Chapter 42 Fluid, Electrolyte and Acid-Base Balance PDF

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Fluid and Electrolytes + Acid bases imbalance review...

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Chapter 42: Fluid, Electrolyte and Acid-Base Balance Location and Movement of Water and Electrolytes ● Water is about 60% of the body weight in an adult male – decreases with age ● Women usually have less water content than men ● Obese people have less water in their body because fat contains less water than muscle ●

Fluid – means water that contains dissolved or suspended substances such as glucose, mineral salts and proteins

Fluid Distribution ● Fluids are in two distinct compartments: ● Extracellular fluid (ECF) – outside the cells ● ●

Approximately 1/3 of total body water Two major divisions: ● Intravascular fluid – liquid part of the blood (plasma) ● Interstitial fluid – located between the cells and outside the plasma

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Minor division – transcellular fluid – cerebrospinal, pleural, peritoneal, and synovial fluids are secreted by epithelial cells Intracellular fluid (ICF) – inside the cells ● Approximately 2/3 of total body water

Composition of Body Fluids ● Electrolytes – mineral salts ● Separates into ions (charged particles) when it dissolves in water ● Cations – positively charged ions ● ● ●

● Sodium, potassium, calcium, magnesium Anions – negatively charged ions ● Chloride, bicarbonate Anions and cations combine to make salts

Laboratory normal values for adults:

Item Measured

Normal Value in Serum or Blood

Osmolarity

280-300 mOsm/kg H2O

Electrolytes Sodium (Na)

135-145

Potassium (K) Chloride (Cl)

3.5-5.0 98-106

Total CO2

22-30

Total Calcium (Ca)

Arterial: 22-26 Venous: 24-30 8.4-10.5

Ionized Calcium Magnesium (Mg)

4.5-5.3 1.5-2.5

Phosphate Anion Gap

2.7-4.5 5-11

Arterial Blood Gas (ABG) pH

7.35-7.45

PaCO2

35-45

PaO2

80-100

O2 saturation

95%-100%

Base excess

-2 to +2 mmEq/L

Bicarbonate (HCO3)

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Fluid that contains a large number of dissolved particles is more concentrated than the same amount of fluid that only contains a few particles Osmolarity – measure of the number of particles per kilogram of water Isotonic – fluid with the same tonicity as blood Hypotonic – solution is more dilute than the blood Hypertonic – solution is more concentrated than normal blood

Movement of Water and Electrolytes ● Active transport – requires energy in the form of ATP to move electrolytes across cell membranes against the gradient (from areas of lower concentration to higher concentration) ● Na, Cl, HCO3 –  concentration higher in the ECF ● K, Mg and phosphate – concentrations higher in the ICF ● Example: sodium-potassium pump ● Diffusion – passive movement of electrolytes or other particles down a concentration gradient (from areas of higher concentration to areas of lower concentration) ● Diffusion of electrolytes across cell membranes requires proteins that serve as ion channels ● Osmosis – a process by which water moves through a membrane that separates fluids with different particle concentrations ● Water moves into the compartment that has higher osmotic pressure (inward-pulling force) until the particle concentration is equal in the two compartments ● Filtration – fluid moves into and out of the capillaries (between the vascular and interstitial compartments) by the process of filtration ● The net effect of four forces, two that tend to move fluid back into them ● Hydrostatic pressure – the force of the fluid pushing against a surface ● Capillary hydrostatic pressure – relatively strong outward-pushing force that helps move fluid from capillaries into the interstitial area ● Interstitial fluid hydrostatic pressure – weaker opposing force that tends to push fluid back into capillaries ● Colloids – albumin and other proteins contained in the blood ● Most are too large to leave capillaries in the fluid that is filtered; thus they remain in the blood ● Colloids exert osmotic pressure ● Blood colloid osmotic pressure (oncotic pressure) – inward-pulling force caused by blood proteins that helps move fluid from the interstitial area back into capillaries ● Arterial end of a normal capillary – capillary hydrostatic pressure is the strongest; fluid moves from the capillary into the interstitial area, bringing nutrients to the cell ● Venous end capillary hydrostatic pressure – weaker; colloid osmotic pressure of the blood is stronger; fluid moves into the capillary at the venous end, removing waste products from cellular metabolisms ● Edema – caused by a disruption of these processes usually due to disease processes; accumulation of fluid in the interstitial space Fluid Balance ● To maintain fluid balance, fluid intake must equal output Fluid Intake ● Orally through drinking and eating – average intake in an adult is 2300 mL ● Other routes include – IV, rectal (enemas), and irrigation of body cavities that absorb fluid ● Thirst – important regulator of intake – when plasma osmolarity increases or the blood volume decreases

