Hyperthermia is defined as a core body temperature > 41° C for more than 60 minutes and can be used as an adjunctive treatment or as a salvage treatment in patients with a variety of malignancies. 1 It is known that tumor cells are more sensitive to heat than normal cells, and neoplastic cells can be consistently killed at temperatures 1.0 to 2.0° C lower than normal tissue cells. 2–4 Because neoplastic tissue is more vulnerable to destruction than normal tissue at temperatures of 41 to 43° C, cancer can be preferentially damaged and killed at temperatures above 41.0° C in a time and temperature dependent fashion. 5–7In vitro studies have shown that the cytotoxic activity of some chemotherapeutic agents can be enhanced by mild or moderate hyperthermia. Data exist for compounds such as doxorubicin, cisplatin, carboplatin, melphalan, and methotrexate, demonstrating that the maximal tumor cytotoxicity occurs when the drug is used simultaneously with hyperthermia. 8
The technique of isolated limb perfusion has successfully employed hyperthermia and chemotherapeutic agents such as melphalan and tumor necrosis factor alpha in the treatment of in-transit metastasis from malignant melanoma. 9 However, the extrapolation of hyperthermia to a systemic technique for treatment of metastatic cancer has been limited because of significant toxicities. At elevated temperatures, the heart malfunctions, leading to cardiac arrhythmias and hypotension. 10,11 Electrolyte abnormalities, necessitating the use of dialysis to restore serum electrolyte values to normal, limits use of the procedure. 12 The brain is also vulnerable to damage from hyperthermia that can lead to cerebral edema and seizure activity when the temperature is elevated above 43° C. 13
Despite these difficulties, systemic hyperthermia has been recently used to treat patients with lung cancer by using an extracorporeal venovenous perfusion circuit. 7 Zwischenberger and colleagues 7 were able to achieve a core target temperature of 42.5° C for 2 hours in these patients. Another modality of creating whole body hyperthermia in patients with cancer has been the use of an Aquatherm (Lakewood, New Jersey) radiant heat device. 14 This device uses circulated hot water in a cylinder constructed of copper tubing. The tubing is coated with a high emissivity finish and includes a humidification system to eliminate evaporative loses. Pilot studies have been conducted using the Aquatherm system to achieve whole body hyperthermia at 41.8° C, along with the systemic administration of chemotherapy to treat a range of malignancies. 15–17
We have previously reported a systemic hyperthermic perfusion system that kept the proximal aorta 1° C cooler for 4 hours. 18 In our current study, we modified the previous system by adding a separate venous cooling circuit to extend the temperature differential and safe hyperthermic time. The perfusion circuit was constructed to allow splitting of the venous drainage into two streams. One portion of the drained blood was heated and perfused arterially into the distal aorta to create hyperthermia in the abdomen and pelvis, and a second portion was cooled and perfused into the right atrium to lower the venous return blood to normal body temperature before passage through the heart and lungs. The aim of this new circuit is to allow prolonged hyperthermic treatment for malignancies of the abdominal and pelvic organs while protecting the heart, lungs, and brain from the deleterious effects of elevated blood temperature.
Materials and Methods
The experimental protocol was approved by the University of Michigan Committee on Use and Care of Animals, Ann Arbor, Michigan. All animals received humane care in compliance with University guidelines, State and Federal regulations, and the standards of the Guide for the Care and Use of Laboratory Animals, published by the National Institutes of Health (NIH Publication No. 86–23, revised 1985).
Eleven mongrel dogs (23.3 ± 0.9 kg) were induced with intravenous ketamine (20 mg/kg) and diazepam (1.0 mg/kg), endotracheally intubated, and placed under 0.6 to 1.5% halothane general anesthesia. Mechanical ventilation (Narkomed 2, North American Drager, Telford, PA) was provided at an initial tidal volume of 15 ml/kg, respiratory rate of 10 breaths/minute, and FiO2 1.0, with subsequent adjustments to maintain pCO2 between 35 and 45 mm Hg. An intravenous drip of Lactated Ringer’s solution (Abbott Laboratories, Chicago, IL) was initiated and a 500 mg bolus of cefazolin (Marsam Pharmaceuticals, Inc., Cherry Hill, NJ) administered. Noninvasive temperature probes (Opticath, Abbott Laboratories, Chicago, IL, accuracy of ± 0.1°C, two point calibrated and standardized) were placed in the rectum, bladder, and right tympanic canal.
