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Step 2 Secrets 🍾 > Acid-Base and Electrolytes > Flashcards

Acid-Base and Electrolytes Flashcards

1
Q

How do you analyze arterial blood gas values?

A
  1. pH tells you acidosis or alkalosis as primary event
  2. Look at CO2
  3. Look at bicarbonate
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2
Q

True or false: The body does not compensate beyond a normal pH.

A

True. Overcorrection does NOT occur.

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3
Q

Common causes of respiratory acidosis?

A

COPD, asthma, drugs (e.g. opioids, benzos, barbs, alcohol, other respiratory depressants), chest wall problems (paralysis, pain), sleep apnea

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4
Q

Common causes of metabolic acidosis?

A

Ethanol, DKA, uremia, lactic acidosis (e.g. sepsis, shock, bowel ischemia), methanol/ethylene glycol, aspirin/salicylate overdose, diarrhea, carbonic anhydrase inhibitors

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5
Q

Common causes of respiratory alkalosis?

A

Anxiety/hyperventilation, aspirin/salicylate overdose

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6
Q

Common causes of metabolic alkalosis?

A

Diuretics (except carbonic anhydrase inhibitors), vomiting, volume contraction, antacid abuse/milk-alkali syndrome, hyperaldosteronism

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7
Q

What type of acid-base disturbance does aspirin overdose cause?

A

Respiratory alkalosis and metabolic acidosis (2 different primary disturbances). Look for tinnitus, hypoglycemia, vomiting, history of “swallowing several pills”. Alkalinization of urine (with bicarb) speeds excretion.

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8
Q

What happens to blood gas of patients with chronic lung conditions?

A

pH may be alkaline during the day because they breathe better when awake.
Just after episode of bronchitis or respiratory disorder, metabolic alkalosis (which usually compensates for respiratory acidosis) becomes primary disturbance (elevated pH and bicarb).

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9
Q

What type of heart failure can sleep apnea and other chronic lung diseases cause?

A

Right-sided heart failure (cor pulmonale)

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10
Q

Should you give bicarb to a patient with acidosis?

A

Almost never. First try IV fluids and correction of underlying disorder. If all other measures fail and pH remains <7.0, bicarb may be given.

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11
Q

Blood gas of a patient with asthma has changed from alkalotic to normal and patient seems to be sleeping. Is patient ready to go home?

A

Patient is probably crashing. pH is initially high in patients with asthma (eliminating CO2). If patient becomes tired and doesn’t breathe well, CO2 will rise and pH will normalize. Eventually patient becomes acidotic and requires intubation. Asthmatic patients are supposed to be slightly alkalotic during an asthma attack; if they are not, you should wonder why.

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12
Q

List the signs and symptoms of hyponatremia.

A

Lethargy, mental status changes/confusion, anorexia, seizures, cramps, coma

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13
Q

Causes of hypovolemic hyponatremia?

A

Dehydration, diuretics, diabetes, Addison’s disease/hypoaldosteronism (high potassium)

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14
Q

Causes of euvolemic hyponatremia?

A

SIADH, psychogenic polydipsia, oxytocin use

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15
Q

Causes of hypervolemic hyponatremia?

A

Heart failure, nephrotic syndrome, cirrhosis, toxemia, renal failure

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16
Q

How do you treat hypovolemic hyponatremia? Euvolemic? Hypervolemic?

A

Hypovolemic - normal saline

Euvolemic and hypervolemic - water/fluid restriction; may need diuretics for hypervolemic

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17
Q

What medication is used to treat SIADH if water restriction fails?

A

Demeclocycline (induces nephrogenic diabetes insipidus)

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18
Q

What happens if hyponatremia is corrected too quickly?

A

Central pontine myelinolysis. Hypertonic saline is used only when patient has seizures from severe hyponatremia, otherwise use normal saline.

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19
Q

What causes spurious (false) hyponatremia?

A

Lab value is low but total body sodium is normal. Do NOT give extra salt or saline.

  • Hyperglycemia (when glucose is >200 mg/dL, sodium decreases by 1.6 mEq/L for each rise of 100 mg/dL in glucose)
  • Hyperproteinemia
  • Hyperlipidemia
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20
Q

What causes hyponatremia in postoperative patients?

A

Most common is a combination of pain and narcotics (causing SIADH) with overaggressive administration of IV fluids.
Rare cause may be adrenal insufficiency (potassium is high, BP is low).

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21
Q

What is the classic cause of hyponatremia in pregnant patients about to deliver?

