Clinical Acid Base Flashcards
What value of pKa is used in the Henderson Hasselbach equation?
6.1
What is carbonic acid concentration in the blood proportional to?
PCO2
How do we estimate the carbonic acid concentration in the blood?
PaCO2 x 0.03
What is the Henderson Hasselbach equation that uses carbonic acid concentration?
pH = 6.1 + log10 (HCO3/0.03x PaCO2)
If PaCO2 decreases acutely from increased minute ventilation, and HCO3 does not change, what will happen to pH?
pH will increase
What is the trigger for renal or respiratory compensation in most scenarios?
serum pH
What is a normal pH value?
7.4
How do we calculate the anion gap?
Na-Cl-HCO3
What is the normal AG level?
10 mEq/L +- 2
What makes up the majority of the gap between anion s and cations in the AG equation?
serum albumin
An increase in unmeasured anions or a decrease in unmeasured cations would have what effect on AG?
it would increase the AG
A decrease in unmeasured anions or an increase in unmeasured cations would do what to AG?
lower AG
What should arterial bicarbonate look like compared to venous bicarbonate?
they should be very close if they’re not, you probably have a data issue
If pH is down and PaCO2 is up, what kind of acid base disturbance is this?
respiratory acidosis
if pH is up and PaCo2 is down, what kind of acid base disturbance is this?
respiratory alkalosis
In the acute setting, what should the change in pH be for the change in PaCO2?
0.08 pH for every 10 mmHg CO2 change
during respiratory acid base disturbances, how does bicarbonate change?
it doesn’t change more than 1-2 mEq, usually in the same direction as PaCO2
How does renal compensation change pH?
changing serum bicarb
if pH is down and PaCO2 is down, what is true of the acid base disturbance?
expected respiratory compensation of metabolic acidosis
if pHi s up and PaCO2 is up, what is true of the acid base disturbance?
expected respiratory compensation of metabolic alkalosis
How do you define metabolic alkalosis or acidosis?
low bicarb = acidosis high bicarb = alkalosis
What type of acid base disturbance is this: 7.20/20(8)
metabolic acidosis with compensatory hyperventilation
With expected respiratory compensation for a metabolic process, what is true of the relationship between pH and PaCO2?
the last 2 digits of pH = PaCO2
For ever 1 mEq/L increase in acid, what happens to bicarbonate?
1 mEq/L decrease
What is indicated by an AG > 20 mEq/L?
metabolic acidosis from acid accumulation (MUD PILES)
What does MUD PILES stand for? What is it the DDx for?
methanol, uremia, diabetic ketoacidosis (or ketoacidosis from another cause), propylene glycol, isoniazid, lactic acidosis, ethylene glycol, salicylates of a metabolic acidosis from acid accumulation , AG > 20
What process is this?
- low bicarb + pH=PaCO2
- AG > 27
–> metabolic acidosis with acid accumulation (MUD PILES)
What is the pneumonic for metabolic acidosis with a normal AG?
USED CARS
uretero-enterostomy with bicarb rich ostomy fluid, saline administration, endocrine disorders (eg, adrenal insufficiency), diarrhea, carbonic anhydrase inhibitors (acetazolamide), ammonium chloride, renal tubular acidosis, spironolactone
What is a hyperchloremic metabolic acidosis?
one with a normal AG
What is the upper limit for bicarb that limits its ability to compensate for metabolic alkalosis?
PaCo2 > 50
What are the 2 types of metabolic alkalosis?
Chloride responsive and unresponsive
what type of acid base disturbance is associated with contraction alkalosis?
chloride responsive metabolic alkalosis
What causes chloride unresponsive metabolic alkalosis?
too much aldosterone
Unless there are extra conditions, what should be true of the delta anion gap v. the delta bicarb?
They should be roughly equal
If the serum bicarbonate is significantly lower than expected by the delta-delta analysis, what should be considered?
- consider a concurrent bicarbonate wasting condition (i.e., a non-elevated AG metabolic acidosis)
If the bicarbonate is significantly higher than expected by the delta-delta analysis what should be considered?
- consider a concurrent bicarbonate excess state (i.e., a concurrent metabolic alkalosis)
Interpret the following:
metabolic acidosis of the elevated AG variety with appropriate respiratory compensation. Note the delta-delta analysis: (delta AG = 27 – 10 = 17 meq/L, if this value is added to serum bicarb the result is 25 meq/L, which is in the normal range suggesting there is no other acid base disorder (namely, a there is no concurrent non elevated AG metabolic acidosis or metabolic alkalosis). Think MUD PILES.
Interpret:
metabolic acidosis of the non-elevated AG variety with appropriate respiratory compensation. This is a bicarb wasted stated so think USED CARS. Note the elevated chloride. Note also a delta-delta analysis does not help: (delta AG = 9 – 10 = negative 1 meq/L, if this value is added to the serum bicarb the result is negative 7 meq/L, which is low - but you already knew that).
Interpret:
metabolic alkalosis with expected respiratory compensation. Urine electrolytes and clinical data will help sort out chloride responsive vs. chloride unresponsive.
Interpret:
respiratory alkalosis (pH and PaCO2 are on opposite sides of normal) and an elevated AG metabolic acidosis (MUD PILES) because AG > 20. Delta-delta does not demonstrate a concurrent non elevated AG metabolic acidosis or metabolic alkalosis (20 - 10 + 16 = 26—which is a normal “corrected” bicarbonate). This is a double acid-base disturbance (eg, aspirin intoxication, which can cause a respiratory alkalosis and elevated AG metabolic acidosis). (Note for delta-delta: 20 is the calculated AG, 10 is the normal AG and 16 is the serum bicarbonate level).
Interpret:
respiratory alkalosis (pH and PaCO2 are on opposite sides of normal) and an elevated AG metabolic acidosis (MUD PILES). Delta-delta demonstrates “too much” serum bicarbonate (29 – 10 + 16 = 35therefore a metabolic alkalosis is present as well). This is a triple acid-base disturbance
Interpret:
elevated anion gap metabolic acidosis with expected respiratory compensation (MUD PILES). Delta-delta demonstrates “too little” serum bicarbonate (24 – 10 + 5 = 19). Thus there is a concurrent non elevated anion gap metabolic acidosis. This is a double acid-base disturbance.
Interpret:
elevated anion gap metabolic acidosis with an equally severe metabolic alkalosis. Delta-delta demonstrates too much bicarbonate (21 – 10 + 24 = 35). This is a double acid-base disturbance.
What’s the differential for high DLCO?
polycythemia
DAH
L to R intracardiac shunt
Obesity
What is on the differential for low DLCO?
anemia
emphysema
ILD
R to L shunt
PAH
What is the differential for a respiratory alkalosis?
fever, pain, anxiety, sepsis, stimulants, PE, cirrhosis, hyperthyroid, pregnancy, and mild lung disease
