Electrolytes Flashcards
What are some of the s/s of severe hypophosphatemia?
effects are primarily related to impairment of cellular engery metabolism
-acute resp failure or failure to wean from vent
-impaired delivery to peripheral tissue
-left shift of oxyhemoglobin cure d/t 2,3-DPG depletion
-extreme muscle weakness
-hemolytic anemia
-impaired leukocyte and plt function
In a pt w/ re-feeding syndrome or who is a concern for re-feeding syndrome, what type of fluids should not be given?
IV dextrose containing fluids
-also high carbohydrate TF or TPN
-these lead to increased insulin levels which worsening hypophosphatemia d/t intracellular shifts of phosphate
What is TURP syndrome?
excessive absorption of irrigant fluid leanding to hypervolemia, hyponatremia, and low serum osmolality
At what level of hypermagnesemia are deep tendon reflexes lost?
10-14mEq/L
-at 5-10mEq/L will see prolonged PR interval and widened QRS
-at 15mEq/L SA/AV node blockade
-at 20mEq/L cardiac arrest
What is the total body water in males?
60% body weight
What is the total body water in females?
50-55% body weight
What is the total body water in a fetus?
90% body weight
What is the total body water in kids?
60-65% body weight
What is the total body water in the obese?
Up to 10-20% lower compared to similar age and gender
What are the main intracellular cations? Anions?
-potassium and magnesium
-phosphate, sulfate, proteins
What are the main exracellular cations? Anions?
-sodium
-chloride, bicarbonate, sulfate, proteins
What determines plasma osmolality?
ratio of plasma salutes and water
What is the normal range for plasma osmolality?
275-290 mOsm/kg
-mostly driven by Na+ w/ small contributions from glucose and BUN
How do you calculate osmolality?
Posm = 2x[Na] + (BUN/2.8) + (gluc/18)
What electrolyte derangement are seen in rhabdomyolysis?
due to myocyte breakdown
-hyperkalemia
-hyperphosphatemia
-hypocalcemia
also see:
-hypoalbumenia
-hyperuricemia
What electrolyte derangements are known to worsen digoxin toxicity?
-hypokalemia
-hypophosphatemia
What is the average volume made and amount of Na Cl K and HCO3 of the stomach?
1-2L
Na 59
K 9.3
Cl 89
HCO¬3 0-1
What is the average volume made and amount of Na Cl K and HCO3 of the duodenum?
100-2000mL
Na 105
K 5.6
Cl 99
HCO3 10
What is the average volume made and amount of Na Cl K and HCO3 of the ileum?
1-3L
Na 112
K 5
Cl 106
HCO3 15-20
What is the average volume made and amount of Na Cl K and HCO3 of the colon (diarrhea)?
500-1700mL
120
90
25
45
What is the average volume made and amount of Na Cl K and HCO3 of the bile?
500-1000mL
Na 145
K 5.2
Cl 100
HCO3 50
What is the average volume made and amount of Na Cl K and HCO3 of the pancreas?
500-1200mL
Na 142
K 4.6
Cl 77
HCO3 70
With normal renal function and perfusion what is the principal regulator of serum osmolarity?
ADH
When both low plasma osmolarity and low blood volume/pressure are present which effect dominates control of ADH?
Low blood volume or pressure will cause an increase of ADH
-this is one of the ways hypovolemic hyponatremia occurs
Why are the elderly more prone to alterations in sodium homeostasis?
Aging leads to reduced GFR which limits the ability to excrete a sodium load
-makes them more prone to overexpansion of the extracellular fluid compartment
-they also have impaired thirst mechanism and decreased ability to concentrate urine
What are causes of euvolemic hyponatremia?
-hyperlipidemia
-hyperproteinemia
What are causes of dilutional (increased plasma osmolality) hyponatremia?
-hyperglycemia
-mannitol
What are causes of hypovolemic hyponatremia?
-diuretics
-plasma, GI, or skin fluid losses
-CHF
-hypoproteinemic states (cirrhosis, nephritis syndrome, malnutrition)
-SIADH
-endocrine disorders (hypothyroidism, hypoadrenalism)
-meds (morphine, TCAs, indomethacin)
How much does Na drop for every 100mg/dL rise in glucose?
1.3mEq/L
What is the most common cause of hypovolemic hyponatremia?
Na losses
What urine studies are diagnostic for SIADH?
Uosm > 100 (maximally dilute urine)
UNa > 30 (renal salt wasting)
Serum osm < 280
Euvolemia
(remember this is unregulated free water retention w/o adequate Na reabsorption)
At what Na plasma level do patients typically become symptomatic in hypernatremia?
Na > 160
What some causes of hypovolemic hypernatremia?
