Fluid Balance Flashcards
5 Components of Body Fluid
Water
Electrolytes
Glucose
Urea
Creatinine
Urea
nitrogenous compound formed in the liver through the breakdown of proteins and is excreted by the kidneys
Creatinine
byproduct of muscle metabolism, filtered by the kidneys
Breakdown of Body Fluid Compartments
Intracellular (28L of fluid)
Extracellular (13L of fluid)
Further divided into:
- intravascular: plasma
- interstitial
- transcellular
Components of Intracellular Fluid
Potassium
Phosphate
Protein
Magnesium
Components of Extracellular Fluid
Sodium
Chloride
Calcium
Bicarb
Proteins
8 Regulators of Fluid Balance in the Body
- Nervous System
- Arterial Baroreceptors
- Pituitary
- Adrenal Cortical
- Renal
- Cardiac
- GI
- Insensible water loss
How does the nervous system regulate fluid balance?
- Hypothalamus- senses changes in body fluid deficits
a) Triggers Thirst – primary trigger of regulation in CONSCIOUS patients
§ Unconscious patients unable to regulate thirst; we must do this for them
How do arterial baroreceptors regulate fluid balance?
blood pressure receptors
* When a decrease in arterial BP occurs the SNS responds with vasoconstriction.
* Vasoconstriction of renal arteries = a decreased GFR = reduced urine output > increased blood volume
How does the pituitary gland regulate fluid balance?
- ADH: affects only water reabsorption and therefore can cause water retention
- Plasma osmolality decreases (flooded with H20).
- SIADH – syndrome of inappropriate anti-diuretic hormone
- Anti-diuretic = reduce the production of urine or decrease urinary excretion
How does adrenal/cortical glands regulate fluid balance?
- Cortical = ‘cortisol’ is glucocorticoid, a hormone excreted by the kidneys that responds to stress and causes:
a) Sodium retention - Where sodium goes… water goes! - Aldosterone: hormone by product of RAAS system (stimulated by decreased fluid) that is sodium retaining/ potassium excreting and thus increase plasma osmolality
How do the kidneys regulate fluid balance?
Adjust urine volume
a) Balanced excretion of urine along with electrolytes to maintain homeostasis.
The renin-angiotensin-aldosterone system. Decreased blood volume and renal perfusion set off a chain of reactions leading to release of aldosterone from the adrenal cortex. Increased levels of aldosterone regulate serum K+ (decrease) and Na+ (increase), blood pressure, and water balance through effects on the kidney tubules.
How does the heart regulate fluid balance?
ANF: responsive to increased atrial pressure; decreases pressure/fluid/volume
a) If fluid volumes (increased pressure) increases, ANF causes vasodilation and increased urinary excretion of Na+ and H20
How does the GI regulate fluid balance?
- Secretes ~8000 mL fluid in normal intestinal operations
- Reabsorbs majority
- Diarrhea and vomiting > significant fluid losses.
How does insensible water loss regulate fluid balance?
- ~900 mL – sweat
Diffusion
the spontaneous movement of particles or molecules from an area of higher concentration to an area of lower concentration, driven by the aim to equalize the concentration gradient.
Active Transport and example for fluid regulation
§ Process in which molecules move against concentration gradient
* Example: sodium–potassium pump
§ External energy required
Osmosis
movement of solvent molecules, usually water, across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration, equalizing the concentration on both sides.
Osmolality
an estimation of the osmolar concentration of plasma
Measure of the concentration of osmotically active particles (such as ions and molecules) per kilogram of solvent in a solution, reflecting its impact on osmotic pressure.
Concentration of solutes
When is serum osmolality increased?
renal failure; dehydration, DM (Hyperglycemia/ HHS/ DKA); hypovolemic shock
When is serum osmolality decreased?
hyponatremia; overhydration; ++ diuretic therapy
What pressures cause the movement of water into and out of capillaries?
Capillary hydrostatic (water/fluid) pressure and interstitial/tissue oncotic (protein) pressure cause the movement of water out of the capillaries.
Explain fluid pressures at arterial end of capillary
capillary hydrostatic pressure exceeds plasma oncotic pressure, and fluid is moved into the interstitium.
Explain fluid pressures at venous end of capillary
the capillary hydrostatic pressure is lower than plasma oncotic pressure, and fluid is drawn back into the capillary by the oncotic pressure created by plasma proteins.
Explain the movement of fluid between body fluid compartments
Blood will enter into an arteriole, go through a capillary and drain into a venule
Artery has higher pressure than vein (32mmHg – 12mmHg)
* Hydrostatic pressure > at arteriole end
* Due to semi-permeable capillary membrane, arterial hydrostatic pressure causes water molecules to get out and form tissue fluid in interstitial compartment
Large plasma proteins (albumin) in capillary generate oncotic pressure (25mmHg)
o At arteriole end, fluid still being forced out because 32>25
o At venous end, 25>12, so tissue fluid will be reabsorbed
Oncotic pressure, also known as colloid osmotic pressure, is higher intravascularly (within the blood vessels) than intracellularly (inside the cells). This pressure is primarily exerted by large proteins, such as albumin, in the blood plasma, contributing to the regulation of fluid balance between the intravascular and interstitial compartments.
What does a volume deficit result from?
Extracellular contraction
water deficiciency: hypernatremia
sodium deficiency: hyponatremia
isotonic ECF deficit: normal sodium
What does volume excess result from?
