Asthma and COPD Q 56

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A nurse is caring for a client with renal failure. Blood gas results indicate a pH of 7.30; a PCO2 of 32 mm Hg, and a bicarbonate concentration of 20 mEq/L. The nurse has determined that the client is experiencing metabolic acidosis. Which of the following laboratory values would the nurse expect to note?

  

     A. Sodium level of 145 mEq/L

     B. Magnesium level of 2.0 mg/dL

     C. Potassium level of 5.2 mEq/L

     D. Phosphorus level of 4.0 mg/dL

    

    

Correct Answer: C. Potassium level of 5.2 mEq/L

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Clinical manifestations of metabolic acidosis include hyperpnea with Kussmaul’s respirations; headache; N/V, and diarrhea; fruity-smelling breath resulting from improper fat metabolism; CNS depression, including mental dullness, drowsiness, stupor, and coma; twitching, and coma. Hyperkalemia will occur. Hyperkalemia decreases proximal tubule ammonia generation and collects duct ammonia transport, leading to impaired ammonia excretion that causes metabolic acidosis.

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Option A: The sodium level in this choice is normal. Metabolic acidosis occurs when a relative accumulation of plasma anions in excess of cations reduces plasma pH. Replacement of sodium bicarbonate to patients with sodium bicarbonate loss due to diarrhea or renal proximal tubular acidosis is useful, but there is no definite evidence that sodium bicarbonate administration to patients with acute metabolic acidosis, including diabetic ketoacidosis, lactic acidosis, septic shock, intraoperative metabolic acidosis, or cardiac arrest, is beneficial regarding clinical outcomes or mortality rate.

Option B: Chronic metabolic acidosis results in renal magnesium wasting, whereas chronic metabolic alkalosis is known to exert the reverse effect. Chronic metabolic acidosis decreases renal TRPM6 expression in the DCT, increases magnesium excretion, and decreases serum magnesium concentration, whereas chronic metabolic alkalosis results in the exact opposite effects.

Option D: Phosphorus excretion helps with the disposal of the acid, although, unlike ammonia secretion that can increase several folds with acidosis, phosphorus excretion rate does not change much and therefore its contribution to acid/base homeostasis is limited. Occasionally, loss of bicarbonate from the gastrointestinal tract due to diarrhea or ingestion of acid from endogenous or exogenous sources can be the cause of metabolic acidosis.

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