FR2687064A1 - Device for reestablishing and maintaining normothermia - Google Patents

Abstract

This device consists of a heating means arranged to be applied over the entire periphery of at least a part of a limb of the patient. This heating means preferably consists of a heating structure which is closed at one of its ends to form a longitudinal bag (2) for receiving the limb, which bag is combined with a heating system of the type with heat-exchange fluid or electrical resistor, for example. The cylindrical structure of the device according to the invention makes it possible to reheat the limb by thermal conduction in optimal manner, and then the entire body by circulatory convection. The increase in the temperature of the limb leads to an increase in its blood flow rate, which makes it possible to enable transfer of heat. This device is, in particular, usable in anaesthesia during and after operation and in recovery, for treating hypothermia and, optionally, hyperthermia.

Description

 The present invention relates to the medical field; it relates to a device for restoring and maintaining normothermia, intended in particular for preventing and treating hypothermia, in particular but not exclusively in per and post-operative anesthesia and in resuscitation.

 During a surgical procedure, the installation of hypothermia in a patient is a complication whose frequency and potential severity are underestimated.

 The intraoperative consequences are of a cardiocirculatory nature and we can observe a drop in cardiac output, cardiac arrhythmias and conduction which may appear from 35 "C in the cardiac, or even ventricular fibrillation refractory to external electric shocks, in case of deep hypothermia.

These consequences are also blood (increased blood viscosity and fibrinolytic activity), respiratory (increased risk of bronchospasm), or even metabolic (increased elimination half-life of many anesthetic substances resulting in delayed awakening) .

 Hypothermia also has harmful consequences during the post-operative period.

 During this period, the spontaneous warming of the patient leads to an increase in metabolism which corresponds to the energy debt contracted during the operation. The energy consumed during the awakening phase is closely correlated with the amount of heat lost during the operating period. The repayment of this energy debt can lead to the subject at risk (cardiac or respiratory insufficiency, coronary) cardiac or respiratory failure.

In healthy subjects, even if the risk is minor, the occurrence of chills leads to significant discomfort.

On the other hand, warming can also be the cause of a collapse of redistribution at the time of the lifting of peripheral vasoconstriction, all the more marked when there is hypovolemia.

 Many prevention or treatment methods have been proposed to alleviate the various problems or risks associated with hypothermia.

 Among these means, those called "passive" simply contribute to reducing losses; they do not require energy and involve no intake of calories.

 They consist of insulation means such as insulated blankets, block clothing, or even mattresses placed under the patient. This category also includes hydrophobic heat and moisture exchanger filters intended to be placed on the respiratory circuit.

These passive means contribute to the fight against hypothermia but are not effective on their own.

 The "active" means of combating hypothermia use energy and provide calories to the body.

 Among these active means is known the heating mattress (electric, water convection or infrared radiation), disposed between the patient and the operating table. This type of material is not very effective in adults; it minimizes losses but does not allow normothermia to be maintained in all situations.

 It is also common to cover the patient with a blanket heated by means of an electrical resistance.

The effectiveness of these covers is however quite limited; moreover, they are bulky and are therefore used only in post-operative period.

These covers have been perfected and there are currently structures on the market which use hot air circulation within a multi-perforated cellulose sheet. Although of a shape adapted to the operating site, these structures are not easy to use in the operating room, because of their size.

The other techniques (infrared radiant sources, esophageal heater and humidifier-heater of inhaled gases) are of low efficiency if used alone; they are, for some, difficult to use during the intraoperative period or consist of invasive techniques which are difficult to implement.

 The object of the present invention is to propose a device for restoring and maintaining normothermia, which can be used in particular for the prevention and treatment of hypothermia, or hyperthermia, which is effective, of simple structure, easy to implement and not bulky or annoying during the intraoperative period.

 According to the invention, this device consists of an external temperature management means, by heating or cooling, arranged to come to be applied over the entire periphery of at least part of a member of the patient, and preferably substantially over the entire skin surface of the limb.

 It is advantageously in the form of a sleeve-shaped structure, arranged to surround substantially the entire length of a member of the patient.

 In the case of hypothermia, the presence of a heat source distributed substantially uniformly around the entire periphery of the limb ensures optimum heating of the latter; this local heating helps prevent or treat a general decrease in body temperature.

