WO2015092627A1

WO2015092627A1 - Continuous temperature profiling and control during surgery

Info

Publication number: WO2015092627A1
Application number: PCT/IB2014/066782
Authority: WO
Inventors: Louis Nicolas ATALLAH; Edwin Gerardus Johannus Maria Bongers
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-12-18
Filing date: 2014-12-11
Publication date: 2015-06-25

Abstract

A system and method for continuously profiling and controlling the temperature of a patient during surgery comprises a flexible substrate comprising a matrix of two or more modules of zero heat flux sensors to measure core temperature. The modules are attached to or embedded within the substrate, which substrate may also comprise temperature sensors, pressure sensors, and/or heating elements. The matrix communicates with a device that processes information from the matrix to continuously provide profiles or maps of core or core and periphery temperatures, so that the operator can decide whether to provide heat to the patient, assess the patient's condition, or determine the effect of anaesthesia. The system may also comprise one or more digital or thermal cameras whose images may be combined with the other information processed.

Description

CONTINUOUS TEMPERATURE PROFILING AND

CONTROL DURING SURGERY

FIELD OF THE INVENTION

[0001] The present invention relates to temperature control during surgery and, in particular, to a system and method for profiling a patient's temperature during surgery and using that information to control the patient's temperature.

BACKGROUND OF THE INVENTION

[0002] Human core body temperature is normally actively maintained within a narrow range (36.5-37.3°C). Anaesthesia disrupts many aspects of thermoregulation, leading to peri-operative hypothermia which has serious adverse events on patient outcome. These adverse events include an increased incidence of myocardial ischemia and cardiac morbidity, arrhythmias, increased blood loss and post-operative shivering. S. Rao, et al. "Heat Production and Loss." Update in Anaesthesia. 2008; http://update.anaesthesiologists.org/wp-content/uploads/2008/12/Heat- Production-and-Loss.pdf. Mild hypothermia has an increased risk of post-operative sepsis or surgical wound infection, as well as prolonged hospitalization. Studies have shown that hospital stays can be anywhere from 20% to 65% longer for patients who become hypothermic during surgery (http ://www. inditherm. com), which of course has cost and performance implications to the hospital involved.

[0003] To explain the physiology of thermoregulation during surgery, the authors in Rao et al, supra, constructed a two-compartment model of the human body, assuming that the body is divided into a central core thermal compartment, or core, surrounded by a peripheral thermal compartment, or periphery. The core is made up of major thoracic and abdominal organs and the brain, holds two-thirds of the body heat content, and is maintained within a narrow temperature range (36.6 to 37.4°C). The periphery comprises the limbs and skin and subcutaneous tissue, and contains about one-third of the body heat content. The temperature of the periphery varies widely from 0°C up to 40°C dependent upon the environment, but is usually 30-32°C. This 5- 7°C difference between core and peripheral body temperatures is maintained by vasoconstriction in the blood vessels leading to the peripheral tissues. By inhibiting tonic vasoconstriction, both general and regional anaesthesia decrease core temperature by redistribution of heat from the central core thermal department to the peripheral thermal compartment, which may result in core hypothermia.

[0004] A patient under anaesthesia loses or gains body heat via some combination of the following:

conduction (1 -2% of heat loss) due to direct contact with colder objects,

convection (25% of heat loss), which can be worse in operation rooms with forced airflow.

radiation (60% of heat loss), the major cause of heat loss in the operation room. It is due to the transfer of heat by infrared waves from the body to the surrounding. The amount of heat loss via radiation depends on the forth power of the temperature difference between the body and the surrounding environment. Thus, an environmental temperature drop of 2°C increases the heat loss by a factor of 16.

respiration (accounts for 10% of the heat loss).

evaporation, which is normally worse for surgeries involving open cavities for long periods. Evaporative heat loss is also significant for neonates due to their high skin permeability.

