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Table 1: Validation Studies Concerning Arterial-pressure-based Continuous Cardiac Output in Children
Study Method Circumstances Subjects Gold Standard Mean CO Bias Limits of Percentage Correlation
Fakler et al.
PCCO Congenital cardiac 24 patients TPTD 4.5l/min/m
surgery 1.4–15.2 years
Mahajan et al.
PCCO Congenital cardiac 16 patients TPTD 3.7l/min/m
surgery 1–36 years
Kim et al.
PulseCO Cardiac catheterisation 20 patients PATD 3.3l/min/m
Calamandrei PRAM Critically ill children 48 patients Doppler 2.7l/min 0.12l/min 0.6l/min 21% r=0.99
López-Herce PCCO Animal study 51 pigs TPTD 1.73l/min 0.04l/min 1l/min 57 % r=0.7
Piehl et al.
PCCO Animal study 10 piglets PATD 2.8l/min 0.1l/min 0.4l/min 14% r
24–37 kg calibrated
Min = minute; CO = cardiac output (CO); TPTD = transpulmonary thermodilution; TPLD = transpulmonary lithium dilution technique; PATD = pulmonary artery thermodilution;
PCCO = pulse contour cardiac output (Pulsion, Munich, Germany); PulseCO (LidCO, Cambridge, UK); PRAM = pressure recording analytical method (Mostcare, BioSi, Florence, Italy).
Limits of agreement = 1.96. Percentage error = limits of agreement/mean CO value. * standard deviation (SD) of differences between two techniques.
Performance of Arterial-pressure-based Specific Considerations with Arterial-pressure-based
Continuous Cardiac Output Methods Continuous Cardiac Output in Children
In general the systems that use calibration have the advantage that CO The difference between systolic and diastolic pressure is called pulse
can always be intermittently measured using a reliable system when there pressure. An increase in pulse pressure causes an increase of windkessel
are doubts concerning the APCCO value.
Although the lithium volume in the aorta, and thus a larger stroke volume. However, there is no
dilution technology has been validated in children, the manufacturer linear relationship between pressure and volume in the aorta. A pulse
states that a bodyweight of less than 40kg is a contraindication for its use pressure of 40mmHg at a level of 80/40 will probably be accompanied by
(www.lidco-ir.co.uk/html/technology/faqs.asp). a larger stroke volume than the same pulse pressure at a level of
120/80mmHg. Therefore, a simple linear model will not give accurate
The PulseCO method incorporated into the LiDCO device and the pulse results. Furthermore, aortic compliance increases with age, but normalised
contour method (PCCO) incorporated into the PiCCO device have been for body surface area it decreases. This is caused by a developmental
studied extensively in adults. They show comparable and acceptable increase in arterial size combined with a decreasing arterial wall
results, although regular recalibration improves their performance.
distensibility with age (most importantly between three and seven years of
The Flotrac system has been introduced more recently. In adults its bias is age).
Also, systemic vascular resistance decreases more than twofold
relatively small but the percentage error varies considerably.
It seems during development.
The distance between the heart and the femoral (or
that newer software versions perform better. Studies using this system in radial) artery is much shorter than in adults. As in adults, more peripheral
children have not been performed. It must be remembered that none of collected pulse traces must be compensated for resonance.
these systems are designed for a paediatric population.
Due to the small intra-arterial catheters used in children there is an
Studies in Children increased risk of damped waveforms caused by partial occlusion or
Table 1 depicts published paediatric studies concerning the APCCO kinking hampering APCCO performance (specifically when there is no
methods. Unfortunately, all published studies analysed only absolute calibration available). On the other hand, sufficient stroke-volume
values of CO reflected in bias and limits of agreement (with or without estimation in neonatal waveforms under overdamped pressure waveform
percentage error). Specific capabilities to track changes in CO have not conditions has been described.
Other factors also influence the reliability
been studied so far. However, it is this capability to track changes in of these methods. Heart rate is higher, blood pressure lower and stroke
CO that makes these techniques most powerful. All studies had volume much lower. For instance, in a 7kg critically ill child in circulatory
different set-ups and patient groups. One study even included children shock we measured a systolic blood pressure of 50mmHg and a diastolic
with cardiac shunts.
Shunts influence the pulse pressure and thereby pressure of 29mmHg. Heart rate was 168 and cardiac index 2l/minute/m
the APCCO method. Apart from validation, the successful clinical use the underlying cardiac stroke volume was 4ml. Specifically under these
of APCCO in children has also been described.
circumstances we want these systems to work reliably. A measurement
error of 1ml represents in these cases an error of 25%.
One of the problems with these validation studies is the gold standard. Since
CO is not easy to measure reliably in children it is difficult to study APCCO Algorithms designed for children must take all of the above-mentioned
in children. The calibrated APCCO methods can also only be studied in factors into account. A ‘simple’ translation of adult algorithms will
between two calibrations. In animal experiments a gold standard is readily probably not be sufficient. Some conditions render APCCO unreliable or
available using preferably ultrasound flow probes. However, APCCO even impossible. This includes cardiac arrhythmias, rapid changes
methods in animals cannot automatically be translated to children since the in vascular tone, aortic (vascular or valve) abnormalities and intra- or
vascular characteristics of animals can be different to humans. extra- cardiac shunts.
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