Continuous Renal Replacement Therapy Dosing in the Severely Underweight: A Case Report

Abstract Guidelines recommend that patients treated with continuous renal replacement therapy (CRRT) be delivered an effluent dose of 20-25 mL/kg/hr. There is debate, especially at the extremes of body mass index, as to whether actual or ideal body weight (IBW) should be used in these dose calculations. A middle-aged woman with severe anorexia presented with 48 hours of altered mental status. Labs showed severe metabolic acidosis necessitating intubation, which was ultimately found to be due to non-prescribed use of metformin for weight loss. The patient became anuric and was initiated on continuous venovenous hemodialysis. Due to refractory acidosis, the modality was converted to continuous venovenous hemodiafiltration by adding post-filter hypertonic bicarbonate solution. Based on changes in sodium and bicarbonate over 4 hours with hypertonic bicarbonate, we were able to calculate an “effective” volume of distribution for this severely underweight patient. Our calculations suggest that IBW gives a better approximation of “effective” volume of distribution than actual body weight in a severely underweight woman. Inadequate effluent flow rate calculated based on actual rather than ideal body weight may lead to insufficient correction of metabolic derangements in extremely underweight patients.