The relationship between heating time and temperature for rat tail necrosis with and without occlusion of the blood supply

Influence of Surgical Technique on Post-Operative Complications in the Extraction of the Lower Third Molar: A Retrospective Study

The surgical extraction of the impacted third molar is frequently associated with several complications. The purpose of this study is to assess how two different surgical protocols affect post-operative complications during the extraction of the lower impacted third molars. In order to compare and evaluate two different techniques (triangular flap vs. envelope flap), and the relative post-extraction complications, two groups of 150 patients each underwent to surgical impacted third molar extraction and 60 days of follow-up. The complication rate in the two groups was 14.00% in group A and 17.33% in group B. There was a strong association between smoking (OR: 2.8) and the use of oral contraceptives (OR: 1.75) with complications. The age- and sex-related incidence of complications in hard tissue healing has great variability in the literature; the analysis performed on our data did not show a statistically significant association between them. Even though related to a higher incidence of transient changes in sensitivity, it was found that the envelope flap saw a lower percentage of complications. There is still no clarity on which is the best protocol for the extraction of the lower impacted third molar, and the choice often depends on the surgeon's experience.

In vitro temperature evaluation during cement augmentation of proximal humerus plate screw tips

BACKGROUND

The treatment of proximal humerus fractures in patients with poor bone quality remains a challenge in trauma surgery. Augmentation with polymethylmethacrylate (PMMA) cement is a possible method to strengthen the implant anchorage in osteoporotic bone and to avoid loss of reduction and reduce the cut-out risk. The polymerisation of PMMA during cement setting leads, however, to an exothermic reaction and the development of supraphysiological temperatures may harm the bone and cartilage. This study addresses the issue of heat development during augmentation of subchondrally placed proximal humerus plate screws with PMMA and the possible risk of bone and cartilage necrosis and apoptosis.

METHODS

Seven fresh frozen humeri from geriatric female donors were instrumented with the proximal humerus interlocking system (PHILOS) plate and placed in a 37°C water bath. Thereafter, four proximal perforated screws were augmented with 0.5 ml PMMA each. During augmentation, the temperatures in the subchondral bone and on the articular surface were recorded with K-type thermocouples. The measured temperatures were compared to threshold values for necrosis and apoptosis of bone and cartilage reported in the literature.

RESULTS

The heat development was highest around the augmented tips of the perforated screws and diminished with growing distance from the cement cloud. The highest temperature recorded in the subchondral bone reached 43.5°C and the longest exposure time above 42°C was 86s. The highest temperature measured on the articular surface amounted to 38.6°C and the longest exposure time above 38°C was 5 min and 32s.

CONCLUSION

The study shows that augmentation of the proximal screws of the PHILOS plate with PMMA leads to a locally limited development of supraphysiological temperatures in the cement cloud and closely around it. The critical threshold values for necrosis and apoptosis of cartilage and subchondral bone reported in the literature, however, are not reached. In order to avoid cement extravasation, special care should be taken in detecting perforations or intra-articular cracks in the humeral head.

Potential femoral head osteonecrosis model induced by high-intensity focused ultrasound

Osteonecrosis of the femoral head is a common disease that can result in complex hip replacement. To evaluate potential treatments, a model that consistently creates osteonecrosis is needed. We studied and demonstrated the possibility of developing an osteonecrosis model using high-intensity focused ultrasound (HIFU) on canine femora in vitro. To achieve these goals, the temperature in the medullary cavity of the femoral head was measured. A phenomenological model was developed to fit the measured temperature variations with the HIFU parameters for similar HIFU experiments on femoral heads. The average temperature discrepancy between model and measured values was less than 0.83°C. Histology confirmed that the temperature in the medullary cavity can be elevated to a level at which an acute thermal injury is created. HIFU has the potential to be used in a non-invasive model of osteonecrosis.

Effects of repeated drill use on temperature of bone during preparation for osteosynthesis self-tapping screws

Drills used during preparation for osteosynthesis with self-tapping screws are often used repeatedly until they become blunt and ineffective. Because the sharpness of the drill is one of the most important factors in its cutting efficiency, blunt drills may require the application of extra force, which in turn may contribute to excessive frictional heat produced during preparation of screw holes. Large rises in temperature can impair bony regeneration around screws and contribute to failure of internal fixation. In an attempt to quantify the potential increase in temperature produced by blunt drills, we devised an in vitro experiment to simulate preparation for osteosynthesis by using drills with different degrees of wear. Three drills were used: one was new, one had drilled 600 holes, and the third drill had been in use in theatre for several months. The mean (range) rise in temperature for the three drills were: new drill 7.5 degrees C (0.6-20.5 degrees C); drill after 600 holes 13.4 degrees C (5.7-28.3 degrees C); and drill from theatre 25.4 degrees C (12.4-41.3 degrees C). There was a highly significant difference in the temperatures generated by the three drills, and the changes in temperature were related to the amount of wear. The cost of drills is low, and as their repeated use can compromise the results of the operation they must be discarded after single use.

