Electrolyte/Acid Base Disorders Flashcards
Functions of the kidney?
- Primarily responsible for regulation of fluid and electrolyte balance (maintenance and regulation)
- Secretion of hormones that participate in regulation of systemic/renal hemodynamics, RBC production, Metabolism of Ca++, phosphorus & bone
Maintenance of the kidney?
Maintains constant extracellular environment so cells can function
Regulation of kidney?
Regulates excretion of water and solutes (Na+, K+, H+)
Hormones secreted by kidney for regulation of hemodynamics?
Renin, prostaglandins, bradykinin, erythropoietin
Common electrolytes in electrolyte disorders?
Na+, K+, Mg, Ca+, Phosphorus (P), Chloride (Cl), Bicarb (HCO3)
Where are electrolytes found?
Serum
What are electrolytes?
Chemicals that are dissolved in water –> producing ions that enable flow of electrical signals through body
What do ions aid in?
Nerve excitability, endocrine secretion, membrane permeability, body fluid buffering, controlling movement of fluid between compartments
How do ions enter the body?
Digestive tract (90%)
How are ions excreted?
Kidneys (small amount lost through sweat/feces)
What does serum osmolality measure?
Body’s electrolyte-water balance (measured by labs)
What are the primary circulating solutes?
Sodium salts (Cl, HCO3), glucose, urea
The osmolality of extracellular fluid and intracellular fluid are approximately ______?
Equal
What is tonicity a measure of?
Effective osmotic pressure gradient; the water potential of two solutions separated by semipermeable cell membrane
(relative concentration of solutes dissolved in solution that determine direction/extent of diffusion)
Tonicity is influenced only by what solutes?
Solutes that cannot cross the cell membrane (exert an effective osmotic pressure)
What are the three classifications of tonicity?
Hypertonic, Hypotonic, Isotonic
*used to compare osmolarity of cell to osmolality of extracellular fluid around it
Hypertonic fluid/electrolyte disorders cause what?
Fluid/H2O to flow out of cell (dehydrate)
Hypotonic fluid/electrolyte disorders cause what?
Fluid/H2O to flow into cell (overhydrate)
What happens to fluid/electrolyte balance in dehydration?
Serum osmolality increases leading to:
Hypertonic dehyration or Hypotonic dehydration or Isotonic dehydration
BY release of ADH
What happens to fluid/electrolyte balance in excessive water intake?
Serum osmolality decreases leading to: hypervolemia
What is the anion gap?
Difference between measured cations and anions in serum, plasma, or urine
Serum anion gap formula?
Serum AG = measured cations - measured anions
OR
Serum AG = Na - (Cl + HCO3)
Serum anion gap (AG) is used in the differential diagnosis of what?
Metabolic acidosis
What does a high/increased AG indicate?
Metabolic acidosis**, hyperalbuminemia, hyperphosphatemia, lab error
What does a low/decreased AG indicate?
Lab error**, hypoalbuminemia, hyperkalemia, hypercalcemia, hypermagnesia, lithium toxicity
Sodium is a ______ _______ of ECF?
Major cation
Sodium is responsible for 50% of the osmotic pressure gradient existing between what?
ICF and ECF
How is Na+ excreted?
Kidneys
How much sodium is typically consumed daily in the western diet?
130-160 mmol
What occurs in hyponatremia?
Dec. serum osmolality: water moves from ECF to ICF
Hyponatremia is typically associated w/ what?
Excess water accumulation (dilutes Na+) or diuretic use (inc. water and Na+ excretion)
Early clinical manifestations of acute hyponatremia?
Nausea and malaise (125-130 mEq/L)
Delayed clinical manifestations of acute hyponatremia?
Headache, lethargy, obtundation, seizure, resp. arrest (115-120 mEq/L)
Severity of symptoms of hyponatremia reflects what?
Degree of cerebral involvement/over-hydration and edema
What is a concern with excessive cerebral edema as a result of hyponatremia?
Herniation of the brain
Clinical manifestations of chronic hyponatremia?
cerebral adaptation allows for pts to be relatively asx
If sx: fatigue, N/V, dizziness, gait disturbance, confusion, lethargy
Causes of Hyponatremia?
Diuretic use**, diarrhea, CHF, Liver and renal dz, SIADH
Chronic diseases that cause retention of sodium and fluid: body retains more water than Na+ (dilutes Na+ conc.)
