Comparison of forced-air warming and resistive heating.

BACKGROUND: Perioperative hypothermia is common during anesthesia and surgery and is accompanied by several complications. Forced-air warming is recognized as an effective procedure to prevent hypothermia. The aim of this study was to compare a resistive heating device with a forced-air warming device. METHODS: Prospective randomized trial. SETTING: heat transfer laboratory of a University hospital. PARTICIPANTS: six healthy volunteers. INTERVENTIONS: warming with a forced-air warming device (BairHugger 505 and Upper Body Blanket 522; Arizant Healthcare Inc., Eden Prairie, MN, USA) or a resistive heating device (Geratherm Adult system; Geratherm Medical AG, Geschwenda, Germany). MEASURES: heat transfer was measured with 11 calibrated heat flux transducers on the upper body. Additionally, blanket and skin temperatures were measured. The t-test for matched pairs was used for statistical evaluation. RESULTS: Skin temperature under the covered surface was not statistically different between the two groups (37.3+/-0.2 degrees C in the forced-air warming group and 37.8+/-0.2 degrees C in the resistive heating group). In contrast, blanket temperature (40.3+/-0.6 degrees C vs 38.1+/-0.4 degrees C, P=0.002) and heat transfer (13.2+/-3.6 W vs 7.8+/-1.9 W, P=0.048) were significantly higher in the resistive heating group. CONCLUSION: Heat transfer in the resistive heating system was significantly greater than that of the forced-air warming system.

[Heat transfer by conductive warming with circulating-water mattresses]. / Wärmetransfer bei konduktiver Wärmung durch Wassermatten.

AIM OF THE STUDY: To determine the heat transfer by circulating-water mattresses placed under the back and over both legs of human volunteers. METHODS: With approval by the local ethics committee and informed consent eight minimally clothed volunteers were included in the study. Six calibrated heat flux transducers were placed on the back and additionally eight sensors were placed on both legs of each volunteer. The volunteers reclined on a circulating-water mattress (ComfortPad Plus(R), Cincinnati Sub-Zero Products Inc., Cincinnati, OH, USA) coated with gel (Granulab International, Armersfoort, Niederlande). Another circulating-water mattress (Plastipad trade mark, Cincinnati Sub-Zero Products Inc.) was placed over both legs. Both devices were heated to 41 degrees C by a hypo-hyperthermia system (Hico-Variotherm 530, Hirtz and Co. Hospitalwerk, Cologne, Germany). Heat flux data were sampled during steady-state conditions. After determination of the contact area between the mattresses and the skin, heat transfer was calculated by multiplication of the heat flux per area by the contact area. RESULTS: Heat flux per area to the back was 45.6 +/- 4.5 W m (- 2), the contact area was 0.39 +/- 0.03 m (2). This resulted in a heat transfer of 18.0 +/- 2.4 W. Heat flux per area to the legs was 24.7 +/- 4.3 W m (- 2), the contact area was 0.12 +/- 0.01 m (2). This resulted in a heat transfer of 2.9 +/- 0.6 W. CONCLUSION: The heat transfer of the circulating-water mattress to the back was much higher than the heat transfer to the legs. Nevertheless, model calculations show that conductive warming of the legs is more important for the prevention of perioperative hypothermia than conductive warming of the back, because it has a higher impact on the heat balance.

Perioperative thermal insulation: minimal clinically important differences?

