Acid Base 1B Flashcards
Acidemia (pH <7.38) due to decreased bicarbonate is:
- metabolic acidosis.
- decreased pH + decreased bicarbonate.
Alkalemia (pH >7.44) due to increased bicarbonate is:
- metabolic alkalosis.
- increased pH + increased bicarbonate.
Nephrons are:
- renal tubules.
- structures in kidney making what will eventually be excreted urine.
Four functions of nephrons regarding acid-base balance:
- Reclaim HCO3 filtered from blood.
- Generate new HCO3.
- Titrate/neutralize secreted H+.
- Excrete titratable acids and HCO3.
Fate of proton absorbed from interstitium into cytoplasm of renal tubule cell:
- Proton absorbed from interstitium into cytoplasm of renal tubule cell.
- Proton secreted into forming urine.
- Proton in forming urine reacts with a hydroxide ion (OH-) from filtered bicarbonate to form water.
- Water is reabsorbed into renal tubule cell, where it dissociates into proton and hydroxide ion.
- Hydroxide portion reacts with CO2 in renal tubule to form bicarbonate
- Bicarbonate reabsorbed into interstitium/blood plasma.
Anytime in the kidney a proton gets secreted into forming urine by one mechanism or another, what occurs?
- a bicarbonate is reabsorbed into the interstitium/plasma.
What can cause low plasma bicarbonate?
- simply losing bicarbonate (diarrhea).
- bicarbonate being used up buffering non-physiologic non-carbonic acid.
What chemoreceptors are immediately activated during metabolic acidosis?
- pH-sensitive chemoreceptors located within the carotid bifurcations and aortic bodies.
- low pH (elevated H+) and increased PCO2 activates these chemoreceptors.
What chemoreceptors have a lag in activation during metabolic acidosis?
- central chemoreceptors that detect CSF pH.
What occurs once chemoreceptors detect low pH?
- CN 9/10 relay information to medullary respiratory center.
- Kussmauls breathing (ventilations increase) to blow-off CO2.
- plasma H+ concentration lowers, pH rises.
Steps in why there is a lag in the central chemoreceptor response to metabolic acidosis:
- low plasma pH activates peripheral chemoreceptors.
- kussmauls breathing activated.
- plasma PCO2 drops.
- CO2 from CSF diffues into plasma down concentration gradient.
- CSF chemoreceptors detect slight alkalemia.
- Bicarbonate levels eventually drop in CSF, CSF pH drops accordingly, and central respiratory drive is stimulated.
Why does acute compensation to metabolic acidosis fail in the chronic stage?
- Acute Kussmaul breathing lowers PCO2, which increases plasma pH.
- Renal HCO3- reabsorption lowers due to increased plasma pH.
- Plasma HCO3- levels lower further.
Winter’s formula is useful to determine:
- if appropriate respiratory compensation to metabolic acidosis has occurred versus presence of a second (respiratory) acid-base disorder:
- PCO2 = 1.5[HCO3-] + 8 ± 2
Winter’s formula:
PCO2 = 1.5[HCO3-] + 8 ± 2
- Calculated PCO2 = measured PCO2, appropriate compensation.
- Calculated PCO2 < measured PCO2, respiratory acidosis or no compensation.
- Calculated PCO2 > measured PCO2, respiratory alkalosis.
Compensation rule for metabolic acidosis:
“1.5 + 8”
PCO2 = 1.5[HCO3-] + 8 ± 2
- Calculated PCO2 = measured PCO2, appropriate compensation.
- Calculated PCO2 < measured PCO2, respiratory acidosis or no compensation.
- Calculated PCO2 > measured PCO2, respiratory alkalosis.
Elevated pH with elevated plasma HCO3- is:
metabolic alkalosis
Common causes of metabolic alkalosis:
- administration of HCO3- or H+ loss.
- diarrhea.
- vomiting/nasogastric suction.
Hypokalemia and hypochloremia are associated with which acid-base disorder?
metabolic alkalosis
Compensation rule for metabolic alkalosis:
“0.7 + 20”
PCO2 = 0.7[HCO3-] + 20 ± 5
Why does acute compensation to metabolic alkalosis fail in the chronic stage?
- acute reduced respirations lead to increased PCO2.
- plasma H+ levels rise, plasma pH rises.
- kidneys secrete more H+, more HCO3- reabsorbed.
- HCO3- plasma levels rise, pH rises.
The two compensation rules for metabolic disorders:
- metabolic acidosis: 1.5 + 8 (Winter)
- metabolic alkalosis: 0.7 + 20
Draw algorithm for metabolic acidosis:
low pH; low HCO3- (<24)
Draw algorithm for metabolic alkalosis:
high pH; high HCO3- (>24)