Diagnostic testing for Hyponatremia?
CBC, CMP, urine osmolality (24 hrs), Mg, Phos
Treatment of hyponatremia depends on what?
The cause
Treatment of hyponatremia?
H2O restriction, Sodium and water repletion SLOWLY
-Vaptans: nonpeptide vasopressin antagonist (interfered w ADH) *useful for hypervolemic, hyponatremia secondary to CHF/Liver failure
What is hypernatremia?
Inc. serum osmolality, water movement from ICF to ECF
*most often d/t water depletion
Clinical manifestations of hypernatremia?
Early/mild: thirst, weakness, nausea, loss of appetite
Severe: confusion, lethargy, muscle twitching, intracerebral hemorrhage
Causes of hypernatremia?
Vomiting, diarrhea, DI (unreplaced water loss), dehydration (pts w/ dementia, end of life/failure to thrive), severe exercise or seizure (water loss into cells), overload of Na+/hypertonic solution
Hypernatremia is seen in those with impaired ability to do what?
Impaired ability to obtain water or experience thirst
Treatment of hypernatremia?
If due to water loss (dehydration) or hypovolemia (Na+ and water loss): determine etiology, calculate water deficit, fluid repletion (D5W)
How to calculate water deficit?
Plasma Na = (total body Na + total body K)/TBW
Potassium is a major ________ _______?
Intracellular cation
What does Potassium help establish?
Resting membrane potential in neurons and muscle fibers
Effect of potassium on osmotic pressure?
Very little effect (unlike Na+)
What maintains potassium gradients between ICF and ECF?
Sodium-potassium pumps in cell membranes
How is potassium excreted?
Kidneys
Recommended adult daily consumption of potassium?
4700mg
Hypokalemia typically results from what?
Unreplenished GI or urinary loss of K+
Symptom severity of hypokalemia is directly related to what?
Degree/duration of K+ reduction
Clinical manifestations of hypokalemia (<3.0mEq/L)?
Muscle weakness (LE to UE), muscle cramps, rhabdo, N/V/D and ileus, Cardiac arrhythmias/EKG abnormalities***
Cardiac arrhythmias with hypokalemia?
PAC’s, PVC’s, sinus brady, AV block, Vtach, Vfib
Characteristics EKG findings associated with hypokalemia?
ST depression, decreased T wave amplitude, increased amplitude of U wave, prolonged QT interval
Causes of hypokalemia?
Vomiting, diarrhea, diuretics (non-K+ sparing), DKA
Diagnostics for hypokalemia?
Hypo-K and Hypo-Mg concurrent loss, CMC, CMP, Mg, Phos, EKG, ABG, serum ketones
Assume what with hypokalemia tx?
Intracellular and extracellular K+ is equal
Management methods for hypokalemia?
-Careful monitoring in repletion to avoid hyperkalemia (overcorrection risk increases w/ renal insuff.)
-Determine Cause & replete IV or PO
Preparations for repletion of K+ in hypokalemia?
Potassium chloride preferred in most cases (IV, PO)
Treatment for mild-mod hypokalemia (3.0-3.4 mEq/L)?
K+ 10-20 mEq BID (tabs, liquid, or K+ rich foods)
+/- potassium sparing diuretic
Treatment for severe hypokalemia (<2.9mEq/L)?
Admit
K+ 20 mEq PO
10-20 mEq/hr in 100-200mL saline (K-rider)
What is transient correction of hypokalemia?
OK for several hours and then drops (most exogenous K+ taken into cells)
What is hyperkalemia?
-Impaired urinary K+ excretion by CKD, meds
-Inc. K+ release from cells (DKA)
Hyperkalemia is rare in most healthy individuals due to what?
Cellular and urinary response mechanisms to prevent excess K+ accumulation in ECF
Clinical manifestations of hyperkalemia (>7.0 mEq/L)
Muscle weakness/paralysis, cardiac arrhythmias/EKG changes
Characteristic EKG changes with hyperkalemia?
Peaked T-waves, Shortened QT interval
Causes of hyperkalemia?
Inc. potassium release from cells: DKA***, succinylcholine, exercise, rhabdo, crush injury
Reduced urinary excretion: acute & chronic kidney disease
Diagnostic testing for hyperkalemia?
