Anselm Bräuer

Prospective Clinical and Fiberoptic Evaluation of the Supreme Laryngeal Mask Airway

Background:In March 2007, a new disposable laryngeal mask airway (LMA) became available. The LMA Supreme™ (The Laryngeal Mask Company Limited, St. Helier, Jersey, Channel Islands) aims to combine the LMA Fastrach™ feature of easy insertion with the gastric access and high oropharyngeal leak pressures of the LMA ProSeal™. Methods:The authors performed an evaluative study with the LMA Supreme™, size 4, on 100 women to measure the ease of insertion, determinate the laryngeal fit by fiberoptic classification, evaluate the oropharyngeal leak pressure, and report adverse events. Results:Insertion of the LMA Supreme™ was possible in 94 patients (94%) during the first attempt, and in 5 patients (5%) during the second attempt. In one small patient, the LMA Supreme™ could not be inserted because of limited pharyngeal space. This patient was excluded from further analysis. Insertion of a gastric tube was possible in all patients at the first attempt. The median time for LMA Supreme™ insertion was 10.0 s (±4.7 s; range, 8–30 s). Laryngeal fit, evaluated by fiberscopic view, was rated as optimal in all patients, both immediately after insertion of the LMA Supreme™ and at the end of surgery. After equalization to room pressure, the mean cuff volume needed to achieve 60 cm H2O cuff pressure was 18.4 ml (±3.8 ml; range, 8–31 ml). The mean oropharyngeal leak pressure at the level of 60 cm H2O cuff pressure was 28.1 cm H2O (±3.8 cm H2O, range, 21–35 cm H2O). Eight patients (8.1%) complained of a mild sore throat. No patient reported dysphagia or dysphonia. Conclusions:Clinical evaluation of the LMA Supreme™ showed easy insertion, optimal laryngeal fit, and low airway morbidity. Oropharyngeal leak pressure results were comparable to earlier data from the LMA ProSeal™.

Comparison of forced-air warming systems with lower 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.

Randomized comparison of the i-gel™, the LMA Supreme™, and the Laryngeal Tube Suction-D using clinical and fibreoptic assessments in elective patients

BackgroundThe i-gel™, LMA-Supreme (LMA-S) and Laryngeal Tube Suction-D (LTS-D) are single-use supraglottic airway devices with an inbuilt drainage channel. We compared them with regard to their position in situ as well as to clinical performance data during elective surgery.MethodsProspective, randomized, comparative study of three groups of 40 elective surgical patients each. Speed of insertion and success rates, leak pressures (LP) at different cuff pressures, dynamic airway compliance, and signs of postoperative airway morbidity were recorded. Fibreoptic evaluation was used to determine the devices’ position in situ.ResultsLeak pressures were similar (i-gel™ 25.9, LMA-S 27.1, LTS-D 24.0 cmH2O; the latter two at 60 cmH2O cuff pressure) as were insertion times (i-gel™ 10, LMA-S 11, LTS-D 14 sec). LP of the LMA-S was higher than that of the LTS-D at lower cuff pressures (p <0.05). Insertion success rates differed significantly: i-gel™ 95%, LMA-S 95%, LTS-D 70% (p <0.05). The fibreoptically assessed position was more frequently suboptimal with the LTS-D but this was not associated with impaired ventilation. Dynamic airway compliance was highest with the i-gel™ and lowest with the LTS-D (p <0.05). Airway morbidity was more pronounced with the LTS-D (p <0.01).ConclusionAll devices were suitable for ventilating the patients’ lungs during elective surgery.Trial registrationGerman Clinical Trial Register DRKS00000760

Conductive Heat Exchange with a Gel-Coated Circulating Water Mattress

The use of forced-air warming is associated with costs for the disposable blankets. As an alternative method, we studied heat transfer with a reusable gel-coated circulating water mattress placed under the back in eight healthy volunteers. Heat flux was measured with six calibrated heat flux transducers. Additionally, mattress temperature, skin temperature, and core temperature were measured. Water temperature was set to 25°C, 30°C, 35°C, and 41°C. Heat transfer was calculated by multiplying heat flux by contact area. Mattress temperature, skin temperature, and heat flux were used to determine the heat exchange coefficient for conduction. Heat flux and water temperature were related by the following equation: heat flux = 10.3 × water temperature − 374 (r2 = 0.98). The heat exchange coefficient for conduction was 121 W · m−2 · °C−1. The maximal heat transfer with the gel-coated circulating water mattress was 18.4 ± 3.3 W. Because of the small effect on the heat balance of the body, a gel-coated circulating water mattress placed only on the back cannot replace a forced-air warming system.

Preventing inadvertent perioperative hypothermia.