Osteonecrosis of the femoral head of laboratory animals: the lessons learned from a comparative study of osteonecrosis in man and experimental animals

Animal models of osteonecrosis of the femoral head are indispensable to the understanding of successful treatment modalities for avascular necrosis of the femoral head in adults and in children with Legg-Calvé-Perthes disease. Many of these models adequately reflect the current "vascular deprivation" theory regarding the etiology of the disease. In addition to spontaneous occurrence, surgical- and corticosteroid-induced models are suitable, common experimental ones. Osteonecrosis of spontaneously hypertensive rats appears to be due to defective bone formation and compression of the arteries entering the femoral head at its lateral facets by daily weight-bearing loads. Successful modeling of surgical-induced femoral capital necrosis can be a challenge in animals with a dual epiphyseal blood supply. High doses of corticosteroids are a pivotal risk factor in the development of osteonecrosis. The pathogenesis of corticosteroid-induced osteonecrosis likely resides in reduced blood flow. Steroids may reduce blood flow by numerous mechanisms, including marrow adipocytic hypertrophy leading to sinusoidal compression, venous stasis and, eventually, obstruction of the arteries, and arterial occlusion by fat emboli and lipid-loaded fibrin-platelet thrombi. Other, less common varieties of osteonecrosis include those secondary to endotoxin-induced disseminated intravascular coagulation, immune reactions, immoderately low or high temperatures, and high-impact-related injuries. Common to these diverse forms of osteonecrosis are fibrin thrombi clogging arterioles and small arteries.

THERMAL DOSE REQUIREMENT FOR TISSUE EFFECT: EXPERIMENTAL AND CLINICAL FINDINGS

In this review we have summarized the basic principles that govern the relationships between thermal exposure (Temperature and time of exposure) and thermal damage, with an emphasis on normal tissue effects. We have also attempted to identify specific thermal dose information (for safety and injury) for a variety of tissues in a variety of species. We address the use, accuracy and difficulty of conversion of an individual time and temperature (thermal doses) to a standardized value (eg equivalent minutes at 43 degrees C) for comparison of thermal treatments. Although, the conversion algorithm appears to work well within a range of moderately elevated temperatures (2-15 deg C) above normal physiologic baseline (37-39 deg C) there is concern that conversion accuracy does not hold up for temperatures which are minimally or significantly above baseline. An extensive review of the literature suggests a comprehensive assessment of the "thermal does-to-tissue effect" has not previously been assembled for most individual tissues and never been viewed in a semi-comprehensive (tissues and species) manner. Finally, we have addressed the relationship of thermal does-to-effect vs. baseline temperature. This issues is important since much of the thermal dose-to-effect information has been accrued in animal models with baseline temperatures 1-2 deg higher than that of humans.

Local warming and insertion of peripheral venous cannulas: single blinded prospective randomised controlled trial and single blinded randomised crossover trial

OBJECTIVE

To determine whether local warming of the lower arm and hand facilitates peripheral venous cannulation.

DESIGN

Single blinded prospective randomised controlled trial and single blinded randomised crossover trial.

SETTING

Neurosurgical unit and haematology ward of university hospital.

PARTICIPANTS

100 neurosurgical patients and 40 patients with leukaemia who required chemotherapy.

INTERVENTIONS

Neurosurgical patients' hands and forearms were covered for 15 minutes with a carbon fibre heating mitt. Patients were assigned randomly to active warming at 52 degrees C or passive insulation (heater not activated). The same warming system was used for 10 minutes in patients with leukaemia. They were assigned randomly to active warming or passive insulation on day 1 and given alternative treatment during the subsequent visit.

MAIN OUTCOME MEASURES

PRIMARY: success rate for insertion of 18 gauge cannula into vein on back of hand. SECONDARY: time required for successful cannulation.

RESULTS

In neurosurgical patients, it took 36 seconds (95% confidence interval 31 to 40 seconds) to insert a cannula in the active warming group and 62 (50 to 74) seconds in the passive insulation group (P=0.002). Three (6%) first attempts failed in the active warming group compared with 14 (28%) in the passive insulation group (P=0.008). The crossover study in patients with leukaemia showed that insertion time was reduced by 20 seconds (8 to 32, P=0.013) with active warming and that failure rates at first attempt were 6% with warming and 30% with passive insulation (P<0.001).

