CA2751028A1

CA2751028A1 - Temperature measurement system

Info

Publication number: CA2751028A1
Application number: CA2751028A
Authority: CA
Inventors: Ellis D. Kent
Original assignee: LMA Medical Innovations Ltd
Current assignee: Medline Industries LP
Priority date: 2009-01-30
Filing date: 2010-02-01
Publication date: 2010-08-05
Also published as: GB0901609D0; CN102300523A; WO2010086740A1; EP2391317A1; MX2011008025A

Abstract

A temperature measurement system for use with a heated mattress pad, which comprises at least three temperature sensors and at least one converter module. At least one of the temperature sensors being adapted to be fixed to the heating element of the mattress pad, at least one of the temperature sensors being adapted to be fixed to the pad and at least one of the temperature sensors being adapted to be fixed to a patient on the pad. This allows the temperature of the patient and the pad to be monitored simultaneously, and prevents overheating. A patient warming system including the temperature measurement system and use of the temperature measurement system is also disclosed.

Description

Temperature Measurement System This invention relates to a temperature measurement system.

Every year, millions of patients suffer from the effects of unintended hypothermia. Operating rooms are kept cold and operating table surfaces mirror the room temperature prior to the patient's arrival. Patients are uncovered, surgical sites are open and often cold fluids are infused. If patients undergoing general and major regional anaesthesia are not warmed during surgery they may suffer from unintended hypothermia. The problems of unintended hypothermia are especially acute with major abdominal or orthopaedic surgery as they tend to involve large incisions exposing the internal organs and patient's tissue to the cold operating theatre.

Hypothermia can happen quickly. Often, the patient begins losing body temperature during pre-operative preparations and arrives in the operating room below normothennia. Anaesthetic agents themselves interfere with the ability of the body to regulate temperature and certain patient types are more prone to losing body heat than others. As a result, patients are frequently transferred to recovery in a hypothermic state. In the post anaesthesia care unit, coldness is one of the most frequent patient complaints. In a survey of post operative nurses, wannth was cited as the chief comfort concern followed by pain. Warm blankets are piled on the patient to relieve the effects of hypothermia, increasing the amount of time spent in recovery.
Hypothermia has a number of deleterious effects and a relatively small drop in core temperature can result in major complications or even death. These deleterious effects are well documented and include:
1. increases in surgical site infections;

2. increased blood loss;

3. increases in the number of cardiac events (including myocardial ischemia and ventricular tachycardia); and 4. a prolonged and altered effect of the drugs used during anesthesia.

The LMA PerfecTempTM patient warming system has been designed to aid in the maintenance of patient nornothermia before, during and after surgery for both paediatric and adult patients. It is lightweight, durable, and easy to clean. Since the system does not use a blanket, there is no problem with surgical access. Additionally it is radio translucent, so it won't interfere with X-rays, and it is silent, so it won't distract the physicians.

The LMA PerfecTempTM patient warming system comprises an electrical heating element sandwiched between foam layers to form a heated mattress pad. Heat is gently transferred to the patient conductively, the most efficient method of heat transfer, with conductive warning temperatures selected by physicians. The type of foam used enables pressure reduction, which helps prevent decubitus ulcers (the pressure reducing properties are effective for patients up to 500 lbs / 225 kg in weight).

Clearly for the LMA PerfecTempTM patient warming system, and other heated mattress pad patient warning systems (such as mattress pads using water or gel based heating elements to heat the patient), to work efficiently the temperature of the mattress pad needs to be monitored to ensure normothermia is maintained.
The present invention offers a safe and accurate temperature monitoring system suitable for use with a heated mattress pad.

In accordance with a first aspect of the present invention, there is provided a temperature measurement system for use with a heated mattress pad, which heated mattress pad comprises a heating element, said system comprising at least three temperature sensors and at least one converter module, at least one of the temperature sensors is adapted to be fixed to the heating element, at least one of the temperature sensors is adapted to be fixed to the pad and at least one of the temperature sensors is adapted to be fixed to a patient located on the pad. This system allows the temperature of the patient and the pad to be monitored simultaneously, and ensures the heating element does not overheat.

