Ch 7: Fluids, Electrolytes, and Acid Base Disorders Flashcards
What is the dominant extracellular osmole holding water in the extracellular space?
Sodium
What is the formula for adjusted body weight in obesity?
Obesity adjusted weight = [(actual BW- IBW) x0.25} + IBW
What are normal potassium requirements?
Normal potassium requirements range from 0.5-2.0 mEq/kg
What does an anion cap calculate, and what is the normal range?
Metabolic acidosis; Normal anion gap is 9 mEq/L (range 3-11 mEq/L)
What is the most common reason for hypercalcemia? (total serum > 10.2 or ionized> 1.3)
Hyperparathyroidism or cancer with bone metastasis
Low serum calcium stimulates release of _____ which ____ bone resorption, augments renal ____ of calcium, and ______ vitamin D which in turn_____ intestinal calcium absorption.
PTH; increases, conservation; activates; increases
Of all the body tissues, which is least hydrated?
Adipose; individuals with more body fat have proportionally less total body water
How can chronic or asymptomatic hypocalcemia can be treated?
Oral Calcium and Vitamin D supplements
What is the main intracellular anion and also helps maintain normal pH and bone and cell membrane composition?
Phosphorus
What is the primary intracellular osmole holding water within the cells?
Potassium
_____ is released by thyroid gland in response to elevated serum calcium concentrations (inhibits bone resorption and increases urinary Ca excretion)
Calcitonin (inhibits bone resorption and increases urinary Ca excretion)
By how much do fluid needs increase in patients with a temperature?
7% for each degree F above normal
13% for each degree C above normal
How much fluid does a healthy adult require?
30-40 mL of fluid per kg of body weight/d
Weight based equations tend to over overestimate fluid requirements for large people and underestimate those for small people
What % of body weight is water?
50-60%
What is the targeted rate of sodium correction for hyponatremia?
To prevent osmotic demyelination, targeted rate of sodium correction for hyponatremia should not exceed 10-12 mEq/L/d if acute or 6-8 mEq/L/day if chronic or duration is unknown
To prevent dehydration, some experts discourage use of energy-based formulas in patients > 65 years and instead recommend which formula?
Adjusted Holliday-Segar (1,500 mL for first 20kg of body weight + 15 mL/kg for remaining body weight)
30 mL/kg with a minimum of 1500 mL
1500-2000 mL/day
Which direct measurement of Ca is the most accurate method to assess calcium abnormalities?
Ionized Calcium
What % of TBW is contained in the ICF and ECF?
What % of TBW accounts for the TCF?
2/3rds of TBW is contained in ICF
1/3 is in ECF.
The TCF accounts for about 3% of TBW
What is considered clinically relevant hyponatremia?
< 130 mEq/L
What is the normal pH of arterial blood?
pH of arterial blood is normally maintained within a narrow range of 7.35-7.45
Which electrolyte should be repleted before potassium?
Magnesium (potassium levels are rarely corrected unless the magnesium deficit is corrected first)
Which drugs are implicated in the etiology of hypocalcemia?
Bisphosphonates,calcitonin, furosemide, foscarnet, and long-term therapy with phenobarbital and phenytoin.
What is the calculation for corrected calcium?
Corrected total serum Ca= Measured total serum Ca + {0.8 x (4-serum albumin)}
What is contained the the extracellular fluid?
Intravascular and interstitial spaces.
Where is Magnesium mostly found?
Intracellular fluid
How much sodium is contained in normal (0.9%) saline?
Sodium - 154 mEq/L and Chloride 154 mEq/L.
Which acid base disorder is consequence of chronic diuretic therapy?
Metabolic acidosis; caused by loss of bicarbonate poor, chloride rich extracellular fluid leading to contraction of extracellular fluid volume
Which mineral is absorbed in the small intestine with only about 10% lost in urine and feces?
Potassium
What is the equation for converting mg to mEq
mg x valence/ atomic weight
How should mild hypercalcemia, defined as a total serum calcium of 10.3-11.9 mg/dL, be treated?
Mild hypercalcemia usually responds to hydration and ambulation and requires no further intervention.
Which electrolyte abnormality may sulfamethoxazole/trimethoprim cause?
Hyperkalemia
What is first line treatment for hyperkalemic emergencies?
Calcium Gluconate
Prolonged NGT suction can cause loss of which electrolyte?
Potassium
Nasogastric output results in a loss of gastrointestinal secretions primarily from the stomach. Hypokalemia is a common issue with continued nasogastric output as the normal potassium concentration of gastric fluid is 10 mEq/L. Other possible electrolyte abnormalities include hyponatremia and hypochloremia.
Bicarbonate, calcium and phosphorus are not directly lost from gastric suction.
Which acid base disorder is most likely to occur from diarrhea?
Metabolic acidosis; Diarrhea induces gastrointestinal losses of bicarbonate and can cause a metabolic acidosis (normal anion gap).
Metastatic calcification is a complication of what?
Hyperphosphatemia
This occurs when the calcium-phosphorus product exceeds 55 mg^2/dL^2.
Additional consequences of hyperphosphatemia include secondary hyperparathyroidism and renal osteodystrophy.
Patients with chronic heart failure are typically on a loop diuretic. These patients are at risk for what?
Azotemia; Loop diuretics are known to cause electrolyte abnormalities as a result of increased urine output. Specific disturbances include excess potassium and magnesium excretion which can result in hypokalemia and hypomagnesemia. Azotemia can occur related to volume depletion.
A patient with chronic heart failure on high-dose furosemide is started on enteral nutrition for an inability to consume adequate oral nutrition. Despite a slow advancement to goal feeding rate, he suffers from electrolyte imbalance and peripheral neuritis. Deficiency of which vitamin should be suspected in the cause of his symptoms?
Thiamin
A patient with refractory hypokalemia should be assessed for what related electrolyte disorder?
Hypomagnesemia
Symptoms of manganese toxicity are associated most commonly with accumulation of the mineral in which organ?
Brain
Metabolic acidosis, tissue catabolism, and pseudohyperkalemia results in an extracellular shift of which electrolye?
potassium
What is the difference between hypervolemia vs dehydration?
Dehydration is the loss of water only; whereas hypovolemia is excessive fluid loss (often due to hemorrhage, vomiting, diarrhea, and/or diuresis)
What is the principal cation in the ECFF?
Sodium; it is the major osmotic determinant in regulating ECF volume and water distribution in the body
What is the appropriate treatment for SIADH?
Fluid restriction of 500-1000 mL/day
True or false: Dextrose solutions should be avoided in a hypokalemic patient?
True; dextrose solutions may worsen hypokalemia by stimulating insulin release that promotes intracellular shift in potassium
What are fluid needs for the following age groups? 18-55 years old 55-75 years old >75 years old Fluid restricted
18-55 years old: 35 mL/kg
55-75 years old: 30 mL/kg
>75 years old: 25 mL/kg
Fluid restricted: < 25 mL/kg
