Surgery – Diagnostic testing – Temperature detection
Reexamination Certificate
2000-01-18
2002-05-07
Shaver, Kevin (Department: 3736)
Surgery
Diagnostic testing
Temperature detection
C600S435000
Reexamination Certificate
active
06383144
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and devices for measuring the body temperature of a patient in conjunction with the placement within the patient of an access device, for example, a catheter or introducer.
DESCRIPTION OF THE RELATED ART
The needs to properly treat a patient and to gain as much information as possible about the physiological state of a patient are often at odds with the desire to reduce discomfort to the patient as much as possible. For example, there is frequently a need both to deliver various medications to a patient, and also to monitor the patient's body temperature. Accordingly, catheters are often inserted into the vasculature of a patient to allow delivery of various medications, hydrating fluids, etc., and to measure blood pressure. The patient's body temperature, however, is monitored with a separate device, which is inserted separately.
Conventional devices for measuring temperature include the well-known oral thermometer, rectal, axillary (armpit), and tympanic (ear) thermometers and probes, as well as Foley catheters (bladder temperature), and nasopharyngeal probes (esophagus) probes. Each of these devices suffers from one or more shortcomings. The first disadvantage is obvious to anyone who has ever been the patient: It is uncomfortable enough to have a catheter inserted into one's vein or artery without also having to have a separate device inserted into one's rectum, bladder, ear or nose, or down one's throat.
The second disadvantage has to do with accuracy—taking a patient's temperature by placing a thermometer under her armpit or in her mouth may cause the least discomfort to the patient, but the temperature value this provides is usually less accurate and much more dependent on placement than temperature measurements of blood in a major vessel.
One way to overcome these disadvantages is to include some form of temperature sensor within the inserted catheter itself. This allows for measurement of the blood temperature, which is in most cases much closer to the patient's actual body core temperature. The problem then arises that other elements of the catheter system may have thermal properties that themselves affect the temperature that the sensor senses. This problem arises in the context of thermodilution systems for measuring cardiac flow. U.S. Pat. No. 4,817,624 (Newbower, Apr. 4, 1989), U.S. Pat. No. 5,176,144 (Yoshikoshi, Jan. 5, 1993), and Published European Patent Application 0 357 334 B1 (Inventors: Williams, et al., Mar. 7, 1990) for example, describe such systems. As is well known, in such a thermodilution system, the temperature of the cardiac blood flow is modulated according to a predetermined pattern that is created by the injection of an indicator, which is usually either a series of boluses of a relatively colder fluid, or heat. The downstream response to the temperature modulation is sensed by a thermistor and is used to calculate and estimate blood flow.
In systems such as Newbower's, temperature modulation is accomplished by cooling the blood through precisely dosed boluses of a thermally well-controlled fluid colder than the blood. In Williams, modulated cooling of the blood is accomplished using a heat exchange mechanism that does not require actual injection of any bolus into the blood stream. In systems such as Yoshikoshi's the blood is instead heated locally using a heating element that is mounted near the far (distal) end of a cardiac catheter. As before, a thermistor senses the downstream response profile, whose characteristics are used to calculate cardiac flow.
Such thermodilution systems have certain clinical limitations, since they must deal with several problems specific to this application. First is the problem of retrograde flow: If the thermistor is located proximal to the heater or bolus injection port, then the heated/cooled blood will flow back over the catheter tip. The temperature of the catheter itself, which may contain various other lumens, injectates, control wires, etc. can then affect the temperature profile of the thermally modulated blood and degrade the flow calculations.
To overcome this effect, the injection is replaced by a continuous infusion of indicator in order to obtain a new steady-state baseline; however, this is an undesirable clinical limitation due to the volume-loading the patient. Even when the thermistor is located distal relative to the heater/bolus port, this problem may still arise.
These thermodilution system catheters normally have a distal infusion lumen that passes beneath the thermistor or temperature sensor and exits at the tip of the catheter. Since the flow in such an infusion lumen can severely degrade the accuracy of the temperature sensor measurements, the flow is limited to a maximum amount in order for the blood flow measurement to still be accurate. Of course, such a limitation on infusion lumen flow is also undesirable from the clinical perspective.
An analogous problem of insulation arises in other cardiac devices as well, such as the catheter-based cardiac ablation system described in U.S. Pat. No. 5,688,266 Edwards, et al., Nov. 18, 1997). In Edwards' system, an ablation electrode is used to kill tissue locally using heat, and one or more temperature-sensing elements are used to sense the temperature of the tissue to be ablated and allow precise control of the ablation temperature and time. Isolation, provided primarily by physical separation, is thus required between the electrode and the temperature sensors; otherwise, the sensors will tend to give readings that are too high.
At least one factor limits the use of these known systems in general use for measuring a patient's body temperature: These systems are not arranged to measure the patient's actual, natural body temperature at all, but rather the temperature of blood or some body tissue whose temperature the system itself has deliberately altered.
There are other devices, such as central venous catheters (CVC), peripheral catheters, and other catheter-like instruments such as introducers. As their names imply, such catheters do not require placement into the heart and are consequently used more frequently in different areas of the hospital. Unlike cardiac catheters, which are often more than 100 cm long and require an introducer for insertion, these devices are seldom longer than about20-30 cm and can be inserted by the Seldinger technique. A CVC, for example, is often placed in a patient's jugular vein and is used for various infusions, for monitoring blood pressure, etc., through a number of lumens within the device.
An instrument such as a CVC often includes several different lumens which may carry a range of fluids (such as medications and other infusions), as well as instruments such as pressure transducers. Each of these fluids and instruments may be at different temperatures, or may have varying thermal properties, or both. Any measurement of temperature using such a catheter would thus risk serious thermal contamination from other portions of the catheter.
There are at present no known devices such as a CVC, peripheral catheter, or introducer that incorporate an arrangement for measuring blood temperature accurately. Therefore, it would be advantageous to be able to accurately measure temperature in conjunction with such access devices as catheters and introducers while eliminating the need to insert a secondary device into the patient in order to measure temperature, as is the current practice. Such devices would also provide a more accurate and less time-consuming body temperature measurement than non- or less invasive devices. This invention provides such an arrangement.
It would also be advantageous to be able to connect a CVC or similar catheter to a standard patient monitor. Not only would this bring the obvious benefit that the patient's temperature could be viewed at a glance along with other monitored parameters, but it would also make the temperature values available for other processing as ne
Konno Mark
Mooney Charles R.
Edwards Lifesciences Corporation
Shaver Kevin
Slusher Jeffrey
Vinitskaya Lena I.
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