Fluids and Electrolytes Flashcards
When the dry body weight of a patient is greater than _____% of their IBW, use the nutrition body weight for calculating _____, _________, and _______ parameters.
130%, NBW used for calculating fluid, electrolyte, and nutrition (FEN) parameters
What is the difference between sensible and insensible fluid losses?
Sensible fluid losses are measurable, while insensible losses are not.
What are some examples of sensible and insensible fluid losses?
sensible-urine (400-1500 mL/day), feces (100-200 mL/day), wounds (varies)
insensible-loss from skin and lungs (both 350-400 mL/day)
Name some additional ways we lose fluid that may or may not be measurable.
NG suctioning, vomiting, large wounds, bleeding, fistulas, drains, diarrhea, burns
Osmosis is the movement of _______ and affects the concentration of _______ in the blood.
water, electrolytes
Capillary filtration involves regulation of ______ ______ by the movement of both ______ and ______ through the capillary wall.
blood volume, solutes and fluids
What is the driving force behind capillary filtration?
hydrostatic pressure
Oncotic pressure is driven by what kind of molecule?
protein (albumin, hgb)
Name and describe the effects of the 3 principal hormones involved in volume regulation.
ADH (vasopressin)-reduces diuresis by allowing the insertion of aquaporin channels in the collecting duct, draining water from the urine and concentrating it
RAAS- aldosterone stimulates increased sodium, chloride, and water retention
ANP- released by atria in response to stretching, decreases the effects of ADH and counteracts RAAS system
What range of osmolarity is considered isotonic to human cells?
275-290 mOsm/L
What is the sodium concentration of normal saline? What is its osmolarity in mOsm/L?
154 mEq/L, 308 mOsm/L
What is the modified Holliday Seger equation/what is it used for?
1500 mL + 20 mL for each kg above 20 kg
used for calculating the amount of daily MIVF needed for a particular patient
Using a clinical estimate, how many mL of fluid are given per kg of body weight in an adult patient?
30-40 mL/kg
Describe crystalloid fluids (tonicity and examples).
Crystalloid fluids may be hyper, hypo, or isotonic. Examples include NS, LR, 1/2NS, D5W, and balanced salt solutions.
Describe colloid fluids (tonicity and examples).
Colloid fluids are only ever hypertonic. They are used to draw fluid back into the vasculature, and are known as “plasma expanders”. Examples include albumin, hetastarch, blood, tetra starch, and plasmanate.
What are crystalloid solutions primarily used for?
fluid/salt replacement, maintain the osmotic gradient between vasculature and tissues
Which crystalloid solution is used for free water replacement in dehydration? What other characteristics are unique to this solution?
D5W
NOT to be used as a MIVF by itself and NOT for resuscitation
Which of the crystalloids most closely resembles human plasma and can be used in cases of blood loss?
LR, used for resuscitation
Which of the crystalloids can be used as a maintenance fluid?
1/2NS
What is normal saline’s place in fluid/electrolyte therapy?
used for fluid replacement (resuscitation, hypotension, septic shock)
A balanced salt solution is a crystalloid that contains physiologic levels of _______ and _______.
chloride and buffer
What are some examples of balanced salt solutions?
LR, plasmalyte, normosol
What is the general role of colloid solutions in fluid/electrolyte therapy?
“plasma expander”–pulls fluid from interstitial compartment into the vasculature, useful for volume expansion
Colloids are used as first-line therapy for __________ shock, but second-line for __________ shock.
hemorrhagic (blood is a colloid), hypovolemic
What are three potential adverse effects associated with albumin infusion?
(1) hypervolemia
(2) azotemia
(3) infusion related anaphylaxis
What are the most common indications for albumin infusion?
(1) volume expansion
(2) shock
(3) burn
(4) ARDS
(5) cardiopulmonary bypass
(6) intraoperative fluid repletion
Increased mortality, hyperchloremic metabolic acidosis, required blood transfusions, renal injury, hyperkalemia, and postoperative infection are all complications associated with administration of _______ instead of a balanced salt solution.
