T3- Fluid + Electrolytes Part 1 Flashcards
How much of our body weight is composed of water?
50-60%
What stuff other than water makes up our body?
Primarily proteins, followed by lipids, minerals, carbohydrates, and miscellaneous.
How is the composition of weight broken down in a male vs a female?
A male has around 33% intracellular fluid, 21.5% interstitial fluid, 4.5% plasma, and 2% other.
In a female, 27% is intracellular, 18% interstitial fluid, 4.5% plasma, and 1.5% other.
Females have 50% of their body weight in solids, whereas males have 40%.
How does our body water change as we age?
For females, total body water, ICF, and ECF fluid all decrease.
For males, total body water and ECF decrease. ICF stays about the same.
What two organs are barely made of water?
Skeleton (bone 22%)
Adipose tissue (10%)
What two organs/things in our body are made almost entirely of water?
Blood (83%)
Kidneys (82.7%)
How much of our total body water is intracellular fluid?
2/3 of our body water.
How is ECF broken down into its components?
25% is plasma, inside the blood vessels.
74-75% is interstitial fluid, outside of the body’s cells.
1% is transcellular compartment, such as the CSF, joint spaces, GI/GU tracts and the 3 main body cavities.
What does a body fluid contain?
Electrolytes (NaCl)
Ions (cations + anions)
Non-electrolytes (glucose, urea, ethanol)
What is the predominant cation found in the ECF?
Sodium
What is the predominant cation found in the ICF?
Potassium
What is the predominant anion found in the ECF?
Chloride
What is the predominant anion found in the ICF?
Hydrogen phosphate.
What are the 3 primary cations found in the ICF?
Potassium, Sodium, Magnesium
Define diffusion.
Movement of particles along a concentration gradient, from higher to lower conentration.
Define osmosis.
Movement of water across a semipermeable membrane. (aka not all solutes can cross)
Define osmotic pressure.
The pressure water creates as it moves across a semipermeable membrane.
Specifically, it is the hydrostatic pressure needed to counter the movement of water across the membrane.
Define osmolality/osmolarity.
Osmolarity is # of solutes per L of solvent.
Osmolality is # of solutes per kg of solvent.
The greater the number, the greater the osmotic activity/pull, which draws water from one side of a membrane to another.
What is plasma osmolality?
Posm
It is the ratio of plasma solutes to water.
Plasma solutes are mainly NaCl and sodium bicarb.
Normal: 275-290 Posm.
Walmart version: 2x serum sodium!!!!!
Note: Glucose and urea account for about 5% of osmotic pressure.
What can cause rare changes in Posm?
Alcohol and acetones!
What are plasma and ECF osmolality generally the same as?
ICF
Cell membranes are mostly permeable to water, so equilibrium is established.
What is Urine osmolality?
of solutes per unit of water in urine.
Higher Uosm = concentrated urine.
What is the effect of ADH on Uosm?
Increases it.
We secrete ADH when we need to retain water, so increased ADH would concentrate our urine, making the Uosm high. We would secrete ADH when our Posm is high, since we want more water to dilute our Posm.
High Posm => increased ADH => increased Uosm
What is normal Uosm? How does it change if I am dehydrated?
500-800 mOsm/kg.
12-14 hrs of restricted fluid intake can increase it to 850.
Clinically dehydration can increase it to 1000.
What happens to my urine specific gravity if I am dehydrated?
Increases, because my urine is more concentrated.
Define tonicity.
Effect that the effective osmotic pressure of a solution has on the SIZE OF CELLS.
It is dependent on the membrane’s permeability to certain solutes.
What is tonicity also known as?
Effective Plasma Osmolality.
What are the receptors that monitor our Posm and where are they found?
Osmoreceptors, found in the hypothalamus and carotids.
What are the 3 types of tonicity?
Isotonic = same osmolality as the ICF.
Hypotonic = decreased osmolality relative to the ICF.
Hypertonic = increased osmolality relative to the ICF.
What happens to an RBC in a hypotonic solution?
It will swell up like a balloon.
