Fluid Balance (Notes)

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What are the 2 main fluid compartments of the body?: 1. ICF
2. ECF
What are the 2 ECFs?: 1. Interstitial Fluid (ISF) - between cells
2. Intravascular Fluid (IVF) - in the vessel
What type of pump transfers Na+ and K+? (also requires ATP): Na+ Pump
What is the major IC ion?: K+
What is the major EC ion?: Na+
What is a key factor to fluid/electrolyte balance?: Na+ (water follows Na+)
What is isotonic?: Na+ = Vol of H2O
What is hypertonic?: higher [Na+] in ECF compared to ICF
- causes fluids shift from inside the cell toward the ECF (cell will be shrivelled)
What is hypotonic?: lower [Na+] in ECF compared to ICF
- causes fluids shift from outside the cell into the IC compartment
What are 2 key determinants of Fluid Balance?: 1. Osmotic Pressure
2. Hydrostatic Pressure
What is a key factor for osmotic pressure?: Na+
What is key in hydrostatic pressure?: plasma proteins (Albumin)
- arises from cardiac contraction (if there is low albumin, fluid will leak out)
What is hypervolemia?: too much water in intravascular space (vessel)
What are 2 causes of hypervolemia?: 1. Decreased kidney function
2. Too much IV solution
What are 4 S&S of Hypervolemia?: 1. increased BP
2. increased JVD (can see the increased volume)
3. Bounding pulse (increased vol --> increased CO --> more fluid pushed against arteries)
4. Weight Gain
How does the body compensate for hypervolemia?: - fluid shift (it will try to move the fluid from the IV space to the IS space - "third spacing")
- quicker
- compensation will cause peripheral (tissue) edema or pulmonary (lungs) edema
What does "third spacing" mean?: a fluid shift from intravascular space to interstitial space
How does the body correct hypervolemia?: - increased renal output is the only correction
- slow (but most effective long term)
What is hypovolemia?: not enough water in the intravascular space
What are 2 causes of hypovolemia?: 1. decreased H2O intake
2. increased renal elimination of free water (due to impaired tubular function OR inability to concentrate urine)
What are 4 S&S of hypovolemia?: 1. decreased BP (b/c BP = HR x Vol x PVR (peripheral vascular resistance)
2. increased HR (HPA)
3. Weight loss
4. Weak Pulse
How does the body compensate for hypovolemia?: fluid shift (tries to move fluid from interstitial space to intravascular space)
How does the body correct hypovolemia? (2 ways): 1. Thirst
2. Kidney - ADH system (release of ADH)
- RAA System (release of Renin)
What are 4 secondary S&S of hypovolemia after fluid shift?: fluid shift from IS or IC spaces into IV space will cause intracellular dehydration causing:
1. dry skin
2. poor skin turgor
3. dry mucous membranes
4. confusion (brain cells also dehydrated)
How does thirst help to correct hypovolemia? (***thirst & kidney (ADH & RAA) help to correct imbalance): - increased osmolarity triggers mouth osmoreceptors --> stimulates "thirst center" of hypothalamus --> person wants to drink --> some lost fluid replaced & ECF osmolarity diluted
What are 3 things that trigger thirst?: 1. Increased osmolarity (osmoreceptors)
2. Decreased circulating blood volume (baroreceptors)
3. Dryness of mucous membranes of mouth
How does ADH system help to correct hypovolemia? (***thirst & kidney (ADH & RAA) help to correct imbalance): increased osmolarity and/or decreased plasma volume ---> hypothalamic osmoreceptors stimulated --> posterior pituitary to release ADH --> ADH adds pores which increase renal tubular permeability --> increased H2O reabsorption & decreased urine output --> return plasma osmolarity to normal
What are 3 mechanisms of sodium balance?: 1. Fluid shifts
2. RAA/Aldosterone
3. ANP
What is hyponatremia?: low sodium (Na+) in intravascular space
What are 3 causes of hyponatremia?: 1. Increased Na+ loss (N/V, burns, diuretics)