NS
Contrast the two concentrations of albumin solution (how they are supplied, concentration, indications)
5%-supplied in 250 or 500 mL vials at 50 mg/mL, good for hypovolemic or intravascularly depleted patients
25%-supplied in 50 or 100 mL vials at 250 mg/mL, good for patients who need protein but cannot handle lots of fluid
If a solution has a high substitution ratio (>0.5), what is its effect on intravascular expansion?
it is prolonged compared to other solutions with a lower SR
What are some indications for use of packed RBCs?
(1) hemoglobin deficiency
(2) inadequate resuscitation from fluids alone
(3) acute blood loss
(4) preoperative fluid
What are important monitoring parameters for a patient’s fluid status?
(1) daily weight
(2) daily ins and outs
(3) vital signs (HR, BP)
(4) volume status
(5) urine output in mL/kg/hr (desired greater than 0.5)
What examinations can be used to assess wether or not a patients is dehydrated?
(1) skin turgor (“tenting” if decreased)
(2) delayed capillary refill (how long it takes for fingertips to return to normal color after squeezing)
(3) dryness of mucus membranes
(4) hypotension despite reflex tachycardia
(5) weak peripheral pulse
(6) BUN/SCr ratio >20
What are the goals for CVP, MAP, and UOP in a patient recovering from shock?
(1) CVP=central venous pressure=8-12 mmHg
(2) MAP > 65 mmHg
(3) UOP > 0.5 mL/kg/hr
What is the equation for blood osmolarity calculation?
2xNa + (BUN/2.8) + (glucose/18)
What is an osmol gap and what does it signify?
An osmol gap occurs when a patients calculated osmolarity differs from the lab value obtained. It signifies the presence of unidentified particles that are contributing to the increased osmolarity.
If you suspect a patient is hyponatremic, what are the first and second questions you should ask to determine the proper treatment?
(1) What is the patient’s osm? This will tell you about the tonicity of the patient’s blood.
(2) If hypotonic, what is the patient’s volume status? This will complete the diagnosis of hyponatremia and allow you to start looking for causes.
What type of hyponatremia is a patient as risk of with elevated lipids or proteins?
pseudohyponatremia (isotonic)
The patient’s calculated osm will be low and sodium will appear to be low, but this is due to the diluting effect of elevated lipids or protein. The patient will have an osmol gap.
What sodium imbalance is most often caused by elevated glucose?
hypertonic hyponatremia
How do you calculate a corrected sodium level in the event of hypertonic hyponatremia?
Serum sodium falls by 1.6 mEq/L for every 100 mg/dL increase in glucose above 100mg/dL. So, corrected sodium is calculated as follows:
(measured Na) + (BG-100/100)*1.6
How is hypertonic hyponatremia treated?
Usually with insulin, since elevated BG is most often the cause. Corrections of BG will correct sodium as well.
If it is established that a patient has hypotonic hyponatremia, what is the next step in diagnosis and treatment?
assessment of volume status
What are the most common renal causes of hypovolemic hypotonic hyponatremia?
(1) excessive diuresis
(2) mineralocorticoid insufficiency
(3) cerebral salt wasting
(4) salt-losing nephropathy
characteristics of hypovolemic hypotonic hyponatremia
low osm, low sodium, decrease TBW
patient has lost both sodium and water
List non-renal causes of hypovolemic hypotonic hyponatremia.
(1) blood loss/hemorrhage
(2) skin losses (burn, sweat)
(3) GI loss (vomiting, diarrhea, NG suction)
SIADH is the most common cause of what sodium imbalance?
isovolemic hypotonic hyponatremia
Describe how SIADH causes isovolemic hypotonic hyponatremia.
ADH causes water retention in the collecting duct, concentrating the urine and diluting the blood. Enough water is retained to dilute sodium, but not to increase volume significantly. In addition, aldosterone release is inhibited by the increased retention of water. This means that some filtered electrolytes and water still escape. This is why these patients are euvolemic but still low on sodium.
