Acids & bases highlights

Question 1

1) What is anion gap?
2) What is it made of?
3) What is high AG?

Answer 1

1) difference between measured cations and measured anions in the extracellular space
2) AG = Na+– (Cl−+ HCO3−)
3) >12

Question 2

Measured cations normally outnumber measured anions; the difference is made up by what?

Answer 2

The anion gap

Question 3

As your anion gap goes up, what goes down?

Answer 3

Bicarb and chloride (measured anions)

Question 4

1) What does the anion gap measure?
2) When does it increase?

Answer 4

1) Represents unmeasured anions
2) With accumulation of acid anions (e.g., lactate, acetoacetate)

Question 5

1) What is the anion gap useful in?
2) Explain

Answer 5

1) Useful in narrowing down the cause of metabolic acidosis
2) AG >12 = HAGMA
AG ≤12 = NAGMA

Question 6

1) What is the principal unmeasured anion usually responsible for the anion gap?
2) When must the anion gap be corrected?

Answer 6

1) Albumin
2) Hypoalbuminemia

Question 7

How do you differentiate between acute and chronic respiratory acidosis?

Answer 7

<3 days or >3 days

Question 8

What can the anion gap look like in metabolic acidosis?

Answer 8

Normal anion gap (NAGMA) or high anion gap (HAGMA)

Question 9

Differentiate between compensation by the kidneys and lungs

Answer 9

1) Kidneys: metabolic via HCO3 level changes; slower
2) Lungs: respirations change pCO2 levels; faster

Question 10

With metabolic acidosis:
1) What happens to pH and bicarb?
2) What happens to alveolar ventilation? What does this do?
3) What does this do to pH?

Answer 10

1) Low; low
2) Increases; decreases pCO2
3) Returns pH close to normal

Question 11

In compensation, the HCO3 and pCO2 move in what direction(s)?

Answer 11

In the same direction

Question 12

Mixed acid-base disorder: give 1 reason to suspect this

Answer 12

Changes in pCO2 and HCO3 are in opposite directions

Question 13

What are the 3 potential causes of metabolic acidosis?

Answer 13

1) Increased acid generation
2) Loss of bicarbonate
3) Diminished renal acid excretion

Question 14

True or false: In compensation, the HCO3 and pCO2 move in the same direction

Answer 14

True

Question 15

What is the hallmark of metabolic acidosis?

Answer 15

Decreased HCO3– (<22 mEq/L so pH < 7.35)

Question 16

What are the 3 classifications of metabolic acidosis?

Answer 16

Classified by anion gap:
1) Decreased (<6 mEq)
2) Increased (>12 mEq) (aka, high AG, HAGMA)
3) Normal (6-12 mEq) (aka, hyperchloremic, nongap, NAGMA)

Question 17

Metabolic acidosis and is associated with too much of what ion? (each can cause the other)

Answer 17

Potassium (hyperkalemia)

Question 18

What are the 4 main causes of HAGMA?

Answer 18

1) Ketoacidosis (diabetic/alcohol/starvation)
2) Uremia (severe renal dysfunction)
3) Lactic acidosis
4) Toxins (ethylene glycol [antifreeze], methanol, salicylate OD, many others)

Question 19

In compensation, what 2 things move in the same direction

Answer 19

HCO3 and pCO2

Question 20

Lactic Acid (Lactate):
1) Primarily produced by _________________ of glucose (glycolysis) in tissues
2) Buildup of lactic acid (via overproduction and/or reduced metabolism) leads to what?

Answer 20

1) anaerobic metabolism
2) Lactic acidosis (LA) – a HAGMA

Question 21

1) Lactic acidosis is usually due to what?
2) Elevated lactic acid potentially indicates __________ tissues.

Answer 21

1) Impaired tissue oxygenation leading to increased anaerobic metabolism
2) hypoxic

Question 22

Lactic Acidosis (HAGMA)
1) What are elevated?
2) Define lactic acidosis numerically
3) Lactic acidosis produces decreased ____ and usually elevated _____

Answer 22

1) Lactate levels
2) >4 mmol/L
3) pH; AG

Question 23

List and describe the 2 kinds of L-lactate acidosis

Answer 23

1) Type A (hypoxic): from decreased tissue perfusion and hypoxia; leads to anaerobic glycolysis; more common
1) Type B: not due to decreased tissue perfusion/hypoxia; from metabolic causes (DM, kidney dz, etc) or toxins

Question 24

1) Type A (hypoxic) L-lactate acidosis results from what?
2) What kind of glycolysis does it lead to?
3) Which type of L-lactate acidosis is more common?
4) Which type can be due to metabolic causes (like DM or kidney dz) or toxins?

