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SOLUBILITY

SOLUBILITY. BY DR ABDUL JALIL ASSISTANT PROFESSOR DEPARTMENT OF ANAESTHESIA AND ICU LAHORE GENERAL HOSPITAL/PGMI LAHORE. Solubility. Vapour Pressure Equilibrium State Saturated Vapour Pressure. Factors Affecting Solubility. Partial Pressure Temperature Gas Concerned

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SOLUBILITY

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  1. SOLUBILITY BY DR ABDUL JALIL ASSISTANT PROFESSOR DEPARTMENT OF ANAESTHESIA AND ICU LAHORE GENERAL HOSPITAL/PGMI LAHORE

  2. Solubility • Vapour Pressure • Equilibrium State • Saturated Vapour Pressure

  3. Factors Affecting Solubility • Partial Pressure • Temperature • Gas Concerned • Liquid Concerned

  4. Effect of Partial Pressure Effect of partial pressure on solubility can be well understood by taking into account the statement of Henry’s Law: “AT A PARTICULAR TEMPERATURE THE AMOUNT OF A GIVEN GAS DISSOLVED IN A GIVEN LIQUID IS DIRECTLY PROPORTIONAL TO THE PARTIAL PRESSURE OF THE GAS IN EQUILIBRIUM WITH THE LIQUID”

  5. Applied aspect of effect of pressure • Decompression Sickness or ‘The Bends’

  6. Effect of Temperature The temperature of the liquid has an inverse relationship to the solubility of gas in it.

  7. Applied aspect of effect of temperature IV Fluid in OT (bubbles of air may form in saline in an infusion line which has passed through a blood-warming coil).

  8. Effect of Gas Concerned Different gases are found to have different solubilities.

  9. Effect of Liquid Concerned The solubility of a given gas varies with the type of the liquid present.

  10. Summary To summarize, the solubility of a gas depends on: • The Partial Pressure • The Temperature • The Gas and The Liquid Concerned

  11. Solubility Coefficients • Solubilty of solids (moles, millimoles) • Solubility of Gases (in terms of volume; at constant temperature and pressure)

  12. Bunsen Solubility Coefficient “Volume of a gas corrected to STP, which dissolves in 1 unit volume of the liquid” Usually quoted in: • Scientific Tables • Text Books

  13. Ostwald Solubility Coefficient “The volume of a gas which dissolves in 1 unit volume of the liquid at the temperature concerned” • Volume of gas is not corrected to STP in this case but, instead, is measured at a known temperature and pressure. • Pressure does not modify the dissolved volume, provided that the volume is measured at the ambient pressure

  14. Partition Coefficient “The ratio of the amount of substance present in one phase compared with another, the two phases being of equal volume and in equilibrium”

  15. Partition Coefficient • Temperature (37°C) • Phases (blood and gases) • Relative order of the phases (N2O blood- gas partition coefficient 0.47 and N2O gas- blood partition coefficient 2.1)

  16. Partition Coefficient It can be applied to two liquids, in contrast to Ostwald solubility coefficient.

  17. Tension of a Gas • Tension is used in place of partial pressure. • “The tension of a gas in solution is the partial pressure of the gas which would be in equilibrium with it”

  18. Solubility and Uptake of Anaesthetics Clinical applications of solubility • Solubility coefficient of different anaesthetics determines their solubility in blood.

  19. The greater the solubility of anaesthetic, the greater is its transportation across alveolar wall and the lesser is the build up of its concentration in the alveolar air.

  20. From the above mentioned facts it is concluded that during the course of an inspiration of a gas mixture containing N2O, N2O is absorbed into the blood stream faster than O2 or N2, so at peak inspiration, when the pressure in the alveoli has equalized with ambient pressure, there is net surplus of N2 and O2 molecules; this phenomenon is referred to as the “second gas effect”

  21. Diffusion Hypoxia • Excretion of N2O at the end of anaesthesia • N2O from blood to alveoli • Gases in the alveolar air are diluted • Resulting into fall of O2 concentration; known as “DIFFUSION HYPOXIA”

  22. Oil Solubility And Anaesthetic Potency Oil is used in measurements because: • Fat and Oil are similar • Fat is a normal constituent of cell membranes and neurons in particular.

  23. MAC • “MAC (Minimum Alveolar Concentration) refers to the concentration at which 50% of the patients cease to move in response to a stimulus” • Anaesthetics with high solubility in oil have a low MAC value and hence, are more potent. This effect is due to: Mild attraction between anaesthetic molecule and fatty acid chains, interference in molecular configuration of long chain fatty acids in the brain, the attachment being readily reversible and loose with van der Waal type bonds . (Long chain fatty acids)

  24. Long Carbon Chain Molecules • Anaesthetics are attracted to long carbon chain molecules in rubber and plastics. • Substantial quantities of anaesthetics may be absorbed into the tubing used in breathing system and may later be released and administered to patients even if no anaesthetic vaporizer is turned on. • The anaesthetic released in this way might be small but the quantity can be sufficient to trigger the onset of “MalignantHyperthermia”.

  25. THANK YOU

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