-fever
-hyperventilation
-burns
-hypotonic fluid loss (perspiration, severe diarrhea)
-excessive renal free water loss (hyperglycemia, mannitol)
What fluids should you give to treat hypovolemic hypernatremia?
-if hypovolemia is severe enough to cause tissue malperfusion = NS
-if tissue perfusion is adequate = 0.5 NS or D5W
The recovery phase of which renal disorder can be characterized by high-output renal failure leading to severe hypernatremia?
acute tubular necrosis
What treatment is both diagnostic and therapeutic for central DI induced hypernatremia?
dDAVP (1-desamino-8d-arginine vasopressin)
What is the rate at which hypernatremia should be corrected?
no faster 0.5 - 1mEq/L per hour
-if pt is experiencing seizure activity give free water to reduce to level before sz began, or reduce by ~6mmol/L
How do you calculate free water deficit?
water deficit = total body water x {1-(serum Na/140)}
What is the amount of potassium typically found in the human body?
-intracellular = 40 - 50mmol/kg body weight
-only 2% of total body potassium is found extracellular
What are the typical extrarenal causes of hypokalemia in a surgical patient?
-GI losses (emesis, NGT)
-diarrhea
-burns
-profuse perspiration
What are the typical renal causes of hypokalemia in a surgical patient?
-diuretic therapy
-tubular disorders (type 1 renal tubular acidosis)
-meds (cisplatin, amphotericin B)
What can cause hypokalemia due to an intracellular influx of K+?
-metabolic alkalosis
-insulin
-beta2-adrenergic stimulation
What are some disorders that can cause hypokalemia?
-primary hyperaldosteronism
-renal artery stenosis
-Cushing syndrome
How does vomiting lead to hypokalemia when gastric secretions only ave about 10mEq/L of K?
-ECV contraction leads to elevated levels of aldosterone
-elevated aldosterone causes enhanced renal Na reabsorption and increased K secretion
What is the most serious consequence of hypokalemia?
cardiac arrhythmias
What are some factors that can exacerbate the potential for arrhythmias in hypokalemia?
-metabolic alkalosis
-digoxin
-hypercalcemia
What EKG changes are seen in hypokalemia?
-flattened T waves
-T wave inversion
-depressed ST segments
-U waves
-prolonged QTc
At what level does weakness typically manifest in hypokalemia?
K < 2.5
What is the total K deficiency when the plasma value drops from 4 to 3?
100 - 400mmol^3
What can cause hyperkalemia due to an extracellular flux of K+?
-severe metabolic acidosis
-insulin deficiency (DM)
-rhabdomyolysis
-succinylcholine (transient) - most commonly seen following paralysis or prolonged bed rest
What EKG changes are seen in hyperkalemia?
-peaked T-waves
-reduced P-wave amplitude
-QRS widening
-sinusoidal complex
-Vfib
What are the approximate total body stores of calcium?
1000gm w/ almost 99% in the bones
Why does hyperventilation cause hypocalcemia?
-acid-base alterations effect the binding of calcium to albumin
-respiratory alkalosis increases the binding affinity of calcium for albumin
-causes reduction in the serum ionized calcium
Which patient populations are prone to alternations in calcium homeostasis?
-major fluid shifts
-prolonged immobilization
-alterations in GI absorption
-post-op from thyroid or parathyroid cases
What is the most frequent cause of hypocalcemia?
low serum albumin
What are causes of hypocalcemia not due to hypoalbuminemia?
-acute pancreatitis
-massive soft tissue infection
-small bowel fistulae
-hypoparathyroidism
-MTP d/t chelation of calcium w/ citrate
Approximately how much citrate does each unit of blood contain? How fast can the liver metabolize citrate?
-3gm per unit of blood
-metabolizes 3gm every 5 minutes
What are the s/s of hypocalcemia?
-circumoral numbness or tingling
-numbness or tingling at the finger tips
-tetany
-carpopedal spasm
-seizures
-EKG changes = bradycardia, prolonged QTc
What is the most common cause of hypercalcemia?
hyperparathyroidism
-primary HPT and malignant causes account for 90% of hypercalcemia
What are the s/s of hypercalcemia?
-confusion, lethargy, come
-muscle weakness
-anorexia, nausea, vomiting
-constipation
-pancreatitis
-renal stones (in prolonged cases)
-polyuria (d/t induced nephrogenic DI)
-EKG changes (shortened QT)
What medication can exacerbate arrhythmias due to hypercalcemia?
digitalis
When is treatment for hypercalcemia considered urgent?
Ca > 15 or EKG changes
What is the treatment protocol for hypercalcemia?
