,
Methohexitone sodium,
Propofol, Etomidate
Dissociative Anaesthesia:Ketamine
Neuroleptanalgesia: Fentanyl+Droperidol
(Analgesic)(Neuroleptic)
BZDs: Diazepam,Lorazepam,Midazolam
![Page 4: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/4.jpg)
Pharmacokinetics• Rapidly diffuse across the alveoli
• Alveoli blood brain
• Depth of anaesthesia-potency & pp
• Induction & Recovery-rate of change of pp
![Page 5: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/5.jpg)
Minimum Alveolar Concentration
• Conc of the inhalational GA that renders 50% of the subjects immobile when exposed to a strong noxious stimulus Halothane 0.75%
Ether 1.9%
Enflurane 1.68%
Isoflurane 1.2%
Desflurane 6%
Sevoflurane 2%
Nitrous oxide 105%
![Page 6: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/6.jpg)
• 0.3 MAC→mild analgesia
• 0.5 MAC→amnesia
• 1.0 MAC→50% patients immobile even after stimulation
• 1.3 MAC→sympathetically mediated response blunted
• 2.0 MAC→potentially lethal
• MAC α 1/Potency
![Page 7: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/7.jpg)
Minimum Alveolar Concentration
limitations1. Leaves 50% subjects
2. At 1.3MAC awareness & recall may still exist
3. Large no. of patients receive muscle relaxants
4. Other indicators of awareness-highly suggestive when present but not definitive when absent
5. A patient who moves with incision is not necessarily awake &one who does not move is not necessarily unconscious
![Page 8: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/8.jpg)
Factors affecting pp of anaesthetic in brain
• PP of anaesthetic in inspired air• Pulmonary ventilation rate• Alveolar exchange• Solubility of anaesthetic in blood• Solubility of anaesthetic in tissues• Cerebral blood flow
![Page 9: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/9.jpg)
1.PP of the anaesthetic in 1.PP of the anaesthetic in inspired airinspired air
![Page 10: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/10.jpg)
PP of the anaesthetic in inspired air
• 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
• Used for mod soluble-halothane- 3-4% →1-2%
![Page 11: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/11.jpg)
Fick’s Law of Diffusion
•
•
•
Flux=diff in conc x A x Permeability
• Thickness of the path
![Page 12: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/12.jpg)
2.PULMONARY VENTILATION
lung animation.gif
![Page 13: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/13.jpg)
2.Pulmonary Ventilation Rate
• The rate of rise of anaesthetic gas conc in the arterial blood is directly dependent on both rate & depth of ventilation
• Effects- solubility
• 4x ↑ In VR 2x T of halothane bt only 15% ↑ in T of nitrous oxide
![Page 14: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/14.jpg)
3.ALVEOLAR EXCHANGE
![Page 15: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/15.jpg)
ALVEOLAR EXCHANGE
• GAs diffuse freely across alveoli
• Ventilation Perfusion mismatch delays the attainment of equilibrium between blood and alveoli
![Page 16: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/16.jpg)
4.SOLUBILITY IN BLOOD
![Page 17: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/17.jpg)
SOLUBILITY IN BLOOD
• One of the most important factor
• Blood:Gas Partition co efficient –index of solubility
• 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
![Page 18: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/18.jpg)
5.SOLUBILITY IN TISSUES5.SOLUBILITY IN TISSUES
![Page 19: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/19.jpg)
SOLUBILITY IN TISSUES
• Relative solubility of the anaesthetic in blood and tissue determines its conc in the tissue at equilibrium
• expressed as tissue : blood pc
• =ly soluble in lean tissue & blood. More soluble in fat
• Conc ↑ in white than in grey matter
![Page 20: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/20.jpg)
6.CEREBRAL BLOOD FLOW6.CEREBRAL BLOOD FLOW
![Page 21: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/21.jpg)
CEREBRAL BLOOD FLOW
• Brain is highly perfused
• GAs are quickly delivered
• CO2 inhalation
![Page 22: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/22.jpg)
Second gas effect
• 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
• Eg: halothane when given with N2O, delivered at same rate
![Page 23: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/23.jpg)
Concentration effect
• When an anaesthetic is administered in high conc, its alveolar tension rises more rapidly than when the same gas is inhaled in lower conc.
![Page 24: Classification of general anaesthetics and pharmacokinetics](https://reader035.fdocuments.us/reader035/viewer/2022062319/556570aad8b42a95028b4698/html5/thumbnails/24.jpg)
eElimination• gradients reversed
• Through lungs- unchanged,
• Metabolism-halothane>20% in liver
• Lipid soluble anaesthetic-delayed recovery