Devices and methods for maintenance of temperature and pressure during islet shipment

Exposure to extreme temperatures and pressure fluctuations during shipment by air may have a detrimental impact on islet quality. In this study, we sought to assess the ability of methods and devices to provide better control of the internal environment of islet shipping containers in terms of temperature and pressure. METHODS: Experimental islet shipping containers were packed with 21 panels of commercially available TCP Phase 22 Phase Change Material (TCP). The containers were then exposed for at least 15 hours to three constant external temperature conditions, namely, -20 degrees C, 4 degrees C, and 40 degrees C, and then evaluated for their ability to maintain an internal temperature close to the desired value of 22 degrees C. Custom-designed pressure regulated gyroscopic shipping containers (PRGSC) placed in a vacuum chamber were exposed to an absolute pressure of 250 mm Hg (substantially lower than that experienced during shipment by air) for 25 minutes to assess their ability to control internal pressure under vacuum. Electronic data loggers were used to monitor internal and external temperatures and pressures under all conditions. RESULTS: Twenty-one TCP panels placed in a single islet shipping container were able to maintain the internal temperature between 17 degrees C and 24 degrees C for a minimum of 15 hours at all three external temperatures. The PRGSC tested were able to maintain a constant internal pressure of 760 mm Hg when exposed to vacuum. CONCLUSIONS: Our results demonstrated that the use of containers equipped with TCP and PRGSC exert excellent environmental control over islet shipments by minimizing temperature and eliminating pressure fluctuations.     

Randomized prospective comparison of forced air warming using hospital blankets versus commercial blankets in surgical patients

BACKGROUND: The purpose of this study was to evaluate the efficacy of an experimental approach to forced air warming using hospital blankets or a Bair Hugger warming unit (Augustine Medical Inc., Eden Prairie, MN) to create a tent of warm air. METHODS: Adult patients undergoing major surgery were studied. Patients were randomized to receive forced air warming using either a commercial Bair Hugger blanket (control group, n = 44; set point, 43 degrees C) or standard hospital blankets (experimental group, n = 39; set point, 38 degrees C). Distal esophageal temperatures were monitored. Patients were contacted the following day regarding any problems with the assigned warming technique. RESULTS: Surface area covered was 36 +/- 12% (mean +/- SD) in the experimental group and 40 +/- 10% in the control group. Final temperatures at the end of surgery were similar between groups: experimental, 36.2 +/- 0.6 degrees C; control, 36.4 +/- 0.7 degrees C. A similar number of patients had esophageal temperature less than 36 degrees C at the end of surgery in both groups (experimental, 12 of 39 [31%]; control, 12 of 44 [27%]). The majority of patients were satisfied with their anesthetic and warming technique: experimental, 38 of 39 patients; control, 44 of 44 patients. There were no thermal injuries. CONCLUSIONS: Standard hospital blankets heated to 38 degrees C forced air were equally as effective as commercial blankets heated with forced air at 43 degrees C. However, based on concerns expressed by the manufacturer, this experimental technique should not be used until further safety evaluation has been undertaken.     

Intra-atrial temperatures in radiofrequency endocardial ablation: histologic evaluation of lesions

BACKGROUND: Because of the limited information on the effects of ablation in human tissues, we studied intra-atrial temperatures during endocardial radiofrequency applications. We correlated the intra-tissue temperatures with the tissue thickness and with the histologic appearance of the lesions. METHODS: Radiofrequency currents were delivered to human atrial tissue, simulating conditions in endocardial ablation during surgery at set temperature of 70 degrees and 80 degrees C, and intra-tissue temperatures were measured with thermocouples. Radiofrequency applications at 70 degrees C were performed in patients undergoing mitral valve surgery and biopsy specimens were obtained. Samples from in vitro studies and from patients were assessed histologically. RESULTS: The subepicardial temperatures were usually over 60 degrees C in applications in vitro at 70 degrees C and over 70 degrees C in applications at 80 degrees C. Values were higher when the interior of the tissue was warmer than its surface as a result of consecutive radiofrequency applications over the same area. Histologic examination of 12 in vitro samples showed that 10 had transmural lesions. Five of 10 samples from patients with mitral valve surgery had lesions confined to the endocardium, 3 had damaged variable portions of the myocardium, and 2 had transmural lesions. CONCLUSIONS: Although it is possible to obtain transmural lesions in vitro and in vivo with endocardial applications at 70 degrees C, it is significantly more difficult to achieve transmural lesions in patients with mitral valve disease than in normal atrial tissue in vitro. Consecutive applications can raise the intra-tissue temperatures to values significantly higher than those used for application. Our findings suggest that the composition of the endocardium and of the myocardium is a major determinant in lesion formation.     

