Fluid Balance and Electrolytes

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1

60%

percent of body weight made up of water

2

66%

water found in intracellular fluid

3

33%

water found in extracellular fluid

4

osmoreceptors

detect change in concentration of solutes in blood

5

hypothalamus

signals thirst response and hormone release by signaling osmoreceptors to drink more fluids and the pituitary to release ADH/vasopressin

6

osmolality

reflects the status of hydration of the intracellular and extracellular compartments as part of the total body hydration; measures amount of dissolved particles per unit of water; reflects changes in properties of a solution in relation to water

7

polydipsia

excess water seen as low plasma osmolality

8

water deficit-increased osmol

AVP and thirst activated; kidneys respond to ADH signal to retain water and reabsorb in the collecting ducts

9

renin angiotensin aldosterone system

the response to decreased blood volume; blood pressure decreased, heart signaled to increase contraction strength, kidneys signaled to secrete hormones to stimulate thirst (angiotensin II) and stimulate hormone secretion to reabsorb sodium in DCT, adrenal glands stimulated to release aldosterone

10

antidiuretic hormone - vasopressin

controls amount of water reabsorbed from kidney; produced in hypothalamus delivered to posterior pituitary; constricts arterioles in peripheral circulation

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renin

enzyme produced, stored, and secreted by kidney (glomerulus) in response to low sodium; acts on angiotensinogen to produce angiotensin I

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angiotensin I and II

hormones; I becomes II by ACE causing vasoconstriction to help increase blood pressure; acts on hypothalamus to increase thirst and kidneys to increase sodium reabsorption; stimulates release of aldosterone

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aldosterone

hormone from adrenal cortex; acts on distal tubule and collecting duct in nephron to reabsorb Na and excrete K; regulates blood pressure through sodium diffusion in ECF; as it increases K decreases through excretion by renal tubule into urine

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urine osmolallity

diagnose renal concentration disorders (concentration ability, electrolyte balance, and polyuria) as well as patient hydration status; increased in hypovolemia, SIADH; decreased in diabetes insipidus, polydipsia

15

serum osmolality

diagnose renal concentration disorders as well as patient hydration status; increased in dehydration, hyperglycemia, DKA, diabetes insipidus, ingestion of alcohols; decreased in overhydration, hyponatremia, SIADH

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Na, Cl, and HCO3

three main analytes that affect osmolality

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275-295 mOsm/kg

normal serum osmolality

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500-800 mOsm/kg

normal 24 hour urine osmolality

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300-900 mOsm/kg

normal random urine osmolality

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2Na + gluc/20 + BUN/3

calculated osmolality equation

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osmolal gap

calculated difference between measured and calculated osmo; shows presence of substances other than Na, urea, and glucose such as alcohols, lactate, beta-hydroxybutyrate

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5-10 mOsm/L

reference range for osmolal gap

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Na, Cl, K

electrolytes that regulate fluid volume and osmotic pressure

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K, Mg, Ca

electrolytes that regulate myocardial rhythm and contractility

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Mg, Ca, Zn

electrolytes that activate enzymatic reactions/cofactors

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Mg, Ca

electrolytes that activate coagulation cascade

27

Mg

electrolytes that regulate ATPase ion pumps

28

HCO3, K, Cl

electrolytes that maintain acid base balance

29

K, Mg, Ca

electrolytes that aid in neuromuscular excitability

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Ca

cofactors necessary for coagulation

31

Mg, PO4

electrolytes that produce ATP from glucose

32

sodium

largely determines plasma osmolality; major extracellular cation in ECF (90%); active transport systems maintain correct ICF/ECF concentrations; 60-75% reabsorbed in PCT; kidneys can conserve of excrete large amounts; regulated by water intake, excretion, and blood volume (RAAS)

33

hyponatremia

low plasma sodium <135 leading to nausea, vomiting, lethargy, and ataxia; caused by increased sodium loss (dehydration, burns, K deficiency, decreased aldosterone), increased water retention (renal tubal disorders, nephrotic syndrome, hepatic cirrhosis, CHF), and water imbalance (polydipsia, SIADH)