2. decreased Na+ intake (rare)
3. Dilution of Na+
- replaced fluid losses with D5W (glucose in D5W metabolized to H2O --> increased H2O --> dilute Na+
- sweating --> stimulates thirst --> increases H2O intake --> dilute Na+
- impaired excretion of H2O caused by CHF (congestive heart failure), renal failure or cirrhosis --> dilute Na+
What are 3 causes of diluted Na+?: 1. replaced fluid losses with D5W (glucose in D5W metabolized to H2O--> increased H2O --> dilute Na+
2. sweating --> stimulates thirst --> increases H2O intake --> dilute Na+
3. impaired excretion of H2O caused by CHF (congestive heart failure), renal failure or cirrhosis --> dilute Na+
What are 3 S&S of hyponatremia?: 1. Edema (swelling caused by increased fluid in IS space
2. Vascular hypovolemia
- increased BP (BP = HR x Vol x PVR)
- increased HR (HPA via epi acting on SA node --> increased firing)
3. Behavioural/Neurological
- less Na+ available to depolarize cells
- lethargy, confusion, seizures (LCS)
How does the body compensate for hyponatremia?: Fluid shift (fluid will move from IV space to IS space only)
- results in edema and IV hypovolemia
How does the body CORRECT hyponatremia?: RAA/Aldosterone
- decreased circulating blood volume or low [Na+] in plasma --> stimulates release of renin (enzyme secreted by juxtaglomerular cells in kidney) --> stimulates formation of angiotensin (inactive polypeptide) --> converted to angiotensin II by ACE (angiotensin converting enzyme) --> stimulates secretion of aldosterone --> primary response is increased Na+ reabsorption --> secondary response is increased H2O reabsorption (***angiotensin II also causes vascular remodelling as well as vasoconstriction --> increased BP)
What are 5 characteristics of aldosterone?: 1. mineral CORTICOID (steroid hormone) 2. synthesized secreted from the ADRENAL CORTEX
3. secreted when Na+ low OR when K+ high
4. increases REABSORPTION of Na+ and secretion of K+ by distal tubule of kidney
5. results in increased Na+ in ECF & K+ is excreted in urine (secondary: reabsorption of H2O)
What is Hypernatremia?: too much sodium (Na+) in the intravascular space
What are 5 causes of hypernatremia?: 1. increased Na+ intake (rare)
2. inappropriate administration of hypertonic saline solution (D5 NS)
3. over-secretion of aldosterone (Cushing's)
4. Renal Failure
5. Altered Na+ loss in relation to H2O loss (diabetes insipidus (problem with kidneys and losing too much fluid), ADH, DM, polyuria, profuse sweating, diarrhea)
Altered Na+ loss in relation to H2O loss? (6 causes): 1. diabetes insipidus (problem with kidneys - lose too much fluid)
2. ADH
3. DM
4. polyuria
5. profuse sweating
6. diarrhea
How does the body compensate for hypernatremia?: fluid shift (fluid will move from IS space and IC space into the intravascular space) --> causes intracellular dehydration --> thirst, fever, dry mucus membranes, restlessness (b/c water is lost from cells) & hypervolemia (now increased IV volume) --> weight gain (long term), bounding pulse, increased BP
What 2 S&S of hypernatremia? (as well, 3 S&S for each category): 1. intracellular dehydration --> thirst, fever, dry mucus membranes, restlessness (b/c water is lost from cells) 2. hypervolemia (now increased IV volume) --> weight gain (long term), bounding pulse, increased BP
How does the body CORRECT hypernatremia?: ANP (Atrial Natriuretic Peptide):
- increased fluid volume --> increased stretch of the heart --> triggers atrial cells (in the heart) to release ANP --> increases glomerular filtration rate & INHIBITS RAA --> decreased Na+ reabsorption --> increased Na+ excretion by kidney
Sudden increases in _____ could be fatal, but body can adapt to small gradual increases ( _________ adaptation).: K+; K+
What is hypokalemia?: low K+ (potassium) levels in intravascular space