Changes of body temperature and heat in cardiac surgical patients

Changes in body temperature were assessed in ten adult patients undergoing surgery involving cardiopulmonary bypass (CPB) and induced hypothermia. Intraoperatively, in comparable time intervals before CPB and after rewarming, the patients lost body heat. Between the time of induction of anaesthesia and CPB, the temperature of blood in the pulmonary artery fell 1.46 (SD 0.28 degrees C); between CPB and the end of surgery the fall was 1.55 (SD 0.86 degrees C). The extent of spontaneous hypothermia did not correlate with the amount of subcutaneous fat. Hypothermia was induced to obtain a stable deep body temperature of 27.2 (SD 1.3) degrees C, when mean skin temperature averaged 2 degrees C higher. The CPB machine returned approximately 2000 kJ of heat in the rewarming period, to produce pulmonary artery and mean skin temperatures of 37.1 (SD 0.7) degrees C and 31.4 (SD 2.1) degrees C respectively. Intraoperative deep body temperatures demonstrated the expected exponential relationship with metabolic rate. Postoperatively, increase in metabolic rate was associated with rising deep body and skin temperatures. Low resistance to the flow of heat toward the skin surface was demonstrated by low postoperative values for thermal insulation, which may indicate good peripheral perfusion seen during continuing vasodilator therapy.     

The effect of radiofrequency energy on the length and temperature properties of the glenohumeral joint capsule

The purpose of this in vitro study was to evaluate the effect of radiofrequency energy on the length and temperature properties of the glenohumeral joint capsule in a sheep model. Dissected glenohumeral joint capsules were placed in a 37 degrees C tissue bath and treated with radiofrequency energy at temperature settings of 60 degrees, 65 degrees, 70 degrees, 75 degrees and 80 degrees C. Pretreatment and posttreatment tissue length was measured, and tissue temperature changes were recorded at distances of 0.0, 0.5, 1.0, 1.5 mm away from the probe path. Tissue shrinkage was found to be less than 4% for treatments below 65 degrees C, and increased to 14% for treatments at 80 degrees C. Posttreatment lengths of tissues treated at 65 degrees, 70 degrees, 75 degrees, 80 degrees C were significantly shorter than pretreatment lengths. The maximum tissue temperatures directly below the probe were observed to be 3.7 degrees to 6.7 degrees C lower than the set temperatures. As the distance from the probe was increased, the tissue temperature was found to decrease, reaching a value of less than 45 degrees C at 1.5 mm for all five treatment temperature settings. This study provided basic information on temperature settings, tissue shrinkage, and tissue temperature distribution of radiofrequency treatment.Arthroscopy 1998 May-Jun;14(4):395-400     

A comparison of the effects on bispectral index of mild vs. moderate hypothermia during cardiopulmonary bypass

