Fluids and Electrolytes PDF

Fluids and Electrolytes  Fluid balance – Important in IV daily maintenance – Intake & output ( I &O ) Note: Insensible loss ( from skin + lungs) = 1000 cc/day The Cell Has a Limited Repetoire...

Fluids and Electrolytes  Fluid balance – Important in IV daily maintenance – Intake & output ( I &O ) Note: Insensible loss ( from skin + lungs) = 1000 cc/day The Cell Has a Limited Repetoire H20 moves passively Across cell membrane According to the osmotic gradient K+140 meq/L 280 milliosmoles/L Na+140 meq/L 280 milliosmoles/L High Osmolality Outside The Cell=Shrinkage H2O K+140 meq/L 280 milliosmoles/L Na+150 meq/L 300 milliosmoles/L Low Osmolality Outside The Cell=Swelling H20 K+140 meq/L 280 milliosmoles/L Na+120 meq/L 240 milliosmoles/L RUPTURE  Body Fluid Compartments 2/3 (65%) of TBW is intracellular (ICF) 1/3 extracellular water 25 % interstitial fluid (ISF) 5- 8 % in plasma (IVF intravascular fluid) 1- 2 % in transcellular fluids – CSF, intraocular fluids, serous membranes, and in GI, respiratory and urinary tracts;  Body Fluids Water is most abundant body compound“Average” body water volume in reference tables based on healthy, nonobese 70-kg male Volume averages 42 L in a 70-kg male Plasma (3.5 L) Interstitial fluid (10.5 L) Intracellular fluid (28 L) Water is about 75%-80% of body weight in newborn; about 60% in adult males; and about 50% in adult females OSMOLALITY Measure of solution’s ability to create osmotic pressure & thus affect movement of water. Number of osmotically active particles per kilogram of water. Plasma osmolality is 280-300* mOsm/ kg. ECF osmolality is determined by sodium. MEASURE used in clinical practice to evaluate serum & urine.  Osmolality In Clinical Practice Serum 280-300mOsm/kg. Serum osmolality can be estimated by doubling serum sodium: More prescisely. Serum osmolality = (2 x Na) + urea + glucose. Osmolarity Regulation ICF Osm. = ECF Osm. Interstitial Osm = Serum Osm. Hypothalamus is the serum osmostat. It stimulates thirst and ADH secretion. Primary Defense for Osmolarity = Thirst Primary Defense for Osmolarity = Renal excretion of water via inhibiting the ADH effect (enhances diuresis). ADH= (Antidiuretic hormone) Fluid Balance  Primary Regulatory Hormones Affect fluid and electrolyte balance: 1. antidiuretic hormone (ADH) 2. aldosterone 3. natriuretic peptides  Antidiuretic Hormone (ADH) Stimulates water conservation at kidneys: Reducing urinary water loss. Concentrating urine. Stimulates thirst center: Promoting fluid intake.  ADH Production Osmoreceptors in hypothalamus monitor osmotic concentration of ECF (plasma, CSF). Change in osmotic concentration in plasma and CSF alters osmoreceptor activity. Osmoreceptor neurons secrete ADH in proportion to osmotic concentraiton via the posterior pituitary.  Aldosterone: Is secreted by adrenal cortex in response to: rising K+ (sensed at the adrenal cortex) or falling Na+ levels in blood. activation of renin–angiotensin system (usually due to changes in blood volume). Determines rate of Na+ absorption and K+ loss along DCT and collecting system. “Water Follows Salt”: High plasma aldosterone concentration causes kidneys to conserve salt. In case of low sodium level: there will be conservation of Na+ by aldosterone also stimulates water retention. Aldosterone Figure 26.8 Natriuretic Peptides ANP (atrium natriuretic peptide) and BNP (brain natriuretic peptide) are released by cardiac muscle cells in response to abnormal stretching of heart walls due to elevated blood pressure or volume: Reduce thirst. Block release of ADH and aldosterone. Cause diuresis. Lower blood pressure and plasma volume. Water Losses/ dehydration: Loss is generally from ECF Mild dehydration = ˂ 2% in body weight Moderate dehydration = 2-5 % loss of body weight Severe dehydration ≥ 8% loss Loss of water usually accompanied by loss of electrolytes Remember water follows salt But can get 3 types of dehydration (1) Isotonic dehydration = equal loss of both fluid & lytes. (2) Hypotonic dehydration = loss of lytes is more than loss of water. (3) Hypertonic dehydration = loss of fluid is more than loss of lytes. Water Loss/ dehydration Causes Vomiting & diarrhea, N-G suction Excess sweating Diabetic ketoacidosis Insufficient water intake Fever Burns Diabetes insipidus Low ADH secreation Diuretic phase of acute RF Use of diuretics  Effects of dehydration: Dry mucous membranes. Decreased skin turgor. Decreased BP. Increased hematocrit. Compensatory mechanisms: Increase thirst. Increase pulse. Constriction of vessel to skin: Get pale, cool skin. Decreased urine output. If brain cells lose water, can get confusion, unconsciousness, & coma.  