-large volume hydration w/ NS
-once hydrated –> furosemide
-if severe may need diphosphonates, calcitonin, or mithramycin
What is the MOA for diphosphonates and calcitonin in treating severe hypercalcemia?
-diphosphonates = inhibits osteoclast resorption and reduces Ca levels by forming Ca-phosphate complexes
-calcitonin = inhibits osteoclast resorption
What is the principal intracellular divalent cation?
Mg2+
Where is 50% of the body’s Mg found?
in bone
Where does Mg absorption occur?
small intestine
-reabsorbed by the renal tubules
What are the s/s of hypomagnesemia?
similar to hypocalcemia w/ neuromuscular and CNS excitability
-tremor
-tetany
-fasciculations
-Chvostek and Trousseau signs
-impaired parathyroid hormone excretion
-can induce hypocalcemia that is refractory to Ca supplementation
What are the s/s of hypermagnesemia?
rare to see outside of renal failure or iatrogenic
-flaccid paralysis
-hypotension
-confusion
-EKG changes similar to hyperkalemia
What is the treatment for severe hypermagnesemia?
-emergently = administration of calcium as calcium gluconate or calcium chloride
-definitive = hydration and diuresis to increase renal excretion, dialysis if there is renal impairment
What are common causes of hypophosphatemia?
-impaired intestinal absorption
-increased renal excretion
-hyperparathyroidism (d/t increased renal excretion)
-s/p major liver resection d/t rapid phosphate utilization of regenerating hepatocytes
-refeeding syndrome
What are some adverse effects of severe hypophosphatemia?
-impaired tissue oxygen delivery d/t decreased 2,3-DPG
-muscle weakness
-rhabdomyolysis
How is Na transported out of the nephron?
ENaC (epithelial sodium channels) = specialized Na-K ATPase
-these are stimulated by aldosterone
-their activation is triggered by hypovolemia, hypotension, and ANP d/t atrial overdistention
Which ion channel in the nephron does furosemide act on?
inhibits Na reabsorption via Na-K-Cl cotransporter in the loop of Henle
Which part of the nephron does furosemide act on?
loop of Henle
Which channels in the nephron specialize in water reabsorption?
aquaporins
-open in response to ADH
-results in movement of water into the medullary interstitium
Where in the nephron do you first find aquapornins?
collecting ducts
What is DI?
inadequate or absent effect of ADH leading to closed aquaporins and excessive free water excretion but not Na d/t:
-injury of pituitary (central)
-desensitization of the collecting ducts (nephrogenic), usually d/t toxic effects (ie. lithium)
What are the s/s of DI?
-very dilute polyuria
-hypernatremia
-hypovolemia
What cardiac specific symptoms are seen w/ hypocalcemia?
-bradycardia
-CHF
-cardiomyopathy
What hematologic specific symptoms are seen w/ hypophosphatemia?
-hemolytic anemia
-impaired leukocyte function
-impaired platelet function
What are some of the etiologies of hyperkalemia (surgery and trauma specific)?
-crush injuries
-reperfusion syndrome
-AKI
-severe metabolic acidosis
-succinylcholine
-hypoaldosteronism
What are some of the etiologies of hypermagnesemia (surgery and trauma specific)?
rare in the absence of renal failure
-large vol. tissue necrosis (large burns, large crush injuries)
-medication induced (laxative abuse, antacids, lithium)
What are some of the etiologies of hyperphosphatemia in critically ill patients?
-exogenous = phosphate-based laxatives/enemas or high dose fosphenytoin
-endogenous = rhabdomyolysis or tumor lysis
-extracellular shifts
How do the T-waves in hyperkalemia differ from those in hypercalcemia
both are peaked
-hyperkalemia = narrow based
-hypercalcemia = broad based
What is the goal UOP in a patient being hydrated for hypercalcemia?
100-150mL/hr
What two electrolyte derrangements can lead to hypocalcemia?
-hypomagnesemia
-hyperkalemia
What is the fastest rate at which you should correct hypernatremia?
0.5mEq/L/hr
What are the principal regulators of serum osmolarity?
all determined on the kidneys ability to excrete urine, so:
-intact renal function
-appropriate ADH secretion
When both low plasm osmolarity and low blood volume/pressure are present what effects dominates the renal response?
low blood volume/pressure
-this can lead to hypovolemic hyponatremia
For every 100mg/dL rise in glucose by how much does sodium fall?
1.3mEq/L
How much will the drop of albumin by 1g/dL reduce the baseline anion gap?
by 2.5mEq
What are typical serum osmolality, urine osmolality, urine sodium, and volume status of SIADH?
-serum osm < 280mOsm/kg
-Uosm > 100mOsm/kg
-UNa > 30mEq/L
-euvolemic
