Fluid Assessment and Balance Flashcards
What are the relative ion concentrations in intracellular fluid?
Rich in K
Low in Na
What determines the water content in a body compartment?
Electrolyte content
How is water and ions transported in the extracellular compartment?
Free movement of water
Active transport of Na and K
What are the relative ion concentrations in extracellular fluid?
Rich in Na
Low in K
What percentage of body weight is total body water?
60%
What are the factors that control sodium intake?
Largely voluntary
What are the factors that control sodium excretion?
Kidney
What is the relationship between sodium content and volume?
Low Na content = low volume
High Na content = high volume
What is the effect of water and sodium intake on intracellular volume?
Decreasing water and Na intake will eventually decrease intracellular volume
Increasing water intake doesn’t often affect intracellular volume, because excess water excreted
How is intracellular volume assessed?
Difficult to asses
Practically, assess osmolarity/as substitute, plasma Na
What is the relationship between plasma sodium and osmolarity?
Plasma Na increased = osmolarity increased
Plasma Na decreased = osmolarity decreased
Does osmolarity change between the extracellular and intracellular compartments?
No, it’s the same
How is saline solution distributed across the extracellular and intracellular compartments?
Because Na in extracellular compartment, water remains there, so extracellular volume increases, with no change in intracellular volume
What are the signs of increased extracellular volume?
Oedema
Possible raised JVP
Pulmonary oedema if CVD
Plasma Na and osmolarity unchanged
How is pure water distributed across the extracellular and intracellular compartments?
Distributes itself evenly across extracellular and intracellular compartments to maintain osmolarity
How do you detect the change in extracellular volume after giving just water?
Hard to detect change because of natural variation
How do you detect the change in intracellular volume after giving just water?
Plasma Na and osmolarity decrease
What happens when sodium rich fluid is lost from total body water?
Extracellular volume decreases because of loss of Na
Plasma Na concentration remains normal
No change in intracellular volume
What are the signs of loss of extracellular volume?
Low BP Tachycardia Low JVP Peripheral vasoconstriction Low urine Na, but concentrated urine Decreased tissue turgor not particularly sensitive, especially in adults over 40-50
What happens when just water is lost from total body water?
Loss of proportional water from both compartments
What are the signs of just water loss from total body water?
Extracellular compartment - Hard to detect on examination of CVS unless CVS disease Intracellular compartment - Dry tongue - Axilla - Low tissue turgor in young Plasma Na/osmolarity increased Concentrated urine
How do you adjust the volume in the extracellular compartment?
Modify Na and water intake/concentration
How do you adjust the volume in the intracellular compartment?
Modify water intake
What causes a high plasma osmolarity/sodium?
Water intake below
- Obligatory water loss
- Access to water
- Increased loss
What causes a low plasma osmolarity/sodium?
Water intake greater than ability to excrete
- Increased ADH
- Decreased distal tubule flow
- Other tubular factors limiting free water excretion
- Drugs, with variable contributions from above factors
- Diuretics
- Carbamazepine
- Antidepressants
What is the relationship between changes in extracellular volume and blood volume?
Correlate unless there’s hypoalbuminaemia/leaky capillaries
Why do changes in extracellular fluid status occur without a change in plasma sodium concentration?
Osmotic control frequently overrides volume control
What can an abnormal plasma potassium indicate?
Shift between intra- and extracellular space
Deficiency
Excess
What things shift potassium into cells?
Insulin
Beta agonists
Aldosterone
Alkalosis
What things shift potassium out of cells?
Lack of - Insulin - Beta agonists - Aldosterone Acidosis
What is the normal plasma potassium concentration?
3.5-5 mmol/L
When are you concerned about plasma potassium concentration?
Less than 3.5 mmol/L
More than 5.5 mmol/L
