Fluids & Electrolytes Flashcards
Intracellular fluid: How much of total body fluid + Electrolyte concentrations
(2/3rds of all body fluid)
- Large amounts of K+
- Moderate amounts of Mg2+
- Small amounts of Na+, Cl-, HCO3-, PO3-
- Almost no Ca2+
Extracellular fluid: How much of total body fluid?, how much plasma vs interstitial fluid? what form is IF fluid and why? Electrolyte concentrations in ECF?
- Plasma: 1/4 of ECF
- Interstitial fluid (IF) 3/4 of ECF. Most IF fluid is in gel form. This cushions cells, and opposes outflow of water from capillaries, preventing accumulation of free water in interstitial spaces.
- Large amounts of Na+ and Cl-
- Moderate amounts of HCO3-
- Small amounts of K+, Mg2+ Ca2+ and PO3-
5 places of 3rd space transcellular compartment. How much of ECF is 3rd space
CSF, peritoneal cavity, joint spaces, pleural space, pericardial space.
1% of ECF.
How does ADH work?
Baroreceptors present in vascular system sense changes in pressure, prompting hypothalamus to send impulse to posterior pituitary
Pituitary sends ADH to collecting duct of kidney, which prompts kidney to retain water
How does RAAS work?
- When there is a decrease in blood, the pressure-sensitive receptors in kidney prompts it to secrete renin.
- In the bloodstream renin meets angiotensinogen which comes from the liver. When they meet, they make angiotensin I. Angiotensin I will meet angiotensin-converting enzyme (ACE) in the lungs, which turns it into angiotensin II.
- Angiotensin II is a potent vasoconstrictor and also acts directly on renal tubules to increase sodium reabsorption.
- This increases BP in the kidney, prompting less renin to be released, and maintaining homeostasis.
- Angiotensin II also goes to adrenal cortex, causing it to secrete aldosterone.
- Aldosterone goes to the kidney and causes sodium and water to be reabsorbed in the distal convoluted tubule. This also causes increased blood volume and pressure.
Aldosterone also causes potassium and magnesium to leave the blood stream due to ionic exchange.
How do natriuretic peptides work?
- Baroreceptors in the atria of the heart senses increases in stretch and blood volume, and releases ANP and BNP.
ANP causes kidney to excrete more sodium (natriuresis means diuresis of sodium), reducing the blood volume.
4 Physiologic mechanisms that contribute to edema formation
- Increased hydrostatic pressure
- Decreased colloidal osmotic pressure
- Increased capillary permeability
Obstruction to lymph flow
Causes of increased hydrostatic pressure
○ Increased vascular volume or venous congestion
○ Heart disease
○ Pregnancy
Kidney disease
Causes of Decreased colloidal osmotic pressure
○ Increased loss of plasma proteins
○ Malnutrition
○ Kidney disease
○ Burns
Liver disease
Causes of increased capillary permeability
○ Inflammation
○ Allergic reaction
○ Tissue injury/burns
Malignancy
Generalized vs localized edema
- Localized edema occurs in a limited anatomic site, often from tissue injury, local inflammation, etc.
- Generalized edema is frequently the result of increased vascular volume common in congestive heart failure.
- Edema resulting from increased capillary pressure commonly causes fluid to accumulate in dependent parts of the body like the ankles and feet, called dependent edema.
- Right sided heart failure causes blood to pool throughout the venous system causing organ congestion and edema of dependent extremities.
Complications of edema
- Makes it difficult for O2, CO2 and nutrients to be transported to cells
- Can separate tight junctions making it easier for microbes to enter cells
Interstitial edema can be life threatening in the brain, throat, and inside lungs
- Can separate tight junctions making it easier for microbes to enter cells
3rd space accumulation: 5 names for different places, most common cause, what can effusion fluid contain
- Usually due to lymph obstruction
- Pericardial effusion, pleural effusion, joint effusion, hydrocephalus in arachnoid space, ascites in pericardial space.
Effusion can contain blood, plasma proteins, inflammatory cells, and ECF.