Extracellular expansion
water excess: hyponatremia
sodium excess: hypernatremia
isotonic ECF excess
Clinical signs of FV deficit
- ↓ skin and tongue turgor
- Decreased moisture in mouth cavity. May be due to FVD or mouth breathing
- In marked and severe body fluid loss the hematocrit, hemoglobin, creatinine & BUN are ↑
- ↓ urinary output
- Marked dehydration= increased urine concentration –measured by specific gravity of urine ↑ (normal 1.010 to 1.020).
- 5% weight loss is associated with 3-5 litres of fluid loss.
- Postural hypotension-a drop in systolic pressure of 20 mm/Hg accompanied by tachycardia, suggest FVD.
- Prolonged Cap Refill
Normal specific graity
normal 1.010 to 1.020
5% weight loss is associated with
3-5 litres of fluid loss.
Define first, second, and third spacing in fluid excess
First spacing
* Normal distribution of fluid in ICF and ECF
Second spacing
* Abnormal accumulation of interstitial fluid (edema)
Third spacing
* Fluid accumulation in part of body where it is not easily exchanged with ECF
* Where? Cerebral Vault
3 Causes of FVE
↑retention of Na & H20:
* Examples- Heart failure, liver failure, nephrotic syndrome, glucocorticosteroids, SIADH
↓ excretion of Na & H20: Renal failure
Excess administration of IV fluids : crystalloid/colloid solutions, blood products, TPN
Examples of when increased retention of Na/H20 would cause FVE
Heart failure, liver failure, nephrotic syndrome, glucocorticosteroids, SIADH
Examples of when increased excretion of Na/H20 would cause FVE
Renal failure
Explain how edema occurs
§ Accumulation of fluid in the interstitial space.
§ When there is excess in volume, fluid pressure is greater than the colloidal osmotic pressure, therefore more fluid is pushed into the interstitial spaces.
§ ↑ hydrostatic pressure in capillaries forces fluid into the interstitial spaces → can occur because of a mechanical blockage
§ ↓ plasma colloid osmotic pressure from ↓ protein content of plasma → fluid flowing from plasma to interstitial spaces.
§ ↑ permeability of capillaries allows protein to seep into the interstitial spaces and create an osmotic pull.
Explain Evaluation of Edema
+1: slight, no obvious distortion
+2: deeper pit, no obvious distortion
+3: pit is obvious, extremities are swollen
+4: pit remains with obvious distortion
7 Management Points for FVE
§ Sodium restricted diets
§ Heart failure, hepatic failure with ascites, renal failure & hypertension.
§ Diuretics – such as lasix
§ Monitor intake & output, weights, vital signs/respirations
§ Monitor edema in dependent parts of body. Assess for pitting edema
§ Turn and position regularly as edematous areas are prone to skin breakdown.
§ Monitor lab values - Which ones? Electrolyte, hematocrit (concentration of RBC for hemodilution)
Symptoms of Pulmonary Edema
§ Shortness of breath
§ Blood tinged frothy white sputum.
§ Moist crackles in lungs
§ Anxiety
§ Oxygenation compromised
§ Life threatening
Define Intracellular FVE
Results from excess of water or decrease in the solutes in the intravascular systems.
Fluid in the blood vessels is hypo-osmolar.
By osmosis, water moves from an area of less solute concentration to an area of greater solute concentration, so fluid moves from vascular space to the cells.
Cerebral cells are usually the first to be involved; cerebral edema in hyponatremia
What is central venous pressure reflective of and what does an elevated level indicate?
which correlates with RV pressure when the tricuspid valve opens.. It is used to measure “volume status” (preload) of R side of heart.
Elevated CVP = elevated fluid status
What do isotonic IV fluids do?
IV fluids remain in intravascular space
remains in the vascular system
What do hypotonic IV fluids do
IV fluids shift into the cells
If a cell is surrounded by hypotonic fluid, water moves into the cell, causing it to swell and possibly to burst.
Fluid moves from the extracellular fluid compartments to the intracellular fluid
What do hypertonic IV fluids do
IV fluids pull fluid from intracellular and extracellular compartments into intravascular compartment
If a cell is surrounded by hypertonic fluid, water leaves the cell to dilute the ECF; the cell shrinks and eventually may die.
Fluid moves from the intracellular to the extracellular fluid compartment
Crystalloid vs Colloid Fluids
Crystalloids consist of isotonic saline or balanced electrolyte solutions and widely distribute across extracellular fluid compartments,
Colloids contain high-molecular-weight molecules suspended in crystalloid carrier solution and do not freely distribute across the extracellular fluid compartments.
Isotonic IV solutions
0.9% NaCl, Ringer’s Lactate, 2/3-1/3 soln
remains in the vascular system
Hypertonic IV solutions
10% DW, 5%D/0.9%NaCl, D5%/.45%NaCl
Fluid moves from the intracellular to the extracellular fluid compartment
Give more solutes
symptomatic hyponatremia
Hypotonic IV solutions
0.45% NaCl
Fluid moves from the extracellular fluid compartments to the intracellular fluid
Give more water than electrolytes
Used for dehydration, diarrhea, n/v
Typical Adult Fluid Requirement
35 ml/kg/day
§ Quick trick for calculating maintenance fluids=
* 40 +weight (kg) = amount required/hour
