Solvents, Solutes & Gases in solution Flashcards
What are the 4 factors that affect solubility of gases?
- Partial pressure of the gas
- Temperature of the liquid/gas
- Type of gas
- Type of liquid
Describe Henry’s Law
The amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in equilibrium.
What is the effect of increasing temperature on the solubility of a gas in a solution?
Higher temperature = less soluble gas in solution.
Which is more soluble O2 or CO2?
- CO2
- CO2 equilibrates in alveolar capillary more rapidly
- When diffusion impaired O2 transfer more greatly affected
Which is more soluble N2 or NO2?
- NO2
Why is NO2 contraindicated in pneumothorax?
Can increase size
Nitrogen diffuses out more slowly than NO2 enters
Which is more soluble oil or blood in relation to an inhalation agent?
Oil
What is the solubility coefficient?
The volume of gas that dissolves in a given volume of liquid
What is the Bunsen solubility coefficient?
Volume of gas corrected to standard temp/pressure that dissolves in 1unit volume of the liquid.
What are the limitations of the Bunsen solubility coefficient?
- Dependent on pressure ( 1 atmosphere)
- Requires vol of gas to be corrected to standard conditions
- Not used in anaesthetic practise
What is the Ostwald solubility coefficient?
The volume of gas that dissolves in 1 unit volume of liquid at temp concerned.
What are the advantages of the Ostwald solubility coefficient?
- Independent of pressure
- Not corrected to STP
What is the partition coefficient?
The ratio of the amount of substance present in equal volume phases of liquid & gas in a closed system.
What are the important coefficients when it comes to inhalation agents?
- Blood: Gas = How soluble agent is in blood
- Oil: Gas = How soluble agent is in oil
What does the blood: gas coefficient influence?
Rate of onset of agent
What does the oil: gas coefficient influence?
How potent an agent is
How is the rate of uptake of an agent described?
Ratio of alveolar to inspired concentration over time
At equilibrium what is alveolar concentration of an agent equivalent to?
Brain concentration
What does a high blood: gas solubility coefficient mean?
Takes longer to reach equilibrium and therefore slower onset than a poorly soluble agent.
The more soluble the agent the longer it takes to work
What is the order of solubility of inhalation agents starting with most.
1) Desflurane
2) Sevoflurane
3) Isoflurane
4) Halothane
What does a Meyer-Overton graph show?
The higher the oil:gas coefficient is the more potent an agent is
What are the important features of the Meyer-Overton graph?
- Scales are logs so a line of best fit can be drawn
- X-axis is MAC which is inversely proportional to potency
- Not all agents fit the line
What is it about particles that influences osmolality & osmolarity?
- Number NOT size/type
What is the difference between osmolality & osmolarity?
- Osmolality: The no. of osmoles of solute per kg of solvent
- Osmolarity: The no. of osmoles of solute per L of solution
What is the average plasma osmolarity?
300 mOsm/kg
How do we measure plasma osmolarity?
2 x (Na + K) + Ur + Glu
What is osmotic pressure?
The pressure a solution containing particles exerts e.g the force that pulls H2O from an area of low to high solute concentration
What are colligative properties?
- Osmotic pressure
- Freezing point
- Boiling point
- Solvent vapour pressure
What is tonicity?
The osmolality due to effective osmoles
Only particles restricted to one compartment influence osmolality and therefore osmotic pressure
Which molecules are termed ineffective osmoses?
- Glucose
- Urea
- ETOH
How are the colligative properties affected by increase in osmolarity?
- Pressure increases
- Freezing point decreases (by 1.86 degrees)
- Boiling point increases
- Solvent pressure decreases
How do osmometers measure osmolarity?
- Use colligative properties
- Most use freezing point depression