[0005] The effect of anaesthesia on heat balance is shown in Figures 1(a) and 1(b). In the baseline of Figure 1(a), a patient's central core is warmer than the periphery. However, by inhibiting tonic vasoconstriction, anaesthesia decreases core temperature by redistribution of heat from the core to the peripheral areas, as shown in Figure 1(b). This results in warmer peripheral areas and a decreased core temperature.

[0006] For clinicians, a 20°C ambient temperature in the operating room is a comfortable temperature with which to work. However, for a patient undergoing surgery without any thermal insulation, this temperature is very low and does not help in preventing hypothermia during surgery.

[0007] Although body temperature can be measured at different sites in the body, a continuous profiling of temperature distribution is currently not provided to anaesthesiologists. Core temperature can be measured in the nasopharynx or lower esophagus. Rectal and bladder temperatures can be inaccurate approximations of core temperature during surgery.

[0008] Thermal cameras are expensive, affected by the presence of clinical staff around the patient, and do not provide an accurate measure of core temperature. Moreover, thermal cameras have to deal with reflective coefficients of different surfaces to provide a useful absolute temperature measurement. Also, a single auxiliary temperature is a bad approximation for core temperature, and would not provide the whole picture covering core and peripheral temperatures as well as temperature dissipation between them. A thermal map of the upper body of a patient is shown in Figure 2.

[0009] Providing warming during surgery has several advantages, such as reducing the risk of surgical infection, lowering post-operative pain, and lowering rates of cardiac morbidity and the occurrence of arrhythmia. There are several known solutions for warming during surgery:

A water mattress could be used for cooling or heating, has a low risk of burning, and can provide pressure relief. However, a water mattress is bulky and heavy, could suffer from water leakage, and is difficult to handle. J. Hynson, et al. "Intraoperative Warming Therapies: A Comparison of Three Devices." J Clin. Anesth. (1992);4; 194-199.

Use of warming IV fluids has been shown to prevent hypothermia for several types of patients. However, active fluid warming will prevent hypothermia but not actually warm a patient unless large amounts of blood/fluid are transfused rapidly. Y. Camus, et al. "The effects of warming intravenous fluids on intraoperative hypothermia and postoperative shivering during prolonged abdominal surgery." Acta Anaesthesiol Scand (1996); 40; 779-782.

While the use of forced warm air provides a fast warm up time and high warming performance, it also warms up the surroundings, with no cooling option, which could decrease comfort for medical staff. P. Janicki, et al. "Comparison of Two Different Temperature

Maintenance Strategies during Open Abdominal Surgery: Upper Body Forced-air Warming versus Whole Body Water Garment." Anesthesiology (2001); 95; 868-874.

Using electrical heating elements does not warm surroundings and does not require consumables. However, this is characterized by poor warming performance, long warm up time, and the need for separate pressure relief. Y. Matsuzaki, et al. "Warming by resistive heating maintains perioperative normothermia as well as forced air heating." British Journal of

Anaesthesia (2003); 90(5); 689-691.

Electrical heating with carbon polymer technology has the advantages of a large uniform warming area, no electrical elements to break (no risk of burning), fast warm-up time, and no consumables. However, there are no cooling options, there is equal distribution of heat, and the heating elements are not disposable, http: //www. inditherm. com.

Use of a radiant heater, which should be close to a patient, provides fast warm up.

However, the surrounding area is also heated, and access to the patient is obstructed. J. Bar- Maor, et al. "Protection of the pediatric surgeon from heat stress caused by the overhead radiant heater during surgery." Journal of Pediatric Surgery (1988); 23; 846-847.

An infrared warmer can be located near a patient or even embedded in a patient's garment, and avoids heating the surroundings. However, an infrared warmer is not necessarily targeted to the patient, is not transparent to x-ray devices, does not use core temperature for deciding temperature distributions, and may cause eye damage. Also, there are no cooling options. J. Hendriks, U.S. Published Patent Application No. Patent 2010/0094385.

[00010] Most warming techniques currently available provide an equivalent amount of heat throughout the patient's body. Also, most of them are heating devices and not temperature measuring devices, which could mean that a profile of core and peripheral temperatures is hardly ever obtained for patients undergoing surgery.