EKG, CBC, CMP, Mg, Phos, consider ABG and serum ketones
Management of hyperkalemia?
-Calcium antagonizes membrane actions of hyperkalemia (stabilizes cardiac tissue)
-Insulin (w/ IV glucose) drives extracellular K+ into cells
-Inhaled beta-agonists (Albuterol)
-Remove K+ from body: IV diuretics (+/- IV saline), Polystyrene sulfonates (Kayexalate PO), hemodialysis (ESRD)
Hypomagnesemia occurs in what % of hospitalized populations?
12%
Symptoms of hypomagnesemia are typically associated with what?
Concurrent hypokalemia, hypocalcemia and/or metabolic acidosis
Causes of hypomagnesemia?
GI loss/diarrhea, chronic PPI use, Renal loss (loop/thiazide diuretics, nephrotoxic drugs), alcohol (secondary to urinary excretion, diarrhea, dietary deficiency), Hypercalcemia
Most of the body’s magnesium stores are where?
Intracellular, 60% in bone
Extracellular magnesium can be ionized (free) or bound to what?
Protein
Magnesium helps to maintain what?
Normal nerve and muscle function, blood glucose control, BP regulation, contributes to construction of bone
Magnesium is required for what?
Energy production
What does magnesium help transport across cell membranes?
Calcium and potassium
Diagnostic testing for hypomagnesemia?
EKG, CMC, CMP, Mg, Phos, consider ETOH
Treatment for hypomagnesemia?
Identify cause, IV/PO repletion
Hypermagnesemia is uncommon in the absence of what?
Mg+ repletion or kidney disease
Clinical manifestations of hypermagnesemia?
Nausea, flushing, headache, lethargy, comnolence, hypocalcemia, absent deep tendon reflexes, hypotension, bradycardia, muscle paralysis, apnea, resp. failure, heart block
Causes of hypermagnesemia?
Kidney disease/failure (no Mg regulation other than urinary excretion), Mg infusion/repletion
Diagnostic testing for hypermagnesemia?
EKG, CBC, CMP, Mg, Phos
Treatment of hypermagnesemia?
Determine cause, prevention, improve renal elimination by loop diuretics and IV saline or hemodialysis
99% of calcium is found where?
Bone and teeth
1% of calcium is in the serum and is required for what?
Vascular function, muscle function, nerve transmission
Serum calcium is regulated and does not fluctuate with what?
Dietary intake
The body uses what as a reservoir to maintain constant Ca concentration?
Bone
45% of calcium in the serum is bound to what?
Albumin
The 40% of calcium in the serum not bound to albumin is ____ _____ ______?
Ionized free calcium (not bound to proteins)
Average recommended daily intake of calcium varies with what?
Age (most adults 1000-1300mg)
Hypocalcemia values must be corrected if patients have what?
An abnormal albumin level
How to calculate corrected calcium?
Corrected calcium = measured total Ca + 0.8 (4.0 - serum albumin)
Clinical manifestations of acute hypocalcemia?
Tetany** (HALLMARK), fatigue, hyperirritability, anxiety, QT prolongation
Trousseau’s and Chvosteks’s signs
What is Trousseau’s sign?
Induction of carpal spasm by inflation of BP cuff
What is Chvosteks’s sign?
Contraction of the ipsilateral facial muscles elicited by tapping facial nerve anterior to the ear
Causes of hypocalcemia?
Vitamin D/ phosphate influence on serum calcium, hypoalbuminemia (pseudo-hypocalcemia), Hypoparathyroidism due to excision, Vit D deficiency, CKD, Sepsis
Diagnostics for hypocalcemia?
EKG, CBC, CMP, Mg, Phos, Ionized Ca
Treatment of hypocalcemia?
Determine cause
Severe: IV calcium gluconate (over 10-20 min*** NEVER FASTER)
Mildly symptomatic/chronic: PO calcium gluconate
Is hypercalcemia common?
No, relatively uncommon
Causes of hypercalcemia?
Primary hyperparathyroidism and malignancy (90% of cases), Drug-induced hypercalcemia
Clinical manifestations of hypercalcemia?
No specific manifestation, depends on cause
Diagnostics for hypercalcemia?
Confirm dx, Measure PTH, Vit D levels
Treatment of hypercalcemia?