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Hypothalamus – thirst control mechanism Infants, patients with neurological and psychological problems, and some older adults who are unable to perceive or communicate their thirst are at risk for dehydration

Fluid Distribution ● The movement of fluid among different compartments ● Osmosis – fluid distribution of the intracellular and extracellular compartments ● Filtration – fluid distribution between the vascular and interstitial parts of the ECF Fluid Output ● Normally occurs through four organs: the skin, lungs, GI tract and kidneys ● Abnormal fluid output includes vomiting, wound drainage, or hemorrhage ● Insensible water loss – through the skin and lungs; continuous; not visible ● Sweat – contains sodium; occurs intermittently; major source for fluid loss ● GI tract – 3 to 6 L of fluid moves into the GI tract daily and returns to the ECF; average adult only secretes 100 mL of fluid per day through feces (diarrhea – much more) ● Kidneys – major regulator of fluid output; regulated by: ● Antidiuretic hormone – regulates the osmolarity of the fluids by influencing how much water is excreted ● Synthesized in neurons in the hypothalamus that release it from the posterior pituitary gland ● Circulates in the blood to the kidneys where it acts on the collecting ducts ● Causes renal cells to reabsorb water taking water from the renal tubular fluid and putting it back in the blood – decreases urine volume ● More ADH is released if body fluids become more concentrated – severely decreased blood volume (dehydration, hemorrhage), pain, stressors, and some medications ● Decrease if the body fluid becomes to dilute – allows more water to be excreted; when people drink alcohol ● Renin-angiotensin-aldosterone system – regulates ECF volume by influencing how much sodium and water are excreted by urine; contributes to regulation of BP ● Specialized cells in the kidneys release renin; renin acts on angiotensinogen, an inactive protein secreted by the liver; renin converts angiotensinogen to angiotensin I, which is converted to angiotensin II by other enzymes in the lung capillaries ● Angiotensin II stimulates the release of aldosterone from the adrenal cortex – circulates to the kidneys where is causes reabsorption of water in the renal tubules – removes sodium and water from the renal tubules returning it to the blood increases the volume of the ECF; contributes to acid-base balance by increasing urinary excretion of potassium and hydrogen ions ● Atrial natriuretic peptide – influences how much sodium and water are excreted in urine ● Cells in the atria of the heart release ANP when they are stretched ● ANP is a weak hormone that inhibits ADH by increasing the loss of sodium and water in the urine ● Opposes the effect of aldosterone Fluid Imbalances: ● Volume imbalances – disturbances of the amount of fluid in the extracellular compartment ● Osmolarity imbalances – disturbances of the concentration of body fluids

Extracellular Fluid Volume Imbalances ● ECV deficit – present when there is insufficient isotonic fluid in the extracellular compartment; there is a lot of sodium in the ECF ● With ECV deficit, output of isotonic fluid exceeds intake of sodium-containing fluid ● Because ECF is both vascular and interstitial, signs and symptoms arise from lack of volume in both of these compartments ● Hypovolemia – decreased vascular volume ● ECV excess – occurs when there is too much isotonic fluid in the extracellular compartment; intake of sodium-containing isotonic fluid has exceeded fluid output; hypervolemia Osmolarity Imbalances ● Hypernatremia – water deficit; hypertonic condition ● Loss of relatively more water than salt or a gain of relatively more salt than water ● When the interstitial fluid becomes hypertonic, water leaves cells by osmosis, and they shrivel (crenate) ● Signs and symptoms: neurological (when brain cells shrivel) ● May occur in combination with ECV deficit; this combined disorder is called dehydration ● Hyponatremia – water excess, or water intoxication; hypotonic condition ● Arises from gain of relatively more water than salt or loss of relatively more salt than water ● Excessively dilute condition causes water to enter the cell by osmosis, causing the cells to swell ● Signs and symptoms: cerebral dysfunction occurs when brain cells swell Imbalance and Related Causes

Signs and Symptoms

Isotonic Imbalances – water and sodium lost or gained in equal or isotonic proportions: Extracellular fluid volume deficit (hypovolemia) – body fluids have decreased but normal osmolarity caused by: Severely decreased oral intake of water and salt Increased GI output: vomiting, diarrhea, laxative overuse, drainage from fistulas or tubes Increased renal output: use of diuretics, adrenal insufficiency (deficit of cortisol and aldosterone) Loss of blood or plasma: hemorrhage, burns Massive sweating without water and salt intake

