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Freezing nerve blockade for relief of chronic and postoperative pain
608
ABSTRACTS,
17th ANNUAL
analgesic so that general anaesthesia can usually be avoided. Postoperative pain is also nonexistant since tine nerve terminals have been destroyed. Second, small blood vessels contract and thrombose so there is very little postsurgical bleeding. Third, healing is excellent and often free from scarring although colour changes in pigmented skin and hair do occur. Finally, biopsy of the frozen lesion is possible without anaesthesia or suturing, and histological interpretation is satisfactory. Cryotherapy should be considered as a useful tool in the management of many superficial lesions to be used instead of, alongside or after excision surgery, radiotherapy and chemotherapy. 43. Critical Temperature for Skin Necrosis in Experimental Cryosurgery. ANDREW A. GAGE AND
JOSEPHA. CARUANA, SR. (SUNYAB School of Medicine and Veterans Administration Medical Center, Buffalo, New York). In clinical cryosurgery, controlled technique requires selection of an appropriate temperature goal to achieve destructive results. Differences in recommendations for lethal tissue temperature has stimulated the following experiments which were performed with the objective of determining the temperature for skin necrosis in dogs. Dog skin was frozen with cryosurgical apparatus cooled by liquid nitrogen. The skin was tattooed to permit accurate identification of freezing sites. The tattoos served as sites for insertion of copper-constantan thermocouples mounted in 22gauge needles inserted 2 mm deep perpendicular into the skin. Continuous tracings of temperatures were made on recorders during the freezing-thawing process. Fifty skin sites, each with four tattoo points in which temperature was measured, yielded 200 biopsies. The tattoos were removed 3 days after freezing for histologic examination to determine the extent of damage. The histologic findings permitted classification of the biopsy tissue into three groups, that is, viable, borderline (edge of necrosis seen on slide), or necrotic. Borderline biopsies were important because the minimal lethal temperature was identified accurately. The temperature at biopsy sites ranged from 0 to 64°C. Viable specimens were scattered through the 0-30°C range. All specimens frozen to -10°C or warmer were viable. In biopsies classified as borderline, the range of viability extended to -50°C. The necrotic zone covered a range of - 14 to -64°C. Cell death was certain at temperatures colder than -50°C. Overall, the data showed a substantial spread of cell death over a range of temperatures with viability reasonably certain at - 10°C or colder. These experiments indicate that certainty of cell death in clinical cryosurgery will require that temperatures of -50°C or colder be produced in the tissues. The use of warmer temperature goals, that is, -3O”C, will provide extensive tissue destruction but the chance of survival of
MEETING
cells is sufficiently great to imperil results in the treatment of cancer. 44. Freezing Nerve Blockade for Relief of Chronic and Postoperative Pain. C. J. GREEN, J. W.
LLOYD, AND P. J. D. EVANS (Division of Comparative Medicine, Clinical Research Centre, Watford Rd., Harrow, Middlesex, United Kingdom, England). To be effective, nerve blockade for pain relief should be reliable in interrupting conduction in nerve pathways without precipitating secondary neuritis or neuralgia; it should be a simple technique readily acceptable to patients on an outpatient basis, and it should preferentially block pain pathways with minimal motor or sensory loss. For the past 5 years, we have found cryogenic blockade an effective method of relieving both acute and chronic pain. The general tissue reaction following cryotherapy shows minimal inflammatory response and scarring, and nerve regeneration proceeds without neuroma formation. It has several advantages over other methods of peripheral nerve blockade. We are currently investigating the effects of temperature and the freeze-thaw cycle on the rate of regeneration of rat sciatic nerves. Below -20°C interruption of nerve conduction was complete and not significantly affected by lowering the temperature further. Above -2O”C, the effects were sometimes transient and often unpredictable in duration. The mean duration after an efftcient freeze of motor loss was 40 days and sensory loss was 42.5 days. Similar lengths of time are experienced clinically but return of pain may be delayed much longer or even indefinitely. 45. Differential Hypothermia as a Potential Means for Increasing Chemotherapy Effectiveness. V. P. POPCJVIC,P. POPOVIC, AND E. C. BUR-
DETTE (Department of Physiology, Emory University, Atlanta, Georgia). Experiments were conducted using pregnant female rats. The animal’s body was maintained under hypothermia (15-20”(Z) conditions while the uterine horn (which had been surgically exposed) was warmed using either a 37°C waterbath or 2450 MHz microwave radiation. The large body/uterine horn temperature differential was maintained over a treatment period of 30-60 min. Microwave radiation was applied using a specially designed dielectric-loaded applicator for uniform heating of the uterine to either 37 or 42°C. Temperature was measured using subminiature highresistivity thermistor probes placed orthogonal to the electric field of the applied microwave signal. Tissue (uterine horn embryos) heated to 42°C using microwave radiation (while maintaining whole body hypothermia) was found to be severely damaged upon histologic examination. These effects were consid-
