Exam 2 Craven Ch 28 Fluid Electrolytes and Acid–Base

Any substance capable of releasing hydrogen ions in solution

• Movement of substances across a cell membrane against an electrochemical gradient
• Ions and other molecules are moved across membranes from an area of lesser concentration to an area of greater concentration. Energy is required to move ions against a concentration gradient. Enzymes, such as sodium–potassium adenosine triphosphatase (Na, K-ATPase), are involved in active transport. (Sodium-potassium pump)

Negatively charged ions

Accumulation of serous fluid in the peritoneum

Stretch receptors located in major arteries and veins that monitor vascular volume

Any substance that can combine with and decrease hydrogen ions in solution; alkali

Compounds that help stabilize the pH of a solution by neutralizing added acid or base

Positively charged ions

Movement of molecules from an area of higher concentration to one of lower concentration

Chemical compounds that dissociate into ions when in solution; usually refers to extracellular sodium, potassium, and chloride

• Body fluid outside the cells; mainly interstitial fluid and plasma
• 1/3 of fluids in body

• Passage of a solution through a semipermeable membrane from a region of higher pressure to a region of lower pressure
• Hydrostatic pressure, or the pressure exerted by fluid against the walls of its container, promotes the flow of fluid out of the capillaries. Filtration occurs within the kidney’s glomerular capillaries and in blood capillaries.

One compartment contains a greater concentration of a dissolved substance (hyperosmolar) than the other compartment (hypoosmolar)

Of greater concentration than in body fluids

One compartment contains a lesser concentration of a dissolved substance (hypoosmolar) than the other compartment (hyperosmolar)

Of lower concentration than in body fluids

• Fluid between the cells
• component of extracellular fluid

• Portion of body fluid contained within the cells
• 2/3 of fluids in body

• Fluid inside the blood and lymphatic vessels
• component of extracellular fluid

Charged particles formed by the dissociation of electrolytes in a solution

Unit used to give the concentration of an electrolyte in solution; commonly expressed as mEq/L

Concentration of solutes in a solution, expressed as milliosmols per kilogram

Concentration of solutes in a solution expressed as milliosmols per liter

Movement of a fluid through a semipermeable membrane from a region of lower to higher solute concentration

• Pressure exerted by nondiffusible particles in a solution across a semipermeable membrane; tends to hold fluid within its container and is opposed by hydrostatic pressure
• Plasma proteins contribute to the osmotic pressure because they attract water.
• Osmotic pressure depends on the solution’s osmolality.

colloid oncotic pressure

Fluid’s effect on cell size

• Na+
• Cation
• 136–145 mEq/L
• Corbett p107
• Course booklet p 180

• K+
• Cation
• 3.5–5.1 mEq/L
• Corbett p107
• Course booklet p 180

• Ca++
• Cation
• Total serum calcium = 9.0–10.5 mg/dL
• Corbett p 160
• Course booklet p 180

• Mg++
• Cation
• 1.8–3.0 mEq/L
• Corbett p 173
• Course booklet p 180

• Cl−
• Anion
• 98–107 mEq/L
• Corbett p 107
• Course booklet p 180

• HCO3−
• Anion
• 21–30 mEq/L Adult
• Corbett p 107
• Course booklet p 180

• HPO4−, H2PO4−
• Anion
• 3.0–4.5 mg/dL
• Higher in children and even higher in infants
• Corbett p 169
• Course booklet p 180

• sodium, chloride, calcium, and bicarbonate
• Sodium is the most abundant

potassium, phosphate, and magnesium

water will follow

normal cardiac, neural, and muscle function and contractility of all muscles

• insulin and aldosterone
• Insulin, a pancreatic hormone, promotes the transfer of potassium (and also glucose) from the ECF into skeletal muscle and liver cells.
• Aldosterone enhances renal excretion of potassium.

