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Case Studies on Acid-Base Disorders
William T. Browne, M.D.
Important concepts
• -emia refers to a pH
• -osis refers to an abnormal condition or process
Normal ranges
• pH 7.36-7.44
• pCO2 38-42 mm Hg
• HCO3- 22-28 mEq/L
Fact or Fiction?
• A pCO2 < 40 mm Hg always implies a respiratory alkalosis
•FICTION!
Fact or Fiction?• A patient cannot have a
metabolic acidosis and a metabolic alkalosis simultaneously
•FICTION!
Fact or Fiction?• A patient can have a metabolic
acidosis with a compensatory respiratory alkalosis
•FICTION!
Important concepts
• -emia refers to a pH
• -osis refers to an abnormal condition or process
Six Steps for Acid-Base Analysis
Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Six Steps for Acid-Base Analysis
Step 2. Is the primary process metabolicor respiratory?
Six Steps for Acid-Base Analysis
Step 3: If the primary process is respiratory, is it acute or chronic?
Six Steps for Acid-Base Analysis
Step 4: Is there an anion gap?
Na+ - Cl- - HCO3- > 12?
Six Steps for Acid-Base Analysis
Step 5: Is the respiratory compensation adequate?
Expected pCO2 range =[1.5(measured HCO3
-)]+8+/- 2
Six Steps for Acid-Base Analysis
Step 6: Are there any other metabolic disturbances?
Corrected HCO3- =
(Measured HCO3-) + (AG-12)
Problem #1
• 60 yo male presents to the ED from a nursing home. You have no history other than he has been breathing rapidly and is less responsive than usual.
• Na+ 123 Cl- 99 HCO3- 5
• pH 7.31 pCO2 10
Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Acidemia
Six Steps for Acid-Base Analysis
Step 2. Is the primary process metabolicor respiratory?
pCO2 = 10 should drive pH ↑HCO3
- = 5 should drive pH ↓
Six Steps for Acid-Base Analysis
Step 3: If the primary process is respiratory, is it acute or chronic?
Skip this step as primary process is metabolic!
Six Steps for Acid-Base Analysis
Step 4: Is there an anion gap?
Na+ - Cl- - HCO3- > 12?
123 - 99 - 5 = 19Anion Gap Metabolic Acidosis
Causes of anion gap metabolic acidosis
• Methanol• Uremia• Diabetic ketoacidosis• Paraldehyde• Isopropyl alcohol
• Lactic acidosis• Ethylene glycol• Salicylates• Rhabdomyolysis
Six Steps for Acid-Base Analysis
Step 5: Is the respiratory compensation adequate?Expected pCO2 range =[1.5(measured HCO3
-)]+8+/- 2
[1.5 (5) +8] +/- 2 = [13.5 – 17.5]
pCO2 = 10, therefore it IS a respiratory alkalosis
Six Steps for Acid-Base Analysis
Step 6: Are there any other metabolic disturbances?Corrected HCO3
- = (Measured HCO3
-) + (AG-12)
(5) + (19-12) = 12Since this does not correct bicarbonate back to normal, there is a non anion gap acidosis
Causes of non anion gap acidosis with hypokalemia
• Diarrhea• Ureteral diversion• Renal tubular acidosis
– Proximal– Distal
• Mineralcorticoid deficiency
• Carbonic anydrase inhibitor– Acetazolamide– Mefenamic acid
• Post hypocapneic state
Causes of non anion gap acidosis with hyperkalemia
• Early renal failure• Renal disease
– SLE interstitial nephritis
– Amyloidosis– Hydronephrosis– Sickle cell
nephropathy
• Acidifying agents– Ammonium chloride– Calcium chloride– Arginine
• Sulfur toxicity
Problem #2
• 42 yo female has the flu for four days with incessant vomiting. She presents to the ED two days after stopping insulin due to no food intake
• Na+ 130 Cl- 80 HCO3- 10
• pH 7.21 pCO2 25
Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Acidemia
Six Steps for Acid-Base Analysis
Step 2. Is the primary process metabolicor respiratory?
pCO2 = 25 should drive pH ↑HCO3
- = 10 should drive pH ↓
Six Steps for Acid-Base Analysis
Step 3: If the primary process is respiratory, is it acute or chronic?
Skip this step as primary process is metabolic!
Six Steps for Acid-Base Analysis
Step 4: Is there an anion gap?
Na+ - Cl- - HCO3- > 12?
130 - 80 - 10 = 40!!Anion Gap Metabolic Acidosis
Six Steps for Acid-Base Analysis
Step 5: Is the respiratory compensation adequate?Expected pCO2 range =[1.5(measured HCO3
-)]+8+/- 2
[1.5 (10) +8] +/- 2 = [21 - 25]pCO2 = 25, therefore this is normal respiratory compensation
Six Steps for Acid-Base Analysis
Step 6: Are there any other metabolic disturbances?Corrected HCO3
- = (Measured HCO3
-) + (AG-12)
(10) + (40-12) = 38Since this over corrects bicarbonate there is a metabolic ALKALOSIS!!
Problem #3
• 30 year old female BMT patient with neutropenic fever has been receiving multiple antibiotics including amphotericin B. You are called to the bedside for her fevers, rigors, and dyspnea
• Na+ 125 Cl- 100 HCO3- 8
• pH 7.07 pCO2 28 K+ 2.5
Six Steps for Acid-Base Analysis
Step 1. Is there an acidemia or alkalemia?
Acidemia
Six Steps for Acid-Base Analysis
Step 2. Is the primary process metabolicor respiratory?
pCO2 = 28 should drive pH ↑HCO3
- = 8 should drive pH ↓
Six Steps for Acid-Base Analysis
Step 3: If the primary process is respiratory, is it acute or chronic?
Skip this step as primary process is metabolic!
Six Steps for Acid-Base Analysis
Step 4: Is there an anion gap?
Na+ - Cl- - HCO3- > 12?
125 - 100 - 8 = 17Anion Gap Metabolic Acidosis
Six Steps for Acid-Base Analysis
Step 5: Is the respiratory compensation adequate?Expected pCO2 range =[1.5(measured HCO3
-)]+8+/- 2
[1.5 (8) +8] +/- 2 = [18-22]pCO2 = 28, therefore this is a respiratory acidosis even though the value is below 40!!
Six Steps for Acid-Base Analysis
Step 6: Are there any other metabolic disturbances?Corrected HCO3
- = (Measured HCO3
-) + (AG-12)
(8) + (17-12) = 13Since this is below the normal range after correction, there is a non anion gap acidosis
If data doesn’t make sense, check the validity of your data!
24 (pCO2)/(HCO3-) = [H+]
80 – [H+] = xx
xx should equal the last two digitsof the pH. 7.xx
brow2110@umn.edu
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