Acid Base Homeostasis
CO2+H2O H2CO3 HCO3- + H+
How much acid do we produce daily?
What is our tolerance?
Where do we buffer the majority of our acid? What form is it removed as?
Where is the secondary buffering organ?
The lungs as CO2
How does the kidney buffer acid?
What is the typical urine pH?
- Bicarbonate reabsorbed via carbonic annhydrase in the proximal tubule
- Hydrogen ions excreted at distal convoluted urine
Urine pH: 6-6.5
What is needed to elucidate pH disturbances?
What is the normal pH?
Arterial blood gas (pCO2 and pH)
Basic chemistry (bicarbonate, sodium, chloride)
What is primary respiratory acidosis?
What is primary respiratory alkalosis?
What can cause respiratory acidosis?
pCO2 > 40 mm Hg
pCO2 < 40 mm Hg
What is primary metabolic acidosis?
What is primary metabolic alkalosis?
HCO3- < 24 mmol/L
HCO3- > 24 mmol/L
What is mixed acid-base disturbance?
A combination of 2 or 3 of the acid-base disturbances (respiratory/metabolic acidosis/alkalosis)
What is the systemic approach for determining acid-base disorders?
- pH relative to normal (7.4)
- Determine primary disorder (Metabolic or Respiratory)
- Calculate expected compensation
- Calculate anion gap
- Review change in [HCO3-] and change in AGAP (Δ/Δ)
What is the expected compensation for metabolic acidosis?
What is the expected metabolic alkalosis?
Which direction does pCO2 compnsate towards relative
pCO2 = 1.5 * [HCO3-] + 8
pCO2 = last 2 digits of pH
pCO2 = 0.9 * [HCO3-] + 9
pCO2 compensates in the same direction as bicarb Δ
What is the expected compensation for respiratory acidosis?
What is the expected compensation for respiratory alkalosis?
What determines the acute versus chronic response?
Acute: bicarb increases by 1 mM per 10 mm Hg increase in PaCO2
Chronic: bicarb increases by 4 mM per 10 mm Hg increase in PaCO2
Acute: bicarb decreases by 2 mM per 10 mm Hg decrease in PaCO2
Chronic: bicarb decreases by 4 mM per 10 mm Hg decrease in PaCO2
Chronic response change due to changes in expression for carbonic anhydrase
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?
AG = [Na+] - ([HCO3++Cl-)