Case Studies In Acid Base Disorders

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


Step 1. Is there an acidemia or alkalemia?


Step 2. Is the primary process metabolicor respiratory?


Step 3: If the primary process is respiratory, is it acute or chronic?


Step 4: Is there an anion gap?

Na+ - Cl- - HCO3- > 12?


Step 5: Is the respiratory compensation adequate?

Expected pCO2 range =[1.5(measured HCO3

-)]+8+/- 2


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



Acidemia



pCO2 = 10 should drive pH ↑HCO3

- = 5 should drive pH ↓



Skip this step as primary process is metabolic!



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


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


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



Acidemia



Na+ - Cl- - HCO3- > 12?

130 - 80 - 10 = 40!!Anion Gap Metabolic Acidosis



-)]+8+/- 2

[1.5 (10) +8] +/- 2 = [21 - 25]pCO2 = 25, therefore this is normal respiratory compensation



- = (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



Acidemia



Na+ - Cl- - HCO3- > 12?

125 - 100 - 8 = 17Anion Gap Metabolic Acidosis



-)]+8+/- 2

[1.5 (8) +8] +/- 2 = [18-22]pCO2 = 28, therefore this is a respiratory acidosis even though the value is below 40!!



- = (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

[email protected]

Case Studies In Acid Base Disorders

Health & Medicine

Transcript of Case Studies In Acid Base Disorders