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Cpr exam 3 > Z Approach to Acid-Base Disorders > Flashcards

Z Approach to Acid-Base Disorders Flashcards

1
Q

What is arterial pH regulated between?

What is intracellular pH regulated between?

A
  1. 35-7.45

7. 0-7.3

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2
Q

Acidic metabolites are constantly produced by the cell. How is pH regulated in the extracellular compartment?

A

The bicarbonate buffer system (HCO3- and CO2)

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3
Q

What is the equation for the bicarbonate buffer system?

A

CO2 + H2O <> H2CO3- <> H+ + HCO3-

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4
Q

What is the Henderson Hasselbalch equation?

A

pH = 6.1 + log ([HCO3-]/(0.03x[PCO2]))

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5
Q

Increase in HCO3- leads to:

Increase in PCO2 leads to:

A

Increased pH (more basic)

Decreased pH (more acidic)

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6
Q

How do the lungs affect the bicarbonate system?

A

They control the [PCO2] by adjusting RR.
Increased RR = more CO2 blown off (dec. CO2, inc. pH)
Decreased RR = less CO2 blown off (inc. CO2, dec. pH)

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7
Q

How do the kidneys affect the bicarbonate buffer system?

How?

A

They regulate pH by excreting either acidic or alkaline urine.

Large amounts of HCO3- are filtered into the urine and lots of H+ are secreted into the tubular lumen by the tubular epithelial cells, so the kidneys are able to adjust the pH quickly by adjusting these concentrations.

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8
Q

Metabolic acidosis =

Metabolic alkalosis =

Respiratory acidosis =

Respiratory alkalosis =

A

Metabolic acidosis = low serum HCO3-

Metabolic alkalosis = high serum HCO3-

Respiratory acidosis = high PCO2

Respiratory alkalosis = low PCO2

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9
Q

What is HAGMA vs. NAGMA?

A

HAGMA is “high anion gap metabolic acidosis”

NAGMA is “normal anion gap metabolic acidosis”

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10
Q

What is associated with saline-responsive metabolic alkalosis?

What is associated with saline-non-responsive metabolic acidosis?

A

Saline-responsive metabolic alkalosis - hypovolemia (contraction alkalosis)

Saline-non-responsive metabolic acidosis - euvolemia

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11
Q

Respiratory acidosis and alkalosis can be either…

A

Acute or chronic

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12
Q

How is metabolic acidosis compensated?

A

The lungs increase RR and cause a respiratory alkalosis.

Decrease HCO3- and PCO2.

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13
Q

How is metabolic alkalosis compensated?

A

The lungs decrease RR and cause a respiratory acidosis.

Increase HCO3- and PCO2.

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14
Q

How is respiratory acidosis compensated?

A

The kidneys reclaim and generate new HCO3- and lead to metabolic alkalosis.

Increase PCO2 and HCO3-.

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15
Q

How is respiratory alkalosis compensated?

A

The kidneys decrease the rate of HCO3- reclaimation and leads to a metabolic acidosis.

Decrease PCO2 and HCO3-.

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16
Q

Compensation formula for metabolic acidosis =

A

Winter’s formula

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

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17
Q

How is compensation for metabolic alkalosis determined?

A

PCO2 will increase by 0.7 mmHg for each 1.0 mEq/L increase in HCO3- from normal (24).

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18
Q

How is compensation determined for acute vs. chronic respiratory acidosis?

A

Acute: HCO3- will increase by 1 mEq/L for every 10 mmHg increase in PCO2 from normal (40)

Chronic: HCO3- will increase by 3.5 mEq/L for every 10 mmHg increase in PCO2 from normal (40)

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19
Q

How is compensation determined in acute vs. chronic respiratory alkalosis?

A

Acute: HCO3- will decrease by 2 mEq/L for every 10 mmHg decrease in PCO2 from normal (40)

Chronic: HCO3- will decrease by 5 mEq/L for every 10 mmHg decrease in PCO2 from normal (40)

20
Q

Anion gap is….

