A 70 kg patient with septic shock has received 4 L of 0.9% normal saline resuscitation in 6 hours and remains oliguric with worsening metabolic acidosis. Serum chloride is 120 mEq/L. What is the likely acid-base diagnosis and preferred resuscitation fluid?
- A Hyperchloremic metabolic acidosis from 0.9% saline; switch to a balanced crystalloid (Ringer's lactate or Plasma-Lyte) ✓
- B Lactic acidosis from persistent hypoperfusion; continue 0.9% normal saline with bicarbonate supplementation
- C Respiratory alkalosis from mechanical ventilation; reduce tidal volume
- D Anion gap metabolic acidosis from acute renal failure; initiate renal replacement therapy
Explanation
Large-volume 0.9% normal saline (154 mEq/L chloride) causes hyperchloremic non-anion gap metabolic acidosis due to excess chloride causing relative bicarbonate displacement (Stewart's physicochemical model: high strong ion difference decreases pH). The SMART and SALT-ED trials demonstrated that balanced crystalloids (Ringer's lactate, Plasma-Lyte) reduced the composite outcome of major adverse kidney events (MAKE30) compared to 0.9% saline in critically ill adults. Current guidelines (ESICM, SCCM) recommend balanced crystalloids as first-line resuscitation fluids for septic shock, reserving 0.9% saline for specific indications like hyperkalemia or traumatic brain injury where lactate metabolism may be an issue.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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