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Fluids, electrolytes, acid-base balance and intravenous therapy
Jennifer kean msn, rn, ccrn
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water An adult’s body is about 45% water
Infants, children, and older adults are more likely to become dehydrated Water in the body has 4 main functions: Be a vehicle for the transportation of substances to and from the cells Aid heat regulation by providing perspiration which evaporates and cools the body Assist in maintenance of hydrogen (H+) balance in the body Serve as a medium for the enzymatic action of digestion
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diffusion Diffusion is a process by which solutes pass through a semipermeable membrane from a higher concentration to a lower concentration until they are evenly distributed in the available space
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osmosis Osmosis is the movement of pure solvent (liquid) across a membrane When there are differences in concentration on either side of the membrane, osmotic pressure will move solute particles from the area of greater concentration of solutes to the area of lesser concentration This process takes place via a semipermeable membrane Fluid moves between the interstitial and intracellular and between the interstitial and intravascular compartments by osmosis Diffusion and osmosis are done via passive transport
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osmosis
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filtration Filtration is the movement of water and solutes through a semipermeable membrane as a result of a pushing force (hydrostatic pressure) on one side of the membrane In the body this happens in the capillaries The pumping action of the heart creates this hydrostatic pressure in the body Water and electrolytes move through the capillary wall to the interstitial fluid Filtration also occurs in the kidney, where waste substances and excess water are eliminated Filtration is accomplished through active transport
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filtration
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Passive and active transport
Diffusion and osmosis are all processes that occur with the process of passive transport (no cellular energy is required) Glucose, oxygen, carbon dioxide, water and other small molecules move across cell membranes via passive transport in active transport, these processes require cellular energy Active transport moves solutes from areas of lower concentration to higher concentration (filtration) The energy in the body is produced by adenosine triphosphate (ATP)
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Fluid balance Body fluids are continually moving in and out of the blood and lymph vessels (intravascular), through the spaces surrounding the cells (interstitial), and in and out of the cells (intracellular) Osmoreceptors (volume sensors) in the hypothalamus control the fluid volume by sensing when the intake of fluid (thirst mechanism) is needed Antidiuretic hormone, released by the posterior pituitary, controls how much fluid leaves the body through urination Aldosterone regulates the reabsorption of water and sodium ions from the kidney tubules Baroreceptors in the carotids and aortic arch sense blood pressure changes and stimulate the sympathetic or parasympathetic nervous system to return the pressure to normal via the release of these hormones
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dehydration Any seriously ill patient is at risk for a fluid and electrolyte imbalance It is important to remember that water follows sodium in the body through osmosis Water loss occurs through the processes of urination and perspiration (sensible water loss) and also through defecation and respiration (insensible water loss) The processes of vomiting, diarrhea, hemorrhage, excessive wound drainage or diuretic therapy may cause excessive fluid losses
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Signs and symptoms of dehydration
Thirst Poor skin turgor Weight loss Weakness Dizziness Postural hypotension Decreased urine production Dark urine Dry lips and tongue Dry mucous membranes Sunken eyeballs Thick saliva Dry, scaly skin Flat neck veins when lying down Rapid, weak, thready pulse Elevated temp (>100.6) Increased hematocrit High urine specific gravity
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Signs and symptoms of overhydration
Weight gain Slow, bounding pulse Elevated blood pressure Firm subcutaneous tissues Edema Possibly crackles on lung auscultation Lethargy, possible seizures Possibly visible neck veins when lying down Decreased serum sodium Decreased hematocrit from hemodilution Low urine specific gravity
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edema Localized: often occurs with inflammatory process (injury, surgery, etc.) Dependent: noted in feet, ankles and lower legs in chf patients; is an effect of gravity Pitting vs. non-pitting 1+, 2+, 3+, 4+ Generalized (anasarca): occurs in critically ill patients
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Meds commonly used to treat nausea and vomiting
Hydroxyzine (vistaril) Antihistamine and antiemetic Never give iv-give by z-track method Promethazine (Phenergan) Depresses the cns Monitor for dizziness and hypotension Ondansetron (Zofran) Blocks serotonin centrally and peripherally Monitor for extrapyramidal symptoms Metoclopramide (reglan) Decreases reflux and stimulates stomach emptying Monitor for extrapyramidal symptoms and renal function