BACKGROUND AND OBJECTIVE: Bispectral Index correlates with depth of hypnosis in adult patients. Bispectral index monitoring has been separately examined and validated during both mild and moderate hypothermic cardiopulmonary bypass. However, the effect on bispectral index of these two differing cardiopulmonary bypass temperature regimes has not previously been compared, particularly with the use of volatile anaesthetic agents. METHODS: Following Institutional Ethics Committee approval and informed consent, 30 patients undergoing coronary artery bypass grafting had additional bispectral index monitoring. Sixteen patients had mild hypothermic bypass (32-34 degrees C), and 14 had moderate hypothermic bypass (28-30 degrees C). Anaesthesia was standardized, and was maintained with enflurane throughout surgery. Scores were recorded at 14 specific event-related time points during surgery. RESULTS: This study has demonstrated that in this adult population, a relationship exists between bispectral index score and temperature throughout the duration of cardiac surgery, which included mild or moderate hypothermic cardiopulmonary bypass. It also demonstrated that patients which were categorized as having received moderately hypothermic cardiopulmonary bypass had lower bispectral index scores than those patients who received mild hypothermic cardiopulmonary bypass, at time points corresponding approximately with median steady-state bypass temperature, pre-re-warming and early re-warming periods. CONCLUSIONS: Moderate hypothermic cardiopulmonary bypass has lower bispectral index scores when compared to mild hypothermic cardiopulmonary bypass, at a steady state of inspired enflurane. This may reflect an actual increase in the depth of hypnosis. However, as this study did not address the physico-chemical changes of the volatile agent or the accuracy of the bispectral index algorithm at lower temperatures, we would not advocate a change in practice based solely on this report.     

Randomized Prospective Comparison of Forced Air Warming Using Hospital Blankets versus Commercial Blankets in Surgical Patients

Background: The purpose of this study was to evaluate the efficacy of an experimental approach to forced air warming using hospital blankets or a Bair Hugger warming unit (Augustine Medical Inc., Eden Prairie, MN) to create a tent of warm air.

Methods: Adult patients undergoing major surgery were studied. Patients were randomized to receive forced air warming using either a commercial Bair Hugger blanket (control group, n = 44; set point, 43[degrees]C) or standard hospital blankets (experimental group, n = 39; set point, 38[degrees]C). Distal esophageal temperatures were monitored. Patients were contacted the following day regarding any problems with the assigned warming technique.

Results: Surface area covered was 36 +/- 12% (mean +/- SD) in the experimental group and 40 +/- 10% in the control group. Final temperatures at the end of surgery were similar between groups: experimental, 36.2 +/- 0.6[degrees]C; control, 36.4 +/- 0.7[degrees]C. A similar number of patients had esophageal temperature less than 36[degrees]C at the end of surgery in both groups (experimental, 12 of 39 [31%]; control, 12 of 44 [27%]). The majority of patients were satisfied with their anesthetic and warming technique: experimental, 38 of 39 patients; control, 44 of 44 patients. There were no thermal injuries.     

Thermal laser probe angioplasty: influence of constant tip temperature, plaque composition, and probe/vessel diameter ratio

Thermal laser angioplasty uses constant laser power, producing widely variable tip temperatures in vivo. Results have been suboptimal. We studied the effect of 50-400 degrees C tip temperatures on depth of ablation at 192 sites on plaqued and normal human aorta in vitro, and the angiographic and histologic response in vivo of 300-400 degrees C at probe/vessel ratios of 0.5-1.0, in 40 normal canine femoral artery segments. In vitro, there was a direct relationship between tip temperature and depth of ablation, r = 0.71 (all segments), r = 0.74 for fibrous plaque, but a poor correlation in fatty plaque r = 0.35. In fibrous plaque, there was proportionately more ablation at tip temperatures greater than 300 degrees C, mean depth 0.62 mm, than at 150-300 degrees C, mean 0.37 mm, (P less than .001). Ablation was similar in plaqued and normal aorta. In vivo, 300 degrees C, 350 degrees C, and 400 degrees C produced similar effects. At probe/vessel ratios less than 0.8, only disruption of internal elastic lamina was observed. At ratios greater than or equal to 0.8, spasm occurred in 39% (7/18), transmural damage in 28% (5/18), and perforation in one of 18. Ablation is not selective for plaque and is highly variable in fatty plaque. Tip temperatures above 300 degrees C produce greater ablation than at lower temperatures. In clinical applications, probe/vessel rations less than or equal to 0.7 may be most appropriate, and it appears that thermal remodeling may contribute more to outcome than plaque ablation.     