Physical examination: sudden weight loss (overnight), postural hypotension, tachycardia, thread pulse, dry mucous membranes, poor skin turgor, slow vein filling, flat neck veins when supine, dark yellow urine If severe: thirst, restlessness, confusion, hypotension, oliguria (urine output below 30 mL/hr); cold clammy skin; hypovolemic shock Laboratory findings: increased hematocrit; increased BUN above 25 mg/dL; urine specific gravity usually above 1.030 unless renal cause

Extracellular fluid volume excess (hypervolemia) – body fluids have increased volume but normal osmolarity caused by: Excessive administration of sodium-containing isotonic IV fluids or oral intake of salty foods and water Renal retention of sodium and water: heart failure, cirrhosis, aldosterone or glucocorticoid excess, acute or chronic oliguric renal disease Osmolarity Imbalances: Hypernatremia (water deficit; hyperosmolar imbalance) – body fluids too concentrated Loss of Relatively More Water Than Salt: Diabetes insipidus (ADH deficiency) Osmotic diuresis Large insensible perspiration and respiratory water output without increased water intake Gain of Relatively More Salt Than Water: Administration of tube feedings, hypertonic parenteral fluids, or salt tablets Lack of access to water, deliberate water deprivation, inability to respond to thirst (ex: immobility, aphasia) Dysfunction of osmoreceptor-driven thirst Hyponatremia (water excess; water intoxication; hypo-osmolar imbalance) – body fluids too dilute Gain of Relatively More Water Than Salt: Excess ADH Psychogenic polydipsia or forced excessive water intake Excessive IV administration of D5W Use of hypotonic irrigating solution Tap-water enemas Loss of Relatively More Salt Than Water: Replacement of large body fluid output (diarrhea, vomiting) with water but no sale Combined Volume and Osmolarity Imbalance:

Physical examination: sudden weight gain (overnight), edema (especially in dependent areas), full necks veins when upright or semi-upright (jugular vein distension), crackles in lung If severe: confusion, pulmonary edema Laboratory findings – decreased hematocrit, decreased BUN below 10 mg/dL

Physical examination: decreased level of consciousness (confusion, lethargy, coma), perhaps thirst, seizures if develops rapidly or is very sever Laboratory findings: serum Na level above 145 mEq/L, serum osmolarity above 300 mOsm/kg

Physical examination: decreased level of consciousness (confusion, lethargy, coma), seizures if develops rapidly or is very severe Laboratory findings: serum Na level below 135 mEq/L, serum osmolarity below 280 mOsm/kg

Clinical Dehydration (ECV deficit plus hypernatremia) – body fluids have decreased volume and are too concentrated Sodium and Water Intake Less Than Output, With Loss of Relatively More Water Than Salt: All of the causes of ECV deficit plus poor or no water intake, often with fever causing increased insensible water output

Physical examination and laboratory findings: combination of those for the ECV deficit plus those for hypernatremia

Electrolyte Imbalances: Potassium Imbalances ● Hypokalemia – abnormally low potassium concentration in the blood ● Results from decreased potassium intake and absorption, a shift of potassium from the ECF into cells, and increased potassium output ● Common causes of hypokalemia from increased potassium output include diarrhea, repeated vomiting, and use of potassium-wasting diuretics ● Causes muscle weakness that can become life threatening if it includes respiratory muscles and potentially life-threatening cardiac dysrhythmias ● Hyperkalemia – abnormally high potassium ion concentration in the blood ● Causes are increased potassium intake and absorption, shift of potassium from cells into the ECF, and decreased potassium output ● Oliguria (decreased urine output) – high risk of hyperkalemia from the resultant decreased potassium output unless their potassium output also decreases substantially ● Remember to check urine output before you administer IV solutions containing potassium ● Can cause muscle weakness, potentially life-threatening cardiac dysrhythmias, and cardiac arrest

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Calcium Imbalances Hypocalcemia – abnormally low calcium concentration in the blood ● Total blood calcium contains active and inactive forms; inactive forms are bound to plasma proteins and small anions such as citrate ● People who have acute pancreatitis frequently develop hypocalcemia because calcium binds to undigested fat in their feces and is excreted – decreases absorption of dietary calcium and increases calcium output by preventing reabsorption of calcium contained in GI fluid ● Increases neuromuscular excitability Hypercalcemia – abnormally high calcium concentration in the blood ● Results from increased calcium intake and absorption, shift of calcium from bones into the ECF, and decreased calcium output ● Patients with some cancers such as lung and breast cancer often develop hypercalcemia because some cancer cells secrete chemicals into the blood that are related to parathyroid hormone – causes a shift of calcium from the bone into the ECG ● Decreases neuromuscular excitability; most common S/S is lethargy Magnesium Imbalances Hypomagnesemia – abnormally low magnesium concentration in the blood ● Causes are decreased magnesium intake and absorption, shift of plasma magnesium to its inactive bound form, and increased magnesium output

