Case 7 A 62 year old woman with severe COPD comes to the ER complaining of increased cough and shortness of breath for the past 12 hours. There are no baseline ABGs to compare to, however, her HCO3- measured during a routine clinic visit 3 months ago was 34 mEq/L. ABG: pH 7.21 Chem 7: Na+ 135 pCO2 85 K+ 4.0 HCO3- 33 Cl- 90 HCO3- 34 pO2 47 Urine pH 5.5 1. What is the “predominant” acid-base disorder? Respiratory Acidosis. Given that she has a history of severe COPD, and an elevated HCO3- level in the past, at least part of the respiratory acidosis is probably chronic. 2. Is the degree of compensation appropriate? No. For a pCO2 of 85, we would expect the pH to be 7.40 – [0.03 x (85-40)] = 7.27. Therefore, since the pH is lower than expected, an additional acidosis must be present. 3. Is there another disorder present? Yes. This may be either a normal gap metabolic acidosis or an acute respiratory acidosis. It is impossible to tell which is present from the ABG alone, although the history strongly suggests the latter diagnosis. 4. What is the differential diagnosis? Most likely this patient is experiencing a COPD exacerbation, superimposed on her already poor pulmonary status. However, an acute respiratory acidosis, hypoxia, and a cough would all also be consistent with pneumonia.
Posted on: Sat, 08 Mar 2014 01:59:19 +0000
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