Laser surgery of port wine stains using local vacuum [corrected] pressure: changes in calculated energy deposition (Part II)

BACKGROUND AND OBJECTIVES: Application of local vacuum pressure to human skin during laser irradiation results in less absorption in the epidermis and more light delivered to targeted vessels with an increased blood volume. The objective of the present numerical study is to assess the effect of applying local vacuum pressure on the temperatures of the epidermis and small vessels during port wine stain (PWS) laser treatment. STUDY DESIGN/ MATERIALS AND METHODS: Mathematical models of light deposition and heat diffusion are used to compute absorbed energy and temperature distributions of skin and blood vessels with different diameters (10-60 microm) at various depths (200-800 microm) exposed to laser irradiation under atmospheric and vacuum pressures. RESULTS: Under 50 kPa (15 in Hg) vacuum pressure, peak temperatures at the inner walls of small diameter vessels (10-30 microm) located 200-300 microm below the skin surface are approximately 10 degrees C higher than those under atmospheric pressure, and peak temperatures in the epidermis of patients with skin phototype II are approximately 5 degrees C lower. In patients with darker skin phototype (IV), the peak temperature at the inner wall of a 10 microm diameter vessel located 200 microm below the skin surface is approximately 5 degrees C higher than that under atmospheric pressure, and the peak temperature in the epidermis is approximately 10 degrees C lower. CONCLUSIONS: Additional energy deposition in a larger blood volume permits higher temperatures to be achieved at vessel walls in response to laser irradiation. While more energy is deposited in every vessel, temperature gains in small diameter vessels (10-30 microm) are greater, increasing the likelihood of irreversible thermal damage to such vessels. In addition, temperatures in the epidermis decrease because less energy is absorbed therein due to reduced epidermal thickness and concentration of melanin per unit area.     

Usefulness of monitoring forehead deep-tissue temperature as an index of core temperature in adult patients undergoing laparotomies under general anesthesia--investigation in operating rooms with air-movement control system using vertical flow

BACKGROUND: Acute changes in air temperature in the vicinity of the patents' forehead may impair clinical usefulness of the forehead deep-tissue thermometry. We thus investigated usefulness of monitoring the forehead deep-tissue temperature as an index of core temperature in 12 adult patients undergoing laparotomies in operating rooms with air-movement control system using vertical flow. METHODS: Nasopharyngeal, forehead deep-tissue, palm deep-tissue, and fingertip skin-surface temperatures were recorded during surgery every 5 minutes in operating rooms where room temperature was thermostatically controlled at approximately 25 degrees C. The patients were not actively warmed with forced-air warmers, but covered with cotton blankets where possible. The deep-tissue and fingertip skin-surface temperatures were compared with the nasopharyngeal temperature using regression and Bland and Altman's analyses. RESULTS: The four temperatures continued decreasing during surgery, and the nasopharyngeal temperature decreased to below 36 degrees C 2 hours after induction of anesthesia. Only the forehead deep-tissue temperature satisfactorily correlated with the nasopharyngeal temperature (r = 0.76, n = 300, P < 0.0001). The difference between nasopharyngeal and forehead temperatures was +0.26 degree C, and its standard deviation was 0.34 degree C. CONCLUSIONS: The forehead deep-tissue temperature has sufficient accuracy and precision for clinical use in operating rooms with air-movement control system using vertical flow. However, the core temperature appears to be slightly underestimated with the forehead deep-tissue thermometry.     