A

Not real. All cations must equal the amount of anions in the body.

21
Q

What are the major cations and anions in the body?

A

Cations: Na+, K+, Mg+, etc.

Anions: Cl-, HCO3-, proteins- (albumin-), etc.

22
Q

What is the equation for anion gap?

What is a normal value?

A

Anion gap = Na+ - (HCO3- + Cl-)

Normal = 12+/- 2

23
Q

When is determining anion gap useful?

A

Differentiating between etiologies of metabolic acidosis (HAGMA vs. NAGMA)

24
Q

NAGMA is AKA as:

Why does the anion gap remain normal?

A

Hyperchloremic metabolic acidosis

If an acid like HCl is added to blood, H+ is buffered by HCO3-, so HCO3- levels drop. However, Cl- levels rise as a result, so the AG remains normal.

25
Q

What does hypoalbuminemia do to AG?

What calculation adjustment is made as a result?

A

It falsely lowers AG, thus it must be corrected.

For every 1 g/dL drop in albumin, the AG increases by 2.5 mEq/L (ex: if someone had a normal anion gap of 12, but now has an [albumin] that is 2 g lower than normal, the AG is now 17).

26
Q

What is the calculated serum osmolality equation?

What is the equation for osmolar gap?

A

Serum Osm = 2(Na+) + (Glc/18) + (BUN/2.8)

Osmolar gap = measured serum Osm - calculated serum Osm

  • normal is < 10 mOsm/L
  • if > 10 mOsm/L, it’s suggestive of additional solutes
27
Q

When is the osmolar gap clinically useful? (3)

A

In screening for alcohol ingestions, particularly in HAGMA cases (AG > 20 should be suspicious for EtOH ingestion)

Screening for ketoacidosis

Sceening for lactic acidosis

28
Q

When is the delta-delta gap useful?

How is it calculated?

A

In patients with HAGMA to determine if there is a coexistent NAGMA or metabolic alkalosis present.

For every increase in AG, there should be an equal decrease in serum HCO3-.

29
Q

What is the normal delta HCO3-?

What is present if it is greater than that value?

What is present if it is less than that value?

A

Approx. 16

> 16 means a metabolic alkalosis is present in addition to the HAGMA

< 16 means a NAGMA is present in addition to the HAGMA

30
Q

What is the 4 step approach to acid-base disturbances?

A
  1. Determine if it is acidosis or alkalosis
  2. Determine if it is primarily metabolic or respiratory
  3. If metabolic acidosis is present, calculate the anion gap
    - if hypoalbuminemia is present, calculate the corrected anion gap
    - if HAGMA is present, calculate the osmolar gap (screen for possible EtOH ingestion) and the delta-delta gap (screen for NAGMA or metabolic alkalosis w/ HAGMA)
  4. Determine if there is appropriate compensation for primary acid-base disorder (is it a simple acid-base disorder, or a mixed disorder, etc.)
31
Q

Normal ABG values for:

pH (normal, acidosis, alkalosis)
HCO3-
PCO2
Anion gap
Osm gap
A

Normal pH: 7.35-7.44
Acidosis: pH < 7.35
Alkalosis: pH > 7.44

HCO3-: 24
PCO2: 40
AG: 12
Osm gap: 10

32
Q

What is on the DDx for HAGMA?

A

GOLD MARK

Glycols
Oxoproline (acetaminophen toxicity)
L-lactic acid
D-lactic acid

Methanol
Aspirin
Renal failure
Ketoacidosis (alcoholic, diabetic, starvation, etc)

33
Q

Pyroglutamic (5-oxoproline) acidosis is seen mostly in…

How is it diagnosed?

What is the pathophysiology?

A

Malnourished or critically ill females who use lots of acetaminophen.

Urinary organic acid screening.

Glutathione is depleted due to increased acetaminophen. Pyroglutamic acid build up and causes and acidosis.

34
Q

What is on the DDx for increased osmolar gap?