Following sterile preparation, the left common femoral artery, right common femoral artery, right femoral vein, and right external jugular vein were isolated by surgical cut-down. A 5 cm midline laparotomy incision was performed and an Opticath temperature probe was placed into the peritoneal cavity and anchored to the left psoas muscle with a 2-0 Vicryl stitch (Ethicon, Somerville, NJ). The laparotomy incision was closed in layers. The dogs were anticoagulated with an intravenous injection of 100 units/kg porcine heparin solution (Elkins-Sinn, Inc., Cherry Hill, NJ), followed by incremental boluses to keep the activated clotting time as measured on a Hemochron 800 (International Technidyne Corp., Edison, NJ) between 200 and 300 seconds. A 9 Fr polyurethane sheath with side port and hemostasis valve (Arrow International, Inc., Reading, PA) was inserted into the right common femoral artery for arterial pressure monitoring. An Opticath catheter was inserted through the hemostasis valve to a distance of 50 cm to serve as the proximal aortic temperature probe. A 15 Fr drainage cannula (Bio-Medicus, Medtronic Inc., Eden Prairie, MN) was placed in the right femoral vein, and a 12 Fr reinfusion cannula (RMI, Baxter Health care Corp., Midvale, UT) was inserted 15 cm into the left common femoral artery. A 14 Fr dual lumen catheter (Kendall Health care Products, Kendall Company, Mansfield, MA) was placed into the right atrium via the right external jugular vein. An Opticath catheter was inserted through the drainage port of the dual lumen catheter and floated into the pulmonary artery for temperature measurement. The reinfusion port was used to introduce cooled blood from the perfusion circuit into the right atrium.
The perfusion circuit was constructed from Tygon tubing (1/4 inch internal diameter and [1/16] inch wall thickness, Norton Performance Plastic Corp., Akron, OH) and is schematically illustrated in Figure 1. Before being used, the circuit was primed with 600 ml Lactated Ringer’s solution and recirculated for 1 hour. Temperature probes were placed in the circuit blood path to measure the cool and hot circuit outflow temperatures. Venoarterial perfusion was instituted at a flow of 30 ml/kg/min with a blood roller pump (Sarns/3M, Ann Arbor, MI). The perfusate was warmed to 44 to 45° C using a countercurrent heat exchanger (Biotherm Heat Exchanger, Avecor Cardiovascular, Inc., Plymouth, MN) and circulating water heater (Travenol Laboratories, Sarns/3 M, Ann Arbor, MI). Temperature and hemodynamic data (HR, heart rate; SBP, systolic blood pressure; DBP, diastolic blood pressure) were collected every 15 minutes during the perfusion period. Arterial blood gas and activated clotting time measurement were performed every 30 minutes. The rectal temperature was elevated to ≥ 42° C for 4 hours. A small amount of venous drainage blood (5–6 ml/kg/min) was cooled to 28 to 30° C and reperfused into the right atrium to maintain the pulmonary artery temperature ≤ 38° C. At the end of the perfusion, the anticoagulation was reversed with intravenous protamine 1 mg/kg (Elkins-Sinn, Inc., Cherry Hill, NJ). The animal was then decannulated with surgical repair of venotomy/arteriotomy sites, recovered, and returned to its cage. On postoperative day 7, each dog was euthanized with 7 ml intravenous Beuthanasia-D (Schering-Plough Animal Health Corp., Kenilworth, NJ).
Blood samples were obtained pre- and postoperation and on postoperative day 7. Biochemical analysis of blood samples was performed by the clinical pathology laboratory of the University of Michigan Hospital. Arterial blood gas analysis was performed on an ABL 505 blood gas and electrolyte system (Radiometer Copenhagen, Radiometer America, Cleveland, OH). General physical and neurologic examinations were performed preoperatively, on postoperative day 1 and on postoperative day 7. A previously published canine neurologic scoring system was used, and two examiners performed the clinical assessments. 19 All data are expressed as the mean ± standard error of the mean. Biochemistry data was analyzed using StatView for Windows (Abacus Concepts Inc., Berkeley, CA). Comparison to baseline values was made using analysis of variance (ANOVA) and two-way, paired Student’s t-test. A p value < 0.05 was considered significant.
Ten of 11 dogs survived the operative procedure (Table 1). One animal died during the hyperthermic perfusion period from aortic insufficiency caused by an improperly placed aortic temperature probe. There were no measurable neurologic deficits observed in any of the surviving dogs. Seven of the 10 surviving animals were completely free of morbid complications. Two dogs were euthanized before the end of the 7 day observation period because hind leg swelling limited their mobility. At autopsy, the leg swelling was due to venous congestion, and there was no evidence of muscle necrosis. One dog experienced hemolysis and pigmented urine after the perfusate blood temperature climbed to > 48° C transiently for a period of 10 minutes. This dog was euthanized on postoperative day 1 on the advice of the University Laboratory Animal Management veterinary staff.
The mean urine output was 367 ± 28 ml over the 4 hour perfusion period. On average, each animal required infusion of 2316 ± 295 ml of crystalloid intravenous fluid during the same time period. Blood pressure and HR remained stable throughout the experiment and are illustrated in Figure 2. A small rise in SBP and DBP occurred at the end of the experiment when circuit blood was returned to the animal as a fluid bolus. The rectal temperature was successfully elevated to ≥ 42° C for 4 hours while maintaining the pulmonary artery, proximal aorta, and tympanic canal temperatures at ≤ 38° C (Figure 3). To achieve a rectal temperature of 42° C, the hot femoral artery perfusate had to be heated to between 44 and 45° C (Figure 4), with a circuit flow rate of 27 to 31 ml/kg/min (Figure 5). The heart and brain temperature were maintained at ≤ 38° C by perfusion of blood cooled to 27 to 30° C at a flow rate of 5 to 6 ml/kg/min into the right atrium.