What happens to an RBC in a hypertonic solution?
It will shrivel up like a raisin.
What are the 4 forces that affect the movement of water from the plasma to the interstitium?
Capillary filtration (hydrostatic) pressure.
Capillary colloidal osmotic pressure.
Interstitial hydrostatic pressure.
Tissue colloidal osmotic pressure.
Note:
Colloidal draws water into wherever it is, aka capillary colloidal would draw water INTO the capillary.
Hydrostatic pushes water OUT of wherever it is, aka capillary hydrostatic would push water OUT of the capillary.
What happens if the pressure inside a vessel is greater than the interstitium?
It will exit the vessel.
Define edema.
Palpable tissue swelling caused by expansion of interstitial fluid volume.
What are the two types of edema in terms of palpation?
Pitting edema: fluid exceeds the absorptive capacity of the gel-based interstitial matrix. AKA when you press on someone, it makes a pit, rather than returning back to normal.
Non-pitting edema: Usually excess plasma proteins in interstitial tissue. Often seen in infection, trauma, lymph system abnormalities, and thyroid disease.
What are the 4 primary pathophysiological phenomena that contribute to the development of edema?
Increased capillary filtration pressure (aka pushing fluid out of the capillaries). This results in increased intravascular volume and/or venous obstruction.
Decreased capillary colloidal osmotic pressure. (aka inability to keep fluid in the capillaries). This is due to increased loss or decreased protein production.
Increased capillary permeability.
Obstruction of lymph flow.
What is the key difference in fluid composition of pitting edema vs non-pitting edema?
Pitting edema is mainly water.
Non-pitting is proteins, salts, and water.
How much water does the average person need?
100 mL of water per 100 calories metabolized.
AKA about 2L of water for a 2k calorie diet.
What does fever do to our thirst?
Increases it.
We get a higher metabolic and respiratory rate when we are feverish.
What parts of our body cause us to lose water?
Kidneys 1500mL
Skin 600 mL
Lungs 300 mL
GI Tract 100 mL
What causes us to gain water?
Drinking water 1600mL
Eating food 700 mL
Metabolic water 200 mL
How does my cell maintain most sodium outside?
Na/K/ATPase pump to kick it out.
Why is sodium so important?
Regulates ECF volume.
Contributes to excitability of tissues.
Helps with acid base balance as a part of sodium bicarb.
What receptor monitors our effective circulating volume?
Baroreceptors, found in the heart and blood vessels.
What regulates our water intake and water output?
Intake is through thirst, which is stimulated by increased ECF osmolality or decreased volume.
Output is through ADH, which is stimulated by increased ECF osmolality or decreased volume.
ADH will cause vasoconstriction and increased reabsorption of water at the collecting duct.
What are polydipsia, hypodipsia, SIADH, and DI?
Polydipsia = very thirsty a lot
Hypodipsia = almost never thirsty
SIADH = syndrome of inappropriate ADH secretion, aka your body makes way too much ADH.
DI = diabetes inspidus, which makes you always thirsty and causes you to pee dilute urine a lot.
What will our body do if it detects a drop in osmotic pressure or blood volume?
Increased:
Sympathetic NS output
RAAS activation
ADH secretion
Thirst
Decreased:
Atrial natriuretic peptide (ANP)
What will our body do if it detects an increase of osmotic pressure or blood volume?
Decreased:
SNS output
RAAS deactivation
ADH
Thirst
Increased:
ANP
What is the pathophys of an isotonic fluid deficit?
Decrease in overall ECF volume, with a PROPORTIONATE loss of water and sodium. No change in tonicity!!
Etiology:
Decreased fluid intake
Excessive fluid loss from GI, renal, or skin issues.
Excessive third spacing from edema or ascites.
What happens if my body stays in an isotonic fluid deficit?
Decreased intravascular volume will lead to decreased capillary filtration pressure. This means stuff is not leaving the capillaries well, so exchange of stuff is impaired.
How do I compensate for isotonic fluid loss?
Increased thirst
Decreased urine output.
What kind of lab abnormalities do I see in isotonic fluid loss?