CONCLUSIONS

Local warming facilitates the insertion of peripheral venous cannulas, reducing both time and number of attempts required. This may decrease the time staff spend inserting cannulas, reduce supply costs, and improve patient satisfaction.

The effects of operator technique and bur design on temperature during osseous preparation for osteosynthesis self-tapping screws

OBJECTIVE

Although the importance of atraumatic preparation of bone before the placement of osseointegrated implants has long been emphasized, the situation during placement of self-tapping screws has received little attention. Because the production of excessively high temperatures during osseous drilling is known to impair bony regeneration, the strict thermal criteria that are set for implant placement should theoretically be extended to trauma and orthognathic internal fixation.

STUDY DESIGN

Temperatures achieved during the drilling of thawed human cadaveric bone before the insertion of osteosynthesis self-tapping screws were measured in vivo with thermocouples. Combinations of 2 drilling systems and 2 bur designs were studied. Variations in surgical technique were incorporated by altering both the force applied by the operator and the application of irrigant. Statistical significance was examined through use of a Student t test.

RESULTS

One of the 2 bur designs and careful operator technique were associated with significantly smaller increases in temperature. Irrigation had the greatest effect on temperature recorded, the absence of irrigant resulting in temperatures in excess of 70 degrees C.

CONCLUSIONS

These findings emphasize the importance of careful surgical technique and constant irrigation during osseous preparation if the potential for bone regeneration around osteosynthesis self-tapping screws is to be maximized.

Local radiant heating increases subcutaneous oxygen tension

BACKGROUND

We evaluated a novel bandage that incorporates a thermostatically controlled radiant heater. We first determined optimal bandage temperature, based on increases in subcutaneous oxygen tension, a measure correlating well with resistance to infection and wound strength. We then tested the hypothesis that prolonged radiant heating would increase collagen deposition in experimental thigh wounds.

METHODS

The experimental bandages were positioned on the anterior thigh of 8 volunteers, and heated for 2 hours at 38 degrees C, 42 degrees C, or 46 degrees C, in a random order. Subcutaneous oxygen tension under the bandage was recorded from an electrode positioned within a subcutaneous tonometer. We studied 10 volunteers in the second protocol. For 1 week, the experimental bandage was continuously applied to one thigh, and heated to 38 degrees C using a 2-hour on/off cycle. On the alternate week, a standard gauze bandage was applied to the contralateral thigh. Treatment order was randomly assigned. Wound collagen deposition under each bandage was evaluated with subcutaneous polytetrafluoroethylene tubes, which were removed and assayed for hydroxyproline on the eighth day. Data are presented as means +/- SDs.

RESULTS

Skin temperature during heating ranged from 36 degrees C to 37.5 degrees C. Oxygen tension increased approximately 50% during heating, but the increase was comparable at the three tested temperatures. Even after heating was discontinued, subcutaneous oxygen tension remained elevated for the remaining 3 study hours. Collagen deposition after 1 week of active heating was 3.4 +/- 1.0 microg/ cm. After 1 week of control treatment, collagen deposition was 3.2 +/- 1.1 microg/cm (P = not significant).

CONCLUSIONS

Our data suggest that radiant heating at 38 degrees C significantly increases subcutaneous oxygen tension, and presumably resistance to infection. However, prolonged heating at this temperature does not increase wound collagen deposition.

Temporary vascular occlusion and glucose: effects on tumour and normal tissue pH in animal experiments

The relationship between duration of a period of vascular occlusion and magnitude of pH decrease in tumour and normal tissue was investigated in rats. To acidify tissue pH further, moderate dose glucose (2.4-3.0 g.kg(-1).hr(-1)) was administered intravenously through a catheter positioned in a tail vein, immediately after the clamp was released. This sequence of pH modifying modalities was chosen since it is employed in clinical regional isolation perfusion for recurrence of malignant melanoma of the limbs. Tumour pH in rat rhabdomyosarcoma BA1112 decreased more than normal tissue pH under 10, 20, 30 or 60 min of temporary vascular occlusion. Administration of glucose following any period of clamping always decreased tumour pH further. The largest pH decrease (0.29 pH units) was obtained after 30 min of clamping followed by 60 min glucose and 60 min saline infusion. In the clinic the combination of a maximum of 30 min of clamping followed by moderate dose glucose infusion, which can decrease tumour pH effectively, can be easily achieved in the setting of regional isolation perfusion. It can be used for treatment modalities that are known to be enhanced at lowered tissue pH, such as hyperthermia and certain chemotherapeutic drugs. These results form the basis for studying the therapeutic gain which can be obtained with this model.