BACKGROUND: Reduction of heat losses from the skin by thermal insulation is used to avoid perioperative hypothermia. However, there is little information about the physical properties of various insulating materials used in the operating room. METHODS: The following insulation materials were tested using a validated manikin: cotton surgical drape tested in two and four layers; Allegiance drape; 3M Steri-Drape; metallized plastic sheet; Thermadrape Barkey thermcare 1 tested in one and two layers; hospital duvet tested in one and two layers. Heat loss from the surface of the manikin can be described as: Q(*);= h.DeltaT.A where Q(*); is heat flux, h is the heat exchange coefficient, DeltaT is the temperature gradient between the environment and surface and A is the area covered. The heat flux per unit area (Q(*); A(-1)) and surface temperature were measured with nine calibrated heat-flux transducers. The environmental temperature was measured using a thermoanemometer. DeltaT was varied and h was determined by linear regression analysis as the slope of DeltaT vs Qdot; A(-1). The reciprocal of h defines the insulation. RESULTS: The insulation value of air was 0.61 Clo. The insulation values of the materials varied between 0.17 Clo (two layers of cotton surgical drapes) to 2.79 Clo (two layers of hospital duvet). CONCLUSIONS: There are relevant differences between various insulating materials. The best commercially available material designed for use in the operating room (Barkey thermcare 1) can reduce heat loss from the covered area by 45% when used in two layers. Given the range of insulating materials available for outdoor activities, significant improvement in insulation of patients in the operating room is both possible and desirable.

[Warming efficacy and blood damaging of blood and infusion warmers]. / Erwärmungseffektivität und Erythrozytentraumatisierung verschiedener Infusions- und Bluterwärmungssysteme.

QUESTION: Inadequately warmed blood or infusions contribute to the development of perioperative hypothermia. Therefore we analysed the efficiency of several infusion warmers. METHOD: Tested infusion warmers: Model Autoline (Barkey) 500OR/241(Arizant), BW 385L(Biotest), H250/D50 und D60 (Level-1), H500/D300 (Level-1), Warmflo FW537-I/HEC40 (Tyco). Different solutions (saline, colloid solution and packed red blood cells PRBC) were tested varying the infusion flow, temperature of the solution and infusion pressure. Effective warming was defined as an infusion temperature > or = 33 degrees C. Haemolysis was measured by the increase of free plasma haemoglobin. RESULTS: The infusion warmers were effective within the following flow ranges: Low flow rate (< 250 ml/h): Autoline, 500OR/241 and H250/D60. Medium flow rate (250-2500 ml/h): Autoline, 500OR/241, BW385L (> 480 ml/h), H250/D 60 und D50 (> or = 1300 ml/h), FW537-I/HEC40 (> 950 ml/h. High flow rate (2500-10,000 ml/h): BW385L (up to 5000 ml/h), H250/D50, H250/D60, H500/D300 and FW537-I/HEC 40(R). Highest flow rates (> 10,000 ml/h): H250/D60, H500/D300 and FW537-I HEC40. Colloidal solutions were warmed nearly as good as saline, cooled PRBC had a smaller range of effective warming. There was no relevant haemolysis in any of the tested systems (plasma free haemoglobin raise < 24 mg/dl in all systems). CONCLUSION: The warming capacity of the system and the length of the uninsulated infusion system determine the efficiency of an infusion warmer. The range of effective warming of an infusion warmer should be known for proper application.

Differences among forced-air warming systems with upper body blankets are small. A randomized trial for heat transfer in volunteers.

BACKGROUND: Forced-air warming is known as an effective procedure in prevention and treatment of perioperative hypothermia. Significant differences have been described between forced-air warming systems in combination with full body blankets. We investigated four forced-air warming systems in combination with upper body blankets for existing differences in heat transfer. METHODS: After approval of the local Ethics Committee and written informed consent, four forced-air warming systems combined with upper body blankets were investigated in a randomized cross-over trial on six healthy volunteers: (1) BairHugger trade mark 505 and Upper Body Blanket 520, Augustine Medical; (2) ThermaCare trade mark TC 3003, Gaymar trade mark and Optisan trade mark Upper Body Blanket, Brinkhaus; (3) WarmAir trade mark 134 and FilteredFlow trade mark Upper Body Blanket, CSZ; and (4) WarmTouch trade mark 5800 and CareDrape trade mark Upper Body Blanket, Mallinckrodt. Heat transfer from the blanket to the body surface was measured with 11 calibrated heat flux transducers (HFTs) with integrated thermistors on the upper body. Additionally, the blanket temperature was measured 1 cm above the HFT. After a preparation time of 60 min measurements were started for 20 min. Mean values were calculated over 20 min. The t-test for matched pairs with Bonferroni-Holm-correcture for multiple testing was used for statistical evaluation at a P-level of 0.05. The values are presented as mean+/-SD. RESULTS: The WarmTouch trade mark blower with the CareDrape trade mark blanket obtained the best heat flux (17.0+/-3.5 W). The BairHugger trade mark system gave the lowest heat transfer (8.1+/-1.1 W). The heat transfer of the ThermaCare trade mark system and WarmAir trade mark systems were intermediate with 14.3+/-2.1 W and 11.3+/-1.0 W. CONCLUSIONS: Based on an estimated heat loss from the covered area of 38 W the heat balance is changed by 46.1 W to 55 W by forced-air warming systems with upper body blankets. Although the differences in heat transfer are significant, the clinical relevance of this difference is small.