• iodized and bound to protein
• Approximately 50% is ionized, with the remainder bound to proteins, mainly albumin.
• Check serum albumin levels when checking calcium levels - when albumin levels are decreased the total serum calcium may be decreased but the iodized levels may be within the normal range.

phosphorus

iodized calcium level

• cell membrane structure, for cell-to-cell adhesion
• wound healing
• synaptic transmission in nervous tissue
• membrane excitability
• muscle contractility
• teeth and bone structure
• blood clotting
• metabolic reactions involved in energy production (glycolysis)

• (Reciprocal electrolyte is phosphorus)
• Parathyroid hormone (PTH)
• vitamin D
• calcitonin (to some extent)

• PTH increases calcium levels but decreases serum phosphate levels
• Conversely, decreased secretion of PTH lowers serum calcium levels and increases the serum phosphate concentration
• PTH causes serum calcium levels to increase by increasing intestinal and renal reabsorption of calcium and releasing calcium from bone

• 50-60%
• The rest is in soft tissue and body fluids

neuromuscular function and cardiac activity

potassium

The kidney regulates magnesium levels by reabsorbing the ion when serum levels are low and excreting it when serum levels are high.

• 85%
• 14% in ICF, 0.1% in ECF

• Kidney
• Blood levels of phosphorus are controlled by the regulation of renal excretion under the influence of vitamin D and PTH

• energy metabolism
• structure of bones and membranes
• synthesis of nucleic acids (RNA and DNA)

• Increased hydrostatic pressure:
• -Elevated blood pressure
• -Fluid overload
• -Decreased cardiac output with backup of blood, e.g., heart failure
• Decreased colloid oncotic pressure (decreased plasma proteins):
• -Malnutrition
• -Liver failure
• -Nephrosis
• Blockage or removal of lymph nodes:
• -Mastectomy
• -Lymphoma
• Increased capillary permeability:
• -Allergies
• -Septic shock
• -Pulmonary edema

• Oral fluids - 1300 mL
• Fluid in food - 1000 mL
• Oxidation of food - 300 mL
• Total 2600 mL

• Urine - 1500 mL
• Feces - 200 mL
• Perspiration - 100-200 mL
• Insensible loss:
• Skin - 300-400 mL
• Respiration - 300 mL
• Total 2400-2600 mL

• If sufficient gastric juice (ECF with additional acid) is lost from the stomach, hydrogen, sodium, and chloride ions are depleted, increasing the risk of ECF volume deficit and/or metabolic alkalosis.
• Gastric fluid also is high in potassium, and excessive losses may contribute to hypokalemia.
• Vomiting compounds fluid and electrolyte problems because the ability to maintain adequate intake is reduced.

• Intestinal secretions contain bicarbonate. For this reason, diarrhea may result in metabolic acidosis due to depletion of base.
• Intestinal contents also are rich in sodium, chloride, water, and potassium, possibly contributing to an ECF volume deficit and hypokalemia.

• Diaphoresis, or excessive sweating, can occasionally increase the loss of fluid and electrolytes.
• Sweat is a hypotonic fluid containing sodium, potassium, and chloride.
• Diaphoresis can occur with increased and/or prolonged physical activity, fever, or exposure to elevated environmental temperatures.

• Diuretics are prescribed to increase the excretion of sodium, chloride, and water in patients with high blood pressure or with chronic heart, renal, or liver problems.
• At times, the medications may remove too much ECF from the body, resulting in a deficit.
• Diuretics, except for the potassium-sparing diuretics, also promote the excretion of potassium and magnesium from the body, increasing the risk of electrolyte deficits as well.

• Stress caused by many factors, such as physical trauma, anxiety, and pain, can affect fluid and electrolyte balance.
• When stress occurs, aldosterone production is increased, causing ECF retention.
• Stress also increases ADH production, resulting in decreased renal excretion of water.

• hyperkalemia and hypocalcemia
• (metabolic acidosis occurs when the kidneys fail)

• As the heart fails to pump effectively, blood pressure falls. The secretion of aldosterone and ADH is stimulated, often resulting in ECF volume and water excesses.
• This fluid collects in the lungs, increasing the risk of pulmonary edema, and in the rest of the body, where it appears as pitting or dependent edema.
• Fluid volume excess is complicated by the fact that as the heart pumps less effectively, blood flow to the kidneys decreases, resulting in decreased fluid excretion.

