Assessment of Acid-Base Status Flashcards
What is the isohydric principle?
It is the phenomenon where multiple A/B pairs in solution are in equilibrium tied to each other via H+
How is the isohydric principle important in the overall A/B balance?
Any change in H+ will change the balance of a single buffer system that will also change the balance of all the other buffer systems as the H+ ions shift back and forth from each system.
Why does only one buffer system need to be examined in order to understand the [H+] in the buffer space?
Due to the isohydric principle all the buffer systems are linked via a common H+
For medical purposes what are the 1st, 2nd and 3rd most important buffer systems?
1st: Bicarbonate
2nd: Hb
3rd: Phosphate
What is used to examine the acid-base status of the body?
Arterial blood - NOT venous blood because the arterial blood is highly buffered and pH controlled but venous blood is not.
What buffer system is an open system?
Bicarbonate
What buffer systems are closed systems?
Phosphate and protein (Hb)
What is the bicarbonate system?
•Open Buffer: CO2 + H2O HCO3– + H+ (pK = 6.1)
What is the Hb system?
•Closed Buffer: Hb-H+ Hb + H+ (pK = 7.0)
What happens with insufficient CO2 removal?
Respiratory acidosis -> acidemia
What happens with excessive CO2 removal?
Respiratory alkalosis -> alkalemia
What can happen as an A/B renal disturbance?
Improper H+ and HCO3- secretion or reabsorption
what happens with extra-renal disturbances that can lead to A/B imbalance?
Excessive CO2 or H+ formation
How rapid is kidney compensation for lung dysfunction?
Slow
How rapid is lung compensation for kidney dysfunction?
Rapid
What occurs in respiratory acidosis?
Increased PaCO2
What happens with respiratory alkalosis?
Decreased PaCO2
What happens with metabolic acidosis?
Low [HCO3-]
What happens with metabolic alkalosis?
High [HCO3-]
What is the anion gap?
Accounts for unmeasured anions that must be present to neutralize the charge of the measured cation, Na+
What is the anion gap used for?
It allows you to differentiate between acid-base disorders that are due to renal/GI problems or other metabolic disorders.
What does a normal anion gap indicate?
It indicates a renal/GI problem
What does a high anion gap indicate?
It indicates other metabolic disorders (diabetes)
What is the normal range for pH?
7.35-7.45
What is the normal range for PaCO2?
35-45 mmHg
What is a double A/B disturbance?
It occurs if the plasma pH is abnormal and both the HCO3- and PaCO2 levels are abnormal and causes severe alkalosis or acidosis.
What is a mixed A/D disturbance?
When the plasma pH is normal and both the HCO3- and CO2 are not normal.
Low CO2 with low HCO3 or vice versa
Can secondary compensations make up for primary disturbances?
Yes but they can never be complete.
What is the compensation for metabolic acidosis?
Decrease CO2
What is the more common acid base disorder?
Acidosis
What A/B is more easily regulated?
Acidotic distrubances. Respiratory ones in particular are much less complicated.
What is the cause of primary respiratory acidosis?
Hypoventilation (COPD/barbituate posioning)
What is the result of primary respiratory acidosis?
Increased PaCO2 and decreased pH
What is the compensation for primary respiratory acidosis?
Increased HCO3- retention via CO2’s effect on the PT
What is the cause of primary respiratory alkalosis?
Hyperventilation
What is the result of primary respiratory alkalosis?
Decreased PaCO2 and increased pH
What is the compensation for primary respiratory alkalosis?
Decreased HCO3- retention via reverse CO2 effect on PT
What is the cause of primary metabolic acidosis?
Renal and extrarenal causes:
- Diabetes (larger anion gap)
- Renal Increased H+ Retention (normal anion gap)
What is the result of primary metabolic acidosis?
Increased H+ and/or decreased HCO3- leading to decreased pH
What is the compensation for primary metabolic acidosis?
Increased CO2 elimination via ventilation
What is the cause of primary metabolic alkalosis?
Renal and extrarenal causes:
- Chronic Potassium Depletion
- Dehydration
What is the result of primary metabolic alkalosis?
Decreased H+ and/or increased HCO3- leading to increased pH
What is the compensation for primary metabolic alkalosis
Increased CO2 retention and a decrease in ventilation
If there is chronic depletion of K+ ions, what happens to the urine?
It will be very acidic
