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fluid and electrolytes
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Clinical Applications:Fluids & ElectrolytesV. Doreen Wagner, PhD, RN, CNORBiology 3317 ~ Pathophysiology
Fluid Balance Review
Primary component of bodyH2O
Functions of water in body
Body composition/distribution
Fluid DistributionIntracellular compartmentExtracellular compartmentInterstitial spacesPlasma (vascular) compartmentTranscellular compartment
Gains & LossesSkin
Lungs
Kidneyshttps://www.youtube.com/watch?v=vB7tSHqR1eY
Intestines
Fluid Balance RegulationThirstEndocrine system (Hormones)Antidiuretic Hormone (ADH) http://www.youtube.com/watch?v=8dQdfbE8kFU (15 mins)Aldosterone http://www.youtube.com/watch?v=Z0XPMFL45oo (10 mins)Renin-angiotensin-aldosterone system http://www.youtube.com/watch?v=BVUeCLt68Ik (14 mins)Cardiac systemAtrial Natriuretic Peptide (ANP)KidneysGI system
Forces - Moving Fluid In and Out of Capillaries
Tonicity of FluidsIsotonicEqual osmolarity to serumAdds to intravascular space without shiftsHypotonicLower osmolarity than serumShifts fluid out of intravascular space to hydrate cells and interstitial spaceHypertonicHigher osmolarity than serumDraws fluid into intravascular space from cells and interstitial space
Controlling Blood OsmolarityHigh osmolarity causes:Thirst increased water intakeADH release water reabsorbed from urineLow osmolarity causes:Lack of thirst decreased water intakeDecreased ADH release water lost in urine
Antidiuretic Hormone (ADH)Regulates H2O reabsorption in bodyPosterior Pituitary GlandADH Released H2O reabsorption in kidneys
ADH ImbalancesDiabetes insipidus (DI)Neurogenic or CentralNephrogenic
Syndrome of inappropriate ADH (SIADH)
Which may cause hyponatremia?
Diabetes Insipidus (DI)Too little ADH secretion from Posterior Pituitary ADH secretion H2O reabsorption Urine Output Blood VolumeHypernatremia
Clinical ManifestationsExtreme Polyuriaup to 30 liters/day!PolydipsiaNocturiaNatriuresis (excretion of Na+ in the urine)
May present with hypernatremia and dehydration - if unable to replace fluids
Syndrome of Inappropriate Antidiuretic Hormone (SIADH)Too much ADH secreted from Posterior Pituitary
Clinical ManifestationsFluid Volume Excess increased body weightHyponatremia (dilutional)ThirstDyspnea on exertionDulled sensoriumMuscle cramps & weaknessLow urine outputWhen serum sodium level falls < 120 mEq/LN&VMuscle cramps abdominal Seizures
~ Summary ~
The Rising TideFluid Volume ExcessEdema capillary pressure colloidal osmotic pressure capillary permeabilityLymphatic flow obstructionIncreased intake of fluidThird-Spacing
What to Look For in HypervolemiaOverloadBounding pulse/bradycardia/HTNRapid wt. gainPulmonary edemaTypical Lab results HCT hemodilutionWNL or HIGH serum sodium serum osmolality oxygen level
Dehydration vs. HypovolemiaDehydration Intracellular loss (increased solutes)Kidneys retain water
Hypovolemia Extracellular loss (isotonic loss)Loss of fluids and solutesLoss of circulating volumeBleeding3rd space fluid shift
DehydrationWhat tests show hematocrit serum osmolality serum sodiumUrine specific gravity above 1.030
How its treatedReplace missing fluidsGive fluids gradually
HypovolemiaWhat to Look for HR & thready, BPRestlessness, anxietyCool, clammy & pale skin (extremities)Delayed capillary refill Acute weight loss (>5-10%)More fluid loss = mental statusExtreme thirst urine output (10 30 mL/hr)> 40% isotonic loss leads to shock
Lab tests showLow to low normal electrolytes HGB & HCT w/hemorrhage urine specific gravity serum osmolality
How its treatedFlood of fluid replacementIsotonic IV fluids to expand circulating volumeBolusPlasma proteinsHypovolemia
Electrolyte Balance ReviewMajor Extracellular ElectrolytesSodiumCalcium
Major Intracellular ElectrolytesPotassiumPhosphorusMagnesium
SodiumMost abundant cation in bodyApprox. 60 mEq/kg of body weight135 145 normal valuesFound in ECF compartmentVery small amount in ICF Regulates ECF volumeIncluding vascular compartment fluidsPart of sodium bicarbonate moleculeImportant in acid-base balanceContributes to nervous system function
Osmolality and SodiumNormal level = 135145 mEq/LRegulates extracellular fluid volume and osmolarity
Question:Why would retaining sodium cause high blood pressure?
Sodium ImbalancesHyponatremia (145 mEq/L)Water deficitNa+ administration
PotassiumNormal level is 3.55.0 mEq/LMaintains intracellular osmolarityControls cell resting potentialNeeded for Na+/K+ pumpExchanged for H+ to buffer changes in blood pH
PotassiumCan be disturbed by diseases, injuries, medications & therapiesMust be ingested daily (40mEq)Body cant conserve K+Maintains balanceSodium-potassium pumprenal regulationpH levelControls cell resting potentialMaintains intracellular osmolarity
What Happens to Blood K+ Levels When:A person hasHyperaldosteronism?Alkalosis?An injection of epinephrine?Convulsions?Loop diuretics?Crush injury?