What are some common causes of SIADH?
tumors, CNS disorders (head trauma, stroke, meningitis), DRUGS
How is SIADH treated?
(1) removal of underlying cause if possible
(2) free H2O restriction (fluid replacement will only make hyponatremia worse
(3) vaptans if free H2O restriction fails after 24-48 hours
Describe Conivaptan use (indications, mechanism of action, dosing, contraindication).
Conivaptan (IV): 20 mg bolus infused over 30 minutes followed by 20-40 mg over 24 hours for 2-4 days
This is not first line therapy due to their high cost. They work by promoting free water excretion by the inhibiting arg-vasopressin receptor. This results in free water excretion without electrolyte loss.
Contraindication: hypovolemic hyponatremia
Describe Tolvaptan use (indications, mechanism of action, dosing, contraindication)
Tolvaptan (PO): 15 mg PO daily titrating up to a max of 60 mg daily for no longer than one month
Mechanism of action, contraindication are the same as conivaptan. However, conivaptan is reserved for cases of severe euvolemic hyponatremia, while the oral dosage form tolvaptan is used in asymptomatic, euvolemic, hyponatremic patients.
How often should symptomatic hyponatremic patients be monitored for serum sodium concentrations?
every 2-4 hours until asymptomatic, then every 4-8 hours
If a patient is deemed hypernatremic, what is the next question you must ask to determine proper treatment?
What is the patients volume status?
An osm calculation is not necessary because hypernatremia is always associated with hypertonicity.
How is a hyponatremic patient’s sodium deficit calculated?
Na deficit = TBW (Na goal - Na serum)
The term “Na goal” is used here because you should never replace more than 12 mEq/L of sodium per 24 hours in any patient. You run too high a risk of overcorrecting. Set your goal at a maximum of 12 mEq/L replacement over the next 24 hours.
How is a patient’s sodium deficit replaced?
Once the deficit is calculated, use the rule of 8’s. Replace 1/2 of the calculated deficit over the first 8 hours, then 1/4 of the deficit over the next two 8 hour periods.
What are the potential causes of hypervolemic hypernatremia?
(1) excess NaHCO3 administration
(2) resuscitation with hypertonic saline
(3) excess dietary salt
How is hypervolemic hypernatremia treated?
Once the underlying cause is determined, you simply remove it. The excess sodium will be rapidly excreted. If necessary, a loop diuretic may be administered to speed up the process.
A free water deficit must be calculated in order to treat which sodium imbalance? How is it calculated?
hypovolemic hypernatremia
FWD = normal TBW * [(Na serum/140)-1]
What is the schedule for replacement of a free water deficit?
FWD is replaced slower than a sodium deficit. 1/2 is replaced over the first 24 hours, and the remaining 1/2 is given over the next 24-48 hours.
How often should serum sodium be taken in monitoring a patient recovering from hypernatremia? What are other important monitoring parameters?
q3-6h while symptomatic, then about once a shift once sodium falls below 145 mEq/L
I/O, CVP, UOP, weight should also be documented with each shift to monitor overall fluid status.
What is the most common cause of isovolemic hypernatremia?
diabetes insipidus (central or nephrogenic)
In both types of DI, patient’s produce a large amount of dilute urine because the kidneys cannot properly regulate the amount of fluid leaving the body (ADH release/use is hindered).
What are the main factors that play a role in serum potassium levels?
(1) Na/K ATPase
(2) catecholamines
(3) insulin
(4) kidneys (aldosterone)
(5) glucagon
(6) arterial pH (acid base status)
What are the common causes of hypokalemia?
(1) potassium wasting diuretics
(2) beta-agonist meds (albuterol)
(3) metabolic alkalosis (bicarb pushes potassium back into cells)
(4) magnesium depletion (Mg is a cofactor for Na/K pump, if you can’t pump K back into cells then more of it will be wasted in kidneys)
What is the most serious complication of altered serum potassium levels?
Arrhythmias
For every _____ mEq of potassium given, you can expect a _____ mEq/L rise in serum potassium levels.