All three temperature sensors may be connected to a single converter module, or multiple converter modules may be used with some temperature sensors connected to a first converter module and others connected to a second converter module. For example, the at least one temperature sensor adapted to be fixed to the heating element and the at least one temperature sensor adapted to be fixed to the pad may be connected to a first converter module and the at least one temperature sensor adapted to be fixed to a patient may be connected to a second converter module. In embodiments using this arrangement of temperature sensors and converter modules, the first converter module may be located within a heated mattress pad whilst the second converter module may be separate from the heated mattress pad.

In use, the at least one temperature sensor fixed to the heating element acts as a safety sensor. In the absence of a patient the two temperature sensors adapted to be fixed to the pad and adapted to be fixed to the patient do not provide any temperature feedback and so if the heating element were switched on it could overheat. However, because at least one temperature sensor is fixed to the heating element, the temperature of the heating element itself is monitored and the heating element can be prevented from reaching excessively high temperatures.

In use, the at least one temperature sensor fixed to the pad will commonly be located on the outer surface of the mattress pad or on the lower surface of the mattress pad's surface covering, but beneath the mattress pad's surface covering (which the patient lays on). In the context of the invention being "adapted to be fixed to the pad" encompasses both being adapted to be fixed to the pad itself and being adapted to be fixed to the pad's surface covering.
The important feature is that the location of this sensor allows for accurate measurement of the temperature of the interface between the mattress pad and the patient. The interface sensor will commonly be located in the area of greatest weight placement, such as the shoulders area, the buttocks area and/or the upper thigh area.
In use, the at least one temperature sensor fixed to the patient will be fixed to the patient's skin and will enable the patient's body temperature to be monitored. In the context of this invention the patient's body temperature encompasses a patient's core temperature, a patient's skin temperature, the temperature of a particular organ, and any other temperature that it may be important to monitor during surgery.

Of course, more than one temperature sensor may be used in each of the locations, for example two sensors may be fixed to the patient such that the temperature measurement system comprises four temperature sensors. During an invasive procedure one temperature sensor may be fixed to the patient's skin and another temperature sensor may be fixed in an invasive location.

Due to the variability of the weight of a patient on the mattress pad (e.g. 5 kg child - 200 kg adult) calibration of the "interface sensor" can be difficult.
Therefore, careful monitoring of the temperature of the heating element and the temperature of the patient are also necessary. However, the "interface sensor" is important as, in the event that the sensor fixed to the patient is not properly located and so is not providing accurate temperature feedback, the "interface sensor" ensures the pad is not allowed to reach excessive temperatures that could hann the patient. Hence it is clear that each of the at least three temperature sensors of the temperature measurement system of the present invention are key to enabling the safe and efficient operation of a heated mattress pad.

5 Temperature sensors suitable for use in the present invention include electrical temperature sensors such as thermocouples, thennistors or resistance thermometers (also known as Resistive Temperature Detectors or RTDs) which generate electrical signals which are then converted into temperature readings.
It is also possible to measure temperature using non-electrical techniques, e.g.
optical temperature measurement techniques. Non-electrical temperature sensors such as fibre optic sensors may also be used with the present invention.
Fibre optic sensors are capable of measuring the full temperature range appropriate to a patient enviromnent (e.g. from 15 C to 50 C). Additionally fibre optic sensors enable accurate temperature measurement (e.g. 0.5 C) and sharp temperature resolution (e.g. 0.1 C). Suitable optical fibre sensors include the Fluotemp range of sensors, available from Photon Control Inc.

Arrays of optical fibres may be used to construct a single fibre optic sensor.
An array of optical fibres forning a single sensor is distinguished over multiple sensors each with a single optical fibre by the manner in which the sensors connect to the converter module. A single connection represents a single sensor, even if multiple optical fibres' signals are merged prior to connection with the converter module.

