ABD_E 2 Flashcards
Minerals (inorganic substances) are dissolved within and form ions called
electrolytes
Fluid compartments
- Interstitial fluid volume varies
- Volume of blood (women < men)
Extracellular fluid (ECF)
Fluid compartments
- Water content varies most here due to variation in:
+ Tissue types (muscle vs. fat)
- Distinct from ECF due to plasma membrane transport
Intracellular fluid (ICF)
Fluid balance
- Primarily absorption along digestive tract
- As nutrients and ions are absorbed, osmotic gradient created causing passive absorption of water
Gains
Fluid balance
- Mainly through urination (over 50%) but other routes too
- Digestive secretions are reabsorbed similarly to ingested fluids
Losses
- Very different composition
- Are at osmotic equilibrium
- Loss of water from ECF is replaced by water in ICF
ICF and ECF compartments balance
Occurs in minutes to hours and restores osmotic equilibrium
Fluid shift
- Results in long-term transfer that cannot replace ECF water loss
- Homeostatic mechanisms to increase ECF fluid volume will be employed
Dehydration
- These are fluids that have osmotic pressure in the range of 280-300 mOsm/L.
- the same as osmotic pressure of plasma, these fluids do not cause any fluid shifts between the extracellular and intracellular spaces.
- When administered, the fluids may move into the interstitial space, but
will still remain as extracellular fluid. - Examples include normal saline (0.9% NaCl), lactated Ringer’s and dextrose 5% in water (D,W).
Isotonic Fluids
- These are fluids that have an osmolality of less than 280 mOsm/L (containing relatively few crystalloid molecules).
- These fluids cause an osmotic shift of fluid into the cell (i.e. cells swell).
- These fluids are used for hydration purposes.
- Examples include sodium chloride 0.45%
Hypotonic Fluids
- These are IV fluids that have an osmolality of greater than 300 mOsm/L and contain relatively large amounts of crystalloid molecules.
- These are IV fluids that have more osmotic pressure than human plasma.
- These fluids cause an osmotic shift of fluid from the intracellular space to the extracellular space (cells shrink).
- Examples of include dextrose 10% in water, dextrose 10% in 0.9% NaCl, dextrose 50% in water
Hypertonic Fluids
Dextrose Water Solutions:
-Hypotonic
- Isotonic
- Hypertonic
- 2.5% GW (hypotonic)
- 5% GW (isotonic)
- 20% and 50% GW (hypertonic).
These solutions provide both fluids and carbohydrates for energy
Sodium Chloride Solutions:
- Hypotonic
- Isotonic
- Hypertonic
- 0.9% NaCl (isotonic) the most common
- 0.45% NaCl (hypotonic)
- 0.2% NaCl (hypotonic)
- 5% NaCl (hypertonic)
- 3% NaCl (hypertonic)
These solutions are mainly used for electrolyte replacement and for extracellular fluid replacement.
NaCl w/ Dextrose Sol
- 1/5” GS is (5% dextrose + 0.18% NaCl) (isotonic)
- 1/3 GS is (5% dextrose + 0.29% NaCl) (isotonic)
- 1/2 GS is (5% dextrose + 0.45% NaCl) (isotonic)
Multiple ELectrolyte Sol:
- Ringers solution: contain (Na + Cl + K+ Ca)
- Ringer lactate solution: contain (Na + Cl + K + Ca + lactate)
Colloid Solutions:
- human albumin
- Hemaccel (gelatin solution)
- Dextran
- Hydroxyethyl starches (Hetastarch)
- store in a 70-kg person exceeds 3500 mEq, with less than 2% located in extracellular uid.
- balance of it is primarily maintained by oral intake and renal elimination.
- Extracellular is dependent on multiple factors, including acid-base balance, the activity and sensitivity of insulin, sodium-potassium adenosine triphosphate dependent exchange channels, and blood insulin and catecholamine levels.
K
Major gain of K is through
digestive tract absorption
Major loss of K is excretion by
kidneys
- Primary ECF potassium regulation by
- Controlled by aldosterone regulating Na/K exchange pumps in
- kidneys
- DCT and collecting duct of nephron
Potassium is highest in ___ due to Na/K exchange pump
ICF
Factors Controlling Potassium Balance
- Approximately 100mEq of K ions are absorbed by the digestive tract each day
- roughly 98% of the K content of the human body is in the ICF, rather than the ECF
- The K+ conc. in the ECF is relatively low. The rate of K+ entry from the ICF through leak channels is balanced by the rate of K+ rcovery by the Na+/K+ exchange pump.
- When K balance exists, the rate of urinary K+ excretion matches the rate of digestive tract absorption
- Below 2 mEq/L in plasma
- Can be caused by:
+ Diuretics
+ Aldosteronism (excessive aldosterone secretion) - Symptoms
+ Muscular weakness, followed by paralysis
+ Potentially lethal when affecting heart
Hypokalemia
- Above 8 mEd/L in plasma
- Can be caused by:
+ Chronically low pH
+ Kidney failure
+ Drugs promoting diuresis by blocking Na/K pumps - Symptoms
+ Muscular spasm including heart arrhythmias
Hyperkalemia
- involves the electrical conduction system of the heart.
- These changes include gradual prolongation of the PR interval (with eventual loss of the P wave), prolongation of the QRS complex, ST- segment elevation, and peaking of T waves that can ultimately lead to ventricular arrhythmias
HYPERKALEMIA
Cardiac conduction changes usually occur when the plasma potassium concentration exceeds ___ mmol/L, but they may develop at lower levels in the setting of acute hyperkalemia.