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Meds commonly used to treat diarrhea
Loperamide (immodium) Slows intestinal motility Monitor for constipation; d/c if ineffective after 2 days Diphenoxylate atropine (lomotil) Monitor for electrolyte imbalances Contains narcotic; may be habit-forming Kaolin/pectin (kaopectate) Decreases gastric motility Monitor bowel pattern
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Major electrolytes Sodium (na+): normal range 135-145 mEq/L
Potassium (K+): normal range mEq/L Calcium (Ca++): normal range mg/dL Magnesium (Mg++): normal range mg/dL Phosphate (po4-): mg/dL Chloride (Cl-): mEq/L Bicarbonate (hco3-): normal range mEq/L
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Hyponatremia (<135 meq/l)
Causes: Occurs from inadequate sodium intake, excessive intake of water, loss of bile, burns, or inappropriate iv therapy s/s: cns and neuromuscular changes resulting from failure of swollen cells to transmit electrical impulses, Fatigue, lethargy, headache, confusion, altered level of consciousness, anxiety, anorexia, nausea, vomiting, muscle cramps, seizures, Decreased sensation and decreased bp Treatment: restrict water intake, administer iv fluids containing sodium, provide salty foods
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Hypernatremia (>145 meq/l)
Occurs from high-sodium diet, inadequate water intake, excessive sweating, diarrhea; high-protein, hyperosmotic tube feedings, dehydration s/s: dry mucous membranes, taut skin turgor, intense thirst, flushed skin, oliguria, weakness, lethargy, irritability, seizures, coma Treatment: encourage increased fluid intake, monitor i&o, give water between tube feedings, restrict sodium intake, monitor temp
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Hypokalemia (<3.5 meq/l)
Causes: Inadequate intake of potassium-rich foods, diarrhea, vomiting, diuretics s/s: muscle weakness. Cardiac dysrhythmias, decreased reflexes, lethargy, confusion Treatment: instruct pt. on diet in potassium-rich foods, observe for digitalis toxicity on patients taking digoxin
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Hyperkalemia (> 5.0 meq/l)
Causes: kidney failure, digitalis toxicity, overuse of salt substitutes s/s: muscle weakness, fatigue, hypotension, nausea, paralysis, cardiac dysrhythmias, EKG changes Treatment: decrease intake of potassium-rich foods, increase fluid intake (will enhance excretion via urination), instruct pt. in proper use of salt substitutes
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Hypocalcemia (<8.4 mg/dl)
Causes: metastatic cancer, inadequate dietary intake, impaired absorption in intestinal tract (overuse of laxatives), hyposecretion of pararthyroid hormone (thyroidectomy) s/s: paresthesias, abdominal cramps, weak pulse, hypotension, seizures, positive Chvostek sign, positive Trousseau sign, cardiac dysrhythmias, dyspnea, wheezing Treatment: encourage intake of calcium-rich foods, have 10% calcium gluconate at bedside of thyroidectomy patient, give calcium supplements 30 minutes before meals to aid in absorption
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Hypercalcemia (>10.6 mg/dl)
Causes: excess intake of calcium (antacids), excess intake of vitamin D, bone tumor, multiple fractures (both cause movement of calcium out of bone and into extracellular fluid), immobility, osteoporosis s/s: anorexia, nausea, constipation, muscle weakness, oliguria, confusion, renal calculi, pathologic fractures, dysrhythmias Treatment: administer diuretics as prescribed to enhance excretion via urination, monitor i&o, encourage high fluid intake ( ml per day)
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Hypomagnesemia (<1.3 meq/l)
Causes: chronic malnutrition, bowel resection with colostomy/ileostomy, chronic alcoholism, thiazide diuretic use, prolonged gastric suction, acute pancreatitis, osmotic diuretic therapy, diabetic ketoacidosis s/s: insomnia, hyperactive reflexes, leg and foot cramps, twitching, tremors, seizures, cardiac dysrhythmias, vertigo, hypocalcemia, positive Chvostek and trousseau signs, hypokalemia Treatment: provide diet counseling to at-risk patients to increase their magnesium levels (milk and cereals), monitor iv infusions closely, monitor i&o
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Hypermagnesemia (>2.1 meq/l)
Causes: overuse of antacids and cathartics containing magnesium, aspiration of sea water as in near-drowning, chronic kidney failure s/s: hypotension, sweating and flushing, nausea, vomiting, muscle weakness, respiratory depression, cardiac dysrhythmias Treatment: teach patient to avoid overuse of laxatives and antacids, encourage fluid intake to increase urinary excretion, monitor i&O, administer diuretics as ordered
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Hypophosphatemia (<3.0 mg/dl)
Causes: vitamin d deficiency or hyperparathyroidism, use of aluminum- containing antacids s/s: confusion, seizures, numbness, weakness, possible coma, osteomalacia (chronic state) Treatment: assess for vitamin d deficiency, hyperparathyroidism, overuse of antacids containing aluminum (amphogel)
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Hyperphosphatemia (>4.5 mg/dl)
Cause: renal insufficiency s/s: anorexia, nausea, vomiting Treatment: assess for restlessness, confusion, chest pain, and cyanosis, monitor respirations, check all electrolyte levels
