Acid-Base Disorders 1 (Quick Guide) Flashcards
Discuss Winter’s formula
Used to predict appropriate respiratory compensation in metabolic acidosis
PCO2 = 1.5 x HCO3 + 8 +/- 2
Measured = Predicted –> pure met acid
Measured > Predicted –> met acid + respi acid
implies inadequate ventilation, don’t give sodium bicarbonate
Measured < Predicted –> met acid respi alk
Discuss delta ratio
∆AG / ∆HCO3
<0.4 –> Pure NAGMA
0.4 -0.8 –> NAGMA + HAGMA
0.8 - 2.0 –> Pure HAGMA
>2.0 –> HAGMA + met alk (or preexisting compensated resp acid)
normal AG is 12. normal HCO3 is 24
another take on expected compensation in metabolic acidosis
for every dec in HCO3 by 1 mEq/L, there is dec in PCO2 by 1 mm Hg
Potential indications for bicarbonate therapy in metabolic acidosis
- Severe hypobicarbonatemia (<4 mEq/L)
insufficient buffer concentrations may lead to extreme increases in acidemia with small increaeses in acidosis - Severe acidemia (pH <7.00 to 7.15) in cases of HAGMA, with signs of shock or myocardial iritability that has not responded to supportive measures including
- adequate ventilation
- fluid resuscitation - Severe hyperchloremic acidemia
Lost bicarbonate must be regenerated by kidneys and liver, which may require days
Compensation in respiratory acidosis
acute:
inc in HCO3 by 1 mEq/L for every inc in PCO2 by 10 mmHg
chronic:
inc in HCO3 by 3.5 mEq/L for every inc in PCO2 by 10 mmHg
with near-normal pH
How to determine if respiratory acidosis is acute or chronic?
Ratio of change in pH and change in PCO2
(delta pH / Δ PCO2)
>0.8: concomitant metabolic acidosis
=0.8:acute
0.33-0.8: acute on chronic
=0.33: chronic
<0.33: concomitant metabolic alkalosis
Discuss respiratory alkalosis
predicted relationship:
dec in [H+] by 1-mmol results from dec in PCO2 by 1 mmHg
“Chornic respiratory alkalosis is unique among the acid base disorders in that its compensation may be complete*
- bicarbonaturia and dec in acid excretion requires 6 to 72 hours to develop fully
- at at least 1 week to normalize pH