SUMMARY OF THE I VENTION

[00011] It is an object to provide continuous profiling of core and peripheral temperatures of a patient during surgery, allowing clinicians to observe a heat map over time and to make adjustments.

[00012] It is also an object to provide a system and method for controlled warming of a patient during surgery.

[00013] It is a further object to provide warming for a patient during surgery based on the temperature profile obtained and to allow clinicians to control and observe the heat map over time. [00014] It is an advantage to provide an accurate temperature profiling device during surgery, that is, core/peripheral temperature monitoring, which is not normally performed during surgery. It is also an advantage to provide an adaptive warming solution during surgery. As discussed above, there are a multitude of known warmers useful to warm a patient in surgery. However, most have no measure of core temperature and, despite providing warming, offer clinicians no understanding of the patient's core and peripheral heat distribution or of the patient's heat diffusion over time.

[00015] It is further an advantage to address a perceived lack of understanding of how heating of a patient is affecting the overall outcome of surgery. By linking a temperature profiling device to the patient monitor, core/peripheral temperature variation can be observed as a physiological parameter, and heating can be controlled to improve overall patient outcome. Also, heat diffusion can be observed, and this is an important feature for anaesthesiologists in observing the progress of surgery.

[00016] Therefore, it should now be apparent that the invention substantially achieves all the above aspects and advantages. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be inherent from the description, or may be appreciated by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[00017] The accompanying drawings illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts.

[00018] Figures 1(a) and 1(b) are each a schematic representation of temperature distribution in a patient;

[00019] Figure 2 is a picture of a thermal map of the upper body of a patient; [00020] Figure 3 is a schematic representation of an embodiment of the invention;

[00021] Figure 4 is a representation of a heat map on a display; and

[00022] Figure 5 is a schematic representation of another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[00023] According to the invention, a module that comprises one or more zero heat flux (ZHF) elements or sensors is imbedded in or attached to a substrate positioned under, around, or atop a patient. The ZHF elements or sensors create an insulated area and measure core temperature. Peripheral temperature can be measured with simple thermistors or temperature probes.

Optionally skin temperature can be measured by simple thermistors. By providing several of these modules and thermistors in a matrix that is completely pervasive and attached to or embedded in a substrate, a profile of temperature distribution within a patient's body can be provided. Detailed temperature distribution information is used to provide temperature control strategies to either heat certain areas of the patient that are losing heat rapidly or to maintain areas at their current temperature. The modules or a matrix of modules or sensors can be attached to a device or processor such as a controller or other instrumentation having a display or connected to a display or a patient monitor through wires. Optionally each module or the matrix can send information wirelessly to a device or processor such as a controller or other

instrumentation having a display or connected to a display or a patient monitor. Other instrumentation could include, but is not limited to, a smartphone, iPad, tablet, laptop computer, or something similar.

[00024] In an embodiment of the invention, a thin sheet comprising ZHF elements or sensors is placed under a patient. In another embodiment, in addition to the thin sheet under the patient, ZHF elements or sensors are attached to or positioned within a flexible substrate such as a blanket, sheet, clothing item, or strap that can be placed over the patient to better control heat dissipation.

[00025] A matrix can also include temperature sensors or thermistors to measure peripheral or skin temperature, pressure sensors to indicate the exact position of the patient and/or heating elements to provide heating (or perfect insulation) at those points. The pressure measurements can also help to facilitate developing strategies to alleviate pressure at those positions. By providing an image (or a measurement of the whole matrix) at a time point, a clinician would be provided with a temperature (and pressure if available) image at a certain point. This image would contain core and peripheral temperatures as well as their distributions across the matrix. Optionally the system may comprise one or more digital or thermal cameras positioned above or obliquely to a patient, and the images from these cameras can be transmitted on the web or processed separately or in the same processor as the information from a matrix. The

combination of images from the cameras with other information from the matrix could result in better thermal mapping or a better indication of the position of the patient.