Comparison of two convective warming systems during major abdominal and orthopedic surgery

PURPOSE: Convective warming is routinely employed to maintain perioperative normothermia. However, due to differences in nozzle temperature and air flow of the power units, there are clinically relevant differences in heat transfer among convective warming systems. The purpose of this study was to evaluate the use of a quieter, convective warming system (WarmAir, sound pressure level 49 dba, air flow 35 cfm). The WarmAir system was compared to the standard, higher air flow system (Bair Hugger Model 750, sound pressure level 55 dba, air flow 48 cfm) with regards to temperature outcome. METHODS: Patients undergoing general anesthesia for major abdominal and orthopedic surgery were randomized into one of two groups: WarmAir or Bair Hugger. Both groups received an upper body, convective blanket using coverage appropriate for the given surgical procedure. Convective warming, at the high setting, was started after prepping and draping, and distal esophageal or nasopharyngeal temperature was measured intraoperatively. Sublingual temperature was measured preoperatively and on admission to the postanesthesia care unit. RESULTS: The WarmAir (n = 89) and Bair Hugger (n = 95) groups were similar with respect to age, gender, body mass index, ASA status, fluid balance, and duration of surgery. There was no difference in temperature outcomes between groups. In the WarmAir group, preoperative, lowest intraoperative, end of surgery, and postanesthesia care unit admission temperatures were (means +/- SD); 36.3 +/- 0.5, 35.4 +/- 1.1, 36.4 +/- 0.7, and 36.4 +/- 0.6 degrees C, respectively. Corresponding temperatures in the Bair Hugger group were; 36.3 +/- 0.6, 35.6 +/- 1.0, 36.5 +/- 0.6, and 36.4 +/- 0.5 degrees C, respectively. CONCLUSION: Despite differences in heating characteristics, both convective warming systems were effective in maintaining perioperative normothermia in patients undergoing major abdominal and orthopedic surgery. Therefore, choice of warming system is dependent on other factors such as ergonomics and cost.     

Effectiveness of forced air warming after pediatric cardiac surgery employing hypothermic circulatory arrest without cardiopulmonary bypass

STUDY OBJECTIVE: To evaluate the effectiveness of forced-air warming compared to radiant warming in pediatric cardiac surgical patients recovering from moderate hypothermia after perfusionless deep hypothermic circulatory arrest. DESIGN: Prospective unblinded study. SETIING: Teaching hospitals. PATIENTS: 24 pediatric cardiac surgical patients. INTERVENTION: Noncyanotic patients undergoing repair of atrial or ventricular septal defects were cooled by topical application of ice and rewarmed initially in the operating room by warm saline lavage of the pleural cavities. On arrival at the intensive care unit (ICU), patients were warmed by forced air (n = 13) or radiant heat (n = 11). The time, heart rate, and blood pressure at each 0.5 degrees C increase in rectal temperature were measured until normothermia (36.5 degrees C) to determine the instantaneous rewarming rate. MEASUREMENTS AND MAIN RESULTS: Baseline characteristics were not different in the two groups. The mean (+/- SD) age was 5.6 +/- 3.4 years, weight was 20 +/- 8 kg, esophageal temperature for circulatory arrest was 25.7 +/- 1.3 degrees C, and duration of circulatory arrest was 25 +/- 11 minutes. The mean core temperature on arrival at the ICU was 29.9 +/- 1.3 degrees C and ranged from 26.1 to 31.5 degrees C. The mean rewarming rate for each 0.5 degrees C was greater (p < 0.05) for forced-air (2.43 +/- 1.14 degrees C/hr) than radiant heat (2.16 +/- 1.02 degrees C/hr). At core temperatures <33 degrees C, the rewarming rate for forced-air was 2.04 +/- 0.84 degrees C/hr and radiant heat was 1.68 +/- 0.84 degrees C/hr (p < 0.05). At core temperatures > or = 33 degrees C, the rewarming rate for forced air was 2.76 +/- 1.20 degrees C/hr and radiant heat was 2.46 +/- 1.08 degrees C/min (p = 0.07). Significant determinants of the rewarming rate in a multivariate regression model were age (p < 0.001), temperature (p < 0.05), time after arrival to the intensive care unit (p < 0.05), pulse pressure (p < 0. 05) and warming device (p < 0.001). The duration of ventilatory support and ICU length of stay was not different in the two groups. CONCLUSIONS: Both forced-air and radiant heat were effective for rewarming moderately hypothermic pediatric patients. When core temperature was less than 33 degrees C, the instantaneous rewarming rate by forced air was 21% faster than by radiant heat.     

