Differential Diagnosis for Acid-Base Disorder in a 22-Month-Old Boy
Single Most Likely Diagnosis
- D) Stool losses of bicarbonate: The patient has had a high frequency of diarrheal stools (12 to 15 per day) for 3 days, which is a significant clue pointing towards stool losses of bicarbonate as the cause of his acid-base disorder. Diarrhea leads to the loss of bicarbonate ions, resulting in metabolic acidosis, which is consistent with the patient's low serum bicarbonate level (4.8 mEq/L) and low urine pH.
Other Likely Diagnoses
- B) Renal losses of bicarbonate: Although less likely given the clinical context, renal losses of bicarbonate (e.g., due to renal tubular acidosis) could also lead to metabolic acidosis. However, the primary presentation of diarrhea points more strongly towards gastrointestinal losses.
- E) Vomiting: Vomiting typically leads to metabolic alkalosis due to the loss of hydrogen ions, but it can also lead to a complex acid-base disorder if there is significant loss of bicarbonate-rich fluids. However, the patient's symptoms and laboratory results do not strongly support vomiting as the primary cause of his acid-base disorder.
Do Not Miss Diagnoses
- A) Laboratory error: Although unlikely, laboratory errors can occur and should be considered, especially if the results do not match the clinical picture. It's crucial to verify laboratory results, especially in critical situations.
- C) Respiratory insufficiency: While the patient has tachypnea (32/min), the arterial blood gas analysis shows a pH of 7.28 with a PCO2 of 30 mm Hg, indicating respiratory alkalosis rather than insufficiency. However, any condition affecting respiratory function could potentially lead to a life-threatening situation and should be considered.
Rare Diagnoses
- Other causes of metabolic acidosis: Rare conditions such as lactic acidosis, ketoacidosis, or ingestion of toxic substances could also lead to metabolic acidosis. These would be less likely given the clinical context but should be considered if the patient's condition does not improve with treatment of the presumed cause or if there are additional suggestive symptoms or signs.