ACID
BASE DISTURBANCES
6-STEP APPROACH
1. Determine pH
2. Determine primary disturbance (examine pCO2
and HCO3)
IF
Respiratory
3. Determine acute vs. chronic
a. acute: 10mmHg
pCO2(0.08 pH
b. chronic
-acidosis:
10mmHg pCO2(0.03 pH
-alkalosis:
10mmHg pCO2(0.02 pH
IF
Metabolic
1. Determine anion gap (AG+ implies H+
accumulation, AG nml implies bicarb loss):
AG = [Na] – ([HCO3] + [Cl]) (nml
12+/-2)
IF AG>12
a. Determine osm gap:
OG = measured osm – 2[Na] + BUN/2.8 +
glucose/18
IF+:
mannitol, IV contrast, ehtylene glycol, methanol,
isopropyl alcohol, ethanol
b. Correct AG for albumin:
corrected AG = AG-2.4X(4.0-alb)
c. Determine urine bicarb loss (urine
AG+):
urine AG = [Na] + [K] - [Cl]
1. Determine if respiratory compensation is
appropriate
a. acidosis: pCO2 = 1.5[HCO3] + 8+/-2 (Winter’s formula) or changePaCO2=1.2 X
change[HCO3]
*last
2 digits of pH = PCO2
b. alkalosis: pCO2 = 0.7[HCO3] + 21+/-2
• Measure urine Cl-:
IF
<15mEq/L, Cl- responsive
IF
>25mEq/L, Cl- resistant
Cl- def(mEq) = 0.3wt(kg) X (100-plasma[Cl-]).
1. Determine if mixed disorder present
Corrected [HCO3] = measured[HCO3] + (AG-12)
Gap-gap = (AG-12)/(24-[HCO3])
Causes of Respiratory Alkalosis
1. hypoxia
2. asthma
3. pneumonia
4. pulmonary edema
5. PE
6. anxiety
7. drugs: salicylates, theophylline
8. cirrhosis (progesterone)
9. sepsis
Cause of AG Metabolic Acidosis
1. Methanol
2. Uremia
3. DKA/alcohol/starvation
4. Paraldehyde
5. Isoniazid
6. Lactic:
hypoperfusion, sepsis, drugs, leukemia
7. Ethylene
glycol
8. Salicylates
Causes of non-AG Metabolic Acidosis
1. diarrhea
2. early RF
Causes of Metabolic Alkalosis
CHLORIDE-RESPONSIVE
1. exogenous bicarbonate: milk-alkali
2. volume contraction
3. vomiting/NG aspirate/villous adenoma
4. diuretics
5. post-hypercapneic
CHLORIDE-RESISTANT
6. hypercalcemia
7. hypomagnesemia, hypokalemia
8. renal artery stenosis
9. hyperaldosteronism
10. licorice ingestion
Henderson
Equation:
[H+]
= 24 X PCO2/HCO3 (nml = 40 nEq/L)
DpH:0.1 = D[H+]:10
(between 7.25 and 7.45)
drop
pH:0.3 = double[H+]