A comparison between the effect of step-down heating in a tumour and a normal tissue in vivo

A comparison between the effect of step-down heating (SDH) obtained in a C3H mammary carcinoma grown in the feet of CDF1 mice and the skin of normal CDF1 feet is presented. Water-bath heating was used, and SDH was obtained by giving a 44.7 degrees C/10 min treatment followed by heating at 42.2 degrees C for variable times. Single heating at 42.2 degrees C and step-up heating (SUH), i.e. 42.2 degrees C followed by 44.7 degrees C/10 min, were used as controls. The endpoint was the heating time at 42.2 degrees C to obtain either a definite tumour growth time (TGT50) or a specific skin score level (RD50) in 50% of the animals. The effect of SDH and SUH was quantified by the step-down ratio (SDR), calculated as the ratio of the heating times at 42.2 degrees C to obtain the specific endpoint. In both assays the effect of SDH was seen as a significant left shift of the SDH dose-response curve compared to the curve for single heating and SUH. For the comparison of the tumour and the normal tissue response, damage levels with comparable heating times for single heating were used. The therapeutic effect was then investigated by calculating the therapeutic gain factor (TGF), where TGF = SDR(tumour)/SDR(normal tissue). Neither SUH nor SDH gave a TGF significantly different from 1. The results suggest that SDH may be used clinically to shorten the heating time without decreasing the therapeutic effect.

Histopathological changes in the spinal cord after 434 MHz microwave hyperthermia in the cervical region of the rat

The time-course of thermal damage to the spinal cord was studied after hyperthermia of the cervical region in the rat. Local 434 MHz microwave heating of the spinal cord (cervical 5-thoracic 2) was obtained by using a ring-shaped applicator. Heat treatment at 42.9 degrees C (+/- 0.4 degrees C) for 38 min resulted in neurological symptoms, ranging from uncoordinated use of the forelegs to paralysis and death in 90 per cent (28/31) of the animals. Histological sectioning of the treated part of the spinal cord was performed immediately, 4, 24 h and 3, 7, 14 and 28 days after hyperthermia. Immediately and 4 h after treatment, neurons in the grey matter of the cord were affected and vacuolization was observed in the white matter. In animals with paralysis 1 day after treatment, we noticed neuronal degeneration, myelin pallor and sometimes haemorrhagic foci in white and grey matter. As a reaction to the thermal injury, gliosis was observed and invasion of macrophages and lymphocytes (day 3-14). Animals which had severe neurological symptoms at day 1 after hyperthermia, but had recovered completely 28 days after treatment, showed focal scar formation and demyelination in the spinal cord. The observed neurological complications correlated well with the localization of the observed histopathological changes in the cervical spinal cord.

Hypothermia following whole-body heating of mice: effect of heating time and temperature

We have observed an acute and prolonged lowering of body temperature (hypothermia) following whole body heating (WBH) of mice. This phenomenon of heat-induced hypothermia and the subsequent recovery of normal temperatures have been systematically investigated. The hypothermic period can be characterized by two parameters: Tnadir and a recovery time constant (tau). For treatment temperatures below 41 degrees C and treatment durations of 1 h or less, a mild hypothermia (Tnadir greater than 33 degrees C) and fast recovery (tau less than 1 h) occur. Tnadir and tau vary slightly with treatment temperature and are almost independent of treatment length. At treatment temperatures 41 degrees C and above for up to 1 h, we observed acute hypothermia (Tnadir as low as 28 degrees C) and slow recovery (tau = several hours). This region of prolonged hypothermia is characterized by a rapid change of Tnadir and tau with temperature, and a much less rapid change with treatment duration. The WBH temperature-time range causing prolonged hypothermia is very narrow, and if exceeded results in lethality. Critical lethal temperatures have been estimated for several treatment durations from the time constant data. Post-WBH hypothermia can be minimized by keeping the animals in a 37 degrees C environment. However, we find that neither survivability nor intestinal cell repopulation is enhanced by this procedure.

Effects of heat treatment in vitro and in vivo on human melanoma xenografts

The heat response in vitro and in vivo of five human melanoma xenografts grown in athymic nude mice was studied. The melanomas differed significantly in terms of heat sensitivity both in vitro and in vivo. At least two different mechanisms governed the overall heat response of the melanomas in vivo: the primary cell death, induced during treatment, was due to direct cytotoxic effects of the heat; the secondary cell death, induced after completion of treatment, was due to heat-induced vascular damage. The activation energies for the melanomas were not significantly different in vitro and in vivo at temperatures above the inflection point of the Arrhenius curves. Below the inflection point, on the other hand, the activation energies were higher in vitro than in vivo, probably as a consequence of differences in the physiological conditions in vitro and in vivo. The heat responsiveness of the melanomas in vivo was not related to the radioresponsiveness, whether the heat treatment was given at a low or a high temperature. All melanomas developed thermotolerance after a priming heat treatment. The thermotolerance differed significantly in magnitude among the five melanomas. It was concluded from the thermotolerance data that clinical treatment protocols probably should not prescribe more than one hyperthermic treatment per week.

