Acid/Base Physiology Flashcards
Normal value for arterial pH
7.35-7.45
Normal value for arterial CO2
35-45 mm Hg (use 40 mm Hg in calculations)
Normal value for arterial O2
80-100 mm Hg
Normal value for arterial bicarb
22-26 (use 24 mEq/L in calculation)
What 2 blood gas components may change your pH? What type of disturbance is each of these correlated with?
HCO3 changes in metabolic disturbances
CO2 changes in respiratory disturbances
When looking at someone with altered acid/base status, how would you determine that it was due to metabolic causes?
If HCO3 and pH change in same direction = metabolic
[Kidneys and other organs control HCO3; changes in HCO3 will produce metabolic acid-base imbalances]
When looking at someone with altered acid/base status, how would you determine that it was due to respiratory causes?
If pH is altered in the setting of CO2 imbalance, it is respiratory (CO2 and pH change in opposite directions)
How is respiratory acidosis generated?
Decreased ventilation –> increased blood PCO2 –> increased conversion of H2CO3 to [H+] –> decreased serum pH
How is respiratory alkalosis generated?
Increased ventilation –> decreased blood PCO2 –> decreased conversion of H2CO3 to [H+] –> increased serum pH
Increased lactic acid, ketoacids in diabetics, etc. would lead to ______ ______
Metabolic acidosis
How are respiratory disturbances compensated?
By metabolic system, in this case via reabsorption/secretion of H+ or HCO3 in the kidneys (mainly PCT)
How is respiratory acidosis compensated?
Kidney secretes H+ via urine and reabsorbs HCO3 in the blood, thus increasing plasma bicarb
There is increased ammonium production and increased bicarb generation
This is renal buffering!
How is respiratory alkalosis compensated?
By decreasing acid filtration: kidney secretes or creates new HCO3 via urine and reabsorbs H+ in the blood, thus decreasing plasma bicarb
Decreased ammonium production and thus decreased acid excretion in urine, along with decreased bicarb regeneration
How is metabolic acidosis compensated for?
Acidemia stimulates chemoreceptors in the carotid bodies that produce an immediate increase in ventilation rate (hyperventilation)
More CO2 will be expired to reduce PCO2 and increase arterial pH
How is metabolic alkalosis compensated for?
Ventilation decreases to retain more CO2 and decrease arterial pH
What are the renal mechanisms for regulating hydrogen and bicarb ion concentrations in the blood?
Reabsorption of virtually all of the filtered HCO3 and excreteion of H+ as titratable acid and ammonium
For each H+ excreted as titratable acid or NH4, one new HCO3 is synthesized and reabsorbed
How would you determine that the respiratory acidosis is acute?
If the change in HCO3 = 1 mEq/L for every 10 mm Hg change in CO2
Expected [HCO3] = 24 + (PaCO2 - 40 mm Hg)/10
How would you determine that the respiratory acidosis is chronic?
If change in HCO3 = 3-4 mEq/L for every 10 mm Hg change in CO2
Expected [HCO3] = 24 + 4(PCO2 - 40 mm Hg)/10
How would you decide that the respiratory alkalosis is acute?
Expected HCO3= 24 -2((PaCO2 - 40 mm Hg)/10
How would you decide that the respiratory alkalosis is chronic?
HCO3 = 24-5(PaCO2 - 40 mm Hg)/10
How would you decide that the respiratory compensation for metabolic acidosis is adequate?
Expected PaCO2 = 1.5[HCO3] + 8 +/- 2
How would you determine if respiratory compensation for metabolic alkalosis is adequate?
Change in PCO2 = (0.5 to 1.0) x change in HCO3
In this case, the change is an increase in CO2
How would you calculate predicted osmolarity?
Osmolarity = 2(serum Na) + (BUN/2.8) + (glucose/18)
Normal osmolarity = 290 mOsm/L
