ESPN 53rd Annual Meeting

ESPN 2021


 
A kinetics based algorithm to treat acute neonatal hyperammonemia
SNAUWAERT EVELIEN 1 DERUDDER JONATHAN 1 VERLOO PATRICK 1 DHONT EVELYN 1 RAES ANN 1 VAN BIESEN WIM 1 ELOOT SUNNY 1

1- GHENT UNIVERSITY HOSPITAL
 
Introduction:

Acute neonatal hyperammonemia is associated with poor neurological outcomes and high mortality, in which decrease in serum ammonia is crucial. We developed, based on kinetic modeling, a widely applicable algorithm to treat acute neonatal hyperammonemia.

Material and methods:

4 hyperammonemic patients (3.24±0.40 kg) underwent 13 hemodialyses, i.e. 5 with the 4008 and FXPaed dialyzer (Fresenius Medical Care, Germany), and 8 with the CarpeDiem (Medtronic, USA) of which 4 with the 0.15m² and 4 with the 0.25m² dialyzer. Blood flows QB were 22-35mL/min. Dialyzer clearance and extraction ratio were derived from the measured ammonia time-concentration curves during dialysis. Ammonia was hereby assumed being distributed in the patient in a single compartment, equal to patient’s total body water. Time-concentration profiles were simulated for different start concentrations, patient weight, dialysis machines/dialyzers and different dialysis settings. To make the model widely beneficial, an algorithm was drawn to guide clinicians.

Results:

Extraction ratios were 38±5% (4008/FXPaed), 10±3%-13±3%(CarpeDiem/0.15-0.25m²). For a start concentration of e.g. 3000µmol/L in a 3kg patient, time to reach 400µmol/L was 315min (QB30) and 190min (QB50) with 4008/FXPaed. The CarpeDiem machine could not decrease ammonia concentrations below 400µmol/L within 4h for start concentrations >800µmol/L. Simulations with CarpeDiem or 5kg patient resulted in longer time intervals. Our institution-specific protocol therefore prescribes 4008/FXPaed for start concentrations >400µmol/L. To calculate the time needed to decrease start ammonia concentration Cstart to target Ctarget, the following algorithm can be used: from patient’s total body water (V) (Wells formula) and dialyzer clearance (K) (by single measurement of ammonia at dialyzer inlet and outlet), time (T) to target T=(-V/K)∙LN(Ctarget/ Cstart).

Conclusions:

 By implementing these formulae in a simple spreadsheet, medical staff can draw its institution-specific flowchart for patient-tailored treatment of hyperammonemia. Due to some made assumptions in kinetics, our own institution-specific protocol will be applied and studied in a prospective study to validate the present results.