HRR: fluid balance Flashcards
What is the total body water percentage in men?
Around 60%
What is the total body water percentage in women?
About 50-55%
What is the total body water percentage in infants?
About 70%
What is the total body water percentage in elderly patients?
About 50%
What fraction of total body water is in the extracellular space?
1/3
What fraction of total body water is in the intracellular space?
2/3
What are the two components of extracellular water?
Interstitial compartment and plasma compartment
How much water is in the interstitial fluid in the extracellular space?
¾
How much water is in the plasma in the extracellular space?
¼
How is plasma osmolality measured?
Freezing point depression
What electrolyte is most abundant in plasma?
Sodium
What is the formula for calculating plasma osmolality?
(2 x sodium) + [(BUN/28) x 10] + [(glucose/180) x 10]
What is the value for normal plasma osmolality?
270-290
What is a normal plasma osmolar gap?
Less than 10
What is a plasma osmolar gap?
The difference between what is measured and what is calculated; this is due to some other compound that we can’t account for with the calculation. This is abnormal.
What are likely culprits for increased plasma osmolar gap?
Ketones, alcohols, lactic acid
What are ineffective osmoles?
They freely cross membranes and increase osmolality but do not influence the movement of water. Urea and glucose are big examples.
What are effective osmoles?
Solutes impermeable to cell membranes. They change osmolality and influence water movement.
What is isotonicity?
Normal osmolality; no change in cell size or net water movement.
What is hypertonicity?
High osmolality; cells shrink due to water leaving the cell to balance the osmolality.
What is hypotonicity?
Low osmolality; cells swell due to water flooding into them to balance osmolality.
Describe sodium as an influence on fluid movement.
Sodium cannot pass through the cell membrane, so it acts as a non-penetrating solute. In order to balance out concentration, the water will have to move as opposed to the sodium moving.
What is the charge of plasma?
Electroneutral
What is a normal anion gap?
Between 5-12
What does it mean if there is an anion gap above 12?
There is an increase in anions other than chloride or bicarb.
Which compartment has higher protein concentration: plasma or interstitial?
Plasma
Compare the osmolality of intracellular, interstitial, and plasma compartments.
They’re all roughly the same! This is because they’re all permeable to water, so the water moves in order to balance out the osmolality.
What generates outward hydrostatic force?
The heart
What generates inward oncotic pressure?
Proteins
What 3 forces cause edema?
- Increased net hydrostatic pressure 2. Decreased osmotic pressure due to lowered albumin or loss of proteins 3. Increased membrane permeability/loss of membrane integrity
Are pulmonary capillaries leaky to protein?
Yes
For edema to be clinically relevant, the interstitium must contain how much additional fluid?
3L
Dextrose (D5W) is a ___ solution?
Isotonic
When dextrose solution is given, where does the water go?
Proportionally with where water is; 2/3 in intracellular space, 1/3 in extracellular space
Is dextrose an effective or ineffective osmole?
Ineffective
When isotonic saline is given, where does the water go?
The water is only distributed within the ECC, mostly between the plasma space and interstitial space (3/4 in interstitial and ¼ in plasma)
What does hypotonic saline do?
Add water to all 3 body water compartments; can treat hypernatremia and DKA
What does hypertonic saline solution do?
Remove water from intracellular compartment; can treat severe hyponatremia
What kind of solution is lactated ringers?
Isotonic; it contains similar electrolytes to plasma as well as lactate
What are plasma expanders?
Solutions that are made of large molecules that cannot pass capillary walls. They increase plasma volume specifically.
What are examples of plasma expanders?
Albumin, blood products, hetastarch
What is iso-osmotic volume contraction?
Loss of iso-ismotic fluid; example is hemorrhage. Loss of extracellular volume.
What is hyper-osmotic volume contraction?
Loss of pure H2O; sweating, fever, diabetes ins. Volume of all compartments is decreased and osmolality increased.
What is hypo-osmotic volume contraction?
Loss of NaCl; adrenal insufficiency. Water shifts from extracellular to intracellular. Both have lower osmolality.
What is iso-osmotic volume expansion?
Gain of iso-osmotic fluid; general edema, infusion of isotonic saline. Increase in extracellular volume.
What is hyper-osmotic volume expansion?
Gain of NaCl; hypertonic saline infusion. Water shifts from intracellular to extracellular and osmolality of both increases.
What is hypo-osmotic volume expansion?
Gain of pure H2O; SIDAH. Volume in both compartments are expanded and osmolality decreased.
