Reference to Related Applications This application claims priority to U. S. Provisional Application No.

60/442,777, entitled"Collapsible Fluid Warmer for the Austere Trauma Environment"filed January 27,2003, which is specifically and entirely incorporated by reference.

Baekgroandt 1. Field of the Invention This invention is directed to devices and methods for warming fluids in trauma environments. The invention is further directed to portable devices and methods that can be attached to existing air temperature controlling systems such as may be found in trauma environments and vehicles.

2. Description of the Background The Forward Surgical Team (FST) is made up of twenty individuals operating a two bed operating room (OR) manned by four surgeons and two anesthetist, an ATLS section, and a four bed intensive care unit (ICU). The FST is highly mobile and has the doctrinal mission of providing far-forward life-saving surgery with immediate evacuation. This mission often calls for surgery to be performed in austere surrounding such as in tents in the field environment. Trauma management is often made even more difficult because of the ambient conditions such as cold temperatures.

Hypothermia has a known deleterious effect on the trauma patient. It is well documented that hypothermia can compound the effects of shock and exacerbate hemorrhage by accentuating a life-threatening coagulopathy.

Hypothermia, and therefore the resulting coagulopathy, can be combated with warming techniques.

The trauma patient may be warmed by external and internal techniques.

External methods would include managing the ambient temperature, application of blankets or other devices to prevent ongoing heat loss, and active warming measures. The latter would include the application of heat packs and use of the Bair Hugger (D Warming Unit or a similar device, which is intrinsic equipment to the FST. Internal warming techniques would include gastric, peritoneal, or bladder lavage, but the most commonly employed technique is the instillation of warmed intravenous (IV) fluids.

Presently most temperature-sensitive materials are transported in containers with one opening for insertion of the desired material and a temperature control device such as a gel pack for maintaining a specific temperature range. These containers have the characteristic of top-down cooling, which means that more heat seeps into the container from the opening as opposed to through the walls of the container. The coolest areas of the container are opposite the opening in the depths of the internal space of the container. This creates uneven and uncontrollable temperature gradients within the container. Top-down cooling also produces hot spots, wide temperature swings and severe temperature gradients throughout the chamber.

Thus, there is a strong need for devices and methods to transport materials that require stable or specific temperatures, or must be maintained within a defined temperature window. Such a container should be durable, lightweight, and preferably reusable, with the capability of transporting hazardous and/or potentially infectious materials in leak proof container that meets applicable criteria.

Summary of the Invention The present invention overcomes the problems and disadvantages associated with current strategies and designs and provides new devices and methods for warming, cooling or simply maintaining desired materials at specific temperatures or temperature ranges in trauma and other similar environments.

One embodiment of the invention is directed to fluid warmers for austere trauma environments comprising a heating unit with a fan or other fluid movement mechanism, and a container of a desired size for transporting a material at a desired

temperature range containing an intake port that allows for warmed air from the heating unit to enter said container, and an exit port for the exit of excess air from said container. Preferably the container comprises an insulated liner and an insert that promotes heat transfer between the air and said material. Containers may further comprise temperature readout systems, for monitoring temperatures within the container or within the materials being transported. Preferred containers are composed of light-weight materials, such as, but not limited to foam, neoprene, plastics, nylon, cardboard, rubber, Styrofoam and combinations thereof. The temperature of the container can be maintained as any desired setting, but is preferably 37°C +/-5°C. Heating or cooling units are commercially available, or can be specifically designed from commercially available components, and are most typically electric or battery operated heaters. The overall fluid warmer is preferably light weight, weighing less than 10 kg, and portable.

