Method of heating medical liquids

A simple and cost-effective method is disclosed to avoid hypothermia and other adverse effects of administration of chilled fluids such intravenous medicating fluid, an intravenous hydrating fluid or blood to a patient during medical procedures such surgery and post-operative recovery. The method provides heat to such fluids, using an elasticized heating device such that each unit can be quickly and easily replaced with another unit when the heating effect of the first significantly diminished, so that the fluid administered is kept at the desirable administration temperature during the entire surgical procedure. The method involves providing a conduit through which the fluid is administered to the patient (usually intravenously or subcutaneously), providing the elasticized device incorporating a semi-solid composition with a relatively high heat capacity, pre-heating the composition to administration temperature; wrapping the device around a length of the conduit; and retaining the device in place by quick release fasteners, so that the pre-heated composition heating the fluid passing through the conduit to the desired temperature immediately prior to administration of the fluid to the patient. Use of two or more devices simultaneously is also disclosed. Further, as the heat content of one device is depleted, the method also includes quick replacement of that device with another, previously pre-heated, so that the heating of the fluid continues substantially continuously at the desire temperature.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention herein relates to medical administration of liquids such as 
intravenous fluids and transfused blood. More particularly it relates to 
methods of maintaining a desired temperature of such fluids. 
2. Description of the Prior Art 
In many medical procedures and situations, it is necessary to administer 
fluids or liquids of one type or another to a patient. Typically a patient 
will be given one or more types of liquid medication or hydrating liquids 
through intravenous administration. Similarly, patients are often provided 
with transfused blood intravenously. Typical of the types of medical 
procedures or situations in which fluids are administered include during 
surgery, in treatment of cardiac arrest, in nurseries, during 
administration of blood from blood banks, to burn patients and during 
post-operative recovery. 
It is well known that such liquids or fluids should not be at low 
temperatures when administered to the patients, since the temperature 
differential between the fluid's temperature and the patient's body 
temperature can have serious adverse effects upon the patient who is 
already in a weakened condition. For instance, when chilled a patient's 
circulatory system has less capacity to carry oxygen. The problem of 
chilling from cold fluids is particularly acute for patients during 
surgery, when a patient's system is already subject to the trauma of 
surgery and is also suppressed by the anesthetic, or during treatment for 
cardiac arrest. See, e.g., Bowen, J. Amer. Assoc. Nurse Anesths., 60, 4, 
369-373 (1992); Bostek, J. Amer. Assoc. Nurse Anesths., 60, 6, 561-566 
(1992); and Anon., Convention Reporter, 22, 2, 9 (Dec. 1992) [Meeting of 
Amer. Society of Anesthesiologists (Oct. 1992)]. 
Unfortunately, however, it is often difficult to deliver fluid to the 
patient at the appropriate temperature. Many fluids are held in 
refrigerated storage until just prior to administration to the patient. In 
addition, it is common practice for operating rooms and recovery rooms to 
be vigorously air conditioned or to use laminar air flow, both of which 
keep the ambient temperature quite low. While there are sound medical 
reasons for this practice, including the comfort of the surgical team 
during lengthy surgical procedures and inhibition of infection in the 
patient, it means that the fluids on hand in the operating room or 
recovery room will remain at lowered temperatures. 
Since it has been recognized that hypothermia of surgical patients is a 
serious problem, and that use of chilled intravenous or transfused fluids 
will aggravate that condition and cause further cooling of internal 
organs, there have been numerous attempts in the past to provide 
techniques and equipment for heating such fluids prior to administration 
to the patient. The Bostek and Bowen articles mentioned above describe 
typical examples. Overall, these various devices have not proved uniformly 
successful. Stand-alone continuous electric heaters through which the 
fluids are passed tend to be cumbersome and must be positioned close to 
the patient, and are thus frequently in the way of the surgical team in 
what is already normally a very crowded area surrounding the operating 
table. They also require electrical power cords, and such cords interfere 
with the surgical team's movements and can be dangerous. In addition, they 
are costly to purchase and operate. Their use is, therefore, frequently 
avoided. 
Alternatively, there have been efforts to use small tube-like devices which 
can be preheated and through which the fluid is flowed prior to 
administration to the patient. Such devices have had shortcomings. Being 
small, they rapidly cool and after a short time no longer heat the fluid 
effectively. Further, such devices have been difficult and time consuming 
to disengage from the fluid flow lines. The result has been that after an 
initial period of adequate heating, the fluid subsequently administered to 
the patient is once again in a chilled condition, since the surgical team 
members do not have the time to engage in lengthy disassembly, reheating 
and replacement of these devices. 
Since the problem of hypothermia in patients and the aggravating effects of 
administration of chilled fluids is an on-going problem, it would 
therefore be advantageous to have a simple method for providing heat to 
these fluids, using a device of a sufficiently simple design that each 
unit could be quickly and easily replaced with another heated unit when 
the heating effect of the first significantly diminished. The fluids 
administered to the patients would therefore be kept substantially 
uniformly at the desirable administration temperature during the entire 
surgical procedure. 