Fibre optic sensors suitable for use in the present invention may comprise at least one optical fibre, and at least one phosphor material located at a distal end of the at least one optical fibre said at least one phosphor material being characterised in that it emits, when excited, detectable optical radiation that varies as a known function of the temperature of the at least one phosphor material. In use, the temperature measurement system may transmit light, optionally pulses of light, from the proximal end of an optical fibre to the distal end of the optical fibre. The light returning from the distal end of the optical fibre to the proximal end of the optical fibre would include light emitted by the at least one phosphor material. Detection of the emitted light and comparison against the known variation of the emitted light as a function of the temperature of the at least one phosphor material enable the temperature at the distal end of the optical fibre to be measured.

The at least one phosphor material should be selected such that the intensity of a line within the emission spectrum of the at least one phosphor material changes across the temperature range of interest. Preferably these changes occur rapidly, to keep pace with any rapid temperature changes that might occur, and occur with good signal strength, to enable accurate temperature measurement. Therefore careful selection of the at least one phosphor material allows temperature measurements across a temperature range of interest to be made quickly and accurately. For example, an accuracy of 0.1 C is achievable in the range of 36 C to 41 C using a phosphor tipped sensor.

The at least one optical fibre should be robust so that it does not easily kink or become bent. This ensures that the detectable optical radiation is transmitted to the proximal end of the at least one optical fibre.

Radio translucent fibre optic sensors may be used with the claimed temperature measurement system and a radio translucent heated mattress pad to ensure that both the patient warming system and the claimed temperature measurement system won't interfere with X-rays. Furthermore, the patient warming system and a temperature measurement system with fibre optic sensors may be used with a radio translucent operating table, such as the Wilson Plus radiolucent Wilson frame. Patient warning systems and the claimed temperature measurement system may also be used with a variety of other operating tables, such as the Jackson table, the Amsco table and the Skytron table.

In one embodiment of the present invention, a combination of electrical temperature sensors and optical temperature sensors may be used. In particular, the at least one temperature sensor adapted to be fixed to a patient located on the pad may be an electrical temperature sensor, and the at least one temperature sensor that is adapted to be fixed to the heating element and the at least one temperature sensor that is adapted to be fixed to the pad may be optical temperature sensors. If used with a radio translucent patient warming system such as the LMA PerfecTempTM, the arrangement of the temperature sensors described above ensures that the heated mattress pad remains radio translucent.

In embodiments using fibre optic sensors, the converter module may be a three channel opto-electronic converter module (or any other device capable of converting optical signals, e.g. a beam splitter).

The at least one converter module may generate an output signal to be transmitted to control means to control the heating of the mattress pad. The control means and the at least one converter module may be located within the same housing, or in embodiments comprising more than one converter module, one of the converter modules may be located within the same housing as the control means and one of the converter modules may be located somewhere else.

Commonly the mattress pad is heated electrically and the control means controls the heating of the mattress pad by adjusting the current flowing through the mattress pad in response to the output signal from the at least one converter module. However alternative means of heating the mattress pad may be used, e.g. using a flow of heated water. Optionally the output signal is transmitted digitally to the control means, either via an electrical cable or wirelessly.

Sensor monitoring means may be used to monitor whether one or more of the sensors becomes disconnected from the converter module. If one or more of the sensors become disconnected from the converter module, the sensor monitoring means may initiate an audible or visible alarm and/or the control means may switch off the heating element. For example, if the mattress pad is heated electrically and the sensor monitoring means detects that one or more of the sensors has become disconnected from the converter module the control means may cut the supply of electrical current to the heating element.
The system may also comprise means suitable for recording and/or displaying temperature information, which means may be integrated with the control means or form a separate device.

The temperature sensors of the present invention may be disposable or reusable or a combination of disposable and reusable temperature sensors may be used. In particular, the at least one temperature sensor adapted to be fixed to a patient located on the pad may be disposable since this temperature sensor makes direct contact with a patient whereas the at least one temperature sensor that is adapted to be fixed to the heating element and the at least one temperature sensor that is adapted to be fixed to the pad will not make direct contact with a patient.