Comparison of forced-air warming systems with lower body blankets using a copper manikin of the human body.

BACKGROUND: Forced-air warming has gained high acceptance as a measure for the prevention of intraoperative hypothermia. However, data on heat transfer with lower body blankets are not yet available. This study was conducted to determine the heat transfer efficacy of six complete lower body warming systems. METHODS: Heat transfer of forced-air warmers can be described as follows:[1]Qdot;=h.DeltaT.A where Qdot; = heat transfer [W], h = heat exchange coefficient [W m-2 degrees C-1], DeltaT = temperature gradient between blanket and surface [ degrees C], A = covered area [m2]. We tested the following forced-air warmers in a previously validated copper manikin of the human body: (1) Bair Hugger and lower body blanket (Augustine Medical Inc., Eden Prairie, MN); (2) Thermacare and lower body blanket (Gaymar Industries, Orchard Park, NY); (3) WarmAir and lower body blanket (Cincinnati Sub-Zero Products, Cincinnati, OH); (4) Warm-Gard(R) and lower body blanket (Luis Gibeck AB, Upplands Väsby, Sweden); (5) Warm-Gard and reusable lower body blanket (Luis Gibeck AB); and (6) WarmTouch and lower body blanket (Mallinckrodt Medical Inc., St. Luis, MO). Heat flux and surface temperature were measured with 16 calibrated heat flux transducers. Blanket temperature was measured using 16 thermocouples. DeltaT was varied between -10 and +10 degrees C and h was determined by a linear regression analysis as the slope of DeltaT vs. heat flux. Mean DeltaT was determined for surface temperatures between 36 and 38 degrees C, because similar mean skin temperatures have been found in volunteers. The area covered by the blankets was estimated to be 0.54 m2. RESULTS: Heat transfer from the blanket to the manikin was different for surface temperatures between 36 degrees C and 38 degrees C. At a surface temperature of 36 degrees C the heat transfer was higher (between 13.4 W to 18.3 W) than at surface temperatures of 38 degrees C (8-11.5 W). The highest heat transfer was delivered by the Thermacare system (8.3-18.3 W), the lowest heat transfer was delivered by the Warm-Gard system with the single use blanket (8-13.4 W). The heat exchange coefficient varied between 12.5 W m-2 degrees C-1 and 30.8 W m-2 degrees C-1, mean DeltaT varied between 1.04 degrees C and 2.48 degrees C for surface temperatures of 36 degrees C and between 0.50 degrees C and 1.63 degrees C for surface temperatures of 38 degrees C. CONCLUSION: No relevant differences in heat transfer of lower body blankets were found between the different forced-air warming systems tested. Heat transfer was lower than heat transfer by upper body blankets tested in a previous study. However, forced-air warming systems with lower body blankets are still more effective than forced-air warming systems with upper body blankets in the prevention of perioperative hypothermia, because they cover a larger area of the body surface.

Comparison of forced-air warming systems with upper body blankets using a copper manikin of the human body.