Normal level 8.5 10.5 mg/dLExtracellularBlocks Na+ gates in nerve & muscle cellsClottingLeaks into cardiac muscle Causing it to fireIntracellularNeeded for all muscle contractionActs as 2nd messenger in many hormone & neurotransmitter pathwaysCalcium
Extracellular Calcium Controls Nerve FiringHypercalcemiaBlocks more Na+ gatesNerves are less able to fireHypocalcemiaBlocks fewer Na+ gatesNerves fire more easilyWhich would cause Trousseaus sign?
Hypocalcemia ManifestationsNeural/Muscle EffectsParesthesia (numbness/tingling)Skeletal muscle spasms/crampsAbdominal muscle spasms/crampsHyperactive reflexesCarpopedal spasmLaryngeal spasmCardiovascular EffectsHypotension & cardiac insufficiencyProlonged QT interval arrhythmiasSkeletal Effects (chronic deficiency)Osteomalacia and bone pain
Hypercalcemia Manifestations Renal EffectsPolyuria w/Increased thirstSigns of acute renal insufficiencySigns of kidney stonesNeural and Muscle EffectsMuscle weakness with loss of toneLethargy Personality/behavioral changesStupor to comaCardiovascular EffectsHypertensionShortening of QT interval AV blockGastrointestinal EffectsAnorexiaNausea & vomitingConstipation
https://www.youtube.com/watch?v=SWv-aY4RH3c
MagnesiumNormal level is 1.82.7 mg/dLCofactor in enzymatic reactionsInvolving ATPDNA replicationmRNA productionBinds to Ca2+ receptorsCan block Ca2+ channels
Hypomagnesemia ManifestationsDisordered functions of Cardiovascular systemNeuromuscular systemSkeletal system
Associated with imbalances of other electrolytes - such as potassium and calcium
Hypermagnesemia ManifestationsKidneys have large capacity for Mg excretion so only occurs inRenal insufficiencyExcessive intake/correctionIf untreated, toxicity progresses toFlaccid paralysis & hyporeflexiaBradycardia and arrhythmiasRespiratory depressionComaCardiac arrest
Acid-Base Balance ReviewAcid-Base BasicsUnderstanding pHDeviation from normal pH
Maintaining Acid-Base BalanceChemical Buffer SystemsRespiratory SystemRenal System
Interpreting Acid-Base Imbalances
Acid (H+)Normal value: pH = 7.357.45Blocks Na+ gatesControls respiratory rateIndividual acids have different functions:Byproducts of energy metabolism (carbonic acid, lactic acid)Digestion (hydrochloric acid)Food for brain (ketoacids)
Respiratory or Volatile AcidCO2 + H2O H2CO3 (carbonic acid)H2CO3 H+ + HCO3- (bicarbonate ion)An increase in CO2 will cause Increases in CO2 (increased PCO2)Increases in H+ (lower pH)Increases in bicarbonate ion
Respiration and Buffers Adjust Blood pHScenario:A woman was given an acidic IV. Soon she began to breathe more heavily. Why?When her blood was tested, it had:Slightly lowered pHLow bicarbonateLow PCO2Slightly increased K+ Her urine pH was slightly loweredWhy?
Buffer Systems
Respiratory Acidosis and AlkalosisCO2 + H2O H2CO3 H+ + HCO3- (bicarbonate ion)
Respiratory acidosisRespiratory alkalosis PCO2 carbonic acid H+ = low pH (7.45) bicarbonate
Respiratory ImbalancesRespiratory Acidosis Alveolar hypoventilation ( PaCO2):Acute pulmonary edemaDepressed drive to breathe ( CNS, oversedation)Chronic respiratory diseaseRespiratory AlkalosisHyperventilation excessive breathingMechanical ventilationAnxiety, pain, fever, septic shock
Metabolic ImbalancesMetabolic acidosisIncreased levels of ketoacids, lactic acid, etc.Decreased bicarbonate levels
Metabolic alkalosisDecreased H+ levelsIncreased bicarbonate levels
Metabolic Acidosis and AlkalosisIncreased metabolic acids raise H+ levelsSome H+ combines with bicarbonate, decreasing itBreathing adjusts CO2 to bring pH back to normal
Metabolic acidosisMetabolic alkalosisH+ = low pH (7.45) bicarbonateLighter/shallow breathing causes PCO2
Metabolic Acidosis Acid and HCO3Acid excessRenal failureDiabetic ketoacidosisLactic acidosisStarvationhyperalimentationIngested toxins (ASA, antifreeze)Base deficitDiarrheaHyperkalemiaIntestinal fistulasCertain drugs
Metabolic AlkalosisMetabolic Alkalosis caused by:Acid lossVomiting or NG suctionHypokalemiaHypochloremiaLoop or thiazide diureticsSteroids
Excessive HCO3 Over correction of acidosis with NaHCO3Massive transfusion of whole bloodOveruse of LR solutionExcessive intake of oral bicarbonate
Beyond pH, PaCO2, & HCO3PaO2Measure of partial pressure of arterial O2WNL = 80 100 mm HgVaries with age after age 60 without signs of hypoxiaMay be lower in people who live at higher altitudes
SaO2Oxygen saturation measurement of percentage of hemoglobin actually carrying oxygenWNL = 95 100%
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