Electrolytes and Body Water ppt

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what percentage of our mass is water?

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what percentage of our mass is water?

60%

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what are the three places water can be?

  • ICF: all water within cell membranes

  • ECF: intravascular and interstitial

  • transcellular water (CSF and vitreous)

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what determines water distribution?

solutes (electrolytes) exert a pressure against water (osmotic pressure)

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osmolality

  • measure of dissolved particles in a soln

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what affects water metabolism?

  • activity levels

  • environmental conditions (humid/dry)

  • disease

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water balance

  • oral (1/2-2/3)

  • kidney (excretion and conservation)

  • skin, lungs, GI = loss of water

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plasma water

  • water phase with ions only (no proteins)

  • ions and chemical activity are normal (not affected by hyperproteinemia/hyperlipidemia)

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electrolyte exclusion effect

  • exclusion of electrolytes from the fraction of the total plasma volume that is occupied by solids which leads to underestimation of electrolytes

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which has the highest conc of cation and anion inside the cell?

potassium and phosphate

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which has highest conc of cation and anion in interstitial and plasma?

sodium and chloride

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difference between plasma and interstitial solutes

practically no protein in interstitial fluid

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balance of water due to...?

  • hydrostatic pressure from heart drives water into tissues

  • plasma proteins draw water into circulation from intracellular spaces

  • so low protein in vessels means most water will remain in tissues

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what can cause permeability b/w ISF and plasma to increase?

some disease states like bacterial sepsis leading to leakage of alb, reduced plasma volume (shock) and hypotension

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osmotic pressure def

  • hydrostatic pressure that develops and is maintained when 2 solns of different concentrations exist on opposite sides of a semipermeable membrane

  • number of solid particles/unit volume or weight of soln

  • force that moves water from dilute solns to conc solns

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osmolarity

  • weight to volume relationship in mOsmole/L

  • inaccurate if hyperlipidemia/hyperproteinemia is present

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osmolality

a weight to weight relationship in mOsmole/kg

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colligative properties

  • related to number of total particles in soln and properties of those particles

  • includes BP, vapor pressure, osmotic pressure, FP

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uses of osmolality

  • determines if serum water content deviates from normal

  • detects the presence of foreign lmw subs in blood

  • use of urine/serum ratios to determine concentrating ability of kidney

  • assess electrolytes and acid base disturbances

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serum osmolality equation

(Na)(1.86) + (BUN)/(2.8) + (glucose)/(18)

(Na)(2) + (BUN)/(3) + (glucose)/(20)

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osmolal gap

should be less than 10 mOsm/kg (6-10)

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causes of increased difference in osmolal gap

  • attributed to other osmotically active cmpds other than sodium, glucose, urea

  • diabetic acidosis (ketones)

  • ethylene glycol poisoning

  • alcohol consumption (ethanol, methanol)

  • inc lipids inc proteins dec %water

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what is the specimen to measure osmolality?

  • serum or random urine (cf if turbid)

  • plasma not recommended because it contains osmotically active ions (anticoag)

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osmometer

finds freezing point depression by supercooling sample and then begin warming under constant value

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what 3 mechanisms regulate water balance?

AVP, RAAS, thirst center

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what is AVP also known as?

ADH (antidiuretic hormone)

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thirst center

  • inc in plasma osmolality (stimulates osmoreceptors in hypothalamus)

  • dec in intravascular volume

  • angiotensin II acts upon neurons in hypothalamus to produce sense of thirst

  • controls the balance of free water and output (without solute) by the kidney and free water intake

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arginine vasopressin hormone (AVP)

  • stimulated by inc plasma osmolality and dec plasma volume

  • produced in posterior pituitary

  • increases water absorption in kidney (collecting ducts)

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renin angiotensin aldosterone system (RAAS)

  • dec blood volume, BP, ECF

  • results in secretion of renin in kidney

  • renin activates plasma angiotensinogen to angiotensin I

  • angiotensin I(in lung) becomes angiotensin II (vasoconstrictor) via ACE

  • aldosterone (adrenal cortex) increases Na absorption and H and K excretion

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ACE inhibitors

  • interfere with RAAS by stimulating dilation of vessels via blocking production of angiotensin II

  • leads to inc sodium and urine excreted, inc venous capacity, dec cardiac output

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natriuretic peptides

  • released in response to intravascular volume expansion (reduces BP and plasma volume)

  • produced in heart and released when heart feels a volume expansion, pressure overload

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ANP

  • reduces venous pressure

  • increases vascular permeability

  • promotes natriuresis and diuresis

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BNP

  • similar to ANP

  • used to measure stuff in ppl with congestive heart failure (chf)

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CNP

  • function not understood

  • potent vasodilator, no natriuretic effects

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clinical significance - osmolality

water load, diabetes insipidus, SIADH, water deficit

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water load

  • xs water intake (polydipsia)

