Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
1998-11-20
2002-04-23
Dvorak, Linda C. M. (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
C607S108000
Reexamination Certificate
active
06375673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat transfer system for and method of controlling a patient's temperature. In another aspect, the present invention relates to a heat transfer blanket for and method of controlling a patient's temperature. In even another aspect, the present invention relates to a heat transfer blanket for controlling a patient's temperature where in the heat transfer blanket comprises independently controlled zones for heating and cooling, and a method for heating and cooling various parts of a patient at different temperatures and rates.
2. Description of the Related Art
Man is considered to be a tropical animal, with normal functioning requiring a body temperature of about 37° C. Relying only upon that protection from temperature stress which is provided physiologically at birth, comfortable human survival would require an environment of 37° C., +/− perhaps 1°. See, “Hypothermia-physiology, Signs, Symptoms and Treatment Considerations”, Search and Rescue Society of British Columbia, compiled by Michael McEwan, 1995. The McEwan article further notes that a body can self-compensate for small upward or downward variations in temperature through the activation of a built-in thermal regulatory system, controlled by temperature sensors in the skin.
For example, the response to an upward variation in body temperature is the initiation of perspiration, which moves moisture from body tissues to the body surface, where evaporation causes cooling. Likewise, the response to a downward variation in body temperature is shivering, which is the body's involuntary contraction and expansion of muscle tissue on a large scale in an attempt to generate heat.
Stiff and Sixta, “Hypothermia Care and Prevention”, 1997, generally define hypothermia as occurring when the body's core temperature drops below its normal 37° C.
The McEwan article defines impending hypothermia as occurring when the core temperature decreases to 36° C.
In the early stages mild hypothermia causes vigorous shivering which is usually accompanied by an increase in pulse and breathing rates. Cold, white hands and feet (as the blood vessels in the skin constrict) are the first signs of blood being shunted away from the body's extremities.
The McEwan article describes mild hypothermia as occurring when the core temperature is dropped to the range of 34-35° C. At this point, uncontrolled, intense shivering begins, although the victim is still alert and able to help self, however, movements become less coordinated and the coldness is creating some pain and discomfort.
The McEwan article defines moderate hypothermia as occurring when the core temperature is in the range of 31 to 33° C. At this point shivering slows or stops, muscles begin to stiffen and mental confusion and apathy sets in. Speech becomes slow, vague and slurred with breathing becoming slower and shallower.
The McEwan article defines severe hypothermia as occurring when the core temperature is below 31° C., with Stiff and Sixta defining severe hypothermia as resulting when the body temperature drops below 33° C. Shunting of the blood continues, manifesting as bluish lips and finger tips from poor oxygenation of the tissues near the body surface. Decreased circulation as results in a build-up of acid metabolites (waste products) in the muscles of the extremities until shivering stops and is replaced by muscular rigidity. The pulse and respirations begin to slow as the body core cools to 30° C. The heart may stop at temperatures of about 28° C. or less.
Hypothermia can occur easily enough during any outdoor excursion, especially in wilderness situations where weather conditions may deteriorate unexpectedly or where travelers may become lost, injured or exhaust food supplies prematurely. Additionally, outdoor activities involving water presents the added possibility of emersion with the body cooling up to 25 times faster in water than in air.
Mild hypothermia is also a common occurrence during major surgery on the body. The usual causes of such perioperative hypothermia or anesthetic-induced impairment of thermal regulation, exposure to cold, altered distribution of body heat, and surgical exposure of the body cavity to a room temperature environment. This is particularly a problem in patients anesthetized for over two hours in where there are large incisions exposing the body's interior to room temperature. Routine measures to reduce heat loss during operation include covering the skin, warming intravenous fluid and transfused blood, and increasing ambient temperature. In most operations, with the exception of those on the brain, prevention of hypothermia is a mainstay of anesthetic management because hypothermia during surgery can adversely affect the outcome. See “Colorectal Surgery Comes in From the Cold”, The New England Journal of Medicine, Vol. 334, No. 19, Mortensen, et al, May 19, 1996.
As discussed above, hypothermia may be encountered as a result of an accident or may be inadvertently acquired during major surgery. In an odd twist, hypothermia may be induced by a physician in the treatment of various conditions usually those in which the physician desires to protect the brain or heart. For example, U.S. Pat. No. 5,486,204, issued Jan. 23, 1996 to Clifton discloses a method of treating a non-penetrating head wound with hypothermia. Such a treatment protocol includes specific defined times, temperatures, rates of change of temperature and the timing of the introduction of medications, and controlled rewarming. Additionally, hypothermia is frequently induced during surgery for intra cranial aneurysms.
The McEwan article notes that treatment of cold injuries has long been controversial. It is also clear that it is not enough merely to reheat a victim suffering from hypothermia, but that controlled heating must be applied. For example, Baron Larrey, Napoleon's Chief Surgeon observed that those soldiers, suffering from hypothermia, who were placed closest to the campfire during Napoleon's retreat from Russian died. These soldiers probably rewarmed rapidly. As a general principle initial management principles for treating hypothermia emphasized prevention of further heat loss, rewarming as soon as it is safely possible at a “successful” rate (slowly) and rewarming the core before the shell in an attempt to avoid inducing lethal side effects during rewarming. This treatment goal is noted as being important, since hypothermia itself may not be fatal above 25° C. core temperature. Fatalities at 25° C. or greater normally occur during rewarming.
The McEwan article notices that hypothermia causes several reactions within the body as it tries to protect itself and retain its heat, the most important of these being vaso constriction, which halts blood flow to the extremities in order to conserve heat in the critical core area of the body. Shivering is noted as maintaining peripheral vaso constriction, which minimizes the severity of vascular collapse during rewarming. Induction of vasodilation in hypothermia patients may precipitate rewarming shock and metabolic acidosis. This may occur where the periphery (legs and arms) are warmed before the core (heart and lungs) are warmed. Furthermore, the rapid shunting of cold blood from the extremities to the core as a direct result of vasodilation may cause the core temperature to drop. Prevention of vasodilation is the reason why it is imperative that the hypothermia victim's extremities not be rewarmed before the core. If vasodilation occurs, cold blood returning to the heart may be enough to put the patient into ventricular fibrillation. Again see, the McEwan article.
The McEwan article notes treatment for the different levels of hypothermia. According to McEwan, treatment for mild hypothermia includes keeping the head and neck covered. Stiff and Sixta note that treatment for mild hypothermia generally includes application of hot packs, water bottles, or warm campfire rocks wrapped in hot, wet t
Clifton Guy L.
Miller Emmy R.
Dvorak Linda C. M.
Ram Jocelyn
Russ LLP Hodgson
The Board of Regents of the University of Texas System
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