BACKGROUND: Forced-air warming with upper body blankets has gained high acceptance as a measure for the prevention of intraoperative hypothermia. However, data on heat transfer with upper body blankets are not yet available. This study was conducted to determine the heat transfer efficacy of eight complete upper body warming systems and to gain more insight into the principles of forced-air warming. METHODS: Heat transfer of forced-air warmers can be described as follows: Qdot;=h. DeltaT. A, where Qdot;= heat flux [W], h=heat exchange coefficient [W m-2 degrees C-1], DeltaT=temperature gradient between the blanket and surface [ degrees C], and A=covered area [m2]. We tested eight different forced-air warming systems: (1) Bair Hugger and upper body blanket (Augustine Medical Inc. Eden Prairie, MN); (2) Thermacare and upper body blanket (Gaymar Industries, Orchard Park, NY); (3) Thermacare (Gaymar Industries) with reusable Optisan upper body blanket (Willy Rüsch AG, Kernen, Germany); (4) WarmAir and upper body blanket (Cincinnati Sub-Zero Products, Cincinnati, OH); (5) Warm-Gard and single use upper body blanket (Luis Gibeck AB, Upplands Väsby, Sweden); (6) Warm-Gard and reusable upper body blanket (Luis Gibeck AB); (7) WarmTouch and CareDrape upper body blanket (Mallinckrodt Medical Inc., St. Luis, MO); and (8) WarmTouch and reusable MultiCover trade mark upper body blanket (Mallinckrodt Medical Inc.) on a previously validated copper manikin of the human body. Heat flux and surface temperature were measured with 11 calibrated heat flux transducers. Blanket temperature was measured using 11 thermocouples. The temperature gradient between the blanket and surface (DeltaT) was varied between -8 and +8 degrees C, and h was determined by linear regression analysis as the slope of DeltaT vs. heat flux. Mean DeltaT was determined for surface temperatures between 36 and 38 degrees C, as similar mean skin surface temperatures have been found in volunteers. The covered area was estimated to be 0.35 m2. RESULTS: Total heat flow from the blanket to the manikin was different for surface temperatures between 36 and 38 degrees C. At a surface temperature of 36 degrees C the heat flows were higher (4-26.6 W) than at surface temperatures of 38 degrees C (2.6-18.1 W). The highest total heat flow was delivered by the WarmTouch trade mark system with the CareDrape trade mark upper body blanket (18.1-26.6 W). The lowest total heat flow was delivered by the Warm-Gard system with the single use upper body blanket (2.6-4 W). The heat exchange coefficient varied between 15.1 and 36.2 W m-2 degrees C-1, and mean DeltaT varied between 0.5 and 3.3 degrees C. CONCLUSION: We found total heat flows of 2.6-26.6 W by forced-air warming systems with upper body blankets. However, the changes in heat balance by forced-air warming systems with upper body blankets are larger, as these systems are not only transferring heat to the body but are also reducing heat losses from the covered area to zero. Converting heat losses of approximately 37.8 W to heat gain, results in a 40.4-64.4 W change in heat balance. The differences between the systems result from different heat exchange coefficients and different mean temperature gradients. However, the combination of a high heat exchange coefficient with a high mean temperature gradient is rare. This fact offers some possibility to improve these systems.

Construction and evaluation of a manikin for perioperative heat exchange.

BACKGROUND: During surgery hypothermia can be avoided only if the heat exchange between the body surface and the environment can be controlled. To allow a systematic analysis of this heat exchange, we constructed and evaluated a copper manikin of the human body. METHODS: The manikin consists of six tubes (head, trunk, two arms and two legs) painted matt-black to simulate the emissivity of the human skin. Hot-water mattresses are bonded to the inner surface of the copper tubes to set the surface temperature. Calibrated heat flux transducers were placed on the following points to determine the heat exchange coefficient for radiation and convection (hRC) of the manikin: Forehead, chest, abdomen, upper arm, forearm, dorsal hand, anterior thigh, anterior leg and foot. Room temperature was set to 22 degrees C. Surface temperature of the manikin was set between 22 degrees C and 38 degrees C. The hRC was determined by linear regression analysis as the slope of the temperature gradient between the manikin and the room versus the measured heat flux. Subsequently we studied five minimally clothed volunteers in a climate chamber. Initial chamber temperature was set to 29 degrees C and was lowered slowly to 12 degrees C. The hRC was determined as described above for each volunteer. RESULTS: The hRC of the manikin was 11.0 W m(-2) degrees C(-1) and hRC of the volunteers was 10.8 W m(-2) degrees C(-1). CONCLUSION: The excellent correlation of hRC between the volunteers and the manikin will allow the manikin to be used for standardised studies of perioperative heat exchange.

