Intravesical monitoring of intra‐abdominal pressure after renal transplantation in children: A safety and feasibility study

IAH after RTX can threaten graft viability. This study aimed to assess the feasibility and safety of longitudinal IAP measurements as an IAH screening method in children after RTX. A cohort of eight children with a mean ± SD [range] age 9.6 ± 6.2 [2‐17] years who underwent RTX and 18 control patients were evaluated between May 2017 and February 2018. We compared longitudinal IAP measurements using a Foley manometer to other clinical monitoring data. In total, 29 IAP measurements were performed in RTX patients and 121 in controls. The mean post‐operative IAP was 7.4 ± 4.3 [1‐16] mm Hg following RTX and 8.1 ± 3.7 [1‐19] mm Hg in controls. We noted IAH in 9 (31%) of 29 IAP measurements after RTX and in 41 (34%) of 121 IAP measurements in controls. No graft dysfunction occurred in RTX patients despite elevated IAP values. The mean ± SD [range] time expenditure for IAP measurement was 2.1 ± 0.4 [0.6‐3.2] minutes. No severe complications occurred during the IAP measurements. Analysis of longitudinal IAP measurements demonstrated that IAP measurement is safe and feasible in children recovering from renal transplantation in the PICU.

We noted IAH in 9 (31%) of 29 IAP measurements after RTX  to produce high IAP and graft dysfunction as part of the renal allograft compartment syndrome. [8][9][10][11] Both, IAH and abdominal compartment syndrome, are also associated with higher mortality. 10 In 2013, the WSACS published consensus guidelines to standardize definitions and management of IAH. In children, IAH is defined as an IAP ≥ 10 mm Hg. 7 IAH affects 15%-45% of the PICU patients. 12,13 Studies in adults suggest the IAH be independently associated with acute renal failure. [14][15][16] There is still a lack of studies about the effects of abnormal IAP, especially after transplantation in children. Increased intra-abdominal pressure can develop not only immediately after intraoperative abdominal wall closure, but also in the further post-operative course after major abdominal surgery. As a very rare complication an abdominal compartment syndrome including renal allograft compartment syndrome can lead to very severe complications including graft loss. Other scientists have therefore suggested further use of monitoring the IAP to prevent its devastating consequences. 8,9 This study aimed to analyze longitudinal IAP measurements in children who underwent RTX. IAP values were compared with other standards of monitoring graft viability, including laboratory and clinical parameters.

| Subjects
This retrospective single-center study was legitimated by the local medical statue (details for blinding omitted), and written informed consent was waived. All examinations were conducted according to the Declaration of Helsinki. We extracted data, including patient demographics, peri-operative findings, complications, and outcomes from the renal transplant database and surgery, anesthesia, and PICU records.

| IAP measurement
According to WSACS's recommendations, 7 we measured IAP intravesical. We used a hydrostatic manometer, the UnoMeter™ AbdoPressure™ IAP Monitoring System (Unomedical, ConvaTec™,) connected to a Foley catheter (Uromed™ Prosil, Kurt Drews KG) as described before. 17 Patients were in a completely supine position at end-expiration during the IAP measurements that were performed in the PICU until discharge. The IAP monitoring device was removed in cases of severe Foley catheter leakage or oliguria for more than 6 hours. In all patients, urine cultures were obtained at least every 7 days. In a random sample of ten IAP measurements, we took the time required for the IAP measurement.

| Statistical analysis
For qualitative data, counts and percentages were calculated. For quantitative data, means and SDs were calculated. We used a t test to compare data between RTX patients and controls. We used a multiple linear mixed model to investigate the potential association of diuresis, volume balance, creatinine, and IAP. All analyses were performed in SPSS 23 for Mac (IBM SPSS Statistics, IBM Corporation), GraphPad Prism V6.0c (GraphPad Software), and R version 3.5.2 (R Core Team). A P value < .05 was considered statistically significant.

| Patients
We included eight pediatric patients who underwent RTX between May 26, 2017, and February 5, 2018, at our center in this study and 18 patients who were treated post-operatively at the PICU for various reasons as controls. Table 1

| IAP
The mean number of IAP pressure measurements performed per patient during the post-operative period ± SD (range) for the eight patients after renal transplantation was 3.6 ± 1.7 (1-6), constituting a total of 29 IAP measurements whereas in the 18 control patients 6.7 ± 5.7 (2-22) measurements were performed, constituting a total of 121 IAP measurements (Figure 1). Nurses spent a mean ± SD (range) of 1.9 ± 0.4 (0.5-3.2) minutes measuring IAP. No complications of IAP measurements occurred, and all urine cultures were negative.

| D ISCUSS I ON
We report on longitudinal measurements of IAP in children following RTX as a tool to screen for intra-abdominal hypertension. Avoiding elevated IAP is considered to be a critical element in the successful surgical management of abdominal surgery and especially of transplantation in children because impairment of blood supply due to IAH can impair graft function of kidney or other organs. [8][9][10][11]17 Already in the past century, Harman et al described the influence of IAP on renal blood flow and GFR in anesthetized dogs: At 20 mm Hg, IAP renal blood flow and GFR decreased to less than 25% of normal and renal vascular resistance increased 555%. 18 Whether the impairment of renal function is caused by parenchymal compression, renal vein pressure or other pathophysiological pathways remains unclear. 10,19 We did not observe any side effects of manometric intravesical IAP measurement, and the time expended to perform the additional measurements was low. Post-operative IAP measurements were similar in patients after renal transplantation and controls ( Figure 1).
However, we observed a relatively high prevalence of IAH episodes in our cohort of RTX patients (31%). In the group of control patients, we observed the occurrence of IAH with a similar frequency (34%). This prevalence is consistent with previous reports in PICU patients. 12,13 In contrast to data in adults, we did not detect a significant effect of IAP on diuresis, fluid balance, or kidney function. [14][15][16] In our cohort of chil-

| Limitations
1. The study design was retrospective and, therefore, subject to potential selection bias.
2. Data were acquired in only a small group of patients.

IAP [mmHg]
assessment that can be performed easily and quickly in children recovering from renal transplantation. The effort to measure intra-abdominal pressure is low and, given the potential advantage of early detection of intra-abdominal compartment syndrome, IAP monitoring may be a useful addition to post-operative monitoring of children after renal transplantation. More studies are needed to determine whether routine post-operative IAP monitoring can improve the quality of post-operative management in children after renal transplantation.

ACK N OWLED G M ENT
The authors thank the entire PICU team for supporting the study.

CO N FLI C T O F I NTE R E S T
There is no conflict of interest.