electrolytes Flashcards
Total body water is _____ of total body weight
60%
Intracellular volume is _____ total body weight
40% or 2/3
Extracellular volume is _____ total body weight
20% or 1/3
Extracellular is split up into what 2 fluid volumes?
Interstitial 75%
Plasma volume 25%
TBW is ___% of a man’s weight
TBW is ___% of a woman’s weight
TBW is ___% of an infant’s weight
55%
45%
80%
Obese individuals have _____ TBW per weight than non-obese individuals
less
Fluid compartments are divided by
water-permeable membranes.
Intracellular space is separated from the extracellular space by the
cell membrane
The ______ _______ separates the components of the extracellular space.
Capillary membrane
all of the fluid compartments are trying to reach equilibrium, what allows this to not happen?
membranes
the intracellular fluid compartment has high concentrations of
potassium
phosphate
magnesium
in the intracellular fluid compartment, what is the primary cation
potassium
in the intracellular fluid compartment, what is the primary anion
phosphate
What maintained the high concentration of K+ in the ICP
Na, K, ATPase (3Na in:2 K out)
Extracellular fluid compartments have high concentrations of
Na and Cl
in the extracellular fluid compartment, what is the primary cation
Na
in the extracellular fluid compartment, what is the primary anion
Cl
1/4 of ECV is high concentration of
plasma proteins (albumin
Capillary membrane essentially impermeable to plasma proteins and they remain in the _______ ________
vascular space
interstitial fluid is _____ of ECV
3/4
What is a normal serum osmolality
285-295
How do you calculate a serum osmolality
(2(NA)) + (BUN/2.8) + (Glucose/18) = serum osmolality
Why is the intravascular fluid space the chief focus of fluid therapy?
Because it is an accessible fluid compartment
Starling forces: hydrostatic pressure in the capillaries (Pc) is the
blood pressure
Starling forces: Hydrostatic pressure in the interstitium (Pi) is
low
slightly negative d/t lymphatics
What is the main determinant of osmotic pressure?
albumin
a positive net driving force favors
filtration into tissues (interstitial fluid)
a negative net driving force favors
reabsorption into vasculature
Factors affecting fluid movement: osmolarity
An expression of the number of osmoles of a solute in a LITER of solution
Factors affecting fluid movement: osmolality
An expression of the number of osmoles of a solute in a KILOGRAM of solvent
Factors affecting fluid movement: tonicity
How a solution affects cell volume
For example – isotonic, hypertonic, hypotonic
Isotonic solutions approximately 285 mOsm/L
How does a hypertonic solution more fluid
fluid moves out of cell (shrinking cell)
How does a hypotonic solution move fluid
fluid moves into the cell (can burst)
Isotonic osmolality should be the same as
serum osmolality
What is the difference between hypovolemia and dehydration?
HYPOVOLEMIA
Loss of extracellular fluid
Absolute loss of fluid from the body
Reduced circulating volume
DEHYDRATION
Concentration disorder
Insufficient water present in relation to sodium levels
What is hypervolemia?
Excess of fluid volume in an isotonic concentration
Not usually a problem in surgical patients
What type of surgical patients would you see hypervolemia in?
CHF
Renal Failure
Overhydration with isotonic fluids
_____ and ____ are responsible for the normal osmotic activity of the ECF
Na and Cl
All gain/loss of Na+ is accompanied by gain/loss of
water
Na:
intracellular
Extracellular
intracellular 25
Extracellular 140
maintained by Na, K, ATPase pump
Lack of permeability to sodium changes the osmotic gradients between fluid compartments, leading to precedence of sodium over plasma proteins as the most important osmotically active substance influencing the _____ _______ of the brain
water content
What is the most common electrolyte abnormality in hospitalized patients
hyponatremia
can be caused by a loss of Na or to much water
What are some S/S of hyponatremia?
headache, malaise, agitation, coma, cerebral edema (MOST signifiant), confusion
Anorexia, N/V
cramps, weakness
What are some causes of hyponatremia?
Vomiting Diarrhea Diuretics Adrenal insufficiency Syndrome of inappropriate secretion of antidiuretic hormone Renal failure Water intoxication CHF Liver failure Nephrotic syndrome
Treatment of hyponatremia
fluid restriction
admin of hypertonic saline AND osmotic or loop diuretic
3% saline if symptomatic
How quickly should Na be replaced?
no more than 1-2 meq/hr (no more than 10 in 24 hours)
What happens if you correct Na levels too rapidly
Correction of serum sodium levels too rapidly can result in neurologic damage and myelinolysis!!!
Most common cause of hypernatramia is
excessive loss of water or inadequate water intake
What else can cause hypernatremia
Exogenous Na+ load
Primary hyperaldosteronism
Diabetes insipidus
Renal dysfunction
S/S of hypernatremia
thirst, weakness, seizure, hallucinations, irritability, disorientation, coma, intracranial bleeding
hypervolemia
polyuria or oliguria, renal insufficiency
treatment for hypernatremia
Correction of hypernatremia is accomplished by replacing the water deficit
Plasma sodium should be decreased by 1-2mEq/hr until the patient is clinically stable.