SUMMARY OF THE INVENTION 
The method of this invention is a quick and simple method for providing 
continuous heating of medical fluids which are administered to patients, 
particularly for patients undergoing intravenous fluid administration 
during surgery and/or post-operative recovery. The devices used in this 
invention are themselves simple and readily available. Equally important, 
the method by which these devices are used provides for very quick 
combination of the fluid supply line and the heating device, and equally 
quick and simple replacement of a freshly-heated device for one which has 
had its heat storage depleted. Further, it is a highly cost-effective way 
to provide for heating of the fluids, particularly as compared to the 
elaborate electrical machines described above. 
In its broadest form, the invention herein is a method of heating fluids to 
a temperature appropriate for administration to a patient which comprises 
providing a fluid supply conduit through which the fluid is passed to be 
administered to the patient, preferably via intravenous or other 
subcutaneous administration, providing an elasticized device, normally 
elongated, having an interior containing a semi-solid composition having a 
relatively high heat capacity, pre-heating the composition within the 
elasticized device to a pre-determined desired administration temperature; 
wrapping the device around a predetermined length of the fluid conduit; 
and retaining the device in place by quick release fastening means; such 
that the pre-heated composition with the device transfers heat to the 
adjacent conduit thereby heating the fluid passing through the conduit to 
the desired temperature immediately prior to administration of the fluid 
to the patient. 
In a further embodiment, the method includes rapidly disengaging the 
quick-release fastener, separating a device from which a significant 
quantity of the heat of its composition has been transferred, providing an 
equivalent device with its included composition pre-heated to the desired 
temperature, and quickly attaching the second device to the fluid conduit 
using quick-release fastening means, such that the heating of the conveyed 
fluid prior to administration to the patient continues substantially 
continuously at the desire temperature. 
In yet another embodiments, a second device is heated and attached to the 
fluid conduit prior to removal of a previously attached device which has 
transferred a significant amount of its heat, and the previously attached 
device is then removed, further such that the heating of the conveyed 
fluid prior to administration to the patient continues substantially 
continuously at the desire temperature.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS 
The process of this invention will be best understood by reference to the 
drawings. In FIG. 1 an elongated elasticized heating device 2 is shown, 
which has the general appearance of an elastic bandage, has enclosed 
within itself one or more pockets 4 each containing a semi-solid 
composition 6 with a high heat capacity. Both the device 2 and the 
composition 6 will be described below in further detail. Prior to use the 
heating device 2 is pre-heated, for instance by use of a microwave heater 
8, so that the semi-solid composition 6 will be heated to the desired 
pre-heat temperature from which it in turn can transfer heat to the fluid 
10 which is to be administered to the patient. The fluid 10 is contained 
in a suitable reservoir such as an IV bottle 12 from which it is conveyed 
to the patient (not shown) through tubing or a similar flexible conduit 14 
as indicated by the arrow 16. 
Once the composition 6 has reached the desired pre-heat temperature, the 
device 2 is transferred from the heater 8 as indicated by arrow 18, 
stretched moderately to activate the elasticity in the device 2 and 
wrapped in abutting or overlapping coils 20 around the outside of an 
extended length of tubing 14. Each end of the wrapped elasticized heating 
device 2 is then secured to the next adjacent coil 20 through a 
quick-release fastener 22. The device 2 is thus placed and retained 
quickly and easily; it can then transfer the heat contained in the 
composition 6 directly through the wall of conduit 14 to the fluid 10 
passing through such that upon administration to the patient, the fluid 10 
is at the appropriate administration temperature. 
After a device 2 has been in place on the tubing 14 for some time, it will 
of course begin to cool as its heat is transferred to the fluid 10. In 
order to maintain the fluid 10 in the desired temperature range on a 
continual basis throughout the medical procedure, it is contemplated that 
as a first device 2 begins to cool, it will be removed from the tubing 14 
and replaced by a second pre-heated device, and that when it cools by a 
third device, and so forth as long as needed or desired. In some cases, as 
where the length of tubing available for wrapping with the device 2 is 
relatively short, the first device will be fully removed before the second 
device is attached. Alternatively, and preferred where there is a 
sufficiently long section of tubing 14, one can put the second device 2 in 
place prior to removal of the cooling first device 2, and thus minimize 
any change in fluid administration temperature. One may establish a 
replacement and reheating schedule for individual devices 2 so that there 
are always two or more devices 2 in place along a section of tubing 14 and 
an essentially constant administration temperature of the fluid is 
maintained. 
The length of the portion of tubing 14 which is to be surrounded by the 
device 2 will depend on a number of factors. These will include the inlet 
temperature and the desired administration temperature of the fluid 10, 
the diameter and wall thickness of the tubing 14, the thickness of the 
device 2, the rate of flow of the fluid 10 through the tubing 14 and the 
length of the device 2 that can be easily handled, wrapped quickly and 
securely and then subsequently unwrapped by surgical team personnel. 
