Lemson_edit.qxp 9/3/09 09:17 Page 15
Arterial-pressure-based Continuous Cardiac Output Monitoring in Paediatric Patients
Figure 1: Basic Haemodynamics Figure 3: Example of a Model of the Circulation
AB Aortic resistance
Controlled variable (baroreflex)
Aorta
e volume
Blood pressure = SVR x CO
Strok
Fluid responsive
Compliance Peripheral resistance
HR x SV
Pre-load, afterload, contractility
Pre-load
Right atrium
CO = cardiac output (l/minute); HR = heart rate; SV = stroke volume.
Figure 2: Flow and Pressure Recording of a 5.7kg Lamb at
Figure 4: Arterial-pressure-based Continuous
Hypovolemic Shock (A), After Fluid Resuscitation (B) and
Cardiac Output Methods
During Dobutamine Therapy (C)
ABC
A. Pulse contour B. PulseCO
8
Pulse contour
7
P(t) dP
∆V/∆bp = cal*250*e
-kbp
+C(p)*
6
Cardiac output = K*HR* dt
SVR dT The algorithm corrects any arterial pressure
Opa
5
HR = heart rate
signal to a standardised volume waveform
(1/min)
4
3
K = factor reflecting specific patient characteristics K = factor reflecting specific patient
2
P = pressure characteristics (determined with use of TPTD)
1
t = time Cal = a calibration factor derived from compliance
0
SVR = systemic vascular resistance bp = blood pressure
-1 C = compliance of aorta k = constant
120
100
80
Opa
C. PRAM D. FlowTrac
A
(1/min)
60
Cardiac output = HR* Cardiac output= PR*sd(AP)*X
40
P/
t
*F
20
HR = heart rate
PR = pulse rate
A = area under the systolic pressure curve
Sd(AP) = pulsatility using the standard deviation
0
P = pressure
of the arterial pressure wave
0 0.2 0.4 0 0.2 0.4 0 0.2 0.4 t = time X = constant (arterial compliance, vascular
Sec Sec Sec
F = dimensional factor inversely related to the
resistance)
instantaneous acceleration of the vessel cross-
section area
Qpa = flow pulmonary artery; Pao = aortic pressure.
opportunity to decrease the afterload of the left ventricle during as shown in Figure 4A. It requires calibration using transpulmonary
the ejection phase, while at the same time helping to increase diastolic thermodilution in order to establish the individual characteristics of the
pressure, enabling diastolic flow through, for instance, the left aortic compliance. The PulseCO method is incorporated in the LidCO
coronary artery. However, the windkessel function is strongly device (LidCO, Cambridge, UK) and uses a pulse power analysis to derive
influenced by the (individually different) compliance of the aorta. the SV. This method uses measurements of the beat and ejection
duration and a series of approximations regarding the relationship
Figure 2 shows an example of an animal experiment. A 5kg lamb is between radial artery pressure, aortic pressure, aortic flow and CO. By
subjected to hypovolaemia, subsequent volume resuscitation and using the entire pressure waveform rather than just the systolic portion
dobutamine therapy. The flow measured with an ultrasound flow probe of the curve, the PulseCO system incorporates the influence of peripheral
around the pulmonary artery reflects actual CO. It can clearly be seen that resistance and the reflected wave from the periphery (see Figure 4B).
the arterial curve shows an increase in absolute pressure and pulse The derived SV is corrected using a calibration factor based on the
pressure concomitant with the increase in CO. However, the curve itself transpulmonary lithium dilution technique.
also changes in shape and magnitude. This change is caused by alterations
in peripheral vascular resistance, resonance, pulse pressure and CO. These Currently, there are two systems that do not require calibration. The
effects can be incorporated into an algorithm to calculate absolute cardiac pressure recording analytical method (PRAM, Mostcare, BioSi,
stroke volume. A simple model is shown in Figure 3. A method of Florence, Italy) uses a routine that identifies the characteristic points of
determining CO using the arterial pressure curve was described long the pressure wave during each beat (diastolic, systolic, dicrotic notch
ago.
20
A simple research device was built by Wesseling et al.
21
and resonant pressure points during the systolic and end-diastolic
phases). The morphological analysis of the beat allows determination
As a result of the unknown individual characteristics of the aorta, a of the stroke volume (see Figure 4C).
22
In the FloTrac system (Vigileo,
second CO technique is often used to calibrate an APCCO method. There Edwards, US) SV is derived using the patient’s vascular resistance and
are currently two methods that require calibration with an established arterial compliance based on sex, height, weight and age and the
CO method. The pulse contour method (PCCO) that is incorporated into pulse pressure (PP) waveform characteristics, while pulsatility is derived
the PiCCO device (Munich, Germany) calculates the area under the from continuous analysis of the shape of the arterial pressure
systolic portion of the arterial pressure waveform and applies an equation waveform (see Figure 4D).
EUROPEAN PAEDIATRICS 15
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68