Approach to Acid-Base Disorders (Selby)

Question 1

definition metabolic acidosis

Answer 1

low serum HCO3-

Question 2

definition metabolic alkalosis

Answer 2

highs serum HCO3-

Question 3

definition respiratory acidosis

Answer 3

high PCO2

Question 4

definition respiratory alkalosis

Answer 4

low PCO2

Question 5

Anion gap formula

Answer 5

= Na - (HCO3 + Cl)

Question 6

When is anion gap used?

Answer 6

to differentiate HAGMA vs.

NAGMA

Question 7

what will falsely lower anion gap?

Answer 7

hypoalbuminemia

Question 8

what is correction factor for anion gap with hypoalbuminemia?

Answer 8

for every 1 g/dL drop in albumin, the AG drops by 2.5 mEq/L

Question 9

normal serum osmolality

Answer 9

275- 290 mosm/L

Question 10

formular for serum osmolality

Answer 10

= 2(Na) + (Glucose/18) + (BUN/2.8)

Question 11

formular for osmolar gap

Answer 11

measured serum osmolality- calculated serum osmolality

Question 12

what is osmolar gap clinically useful for?

Answer 12

• screening for EtOH ingestions (esp. HAGMA cases)
• screening for ketoacidosis
• screening for lactic acidosis

Question 13

When is delta delta gap used for?

Answer 13

in patients with HAGMA to determine if there is coexisting NAGMA or metabolic alkalosis present

Question 14

delta delta gap formulas

Answer 14

delta gap = calculated AG -normal AG (always 12)

delta HCO3 = normal HCO3 (always 24) - delta gap

Question 15

what if measured HCO3 is equal to delta delta gap?

Answer 15

then no additional acid base disorder is present

Question 16

what if measured HCO3 is greater than delta delta gap?

Answer 16

metabolic alkalosis is present in addition to HAGMA

Question 17

what if measured HCO3 is less than delta delta gap?

Answer 17

NAGMA is present in addition to HAGMA

Question 18

normal pH on arterial blood gas

Answer 18

pH 7.35-7.44

Question 19

normal HCO3 on ABG

Answer 19

24 mEq/L

Question 20

normal PCO2 on ABG

Answer 20

40 mmHg

Question 21

normal anion gap on ABG

Answer 21

12

Question 22

normal osmolality gap on ABG

Answer 22

10 mmol/L

Question 23

Differential Dx HAGMA

Answer 23

G- glycols (ethylene and propylene)
O- oxoproline (acetamino tox)
L- lactic acidosis (L-isomer)
D- lactic acidosis (D-isomer)
M- methanol
A- aspirin
R- renal failure
K- ketoacidosis (EtOHism, DM, starvation)

Question 24

Who is pyroglutamic (5-oxoproline) acidosis seen in?

Answer 24

women who are malnourished or critically ill

Question 25

DDx of increased osmolar gap

Answer 25

``` M- methanol E- ethanol D- diethylene glycol I- isopropyl EtOH E- ethylene glycol - propylene glycol - keto/lactic acidosis ```

Question 26

what cause of increased osmolar gap is not associated with metabolic acidosis?

Answer 26

isopropyl alcohol

Question 27

What level of potassium is acidosis associated with ?

Answer 27

hyperkalemia

Question 28

what level of potassium is alkalosis associated with?

Answer 28

hypokalemia

Question 29

NAGMA DDx

Answer 29

``` D- diarrhea U- ureteral diversion R- renal tubular acidosis H- hyperalimentation A- acetazolamide A- addison's disease M- miscellaneous (glue sniffing) ```

Question 30

respiratory alkalosis DDx

Answer 30

anything that increases respiratory rate or tidal volume (including pregnancy)

Question 31

respiratory acidosis DDx

Answer 31

anything that lowers respiratory rate/tidal volume, increases dead space, or worsens airway obstruction

Question 32

what is urine anion gap used for

Answer 32

clinically used to differentiate renal from nonrenal causes of NAGMA

Question 33

what is UAG a marker of

Answer 33

NH4Cl excretion, which indicates proper urinary acidification

Question 34

formula urine anion gap

Answer 34

UAG = (urine sodium + urine potassium) - urine chloride

Question 35

negative UAG meaning

Answer 35

appropriate distal nephron urinary acidification

Question 36

postive UAG meaning

Answer 36

inappropriate distal nephron urinary acidification

Question 37

problem in proximal RTA (type 2)

Answer 37

decreased capacity of proximal tubule to reabsorb HCO3, eventually some reabsorption occurs in other parts of tubule, but at a lower level (--> acidosis)

Question 38

Secretion of what leads to HCO3 reabsorption?

Answer 38

H+

Question 39

what is most common cause of RTA type 2 in children?

Answer 39

cystinosis

Question 40

Common cause of RTA type 2 in adults?

Answer 40

Fanconi syndrome (likely due to multiple myeloma)

Question 41

Problem in distal RTA (type 1)

Answer 41

patients are unable to acidify their urine; lack of net H+ ion secretion prevents urinary acidification and excretion of ammonium

Question 42

common etiologies type 1 RTA

Answer 42

Sjogren's syndrome, glue sniffing

Question 43

clinical manifestations type 1 RTA

Answer 43

nephrolithiasis or nephrocalcinosis

Question 44

4 things for diagnosis RTA type 1

Answer 44

1) NAGMA 2) unable to acidify urine pH <5.5 3) hypokalemia, usually severe 4) UAG is positive

Question 45

Etiology hyperkalemic RTA (type 4)

Answer 45

- deficiency circulating aldosterone - aldosterone resistance in collecting ducts - BOTH lead to impaired Na+ reabsorption by principle cells (leads to hyperkalemia)

Question 46

clinical manifestations type 4 RTA

Answer 46

- usually asymptomatic - NAGMA - hyperkalemia - most patients in 50-70s with h/o DM or CKD

Question 47

Diagnosis type 4 RTA

Answer 47

- variable urine pH (usually >5.5) | - UAG is positive

Question 48

DDx metabolic alkalosis (5 things)

Answer 48

- hypokalemia - vomiting or nasogastric tube suctioning - diuretics (loop/thiazide) - volume depletion - mineralocorticoid excess (Conn syndrome)

Question 49

General cause of metabolic alkalosis

Answer 49

factors that stimulate Na+ reabsorption, secondarily increase H+ secretion and stimulate HCO3- reabsorption

Question 50

what cell is a mirror image of alpha intercalated cells?

Answer 50

beta intercalated

Question 51

Why is there hypochloremia with volume depletion (contraction alkalosis)?

Answer 51

The HCO3-Cl exchanger in beta intercalated cells must replete Cl- to help with HCO3- secretion

Question 52

winters formula

Answer 52

PCO2 = 1.5 [HCO3]+8 +/-2