Another embodiment of the invention is directed to methods for transporting materials at a desired temperature or temperature range comprising placing said materials in a container that possesses an intake port, which allows for air from an air conditioning unit to enter the container, and an exit port for the exit of excess air from the container, and forcing said conditioned air into the container and across said materials. Heating or cooling units can be operationally and functionally connected or easily connectable to such units that already exist in vehicles such as, but not limited to aircraft, ambulance, fire trucks, Humvees, Jeeps, trains, or ships. Preferably the container comprises an insert that promotes heat transfer between air and the material. Materials that can be transported in this manner include, but are not limited to, tissues, cells, IV fluids, bodily fluids such as blood, whole organisms, artificial implants, pathogens, bacteria, organs, biological materials, research or clinical materials, infectious substances, plants and plant- derived material, and temperature-sensitive chemicals and toxins, and pharmaceutical products such as drugs and vaccines, or combinations thereof.

Containers may further contain temperature control devices to assist in maintaining stable temperatures within the container and a preferred temperature control device is a gel pack. With the methods of the invention, all or nearly all of the warmed air

in the container is continually moved across surfaces of the material and continually replaced with fresh air.

Other embodiments and advantages of the invention are set forth in part in the description, which follows, and in part, may be obvious from this description, or may be learned from the practice of the invention.

Description of the Figures Figure 1 One embodiment of the invention including the Bair Hugger Warming Unit operationally coupled to the X-1 and a Propaq monitor temperature recorder and probe.

Figure 2 Graph of IV fluid temperatures in a device of the invention over a thirty minute period in ambient temperatures of 25°C and 33°C.

Figure 3 Graph of time to heat 1, 4,7 and 10 IV fluid bags.

Figure 4 Graph of starting temperature vs. time to heat IV fluid bags.

Figure 5 Graph of heat dissipation over time for 1, 4, 7 and 10 bags of IV fluids.

Figure 6 Graph of comparison of temperature vs. time of heat dissipation for the X-1 with and without mylar liner insulation as compared with ambient temperatures.

Description of the Invention As embodied and broadly described herein, the present invention is directed to devices and methods for warming, cooling, or simply maintaining specific temperatures or temperature ranges of fluids and other materials in and trauma other similar environments.

The Forward Surgical Team (FST) mission includes trauma management in the field environment which can be difficult secondary to hypothermia leading to life-threatening coagulopathy and uncontrolled hemorrhage. A method to combat hypothermia is with ambient warming and infusion of warm fluids. One problem is that warming and maintaining fluids in the field environment is difficult and especially so in any large volume. The warming and maintenance of large volumes of IV fluids is difficult in the FST especially in the cold field environment.

A simple, easy to use and inexpensive device was surprisingly discovered to warm, cool or simply maintain a specific temperature or temperature range of materials in a container. The device comprises a container for holding the desired material. Containers are commercially available or easily modified and manufactured as desired, and can be of any size desired, limited only by the ability of the heating or cooling unit to be attached. Typical containers include picnic coolers and other desired shaped structures that provide at least some insulation against ambient temperatures. Such coolers can be purchased at most store or can be manufactured to desired specifications. In either case, the container will hold the materials and be insulated against ambient temperatures. Insulation may comprise a spacing of air or other material that conducts temperatures poorly, or insulation materials such as conventionally available foams, fluids, liquids, gasses, plastics or gels (e. g. mylar, fiberglass, inert liquids or gasses, air).

Many different types of heating or cooling units can be used with this invention. Electric heaters and other commercially available units are preferred.

Heaters are preferably coupled with a fan that that takes ambient air (i. e. air from the surrounding outside environment) and pushes that air through the warming unit and into the container. Although fans are preferred, other types of air or fluid movement mechanism may also be utilized such as, but not limited to, devises that move fluids based on pressure differentials, gravity, electric fields, magnetism, blowers or combinations thereof.

The container includes an intake port attached to the heating or cooling unit, for receiving the warmed (or cooled) air (or another fluid) from the heating (or cooling) device. Preferred ports will have one-way valves that do not permit back- flow. Containers will also have exit ports or vents that allow for the warmed or cooled air to exit the container as additional fresh air is pushed in by the heating or cooling unit. Preferred exit ports are one-way valves that open in response to a pressure differential such as a one-way flutter valve or other similar mechanism.