[00026] It is an aspect of the invention to provide a reliable determination of core and peripheral temperatures and a moving "image" as well as measurements of heat

diffusion/dissipation over time. Another aspect of the invention is to make warming adaptive, by varying it to warm the parts of a patient's body that need it most. A clinician can choose a temperature profile for a particular subject, and the system would aim to attain that profile at different points during surgery.

[00027] The system of the invention can also be used pre-surgery to warm a patient. This has an important role in preventing post-operative wound infections. See, A. Melling, et al. "Effects of preoperative warming on the incidence of wound infection after clean surgery: a randomised controlled trial." The Lancet (2001); 358; 876-880. Similarly, the system could be used post- surgery or even in a non-surgical clinical, hospital, or nursing home setting.

[00028] The calculation of core temperature from a patient support system is based on the zero heat flux (ZHF) principle. See, for example, A. Cheung, et al, European Patent Application Patent No. 2095081 and A. Padiy, et al., U.S. Published Patent Application No. 2010/0121217, both of which are incorporated herein by reference in their entirety. There is a natural heat flux from the body core to the skin-surface as long as the core temperature is greater than that of the skin. By locally insulating the skin, blocking all heat from going out, the temperature gradient between core and skin will decrease. At that point, the skin temperature directly under the insulated area will rise until it reaches equilibrium with the warmest region under the insulation. At that moment, zero heat flux is established and the core temperature can be measured at the skin. For further details on the mathematical equations behind the ZHF method, see Zeiner A, et al. "Non-invasive continuous cerebral temperature monitoring in patients treated with mild therapeutic hypothermia: An observational pilot study." Resuscitation (2010); 81; 861 -866, incorporated herein by reference.

[00029] It is also within the scope of the invention that a matrix may contain heating elements to heat certain areas, especially the core temperature area, to avoid temperature dropping over time during surgery. This can be done by specifying a temperature profile for the system, and setting the monitor or controller to maintain certain temperatures at different parts of the body. Warming can be done resistively, but in a focused, controlled manner.

[00030] This invention can perhaps be better understood from the drawings. In Figure 3, a patient 2 is positioned lying on a substrate 4, which substrate 4 comprises a matrix 6 of a multitude of ZHF sensor modules, temperature sensors, and optionally pressure sensors and/or heating or warming elements. Matrix 6 in substrate 4 is connected through a wire or wires 8, or wirelessly, to a device or processor 12, which may be a controller or other instrumentation having a display or connected to a display or a patient monitor, to receive information from the ZHF sensors or temperature and/or pressure sensors and enable or provide continuous temperature mapping or profiling. The profiling should show the core and peripheral temperatures as well as the differences between them.

[00031] Figure 4 represents a map 14 of heat or pressure and heat information, as shown on a display 16 on device 12.

[00032] As shown in Figure 5, a second substrate 18 having a matrix 20 comprising ZHF sensors, temperature sensors, pressure sensors, and/or heating or warming elements is positioned on top of patient 2, with wire or wires 22 connecting to device 12, or matrix 20 could be connected to device 12 or another device or processor (not shown) wirelessly. This enables continuous temperature monitoring as well as maintains a perfect thermal isolation, avoiding the occurrence of hypothermia.

[00033] Substrates 4 and 18 are preferably each a flexible material to which ZHF sensor modules can be attached or in which they can be embedded. Such materials include nonflammable polymeric or natural materials that are sterilizable and static-free. Optionally either substrate 4 or substrate 18 could comprise a garment to be worn by a patient, to ensure normothermia during surgery.

[00034] Substrate 4 or 18 preferably comprises ZHF sensor modules that are positioned substantially uniformly in a defined pattern throughout. However, in certain instances the pattern on a substrate may be limited to those areas of the substrate that are expected to contact the patient.

[00035] In is within the scope of the invention that substrate 4 may optionally have pressure sensors (not shown) that are in communication with device 12. In this way temperature sensing and control can be combined with pressure sensing, which would indicate position and could also be used to alleviate pressure later on. By use of pressure sensors, the area of activation of the sensors can be controlled.