  • dec osmol

  • no response from AVP (lose large volumes of water and it causes hyperosmolality and hyponatremia only in ppl with impaired renal excretion

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diabetes insipidus

urine osmol dec

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SIADH

  • increase in AVP leading to in urine osm

  • secondary in asthma, pneumothorax, bacterial/viral pneumonia, copd, right side heart failure

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water deficit

  • inc in plasma osmol

  • triggers AVP and thirst mechanism

  • not usually a concern unless pt is infant, unconscious, elderly, or dec mental status

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electrolyes

  • important substances influencing distribution and retention of water

  • sum all all charges must equal zero between ECF/ICF

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anion gap

  • difference between cations and anions

  • can include or exclude potassium

  • range w: 10-22

  • range w/o: 6-18

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what are the measured electrolytes in the laboratory?

na, k, cl, hco3

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clinical significance of anion gap

  • differential diagnosis of metabolic acidosis

  • QC indicator

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what could a dec AG mean as a QC indicator?

  • lab error (overestimation of cl or underestimation of na)

  • MM: myeloma proteins act as cations

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what is an increase in the anion gap usually caused by?

  • usually by unmeasured anions (cations have little effect)

  • inc organic acids

  • chronic renal disease

  • diabetes mellitus-ketoacidosis

  • salicylate, methanol, ethylene glycol poisoning

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sodium functions

  • maintain osmotic pressure and water distribution

  • acid base balance exchange for hydrogen in renal tubes

  • responsible for 1/2 osmotic strength of plasma

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kidney control of sodium

  • major route of excretion (glomerulus)

  • 80-90% reabsorbed in the proximal tubule

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hormonal control of sodium

  • ADH lessens the filtration of na and GFR

  • aldosterone: inc na reabsorption in distal tubule and collecting duct

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hypernatremia symptoms/causes

  • neurological (ataxia, irritability, fever, confusion, coma)

  • hypovolemia: xssive water loss/failure to replenish lost water

  • hypervolemia: inc in sodium intake

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hypovolemia - xs water loss causes

  • diabetes insipidus (no ADH or no response to ADH)

  • renal disease (damaged glomerulus = dec na excretion)

  • nephrotic syndrome (loss of proteins in urine = low osmotic pressure so fluid shifts to interstitial space)

  • sweating, diarrhea

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hypovolemia - dec water intake

  • seen in older persons, infants, and those with mental impairment

  • most ppl can respond to thirst mechanism so this rarely occurs

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extrarenal water loss

  • urine osm >700

  • Na >20

  • GI/skin loss

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renal water loss

  • urine osm low to normal

  • urine Na high

  • thiazides w/o water replacement

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hypervolemia - inc Na/retention

  • hospitalized pts get hypertonic saline/bicarb

  • hyperaldosteronism: inc Na absorption and potassium excretion, more water retained

  • cushing's syndrome

  • chf: retention and more reabsorbed

  • liver disease: venous pressure in and forces fluid into peritoneal space (lowering plasma volume)

  • pregnancy (unknown interruption b/w sodium and body water)

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osmotic diuresis

  • inc urination from large molecules in the kidneys that draw water from the bloodstream into the urine

  • urine osm 300-700

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hyponatremia symptoms

  • 120 = malaise, nausea

  • 110-120 = generalized weakness, mental confusion

  • 90-105 = mental impairment, seizures, coma, death

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what is the most common electrolyte disorder in hospitalized/non hospitalized pts?

hyponatremia

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hyposomotic causes of hyponatremia

  • inc na los (depletional)

  • inc water retention (dilutional)

  • water imbalance

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hyposomotic - inc Na loss

  • hypoaldosteronism (na excreted)

  • diuretics (thiazides): lose na

  • ketonuria: na loss with ketones

  • renal disorder (salt wasting nephropathy )

  • prolonged vomiting, diarrhea

  • burns

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determining cause of Na loss

  • urine na <10 = extrarenal (GI/skin)

  • urine na >20 = renal (osmotic diuresis, thiazides, adrenal insuff, metabolic alkalosis)

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hyposomotic - inc water retention aka dilutional hyponatremia

  • acute/chronic renal failure

  • nephrotic syndrome

  • hepatic cirrhosis

  • chf

  • detected by weight gain/edema

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hyposmotic - water imbalance

  • normal volume but nacl deficit

  • SIADH

  • defect in AVP prod

  • hypothyroidism

  • adrenal insufficiency

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SIADH

  • inc ADH release causes water to be retained

  • urine osm > plasma osm by 100

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defect in AVP production causes