 This structure is preferably closed at one of its ends to form a longitudinal pocket for receiving the member; it can for example be in the form of a flexible threadable sleeve.

 According to a particular embodiment, the temperature management system consists of a heat transfer fluid (water or hot air for example) conveyed by one or more pipes integrated into the structure. An external generator heats or cools the heat transfer fluid, depending on the patient's temperature, and a pump system ensures the propulsion of the fluid in the structure.

 According to another embodiment, the temperature management system consists of at least one electrical resistance integrated into the structure and connected to a charging generator.

 In all cases, the device is advantageously provided with means for controlling the temperature of the management system as well as with means for controlling the temperature of the skin surface of the limb. Thus, one or more thermal probes can be placed inside the heating structure, in contact with the skin of the limb.

 In the case of hypothermia, the heating structure according to the invention makes it possible to apply to the member a temperature higher than the central temperature of the patient. The blood from the rest of the body heats up in the limb and returns warmer to the heart before being redistributed to the rest of the body, thus compensating for the calorie deficit.

 The calorie intake thus produced is based on the diffusion of heat through the limb and on the transport of calories to the heart by the limb's blood circulation.

 But the invention will be further illustrated, without being in any way limited, by the following description of a particular embodiment, given by way of example and shown in the accompanying drawings in which - Figure 1 is a general view of the invention applied to a patient - Figure 2 is a sectional view along 2-2 showing the device according to the invention adapted to the patient's limb - Figures 3 and 4 show two variants of the invention, in which the devices are not 'do not extend over the entire length of the limb.

 As shown in the figures, the device 1 for preventing and treating hypothermia essentially consists of a heating structure 2 in the form of a longitudinal pocket capable of receiving one of the members of the patient. The structure 2 is arranged to come to be applied over the entire periphery of at least part of the member and preferably to come to surround substantially the entire length of said member.

Its shape and size are adapted to positioning either on the upper limb or on the lower limb; it is closed at one of its ends, on the side of the hand or foot.

 FIG. 1 shows the device for preventing and treating hypothermia, adapted on the arm 3 of a patient. A similar adaptation has been shown in dashed lines on the lower limb 4.

 The bag 2 preferably consists of a flexible structure to facilitate its positioning and not to harm the comfort of the patient. It can be in the form of a single piece threadable sleeve, or have an opening over its entire length. In the latter case, closing means, such as a hook band of the "VELCRO" type for example, can make it possible to limit the heat losses.

The internal face of the pocket 2 is intended to be applied as closely as possible against the skin surface of the limb. However, care should be taken to ensure that any contact of the heating structure on the limb does not entail intolerable pressures which may affect the patient.

 The materials used, plastics or textiles for example, are chosen according to their compatibility with the particular recommended application and with the heating system used. The latter can use any known heating means.

 As shown in Figure 2, these heating means may consist of a heat transfer fluid of the water or air type, for example, conveyed by pipes 5 integrated into the bag 2 and regularly distributed over the latter to obtain homogeneous heating. The distribution of the pipes can be done in any form whatsoever, by longitudinal spans or by helical circuit, for example. An external generator 6 connected to the structure 2 can heat the coolant and be associated with a pump 7 intended to propel said fluid towards the member. The assembly can advantageously operate in a closed circuit.

 According to another possible embodiment, the heating system consists of at least one thermal resistance integrated into the pocket 2 according to a layout allowing a homogeneous distribution of the heat. The electrical resistance can be connected to an external charging generator.

 In all cases, it is advantageous to provide means for controlling the temperature of the heating system (heat transfer fluid or resistance). In addition, the internal face of the bag 2 is advantageously provided with at least one thermal probe 8 intended to control the temperature of the skin surface of the member. These different control means allow manual or automatic thermal management of the device according to the invention and limit the risks for the patient.

 There are shown in Figures 3 and 4 two variants of the invention consisting of structures which extend over only part of the length of the member. Indeed, if that proves sufficient, we can be satisfied with a circumferential application on a segment of member only - hand, or hand and wrist (figure 3) - forearm or arm (figure 4) armband for example.