• Liver failure influences ECF and water balance.
• People with liver failure frequently present with a water excess thought to be related to increased plasma levels of ADH.
• In addition, as the liver fails, plasma levels of albumin decrease, so the distribution of ECF changes, vascular volume decreases, and interstitial volume increases.
• Ascites, an abnormal collection of fluid within the peritoneal cavity, commonly accompanies liver failure.

• A special type of ECF volume balance problem
• It occurs when fluid leaves the vascular volume and is trapped within the interstitial fluid in a given body area.
• A "third space" is any area in which fluid accumulates that is physiologically unavailable to return to its appropriate compartment.
• For example, collection of fluid in the peritoneal cavity is known as ascites.
• There is no actual third space, and the retained fluid is within the interstitial space.
• More appropriate terms for this imbalance would be vascular volume deficit and interstitial volume excess.

• 1 kg = 1 Liter
• in the ECF

• weight gain (1 kg = 1 L)
• increased blood pressure
• bounding pulse
• fullness of neck veins

water osmolality

Hyperosmolality

Hypoosmolality

• (hypoosmolality)
• Symptoms: lethargy, irritability, confusion, personality changes, seizures, coma, and eventually death if there is no treatment or treatment is ineffective
• If water excess develops quickly, there is risk of permanent brain damage; if it develops slowly, the brain cells are able to adapt by extruding osmolytes.
• Additional symptoms include: anorexia, nausea, vomiting, weakness, and cramps.
• Other terms used for water excess include hypotonic disorder, hyponatremia, and hypotonicity.

• Resultant increase in cell membrane responsiveness to stimuli with changes in skeletal, smooth, and cardiac muscle activity; anxiety, irritability; gastrointestinal hyperactivity (diarrhea and intestinal cramping); tall, peaked T waves on electrocardiogram and cardiac dysrhythmias
• Resultant decrease in cell membrane responsiveness if serum potassium is elevated (>8 mEq/L) with symptoms similar to those of hypokalemia; cardiac arrest (especially if serum levels increase rapidly)

• Depends on severity of elevation and onset
• If levels very high: Administer IV calcium gluconate to oppose potassium’s effect on the membrane potential of excitable cells. Infuse insulin and glucose to move potassium into the cell. Remove potassium from body by dialysis or administration of ion exchange resins such as Kayexalate.
• If levels moderately elevated: Administer diuretics and potassium exchange resins. Identify and treat the underlying cause.

Resultant decreased responsiveness of cellular membranes to stimuli and lack of responsiveness to stimuli leading to characteristic skeletal muscle, smooth muscle, renal, and cardiac (symptoms usually appearing when serum potassium is below 3 mEq/L): muscle weakness (begins in lower extremities and moves up trunk to upper extremities); fatigue; impaired respiratory muscle function (if level severely low); abdominal distention, nausea, vomiting, constipation, and paralytic ileus (from decreased gastrointestinal responsiveness); increased urination (polyuria) and thirst (polydipsia); dysrhythmias and flattened T waves on electrocardiogram; elevated blood glucose levels (from suppression of insulin release)

• Increase intake of potassium: encourage potassium-rich foods in diet; administer oral potassium supplements; use potassium-sparing diuretics; and administer IV potassium (if level very low).
• Identify and treat underlying cause.
• Administer oral phosphate replacement if indicated.

Neuromuscular dysfunction; weakness, especially respiratory muscles; fatigue; myocardial depression; ventricular dysrhythmias; rhabdomyolysis; confusion, coma; decreased oxygen delivery to tissues; renal loss of bicarbonate, calcium, magnesium, and glucose; bone changes (osteomalacia); endocrine changes (insulin resistance)

• Identify and treat underlying cause.
• Encourage foods high in phosphorus.
• Administer oral phosphate replacement if indicated.

• Redistribution: Increased carbohydrate calories; respiratory alkalosis
• Depletion: Alcoholism; uncontrolled diabetes mellitus; renal phosphate wasting