Normally the length of the device 2 and degree of pre-heating of the 
composition 6 will be chosen so that the administration temperature of the 
fluid 10 to the patient closely approximates normal body temperature, 
i.e., 37.degree.-38.degree. C. Given the flow rate of the fluid, the known 
temperature of the fluid in the reservoir and the size of the tubing 14, 
it is then a simple matter for one skilled in the art to readily determine 
the required degree of heating of the composition 6 and the length of 
wrapping of the device 2 around the conduit 14. Commonly a length of about 
6-24 inches (15-60 cm) of the tubing 14 will be wrapped and exposed to the 
heat from the device 2, and the composition will be preheated to a 
temperature of about 40.degree.-45.degree. C. Heating of the composition 
in a conventional microwave oven at full power will normally take about 
60-90 seconds to bring the composition from ambient temperature to the 
appropriate heating temperature. 
There are a number of ways of securing the ends of the device 2 to hold it 
in place on the tubing 14. Typically, the fastening device 22 can be a 
toothed clip as shown in FIG. 3, where the curved prongs 28 hook into the 
elasticized fabric 30 of the device 2 and are then readily unhooked when 
the device 2 is to be removed from the tubing. Such clips are 
conventionally used with elastic bandages and are readily obtainable 
commercially. Alternatively and preferably, as shown in FIG. 4, one can 
attach to opposite sides of the fabric 30 short pieces of hook-and-loop 
fastener material 22' (such as that sold commercially under the tradename 
"Velcro"). Thus, when the coils 20 of the device 2 are wrapped around the 
tubing 14, the pieces of hook-and-loop fastener 22' will engage each 
other, thus securing the ends of the device 2 in position. When it is 
desired to unwrap the device 2 and remove it, that can be simply 
accomplished by pulling the two parts of the hook-and-loop fastener 22' 
apart. 
The structure of the device 2 is most easily understood from FIG. 2. The 
device is primarily made from an elasticized woven fabric 30 typical of 
the fabrics from which conventional elastic bandages are made. Embedded 
within the fabric 30 are one or more pockets 4 containing the heatable 
composition 6. The composition is normally a "semi-solid" material, which 
for the purposes of this invention will be considered to be any material 
which has the consistency, flexibility and thixotropic properties of 
materials commonly referred to as "gels" or "slushes," and which has a 
reasonably high heat capacity sufficient to retain and emit significant 
quantities of heat over a prolonged period. There are a number of 
materials known for this purpose, some of which are commercially 
available. Typically they are water-based materials containing significant 
quantities of dihydric alcohols, commonly propylene glycol. The water 
content will normally be on the order of about 60-90 percent by weight of 
the composition, with most of the balance being the dihydric alcohol. The 
composition may also contain various small quantities of stabilizers, 
dyes, biocides and the like. Typical compositions are illustrated in a 
number of publications including Dunshee, U.S. Pat. No. 4,953,550 (1990); 
Mellan, Polyhydric Alcohols (1962), especially pages 46-71, and Monick, 
Alcohols: Their Chemistry, Properties and Manufacture (1968), especially 
Chapter 4. Those skilled in the art will immediately recognize other 
compositions, in addition to the water/dihydric alcohol compositions, 
which will have the desired properties described and which will be usable 
in this invention. Preferably the materials used in composition 6 will be 
non-toxic, non-corrosive and otherwise inert or harmless, so that they 
will not degrade the device 2 and, if a leak should develop, they will not 
harm the patient, medical personnel or equipment. 
It will also be recognized that both the composition 6 and the fabric 30 
must be such that they are not harmed or degraded by heating in the 
heating device 8. The composition 6 must also be such that heating to the 
desired temperature does not generate any significant amount of gas or 
vapor which would cause the pocket 4 to be ruptured or otherwise cause any 
of the composition 6 to leak. Depending on the degree of solidity of the 
composition 6 and the nature of the fabric 30 one may optionally also 
include a liner or pouch 26 surrounding the composition 6 between the 
composition 6 and the fabric 30. Typical materials and configurations are 
shown in the Dunshee patent mentioned above. It may be desirable to have 
the entire fabric 30 covered with an outer protective layer 22 (only a 
portion of which is shown). Layer 32 could be mace of an elasticized 
canvas material with a plastic material incorporated therein, to resist 
the accumulation of dirt or grime because of repeated handling or of being 
thrown aside during the haste which necessarily accompanies many medical 
procedures, and which also permits ready cleaning of the surface. 
In addition, one may wish to have an layer of insulating material 32' 
placed on the exterior of the device 2 on the side which will be opposite 
the surface which is to contact the conduit 14, in order to help retain 
heat within composition 6 and to avoid loss of heat to the ambient 
surroundings. Such will be feasible, however, only if such an insulating 
layer has sufficient flexibility and elasticity to be stretched and 
secured as required for securing device 2 in the present method. 
A typical device 2 which can be used in the process of this invention is 
one sold commercially under the tradename "Champ Hot Wrap" by Carolon 
Company of Winston-Salem, N.C. 
It will be evident to those skilled in the art that there are a number of 
embodiments of this invention which, while not expressly set forth above, 
are clearly within the scope and spirit of the invention. The above 
description is therefore intended to be exemplary only, and the scope of 
the invention is to be limited solely by the appended claims.