Kidney Week

Abstract: FR-PO651

Volume of Distribution in a Severely Underweight Female Is Better Approximated by Ideal Body Weight Than Actual Body Weight

Session Information

• Trainee Case Reports - IV
  October 26, 2018 | Location: Exhibit Hall, San Diego Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Trainee Case Reports

• 701 Dialysis: Hemodialysis and Frequent Dialysis

Authors

• Griffin, Benjamin, University of Colorado, Aurora, Colorado, United States

Benjamin Griffin,

• Teixeira, Joao Pedro, University of Colorado, Aurora, Colorado, United States

Joao Pedro Teixeira,

• Ambruso, Sophia L., University of Colorado, Aurora, Colorado, United States

Sophia L. Ambruso,

• Linas, Stuart L., University of Colorado, Aurora, Colorado, United States

Stuart L. Linas,

• Dylewski, James F., University of Colorado Hospital, Aurora, Colorado, United States

James F. Dylewski,

Introduction

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 BMI, as to whether actual, adjusted, or ideal body weight (IBW) should be used in these dose calculations.

Case Description

The patient is a 50 year-old woman with a history of anorexia who was admitted with altered mental status. Initial vital signs were significant for weight of 27 kg, BMI 10.1 kg/m2, and BP 70/34 mmHg. Labs showed lactate 21 mg/dL, bicarbonate (HCO₃^-) 2 mmol/L, and creatinine 2.1 mg/dL. Arterial blood gas (ABG) showed an initial pH 6.55, PCO₂ 32 mmHg, and calculated HCO₃^- 3 mg/dL. Protocolized sepsis management was initiated, and she was intubated. Shortly thereafter, she became anuric and was initiated on CRRT. The initial dialysate dose, prescribed using actual weight, was 800 ml/hr. Labs 2 hours later revealed pH 6.84, pCO₂ 10 mmHg, and calculated HCO₃^- 3 mg/dL. The dialysate dose, recalculated using her IBW of 58 kg, was increased to 1750 ml/hr. Six hours later, pH was 6.83 with calculated HCO₃^- 3 mg/dL. Lactate remained elevated at 20 mg/dL. Her CRRT prescription was changed to 1500 mL/hr of dialysate with 250 mL/hr of post-filter concentrated bicarbonate solution (6 ampules in 1 L of water or 300 mEq/L of sodium bicarbonate). After 4 hours, pH was 7.39, pCO₂ was 15 mmHg, and measured serum HCO₃^- was 9 mg/dL. Sodium had risen from 143 to 147 mmol/L. Notably, lactate remained elevated at 18 mg/dL. When using appropriate formulas to estimate the expected rate of change in sodium and bicarbonate and comparing to the observed changes, the effective volumes of distribution were those of a typical patient with a weight in the range of 55 – 70 kg, in line with her IBW. Ultimately the patient was found to be surreptitiously taking metformin (later confirmed with serum testing). Her acidosis resolved with 48 hours of CRRT and she was transferred to the floor the next day.

Discussion

This case illustrates the challenges of dosing CRRT in severely underweight patients and suggests that IBW, rather than actual body weight, gives a better approximation of the volumes of distribution of sodium or bicarbonate and therefore may be more appropriate for dosing of CRRT.