In vitro validation of a metabolic monitor for gas exchange measurements in ventilated neonates.

OBJECTIVE: To evaluate the Datex Deltatrac II for measurements in neonates requiring mechanical ventilation. DESIGN: Prospective laboratory evaluation, using a ventilated lung model and gas injection. During simulation of 79 neonatal respiratory settings, assessment of oxygen consumption (VO2), carbon dioxide production (VCO2) and respiratory quotient (RQ) was compared to a reference method (mass spectrometry, wet gas spirometry) using the statistical method of Bland and Altman. INTERVENTIONS: Respiratory variables, which may influence the accuracy and precision of gas exchange measurements, were varied within the following ranges: inspired oxygen fraction (FIO2): 0.21-0.8, expired carbon dioxide fraction (FECO2) and inspiratory-expiratory oxygen fraction (DFO2): 0.0032-0.0256, expiratory flow rate: 1.0-2.5 l/min, inspiratory pressure: 10-55 mbar, respiratory rate 25-60/min, constant RQ of 1. This resulted in 79 tests with VCO2 and VO2 ranging from 8-64 ml/min. MEASUREMENTS AND RESULTS: The coefficient of repeatability for ten single subsequent Deltatrac measurements was 8.09 ml/min for VO2 and 9.17 ml/min for VCO2 compared to 2.02 ml/min and 0.90 ml/min for VO2 and VCO2 with repeated reference measurements. The coefficient of repeatability of the Deltatrac measurements improved considerably when means of subsequent 5 min intervals were compared: 0.68 ml/min for VO2 and 0.28 ml/ min for VCO2. The difference between the two methods (Deltatrac-reference) was -3.8 % (2 s: 11.4%) for VO2, 13.2% (2s: 7.9%) for VCO2 and 17.6% (2s: 16.7%) for RQ. The agreement between methods deteriorated with smaller (FECO2) or DFO2 and increasing FIO2. CONCLUSIONS: Considering limits of agreement of less than +/- 20% as clinically acceptable, results for VO2 assessment indicate acceptable accuracy and precision whereas VCO2 and RQ assessments exceed this limit. Limited accuracy and precision result from detection of CO2 following dilution of expiratory gases and increased sensitivity to error propagation by Haldane equations due to the small differences between inspiratory and expiratory gas fractions.

[Accuracy of intraoperative urinary bladder temperature monitoring during intra-abdominal operations]. / Genauigkeit der Blasentemperaturmessung bei intraabdominellen Eingriffen.

OBJECTIVE: This study investigates whether the site of abdominal surgery or the urine flow rate affects the accuracy of urinary bladder temperature monitoring. METHODS: After approval by the local ethics committee we studied 7 patients during upper abdominal and 10 patients during lower abdominal surgery. Temperatures were recorded with a Hi-Lo Temp Esophageal-Stethoscope (Mallinckrodt Medical) and a Foley Catheter Temperature Sensor FC400-18 (Respiratory Support Products, Mallinckrodt Medical). Each probe and its recording unit were calibrated over a range of 30-40 degrees C against a reference quartz thermometer (Hewlett Packard Model 2801 A) in a water bath before the investigation. Urine flow rate was measured using a urometer. Temperatures and urine flow rate were recorded every 30 min. Agreement between the methods of measurement was assessed as described by Bland and Altman. RESULTS: 124 measuring points could be analyzed. Bladder temperature had a bias (B) of -0.06 degree C compared to oesophageal temperature. Limits of agreement (LOA; +/- 2 s) were +/- 0.68 degree C. In upper abdominal surgery (B: 0.02 degree C; LOA: +/- 0.42 degree C) a higher precision of oesophageal temperature estimation could be demonstrated compared to lower abdominal surgery (B: -0.14 degree C; LOA: +/- 0.82 degree C). Lower urine flow rates generally increased the limits of agreement. Regarding lower abdominal surgery the bias additionally increased to -0.22 degree C. CONCLUSION: Urinary bladder temperature recording is a clinically acceptable method to measure core temperature during abdominal surgery. The accuracy during lower abdominal surgery is decreased compared to upper abdominal surgery, especially in case of a urine flow rate below 250 ml/h.