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Signs and symptoms are similar to hypocalcemia because hypomagnesemia also increases neuromuscular excitability Hypermagnesemia – abnormally high magnesium concentration in the blood ● Causes include end-stage renal disease unless the person decreases magnesium intake to match the decreased output ● S/S are caused by decreased neuromuscular excitability, with lethargy and decreased deep tendon reflexes being the most common

Electrolyte Intake and Absorption, Distribution and Output Electrolyte

Intake and Absorption

Potassium (K+)

Fruits, potatoes, instant coffee, molasses, brazil nuts; absorbs easily

Calcium (Ca2+)

Dairy products, canned fish with bones, broccoli, oranges; require vitamin D for best absorption; undigested fat prevents absorption

Magnesiu m (Mg2+  )

Dark green leafy vegetables, whole grains, Mg-containing laxatives and antacids; undigested fat prevents absorption

Distribution Low in ECF, high in ICF Insulin, epinephrine, and alkalosis shift K+ into cells Some types of acidosis shift K+ out of cells Calcium is low in the ECF, mostly in bones and intracellular Some calcium in blood is bound and inactive, only ionized Ca is active Parathyroid hormone shifts Ca out of the bone; calcitonin shifts Ca into the bone Ca decreases in blood if phosphate rises and vice versa Mg is low in the ECF, mostly in bones and intracellular Some Mg in blood is bound and inactive; only free Mg is active

Output/Loss Aldosterone, black licorice, hypomagnesemia, and polyuria increase renal excretion; oliguria decreases renal excretion Acute or chronic diarrhea increases fecal excretion

Important Function

Maintains resting membrane potential of skeletal, smooth, and cardiac muscle, allowing normal muscle function

Thiazide diuretics decrease renal excretion Chronic diarrhea and undigested fat increase fecal excretion

Influences excitability of nerve and muscle cells; necessary for muscle contraction

Rising blood ethanol increases renal excretion; oliguria decreases renal excretion Chronic diarrhea and undigested fat increase fetal excretion

Influences function of neuromuscular junctions; is a cofactor for numerous enzymes

Phosphate is low in ECF; it is higher in the ICF and in bones Insulin and Milk, processed foods; Phosphate aluminum antacids prevent epinephrine shift phosphate absorption into cells Decreases in blood if calcium rises and vice versa

Imbalance and Related Causes

Oliguria decreases renal excretion

Necessary for production of ATP, the energy source for cellular metabolism

Electrolyte Imbalances Signs and Symptoms

Hypokalemia – Low Serum Potassium (K) Concentration Decreased K Intake: excessive use of K-free IV solutions Shift of K into cells: alkalosis; treatment of diabetic ketoacidosis with insulin Increased K output: acute or chronic diarrhea, vomiting, other GI losses (ex: nasogastric or fistula drainage); use of potassium-wasting diuretics; aldosterone excess; polyuria; glucocorticoid therapy

Physical examination: bilateral muscle weakness that begins in quadriceps and may ascend to respiratory muscles, abdominal distension, decreased bowel sounds, constipation, dysrhythmias Laboratory findings: serum K level below 3.5 mEq/L; ECG abnormalities: U waves, flattened or inverted T waves; ST segment depression

Hyperkalemia – High Serum Potassium (K) Concentration Increased K intake: iatrogenic administration of large amounts of IV K; rapid infusion of stored blood; excess ingestion of K salt substitutes Shift of K out of cells: massive cellular damage (ex: crushing trauma, cytotoxic chemotherapy); insufficient insulin (diabetic ketoacidosis), some types of acidosis Decreased K output: acute or chronic oliguria (ex: severe ECV deficit, end-stage renal diseases); use of potassium-sparing diuretics; adrenal insufficiency (deficit of cortisol and aldosterone)

Physical examination: bilateral muscle weakness in quadriceps, transient abdominal cramps, diarrhea, dysrhythmias, cardiac arrest if severe Laboratory findings: serum K levels above 5 mEq/L; ECG abnormalities: peaked T waves; widened QRS complex; PR prolongation; terminal sine-wave pattern

Hypocalcemia – Low Serum Calcium (Ca2+) Concentration Decreased Ca Intak...