BACKGROUND 25-90% of all patients undergoing elective surgery suffer from inadvertent postoperative hypothermia, i.e., a core body temperature below 36°C. Compared to normothermic patients, these patients have more frequent wound infections (relative risk [RR] 3.25, 95% confidence interval [CI] 1.35-7.84), cardiac complications (RR 4.49, 95% CI 1.00-20.16), and blood transfusions (RR 1.33, 95% CI 1.06-1.66). Hypothermic patients feel uncomfortable, and shivering raises oxygen consumption by about 40%. METHODS This guideline is based on a systematic review of the literature up to and including October 2012 and a further one from November 2012 to August 2014. The recommendations were developed and agreed upon by representatives of five medical specialty societies in a structured consensus process. RESULTS The patients core temperature should be measured 1-2 hours before the start of anesthesia, and either continuously or every 15 minutes during surgery. Depending on the nature of the operation, the site of temperature measurement should be oral, naso-/oropharyngeal, esophageal, vesical, or tympanic (direct). The patient should be actively prewarmed 20-30 minutes before surgery to counteract the decline in temperature. Prewarmed patients must be actively warmed intraoperatively as well if the planned duration of anesthesia is longer than 60 minutes (without prewarming, 30 minutes). The ambient temperature in the operating room should be at least 21°C for adult patients and at least 24°C for children. Infusions and blood transfusions that are given at rates of >500 mL/h should be warmed first. Perioperatively, the largest possible area of the body surface should be thermally insulated. Emergence from general anesthesia should take place at normal body temperature. Postoperative hypothermia, if present, should be treated by the administration of convective or conductive heat until normothermia is achieved. Shivering can be treated with medications. CONCLUSION Inadvertent perioperative hypothermia can adversely affect the outcome of surgery and the patients postoperative course. It should be actively prevented.

Efficacy of forced-air warming systems with full body blankets.

PURPOSE Postoperative hypothermia after cardiac surgery is still a common problem often treated with forced-air warming. This study was conducted to determine the heat transfer efficacy of 11 forced-air warming systems with full body blankets on a validated copper manikin. METHODS The following systems were tested: 1) Bair Hugger 505; 2) Bair Hugger 750; 3) Life-Air 1000 S; 4) Snuggle Warm; 5) Thermacare; 6) Thermacare with reusable Optisan blanket; 7) WarmAir; 8) Warm-Gard; 9) Warm-Gard and reusable blanket; 10) WarmTouch; and 11) WarmTouch and reusable blanket. Heat transfer of forced-air warmers can be described as follows: Q = h x DeltaT x A. Where Q = heat flux (W), h = heat exchange coefficient (W x m-2 x degrees C-1), DeltaT = temperature gradient between blanket and manikin surface (degrees C), A = covered area (m2). Heat flux per unit area and surface temperature were measured with 16 heat flux transducers. Blanket temperature was measured using 16 thermocouples. The temperature gradient between blanket and surface (DeltaT) was varied and h was determined by linear regression analysis. Mean DeltaT was determined for surface temperatures between 32 degrees C and 38 degrees C. The covered area was estimated to be 1.21 m2. RESULTS For the 11 devices, heat transfers of 30.7 W to 77.3 W were observed for surface temperatures of 32 degrees C, and between -8.8 W to 29.6 W for surface temperatures of 38 degrees C. CONCLUSION There are clinically relevant differences between the tested forced-air warming systems with full body blankets. Several systems were unable to transfer heat to the manikin at a surface temperature of 38 degrees C.PurposePostoperative hypothermia after cardiac surgery is still a common problem often treated with forced-air warming. This study was conducted to determine the heat transfer efficacy of 11 forced-air warming systems with full body blankets on a validated copper manikin.MethodsThe following systems were tested: 1) Bair Hugger® 505; 2) Bair Hugger® 750; 3) Life-Air 1000 S; 4) Snuggle Warm®; 5) Thermacare®; 6) Thermacare® with reusable Optisan® blanket; 7) WarmAir®; 8) Warm-Gard®; 9) Warm-Gard® and reusable blanket; 10) WarmTouch®; and 11) WarmTouch® and reusable blanket. Heat transfer of forced-air warmers can be described as follows: Q = h · ΔT · A. Where Q = heat flux (W), h = heat exchange coefficient (Wm−2·°C−1), ΔT = temperature gradient between blanket and manikin surface (°C), A = covered area (m2). Heat flux per unit area and surface temperature were measured with 16 heat flux transducers. Blanket temperature was measured using 16 thermocouples. The temperature gradient between blanket and surface (ΔT) was varied and h was determined by linear regression analysis. Mean ΔT was determined for surface temperatures between 32°C and 38°C. The covered area was estimated to be 1.21 m2.ResultsFor the 11 devices, heat transfers of 30.7 W to 77.3 W were observed for surface temperatures of 32°C, and between-8.8 W to 29.6 W for surface temperatures of 38°C.ConclusionThere are clinically relevant differences between the tested forced-air warming systems with full body blankets. Several systems were unable to transfer heat to the manikin at a surface temperature of 38°C.RésuméObjectifL’hypothermie postopératoire suivant une chirurgie cardiaque est encore un problème courant, souvent traité à l’aide de couverture chauffante à air pulsé. Cette étude a été menée afin de déterminer l’efficacité du transfert de chaleur de 11 systèmes de chauffage à air pulsé avec des couvertures sur un mannequin de cuivre validé.MéthodesLes systèmes suivants ont été testés: 1) Bair Hugger® 505; 2) Bair Hugger® 750; 3) Life-Air 1000 S; 4) Snuggle Warm®; 5) Thermacare®; 6) Thermacare® avec couverture réutilisable Optisan®; 7) WarmAir®; 8) Warm-Gard®; 9) Warm-Gard® et couverture réutilisable; 10) WarmTouch®; et 11) WarmTouch® et couverture réutilisable. Le transfert de chaleur de systèmes de chauffage à air pulsé peut être décrit de cette façon: Q = h · ΔT · A, où Q = flux de chaleur (W), h = coefficient d’échange de chaleur (W·m−2·δC−1), ΔT = gradient de température entre la couverture et la surface du mannequin (δC), A = aire couverte (m2). Le flux de chaleur par unité d’aire et la température de surface ont été mesurés à l’aide de 16 capteurs de flux de chaleur. La température de la couverture a été mesurée à l’aide de 16 thermocouples. Le gradient de température entre la couverture et la surface (ΔT) était modifié et h a été déterminé par une analyse de régression linéaire. Le ΔT moyen a été déterminé entre 32δC et 38δC pour les températures de surface. L’aire couverte a été estimée à 1,21m2.RésultatsPour les 11 appareils, des transferts de chaleur de 30,7 W à 77,3 W ont été observés pour une température de surface de 32δC, et entre -8,8 W et 29,6 W pour une température de surface de 38°C.ConclusionIl existe des différences cliniquement significatives entre les systèmes de chauffage à air pulsé testés avec des couvertures à champ complet. De nombreux systèmes ont été incapables de transférer la chaleur au mannequin á une température de surface de 38δC.