What are 2 causes of hyperkalemia?: 1. decreased intake (elderly, alcoholism, anorexia nervosa)
2. Loss of K+ (renal disorders, GI disorders (diarrhea), vomiting/Cont. NG (nasogastric) suctioning, diuretic use (fluid pills) --> inhibits reabsorption of Na+ --> increased secretion of K+
What are 3 S&S of hypokalemia?: Mild Losses:
1. asymptomatic
Severe Losses:
2. decreased neuromuscular excitability --> skeletal muscle weakness, smooth muscle atony (lacking muscular tone), & cardiac dysrhythmias
3. cardiac dysrhythmias - also due to changes in membrane excitability
- EKG changes
What is hyperkalemia?: high K+ (potassium) in intravascular space
What are 4 causes of hyperkalemia?: 1. increased intake
2. shift of K+ from cells to ECF (cell trauma (burns), insulin deficiency (insulin promotes cellular entry of K+), hypoxia
3. decreased renal excretion
4. K+ sparing diuretics
What are 3 S&S of hyperkalemia?: 1. Muscles:
- early - hyperactive
- late - weakness & flaccid paralysis
2. Cardiac - decreased cardiac conduction (cardiac arrest) & more rapid depolarization
3. Kidney: Oliguria (decreased urine)
Kidney can reabsorb or excrete ______.: K+
What are 2 ways K+ (potassium) can regain balance?: 1. Kidney can reabsorb or secrete K+
2. High K+ --> release of ALDOSTERONE from adrenal cortex --> speeds up ATPase --> 2 K+ pumped out for each Na+ reabsorbed
What is the approximate amount of insensible losses that we lose each day?: 600 mL/day
What are 2 ways to manage fluid/electrolyte imbalances? (if there is fluid excess or severe hypovolemia & intracellular dehydration): 1. Fluid excess - treat with diuretics - promotes excretion
2. severe hypovolemia & intracellular dehydration - fluid replacement (IV solutions)
What are 3 common types of IV solutions?: 1. 0.9% NS (regular strength - usually just written as NS - [normal saline]) - contains 0.9 % Na+ (sodium)
2. D5 - dextrose 5% and it is usually mixed with water, NS, or R/L
3. R/L - ringers lactate (combination of glucose, electrolytes, etc.)
What type of IV solution could you give to correct a hypotonic environment?: 0.45% NS, 0.33% NS
What type of IV solution could you give to correct a hypertonic environment?: D5 with R/L, D5 with 0.45%NS, D5 with NS
What type of IV solution could you give for an isotonic environment?: 0.9%NS, R/L
What does the choice of IV solution depend on?: 1. Na+ (sodium) - does Na+ need to be replaced, eliminated, or maintained?
2. Where do you want the H2O to go? - in the cells, pulled out of the cells, or in the vessels?
(****Correct INTRAVASCULAR deficits before intracellular!!!)
What type of IV solution would you give someone with hyponatremia?: 0.9% NS
What type of IV solution would you give someone with hypernatremia?: D5W - dextrose 5% in water (contains H2O so can dilute out the Na+)
(****DO NOT use 0.9% NS if patient has hypernatremia or at risk for hypernatremia)
What are 3 different combinations of IV solutions you would give someone with hypovolemia?: hypotonic solutions:
1. D5 R/L
2. D5 NS
3. D5 .45% NS
What type of IV solution would you give someone with intracellular dehydration?: Hypotonic solution:
0.45% NS
What types of IV solutions could you give for maintenance of fluid/electrolyte balance?: 1. combinations of dextrose and saline
(ex. D5 0.33% NS or D5 0.66% NS) - provides glucose for energy, free water, and some electrolytes)
2. R/L (ringers lactate) - good replacement of large volume & electrolyte losses (post-surgery or bleeding)
(****D5W - should not give to diabetic; NS - should not give to someone with hypernatremia)
What IV solution could you give to someone who has hypokalemia?: KCL
(****if patient is receiving large amounts of Na+, they are at risk for hypokalemia (b/c high Na+ reaching distal tubules -> some Na+ will be exchanged for K+ --> increased K+ loss)

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