The serum sodium, carbon dioxide, calcium, protein, albumin, and alanine transaminase levels were significantly decreased from baseline immediately postprocedure (Table 2). 20 Chloride, aspartate transaminase, and lactic acid levels were significantly elevated over baseline immediately postprocedure. Only the mean albumin, aspartate transaminase, and lactic acid levels were outside the canine reference ranges directly after the perfusion treatment. The sodium, chloride, carbon dioxide, protein, albumin, alanine transaminase, and lactic acid levels all returned to preoperative baseline values by day 7. On postprocedure day 7, the aspartate transaminase, lactate dehydrogenase, alkaline phosphatase, and creatinine kinase levels had become significantly elevated compared with the baseline values. The serum calcium level was slightly lower than baseline on postprocedure day 7. However, only the mean aspartate transaminase and alkaline phosphatase levels were elevated over both the baseline and canine reference values on postoperative day 7.
Whole body hyperthermia has been induced by a variety of methods; however, the use of extracorporeal blood heating is particularly advantageous as it allows precise control of heat transfer, minimizes skin injury, and allows patients to remain accessible for nursing care. 11,21 In the present study, venoarterial perfusion was capable of raising the rectal temperature to ≥ 42° C and maintaining this temperature with minimal fluctuations during the plateau phase. In vitro studies have shown that exposure to temperatures of 42.5 to 43.0° C for 4 to 8 hours has a significantly greater lethal effect on human tumor cells as opposed to the nonneoplastic cells. 22 With the system used in this study, the precise temperature control crucial to the clinical use of hyperthermia to treat metastatic cancer can be delivered over long periods of time.
Elevated temperature causes acute cardiovascular changes, such as tachycardia and hypotension, which can be quite profound. 23 The increased cardiac work caused by temperature elevation puts an undue strain on patients who tend to be already somewhat debilitated from their neoplastic process before hyperthermic treatment. While tachycardia can be controlled in these patients with β-blockade or the use of calcium channel blockers, the hypotension caused by vasodilation often contraindicates the use of these drugs during whole body hyperthermic treatment. By using a cooling limb in the perfusion circuit of this experimental model, it was possible to abolish the hypotension and tachyarrhythmias normally seen in whole body hyperthermia. Protecting both the heart and brain from adverse elevated temperature during hyperthermic treatment should allow the use of higher target temperatures for a longer period of time, thus increasing the total thermal dose delivered to the tumor.
Minor biochemical abnormalities developed in the immediate postoperative period, and most were corrected by postprocedure day 7. Only the aspartate transaminase, lactate dehydrogenase, alkaline phosphatase, and creatinine kinase levels remained elevated above baseline values on day 7. These laboratory findings are consistent with those published by other investigators and may be indicative of a mild degree of myonecrosis and liver failure. 12 Abnormalities of liver function tests have been reported previously, but no predilection for the type of hyperthermia system being used has been found. One animal experienced hemolysis after the blood perfusate temperature rose to > 48° C. In general, this has not been a problem in the application of whole body hyperthermia treatment. Parks, et al.11 reported on 97 treatments of 41.5 to 42° C hyperthermia averaging 5 hours in 25 patients with no evidence of hemolysis.
As new discoveries are made in the field of tumor biology, it may become possible to combine the favorable aspects of hyperthermic treatment with other anticancer therapies, such as T-cell or cytokine based immunotherapy. Hyperthermia can increase immune surveillance and may also accelerate apoptosis. 10 The emergence of dendritic or antigen presenting cell therapy is another modality where hyperthermia could play a role by providing access to tumor cells via the thermal destructive effect on tumor vascular endothelium. The transition of hyperthermia from isolated limb perfusion to systemic treatment is likely to benefit patients with metastatic cancer, and it is a promising potential component of emerging multimodality cancer therapy.
Our technique of perfusion induced hyperthermia for oncologic therapy, with cardiac and cerebral protection, offers many advantages. It allows for rapid achievement of the treatment temperature of 42° C and precise control of tissue heating once the target temperature is attained. There is little or no danger of skin damage with this technique, and it may allow for prolonged treatment times given its cardiac and cerebral protective component. By using systemic perfusion, more widespread or metastatic tumors can be treated than in techniques that isolate a limb or organ system, such as the liver.
Lower abdominal and pelvic hyperthermia at 42° C can be safely produced and maintained for 4 hours while protecting the heart and brain from temperature elevation by using an extracorporeal perfusion circuit. Production of lower abdominal and pelvic hyperthermia with extracorporeal perfusion causes minimal alterations in biochemical homeostasis. This perfusion technique allows infradiaphragmatic cancer to be treated in a semiselective fashion, rather than subjecting the whole body to hyperthermic stress. A phase I clinical trial in human subjects, approved by an institutional review board, is currently underway at the University of Michigan Medical Center using this technique along with the chemotherapeutic agent melphalan in the treatment of inoperable metastatic cancer limited to abdominal and/or pelvic organs.
Supported by National Institute of Health grant 2T32 CA09672.
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