In a preferred embodiment of the invention, the temperature-sensitive materials are placed in an appropriately sized container. Containers should be designed to have about 25% or more of open space, with the remaining space taken

up by the materials being transported. In a preferred embodiment, all or nearly all of the air surrounding the material is continually moved across the surfaces of the material and replaced with fresh air conditioned air. Any size or configuration of container may be used, and preferably is configured for the contents being transported. Containers may also be collapsible when empty for easy storage. The most typical configuration of a container is square or rectangular.

The desired material to be transported may be contained in a biohazard bag or other flexible pouch for safety reasons, and/or to prevent contact with air, water or water vapor. Containers are of a sufficient size and shape to permit desired air circulation from the temperature control device. In this manner, temperatures within the container are held relatively constant (within a specific desired temperature windows), for example, over a 20°C range, over a 15°C range, over a 5°C range, and preferably over a 2°C range (e. g. 37°C +/-5°C ; 25°C +/-10°C ; 20°C +/-2°C ; 15°C +/-7°C, and combinations thereof). Such temperature ranges can be maintained for as long as desired, limited only by the capability of the heating or cooling unit.

Heat may be provided by a conventional heating unit, such as, forced air electric or gas heaters with a fan. Preferred units include a Bair Hugged (M Warming Unit (BHWU) or similar units, or heating units fixed to vehicles such as cars, trucks (e. g. fire trucks and emergency vehicles), Humvees, Jeeps and most any other military or non-military vehicles. Other vehicles with heating units include aircraft such as fixed wing crafts and helicopters, boats, ships and hovercraft, trains and any vehicle that contains an environmental control. Cooling may be provided by conventional compressor units or simply moving air units (e. g. fans). These coolers may also be a part of vehicles or other transportation or equipment as indicated herein for heating units. When connecting to a vehicle with a combustion engine, care must be taken to connect a host to the heater or cooler hoses, and exclude any connection to engine exhaust. Connections can be easily made by one of ordinary skill in the art using a variety of connectors including simple hoses and clamps, and one way valves. A temperature-controlling device such as, for example, foam, chemical warming or cooling devices, liquid pack or a gel pack, all

of which are commercially available, or other passive temperature-controlling device may also be placed within the container.

Materials that can be heated, cooled, or simply have their temperatures maintained with the device of the invention include, but are not limited to most any liquid, gas, solid, semi-solid, gel. Preferred materials to be warmed include fluids such as IV liquids, blood and other biological substances, and tissues.

Temperature-sensitive materials that can be transported using the container of the invention include, but are not limited to, tissues, cells, IV fluids, bodily fluids such as blood, whole organisms, artificial implants, pathogens, bacteria, organs, biological materials, research or clinical materials, infectious substances, plants and plant-derived material, and temperature-sensitive chemicals and toxins, and pharmaceutical products such as drugs and vaccines, and combinations thereof.

These materials can be placed in containers in their existing packaging, or packaging can be specifically designed to promote heat transfer in containers of the invention. Specific designing may include, increasing the surface are of the packaging, or dividing the material into a plurality of smaller packages.

Typical devices of the invention comprise the container, which comprises both an intake port and a vent port, and the heating or cooling unit. Preferred devices are self contained are battery operated or easily connected to portable power units. Alternatively, devices of the invention may comprise only suitable containers capable of being operationally ad functionally connected to existing heating or cooling units such as the air handling systems of vehicle engines.

Operational and functional connections include suitable one-way valves, pressure sensitive valves, timed valves, and other commercially available valves and other connections. Accordingly, it is preferred that devices of the invention be portable (e. g. hand held), light weight (e. g. less than 20 kg, preferably less that 10 kg, and more preferably less than 5 kg) and, when necessary, in component parts that are easily assembled (e. g. pre-structured container with vent and intake port).

Preferably, containers of the invention are designed for a broad spectrum of users and require little to no special skill or training for assembly. Directions may be included in or with containers to provide preferred assembly instructions and

instructions for emergency situations such as accidental leaks or punctures of the container. In addition, containers can be provided with kits to repair tears or other types of leaks to the container. Thus, containers of the invention are very useful for transporting a variety of materials including medical or biological material for patients. Alternatively, inserts, smaller containers or other holders such as bottles or vials may be placed in support structures (which may also be within the larger container and fixed or removable) such as tube holders, tray holders and the like, which may form a part of the interior of the container or be separate components.