Cerebrovascular tone rather than intracranial pressure determines the effective downstream pressure of the cerebral circulation in the absence of intracranial hypertension.

Cerebral perfusion pressure is commonly calculated from the difference between mean arterial pressure and intracranial pressure because intracranial pressure is known to represent the effective downstream pressure of the cerebral circulation. Studies of other organs, however, have shown that effective downstream pressure is determined by a critical closing pressure located at the arteriolar level. This study was designed to investigate the effects of PCO2-induced variations in cerebrovascular tone on the effective downstream pressure of the cerebral circulation. Sixteen patients recovering from head injury were studied. Intracranial pressure was assessed by epidural pressure transducers. Blood flow velocity in the middle cerebral artery was monitored by transcranial Doppler sonography. Effective downstream pressure was derived from the zero flow pressure as extrapolated by regression analysis of instantaneous arterial pressure/middle cerebral artery flow velocity relationships. PaCO2 was varied between 30 and 47 mm Hg in randomized sequence. Intracranial pressure decreased from 18.5+/-5.2 mm Hg during hypercapnia to 9.9+/-3.1 mm Hg during hypocapnia. In contrast, effective downstream pressure increased from 13.7+/-9.6 mm Hg to 23.4+/-8.6 mm Hg and exceeded intracranial pressure at hypocapnic PaCO2 levels. Our results demonstrate that, in the absence of intracranial hypertension, intracranial pressure does not necessarily represent the effective downstream pressure of the cerebral circulation. Instead, the tone of cerebral resistance vessels seems to determine effective downstream pressure. This suggests a modified model of the cerebral circulation based on the existence of two Starling resistors in a series connection.

The influence of airway pressure changes on intracranial pressure (ICP) and the blood flow velocity in the middle cerebral artery (VMCA).

OBJECTIVE: Due to the exponential shape of the intracranial volume-pressure relation, simple measurement of epidural, parenchymal or intraventricular intracranial pressure (ICP) in traumatic brain injury (TBI) often fails to early recognize patients with a fulminant development of intracranial hypertension even during recently available methods of tissue PO2 and microdialysis measurements. One approach to this problem could be repetitive intracranial volume provocations to evaluate a trend of the intracranial elastance. Several previously published methods use invasive volume challenge through access to the cerebrospinal fluid (CSF). This pilot study describes changes in intracranial pressure due to variations of airway pressure with BIPAP ventilation maneuvers. PATIENTS AND METHODS: Ten patients with severe TBI were enrolled and completed the study. The inclusion was based on radiologic signs due to TBI in the first CT-scan and the clinical indication for insertion of an ICP monitoring device. Patients with elevated ICP above 20 mm Hg were excluded. The epidural ICP response together with haemodynamic parameters in relation to defined airway pressure changes (delta PAW) was detected. The influence of the duration of delta PAW was evaluated additionally. Data of central venous pressure (CVP), ICP, mean arterial pressure (MAP), cerebral perfusion pressure (CPP), airway pressure (PAW) and blood flow velocity of the middle cerebral artery (VMCA) were analyzed on the basis of differences between the maximum (inspiration) and minimum PAW values (expiration). RESULTS: Elevations of PAW in the range of 20 to 35 cm H2O resulted in changes of the ICPmean from 4.1 to 6.0 mm Hg (r = 0.9, p < 0.05). A correlation was estimated for the changes of systolic arterial pressure (Part) and CPPmean due to PAW variations which ranged between 4.5 and 11.6 mm Hg (r = 0.99, p < 0.05). Concerning the transcranial doppler measurements the data of changes of the blood flow velocity of the middle cerebral artery (VMCA) revealed a positive correlation to PAW with a r = 0.99, p < 0.05. CONCLUSIONS: Elevation of the venous outflow resistance and a transient increase in cardiac output have to be considered as mechanisms for transduction of transthoracic pressure changes to intracranial pressure variations. We conclude, that trends of changes in elastance can be derived from intermittent airway pressure variations. This can be useful in easy and on line dynamic monitoring of ICP in traumatic brain injury.