Clinical manifestation of dehydration Diagnose of dehydration: – Dry tongue and thirst. – Poor skin turgor. – Concentrated urine (oligouria ˂ 30 ml urine/hour). – Muscle weakness. – Sunken eyes. – Headache, confusion and coma in sever cases. – Increased temperature. – Tachycardia. – Weight loss.  Laboratory findings in dehydration: Increase Osmolarity > 300 mOs/Kg. Increased or normal sodium level. Increased BUN (blood urea nitrogen) > 25 mg/dL (normal range: 9-23 mg/dL). Increased hematocrit > 55%. Increased Specific gravity of urine > 1.03 (normal range: 1.01 – 1.03). In sever cases --- Hyperglycemia: glucose level > 120 mg/dL (normal range of fasting blood glucose 80 – 100 mg/dL).  Management of Water Losses Mild Dehydration: oral fluid replacement. Moderate –sever dehydration: IV fluids: If the patient can tolerate solid food: oral fluid intake (1200 ml- 1500 ml). If the patient can not tolerate solid food: increase fluid intake to 2500 ml/24 hours.  Water Gains/ Edema If water is gained, but electrolytes are not: ECF volume increases. ECF becomes hypotonic to ICF. fluid shifts from ECF to ICF. Basically the opposite of water loss: may result in overrhydration: destroys cells. changes solute concentrations around enzymes. disrupts normal cell functions.  Water Gains/ Edema If water is gained, but electrolytes are not. ECF is at lower concentration, higher volume. This triggers decrease in ADH release. Causes of water Gain (edema) Edema = excessive amount of fluid in interstitial compartment 7 main causes 1) Increased capillary hydrostatic pressure Etiology Hypertension. Increased blood volume ---- 2o to pregnancy, renal failure, CHF, cirrhosis. 2) Loss of plasma proteins (esp. albumin) Etiology Kidney disease, malnutrition, malabsorption. 3) Obstruction of lymphatic circulation Etiology Cancer, parasitic diseases, post surgical. 4) Increased capillary permeability Etiology Inflammation, toxins, burns. Causes of water Gain (edema) 4) Ingestion of large amount of water. 5) Injection into blood hypotonic solution. 6) Endocrine causes as increased ADH secreation. 7) Inability to eliminate excess water in urine: Chronic renal failure. Heart failure. Cirrhosis. Clinical Manifestation of Edema 1) Constant irritating cough. 2) Dyspnea & crackles in lungs. 3) Cyanosis. 4) Jugular vein distension. 5) Increased blood pressure HTN. 6) Pitting edema. 7) weight gain. 8) Change level of consciousness. jugular venous distension pitting edema  Laboratory Findings of Edema Serum osmolarity ˂ 275 mOm/Kg. Low, normal or high Sodium level. Decreased hematocrit ˂ 45%. Specific gravity of urine ˂ 1.01 (normal range: 1.01 – 1.03). Low level of BUN (blood urea nitrogen) ˂ 8 mg/dL (normal range: 9-23 mg/ dL).  Management of Edema 1) Diuretics (combination between potassium sparing and potassium depleting diuretics). 2) Low sodium diet. 3) In case of CHF treat with ACE-inh and β- blockers. Disorders of Water Balance: Figure 26.7a Electrolyte Balance Electrolyte Balance Requires equal rates of gain and loss for each electrolyte in the body Electrolyte concentration directly affects water balance Concentrations of individual electrolytes affect cell functions Solutes – dissolved particles Electrolytes – charged particles Cations – positively charged ions Na+, K+ , Ca++, H+ Anions – negatively charged ions Cl-, HCO3- , PO43- Non-electrolytes. Proteins, urea, glucose, O2, CO2 39  Rules of Electrolyte Balance Most common problems with electrolyte balance are caused by imbalance between gains and losses of sodium ions Problems with potassium balance are less common, but more dangerous than sodium imbalance Changes in plasma sodium levels affect: Plasma volume, blood pressure ICF and interstitial fluid volumes  Na+, K+ Sodium holds a central position in fluid and electrolyte balance Sodium is the dominant cation in ECF Sodium salts provide 90-95% of ECF osmolarity (concentration): sodium chloride (NaCl) sodium bicarbonate Sodium concentration in the ECF normally remains stable Potassium Is the dominant cation in ICF SODIUM (Na+) Main extracellular fluid (ECF) cation. Helps govern normal ECF osmolality. Helps maintain acid-base balance. Activates nerve & muscle cells. Influences water distribution (with chloride). Normal Na+ plasma level: (135-145) mEq/L.  