A

Oxytocin, which has an ADH-like effect

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22
Q

What are the signs and symptoms of hypernatremia?

A

Basically same as hyponatremia: mental status changes/confusion, hyperreflexia, seizures, and/or coma

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23
Q

In chronic severe symptomatic hyponatremia, the rate of correction should not exceed what?

A

0.5 to 1 mEq/L/hour

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24
Q

What causes hypernatremia?

A

Most common cause is dehydration (free water loss) due to inadequate fluid intake
Also diuretics, diabetes insipidus, diarrhea, renal disease, iatrogenic (hypertonic IV fluids)
Rare causes include sickle cell disease due to renal damage and isosthenuria (inability to concentrate urine), hypokalemia, and hypercalcemia (impair kidney’s concentrating ability)

25
Q

How is hypernatremia treated?

A

Water replacement but due to severe dehydration, use normal saline; when hemodynamically stable switch to 1/2 normal saline. D5W should NOT be used.

26
Q

What are the signs and symptoms of hypokalemia?

A

Muscular weakness leading to paralysis and ventilatory failure, ileus and/or hypotension (smooth muscle involvement)
EKG: loss of T wave or T wave flattening, presence of U waves, premature ventricular and atrial complexes, ventricular and atrial tachyarrhythmias

27
Q

What is the effect of pH on serum potassium?

A

Results from cellular shift. Alkalosis causes hypokalemia; acidosis causes hyperkalemia. This is why bicarbonate is given to severely hyperkalemic patients.

28
Q

Describe the interaction between digitalis and potassium.

A

Heart is particularly sensitive to hypokalemia in patients taking digitalis. Potassium should be monitored carefully, especially is they are also taking diuretics (a common occurrence).

29
Q

How should potassium be replaced?

A

Slowly. Oral replacement is preferred but if it must be given IV, do not give more than 20 mEq/hr. Patient should be on EKG monitor when giving IV potassium because of potential for fatal arrhythmias.

30
Q

When hypokalemia persists even after administration of significant amounts of potassium, what should you do?

A

Check magnesium level. When magnesium is low, body cannot retain potassium effectively.

31
Q

What are the signs and symptoms of hyperkalemia?

A

Weakness and paralysis
EKG: tall, peaked T waves, widening of QRS, prolongation of PR interval, loss of P waves, sine-wave pattern
Arrhythmias include asystole and ventricular fibrillation

32
Q

What causes hyperkalemia?

A
  • Renal failure (acute or chronic)
  • Severe tissue destruction (high intracellular K+ concentration)
  • Hypoaldosteronism (hyporeninemic hypoaldosteronism in diabetes)
  • Meds (stop K-sparing diuretics, beta blockers, NSAIDs, ACEi, ARBs)
  • Adrenal insufficiency (low sodium, low BP)
33
Q

What should you suspect if an asymptomatic patient has hyperkalemia?

A

First consider whether lab specimen is hemolyzed (esp. if normal EKG). Hemolysis causes false hyperkalemia due to high intracellular K+ concentration. Repeat the test.

34
Q

If asymptomatic patient has hyperkalemia and the specimen was not hemolyzed, what is the first treatment?

A

Get an EKG to check for cardiotoxicity. Best therapy for hyperkalemia is decreased potassium intake and administration of oral sodium polystyrene resin (Kayexalate).

35
Q

What is the treatment for a patient with a potassium >6.5?

A

First give calcium gluconate (cardioprotective but has no effect on K+), then sodium bicarbonate (alkalosis causes K+ shift inside cells) and glucose with insulin (insulin forces K+ inside cells, glucose prevents hypoglycemia)
Beta-2 agonists drive K+ into cells
If patient has renal failure or treatment doesn’t work, prepare to institute dialysis emergently

36
Q

What are the signs and symptoms of hypocalcemia?

A

Tetany:
*Chvostek sign (tapping on facial nerve at angle of jaw elicits contraction of facial muscles)
*Trousseau sign (inflation of BP cuff causes hand muscle -carpopedal- spasms)
Also depression, encephalopathy, dementia, laryngospasm, convulsions/seizures
EKG: QT prolongation

37
Q

What should you do if the calcium level is low?

A

Check albumin level and/or ionized or free calcium level to make sure “true” hypocalcemia is present. Protein-bound fraction of Ca2+ is decreased if there is hypoproteinemia. Patient will be asymptomatic because ionized fraction of Ca2+ is unchanged.
For every 1 g/dL decrease in albumin below 4 g/dL, correct calcium by adding 0.8 mg/dL to the given calcium value.