Materials are preferably placed into the container and in an organized fashion to maximize heat retention and/or transfer, and/or surface area of the materials exposed to the desired temperature.

Thickness of the container is determined by insulative properties of the container material and the temperature requirements of the materials being shipped.

The thickness of the container outer walls (walls between the environment and the interior chamber) are generally between about 50 mm and 5 cm, and preferably between about 100 mm about 2 cm. As necessary, they could be thicker or thinner as well. Containers are preferably square or rectangular, but can be most any shape or structure desired. Optionally a temperature-control device may be included within the container, which may be a heating or cooling device, such as, for example, a gel pack for when outside temperatures are elevated above a desired range, or a room temperature gel pack to maintain a relatively constant temperature within the container when outside air temperatures are cooler than the desired temperature range. Also optionally, containers may possess a temperature readout system such as a recorder and/or probe to determine and record temperature of the material in the container or simply the temperature inside (or outside) the container.

Suitable devices are commercially available such as, for example, a Propaq temperature recorder and probe.

Containers may also contain structures or other apparatus for fixing materials being transported. For example, the container is designed for fluid (typically air) to pass across the materials. Preferred embodiments utilize ambient air, but contained systems can be used that contain another fluid such as, but not

limited to, Freon, inert gasses or liquids, nitrogen, helium, hydrogen, and combinations thereof. Further, systems can be easily structured to re-cycle the fluid and thereby take advantage of remaining heat or the lack of heat already existing in the conditioned fluid. Optimizing the surface area of the material will ensure that the materials are maintained at the desired temperature, or brought to the desired temperature as quickly as possible. Material packaging can be so optimized (for example by placing ridges into that packaging), or the placing of materials into the container can be optimizes with support structures that allow the conditioned fluid maximum time in contact with a material surface. Such structures include, but are not limited to, stacking inserts for IV fluid bags, fixed or removable lattice-type structures, or any insert that contains a plurality of areas for holding a plurality of materials which may be the same or different. Separations between the inserts could be open to the air, allow for contact between the materials, or separate and insulated, as desired, for example, for maximal heat retention.

Preferably, containers contain about 15°. or more of open space that allow the conditioned air (or other fluid) to surround the materials. More preferably, the containers contain 20% or more, or even 25% or more of open space. The more open space available for heat transfer between the conditioned air and the materials, the faster heat transfer can take place and, thus, the less variation in temperatures can occur over time, and the less time required for temperature change to occur. Of course, the more material present at a specific desired temperature, the more contact may be desired between units of material to allow convention heating to minimize heat loss. Once fully assembled, containers can be transported over long distances without significant risk to the integrity of the contents.

The prototypical device was referred to as the X-1. The X-1 is a collapsible, five gallon nylon cooler with handles modified with a port for the Bair Flugger hose and a one-way flutter valve vent. A Propaq monitor with temperature probe was utilized to monitor the temperature of saline being warmed in the X-1. The system was tested and the impact of the ambient temperature was documented. The X-1 was tested by varying the number of bags and the starting

fluid temperature. The efficiency of the system to retain fluid temperature was also assessed.

The warming of IV fluids to optimal infusion temperature can be accomplished with the Bair Hugger (g) and X-1. The warming time is influenced by the ambient temperature, the starting temperature of the fluids, and the number of bags being warmed. The warmed fluid can be stored and maintained in the X-1.

The heat retention of the fluids is influenced by the ambient temperature, the number of bags warmed, and the insulating properties of the X-1.

The Bair Huggerg, intrinsic to the FST, can be utilized with the X-1 to warm and store large volumes of IV fluids at optimal infusion temperature in the field environment. Infusion of optimally warmed fluids combats hypothermia in the trauma patient decreasing the risk of life-threatening coagulopathy.

The following examples illustrate embodiments of the invention, but should not be viewed as limiting the scope of the invention.