 The heating structure makes it possible to apply to the member to which it is adapted a temperature higher than the central temperature of the patient. The propagation of heat takes place step by step, by conduction effect, from the surface of the limb to the depth.

Given the substantially cylindrical shape of the structure, thermal diffusion takes place over the entire periphery of the limb and the heat transfer is optimized and carried out very quickly.

 The global warming of the limb makes it possible to heat the without as well in surface as in depth, and throughout its arterial, capillary and venous path.

The calories loaded by the blood will be transported to the heart and propagated throughout the body by circulatory convection.

 This phenomenon is potentiated by the fact that the circulation of a limb is very sensitive to local thermal conditions. An increase in temperature in fact induces a lifting of the vasoconstrictor tone which leads to an increase in blood flow.

This increase in flow is very noticeable at the extremities of the limbs: hands and feet. The flow of the arm and forearm, like that of the leg and thigh, also increases with local temperature, but less dramatically.

 Thus, the increase in the local temperature increases in remarkable proportions the blood flow of the member, and, consequently, the transport of heat by circulatory convection.

 An effective method of prevention or treatment of hypothermia must compensate for caloric losses and maintain normothermia to obtain a zero caloric balance.

 Satisfactory results can be obtained by applying a temperature between 37 and 420C on the limb, preferably close to 40 "C.

The temperature and the time of application must of course be managed on a case-by-case basis, in particular according to the type of recommendation: prevention or treatment, and according to the degree of hypothermia present or envisaged. For severe cases, it will be possible to use several devices on the same patient.

 This type of technique can advantageously be used in anesthesia, for the prevention of intraoperative hypothermia or the treatment of hypothermia in the postoperative phase, in particular in the recovery room. In the area of resuscitation, it allows the treatment of accidental hypothermia, secondary to drowning, intoxication, comas ... Of course, it can also find an application in other fields of medicine.

 The device according to the invention is very easy to implement and consists of a non-invasive method.

 It also allows preferential cardiac warming, which is important in deep hypothermia.

This device does not entail a redistribution collapse. There is a choice of warming site to allow the doctor access to the patient and the continuation of the treatment.

This technique can be used, according to the same principle to treat hyperthermia. In this case, as it is a question of lowering the body temperature, the temperatures chosen will advantageously be between 20 and 350C
The reference signs inserted after the technical characteristics mentioned in the claims are intended only to facilitate the understanding of the latter and in no way limit their scope.

Claims (11)

- CLAIMS  1.- Device for reestablishing and maintaining normothermia, characterized in that it consists of a temperature management means by heating or by cooling arranged to come to be applied over the entire periphery of at least part of a member of the patient.  2.- Device according to claim 1, characterized in that it consists of a structure (2) arranged to surround substantially the entire length of a member of the patient.  3.- Device according to any one of claims 1 or 2, characterized in that it consists of a structure closed at one of its ends to form a longitudinal pocket (2) for receiving the member.  4.- Device according to any one of claims 1 to 3, characterized in that it is in the form of a flexible sleeve (2) threadable.  5.- Device according to any one of claims 1 to 4, characterized in that it comprises a temperature management system by means of a heat transfer fluid conveyed by a network of pipes (5) integrated into the structure (2 ).  6.- Device according to claim 5, characterized in that it comprises an external generator (6) ensuring the heating or cooling of the heat transfer fluid, depending on the temperature of the patient, and a pump system (7) ensuring the propulsion of said fluid in the structure (2).  7.- Device according to any one of claims 1 to 4, characterized in that it comprises a temperature management system consisting of at least one electrical resistance integrated into the structure (2) and connected to a generator. charging.  8.- Device according to any one of claims 1 to 7, characterized in that it comprises means for controlling the temperature of the management system.  9.- Device according to any one of claims 1 to 8, characterized in that it comprises means for controlling the temperature of the skin surface of the member, consisting of at least one thermal probe (8).  10.- Device according to any one of claims 1 to 9, characterized in that it comprises heating means capable of applying to the member on which it is adapted, a temperature higher than the central temperature of the patient, for treatment hypothermia.  11.- Device according to any one of claims 1 to 9, characterized in that it comprises means capable of applying to the member on which it is adapted, a temperature lower than that of the patient, for the treatment of hyperthermia.