Acid-Base

Question 1

Acid Base Homeostasis

Answer 1

CO₂+H₂O <-> H₂CO₃ <->HCO₃^- + H⁺

Question 2

How much acid do we produce daily?

What is our tolerance?

Answer 2

20,000 mmol

140 nmol

Question 3

Where do we buffer the majority of our acid? What form is it removed as?

Where is the secondary buffering organ?

Answer 3

The lungs as CO₂

The kidney

Question 4

How does the kidney buffer acid?

What is the typical urine pH?

Answer 4

1. Bicarbonate reabsorbed via carbonic annhydrase in the proximal tubule
2. Hydrogen ions excreted at distal convoluted urine

Urine pH: 6-6.5

Question 5

What is needed to elucidate pH disturbances?

What is the normal pH?

Answer 5

Arterial blood gas (pCO<sub>2</sub> and pH)
Basic chemistry (bicarbonate, sodium, chloride)

7.4

Question 6

What is primary respiratory acidosis?

What is primary respiratory alkalosis?

What can cause respiratory acidosis?

Answer 6

pCO₂ > 40 mm Hg

pCO₂ < 40 mm Hg

COPD, Smoking

Question 7

What is primary metabolic acidosis?

What is primary metabolic alkalosis?

Answer 7

HCO₃^- < 24 mmol/L

HCO₃^-​ > 24 mmol/L

Question 8

What is mixed acid-base disturbance?

Answer 8

A combination of 2 or 3 of the acid-base disturbances (respiratory/metabolic acidosis/alkalosis)

Question 9

What is the systemic approach for determining acid-base disorders?

Answer 9

1. pH relative to normal (7.4)
2. Determine primary disorder (Metabolic or Respiratory)
3. Calculate expected compensation
4. Calculate anion gap
5. Review change in [HCO₃^-] and change in AGAP (Δ/Δ)

Question 10

What is the expected compensation for metabolic acidosis?

What is the expected metabolic alkalosis?

Which direction does pCO2 compnsate towards relative

Answer 10

pCO₂= 1.5 * [HCO₃^-] + 8
or
pCO₂= last 2 digits of pH

pCO₂ = 0.9 * [HCO₃^-] + 9

pCO₂ compensates in the same direction as bicarb Δ

Question 11

What is the expected compensation for respiratory acidosis?

What is the expected compensation for respiratory alkalosis?

What determines the acute versus chronic response?

Answer 11

Acidosis
Acute: bicarb increases by 1 mM per 10 mm Hg increase in P_aCO₂
Chronic: bicarb increases by 4 mM per 10 mm Hg increase in P_aCO₂

Alkalosis
Acute: bicarb decreases by 2 mM per 10 mm Hg decrease in P_aCO₂
Chronic: bicarb decreases by 4 mM per 10 mm Hg decrease in P_aCO₂

Chronic response change due to changes in expression for carbonic anhydrase

Question 12

What is the anion gap?

Normally should there be a difference between overall (not just measured) cations and anions?

What is the normal anion gap?

Answer 12

AG = [Na⁺] - ([HCO₃⁺+Cl^-)

No.

10.