- Pericardial effusion, pleural effusion, joint effusion, hydrocephalus in arachnoid space, ascites in pericardial space.
Hypovolemia: Isotonic fluid volume deficit: general description and physiology
Loss of water and sodium in equal proportions, concentrations of sodium in ECF remain normal. Vasculature shrinks, poor perfusion, BP decreases.
4 categories of causes of hypovolemia
-1. Inadequate fluid intake
- 2. GI loss of sodium containing fluid
○ Emesis, Diarrhea, Gastric suction, Fistula drainage
- 3. Polyuria
○ Adrenal insufficiency (aldosterone insufficiency), Sodium-wasting renal disorders, Extensive diuretic use
- 4. Other body fluid loss
Hemorrhage, Massive diaphoresis, Third-space fluid accumulation, Paracentesis and similar procedures (fixing 3rd space fluid accumulation), Burns
Clinical manifestations of hypovolemia
- Vitals: Thready, rapid pulse, Orthostatic hypotension, Increase cap refill time
- Signs: Sudden weight loss 3-4lbs in a day, Tenting of skin, Decreased urine output & increased concentration, Sunken eyes, sunken fontanelles
- Symptoms: Thirst, Dizzy, faint
Labs: Increased RBC, hematocrit, Blood Urea Nitrogen
Hypervolemia: Isotonic fluid volume excess: 2 main mechanisms
Inadequate Na and H2O elimination
○ CHF, renal disease/failure
○ Hyperaldosteronism
○ Cushings, corticosteroids (cortisol causes Na+ retention)
Cirrhosis
Excess intake of Na and water
○ Excess dietary intake/OTC meds plus water
- Excessive IV infusion of isotonic solutions
Clinical manifestations of hypervolemia
- Vitals: Fast & bounding pulse
- Signs: Sudden weight gain, Edema, Bulging neck veins, Crackles in lungs, Cough, Bulging fontanelles
- Symptoms: Dyspnea, Orthapnea
- Labs: Decrease in BUN and hematocrit
Related conditions: Ascites and pleural effusion
Complications of hypervolemia
Pulmonary edema
Hyponatremia: general physiology and vulnerable population
Serum sodium <135. Water flows into cells to equalize concentration & cells become swollen
Older populations more vulnerable to hyponatremia due to decreased renal function
Causes of hyponatremia: 3 main physiologic processes
Gain of relatively more water than salt (euvolemic hypotonic hyponatremia)
Loss of relatively more salt than water (hypovolemic hypotonic hyponatremia)
Fluids shift (hypertonic hyponatremia)
Specific causes of gaining relatively more water than salt
○ Dilute infant formula
○ Excessive SIADH
○ Excessive IV dextrose
○ Hypotonic irrigating solutions
○ Tap water enemas
○ Psychogenic polydipsia (mental illness)
○ Beer potomania
○ Ecstasy
○ Near-drowning in fresh water
○ SSRIs
Specific causes of losing relatively more salt than water
○ Diuretics esp thiazides
○ Salt-wasting renal disease
Replacing fluid losses from emesis, diarrhea, gastric suction, diaphoresis or burns with pure water
Mechanism for fluid shift process causing hyponatremia
Sodium in ECF becomes diluted as water moves out of cells in response to the osmotic effects of elevated blood glucose (Hyperglycemia)
Clinical manifestations of hyponatremia
- Anorexia, nausea/vomiting,
- Malaise, weakness, fatigue, Headache
- Muscle cramps,
- Fingerprint edema on sternum,
Seizures, coma (CNS symptoms d/t swelling of brain cells)
Hypernatremia: characteristics
Characterized by hypertonicity of ECF and almost always causes cellular dehydration.
Causes of hypernatremia: 2 main mechanisms
Gain of relatively more salt than water
Loss of relatively more water than salt
Causes of gaining relatively more salt than water
○ Tube feeding
○ IV infusion of hypertonic solution
○ Near-drowning in salt water
○ Overuse of salt tablets
○ Food intake w reduced fluid intake
○ Difficulty swallowing liquids
○ No access to water
Inability to respond to thirst