Examples of the Invention One embodiment of the device of the invention was tested to determine the impact of the ambient temperature, the number of bags of fluid, and the starting fluid temperature on fluid warming and heat retention.

The X-l is a simple collapsible 5 gallon nylon cooler (Wal-Mart) with handles. The X-1 is waterproof and minimally insulated with thin intrinsic foam.

The top has a single layer of mylar. A port for the Bair Hugger (g) hose was cut into the side of the cooler near the bottom and the edges over sewn. A one-way flutter valve was cut into the top of the cooler to allow for airflow (Figure 1).

A standard Model 505 Bair Huggerg Warming Unit (BHWU) was utilized for all of the experiments. The Bair Hugged hose was attached to the X-1 via the created port. The BHWU was set on its highest setting (43°C) for all experiments.

A Propaq monitor with temperature probe was utilized for measuring and recording fluid or ambient temperature at 2 minute intervals. When measuring fluid temperature, the probe was placed inside a punctured bag of IV fluid and immersed in the fluid. Normal saline was utilized for all of the experiments.

Experimental Design

The BHWU was initially tested to determine its ability to effectively raise the air temperature within the empty X-1. The effect of the ambient temperature on the efficiency of this process was also tested. For these experiments the temperature probe was suspended in the middle of the empty X-1 through the flutter valve.

Fluid warming and heat retention were then tested in a series of experiments that were duplicated for each set of conditions. The number of bags of fluid was altered as was the starting temperature of the fluid. The ambient temperature was held constant for these experiments (22. 5°C). When multiple bags were utilized, the bags were stacked in a lattice pattern to allow for maximal airflow around each bag. The temperature probe was placed inside the IV bag and immersed in the saline solution. The probed bag was always placed at the furthest position from the hose port. Although only one bag was continuously monitored, it was verified to be representative of the remaining bags. The starting temperature of the fluid was altered by warming or cooling the fluid as necessary and allowing the fluid to reach a steady state prior to the start of the experiments.

For the heat retention experiments, the BHWU was turned off but not disconnected. A mylar space blanket was utilized as an extra layer of insulation in one set of experiments.

System Assessment An objective of this study was to determine if a simple device could be designed as an attachment to the Bair Huggerg or similar device, and utilized to heat a large quantity of IV fluids to the optimal infusion temperature of 39°C. A simple nylon collapsible cooler was modified for this purpose. Initially, the effectiveness of the BHWU and the X-1 system was tested. With the BHWU set on its maximal output (43°C), a temperature curve was plotted against time for the air temperature in the X (Figure 2). The temperature within the X-1 easily reached 43°C in 5 minutes. The influence of the ambient temperature was also assessed (Figure 2). The system was predictably more efficient in the warmer environment. The poor insulating properties of this particular cooler can be seen in

the rapid equilibration of temperature within the cooler to the ambient temperature (Figure 2).

Fluid Warming The feasibility of the BHWU and X-1 system was tested for the ability to warm fluid to an optimal infusion temperature. Seven liters of normal saline were placed in the X-1 and stacked in a lattice pattern to optimize airflow around each liter bag. The fluid reached 39°C from a starting temperature of 22°C in 180 minutes (Figure 3). The temperature of all 7 bags of fluid was similar. The maximal fluid temperature reached was 40. 5°C.

Influence of the amount of fluid being warmed The number of bags of IV fluid being warmed was then altered to determine the impact of the volume of fluid on the efficiency of the system. Experiments were run with 1,4, 7, and 10 bags of saline (Figure 3). The larger fluid volume required longer to warm. Ten liters of fluid reached optimal infusion temperature (39°C) in 4 hours from an average starting temperature of 22. 5°C.

Influence of the starting temperature of the fluid To determine the impact of the starting fluid temperature on the efficiency of the system, 7 bags of fluid were warmed to 30°C and cooled to 10°C and allowed to reach steady state prior to being placed in the X-1. The temperature curves were plotted against the curve of 7 liters of fluid starting out at the ambient temperature of 22. 5°C (Figure 4). In all three experiments, the fluid reached the optimal temperature. The time required was predictably longer for the cooler fluid; however, even 7 liters of 10°C fluid could be warmed to 39°C in 4 hours.