Tx underlying cause
If normal or low PTH with hypercalcemia, assume what dx?
Malignancy
Phosphorous is an essential mineral and makes up what % of someone’s total body weight?
1%
Phosphorous is present in which cells?
All of them
85% of phosphorous is found where?
Bones & teeth, DNA, RNA
Phosphorous and what ion are interrelated?
Calcium
Phosphorous and calcium metabolism is regulated by what?
Vit. D and PTH
Phosphorous is excreted by what?
Kidneys (w/ renal failure levels rise)
Where is phosphorous absorbed?
Small intestines
Phosphorous can be found in many ____ and _____?
Foods and additives
Causes of hyperphosphatemia?
Acute or chronic kidney disease, acute phosphate load: tumor lysis, rhabdo, exogenous phosphate
Treatment of hyperphosphatemia?
Determine cause, IV normal saline, May require dialysis
Causes of hypophosphatemia?
Increased insulin secretion (when treating DKA), poor absorption (anorexia, alcoholism, chronic diarrhea, short gut synd.), Hyperparathyroidism, Vit D deficiency
Treatment of hypophosphatemia?
Determine cause (may only require tx of underlying cause), repletion often not necessary
What is the physiology of acid-base status?
Humans generate large amounts of acids daily –> must be excreted, expired, metabolized, or buffered
Acid-base is maintained by what?
Normal pulmonary excretion (CO2), Metabolic utilization of acid, Renal excretion of acid
Acid-base is aseessed by measuring what?
Components of bicarb-carbon dioxide buffer system in the blood
Measuring pH is measuring which ions?
H+ ions (balance = regulation of H+ ions)
Concentration of H+ ions in the body has a ____ range for optimal cellular function?
narrow *small deviations in either direction carries significant morbidity and mortality
Buffer system defense mech. of the body in acid-base balance?
HCO3
Respiratory system defense mech. of the body in acid-base balance?
CO2 (expire)
Renal system defense mech. of the body in acid-base balance?
Reabsorbs HCO3, excretes H+
CO2 formed during cellular respiration combines with H2O to form what?
Carbonic acid
What are carbonic acid disscoates?
HCO3 and H+ ion (pH)
a pH of <7.35 (acidemia) and inc. PaCO2 indicates what?
Resp. Acidosis
a pH of <7.35 (acidemia) and dec. HCO3- indicates what?
Metabolic Acidosis
a pH of >7.45 (alkalemia) and dec. PaCO2 indicates what?
Resp. Alkalosis
a pH of >7.45 (alkalemia) and inc. HCO3- indicates what?
Metabolic Alkalosis
How to measure acid-base?
ABG (arterial or venous)
1. identify/monitor acid-base
2. measure PaO2 and PaCO2
3. assess response to tx
4. detect abnormal hemoglobins**
Contraindications of measuring acid-base w/ ABG?
Local infection, thrombus, abnormal anatomy, severe PVD, anti-coagulation pts (relatively C/I)
How to interpret ABG?
Look at pH (acidotic, alkalotic, normal?), look at HCO3 and CO2 –> determine if metabolic or resp.
Low pH w/ High CO2 ABG?
respiratory
Low pH w/ Low HCO3 ABG?
metabolic
High pH w/ Low CO2 ABG?
respiratory
High pH w/ High HCO3 ABG?
metabolic
What indicates compensation?
If CO2 and HCO3 are both high or both low
if pH normal: full compensation
if pH abnormal: partial compensation
Causes of metabolic acidosis?
Lactic acidosis (DKA), Ketoacidosis (ETOH), Ingestions (methanol, ethylene glycol, ASA), Loss of HCO3 (diarrhea), Dec. renal excretion (CKD)
Causes of metabolic alkalosis?
GI loss (excess vomiting/diarrhea, laxative abuse), Renal loss (diuretics)
Causes of respiratory acidosis?
Dec. central respiratory drive (overdose, encephalitis, CVA), Dec. NM respiratory drive (metabolic disorders), Short/shallow breathing (PE, pulm vascular dz, COPD, interstitial lung disease)
Causes of respiratory alkalosis?
CNS (pain, hyperventilation, anxiety/panic, drug withdrawal), Pulmonary (COPD, interstitial lung disease, pneumothorax, pneumonia), High altitude