38
Q

What causes hypocalcemia?

A
  • DiGeorge syndrome (tetany 24-48 hrs after birth, absent thymic shadow on x-ray)
  • Renal failure (low vitamin D)
  • Hypoparathyroidism (esp. post-thyroidectomy patient)
  • Vitamin D deficiency
  • Pseudohypoparathyroidism (short fingers, short stature, mental retardation, normal PTH but end-organ responsiveness)
  • Acute pancreatitis
  • Renal tubular acidosis
39
Q

Describe the relationship between low calcium and low magnesium.

A

It is difficult to correct hypocalcemia until hypomagnesemia (of any cause) is also corrected.

40
Q

How does pH affect calcium levels?

A

Alkalosis causes calcium to shift intracellularly. Most common with hyperventilation/anxiety syndromes (too much CO2 elimination, alkalosis develops, then perioral and extremity tingling). Treat by correcting pH.

41
Q

Describe the relationship between calcium and phosphorus.

A

Usually go in opposite directions. Important in patients with chronic renal failure - must not only try to raise calcium levels but also restrict/reduce phosphorus.

42
Q

What are the signs and symptoms of hypercalcemia?

A

Bones (osteopenia and pathologic fractures)
Stones (kidney stones and polyuria)
Groans (abdominal pain, anorexia, constipation, ileus, nausea, vomiting)
Psychiatric overtones (depression, psychosis, delirium/confusion)
Also peptic ulcer disease and/or pancreatitis
EKG: QT shortening

43
Q

What is the most common cause of hypercalcemia in outpatients?

A

Hyperparathyroidism

44
Q

What is the most common cause of hypercalcemia in inpatients?

A

Malignancy

45
Q

What are some causes of hypercalcemia?

A

Hyperparathyroidism, malignancy, vitamin A or D intoxication, sarcoidosis, thiazide diuretics, familial hypocalciuric hypercalcemia (low urinary calcium), immobilization, hyperproteinemia

46
Q

Why is asymptomatic hypercalcemia usually treated?

A

Can cause nephrocalcinosis and renal failure due to calcium salt deposits in kidney and may result in bone disease secondary to loss of calcium

47
Q

How is hypercalcemia treated?

A

First, give IV fluids. Then give furosemide to cause calcium diuresis.

48
Q

Which diuretics are contraindicated with hypercalcemia?

A

Thiazides

49
Q

In what clinical scenario is hypomagnesemia usually seen?

A

Alcoholism. Magnesium is wasted through the kidneys.

50
Q

What are the signs and symptoms of hypomagnesemia?

A

Similar to those of hypocalcemia (prolonged QT interval on EKG and possible tetany)

51
Q

In what clinical scenario is hypermagnesemia seen?

A

Classically iatrogenic in pregnant patients who are treated for preeclampsia with Mg sulfate.
Also common in patients with renal failure.

52
Q

What is the first sign of hypermagnesemia?

A

Decreased deep tendon reflexes. Then hypotension and respiratory failure.

53
Q

How is hypermagnesemia treated?

A 
Stop any magnesium infusion
ABCs (intubate if necessary)
If patient is stable, start IV fluids
Furosemide can be given if needed to cause Mg diuresis
Last resort is dialysis
54
Q

In what clinical scenarios is hypophosphatemia seen?

A

Patients with uncontrolled diabetes (esp. DKA) and alcoholics

55
Q

What are the signs and symptoms of hypophosphatemia?

A

Neuromuscular disturbances (encephalopathy, weakness), rhabdomyolysis (esp. in alcoholics), anemia, white blood cell and platelet dysfunction

56
Q

What is the IV fluid of choice in hypovolemic patients?

A

Normal saline or lactated Ringer solution (regardless of electrolyte problem). First fill the tank, then correct the imbalances that the kidney cannot sort out on its own.

57
Q

What is the maintenance fluid of choice for patients who are not eating?

A

1/2 NS with 5% dextrose in adults
1/4 NS with 5% dextrose in children under 10 kg
1/3 or 1/2 NS with 5% dextrose in children over 10 kg

58
Q

Should anything be added to IV fluids for patients who are not eating?

A

Usually potassium chloride (10 or 20 mEq) is added to a liter of IV fluids each day to prevent hypokalemia (assuming baseline potassium is normal)

Step 2 Secrets 🍾 (22 decks)

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