Studies relevant to a means of quantifying the effects of hyperthermia

There is as yet no fully satisfactory method of defining 'thermal dose'. However, in order to relate different hyperthermal treatments it has been suggested that the relationship between heating time and temperature be used to derive an isoeffect parameter which might be useful in this context. The equation t2/t1 = RT1-T2, where t is the treatment time, T the temperature, R = 2 for T greater than 42.5 degrees C and R = approximately 6 for T less than 42.5 degrees C, has been shown to fit the isoeffect data from many studies both in vivo and in vitro. Whether or not this relationship is applicable when the temperature is varying has been tested using an animal model system, i.e. the response of the baby rat tail. It has shown that the relationship between time and temperature is indeed characterized by the above equation, and the phenomena of thermotolerance and step-down sensitization were clearly demonstrated. Tails were then alternated between waterbaths at different temperatures in order to simulate varying temperature. The measured effects were, in general, in good agreement with those derived from the formula. The maximum difference between the observed and predicted effect, obtained under rather extreme conditions unlikely to be experienced clinically, amounted to an under-estimate of the effective temperature by approximately 0.3 degrees C, i.e. a net small effect of thermotolerance. It is therefore suggested that the above formula for 'heat dose' provides a reasonable interim method for comparing clinical hyperthermic treatments. The formula does not, however, account for differing absolute sensitivities between tissues nor for effects of fractionating heat treatments.

1985 Douglas Lea memorial lecture. Hyperthermia in the treatment of cancer

There are sound biological reasons for using hyperthermia in the treatment of malignant disease. This review includes a discussion of this rationale and describes effects of hyperthermia either given alone or in combination with ionising radiation to cells in vitro, tumours or normal tissues. Topics discussed include thermotolerance, step-down sensitisation, fractionation, re-treatment of previously irradiated sites, thermal enhancement ratio and thermal dose. Problems of heat delivery and temperature measurement are considered and the current status of clinical studies is stated briefly.

Arrhenius analysis of the heat response in vivo and in vitro of human melanoma xenografts

The response to heat treatment in vivo (40.5-44.0 degrees C) and in vitro (40.5-45.5 degrees C) of five human melanoma xenografts was studied. Specific growth delay was used as a measure of response after treatment in vivo. Colony-forming ability was assayed in soft agar after treatment in vitro. Dose-response curves were established and subjected to Arrhenius analysis. The Arrhenius curves were found to have an inflection point at 42.0-43.0 degrees C in vivo and 41.5-42.5 degrees C in vitro. The activation energies were in the ranges 426-771 kJ/mol in vivo and 676-739 kJ/mol in vitro above the inflection point and 774-1661 kJ/mol in vivo and 1118-2190 kJ/mol in vitro below the inflection point. Above the inflection point the activation energies in vivo and in vitro were not significantly different for any of the melanomas, and furthermore were similar to those reported for rodent tumours, normal tissues and cells in culture in the same temperature range. Below the inflection point on the other hand the activation energies were lower in vivo than in vitro. This difference was probably a consequence of differences in the physiological conditions in vivo and in vitro. The activation energies in vitro in this temperature range were comparable to those reported for normal tissues and cells in culture.

Experimental studies of thermotolerance in vivo. I. The baby rat tail model

A detailed study of the kinetics and magnitude of thermotolerance has been made using the endpoint of loss of vertebrae in the baby rat tail. A range of different priming treatments was used and for analysis each priming treatment (PT) was given in terms of the heat sensitivity of the tissue as defined by the single treatment (Ds) required for a given effect, i.e. fractional priming treatment PT/Ds. A considerable degree of thermotolerance could be induced so that at maximum the tissue sensitivity was reduced by a factor of more than four in heating time to produce a given effect, or by more than the equivalent of 2 degrees C. The main results of the study were: (a) that the time to reach maximum thermotolerance depends primarily on PT/Ds, independent of the particular conditions used in the priming treatment; (b) that the extent of the maximum also depends primarily on PT/Ds, but the precise form of the relationship depends on the method used to define thermotolerance; and (c) that the rate of decay of thermotolerance is independent of the priming treatment. The implications of these results for clinical hyperthermia are briefly discussed.