6.5
Options for acute management rely on _________ and include administration of calcium chloride, sodium bicarbonate, and insulin with glucose
- membrane stabilization
- intracellular shifting of potassium
tall peaked T waves is suggestive of
hyperkalemia
absence of P waves, suggesting a junctional rhythm; however, in hyperkalemia
the atrial muscle may be paralyzed while the heart is still in sinus rhythm.
- For every 1-mmol/L decrease in plasma potassium concentration, the total body potassium store decreases by approximately 200 to 300 mmol.
- Characteristic electrocardiographic changes include gradual prolongation of the QRS interval, with subsequent development of prominent U waves.
HYPOKALEMIA
Hypokalemia is associated with
- increased incidence of atrial
- ventricular arrhythmias
- low serum potassium in acute MI
- weakness and potentiate the effect of neuromuscular blocking agents.
Tx of Hypokalemia
- consider the patient’s total body potassium levels and the chronicity of
the hypokalemia. - Intravenous potassium replacement should be gradual to avoid acute overcorrection and hyperkalemia.
- Respiratory and metabolic alkalosis should be avoided because alkalosis will worsen hypokalemia secondary to intracellular shifting.
is dependent on the relationship of total body sodium levels and total body water.
Serum sodium concentration
Therefore the treatment of abnormal serum sodium concentrations must take into account
- total body sodium stores
- total body water
- is defined as serum sodium concentration of greater than 145 mmol/L and is often associated with a deficiency in total body water.
- Manifestations include mental status changes, hyperreflexia, ataxia, and seizures.
- Free water deficit can be calculated as follows: free water deficit, in liters = (0.6 x weight, in kg) x ([serum sodium/140] - 1).
HYPERNATREMIA
Tx for Hypernatremia
- Free water is administered to correct hypernatremia
- IM or IV vasopressin for severe central diabetes insipidus
- hyprevolemic hypernatremia: diuretics to allow for elimination of both water and sodium while free water is administered.
- is a serum sodium concentration of less than 135 mmol/L.
- may present with mental status changes, lethargy, cramps, decreased deep tendon reflexes, and seizures.
- A serum sodium concentration of less than 120 mmol/L is a potentially life-threatening condition, with associated mortality rates reported to be as high as 50%.
HYPONATREMIA
Mngt: Hyponatremia
- If the correction of hyponatremia occurs too rapidly, a demyelinating brainstem lesion—central pontine myelinolysis—may cause permanent neurologic damage.
- severely symptomatic patients: correct sodium at a rate of 1 to 2 mmol-L-1-h-1 until the serum sodium concentration reaches 125 to 130
mmol/L. - hypervolemic or euvolemic hyponatremia, hypertonic (2%—-3%) saline may be used to treat symptomatic patients or patients who would not tolerate additional intravascular volume.
The total serum calcium concentration comprises three fractions:
- 50% protein-bound calcium,
- 5% to 10% anionbound calcium,
- 40% to 45% free, or ionized, calcium
Maintenance of a normal serum calcium concentration
involves ______, which regulate the release and uptake of calcium and
phosphorus by the kidneys, bones, and intestines through negative-feedback regulation.
parathyroid hormone and calcitonin
Common causes of hypercalcemia include
- hyperparathyroidism
- malignancies that increase mobilization of calcium from bone.
Symptoms of HYPERCALCEMIA
- nausea,
- polyuria, and
- dehydration
- Electrocardiographic monitoring may demonstrate prolonged PR intervals, wide QRS complexes, and shortened QT intervals as hypercalcemia worsens.
Avoidance of respiratory alkalosis may be beneficial because alkalosis lowers the plasma potassium concentration, potentially exacerbating _____
cardiac conduction abnormalities
Management of hypercalcemia includes
- hydration and
- diuresis to promote renal elimination.
- In acute toxicity or renal failure, hemodialysis should be considered.
Multiple factors contribute to the development of hypocalcemia:
- Acquired hypoparathyroidism after neck surgery is a common cause because of decreased parathyroid hormone levels.
- Respiratory or metabolic alkalosis induces hypocalcemia by increasing protein binding to calcium, thereby decreasing the amount of ionized calcium.
Factors that contribute to hypocalcemia
____ decreases the conversion of vitamin D to 1,25-dihydroxyvitamin D, thereby decreasing intestinal and bone absorption while increasing serum phosphate levels; the phosphate then combines with calcium and precipitates as CaPO4
Renal failure
Factors that contribute to hypocalcemia
Massive blood transfusion may also result in hypocalcemia secondary to _____ (ethylenediaminetetra-acetic acid in transfused blood, which chelates calcium).
anticoagulants
Factors that contribute to hypocalcemia
Hypocalcemia is often ____, although severe hypocalcemia may be associated with a prolonged QT interval, bradycardia, peripheral vasodilation, and decreased cardiac contractility, any of which can cause
hypotension.
asymptomatic
Neurologic manifestations of hypocalcemia include
- perioral numbness,
- muscle cramps,
- tetany,
- hyperreexia,
- seizures.
Several factors guide calcium replacement therapy, including
- the absolute serum calcium level,
- the rapidity of the drop in serum calcium concentration,
- the underlying disease process.
Calcium causes ____, and _____ may be associated with morbidity.
- vasoconstriction
- extravascular infiltration
In patients who have no symptoms, ____ may be the most appropriate treatment.
observation
____ contains three times the amount of calcium compared with calcium gluconate.
Calcium chloride
