Targeted control of blood pressure in paediatric renal transplant

Dolan, N, Schmacher, K, Brierley, J, Marks, S
Nephrology Department, Great Ormond Street Hospital for Children
INTRODUCTION: In our renal transplant population, 53% of children are hypertensive
(defined as systolic blood pressure (BP) greater than 95th centile for age, sex and height
centile and/or are on any anti-hypertensive medication). Standard medications to normalise
blood pressure in children predominantly work by either reducing cardiac output (CO) or
systemic vascular resistance (SVR).
AIM: To determine the non-invasive measurement of CO and cardiac index (CI) in renal
transplant recipients (RTR) which may give information for future studies regarding the
choice of antihypertensive treatment to improve BP control.
METHODS: Children attending the paediatric renal transplant clinic were screened from
July to October 2009. Cardiac output was measured transcutaneously using a continuous
wave Doppler ultrasound probe (USCOM Limited, Australia), at the suprasternal notch. A
pilot study was initially undertaken to ensure that there was minimal intra-observer bias.
Three readings were taken on each patient and all were performed by the same investigator
who had been trained in its use.
RESULTS: Thirty (16 females [53%]) paediatric RTR aged 6.9 to 17.3 (median 13.6) years
were investigated during the study period. Two-thirds (20) of RTR were not pre-emptive so
had received renal replacement therapy with peritoneal and/or haemodialysis. The follow-up
time since renal transplantation was 1 - 148 (median 39.5) months. The estimated glomerular
filtration rate was 22 - 74 (median 46) mls/min/1.73m2. Sixteen (53%) patients were on 1 - 4
(median 1) antihypertensive medications during this study period with seven (23%) on at least
two medications (calcium channel blockers [14], beta-blockers [4], ACE inhibitors [3],
diuretics [2], vasodilators [2] and alpha blockers [1]). The systolic BP centiles (for age, sex
and height centiles) were 25th - >95th (median 75th) centile. Of three patients whose systolic
BP were above the 95th centile, two were already receiving antihypertensive therapy; one
patient (relapsed focal and segmental glomerulosclerosis post renal transplant and clinically
nephrotic) was receiving an ACEi, a diuretic and a calcium channel blocker, the other was
receiving a calcium channel blocker. The third patient in this group had normal BP readings
on subsequent visits and did not require medical therapy. The cardiac output and cardiac
index measured for these RTR were 2.5 - 6.8 (median 4.5; normal 4 - 6) litres/minute and 2.0
- 4.5 (median 3.3; normal 2.5 - 4.2) litres/min/m2 respectively.
CONCLUSION: CO and CI were within low-normal limits in our cohort of RTR with lownormal CO suggesting elevated SVR. Antihypertensive therapy should therefore be targeted
to reduce SVR in these patients. Non-invasive measurement of CO is simple to perform and
may be a useful tool for more targeted BP management.