VARIATION IN BLOOD PRESSURE AS A GUIDE TO
VOLUME LOADING IN CHILDREN FOLLOWING
CARDIOPULMONARY BYPASS
Henry Tran
1
, Norbert Froese, MD, FRCPC
2
,
Guy Dumont
1
, Joanne Lim, MASc
2
and J. Mark
Ansermino, MBBCh, FFA(SA)
2
From the
1
Departments of Electrical & Computer Engineering,
The University of British Columbia, Vancouver, Canada V6H
3V4.;
2
Anesthesiology, Pharmacology & Therapeutics, The Uni-
versity of British Columbia, Room 1L7, 4480 Oak Street, Van-
couver, Canada V6H 3V4.
Received 23 June 2006. Accepted for publication 22 September
2006
Address correspondence to J. M. Ansermino, Department of
Pediatric Anesthesia, British Columbia Children
s Hospital, Room
1L7, 4480 Oak Street, Vancouver, Canada V6H 3V4
E-mail: anserminos@yahoo.ca
Henry T, Froese N,Dumont G, Lim J, Ansermino JM. Variation in
blood pressure as a guide to volume loading in children following
cardiopulmonary bypass.
J Clin Monit Comput 2007
ABSTRACT. Objective. Intravascular volume loading is used to
optimize cardiac output in children following weaning from
cardiopulmonary bypass. Central venous pressure (CVP) is
frequently used to titrate fluid administration but it is often
misleading in predicting fluid responsiveness. Variation in the
arterial pressure waveform is exaggerated in patients with
deficient intravascular volume and has been shown to be a good
predictor of fluid responsiveness in adults following cardiac
surgery. The aim of this study was to compare the measures of
variation in blood pressure as a guide to volume loading in
children following cardiopulmonary bypass. Methods. After
ethical approval, we collected continuous real-time measurements
from 25 children during volume loading after cardiopulmonary
bypass. Subjects with moderate or severe tricuspid
incompetence or who did not require volume loading during
weaning from cardiopulmonary bypass were excluded from the
study. Unstable readings were excluded from analysis. Systolic
Pressure Variation (SPV), Pulse Pressure Variation (PPV) and
Systolic Volume Variation (SVV) were retrospectively calculated
before and after each bolus of fluid. Fluid responsiveness was
classified as a change in blood pressure of ‡80 mmHg/L/
m
2
. Results. Forty-four boluses were analyzed from the 25
children. Respiratory variables were similar. CVP was a poor
predictor of fluid responsiveness and a negative relationship
between change in blood pressure and DDown was observed.
Performance in predicting fluid responsiveness as measured by the
areas under the ROC curves were CVP (0.58), PPV (0.67), SPV
(0.74) and SVV (0.74). Conclusions. Variation in blood
pressure was a better guide to volume loading in children than
CVP. Ddown was not useful in predicting fluid responsiveness in
children with open chests following bypass surgery. SPV and SVV
require further testing in prospective clinical trials.
KEY WORDS. systolic pressure variation–heart, left ventricular
preload)heart, central venous pressure–monitoring, hemodynamic–
mechanical ventilation
INTRODUCTION
Intravascular volume loading is used to optimize cardiac
output in children following weaning from cardiopul-
monary bypass. Optimizing the left ventricular end dia-
stolic volume, provides the best cardiac output without
volume overload. When blood volume is insufficient,
intravascular fluid administration augments venous return
and increases cardiac output. However, when blood
volume is excessive, fluid administration results in cardiac
distention and congestive heart failure. Predicting the
response to fluid administration is a significant clinical
Journal of Clinical Monitoring and Computing (2007) 21:1–6
DOI: 10.1007/s10877-006-9051-y
Springer 2006