34

hypernatremia

high plasma sodium >145 leading to altered mental status, lethargy, irritability, seizures; hyperosmolar due to water imbalance (water problem, not sodium problem); caused by excess water loss (sweating, prolonged diarrhea, burns, diabetes insipidus), decreased water intake, increased sodium intake

35

potassium

major intracellular cation; regulates neuromuscular excitability, heart contraction, regulation of ICF volume, pH regulation; reabsorbed by PCT in kidney, excreted and exchanged in DCT and collecting ducts for Na; released by muscles during exercise, hyperosmolality gradually depletes as it leaves with water

36

insulin

promotes potassium entry into skeletal muscle and liver increasing Na/K ATPase pump

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catecholamines

promote cellular entry of potassium

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beta blockers

impair cellular entry of potassium

39

hypokalemia

low plasma potassium <3.5 due to increased renal or GI loss, alkalosis, or insulin use leading to weakness, fatigue, paralysis, and arrhythmia

40

hyperkalemia

high plasma potassium >5.1 caused by another disorder such as decreased excretion in renal failure, cellular shift caused by acidosis, loss of cellular potassium due to insulin insufficiency, hyperosmolality due to water and K being pulled from cells into plasma, tissue breakdown/injury, drugs such as diuretics that increase urine output, ACE inhibitors, digoxin, and collection issues causing false increase; leads to muscle weakness, cramps, mental confusion, tingling or numbness, cardiac arrest

41

chloride

major extracellular anion that maintains osmolality and blood volume; almost completely absorbed through diet by intestinal tract-reabsorbed by renal tubules with Na and excess excreted in urine and sweat; maintains electrical neutrality; aids in Na reabsorption in kidney, loss of HCO3 from cell causes diffusion of Cl from plasma into RBC to maintain neutrality

42

hypochloremia

low plasma chloride <98 caused by excess loss (vomiting and ketoacidosis), DKA, or renal disease

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hyperchloremia

high plasma chloride >107 caused by dehydration, excess HCO3 loss (diarrhea, renal tubular acidosis, metabolic acidosis

44

amperometry

coulometry to generate silver ions which combine with Cl ions to quantitate

45

sweat chloride testing

gold standard for cystic fibrosis diagnosis; CFTR gene mutation on chromosome 7

46

bicarbonate

second most abundant anion in ECF; major component of buffering system in blood; measured as TCO2 in plasma/serum electrolyte panel- bicarb ion HCO3, carbonic acid H2CO3, and dissolved CO2

47

chloride shift

CO2 enters RBC, combines with H2O to form carbonic acid H2CO3, H+ dissociates to form HCO3 which leaves the cell and chloride enters

48

alkalosis

leads to urinary increase in HCO3 excretion

49

acidosis

leads to urinary increase in tubular reabsorption of HCO3

50

decreased bicarb

caused by respiratory alkalosis and metabolic acidosis; inhibition of carbonic anhydrase by diuretics causing renal loss of bicarb

51

increased bicarb

caused by respiratory acidosis and metabolic alkalosis

52

total carbon dioxide

measures total carbon dioxide content-bicarb, carbonic acid, and associated CO2 with proteins; measured by ISE for pCO2 and enzymatic methods

53

23-29

reference range for TCO2

54

anion gap

calculated subtracting anions from the cations to indicate an increase in 1 or more unmeasured anions in serum-QC for analyzer; increase caused by renal failure, ketoacidosis, glycol poisoning, lactic acidosis, MeOH intoxication, ASA OD

55

magnesium

cofactor for >300 enzymes included in glycolysis, transcellular ion transport, neuromuscular transmission, energy production, oxidative phosphorylation, carb, protein, lipid, and nucleic acid synthesis, and release and response to certain hormones; 4th most abundant cation in body, 2nd intracellularly; mostly found in bone and tissue, but also bound to albumin in serum and RBC; found in diet, absorbed through GI tract; regulated by kidneys, aldosterone increases renal excretion, and affected by PTH (enhanced renal and intestinal absorption)

