Quick Links :
 
 

 

 

Module 2 : Clinical Assessment

 

 

Blood biochemistry

 

Serum biochemistry results can be used as an adjunct to other clinical observations in order to gain an idea of a patient’s fluid status.

Below are some of the urea and electrolyte (‘Us and Es’) changes which may be seen in the fluid depleted or overloaded patient:

Urea and creatinine: Levels increase in the dehydrated patient. Urea levels increase proportionately more than creatinine levels.

 

Hyponatraemia:  Most commonly caused by water overload either by excessive water drinking or IV fluids - notably glucose solutions. Therefore the ratio of sodium to water in the blood plasma decreases.

 

Hypernatraemia: This occurs in dehydration; simply referring to depletion of water, thus this increases the plasma sodium concentration.

Since ‘water follows salt’ and osmoreceptors detect a rise in serum osmolality and trigger thirst and ADH secretion as compensatory measures, it can generally only be seen in the following patients:

  • In the very old/young or neurologically disabled who have lost the perception of thirst
  • Too ill to drink
  • In those with an osmotic diuresis (e.g. caused by glycosuira) in which water is lost disproportionately to sodium.

Hypokalaemia: may result from losses of potassium rich GI tract fluid e.g. vomiting and diarrhoea. In such cases, extra potassium supplementation to fluid may be required. See Physiology : Electrolytes in disease states to revise this.


Generally, there are no typical serum marker thresholds to signify when a dehydrated patient should be given fluid, or when a fluid overloaded patient should be fluid restricted. This decision is subjective depending on these results and all the other clinical information you have about the patient.

 

 

Previous Summary Next

 

 

This tab has icon in it.

Suspendisse blandit velit eget erat suscipit in malesuada odio venenatis.