Answer 24

1) Decreased tissue perfusion and hypoxia
2) Anaerobic
3) Type A
4) Type B

Question 25

What are the 3 major causes of NAGMA? Give examples of each

Answer 25

1) HCO3– loss from GI tract (ex. diarrhea) 2) Defects in renal acidification (ex. renal tubular acidosis (RTA), which may be due to hypoaldosteronism or other causes; impaired renal excretion of H+ or reabsorption of HCO3) 3) HCO3- dilution (ex. NS IVF)

Question 26

In NAGMA, a compensatory increase in _____________ (hyper______________) maintains a normal anion gap

Answer 26

serum chloride (hyperchloremia)

Question 27

Metabolic Alkalosis: 1) What is the hallmark? 2) Give an example of why that is

Answer 27

1) High HCO3 2) e.g., due to loss of H+ or gaining/inadequate secretion of HCO3-

Question 28

Metabolic Alkalosis: What 2 things is it most often due to?

Answer 28

1) Excess loss of H+ ions and Cl- from GI tract (e.g., vomiting) or urine (e.g., mineralcorticoid excess/hyperaldosteronism, diuretics) 2) H+ ion movement into cells (e.g., hypokalemia)

Question 29

28

Answer 29

Alkali administration (e.g., antacids) ECF volume contraction around relatively constant amount of extracellular HCO3 (“contraction alkalosis”)

Question 30

28

Answer 30

Metabolic alkalosis and hypokalemia are associated (each can cause the other) Metabolic alkalosis is also associated with hypochloremia (inhibits renal HCO3 secretion)

Question 31

Metabolic alkalosis Causes include (LAVA-UP):

Answer 31

Loop (and thiazide) diuretics: multifactorial, induce secondary hyperaldosteronism Antacid use: alkaline Vomiting: loss of HCl (H+ ions and Cl-) Aldosterone increase (“A-UP”): Na+ and water reabsorbed, K+ and H+ secreted into urine; loss of H+ causes metabolic alkalosis

Question 32

Respiratory Acidosis: 1) What does it result from? 2) What is acute respiratory failure?

Answer 32

1) hypoventilation & hypercapnia (increased pCO2) 2) Acute respiratory failure

Question 33

Respiratory Alkalosis: 1) What does it result from? 2) When is metabolic compensation greater, in chronic or acute form?

Answer 33

1) Hyperventilation (reduces PCO2, increases pH) 3) Chronic

Question 34

Salicylates (e.g., aspirin)

Answer 34

Suspect aspirin toxicity if both respiratory alkalosis + HAGMA (particularly with alkalemia)

Question 35

PAST PH Respiratory Alkalosis (gerber doesn't find this mnemonic very helpful)

Answer 35

Panic attacks Anxiety attacks Salicylates Tumor (CNS) PE (and other pulmonary diseases) Hypoxemia (high altitude, etc.)

Question 36

List the 6 steps of acid-base diagnosis

Answer 36

1) Determine whether the primary disorder is an acidosis or alkalosis by reviewing the pH Determine whether the primary acidosis or alkalosis is metabolic or respiratory by reviewing the HCO3− and PaCO2 Evaluate magnitude of compensation Calculate Anion Gap (AG) If metabolic acidosis exists and the AG is increased, compare ΔAG and ΔHCO3− (delta ratio) Establish the clinical diagnosis

Question 37

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Question 39

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Question 40

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Question 42

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Question 43

Define delta AG/delta HCO3 ratio 2)

Answer 43

1) compare the increase in AG to the decrease in the HCO3 concentration 2) Assume normal AG = 12, normal HCO3 = 24

Question 44

Delta AG/delta HCO3 Ratios: What suggests HAGMA + metabolic alkalosis?

Answer 44

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