56

hypomagnesemia

low plasma magnesium <0.63; rare in healthy, depletion due to severe illness, reduced intake, malabsorption, increased renal excretion, endocrine PTH malfunction, drugs/diuretics; leads to cardiac arrhythmias, tetany, tremors, paralysis, coma; treated with oral supplements, antacids, and injections

57

hypermagnesemia

high plasma magnesium >1.0; rarely seen, caused by decreased renal excretion (renal failure), increased antacids, dehydration, and bone carcinoma; leads to hypotension, flushing, nausea, vomiting; treated by D/C Mg products

58

phosphate

intracellular found everywhere in living cells; found in bone, soft tissue, and 1% in serum; component of phospholipids, DNA, RNA, and ATP-reservoirs are ATP, creatine phosphate; obtained through diet and intestinally absorbed, lost from bone and excreted in kidney; PTH increases renal excretion, vitamin D increases intestinal and renal absorption; diurnal variation

59

high phosphate

phosphate >1.42 seen in acute and chronic renal failure, ALL, and neonates

60

low phosphate

phosphate <0.78 caused by increased renal excretion, decreased intestinal absorption (vit D deficiency or antacid use); enhanced in patients with DKA, COPD, asthma, malignancy, anorexia, alcoholism, and irritable bowel

61

calcium

essential for myocardial and skeletal muscle contraction; needed for hemostasis and bone development; 99% found in bone, 1% in ECF (45% ionized in ECF, others bound to albumin, bicarb, citrate, lactate); regulated by PTH (stimulates osteoclast breakdown to release calcium when low), vitamin D (increases intestinal absorption), and calcitonin (inhibitor)

62

ionized calcium

free biologically active form of calcium used to assess renal function, parathyroid function, and bone disease

63

atomic absorption spectrometry

gold standard for calcium measurement along with ISE for ionized

64

hypocalemia

low plasma calcium <1.03 caused by hypomagnesemia (inhibits PTH and impairs its action with bone, causes vit D resistance), hypoparathyroidism (No PTH, little vit D, decreased calcium absorption) decreased albumin, renal disease; present in critically ill, septic, burned, cardiopulmonary insufficiency, renal failure; monitored during open heart to measure cardiac output; leads to neuromuscular irritability, tetany, cramps, and arrhythmia

65

hypercalcemia

present in excess PTH and malignancy; nonspecific symptoms such as weakness, lethargy, constipation, nausea, and vomiting; treated with estrogen replacement and parathyroidectomy

66

parathyroid hormone

increases serum Ca bone resorption, decreases serum Phos by increasing renal excretion, increases D3, regulated by ionized Ca

67

1,25 dihydroxyvitamin D3

increases Ca and Phos absorption in intestines, increases osteoclast activity with PTH, and increases renal absorption of Ca and Phos

68

calcitonin

decreases Ca and Phos by inhibiting osteoclast bone reabsorption

69

osteoporosis

inadequate dietary calcium and vitamin D; most prevalent metabolic bone disease in adults; DEXA scan to diagnose

70

rickets

caused by abnormal bone mineralization, calcium, phosphate, vit D deficiency; occurs in growing bone leading to deformity of long bones and soft weak bones

71

osteomalacia

caused by abnormal bone mineralization, calcium, phosphate, vit D deficiency; occurs in adults after closure of epiphyseal plates so no deformities

72

lactate/lactic acid

produced by most tissues in the body, highest in muscle, cleared by the liver in gluconeogenesis; measures hypoxia in shock, MI, CHF, PE, blood loss; may be present in metabolic situations, leukemia, liver or renal disease, salicylate or alcohol poisoning; identifies severity of sepsis and effectiveness of treatment

73

renal tubules

reabsorb phos, Ca, Mg, Na, Cl, K, and HCO3

74

Na, K, TCO2, Cl, anion gap

tests included in electrolyte panel

75

Na, K, TCO2, Cl, AG, Gluc, Ca, BUN, Creat

tests included in basic metabolic panel

76

Na, K, TCO2, Cl, AG, Gluc, Ca, BUN, Creat, Alb, TP, ALP, ALT, Tbil

tests included in comprehensive metabolic panel