ABSTRACTS,
17th ANNUAL
analgesic so that general anaesthesia can usually be avoided. Postoperative pain is also nonexistant since tine nerve terminals have been destroyed. Second, small blood vessels contract and thrombose so there is very little postsurgical bleeding. Third, healing is excellent and often free from scarring although colour changes in pigmented skin and hair do occur. Finally, biopsy of the frozen lesion is possible without anaesthesia or suturing, and histological interpretation is satisfactory. Cryotherapy should be considered as a useful tool in the management of many superficial lesions to be used instead of, alongside or after excision surgery, radiotherapy and chemotherapy. 43. Critical Temperature for Skin Necrosis in Experimental Cryosurgery. ANDREW A. GAGE AND
JOSEPHA. CARUANA, SR. (SUNYAB School of Medicine and Veterans Administration Medical Center, Buffalo, New York). In clinical cryosurgery, controlled technique requires selection of an appropriate temperature goal to achieve destructive results. Differences in recommendations for lethal tissue temperature has stimulated the following experiments which were performed with the objective of determining the temperature for skin necrosis in dogs. Dog skin was frozen with cryosurgical apparatus cooled by liquid nitrogen. The skin was tattooed to permit accurate identification of freezing sites. The tattoos served as sites for insertion of copper-constantan thermocouples mounted in 22gauge needles inserted 2 mm deep perpendicular into the skin. Continuous tracings of temperatures were made on recorders during the freezing-thawing process. Fifty skin sites, each with four tattoo points in which temperature was measured, yielded 200 biopsies. The tattoos were removed 3 days after freezing for histologic examination to determine the extent of damage. The histologic findings permitted classification of the biopsy tissue into three groups, that is, viable, borderline (edge of necrosis seen on slide), or necrotic. Borderline biopsies were important because the minimal lethal temperature was identified accurately. The temperature at biopsy sites ranged from 0 to 64°C. Viable specimens were scattered through the 0-30°C range. All specimens frozen to -10°C or warmer were viable. In biopsies classified as borderline, the range of viability extended to -50°C. The necrotic zone covered a range of - 14 to -64°C. Cell death was certain at temperatures colder than -50°C. Overall, the data showed a substantial spread of cell death over a range of temperatures with viability reasonably certain at - 10°C or colder. These experiments indicate that certainty of cell death in clinical cryosurgery will require that temperatures of -50°C or colder be produced in the tissues. The use of warmer temperature goals, that is, -3O”C, will provide extensive tissue destruction but the chance of survival of
MEETING
cells is sufficiently great to imperil results in the treatment of cancer. 44. Freezing Nerve Blockade for Relief of Chronic and Postoperative Pain. C. J. GREEN, J. W.
LLOYD, AND P. J. D. EVANS (Division of Comparative Medicine, Clinical Research Centre, Watford Rd., Harrow, Middlesex, United Kingdom, England). To be effective, nerve blockade for pain relief should be reliable in interrupting conduction in nerve pathways without precipitating secondary neuritis or neuralgia; it should be a simple technique readily acceptable to patients on an outpatient basis, and it should preferentially block pain pathways with minimal motor or sensory loss. For the past 5 years, we have found cryogenic blockade an effective method of relieving both acute and chronic pain. The general tissue reaction following cryotherapy shows minimal inflammatory response and scarring, and nerve regeneration proceeds without neuroma formation. It has several advantages over other methods of peripheral nerve blockade. We are currently investigating the effects of temperature and the freeze-thaw cycle on the rate of regeneration of rat sciatic nerves. Below -20°C interruption of nerve conduction was complete and not significantly affected by lowering the temperature further. Above -2O”C, the effects were sometimes transient and often unpredictable in duration. The mean duration after an efftcient freeze of motor loss was 40 days and sensory loss was 42.5 days. Similar lengths of time are experienced clinically but return of pain may be delayed much longer or even indefinitely. 45. Differential Hypothermia as a Potential Means for Increasing Chemotherapy Effectiveness. V. P. POPCJVIC,P. POPOVIC, AND E. C. BUR-
DETTE (Department of Physiology, Emory University, Atlanta, Georgia). Experiments were conducted using pregnant female rats. The animal’s body was maintained under hypothermia (15-20”(Z) conditions while the uterine horn (which had been surgically exposed) was warmed using either a 37°C waterbath or 2450 MHz microwave radiation. The large body/uterine horn temperature differential was maintained over a treatment period of 30-60 min. Microwave radiation was applied using a specially designed dielectric-loaded applicator for uniform heating of the uterine to either 37 or 42°C. Temperature was measured using subminiature highresistivity thermistor probes placed orthogonal to the electric field of the applied microwave signal. Tissue (uterine horn embryos) heated to 42°C using microwave radiation (while maintaining whole body hypothermia) was found to be severely damaged upon histologic examination. These effects were consid-