A

ME DIE

Methanol
Ethanol
Diethylene glycol (mannitol)
Isopropyl alcohol (rubbing alcohol)
-not associated w/ metabolic acidosis
Ethylene glycol
35
Q

What is the relationship between acidosis and alkalosis and K+ levels?

A

Acidosis is associated with hyperkalemia, due to transcellular shift of cations (H+ and K+) into and out of cells, so the electroneutrality is maintained. In acidosis, H+ enters the cell and K+ exits.

Alkalosis is associated with hypokalemia, due to H+ exiting the cells and K+ entering.

36
Q

What is on the DDx for NAGMA?

A

DURHAAM

  • Diarrhea
  • Ureteral diversion, ileal conduit or fistula
  • RTA

Hyperalimentation
Acetazolamide (a CA inhibitor)
Addison’s Dz (adrenal insufficiency)
Miscellaneous (meds, glue sniffing, toluene toxicity, etc.)

37
Q

What drives HCO3- reabsorption?

A

H+ secretion leads to HCO3- reabsorption.

38
Q

Urine anion gap (UAG) is used to differentiate what?

What is it a marker of?

What is the equation to find UAG?
-what does it mean if it is negative vs. positive?

A

Renal from non-renal causes of NAGMA and the function of the DCT.

Marker of NH4Cl excretion, which indicates appropriate urinary acidification.

UAG = (urine Na+ + urine K+) - urine Cl-

  • if negative, acidification is appropriate
  • if positive, acidification by the distal nephron is not appropriate
39
Q

What is a major consideration for cause of metabolic alkalosis?

A 
Hypokalemia
Vomiting or NG tube placement
*Diuretics (thiazide and loop)
Volume depletion
Mineralcorticoid excess
40
Q

Overall, what can cause metabolic alkalosis?

A

Factors that stimulate Na+ reabsorption, secondarily increase H+ secretion and thus stimulate HCO3- reabsorption leading to potentially to a metabolic alkalosis.

41
Q

Beta-intercalated cells and alpha-intercalated cells are…

HCO3- generated from these cells exits via…

In contraction alkalosis, what must the intercalated cells do?

A

Mirror images

Cl-/HCO3- exchanger into the tubular lumen

Replete Cl- to help with HCO3- secretion

42
Q

What is on the DDx for respiratory alkalosis?

A

Anything that leads to an increase in RR - pneumonia, PE, pulmonary edema, PTX, sepsis, HF, meds, etc.

43
Q

What is on the DDx for respiratory acidosis? (3)

A

Anything that lowers RR/tidal volume, increases dead space or worsens airway obstruction.

Inadequate ventilator settings

Increases in CO2 production

44
Q

What is the main problem in Type 1 RTA?

Where does it occur?

What is the urine pH?

What are [K+] levels?

What is associated with it? (3)

Is the UAG + or -?

A

a-intercalated cells do not secrete H+ into the lumen, due to defects in transporters or gradient.

DCT

Urine pH > 6

Hypokalemia

Renal stones, Sjogren’s, elevated urine Ca++

UAG is +

45
Q

What is the main problem in Type 2 RTA?

Where does it occur?

What happens to the urine pH?

What are [K+] levels?

What is it associated with? (3)

Is the UAG + or -?

A

PT cells do not filter HCO3-.

PCT

Increased urine pH initially, but after time it stabilizes and reaches a steady state.

Mild hypokalemia

Fanconi syndrome, multiple myeloma, cystinosis in kids

Can be either + or -*

46
Q

What is the main problem in Type 4 RTA?

What happens to [K+] levels?

What is the UAG?

A

Decreased aldosterone at DCT leads to decreased ENaC activity, which decreases excretion of H+ and K+, leading to NAGMA and hyperkalemia.

Hyperkalemia

Always +

47
Q

The only RTA associated with hyperkalemia is…

What are the symptoms of these patients?

A

Type 4 RTA

They are usually asymptomatic, but are 50-70 w/ a history of DM

Cpr exam 3 (13 decks)

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