[00036] The ZHF sensor matrix can be connected to a local board in a device such as a patient monitor, controller, or other instrumentation that processes the information and then provides or outputs a map or display of temperature values measured at given periods. This can be done wirelessly or via a cable connected to the device. Core/peripheral temperature, as well as the temperature map itself, can be used in patient decision support, the assessment of patient deterioration or improvement, or the performance of anaesthesia during surgery, or a

combination thereof.

[00037] Due to the importance of thermoregulation during surgery, there are several applications for this invention. One such application is the monitoring and control of core and peripheral temperature during surgery to avoid hypothermia. Hypothermia leads to a 70% higher probability of blood transfusion during surgery or after trauma. The provision of active warming showed in previous studies a reduction of over 65% of infection rates during surgery. The annual burden on the European healthcare systems of surgical site infections is estimated at more than 10 billion Euros. Development of a smart device aims at both accurate core/peripheral temp measurement and providing warming during surgery. This could be a very cost-effective, easy to clean smart temperature control device for surgery.

[00038] The invention described herein is especially applicable to neonates during surgery.

Neonates have a very high risk of perioperative hypothermia due to many factors, including their increased surface area to volume ratio, thin skin with minimal insulating fat, and less effective responses to cold temperatures. Neonates need a higher ambient temperature during surgery (up to 24°C), and they should be wrapped well. Ambient warmers or heated IV fluids are typically used during surgery. The invention described herein would provide an additional device to measure and control heat dissipation from core to peripheral areas. It can also be embedded in a more suitable support system for neonates.

[00039] Although the focus above has been directed to surgical patients, the system and method described herein are applicable to general hospital or nursing patients to keep their whole body temperature monitored and to provide heating mechanisms if the system realizes that there is a dangerous drop of core to peripheral values.

[00040] While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, deletions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description but is only limited by the scope of the appended claims.

Claims

What is claimed is:

1. A system for continuously profiling and controlling body temperature of a patient, which comprises:

a flexible substrate to be placed under the patient;

a matrix comprising two or more modules of zero heat flux sensors, which modules are attached to or positioned within the substrate; and

a device in communication with the matrix,

wherein the device processes information from the matrix and provides a profile of core or core and periphery temperatures of the patient over time.

2. The system of claim 2 which also comprises one or more pressure sensors within the matrix, wherein the device also processes pressure information.

3. The system of claim 1, wherein the matrix also comprises one or more temperature sensors to measure peripheral or skin temperature, wherein the device also provides information regarding peripheral or skin temperature.

4. The system of claim 1 which also comprises one or more heating elements for heating the patient.

5. The system of claim 4, wherein heating elements are attached to or positioned within the substrate.

6. The system of claim 1 which comprises;

a second substrate to be placed over the patient; and

a second matrix comprising two or more modules comprising zero heat flux sensors, which modules are attached to or positioned within the second substrate,

wherein the second matrix is in communication with a device for processing information.

7. The system of claim 6 which also comprises one or more pressure sensors within the second matrix, wherein the device also processes pressure information.

8. The system of claim 6, wherein the second matrix also comprises one or more temperature sensors to measure peripheral or skin temperature, wherein the device also provides information regarding peripheral or skin temperature.

9. The system of claim 6, wherein heating elements are attached to or positioned within the second substrate.

10. The system of claim 1, wherein the communication is wired or wireless.

11. The system of claim 1 , wherein the device is a controller or other instrumentation having a display or connected to a display or a patient monitor.

12. The system of claim 11, wherein the device is a smartphone, a laptop computer, a tablet, or an iPad.

13. The system of claim 1 which comprises one or more digital or thermal cameras.

14. A method of monitoring and controlling the temperature of a patient during surgery, which comprises;

placing the patient in the system of claim 1 ;

reviewing the temperature profile or map provided by the device; and

making any adjustments necessary to keep the temperature of the patient within a desired range.