The use of disposable temperature sensors in medical applications allows new, sterile sensors to be used with each patient. In this case, the disposable sensors should be inexpensive and able to be readily connected to and disconnected from the converter module. Alternatively, reusable temperature sensors may be used in medical applications provided the temperature sensors are isolated such that they do not need to be sterilised or, if they cannot be isolated, the reusable temperature sensors should be sterilised between uses.
In this case, the reusable sensors should be easy to sterilise and able to be readily connected to and disconnected from the converter module.
The temperature sensors may comprise means for fixing the distal end of the temperature sensor in a desired location. The means for fixing the distal end of the temperature sensor may vary depending on the nature of the desired location, i.e. the means for fixing the distal end of the temperature sensor to the heating element may differ from the means for fixing the distal end of the temperature sensor to the pad and may vary from the means for fixing the distal end of the temperature sensor to the patient. Nonetheless, the means for fixing the distal end of the temperature sensor in a desired location may comprise adhesive, for example the means for fixing could be an adhesive pad. The adhesive pads may be designed to ensure the adhesive does not insulate the sensor and distort the sensor's signal. Adhesive pads comprising hypoallergenic adhesive are particularly suited to medical applications.

The temperature sensors of the present invention are principally intended for non-invasive use, however, the skilled person could readily devise means of fixing the distal end of the temperature sensor in an invasive location. For example, an invasive sterile probe could function as a channel for inserting and fixing the distal end of the temperature sensor in an invasive location.
Any insulation effect associated with the invasive sterile probe could be calculated and offset to ensure an accurate temperature reading at the invasive location. Use of the temperature measurement system in an invasive location could better enable a patient's core temperature to be monitored.

Claims

1. A temperature measurement system for use with a heated mattress pad, which heated mattress pad comprises a heating element, said system comprising at least three temperature sensors and at least one converter module, at least one of the temperature sensors being adapted to be fixed to the heating element, at least one of the temperature sensors being adapted to be fixed to the pad and at least one of the temperature sensors being adapted to be fixed to a patient located on the pad.

2. A temperature measurement system according to claim 1, wherein the at least one converter module generates an output signal that is transmitted to control means which control the heating of the mattress pad.

3. A temperature measurement system according to claim 1 or 2, wherein the system comprises sensor monitoring means to monitor whether one or more of the sensors becomes disconnected from the at least one converter module.

4. A temperature measurement system according to claim 3, wherein an audible or visible alarm is initiated if the sensor monitoring means detects that one or more of the sensors has become disconnected from the at least one converter module.

5. A temperature measurement system according to claim 3 or 4, wherein the control means switches off the heating element if the sensor monitoring means detects that one or more of the sensors has become disconnected from the at least one converter module.

6. A temperature measurement system according to any preceding claim, wherein the system comprises means suitable for recording and/or displaying temperature information.

7. A temperature measurement system according to any preceding claim, wherein the temperature sensors are selected from the list consisting of thermocouples, thermistors, resistance thermometers, optical fibre sensors, and any combination thereof.

8. A temperature measurement system according to claim 7, wherein the temperature sensors are optical fibre sensors and each of the optical fibre sensors comprises at least one optical fibre, and at least one phosphor material located at a distal end of the at least one optical fibre said at least one phosphor material being characterised in that it emits, when excited, detectable optical radiation that varies as a known function of the temperature of the at least one phosphor material.

9. A temperature measurement system according to any preceding claim, wherein at least one of the temperature sensors is disposable.

10. A temperature measurement system according to any preceding claim, wherein at least one of the temperature sensors is reusable.

11. A temperature measurement system according to any preceding claim, wherein the temperatures sensor comprises means for fixing the distal end of the temperature sensor in a desired location.

12. A temperature measurement system according to claim 11, wherein the at least one of the means for fixing comprises adhesive.

13 13. A temperature measurement system according to claim 12, wherein at least one of the means for fixing is an adhesive pad.

14. A patient warming system including a temperature measurement system according to any preceding claim.

15. Use of a temperature measurement system according to any of claims 1 to 13.

16. A temperature measurement system substantially as described herein.

17. A fibre sensor substantially as described herein.

18. A patient warming system substantially as described herein.