10 mEq = 0.1 mEq/L increase
Below which level is hypokalemia always treated?
3 mEq/L. Above this level, treatment may be considered, but is debatable and done carefully to avoid overcorrection.
When is PO potassium replacement preferred over IV? IV over PO?
PO is preferred in asymptomatic patients, while IV replacement is preferred in symptomatic patients.
If there is a concomitant abnormality in ________ with potassium, it must be corrected before potassium is.
magnesium
The rate of potassium infusion depends on the severity of the symptoms and the presence (or not) of cardiac monitoring. What are the standard rates of administration in each of the following cases?
without cardiac monitoring: ______ mEq/hr
with continuous cardiac monitoring: ____ mEq/hr
emergent severe hypokalemia: _____ mEq/hr
10, 20, 40-60
Describe the clinical presentation of hyperkalemia.
Patients will show EKG changes, namely a peaked T-wave. In the most severe cases (>9mEq/L), patients may develop Vfib or asystole.
How is hyperkalemia treated?
(1) calcium chloride (raises cardiac AP threshold to stabilize myocardium)
(2) insulin/dextrose (insulin receptor uses potassium)
(3) NaHCO3 (bicarb pushes potassium back into cells)
What is the normal range of serum magnesium?
1.5-2.5 mEq/L
Hypomagnesemia is commonly associated with disorders of which two body parts?
GI tract (decreased absorption, diarrhea) and the kidneys
Which two electrolyte levels are closely associated with magnesium levels?
calcium and potassium
How is hypomagnesemia treated?
Asymptomatic patients can be treated with PO dosages forms (e.g. milk of mag), but symptomatic patients should be treated with IV supplementation.
How is hypermagnesemia treated?
(1) calcium chloride (stabilize myocardium)
The next step is determined by renal function. If okay, just hydrate with NS and allow kidneys to excrete excess. If not, forced diuresis or HD may be necessary.
What is the normal serum calcium range?
8.5-10.5 mg/dL
What are the common etiologies of hypocalcemia?
(1) excess PRBC administration (citrate buffer binds calcium)
(2) hypoalbuminemia
(3) hypomagnesemia
(4) vitamin D deficiency
(5) DRUGS
How is corrected calcium calculated?
Ca serum + [(4-albumin)*0.8]
Thus, for each 1 g/dL decrease in albumin, calcium levels fall by about 0.8 g/dL.
Of the two forms of calcium available for IV administration, which is preferred in code situations and which is preferred for peripheral administration?
Calcium chloride used for codes, but calcium gluconate is preferred in peripheral administration.
If calcium is low, what other electrolyte may be the causative factor?
magnesium. If so, correct this first.
What are the two main etiologies of hypercalcemia?
cancer and hyperparathyroidism
What are the three main mechanisms by which serum calcium levels may increase?
(1) decreased elimination in the kidneys
(2) increased bone resorption
(3) increased GI absorption
What are some possible treatment methods for hypercalcemia?
(1) volume expansion/loop diuretics
(2) calcitonin (“tones” the bones, increases deposition to help reduce blood calcium)
(3) bisphosphonates (good inhibitors of bone resorption)
(4) glucocorticoids (decrease GI absorption)
What is the normal serum level of phosphorus?
2.5-4.5 mg/dL
What are the three most common causes of hypophosphatemia?
(1) decreased intake
(2) intracellular shifts
(3) impaired absorption
Under what conditions would it be appropriate to administer KPhos/NaPhos?
Use KPhos if the patient has a serum potassium concentration of <4mEq/L. If potassium is above 4, use NaPhos.
Describe the clinical presentation of hyperphosphatemia.
You may observe soft tissue calcifications as the excess phosphate precipitates in tissues with calcium. It follows that calcium levels may decrease as it is “stolen” by the excess phosphate.
How is hyperphosphatemia treated?
(1) decrease the GI absorption
(2) if severe/symptomatic, replace calcium
Hypomagnesemia is often associated with which two other electrolyte abnormalities?
hypocalcemia and hypokalemia
