Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2002-02-27
2004-05-18
Hindenburg, Max F. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S483000, C600S549000
Reexamination Certificate
active
06736782
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus, a computer program, a central venous catheter assembly and a method for hemodynamic monitoring.
2. Description of the Related Art
One of the most relevant parameters in hemodynamic monitoring is cardiac output, which currently is usually measured using intermittent bolus thermodilution measurements as described e.g. in U.S. Pat. Nos. 3,651,318, 4,217,910 and 4,236,527.
For bolus thermodilution measurements a certain amount of a liquid at a temperature higher or lower than blood temperature is injected as a bolus through a catheter which is placed in the blood stream of a patient, and the temperature deviation of the blood as a function of time is monitored at a place downstream from the place where the bolus is injected. The Cardiac Output CO can then be determined by algorithms based on the Stewart-Hamilton-equation:
C
O
=
V
L
(
T
B
-
T
L
)
K
1
K
2
∫
Δ
T
B
(
t
)
ⅆ
t
where T
B
is the initial blood temperature, T
L
is the bolus temperature, V
L
is the bolus volume, K
1
and K
2
are constants to consider the specific measurement setup, and &Dgr;T
B
(t) is the blood temperature deviation as a function of time with respect to the baseline blood temperature T
B
.
According to the prior art, usually pulmonary artery catheters are used injecting the bolus through a lumen outlet substantially apart from the distal end of the catheter and detecting the temperature deviation of the blood as a function of time at the distal end of the catheter.
In a typical measurement procedure, a cold bolus of saline at ice or room temperature in an amount of about 5-10 milliliters, or as a guideline 0.1 ml/kg body weight is injected through the pulmonary catheter. Completion of this procedure takes about 2 minutes. In order to obtain sufficient accuracy, it is repeated several times and the results are averaged. Using this conventional method, determining one reliable cardiac ouput value thus requires a measurement time of up to 10 minutes and involves the injection of up to 50 ml of fluid into the cardiovascular system of the patient and, as a consequence, can be carried out only one or two times per hour.
Instead of using cold bolus injections, heating pulmonary artery catheters are used for modified thermodilution methods such as described in U.S. Pat. Nos. 4,507,974 and 5,217,019. Periodic heat pulses at a given pattern are introduced substantially apart from the distal end of the catheter by a heating coil or a thermal filament mounted to the indwelling catheter. Temperature changes of the blood heated passing the heating coil or thermal filament, respectively, are measured downstream by a thermistor at the distal end of the catheter. Cardiac output is determined quasi-continuously based on the data sampled for several minutes using signal processing and averaging algorithms. Thus, the cardiac output values determined are average values over periods of several minutes. Accuracy of modified thermodilution methods using heating pulmonary catheters is sensible to high and unstable blood temerature.
The amount of heat which can be introduced the way described above is limited to avoid a thermocoagulation of the blood or damage to the tissue adjacent to the heater. Approaches to regulate the heat transferred by the catheter are described in U.S. Pat. Nos. 5,701,908 and 5,857,976.
Generally, the use of pulmonary artery catheters is rather highly invasive and includes risks for the monitored patient, such as malignant arrythmias and pulmonary artery rupture or infarction. The so called transpulmonary thermodilution method is less invasive applying a central venous catheter instead of a pulmonary artery catheter. A thermal indicator is injected through a lumen of the central venous catheter and an additional arterial catheter, introduced for example into the femoral artery, is used to detect the thermodilution curve after the thermal indicator has passed the heart. Again, completion of this procedure takes several minutes and is not suitable for repeated cardiac output determinations within short time intervals.
Pulse contour analysis is a continuous method to determine cardiac output by multiplying the heart rate by a beat-to-beat stroke volume for each heart beat. The stroke volume is determined from the shape of and the area under the arterial blood pressure curve of the systole, wherein the arterial blood pressure is measured in the femoral artery or other large artery. In the currently commercially available System PiCCO by Pulsion Medical Systems AG, Germany the so called pulse contour cardiac output PCCO is determined using the relation
P
C
C
O
∝
H
R
∫
S
y
s
t
o
l
e
(
p
(
t
)
S
V
R
+
C
(
p
)
·
ⅆ
p
ⅆ
t
)
ⅆ
t
wherein HR is the heart rate, p(t) the time dependent driving blood pressure (i.e. the time dependent arterial blood pressure AP(t) measured minus the mean central venous blood pressure CVP), dp/dt the first derivative of p(t) with respect to time, SVR the systemic vascular resistance and C(p) the aortic compliance function of the monitored patient. The integral is determined for the systolic phase. Calibration is achieved by conventional cold bolus injection transpulmonary thermodilution methods. The compliance function C(p) characterizes the volume change and subsequent pressure change of the aorta due to the ability of the aorta to expand during the systole and recontract during the diastole. C(p) and SVR also have to be determined by using a reference thermodilution measurement. A method and an apparatus to determine the compliance function C(p) are described in DE 19814371 A1 enclosed herewith by reference. In order to achieve reliable results over an extended period of time, recalibration is necessary. According to the current state of the art, in clinical practice the time consuming recalibration procedure of carrying out a conventional cold bolus injection transpulmonary thermodilution measurement is usually performed every 8 hours.
BRIEF SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide means rendering possible continuous recalibration of pulse contour measurements with only short time intervals between two respective recalibration steps. It is also an objective of the present invention to increase accuracy in determining hemodynamic parameters and, at the same time, keep the invasiveness of applying the medical equipment necessary as low as possible.
In order to accomplish these objectives, the present invention provides an apparatus for hemodynamic monitoring, which comprises a central venous catheter assembly comprising at least one lumen and heating means in the immediate proximity of the distal end of the central venous catheter assembly. The heating means are adapted to emit heat pulses for introducing travelling temperature deviations to a patient's blood circulation. The apparatus further comprises means for determining the power transferred by the heating means as a function of time. The power transferred during emission of each heat pulse thereby represents an input signal corresponding to the respective heat pulse. The apparatus further comprises an arterial catheter assembly comprising temperature sensing means for measuring the local blood temperature in an artery of the patient as a function of time, thus determining for each input signal a corresponding system response. The apparatus further comprises computing means having implemented thereon executable operations for determining a reference cardiac output value of the patient from at least one input signal and respective corresponding system response.
In a preferred embodiment of the invention the computing means has additionall
Burger Thorsten
Pfeiffer Ulrich J.
Hindenburg Max F.
Natnithithadha Navin
Nixon & Peabody LLP
Pulsion Medical Systems AG
Studebaker Donald R.
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