challenge. Although central venous pressure (CVP) is
frequently used to titrate fluid administration, it is often
misleading in predicting fluid responsiveness [1].
The arterial blood pressure waveform varies over the
course of each respiratory cycle. This variation is caused
by respiration-related changes output of the left and right
ventricles. In patients with deficient intravascular volume,
variation in the arterial blood pressure waveform is
exaggerated. The difference between the maximum and
minimum systolic blood pressures during a single positive
pressure breath is the systolic pressure variation (SPV).
These fluctuations in the arterial pressure, synchronous
with respiration, correlate more strongly with intravas-
cular volume status than does CVP. While factors such as
contractility, arterial resistance and arterial elastance may
change over time, breath by breath changes in left
ventricular stroke output are mainly due to changes in
ventricular end diastolic volume [2].
During positive pressure ventilation, the start of inspi-
ration causes an increase in blood returning from the lungs
to the left atrium resulting in a transient increase in left
ventricular output. A transient increase in systolic pressure
is seen (DUp). A decrease in venous return due to an
increase in right atrial pressure and the waterfall effect due
to closure of the venae cavae reduce right ventricular
output causing a delayed reduction in left ventricular
output. A consequent decrease in systolic blood pressure
(DDown) is seen in the latter part of the respiratory cycle.
DUp and DDown are measured as the difference between
the maximum and minimum systolic pressure over a
single respiratory cycle with respect to a reference base-
line. DDown is shown to be a good index of hypovolemia
[2] and a good predictor of response to fluid administra-
tion in patients with septic shock [3].
Measuring DDown requires a baseline systolic blood
pressure measurement during apnea, necessitating an
intervention from the clinician before a measurement can
be performed. In a real-time system this problem may be
overcome by estimating the baseline as the average systolic
pressure at end expiration [4].
Pulse pressure variation (PPV) and systolic volume
variation (SVV) have been proposed as alternative meth-
ods of analyzing the arterial variations. PPV is the differ-
ence between the maximum and minimum arterial pulse
pressure over a single positive pressure breath divided by
the mean [5]; SVV is the difference between the maxi-
mum and minimum area between systolic peaks compared
to the mean volume (area under the curve) over a single
positive pressure breath [6].These measurements may be
more accurate in predicting fluid responsiveness. PPV
removes the influence of the change in pleural pressure.
PPV and SVV also remove any need to measure a baseline
value during apnea.
The aim of our study was to compare SPV, PPV and
SVV to CVP as indicators of fluid responsiveness in
children following cardiopulmonary bypass.
METHODS AND MATERIALS
After study protocol approval from the Institutional
Review Board for this strictly observational study, we
collected continuous real-time measurements from 25
subjects. Children between the ages of 0–17 years
undergoing cardiac bypass surgery with an ASA physical
status of I–III, and having a central venous line and arterial
catheter for intraoperative monitoring were selected.
Subjects with moderate or severe tricuspid incompetence
or who did not need volume loading during weaning
from cardiopulmonary bypass were excluded from the
study. Observations were performed during volume
loading following discontinuation of cardiopulmonary
bypass to assess fluid responsiveness. Fluid boluses con-
sisted of pump blood administered by roller pump via the
arterial cannula. Due to the non-invasive nature of the
study, the conventional baseline systolic pressure mea-
surement during apnea for the calculation of DUp and
DDown was not available. The baseline systolic pressure
was therefore calculated as the systolic pressure at end
expiration [4].
Data collection
A Pentium III, 500 MHz Hewlett Packard Omnibook
laptop computer with Datex-Ohmeda PC Collect

soft-
ware was used to collect continuous waveform and
5-second interval trend data. The laptop was connected to
the Datex-Ohmeda S/5 Anesthesia Monitor through an
asynchronous serial connection. Patient waveform data
was collected during and after weaning from cardiopul-
monary bypass until the removal of the aortic cannula.
Venous and arterial pressures were measured with refer-
ence to the mid-axillary line, with the zero reference level
being atmospheric pressure. CVP and systemic arterial
blood pressure were sampled at 100 Hz; the positive air-
way pressure signal was sampled at 25 Hz and interpolated
to100 Hz by the Collect software. The start and end times
of each fluid bolus administered, as well as any drugs
administered during data collection were electronically
recorded using the snapshot function on the S/5 monitors.
The volume of fluid administered was manually recorded.
Software analysis
A software plug-in module for the Datex-Ohmeda PC
Collect

software was created using the Labview 6.1
2 Journal of Clinical Monitoring and Computing