Increased Uosm.
Increased Urine specific gravity.
Increased hematocrit (aka RBCs per unit of water)
How do I manage isotonic fluid loss?
Correct the underlying cause, give them NS.
What is the pathophys of isotonic fluid excess?
Increased ECF volume.
Etiology: Decreased sodium and water elimination or increased intake.
Decreased elimination can be a result of CHF, liver failure, renal failure, or corticosteroids.
Increased intake can be from diet intakes, excess fluid replacements, or hypertonic fluids.
What will my body do in isotonic fluid excess?
Lower secretion of ADH and aldosterone.
Move fluid out of capillaries.
How is isotonic fluid excess present in lab findings?
Decreased Uosm
Decreased urine specific gravity
Decreased hematocrit.
How do people with isotonic fluid excess compensate?
Drink less water and sometimes pee more.
How is isotonic fluid excess managed?
Correction of underlying cause.
Diuretic therapy
Reduction of sodium and/or fluid intake.
What are the two ways hyponatremia can occur? Hypernatremia?
Overhydration OR loss of sodium and water to below 135.
Dehydration or gain of sodium and water over 135.
What do most causes of hyponatremia typically indicate?
Water imbalance and abnormal water handling.
What happens to cells in hyponatremia?
Swelling!
What is the first step in checking for hyponatremia?
Checking serum sodium.
What can affect my calculation of Posm?
Glucose and BUN.
What are the other steps for checking hyponatremia?
Check serum Osomlality.
Check overall volume status.
How I check someone’s overall volume status?
Physical exam + Urine osmolality plus specific gravity to check the calculation.
What is Uosm often used to measure approximately?
ADH function/acitivity.
What can we add on to an Uosm test to get a better idea of?
We can add a urine sodium to get an idea of RAAS activity as well.
What are the 3 types of hypotonic hyponatremia?
Euvolemic hyponatremia
Hypervolemic hyponatremia
Hypovolemic hyponatremia
What is isotonic hyponatremia sometimes called?
Pseudohyponatremia
What causes isotonic hyponatremia?
Extra molecules in blood, such as extra proteins from IVIG/multiple myeloma or high lipids (such as triglycerides)
Note:
No mention of a volume increase or low sodium, hence why it is isotonic.
What causes hypertonic hyponatremia?
Osmotic shift of water from ICF to ECF.
Sodium in the bloodstream gets diluted, but tonicity stays the same because there is an extra molecule boosting the osmolality up, such as glucose or radiocontrast.
Note:
RBCs will shrivel up since water is leaving them, hence the hypertonic part.
What causes hypovolemic hypotonic hyponatremia?
Water retention in excess to sodium.
AKA
Hypovolemic hypotonic hyponatremia (You lose water with sodium, but you’re losing MORE SODIUM than water)
If you’re losing only a little sodium to your urine, <10 mEq, then it is extrarenal salt loss.
If it is > 20 mEq, then it is renal salt loss.
What causes hypervolemic hypotonic hyponatremia?
Water retention in excess to sodium.
AKA you have so much water diluting your sodium. You could still have above average sodium, but you have way above average water.
MCC: HF, liver disease, and kidney disease.
What causes euvolemic hypotonic hyponatremia?
Water retention in excess to sodium.
It is often due to ADH, such as:
SIADH: body says hold onto water, get rid of sodium.
Hypothyroidism: Decreased CO causes increased ADH, bc the body thinks we need more blood.
Psychogenic polydipsia: We drink so much water at once that our sodium drops rapidly due to dilution.
Beer potomania: We can’t excrete water as well.
Note: Accounts for 60% of all hyponatremias.
What determines the pathophys consequences of hyponatremia?
How quickly the Na concentration changes.
How long does it usually take our body to adjust to hyponatremia?
Usually about 48 hours, as our osmoreceptors will stop water retention.
What happens if too much fluid goes out of a cell too fast?
Osmotic demyelination syndrome/central pontine myelinolysis.
Why do we need to treat hyponatremia slow?
