DISCUSSION
PD, renal failure, blood transfusions, intravascular hypovolemia
RENAL FAILURE, EVENT, HEMODYNAMIC INSTABILITY
Our data showed that the UF rate the NIDUS delivered was closer to the prescribed value than for CVVH or PD. It also suggested that the achieved UF displayed by the NIDUS was a more reliable reflection of the true UF than was the case for the CVVH devices, although this subgroup analysis may have been potentially influenced by some outliers. This is important because even relatively small imprecisions of UF control may cause relative intravascular hypovolemia in infants; nearly a quarter of infants of 2.5 to 5 kg treated with the CARPEDIEM, a conventional CVVH device which has been miniaturized especially for small body size, required volume replacement for hemodynamic instability (These UF results are in concordance with previous clinical compassionate use of NIDUS, as well as animal and in vitro testing (The precision of UF and the rates of biochemical clearance support the view that NIDUS is worth pursuing through regulatory procedures as it has a potential place alongside established RRT modalities, particularly for the smallest of infants, which were the original focus for its development.The survival data reflect the high mortality associated with the underlying clinical diagnoses, but its interpretation is complicated by potential differences in the patients receiving RRT by the different modalities. Although overall mortality was higher in the intervention group, estimates of mortality were smallest for PD and largest for CVVH, with NIDUS in between. These data raise questions about the relative thresholds for starting PD compared with CVVH and NIDUS, and the distribution of complex and unwell babies between these groups. The Pediatric Index of Mortality 3 (PIM3) scores (PIM scoring system based on data collected on admission to PICU) in these groups had medians (quartiles) of 0.02 (0.01–0.05) (PD), 0.027 (0.014–0.131) (NIDUS), and 0.06 (0.01–0.20) (CVVH), although the study was not able to draw any firm conclusions from these statistics (eTable 2Babies who are unwell or postsurgical may require blood transfusions for several reasons. Few babies on PD required blood transfusion, but rates were much higher in babies treated with CVVH and NIDUS, which may be partly related to increased blood sampling. We recorded the event and not the volume of blood transfusion. The high rate of transfusion required in the NIDUS group was unexpected compared with clinical experience of NIDUS in the previous pilot study (NIDUS has an acceptable safety profile compared with other modalities used in this critically unwell population. There were AEs reported in both control subgroups and in intervention cases. There were problems related to the NIDUS disposable components and filters, which were addressed and rectified by the manufacturers to complete the study. In the NIDUS group, 60% required an unanticipated filter change compared with 43% on CVVH. These data support the need to redesign the geometry of the filter to reduce its flow resistance while maintaining its membrane surface area and priming volume.PD is likely to remain a commonly used method for babies with less severe renal failure who require less intensive dialysis. Many postoperative babies (especially those undergoing cardiac surgery) have a PD catheter inserted during surgery, which is sometimes just used for draining ascitic fluid and can be easily used for dialysis as required. However, insertion of a PD catheter is not without its risks, and there is need for future studies questioning the best immediate postoperative renal support modality.The I-KID study had high input from public and parents at all stages, from the early development phase onward, and this has been crucial in ensuring acceptability to participant parents. Importantly, most parents who responded to our questionnaire indicated they felt it was acceptable to be approached about taking part in research despite the circumstances. This is important for future research studies in critical care. User feedback on NIDUS from I-KID has provided vital information on problems encountered and usability, which require addressing.