[Value of reflecting disposable insulation (Thermodrape) in preventing perioperative hypothermia]. / Stellenwert eines reflektierenden Isolationsmaterials (Thermadrape) zur Verhinderung intraoperativer Hypothermie.

OBJECTIVE: The aim of the study was to evaluate the value of reflecting disposable insulation for the prevention of perioperative hypothermia. METHODS: After approval by the local ethics committee 36 patients undergoing long lasting urological intraabdominal surgery were studied. Anaesthesia was performed using etomidate, fentanyl, midazolam, pancuronium and succinylcholine. Patients were randomly assigned to 4 groups. These groups were treated as follows: Gr. 1: Infusion warmer (Hotline HL-90 with System L-70, Level 1 Technologies Inc., Marshfield, USA) and standard O.R. draping with two layers of cotton drapes. Gr. 2: Infusion warmer and reflecting disposable insulation (Thermadrape, O.R. Concepts Inc., Roanoke, USA) covering the legs, upper body, arms and head. Gr. 3: Infusion warmer and convective air warming with upper body blanket (WarmTouch, Mallinckrodt Medical, Hennef/Sieg, Germany). Gr. 4: Infusion warmer, convective air warming and reflecting disposable insulation. RESULTS: After 2 hours of surgery patients of groups 1 and 2 became hypothermic with core temperatures of 35.1 and 35.6 degrees C respectively. No relevant difference could be found between the two groups. The combination of an infusion warmer and convective air warming was an effective method to prevent hypothermia in groups 3 and 4. After 2 hours of surgery these patients had core temperatures of 36.6 and 36.4 degrees C respectively. Reflecting disposable insulation did not improve the effect of convective air warming. CONCLUSION: Reflecting disposable insulation was insufficient in the investigated operative setting.

Severe accidental hypothermia: rewarming strategy using a veno-venous bypass system and a convective air warmer.

OBJECTIVE: To study a rewarming strategy for patients with severe accidental hypothermia using a simple veno-venous bypass in combination with a convective air warmer. SETTING: Eighteen beds in a university hospital intensive care unit. PATIENTS: Four adults admitted with a core temperature less than 30 degrees C. Hypothermia was caused by alcoholic intoxication in three patients and by drug overdose in one patient. MEASUREMENTS AND MAIN RESULTS: All patients were rewarmed by a venovenous bypass and in three cases a convective air warmer was also used. At a bypass flow rate of 100-300 ml/min the mean increase in core temperature was 1.15 degrees C/h (Range: 1.1-1.2 degrees C/h). One patient died 2 days after rewarming as a consequence of a reactivated pancreatitis. The other three patients survived without neurological sequelae. CONCLUSION: This rewarming technique seems safe and effective and allowed the controlled rewarming of our patients who suffered from severe accidental hypothermia

[Ambulatory co-disciplinary risk-adjusted preoperative care]. / Ambulante kodisziplinäre risikoadaptierte Operationsvorbereitung.

Routine preoperative studies in asymptomatic patients are not helpful for perioperative risk evaluation, and the cost is considerable. The decision regarding the status of a patient for elective surgery can be accurately predicted in 95% of cases on the basis of a complete history and physical examination alone; selective testing should be preferred. Interdisciplinary outpatient premedication is suitable for an individual risk evaluation, and a significant reduction in cost and inpatient treatment.