Heat Retention Although not a rapid warming system, the BHWU and X-1 could reliably warm IV fluid to optimal infusion temperature suggesting its use as a warm fluid storage system. Therefore, the ability of the system to maintain the warm fluid was tested. The heat retention was assessed on 7 liters of saline that had been heated to maximal attainable temperature and allowed to reach steady state. The BHWU was turned off but not disconnected. The heat dissipation is plotted in Figure 5. The

ambient temperature was 22. 5°C. The fluid maintained a temperature of >37°C at 2 hours.

Influence of the amount of fluid warmed To determine the impact of the volume of fluid warmed in the X-1 on heat retention, the number of bags was changed. Figure 5 shows the heat retention curves for 1,4, 7, and 10 bags of IV fluids. Although, the larger volume of fluid required longer times to warm, the 10 bags of saline maintained their temperature longer.

Influence of basic insulation The X-1 is a simple nylon cooler with minimal insulation. The impact of the X-1 with and without some added mylar insulation was tested against fluid exposed to the ambient temperature (Figure 6). Seven liters of optimally warmed saline were utilized for these experiments. The simple insulation of the X-1 had an obvious advantage over ambient cooling, but the added mylar layer had minimal impact. However, the system could easily be made more efficient with better insulation. With the current X-1, the BHWU would have to be turned on intermittently to maintain the IV fluid at optimal temperature.

The main objective of this study was to determine if a simple device could be designed as an attachment to the Bair Huggerg or similar device, and utilized to heat a large quantity of IV fluids to the optimal infusion temperature of 39°C. A simple nylon collapsible cooler was modified for this purpose, and we found that the X-1 could be used with the BHWU to optimally warm large volumes of saline.

Although the warming process took time, with intermittent use of the BHWU, many bags of IVF could be maintained at 39°C even in a cold environment.

The warming process was predictably dependent on the ambient temperature, the number of bags of fluid being warmed, and the starting temperature of the IV fluid. The warming process was not necessarily an efficient one requiring as long as 4 hours to optimally warm 10 liters of fluid starting at a temperature of 22. 5°C. However, the system was capable of achieving the optimal fluid infusion temperature of 39°C under every condition tested. Given the time

constraints, however, the system should be thought of and utilized as a warm fluid maintenance and storage system.

Once warmed in the X-1, the fluid's heat retention was impacted by the ambient temperature and the number of bags warmed, and additionally by the insulating properties of the X-1. Since the system would be utilized as a means of maintaining and storing a ready reservoir of warm IV fluid, the heat retention capabilities of the X-1 become very important. These experiments demonstrated a useable system with a simple, poorly insulated, nylon cooler. One skilled in the art can design more efficient chambers and insulations. In addition to insulation, a hose port closure device may also improve the system. Since the X-1 has no such device, the heat retention experiments were performed with the BHWU turned off but still connected. The BHWU may have acted as a heat sink, and, therefore, negatively impacted the heat retention of the X-1. Also, a more efficient one-way valve could be fashioned instead of using the simple flutter valve of the X-1.

Another potential improvement would be a rack system that allowed the bags of fluid to be stored in such a way that air circulates completely around them.

The infusion of optimally warm IV fluid is a major adjunct in fighting hypothermia and the resulting coagulopathy in the trauma patient, especially in the austere field environment of the FST. The warming and maintenance of large volumes of IV fluids is difficult in this environment. However, despite the inefficiencies of the current X-1, 15 bags of saline have been warmed and maintained in this device with periodic re-warming as needed with the BHWU.

The device has been formally tested in the field as previously demonstrated, and also utilized in the care of the combat wounded during Operation Enduring Freedom.

Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. All references cited herein, including all publications, U. S. and foreign patents and patent applications, are specifically and entirely incorporated by reference. It is intended that the specification and examples be considered exemplary only with the true scope and spirit of the invention indicated by the following claims.