  • pulmonary disease

  • malignancies

  • trauma

  • infection

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hyperosmotic hyponatremia

  • inc amts of other solutes

  • caused by severe hyperglycemia

  • causes shift of ECF or ICF shift of Na

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isosmotic hyponatremia

  • pseudohyponatremia (hyperlipidemia/hyperproteinemia - MM)

  • detected by osm (urine > plasma)

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pseudohyponatremia

  • analytical error giving a false low sodium

  • glucose, plasma osm and urea are normal

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potassium functions

  • influences excitability of muscle

  • influences osmotic pressure inside cell

  • involved in cellular metabolism

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kidney control of potassium

  • major route of excretion (glomerulus)

  • almost completely reabsorbed in proximal tubule

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hormonal control of potassium

  • aldosterone: secretion of K in distal tubule and collecting duct

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hyperkalemia causes

  • decreased renal excretion (inc retention)

  • inc K intake

  • redistribution or cellular shift

  • artifactual

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hyperkalemia symptoms

mental confusion, weakness, tingling, flaccid paralysis in limbs, weakness of the respiratory muscles, bradycardia

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7 potassium

vascular collapse and cardiac arrest (check for hemolysis before notifying floor)

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10 potassium

incompatible with life

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hyperkalemia - dec renal excretion

  • acute/chronic renal failure (most common)

  • hypoaldosteronism (ace inhibs block aldo)

  • addison's disease

  • diuretics (potassium sparing)

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hyperkalemia - inc intake

oral or IV replacement therapy

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hyperkalemia - redistribution (cellular shift)

  • acidosis: K shifts to ECF as H shift to ICF

  • muscle/cellular injury

  • hemolysis

  • drugs: digoxin, beta blockers, nsaids, spironolactone, cyclosporine, heparin therapy

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hyperkalemia - artifactual

  • sample hemolysis

  • thrombocytosis/leukocytosis

  • prolonged tourniquet/xssive fist clenching

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hypokalemia causes

  • GI loss

  • renal loss

  • cellular shift

  • dec intake

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hypokalemia - GI loss

  • diarrhea

  • intestinal tumor

  • malabsorption

  • chemo/radiation therapy

  • large doses of laxative

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hypokalemia - renal loss

  • nephritis, RTA

  • hyperaldosteronism (K excretion)

  • cushings syndrome (high cortisol = dec in potassium)

  • hypomagnesemia (promotes K excretion)

  • acute leukemia

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hypokalemia - cellular shift

  • alkalosis (K shifts to ICF as H shifts to ECF)

  • insulin therapy

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chloride functions

  • osmotic pressure regulation

  • production of HCl in gastric

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which cation does chloride follow?

sodium unless there is an acid base disturbance

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kidney control of chloride

  • major route of excretion (glomerulus)

  • 97% reabsorbed by tubules

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hyperchloremia causes

  • renal tubular acidosis (kidney unable to make bicarb)

  • metabolic acidosis (severe diarrhea)

  • prolonged vomiting - loss of nahco3

  • dehydration

  • xssive reabsorption from GI tract

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hypochloremia causes

  • loss of gastric juice (vomiting or pyloric obstruction)

  • inc urinary excretion (diuretics or chronic pyelonephritis - salt losing)

  • metabolic alkalosis (inc bicarb = chloride shift)

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specimen collection for measuring electrolytes

  • plasma or serum

  • heparinized whole blood or arterial/venous specimens from ABG

  • serum for K can be elevated from clotting process

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interferences for sodium

  • high lvl of macromoles (proteins/lipids) will give falsely dec results in indirect methods

  • hemolysis = dilutional effect

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potassium interferences

  • tourniquet in place too long

  • hemolysis

  • leukocytosis/thrombocytosis will falsely inc

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chloride interferences

  • inc with prolonged exposure bc CO2 lost so Cl moves to serum

  • once separated from the cells, the Cl is stable

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test methodologies

  • atomic absorption

  • flame photometry

  • amperometry

  • ISE (direct and indirect)

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what does flame photometry measure?

Na and K

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what does amperometry measure?

Cl

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direct ISE

  • measures free ion activity in plasma water and does not take into account total volume so other solids do not interfere

  • no dilution

  • blood gas analyzers, POCT, single use instruments

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indirect ISE

  • based on sample dilution and based on total volume so solids are included and protein/lipids will interfere

  • measures total ion concentration

  • adv: large sample volume to adequately cover membrane surface

  • more common in lab instruments

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ion selective membranes

potential produced is proportional to the log of ionic activity or conc

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errors of ISE

  • lack of analytical sensitivity

  • repeated protein coating of membrane

  • contam of the membrane or salt bridge

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ISEs

  • used for Na, K, Cl, K

  • uses direct measurement of electrical potential due to acitivity of ion

  • Ag/AgCl: internal reference

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sodium ISE

glass membrane permeable to only Na

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potassium ISE

liquid ion exchange membrane with valinomycin

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