Which electrolyte is largely responsible for resting membrane potential
potassium
how is potassium balanced
GI absorption and renal excretion
Causes of hypokalemia
Gastrointestinal losses Systemic alkalosis (Diabetic ketoacidosis) wrong Diuretic therapy Sympathetic nervous system stimulation Poor dietary intake
the most common electrolyte abnormality encountered during clinical practice
hypokalemia
CV manifestations of hypokalemia
ST-segment depression
Presence of U wave
Flattened or inverted T waves
Ventricular ectopy
neuromuscular manifestations with hypokalemia
Weakness ( respiratory muscle)
Decreased reflexes
Confusion
what will you see with a K < 2.5
paresthesia, depressed deep tendon reflexes, fasciculations, muscle weakness
Below what K level do you question whether the surgery needs to be done now
<3
At what K level do you start to see U waves on the EKG
2
Treatment for hypokalemia
IV potassium supplements (up to 40mEqs can be given per hour)
What do you NOT want to do when a patient has hypokalemia
Avoid hyperventilation of the lungs (makes you more alkalotic and drives K into cells)
Avoid glucose containing IV solutions (If you give glucose, body produces more insulin – drive K into cells )
Avoid rapid infusion of IV K+ supplements
Causes of hyperkalemia
Renal failure
Potassium-sparing diuretics
Excessive IV K+ supplements
Excessive use of salt substitutes (Mrs Dash)
Metabolic or respiratory acidosis Digitalis intoxication Insulin deficiency Hemolysis Tissue and muscle damage after burns Administration on succinylcholine
CV manifestations of hyperkalemia
Tall, peaked and elevated T waves Widened QRS complex Prolonged PR interval Flattened or absent P wave ST segment depression Cardiac arrest tachycardia Vfib
Treatment for hyperkalemia
Insulin and glucose to shift K+ into cells
IV calcium to antagonize cardiac effects of hyperkalemia
albuterol, hyperventilate
What is the upper limit of K for elective procedures
5.5
Where is Magnesium stores
___ - ____% in muscle & bones
____% in cells
____% in serum
40-60%
30%
1%
Where does regulation of magnesium occur
intestines and kidneys
T/F: Mag is a cofactor in enzymatic reactions (Energy metabolism, protein synthesis, neuromuscular excitability, function of NA-K-ATPase)
True
Causes of hypomag
Inadequate dietary intake of magnesium TPN without magnesium supplementation Starvation Gastrointestinal losses Diarrhea Fistulas Nasogastric suctioning Vomiting Chronic alcoholism
ECG changes with hypomag
Flat T-waves U-waves Prolonged QT interval Widened QRS Atrial and Ventricular PVCs
Low Mag has inhibitory effect on NA-K-ATPase which
alters the resting membrane potential
How do you replace IV mag?
1-2 g over 5 min with EKG monitoring
followed by a continuous IV infusion of 1-2g/hr
causes of hypermag
Iatrogenic administration Preeclampsia Antacids/laxatives Renal failure Adrenal insufficiency
what S/S at each mag level
4-7
10
10-15
4-7 = drowsiness, decreased deep tendon reflexes, weakness
10 = respiratory depression
10-15 = respiratory paralysis, coma
15-20 = cardiac arrest
What do you use as an antagonist in urgent hypermag situations (bradycardia, heart block, Resp depression)
Calcium
Mag will potentiate _______, but not enough to clinically effect us
NDNMBs
Where is the majority of calcium found
99% in bones
1% in plasma and body cells
What is the second messenger that couples cell membrane receptors to cellular responses
Calcium
Muscle contraction, hormones, neurotransmitters, coagulation, myocardial contractility
PTH move ca -
CalcitonIN moves Ca
out of bones
INto the bones
Causes of hypocalcemia
Hypoparathyroidism
Malignancy
Chronic renal insufficiency
How does hyperventilation effect calcium
Hyperventilation leads to alkalosis which facilitates protein-binding of Ca
Why do you give Ca when doing large blood transfusions
Citrate in banked blood binds Ca
Neuro S/S of hypocalcemia
Cramps Weakness Chvostek sign Trousseau sign Seizure Numbness tingling
CV S/S of hypocalcemia
Dysrhythmias Prolonged QT interval T-wave inversion Hypotension Decreased myocardial contractility
Pulmonary S/S of hypocalcemia
Laryngospasm
Bronchospasm
Hypoventilation
How to correct low Ca levels
Infusion of Ca Chloride (best option, more rapid correction)
Ca gluconate (slower) 3g Ca gluconate = 1 g Ca Chloride
Causes of hypercalcemia
Hyperparathyroidism (>50% cause)
Tumors/malignancy
Calcium mobilization from bone due to immobility
CV S/S of hypercalcemia
Hypertension
Heart block
Shortened QT interval
Dysrhythmias
Neuromuscular S/S of hypercalcemia
Muscle weakness
Decreased deep tendon reflexes
Sedation
Treatment of hypercalcemia
treat underlying cause
give adequate fluids/loop diuetics
If hypercalcemia with life threatening dysrhythmias = emergent dialysis