Influence of control variables on mannequin temperature in a paediatric operating theatre

BACKGROUND: Core temperature drops in all children having general anaesthesia. Convection heating may be useful, but its effectiveness in the paediatric setting is not established. Additionally, its utility in many paediatric situations is limited by blanket design. METHODS: Using a mannequin model in a sham operation, we assessed the likely safety and effectiveness of a draping technique in association with a 'Bair Hugger' and a heat dissipation unit (HDU). In Part 1 of the study, the influence of ambient temperature was assessed. In Part 2, a simulated laparotomy was set up and a more detailed assessment of air temperatures around the mannequin was made. In addition, the effect of a change in the HDU design was assessed. RESULTS: Part 1: the technique achieved 'near-plateau' temperature within 5-10 min. A difference of 8 degrees C in ambient temperature (between 18 and 26 degrees C) translated only to a 2-3 degrees C difference under the drapes. Part 2: the technique produced sidestream cooler zones at the head and shoulders. Air temperature at these sites was 28-34 degrees C, whereas at other points (irrespective of their distance from the heat source), it was 37-40 degrees C. Warm air reached sufficient skin sites to anticipate adequate heat transfer in the clinical situation. Air temperature at 'skin' surface stayed below 40 degrees C over the 90-min study period. CONCLUSIONS: A customized HDU used in association with a 'Bair Hugger' unit and a careful surgical draping technique provides stable, safe and consistent air temperatures around a mannequin. Net heat gain by a child's body should occur with this arrangement. Further evaluation in a clinical study is underway.     

Is it safe to use a thermocautery device for circumcision? Examination of the histopathological changes emerging after thermocautery-assisted circumcisions

Multiple number of techniques and devices have been described concerning circumcision method so far. One of them is thermocautery device, and it has been widely used. Although there is controversy that the penis may be damaged due to the heat generated during the use of the device, not enough histopathological studies have been conducted. We aimed to determine the histopathological changes in human foreskin caused by heat after circumcision with thermocautery and to demonstrate the safety of the use of a thermocautery-assisted circumcision. Forty-one patients were divided into two groups according to the thermal energy used during cutting with thermocautery as follows: high temperature (Group 1, n = 22) and low temperature (Group 2, n = 19). The effect of the heat intensity and depth of the coagulation necrosis produced with thermocautery-assisted circumcisions performed at low and high temperatures were evaluated. The difference between the groups was not statistically significant. Tissue damage is extremely limited in thermocautery-assisted circumcisions, even when it is used at high temperatures. The thermocautery device can be used for effective and safe circumcisions.     

Preliminary evaluation of the Arctic Sun temperature-controlling system during off-pump coronary artery bypass surgery

BACKGROUND: Maintaining normothermia during off-pump coronary artery bypass (OPCAB) surgery is a challenge not met by currently available medical devices and strategies. The purpose of this study was to determine the efficacy of a new thermoregulatory device, the Arctic Sun temperature-controlling circulating fluid adhesive pad system, in preventing hypothermia during OPCAB surgery. METHODS: Thirteen consenting patients undergoing OPCAB had their temperature managed using the Arctic Sun system. They were matched with 23 consenting control OPCAB patients whose temperature was maintained with standardized, conventional therapy (elevated ambient operating room temperature, warmed intravenous fluids, and a convective forced air warming system placed under the surgical drapes). Nasopharyngeal temperature (recorded at 1-minute intervals) was compared between the two groups by analysis of both the time and area under the curve for a temperature less than 36 degrees C. RESULTS: Multivariate linear regression analysis revealed that the average amount of hypothermia in the Arctic Sun group was significantly less than in the control group, both for time spent less than 36 degrees C (20.7 vs 121.3 minutes, p = 0.0004) and for area under the curve less than 36 degrees C (11.8 degrees C vs 78.1 degrees C x minutes, p = 0.0001). CONCLUSIONS: The Arctic Sun temperature-controlling system is more effective than conventional warming methods in preventing hypothermia during OPCAB surgery.     

