This document discusses inhalational anaesthetics. It covers their classification, mechanisms of action, theories of anaesthesia, and factors that influence inspired, alveolar, and arterial concentrations of anaesthetic gases. Specifically, it notes that anaesthetics are either organic or inorganic, and lists common agents. Their potency is measured by minimum alveolar concentration. Uptake and ventilation influence alveolar concentration, while solubility, blood flow, and partial pressures impact uptake. Arterial concentration depends on alveolar concentration and cardiac output.

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)