People may be adjust to chronic hyponatremia, and correcting it too fast will cause fluid to leave cells, causing cell death.
What happens to muscle cells in hyponatremia?
Swelling, leading to cramps and weakness.
What lab abnormalities signify hyponatremia?
Serum sodium < 135 mEq
Note:
Osmolality and urine Na can vary greatly.
What are the neuro symptoms of hyponatremia?
HA
Anxiety, depression, altered behavior
Confusion/AMS
Lethargy
Decreased DTRs
Seizures
Coma
Respiratory arrest
Death
What are some of the miscellaneous symptoms of hyponatremia?
GI, such as N/V/D, anorexia
Malaise
Pulmonary edema (severe)
Fingerprint edema
How do we manage hyponatremia if asymptomatic?
Management of underlying cause
Do not always fluid restrict.
If asymptomatic:
Diuresis to get rid of excess water, +/- salt tablet or hypertonic saline bolus (50 mL of 3% NS)
How do we manage hyponatremia if symptomatic?
1 or more boluses of hypertonic solution (100 mL of 3%)
The goal: 4-6 mEq/L in the first few hours and then increase.
Loop diuretics (monitor K loss)
How do we manage persistently hyponatremic patients?
Salt tablets
Fluid restriction (<800 mL/day)
Vasopressin (V2) Receptor antagonists:
Block ADH effect, no effect of Na/K excretion.
Meds are conivaptan and tolvaptan.
SE include thirst/polydipsia, polyuria, dry mouth, fatigue.
BLACK BOX WARNING: severe liver injury.
Monitor: LFTs, electrolytes, renal function.
Interactions with grapefruit juice, digoxin, and meds that can cause hyperkalemia.
What is the pathophys of hypernatremia?
Serum Na > 145 mEq/L
This is because Na accounts for 90-95% of ECF osmolality.
High ECF osmolality is always almost indicative of high Na.
What does normal Uosm mean in hypernatremia?
It means that the ability of the kidneys to conserve water is intact.
What does low Uosm mean in hypernatremia?
It is a characteristic of DI.
Neurogenic means inadequate ADH release.
Nephrogenic means kidneys are insensitive to ADH.
What generally causes hypernatremia?
A loss of body water or increased intake of sodium.
Body water loss often comes in the form of excess urination, GI tract, lungs, skin, or poor intake.
Increased sodium intake is generally via ingestion or infusion.
Overall, this causes hypertonicity, which shrinks cells and affects cell metabolism.
What is euvolemic hypernatremia?
TBW is down.
Total body sodium is the same, but proportionately higher.
Caused by DI: excess urine formation, no response to ADH.
What is hypervolemic hypernatremia?
Body gains excess sodium and retained water as a result, but not enough to dilute the sodium.
Caused by: excess NS, sodium bicarb, or excess salt tablets.
Primary aldosteronism.
What is hypovolemic hypernatremia?
TBW and sodium are down.
Water is down faster than sodium.
Caused by:
Low urine sodium dt diarrhea or excess sweating.
High urine sodium dt loop diuretics or severe hyperglycemia.
What are the lab abnormalities I would expect in hypernatremia?
Serum Na > 145 mEq/L
Increased serum osmolality
Normal/low urine osmolality
Urine specific gravity increased
Increased hematocrit and BUN
What can cause increased ADH secretion?
thirst
polydipsia
oliguria/anuria
What neuro symptoms would I expect to see in hypernatremia?
HA
Agitation, irritability, restlessness
Abnormal DTRs (usually depressed)
Delirium
Seizures
Coma
Death
What are common symptoms of dehydration?
Hypotension
Weak, rapid, thready pulse,
Decreased skin turgor
Dry mucous membranes
How do I manage hypernatremia?
Management of underlying cause.
Try to calculate free water deficit, giving free water fluids like 1/2 NS or D5W.
How do I manage acute hypernatremia?
More rapid correction, needs to be adjusted in 24 hours to avoid CNS damage.
How do I manage chronic hypernatremia?
Slowly, decrease 6-12 mEq/L per day.
Fast corrections will cause CNS edema.