Excimer laser (308 nm) recanalisation of in-stent restenosis: thermal considerations

. Excimer laser recanalisation of in-stent restenosis may be a viable modality for improving coronary patency. However, the presence of arterial stents modifies the thermal properties of the irradiated area and may alter temperature patterns generated during ablation. The goal of this study was to evaluate, in vitro, temperature changes during excimer laser ablation of stented vessels and compare them with those obtained from unstented (control) vessels. Six different stent types (AVE Microstent-II, AVE-GFX, ACS Multi-link, JJ Palmaz-Schatz, JJ Crown, and NIR) were deployed in freshly excised porcine coronary vessels. Three control unstented samples were also measured. Blood or saline was infused through the vessels, while the tissue environment was kept at ∼37°C. A 308 nm excimer laser (Spectranetics, CVX300) with an eccentric 2.0 mm laser catheter (Spectranetics, EII) delivered two trains of 200 pulses each, 10 s apart, at 60 mJ/mm², and 40 Hz, simulating maximum clinical exposure. The catheter was positioned midway in the stent, first coaxially parallel to the vessel wall, and then at an angle against the stent and vessel wall. Temperature measurements (n=168 for blood, n=96 for saline) were performed with a ∼210 μm diameter, fast-response thermocouple with 0.1°C resolution. The probe was positioned to within ∼250 μm from the inner surface of the vessels. Tissue temperature was measured at the catheter tip and at the distal and proximal edges of the stents. Maximum recorded temperatures for coaxial and angular alignment, did not exceed 42.2°C (∼6°C above baseline) and 54.2°C (∼18.1°C above baseline) respectively, for all stents types tested, controls, and all probe locations. Both stented and unstented vessels exhibited comparable temperature gradients. The observed maximum temperatures, obtained under extreme lasing conditions, indicated that 308 nm ablation, in the presence of stents under blood or saline infusion, produces clinically acceptable temperatures.     

Effectiveness of two radiofrequency ablation systems in atrial tissue.

OBJECTIVE: The efficacy of the left atrial radiofrequency ablation procedure, for the curative treatment of atrial fibrillation, is dependent upon obtaining a confluent transmural line of hyperthermic cellular death. We compare the in vitro effectiveness of obtaining transmural hyperthermic cellular death (>55 degrees C) of both the Osypka single electrode and Boston Scientific Thermaline multi-electrode radiofrequency systems. METHODS: Isolated cadaver porcine hearts were used to measure epicardial temperatures either 'central' or at the 'edge' in relation to an endocardial applied radiofrequency electrode. Reference set point was 70 degrees C, and 4-6-mm thick atrial tissue was used for all applications. 'Edge' temperatures with the Boston Scientific unit were measured whilst activating both adjacent electrodes. RESULTS: Boston Scientific: Probe temperature closely approximated the set point. 'Central' epicardial temperature was lower than probe temperature until after 40 s application (P<0.05), 55 degrees C was reached at 50 s, maximal mean temperature 63.0+/-8.9 degrees C was reached at 100 s. Epicardial 'edge' temperature remained lower than probe temperature for the entire 120 s (P<0.05). Osypka: Probe temperature tended to overshoot the set point. 'Central' epicardial temperature paralleled and occasionally exceeded probe temperature reaching 55 degrees C within 10 s, maximal mean temperature 76.3+/-12.7 degrees C was reached at 10 s and exceeded the set point thereafter. 'Edge' temperature was no different to probe temperature or 'central' epicardial temperature. The mean epicardial temperatures produced with a 65 degrees C set point was no different to that with the 70 degrees C set point, except for a lower final temperature at 60 s. CONCLUSIONS: The Boston Scientific system (70 degrees C set point) requires a minimum in vitro application of 40 s to transmurally increase 4-6 mm atrial tissue temperature above 55 degrees C, and 120-s duration per application would appear to be a reasonable clinical recommendation. The Osypka system transfers thermal energy more effectively, requiring less than 10 s in vitro to achieve a similar transmural temperature, and a 30-s application can be recommended. However, a tendency to overshoot both probe and set point temperature, suggests that a lower set point of 65 degrees C might be safer and as effective.     

