VBG ABG
pH +0.04
pCO2 -6

Henderson-Hasselbach Equation
H+ = 24 x pCO2/HCO3-
pH H+    
7.50 32 80%
7.40 40
7.30 50 80%
7.20 63
7.10 79 80%
7.00 100
Acid Base Analysis
Metabolic Acidosis - Anion Gap
HCO3-
DDx:
1. Renal failure with uremia
2. Ketoacidosis (IDDM, EtOH withdrawl)
3. Drugs/Poisons
Methanol - osmolal gap, optic papilledema
Salicylates - PT, Respiratory alkalosis
Paraldehyde
Ethylene Glycol - osmolal gap, ozalate crystals
4. Lactic acidosis (IDDM, renal failure, liver disease, tumors, starvation, sepsis)

Calculations:
Anion Gap = Na - Cl - HCO3 (Increased in >11 2)
D10 HCO3 = D10 PCO2
PCO2 expected = 1.5 (HCO3) + (8 2)
Osm
Estimated = 2Na + Glucose/18 + BUN/2.7 = 285 mOsm
measured - estimated < 10
Metabolic Alkalosis
HCO3-
DDx:
1. Fluid volume contraction (GI tract - vomiting, kidneys, skin, lungs, postoperative ascites)
2. Hypokalemia
3. Hyperaldosteronism, Excess glucocorticoids/mineralcorticoids
4. Bartter's syndrome - K+ wasting, polyuria
5. Ingestion of alkali, bicarbonate, e.g. via antacids
6. Rapid correction of hypercapnea (posthypercapnic metabolic alkalosis)
7. Diuretics - H+ secretion

Calculations:
D10 HCO3 = D7 PCO2

Cl- sensitive - urine Cl- < 15 mEq/L (Diuretics, vomiting, villous adenoma

Cl - resistant - urine Cl- > 15 mEq/L
Normal Values
Male
Female
pCO2
40
36
HCO3-
25
23

Metabolic Acidosis - Non Gap
Hyperchloremic
DDx:
K+
1. GI HCO3 losses e.g. diarrhea
2. Renal tubular acidosis
proximal - HCO3 absorption defect
distal - NH4+ into renal vein, liver converts NH4+HCO3- to urea (spironolactone)

K+
3. Carbonic anhydrase inhibitors (acetazolamide)
4. Ureteral diversions
5. HCl or NH4Cl oral CaCl2
6. Chloride gas exposure, sulfur toxicity
7. Adrenal insufficiency, hypoaldosteronism
Respiratory Alkalosis
CO2 pH hyperventilating
DDx:
1. Catastrophic CNS event (e.g. intracerebral hemorrhage)
2. Drug use (salicylates, progesterone)
3. Pregnancy (third trimester)
4. Decreased lung compliance (interstitial fibrosis)
5. Anxiety
6. Cirrhosis (progesterone medulla)
7. Sepsis
8. High altitudes

Complications:
K+ depletion
cells
Ca+ depletion
Left shift of Hb dissociation curve


Calculations:
Acute D10 PCO2 = D1-2 HCO3 (ratio of 5:1)
DpH = 0.08 x (40 - PaCO2)/10

Chronic
D10 PCO2 = D5 HCO3 (ratio of 2:1)
DpH = 0.03 x (40 - PaCO2)/10

Respiratory Acidosis
CO2 pH not breathing enough
DDx:
1. CNS depression (sedatives, CNS disease, obesity-hypoventilation)
2. Pleural disease (pneumothorax, pleural effusion)
3. Lung disease (COPD, ARDS, PE, pneumonia)
4. Musculoskeletal (kyphoscoliosis, Guillain Barre, myasthenia gravis, botulism, polymyositis)

Calculations:
Acute D10 PCO2 = D1-2 HCO3 (ratio of 5:1)
DpH = 0.08 x (PaCO2 - 40)/10

Chronic
D10 PCO2 = D5 HCO3 (ratio of 2:1)
DpH = 0.03 x (PaCO2 - 40)/10