Acute-on-Chronic Salicylate Toxicity in a Patient with CKD

The 68 mg/dL level is important but cannot be interpreted with an acute-ingestion nomogram because this is acute-on-chronic exposure in a patient with CKD. Salicylate metabolism is capacity-limited: glycine conjugation and glucuronidation saturate at therapeutic-to-toxic doses, so elimination shifts toward zero-order and renal excretion becomes proportionally more important. Enteric-coated tablets dissolve slowly and can form concretions, producing delayed and erratic absorption; a level drawn 6 hours after the last dose may not be the peak. CKD reduces renal clearance of salicylic acid and its metabolites, and saturable protein binding means that a falling albumin or rising dose increases free drug. Acidemia increases the fraction of nonionized salicylate that enters the CNS, which explains confusion and tinnitus at a level that might be tolerated in an acute ingestion. The respiratory alkalosis is compensatory; if the patient is intubated and that drive is lost, PaCO2 rises, pH falls, and CNS penetration increases abruptly. High-risk features are altered mental status, vomiting, oliguria with creatinine 2.1, and a chronic level above 60 mg/dL. The concentration should be repeated, but management is driven by the clinical trajectory, acid-base status, renal function, and free-drug risk, not by a single number.

Alkalinization traps salicylate in the urine as the ionized salicylate anion, but it only works if the urine pH is high and there is urine flow. Give sodium bicarbonate 1-2 mEq/kg IV as an initial bolus, then an infusion of three ampoules (150 mEq) in 1 L of 5% dextrose at about 1.5-2 mL/kg/hour, titrated to a urine pH of 7.5-8.0. Check urine pH with each void or via catheter; in this oliguric patient catheterization may be needed. Target serum pH 7.45-7.55, not higher. Monitor potassium every 2-4 hours and replace aggressively because hypokalemia prevents urinary alkalinization; also monitor ionized calcium, sodium, glucose, and volume status. Pitfalls include pulmonary edema from sodium and fluid load, metabolic alkalemia, hypocalcemic tetany, hypernatremia, and failure to achieve alkalinization when urine output is low. Do not use acetazolamide, which acidifies the blood and can worsen CNS toxicity. If the patient cannot make urine or develops volume overload, stop pushing bicarbonate and move to hemodialysis. Avoid unnecessary intubation; if intubation is required, maintain high minute ventilation to preserve the respiratory alkalosis.

Hemodialysis is indicated here even though the level is below the traditional acute-ingestion threshold of 100 mg/dL. In chronic or acute-on-chronic salicylate poisoning, dialysis is considered at levels above 60 mg/dL, and this patient has 68 mg/dL plus altered mental status, vomiting, and oliguric CKD. The Extracorporeal Treatments in Poisoning criteria include altered mental status, new hypoxemia, renal insufficiency, refractory acidosis, and severe volume overload; this patient meets at least two. Dialysis removes salicylic acid, corrects acidosis, and removes fluid, whereas bicarbonate alone is unlikely to be sufficient with a creatinine of 2.1 and 40 mL of urine output. Use intermittent hemodialysis with a bicarbonate bath and monitor electrolytes, especially potassium and calcium. Continue until the salicylate concentration is below about 30 mg/dL, acidosis is corrected, and the patient is clinically improving. Because salicylate redistributes from tissue, check a level 2-4 hours after dialysis and repeat if it rebounds above 30 mg/dL or symptoms recur. Do not delay dialysis for a repeat level if the patient is deteriorating.