fluid , electrolyte balance
DESCRIPTION
Zehra Eren,M.D. Fluid , Electrolyte Balance. LEARNING OBJECTIVES. e xplain g eneral principles of disorders of water balance e xplain general principles of disorders of sodium balance explain general principles of disorders of potassium balance - PowerPoint PPT PresentationTRANSCRIPT
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Fluid, Electrolyte Balance
Zehra Eren,M.D.
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LEARNING OBJECTIVES explain general principles of disorders of water
balance explain general principles of disorders of
sodium balance explain general principles of disorders of
potassium balance recognize hyponatremia, hypernatremia recognize hyperkalemia, hypokalemia
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Assesment of the patient
careful historyphysical examination and assessment
of total body water and its distributionserum electrolyte concentrationsurine electrolyte concentrationsserum osmolality
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Definitions
Total body water Extracellular fluid volume Intracellular fluid volume Effective arterial blood volume: part of the intravascular volume that is in the arterial system and effectively perfusing tissues (700ml/70kg, men)
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Definitions
Total body water Extracellular fluid volume Intracellular fluid volume Effective arterial blood volume: part of the intravascular volume that is in the arterial system and effectively perfusing tissues (700ml/70kg, men)
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Solute Composition of Body Water Predominant solutes in ECF:
Sodium (Na+)Chloride (Cl−)Bicarbonate (HCO3−)
Predominant solutes in ICF: Potassium (K+)Protein−
Phosphate−
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Plasma osmolality
Posm= 2 x [Na] + [glucose]/18 + blood urea nitrogen/2.8
Normal ECF osmolality:275-290mOsm/kgH2O
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Plasma tonicity also called the effective plasma osmolality reflects the concentration of solutes that do not
easily cross cell membranes (mostly sodium salts) and therefore affect the distribution of water between the cells and the ECF
Plasma tonicity= 2 x[Na] + [glucose]/18 (if glucose is measured in mg/dL)
270-285 mosm/kg ECF and ICF are in osmotic equilibrium, at
steady state
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Dehydration reduction in TBW below the normal level
without a proportional reduction in sodium and potassium, resulting in a rise in the plasma sodium concentration
primary loss of free water (as with unreplaced insensible losses or water loss in diabetes insipidus)
the major biochemical manifestation is
hypernatremia
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Regulatıon of water and sodium balance
The kidney regulates water and sodium balance independently since water can be taken in without salt and salt can be taken in without water
Regulation of plasma tonicity and of the effective arterial blood volume involve different hormones
areas of overlap, such as the hypovolemic stimulus to the release of antidiuretic hormone (ADH)
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Dısorders of water and sodium balance
Hyponatremia (too much water)Hypernatremia (too little water)Hypovolemia (too little sodium, the
main extracellular solute)Edema (too much sodium with
associated water retention)
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Hyponatremia
Serum Na <135 mEq/L
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Hyponatremia almost always due to the oral or
intravenous intake of water that cannot be completely excreted
impaired water excretion that is most often due to an inability to suppress the release of antidiuretic hormone (ADH) or to advanced renal failure
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Hyponatremia major causes of persistent ADH
secretion:
-syndrome of inappropriate ADH secretion
(SIADH)
-reduced effective arterial blood volume
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Manifestations of Hyponatremia
The symptoms reflect neurologic dysfunction induced by cerebral edema and possible adaptive responses of brain cels to osmotic swelling
Nausea, malaise, headache, lethargyseizures, coma,respiratory arrest
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Hypernatremia
Serum Na>145 mEq/L
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Causes of HypernatremiaHypovolemic hypernatremia
1.Extrarenal losses (urine Na <20 mEq/L):
-insensible and perspiratory-gastrointestinal
2.Renal losses(urine Na >20 mEq/L)-osmotic diuresis
Ovolemic hypernatremiaDiabetes insipidus (dilute urine, urine Na variable)
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Causes of HypernatremiaHypervolemic hypernatremia
-Hypertonic infusion (eg, NaHCO3)-Tube feeding
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Manifestation of Hypernatremia
Rise in plasma Na and osmolality→water movement out of the brain→rupture of the cerebral veins→focal intracerebral and subarachnoidal hemorrages→possible ireversible neurologic damage
Lethargy, weaknees, irritability, twitching, seuzures, coma,
Osmotic demyelination
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DISORDERS OF POTASSIUM (K)
Total body K determined by internal and external K balance
Internal balance
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DISORDERS OF POTASSIUM (K)
Total body K determined by internal and external K balance
Internal balance
External balance-K freely filtered-Filtered K reabsorbed in proximal tubule -K secretion mediated by Na reabsorption-K secretion regulated by aldosterone secretion
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Hypokalemia
Serum K+ less than 3.5 mEq/L (mmol/L)
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Clinical manifestations Cardiovascular:
-Arrhythmias-Digitalis toxicity
Neuromuscular: 1.Smooth muscle:
-Ileus2.Skeletal muscle:
-Weakness-Paralysis-Rhabdomyolysis
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Clinical manifestations Endocrine:
-Glucose intolerance Renal/electrolyte:
-Vasopressin resistance-Increased ammonia production-Metabolic alkalosis
Structural changes: Renal cystsInterstitial changesPT dilation, vacuolization
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Hyperkalemia
Serum K ≥5.0 mEq/L (mmol/L)
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Psodohyperkalemia
ThrombocytosisLeukocytosis Ischemic blood draw
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Causes of Hyperkalemia
GFR <20 mL/min-Endogenous or exogenous K-Drugs that impair K excretion
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Clinical manifestations Cardiovascular
-T-wave abnormalities-Bradyarrhythmias
Neuromuscular-Ileus-Paresthesias-Weakness-Paralysis
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Clinical manifestations Renal/electrolyte
-Decreased ammonia production-Metabolic acidosis
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SUGGESTED READING Goldman's Cecile Medicine, Goldman L, Schafer AI
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