Forced-air warming: technology, physical background and practical aspects.

Purpose of review There is an ever-increasing number of forced-air warming devices available in the market. However, there is also a paucity of studies that have investigated the physical background of these devices, making it difficult to find the most suitable ones. Recent findings Heat flow produced by power units depends on the air temperature at the nozzle and the airflow. The heat transfer from the blanket to the body surface depends on the heat exchange coefficient, the temperature gradient between the blanket and the body surface and the area that is covered. Additionally, the homogeneity of heat distribution inside the blanket is very important. The lower the temperature difference between the highest and the lowest blanket temperature, the better the performance of the blanket. Summary The efficacy of a forced-air warming system is mainly determined by the design of the blankets. A good forced-air warming blanket can easily be detected by measuring the temperature difference between the highest blanket temperature and the lowest blanket temperature. This temperature difference should be as low as possible. Because of the limited efficacy of forced-air warming systems to prevent hypothermia, patients must be prewarmed for 30–60 min even if a forced-air warming system is used during the operation. During the operation, the largest blanket that is possible for the operation should be used.

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.

What determines the efficacy of forced-air warming systems? A manikin evaluation with upper body blankets.

BACKGROUND: Forced-air warming has gained acceptance as an effective means to prevent perioperative hypothermia. However, little is known about the influence of air flow and air temperature at the nozzle and the influence of heat distribution in the blankets on the efficacy of these systems. METHODS: We conducted a manikin study with heat flux transducers using five forced-air warming systems to determine the factors that are responsible for heat transfer from the blanket to the manikin. RESULTS: There was no relation between air temperature at the nozzle of the power unit and the resulting heat transfer. There was also no relation between the air flow at the nozzle of the power unit and the resulting heat transfer. However, all blankets performed best at high air flows above 19 L/s. The heat exchange coefficient, the mean temperature gradient between the blanket and the manikin correlated positively with the resulting heat transfer and the difference between the minimal and maximal blanket temperature correlated negatively with the resulting heat transfer. CONCLUSIONS: The efficacy of forced-air warming systems is primarily determined by the blanket. Modern power units provide sufficient heat energy to maximize the ability of the blanket to warm the patient. Optimizing blanket design by optimizing the mean temperature gradient between the blanket and the manikin (or any other surface) with a very homogeneous temperature distribution in the blanket will enable the manufacturers to develop better forced-air warming systems.

