Net Filtration

Forces Favoring

Forces Opposing

Net filtration=forces favoring filtration-forces opposing filtration.

Forces favoring filtration: Capillary hydrostatic pressure (BP) (H2O from capillary to interstitial space) & Interstitial oncotic pressure (H2O from capillary to interstitial space via osmosis)

Forces opposing filtration: Plasma oncotic pressure (H2O from interstitial space to capillary via osmosis) & Interstitial hydrostatic pressure (H2O from interstitial space to capillary)

Edema

Water Balance

 Excessive accumulation of fluid within interstitial spaces.

Favored by: increased capillary hydrostatic pressure,

decreased plasma oncotic pressure,

increased capillary membrane permeability,

lymphatic channel obstruction.

Water balance is regulated primarily by ADH. ADH increases water reabsorption into the plasma from the distal tubules and collecting ducts of the kidneys.

Sodium (Na+)

90% of ECF cations.

Normal Range: 136-145 mEq/L

 Regulates extracellular osmotic forces, and thus water balance.

Important in nerve and muscle function.

Regulates acid-base balance (using NaHCO3 & NaPh)

Hormonal regulation of soduim by aldosterone.

Chloride (Cl-)

Major anion in ECF.

Provides elcetroneutrality (esp. in relation to Na+).

Transoprt is generally passive - follows active transport of Na⁺.

Varies inversely with HCO^_3, when Chloride levels go up, bicarbonate levels go down, and vice versa. 

Dehydration

Fluid loss.

Often due to: vomitting, diarrhea, or excessive sweating.

*Decrease in blood volume and blood pressure often occurs.

*Decreased blood volume often causes drop in atrial pressure, triggering secretion of ADH.

Isotonic Alterations

Hypovolemia

 Solution has same concentration of solutes as the plasma.

Isotonic fluid loss causes hypolvolemia.

Hypovolemia: decreased blood volume, capable of causing hypotension, tachycardia, and decreased urine output.

Caused by losses in pure plasma, or ECF; fluid volume is depleted but concentration and type of electrolytes and the osmolality remain in normal range.

Caused by: hemorrhage, severe wound drainage, excessive sweating (diaphoresis), and inadequate fluid intake.

Indicators: rapid heart rate, flattened neck veins, & normal or decreased BP. 

Isotonic electrolyte/glucose solutions given orally or intravaneously.

Isotonic Alterations

Hypervolemia

Isotonic fluid excess - Hypervolemia.

Caused by: excessive administration of intravaneous fluids, hypersecretion of aldosterone, or effects of drugs (cortisone).

Causes: distended neck veins, and increased blood pressure. Increased capillary hydrostatic pressure causes edema

Hyponatremia

Serum sodium level less than 135 mEq/L.

Sodium deficits cause plasma hypo-osmolality and cellular swelling.

Caused by: pure sodium loss, low intake.

Causes: headache, confusion, seizures, weakness, muscle cramps, nausea, vomiting.

Treatment: limit water intake, hypertonic IV solution with caution.

Water Excess

Caused by: compulsive water drinking, decreased urine formation, syndrome of inappropriate ADH.

Causes: cerebral edema (confusion and convulsions), weakness, muscle twitching, nausea, headache, and weight gain.

Treatment: 24 hour fluid restriction, intravaneous hypertonic sodium chloride given when manifestations are severe.

Potassium

Major ICF cation.

Concentration maintained by Na⁺/K⁺ pump

Regulates intracellular electrical neutrality in relation to Na⁺ and H⁺

Determinant of the resting membrane potential.

Essential for transmission and conduction of nerve impulses, normal cardiac rythyms, and skeletal and smooth muscle contraction.

Hypokalemia

Potassium level less than 3.5 mEq/L.

Caused by: decreased intake of potassium, chronic use of diuretics, increased loss of potassium, stress, trauma.

Causes: weakness, respiratory arrest, dysrhythmias, postural hypotension.

Treatment: increase potassium intake slowly by foods or IV piggy back.

*Causes prominent U-wave.

Hyperkalemia

Potassium level greater than 5.5 mEq/L.

Caused by: increased intake of potassium, shift of potassium from ICF to ECF, decreased renal excretion, insulin deficiency, or cell trauma.

Causes: increased neuromuscular irritability (tingling of lips & fingers), restlessness, intestinal cramping, and diarrhea; in severe cases, muscle weakness, loss of muscle tone, and flaccid paralysis, bradycardia leading to cardiac arrest.

*Causes a tall peak T-wave

Calcium

99% in bone.

Serum concentration: 8.8-10.5 mg/dl.

Regulated by parathyroid hormone.