Na+ Regulation So changes in sodium concentration are corrected by ADH (not aldosterone) Figure 27–4  Abnormal Na+ Concentrations in ECF Hyponatremia: usually body water content rises (overhydration). Hypernatremia: usually body water content declines (dehydration). Severe problems with electrolyte concentrations almost always occur secondary to fluid balance problems HYPERNATREMIA Serum Na + level > 148 mEq/L. serum osmolality > 295 mOsm/kg. Etiologies of Hypernatremia Primary Sodium Excess Primary Water Loss - Excess Intake of Sodium -Poor Intake of Water: * Impaired access to water (i.e. infants, elderly patients with dementia or whom are -Decreased Urinary Excretion of bedbound) Sodium: *Impaired thirst sensation/loss of thirst * RF. mechanism: * Hyperaldosteronism Hypothalamic lesions -Increased Urinary Loss of Water: *ADH deficiency (Central Diabetes Isipidus DI) *ADH resistance (Nephrogenic DI) -Increased GI Loss of Water (diarrhea & vomiting). -Increased Transcutaneous Loss of Water. -Transmembrane Shift of Water (most often due to rapid production of intracellular lactate). - Hyperventilation: loss from lungs. HYPONATREMIA Serum Na+ < 135 mEq/L (patient may be asymptomatic until level drops below 125).  Etiologies of Hyponatremia Primary Sodium Loss Primary Water Excess -Poor Intake of Sodium -Excessive Intake of Water (1° polydipsia). -Increased Urinary Loss of Sodium: -Decreased Urinary Excretion of Water: *Diuretics *Decreased GFR. *Proximal RTA (Hyponatremic *Increased ADH. metabolic acidosis). -Heart failure. *Aldosterone deficiency/resistance -Cirrhosis. -Increased GI Loss of Sodium (Fluid loss -SIADH (syndrome of inappropriate ADH). must be followed by repletion with free water): * Vomitting -Transmembrane Shift of Water *Diarrhea -Hyperglycemia -Increased Transcutaneous Loss of Sodium (Fluid loss must be followed by repletion with free water).  Potassium (K+) Balance: 98% of potassium in the human body is in ICF. Normal K+ level: (3.5-5.5) mEq/L. Cells expend energy to recover potassium ions diffused from cytoplasm into ECF. Factors: Rate of gain across digestive epithelium. Rate of loss into urine, regulated along distal portions of nephron and collecting system as Na+ from tubular fluid is exchanged for K+ in peritubular fluid.  Mechanisms of regulation of K+: 1- Renal regulation. 2- Transcellular shift between the intracellular and extracellular compartments.  + 1) Factors in Tubular Secretion of K /Renal: 1. Changes in concentration of ECF: higher ECF concentration increases rate of secretion (just because there is more of K+). 2. Aldosterone levels affect K+ loss in urine: Ion pumps reabsorb Na+ from filtrate in exchange for K+ from peritubular fluid. High K+ plasma concentrations stimulate aldosterone release, to lower K+ but Na+ stays. 3. Changes in pH: low ECF pH (acidosis) lowers peritubular fluid pH. H+ rather than K+ is exchanged for Na+ in tubular fluid so ECF K+ increases.  2) Transcellular shifts 1- Sodium-potassium ATPase Both insulin and epinephrine increase the activity of sodium- potassium pump. (An increase in potassium level stimulates insulin release, in order to help in entering K+ into cells--- a feedback mechanism). 2- Potassium-hydrogen exchange to maintain electrical neutrality In acidosis In alkalosis POTASSIUM (K+) Dominant cation in intracellular fluid (ICF). Regulates cell excitability. Permeates cell membranes, thereby affecting cell’s electrical status. Helps control ICF osmolality & ICF osmotic pressure. HYPERKALEMIA K+ > 5.5 mEq/L Dangerous due to potential for fatal dysrhythmias, cardiac arrest. Major cause is renal disease. Be aware of pseudohyperkalemia due to: 1- Prolonged tourniquet. 3- Hemolysis of blood. 2- Sampling above KCl infusion. Etiologies of Hyperkalemia Renal causes: Cellular causes: - Excessive Dietary Intake. - Internal Redistribution. - Decreased Urinary Excretion: - Transmembrane Shift: *Decreased GFR. * Acidosis. *Aldosterone deficiency: * Exercise. - Adrenal insufficiency. - Cell Lysis: - ACE inhibitors. - Rhabdomyolysis. - Aldosterone resistance. - Tumor lysis syndrome. - Potassium sparing diuretics. Medications: Potassium sparing diuretics, ACE-inh, ARBs. HYPOKALEMIA K+ < 3.5mEq/L. Most common type of electrolyte imbalance. Major cause is increase renal loss most often associated with diuretics. Can increase the action of digitalis (digitalis toxicity).  Etiologies of Hypokalemia - Poor Intake. -Increased GI Losses: - Increased Urinary Excretion: *Diarrhea. *Decreased reabsorption in loop of Henle: *Laxative abuse. * Furosemide. * Hyperaldosteronism: Increased Transcutaneous Losses: - Primary hyperaldosteronism: *sweating * Adrenal adenoma. * Adrenal hyperplasia. Transmembrane Shift: - Secondary hyperaldosteronism: *Alkalosis. *Renovascular hypertension. *Insulin treatment for DKA. * Renin-secreting tumor. *High catecholamine states. Medications: β- agonist, Insulin, Non- potassium sparing diuretics. Symptoms of Electrolyte Loss or Gain: Hyponatremia signs and symptom: Symptoms of hypernatremia: Symptoms of Hypokalemia: Symptoms of hyperkalemia: