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Acid-Base and Electrolytes (Week 12)

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tylerwise's version from 2015-04-13 03:29

Normal Values

LabNormal Range
pH7.35 - 7.45
pCO235 - 45 (40)
Measured in mmHg
PO293 - 100 (100)
HCO322 - 27 (25)
Sodium136 - 145 (140)
Potassium3.0 - 5.0 (4.5)
Chloride96 - 106 (100)
Magnesium1.7 - 2.1
Calcium8.5 - 10.5
Phosphorus2.7 - 4.5
Total CO223 - 28 (26)
Measured in mEq
Serum osmolality275 - 290
BUN< 20
Anion gap8 - 16
memorize

"Rules"

Question Answer
Total body salt rules...Volume
Free water rules...Serum sodium concentration
memorize

Miscellaneous Facts

Question Answer
Intracellular electrolytesAnything with a small normal value
Potassium
Magnesium
Calcium
Phosphorus
Role of ADHRegulates fluid and electrolyte intake
Regulates reabsorption of free water in distal tubules
Secreted when osmolality is high
Role of aldosteroneEnhances sodium reabsorption in distal tubules
Works via sodium/potassium exchange
Secreted when plasma volume is low
Indicated by BUN > 20Dehydration
Serum osmolality equation2[Na] + (Glucose/18) + (BUN/2.8)
Calculating anion gap[Na] - ([Cl] + [HCO3])
Causes of anion gap acidosisMULEPAK
Methanol
Uremia
Lactic acid
Ethylene glycol
Paraldehyde
Aspirin
Ketoacidosis
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Hormonal Regulation of Calcium

Question Answer
PTHIncreases serum calcium
Vitamin DIncreases serum calcium
CalcitoninDecreases serum calcium
Effects of calcitoninReleased from thyroid gland in response to high serum calcium
Stimulates calcium deposit into bones
Reduces calcium uptake from the intestine
Reduces calcium uptake in the kidneys
Effects of PTHReleased from parathyroid glands in response to low serum calcium
Stimulates calcium release from bones
Increases calcium uptake from the intestines
Increases calcium uptake in the kidneys
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Electrolyte Disorders and Phamaceutical Causes

ImbalancePotential Drug Causes
Hyponatremia
Hypotonic, hypovolemic, hyponatremic
Diuretics
Osmotic diuresis
Hyponatremia
Hypotonic, isovolemic, hyponatremic
Carbamazepine
SSRIs
TCAs
Hypernatremia
Isovolemic, hypernatremia
Lithium
Demeclocycline
HypokalemiaInsulin
Albuterol
Diuretics
HyperkalemiaACEIs
ARBs
NSAIDs
Potassium-sparing diuretics (aldosterone antagonists)
Beta-blockers
HypomagnesemiaAminoglycosides
Diuretics
HypermagnesemiaMagnesium-containing antacids
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Hypotonic Hypovolemic Hyponatremia

Question Answer
What it meansSerum sodium is low (due to too much free water)
Total body sodium is low
Volume is low (due to decreased total sodium)
How to treatStop any diuretics!
Give 0.9%NS
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Hypotonic Isovolemic Hyponatremia

Question Answer
What it meansSerum sodium is low
Total body sodium is normal
Volume is normal
How to treatStop offending drugs (Carbamazepine, SSRIs, TCAs)
Give loops (lose more free water than sodium)
Give 0.9%NS
memorize

Hypotonic Hypervolemic Hyponatremia

Question Answer
What it meansSerum sodium is low
Total body sodium is high
Volume is high
How to treatTreat underlying cause (CHF, cirrhosis, renal failure)
Restrict sodium and water intake
Give diuretics
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Hypertonic Hyponatremia

Question Answer
Typical causeHyperglycemia
How to treatTreat hyperglycemia with insulin
Restore volume and free water deficits
CORRECT SLOWLY! Do not correct serum glucose faster than 100/hr
1/2NS preferred to NS
memorize

Hypovolemic Hypernatremia

Question Answer
What it meansSerum sodium is high
Total body sodium is low
How to treatRemove offending drugs
Use NS to replace intravascular volume, then change to 1/2NS
memorize

Isovolemic Hypernatremia

Question Answer
What it meansSerum sodium is high
Total body sodium is normal
Typical causeDiabetes insipidus (lack of ADH production from pituitary)
How to treatTreat underlying cause
Add loop diuretics to remove sodium
D5W
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Hypokalemia

Question Answer
Typical causesMedications (insulin, albuterol, diuretics)
Metabolic alkalosis
GI losses
Hypomagnesemia
How to treatCorrect hypomagnesemia if present
Increase potassium intake (diet and/or supplements)
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Hyperkalemia

Question Answer
Typical causesMedications (ACEIs, ARBs, NSAIDs, K-sparing diuretics, beta-blockers)
Decreased renal function
Metabolic acidosis
Insulin deficiency
How to treatAntagonize cardiac effects
Return potassium to normal level
>>Calcium chloride, insulin + glucose, sodium bicarb, SPS, furosemide, dialysis
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Hypomagnesemia

Question Answer
Typical causesDecreased intake or absorption
Increased renal elimination (drug-/hormone-induced)
Diabetic ketoacidosis
How to treatSupplements (IV if < 1 and PO if 1-1.5)
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Hypermagnesemia

Question Answer
Typical causesRenal failure
Excessive intake
How to treatAvoid magnesium products
If symptomatic:
>>Calcium chloride IV, NS + loops, HD in ESRD
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Acidosis vs. Alkalosis Examples

Lab ValuesCompensated/Non-compensated Acidosis/Alkalosis
pH: 7.13
pCO2: 13
pO2: 95
HCO3: 4
Compensated metabolic acidosis
pH: 7.28
pCO2: 28.9
pO2: 110
HCO3: 10.5
Compensated metabolic acidosis
pH: 7.15
pCO2: 53
pO2: 85
HCO3: 18
Non-compensated respiratory AND metabolic acidosis
pH: 7.5
pCO2: 10
pO2: 98
HCO3: 20
Compensated respiratory alkalosis
pH: 7.53
pCO2: 45
pO2: 92
HCO3: 40
Non-compensated metabolic alkalosis
pH: 7.34
pCO2: 58
pO2: 85
HCO3: 30
Compensated respiratory acidosis
pH: 7.22
pCO2: 33
pO2: 85
HCO3: 13
Compensated metabolic acidosis
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