Letter to the editor: Intermittent high-efficiency hemodialysis remains preferable to CKRT in late ethylene glycol poisoning

Prashek and colleagues present a patient who underwent continuous kidney replacement therapy (CKRT) for removal of ethylene glycol [1]. We commend the authors for publishing such cases due to the scarcity of reports with CKRT, but express caution about the interpretation of many of their observations, calculations, and conclusions. The authors claim that “CVVHDF can effectively remove ethylene glycol with an extraction that is comparable to IHD”. This assumption is based on their calculation of an ethylene glycol half-life of 2.81 h during CVVHDF being comparable to other published cases in which intermittent hemodialysis was used. This ssertion is erroneous as the first ethylene glycol measurement used in their calculation was performed prior to the initiation of both CVVHDF and fomepizole therapy. Using the last 2 data points, we calculated the ethylene glycol half-life as 5.8 h which is in keeping with other cases in which CKRT was performed [2– 4]. This is double the ethylene glycol half-life achieved during high-efficiency intermittent hemodialysis (<3 h) [5]. Further evidence of the inferior performance of CKRT compared to intermittent hemodialysis is the maximum achievable clearance: clearance of solutes is limited by the lesser of either blood or effluent flow. In the present case, CVVHDF was performed with a blood flow = 200 mL/min and an effluent flow = 84 mL/min. Ethylene glycol clearance could therefore not exceed 84 mL/min which again is well under what can be achieved by intermittent hemodialysis (>200 mL/min). Finally, since the patient did not require net ultrafiltration for volume overload, it is unclear why the patient would tolerate CKRT better than intermittent hemodialysis. We agree that if CKRT is the only option available onsite, then it is preferable to use it instead of transferring the patient to a center that offers intermittent hemodialysis. However, when both options are available, we advocate for using the one that can maximize clearance, especially when a patient has evidence of extensive end-organ damage and accumulation of toxic metabolites. We encourage authors and journals to promote increased reliability of cases reporting poison removal during extracorporeal treatment, including more than 2 time points for half-life calculations and regular sampling of effluent and outflow blood concentration [6].