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Acid-base system An acid is a substance capable of giving up a hydrogen ion during chemical exchange a base is a substance capable of accepting a hydrogen ion Acids react with bases to form water and a salt A reaction such as this is called a neutralization reaction: both the acid and the base become neutralized Acids react with carbonates and bicarbonates to form carbon dioxide gas
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Acid-base system and ph
The term ph refers to the concentration of hydrogen ions (h) in a solution The higher the concentration of hydrogen ions, the lower the ph A higher ph indicates the opposite Acidic solutions are lower on the ph scale (<7.0) Basic (alkaline) solutions are higher on the ph scale (>7.0) A chemically neutral solution has a ph of 7.0 The ph of most body fluids are between 7.35 and 7.45; a ph of below 7.25 or above 7.55 is considered life-threatening and a ph<6.8 (acidosis) or >7.8 (alkalosis) is incompatible with life Acidosis is the result of either a loss of base or an accumulation of acid
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Acid-base imbalances Most of the body’s metabolic activity produces carbon dioxide gas, which is acidic The body takes care of this excess of acidic substance by way of the respiratory tract or the renal system
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The respiratory system
Hypoventilation produces excess carbon dioxide gas If the body senses an excess of acids (low ph), the respiratory system will increase the respiratory rate to “blow off” the excess carbon dioxide and return the body to a neutral state If the body senses an excess of bases (high ph), the respiratory system will slow down the respiratory rate to conserve carbon dioxide and thus lower the ph to a neutral state “neutral state” meaning a ph between
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The renal system Hydrogen ions are either conserved or excreted via the kidneys So, if the body senses an acidic state, the glomeruli will conserve more bicarbonate (Hco3) to raise the ph to a neutral state And, if the body senses a basic state, the glomeruli will excrete bicarbonate ions to restore a neutral state with a ph between Bicarbonate ions are a basic substance But, carbon dioxide ions are acidic. The body undergoes chemical reactions to form bicarbonate from carbon dioxide by adding water Water + carbon dioxide= bicarbonate
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Respiratory acidosis Causes: slow, shallow respirations due to respiratory congestion or obstruction Blood gas values Ph <7.35 Paco2 >45 mm Hg In respiratory acidosis, the carbon dioxide value will be increased, as carbon dioxide (co2) is an acidic substance; co2 is retained as it is not being exhaled
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Respiratory alkalosis
Cause: hyperventilation due to anxiety or excitement In respiratory alkalosis the carbon dioxide is being “blown off” in excess Slowing down the respiratory rate will conserve carbon dioxide and lower the ph to a neutral level This can also be accomplished by breathing into a paper bag Ph >7.45 Paco2 >35 mm Hg
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Metabolic acidosis Causes: shock (due to poor circulation), diabetic ketoacidosis, renal failure, diarrhea, hyperkalemia Ph <7.35 Hco3 (bicarbonate) < 22 meq/l The kidneys accomplish ph control by excreting or conserving bicarbonate Bicarbonate is a strong base
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Metabolic alkalosis Causes: vomiting, excessive antacid intake, hypokalemia Ph >7.45 Hco3 >26 meq/l Example: vomiting causes loss of potassium ions; potassium ions are + (k+); therefore, loss of the positive (acidic) ions cause a base state
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Arterial blood gases The levels of these percentages of gases (oxygen and carbon dioxide) and hydrogen ions in the blood are useful in assessing the status of both respiratory and metabolic acid-base balances Blood gas studies are useful in assessing a patient’s progress toward recovery, or lack of it, and also the respiratory and renal systems’ abilities to regulate the retention or elimination of carbon dioxide and bicarbonate Lungs= carbon dioxide Kidneys= bicarbonate
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Intravenous fluid therapy
The three types of solutions: Isotonic: a solution that has the same osmotic pressure as the intracellular fluid Example: 0.9% normal saline Hypotonic: a solution that has a lower osmotic pressure (is less concentrated) than the intracellular fluid Example: d5w or 0.45 % normal saline Hypertonic: a solution that has a higher osmotic pressure (is more concentrated) than the intracellular fluid Example: d5w + 0.9% normal saline The blood has a 0.9% sodium concentration; therefore 0.9% saline solution is isotonic
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When to use which fluid If the patient is dehydrated: the physician will most likely order 0.9% normal saline solution, % normal saline or d5 % water (d5W) Rationale: the osmolarity (concentration) of the solutes in the blood is high and these fluids will provide hydration to dilute the solutes and restore homeostasis If the patient is a surgical or medical patient with no severe fluid imbalances: the physician will most likely order 0.9% normal saline Rationale: maintain homeostasis If the patient is fluid overloaded: probably no fluids will be ordered If the patient is malnourished: the physician will most likely order d5% w+ 0.9 ns Rationale: provide the patient with fluids and dextrose for nutrition while maintaining homeostasis
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