inhalation anaesthetic

1. Inhalational anaesthetics
Khyati phuyal
4th year mbbs student

2. Classification
Organic inorganic
nitrous oxide
halothane
Isoflurane
Desflurane
sevoflurane
enflurane

3. • Minimum alveolar cocentration :lowest
alveolar concentration of anaesthetic in 1 atm
pressure in the pulmonary alveoli that
produce the immobilisation in response to
standard surgical stimulation(skin incision) in
50%of population
• It measure the potency

4. decrease MAC increase MAC
premedication age 6-12 month
increasing age fever
hypotension thyrotoxicosis
myxedema hypernatremia
hyponatremia

5. MOA
• The GABAa receptor gated chloride channel
major target
• It potentiate the action of GABA to open the
chloride channel
• Action of glycine is also augmented
• Nitrous oxide and the ketamine inhibit the
excitatory NMDA type of receptor

6. THEORIES
• Unitary hypothesis
• Critical volume hypothesis

7. 1.Factors affecting the
inspiratory concentration(Fi)
pharmacokinetics

8. • Fresh gas flow rate
• Breathing circuit volume
• Circuit absorption

9. 2.Factors affecting the alveolar gas
concentration (Fa)
• Uptake
• Ventilation
• concentration effect

10. UPTAKE
• Anaestthetic agent are taken by the
pulmonary circulation,so Fa:Fi <1
• The greater the uptake , slower the rate of rise
of alveolar concentration
• alvolar pp will be slow torise and slower the
rate of induction

11. Factor affecting the uptake
• Solubility
• Alveolar blood flow
• Difference in partial pressure between
alveolar gas and venous blood

12. solubility
• It is expressed in the partition coefficient:it is
ratio of the cocentration of anaesthetic gasin
each of two phase at steady state(equal pp in
two phase)
• For eg;the blood gas partition is more,alvolar
pressure rises slowly induction is prologed

13. Alveolar blood flow
• Depend on cardiac output,if absence of
shunting
• High co ,AA agent uptake increase,the rise in
alveolar pp slows and the induction is
delayed(only for soluble)

14. Difference in partial pressure between alveolar gas
and venous blood
• Tissue solubility of agent
• Tissue blood flow
• Difference in Ppbetween the arterial blood
and tissue

15. VENTILATION
• Thepartial pressure of alveoli is increased by
alveolar ventilation

16. concentration effect
• The higher inspired concentration result in
disproportionately higher alveolar
concentration
• Th e extreme case is an inspired concentration
of 100%(100 parts of 100), which, despite a
50% uptake, will result in an alveolar
concentration of 100% (50 parts of anesthetic
remaining in a total volume of 50 parts of gas)

17. • Second gas effect-if inhaled concentration
of anaesthesia is high,susbstantial loss of
alveolar gas occurs and gas mixture will be
sucked in independent of tidal volume?
• If anither potent anaesthetic is given at the
same time,it will also delivered to the blood
higher than the minute volume

18. 3.FACTORS AFFECTING ARTERIAL
CONCENTRATION (Fa)