Infrarot-Temperaturmessung im Gehörgang mit dem DIATEK 9000 Instatemp und dem DIATEK 9000 Thermoguide Einflußgrößen und Vergleich mit anderen Methoden der Temperaturmessung des Körperkerns

ZusammenfassungZwei Infrarot-Gehörgangsthermometer – DIATEK 9000 Instatemp und DIATEK 9000 Thermoguide – wurden unter zwei Hauptgesichtspunkten untersucht: „Wie groß sind die Unterschiede zu anderen Messungen der Körperkerntemperatur?“ bzw. „Welche Variablen beeinflussen das Meßergebnis?“. Bei der Untersuchung der Einflußvariablen zeigte sich, daß zum Erzielen optimaler Meßergebnisse eine Mindestpause von 2 min zwischen zwei Messungen am selben Ohr einzuhalten ist und unnötig lange Verweilzeiten der Geräte im Ohr zu vermeiden sind. Die mit den Infrarotgeräten im CAL-Modus gemessenen Temperaturen lagen mit ca. 0,4 °C signifikant niedriger als die Kontaktmessungen am Trommelfell. Die Unterschiede zur Rektal- bzw. Ösophagealtemperatur betrugen im Mittel −0,19 °C (Rektalmodus) bzw. −0,13 °C (Coremodus). Die Ergebnisse zeigen, daß mit den Geräten nicht die reine Trommelfelltemperatur, sondern vielmehr auch die Temperatur des angrenzenden Gehörgangs miterfaßt wird. Zur Kompensation der systematischen Unterschätzung der Kerntemperatur werden die gemessenen Werte geräteintern in Körperkerntemperaturäquivalente umgerechnet, was zu einer deutlichen Verringerung der systematischen Abweichungen zwischen den Methoden führt.AbstractTemperature of the tympanic membrane is recommended as a “gold standard” of core-temperature recording. However, use of temperature probes in the auditory canal may lead to damage of tympanic membrane. Temperature measurement in the auditory canal with infrared thermometry does not pose this risk. Furthermore it is easy to perform and not very time-consuming. For this reason infrared thermometry of the auditory canal is becoming increasingly popular in clinical practice. We evaluated two infrared thermometers – the Diatek 9000 Thermoguide and the Diatek 9000 Instatemp – regarding factors influencing agreement with conventional tympanic temperature measurement and other core-temperature recording sites. In addition, we systematically evaluated user dependent factors that influence the agreement with the tympanic temperature. Materials andMethods. In 20 volunteers we evaluated the influence of three factors: duration of the devices in the auditory canal before taking temperature (0 or 5 s), interval between two following recordings (30, 60, 90, 120, 180 s) and positioning of the grip relative to the auditory-canal axis (0, 60, 180 and 270°). Agreement with tympanic contact probes (Mon-a-therm tympanic) in the contralateral ear was investigated in 100 postoperative patients. Comparative readings with rectal (YSI series 400) and esophageal (Mon-a-therm esophageal stethoscope with temperature sensor) probes were done in 100 patients in the ICU. The method of Bland and Altman was taken for comparison. Results. Shortening of the interval between two consecutive readings led to increasing differences between the two measurements with the second reading decreasing. A similar effect was seen when positioning the infrared thermometers in the auditory canal before taking temperatures: after 5 s the recorded temperatures were significantly lower than temperature recordings taken immediately. Rotation of the devices out of the telephone handle position led to increasing lack of agreement between infrared thermometry and contact probes. Mean differences between infrared thermometry (Instatemp and Thermoguide, CAL-Mode) and tympanic probes were −0.41±0.67 °C (2 SD) and −0.43 ±0.70 °C, respectively. Mean differences between the Thermoquide (Rectal-Mode) and rectal probe were −0.19±0.72 °C, and between the Thermoguide (Core Mode) and esophageal probe −0.13±0.74 °C. Discussion. Although easy to use, infrared thermometry requires careful handling. To obtain optimal recordings, the time between two consecutive readings should not be less than two min. Recordings should be taken immediately after positioning the devices in the auditory canal. Best results are obtained in the 60° position with the grip of the devices following the ramus mandibulae (telephone handle position). The lower readings of infrared thermometry compared with tympanic contact probes indicate that the readings obtained represent the temperature of the auditory canal rather than of the tympanic membrane itself. To compensate for underestimation of core temperature by infrared thermometry, the results obtained are corrected and transferred into core-equivalent temperatures. This data correction reduces mean differences between infrared recordings and traditional core-temperature monitoring, but leaves limits of agreement between the two methods uninfluenced.