Determinants of core temperature at the time of admission to intensive care following cardiac surgery

OBJECTIVE: To determine the predictors of core temperature on arrival in the intensive care unit (ICU) after cardiac surgery. DESIGN: Prospective, randomized trial.SETTING: Tertiary care medical center, operating rooms (ORs), and ICU.PATIENTS: 72 patients presenting for coronary artery bypass surgery.INTERVENTIONS: Randomized assignment for ambient OR temperature (16-18 degrees C vs. 21-23 degrees C) and rewarming endpoint on cardiopulmonary bypass (CPB; nasopharyngeal and urinary bladder temperatures >/=36.5 degrees C and 34.0 degrees C, respectively, vs. nasopharyngeal and urinary bladder temperatures >/=37.5 degrees C and 36.0 degrees C, respectively) at the time of separation from bypass.MEASUREMENTS AND MAIN RESULTS: The best (and only significant) predictor of core temperature on arrival in the ICU was rewarming endpoint at the time of separation from CPB (p = 0.004). Patient weight, height, body habitus, and nitroprusside administration did not significantly predict core temperature. Ambient temperature affected only body temperature when the duration of time in the OR after separation from bypass was prolonged (>90 min). A weighted average body temperature was a better predictor of complete rewarming than was any single monitoring site.CONCLUSIONS: To reduce the incidence of hypothermia after cardiac surgery, the most important variable is rewarming endpoint achieved before separation from bypass. A warm ambient temperature (>21 degrees C) may be beneficial if the duration of time in the OR after bypass is prolonged (>90 min).     

Convection heating in pediatric general surgery - a comparison of warming alternatives in a mannequin study

BACKGROUND: Numerous methods of patient warming are used to prevent intraoperative hypothermia in children. Commercially available forced air warming blankets are effective, but are single-use items. We tested a custom-designed heat dissipation unit (HDU) against one such commercially available blanket. METHODS: Air temperatures at various points around a mannequin under simulated operating conditions were recorded using thermistors and thermal imaging. The only variable changed was the heating method: a forced air blanket or a customized HDU with two draping techniques - cotton drapes with and without a plastic 'undersheet'. RESULTS: The three methods produced similar temperature increases and plateaux across the 11 thermistor points measured. There were no significant differences between temperatures at 1 h. A plastic sheet did not appear to enhance the effectiveness of the HDU in this study. Thermal imaging photography suggested more uniform heating of the mannequin with the HDU arrangements. CONCLUSIONS: The custom-built HDU compares favorably in our mannequin study with a Bair Hugger forced air warming blanket. As it is reusable, it offers considerable potential savings.     

Convective warming combined with vasodilator therapy accelerates core rewarming after coronary artery bypass surgery

In a prospective, randomized, controlled study, we have investigated the effect of forced air warming on the rate of change of nasopharyngeal and rectal temperatures in 20 patients after coronary artery bypass grafting. All patients had nasopharyngeal temperatures less than 36 degrees C on arrival in the intensive care unit and received an infusion of glyceryl trinitrate 15 mg h-1, but none received inotropes. Ten patients were warmed under an aluminized plastic "space" blanket (control group) and 10 were warmed under a "Bair Hugger" blanket connected to its power unit on "high" setting (Bair Hugger group). The rates of increase in nasopharyngeal temperature were 0.4 and 0.95 degrees C h-1, respectively, in the control and Bair Hugger groups (P < 0.01) during the first 2 h after operation. Over the same period of time, rectal temperatures increased at a rate of 0.25 and 0.75 degrees C h-1 in the control and Bair Hugger groups, respectively (P < 0.01).