Before initiating dialysis, what ABG pattern would you typically expect in a patient with advanced kidney disease?

• A. Metabolic alkalosis with high bicarbonate
• B. Normal acid-base status
• C. Metabolic acidosis with low bicarbonate and low pH
• D. Respiratory acidosis with high CO2

Answer: (C)

Advanced kidney disease impairs the kidney’s ability to excrete acid and regenerate bicarbonate, leading to a net acid load and a bicarbonate deficit. This produces metabolic acidosis, so the arterial blood gas shows a low pH with a low bicarbonate level. The respiratory system often compensates by increasing ventilation, which lowers the CO2, so the overall ABG pattern is acidemia with reduced bicarbonate (and typically a compensatory, lower PCO2). This fits the situation in severe CKD and before dialysis. Other patterns don’t fit: metabolic alkalosis would require excess base or loss of acid; normal acid-base status isn’t typical with advanced kidney failure; respiratory acidosis with high CO2 points to a primary ventilatory problem rather than kidney-driven acid accumulation.