Author: V. Dimov, M.D.
Reviewer: S. Randhawa, M.D.
A 71-year-old African American male (AAM) is admitted to the hospital with the chief complaint of shortness of breath (SOB) which has had become progressively worse during the last 4-5 days.
He also has had diarrhea for one week. He has had cough productive yellow, blood-tinged sputum, night sweats and urge urinary incontinence for 3 days. He reports no fever or chills. The patient took Imodium (loperamide) over-the-counter (OTC) which helped the diarrhea.
Past medical history (PMH)
Hypertension (HTN), chronic obstructive pulmonary disease (COPD) on home O2 3 L/min, inoperable renal cancer, prostate cancer (had surgery 8 years ago).
The report of a previously done CT scan of the abdomen.
Combivent (ipratropium bromide and albuterol sulfate), Cartia XT (diltiazem), Lupron (leuprolide acetate injection), since the surgery for prostate cancer, home O2 3 L/min.
Social history (SH)
Smoker (100 pck-yrs), no EtOH or drugs. Lives with his family.
What is the most likely diagnosis at this point?
AECB (acute exacerbation of chronic bronchitis).
TB (he never had a PPD test).
Lung cancer -- certainly a possibility. Also, he may have an obstructive pneumonia.
Clostridium difficile colitis, although he was not hospitalized or on antibiotic therapy recently.
What is the most likely etiology of his pneumonia?
Remember the SLIM CV mnemonic:
Legionella -- it often causes diarrhea, more common in the elderly.
Influenzae -- Hemophilus
What would you like to do first?
Obtain vital signs and examine the patient.
A thin man in moderate distress. The weight is only 35 kg (5 ft tall). The patient was gradually losing weight according to his family.
SpO2 94% on 4L.
What is your assessment at this point, from the vital signs?
Tachycardia and tachypnea. BP is not well controlled. He is mildly hypoxic but this may be his baseline due to advanced COPD. He is also on home O2.
The rest of the physical examination
Chest: (B) wheezing, right-sided crackles and dullness to percussion.
CVS: Clear S1 S2.
Abdomen: cachectic, +BS, NT, ND.
Extremities: no edema, clubbing or cyanosis.
What would you do next?
What would you like to do first?
ABG, it is quick and may help you reach the correct diagnosis.
Does he need to go to the intensive care unit?
ABG: 7.25-31-62-13-SpO2 91% on 4L of O2.
Are you surprised? Why does he have metabolic acidosis?
Is PaCO2 a little low for a patient with advanced COPD?
It certainly is.
Let's discuss the ABG results systematically, step-by-step. You have to find the answer to 6 questions remembered by the mnemonic ARMADA:
Acidosis or Alkalosis?
Respiratory or Metabolic?
These are the answers:
But expected PaCO2 for this pH is 27.5, so there is some PaCO2 retention, i.e. respiratory acidosis which is not unexpected in somebody with COPD.
Anion gap (AG) = 16 (you need BMP to calculate AG).
Delta AG is 4, so there is a preexistent non-anion gap metabolic acidosis due to the diarrhea.
There are 3 disorders on this ABG: high anion gap metabolic acidosis, respiratory acidosis and initial non-AG acidosis.
What are the causes of this complex acid-base balance disorder?
There are only so many causes of high AG acidosis remembered by the mnemonic MUD PILES.
Let's get a BMP:
BUN 79 mg/dL, creatinine (Cr) 5.1 mg/dL.
Potassium (K+) 5.5 mEq/L is not high in this example of acute renal failure due to the diarrhea, secondary to the potassium loss with the multiple bowel movements.
What is his baseline renal function?
You always have to ask this question.
The creatinine (Cr) was 2.7 mg/dL just two months ago.
A previous CXR (6 months ago), left. Right-sided pneumonia, right. CXR report.
A previous lateral CXR, left. Current lateral CXR, right. CXR report.
What else would you order?
WBC is 8.6 only but the PMN are 91%. It could be just early in the course of his pneumonia.
Urinalysis (UA) showed proteinuria, blood and Trichomonas (it is never "too late" for sexual activity in this "Viagra day and age").
The patient was started on the "pneumonia protocol" with cefotaxime and azithromycin.
Blood cultures (BCx x 2), sputum culture and urine Legionella antigen were done.
Intravenous fluids (IVF) were started for his acute renal insufficiency (ARI).
He felt better soon after the admission and the treatment/work-up continued.
Metabolic acidosis due to acute renal insufficiency (ARI) (no ketones on UA, lactic acid level was 2.2).
Acute renal insufficiency (ARI) due to fluid loss and hypovolemia.
Trichomoniasis (Flagyl 2 gm PO x 1 was given).
The patient became hypoxic overnight and was transferred to ICU where he was placed on non-invasive ventilation with BiPAP. The rest of treatment was continued along with the work-up for his ARI. His condition soon improved, he was transferred back to a regular nursing floor and was evaluated by physical therapy (PT) for discharge disposition.
What did we learn from this case?
Think broad -- one diagnosis is often not enough. Everybody recognized the pneumonia but what about the metabolic acidosis and the acute renal insufficiency (ARI)?
And finally, there is one last mnemonic for differential diagnosis (DDx) of weight loss - WEIGHT:
Westergreen (ESR) elevation due to CTD.
Endocrine, for example new or uncontrolled diabetes.
Head, e.g. depression
Tumor, e.g. cancer
Top 10 Clinical Pearls in Acid-base Disorders. Resident and Staff Physician, Jan 2007.
Acid-base Balance Cases and Calculators. Clinical Cases and Images - Blog, Feb 2007.
Acid-base balance from Oxford handbook of clinical medicine By Murray Longmore, Ian B. Wilkinson, Supraj R. Rajagopalan: