Module 10

Question 1

What are colligative properties directly related to?

Answer 1

The total number of solute particles per mass of solvent.

Question 2

What is osmometry?

Answer 2

Measurement of the total concentration of solute particles.

Question 3

What particles in plasma are measured by osmometry?

Answer 3

Crystalloids (electrolytes)

Colloids (proteins)

Organics

Question 4

What is osmolality expressed as?

Answer 4

Osmol/kg water

Doesn’t fluctuate with temperature

Question 5

What is osmolarity expressed as?

Answer 5

Osmol/L solution

Question 6

What does one osmole of solution represent and how does it affect the freezing point?

Answer 6

One mole of particles in solution

Lowers the freezing point of one kg of water by 1.86°C

Question 7

For substances that dissociate what does one mole produce?

Answer 7

A number of osmoles related to the number of dissociated particles.

Question 8

What are the primary contributors to plasma osmolality?

Answer 8

Electrolytes- Na, Cl, bicarbonate

Glucose and urea

Question 9

How is serum osmolality indirectly calculated?

Answer 9

Using concentrations of the osmolutes that contribute the most.

= 1.86 [Na] + [glucose] + [urea] + 9

= 2 [Na] + [glucose] + [urea]

Question 10

How can total osmolality be measured directly and which method is more commonly used?

Answer 10

Vapour pressure

Freezing point depression- used more often because it can account for volatiles

Question 11

What are the components of freezing point depression?

Answer 11

Freezing bath

Sample holder

Agitator

Thermistor

Processor and display

Question 12

What is the process of freezing point depression?

Answer 12

Sample is cooked rapidly and then slowly to reach a temp below FP without freezing.

Agitator is activated to induce freezing (seeding).

Temp rises due to heat of fusion, reaches a point of equilibrium.

Temp at equilibrium represents the actual freezing point, dependent on total concentration.

Compared to calibration curve.

Question 13

What are possible sources of error in freezing point depression?

Answer 13

Prefreeze

Incorrect sample volume

Inadequate rinse after maintenance with alcohol

Sample carryover due to improper cleansing

Plasma instead of serum

Turbid sample (centrifuge to prevent prefreeze)

Question 14

What are the clinical applications of freezing point depression?

Answer 14

Hyper and hyponatremia

Diuretic and IV therapy

Dehydration

Diabetic ketoacidosis

Diabetes insipidus

Renal disease

Traumatic shock

Screen for volatiles and toxins

Monitoring osmotherapy treatment for cerebral edema

Question 15

What is osmolal gap?

Answer 15

Difference between measured and calculated osmolality.

If increased, represents the presence of unaccounted solutes, volatile screen may be performed.

Question 16

What is unaccounted osmolal gap?

Answer 16

Difference between measured and calculated osmolality plus the concentration of ethanol present.

Question 17

What are some common representative reference ranges in osmolality?

Answer 17

Serum- 280-300mOsm/kg

Random urine- 300-900mOsm/kg

Osmolal gap- = 10mOsm/kg

Unaccounted- = 10mOsm/kg

Question 18

What are the colligative properties of solutions?

Answer 18

Increase in osmotic pressure

Decrease in vapour pressure

Increase in boiling point

Decrease in freezing point