Thorsten Perl

Determination of serum propofol concentrations by breath analysis using ion mobility spectrometry

BACKGROUND We aimed to measure propofol concentrations in exhaled air with an ion mobility spectrometer coupled to a multicapillary column for pre-separation (MCC-IMS). In addition, we aimed to compare the values of these measurements with serum propofol concentrations, as determined by gas chromatography-mass spectrometry (GC-MS). METHODS Thirteen patients, ASA I or II, undergoing elective ENT surgery were studied. Anaesthesia was induced with propofol 2.1 (0.7) mg kg(-1), rocuronium 0.5 (0.1) mg kg(-1), and remifentanil 0.5 microg kg(-1) min(-1). After tracheal intubation, anaesthesia was maintained with a continuous infusion of propofol 3.9 (1.8) mg kg(-1) h(-1) and remifentanil 0.5 microg kg(-1) min(-1). Simultaneously, a venous blood sample was obtained. Propofol concentrations in serum were determined by GC-MS and compared with the height of the respective propofol signals achieved by MCC-IMS. RESULTS Twenty-four pairs of samples were obtained. The comparison of propofol concentrations in exhaled air and serum presented a bias of -10.5% and a precision of +/- 12.3%. With these values, the 95% limits of agreement were 14.1% and -35.1%. CONCLUSIONS MCC-IMS may be a suitable method to determine propofol concentrations in exhaled air, and may be used to predict propofol concentrations in serum.

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.

Detection of characteristic metabolites of Aspergillus fumigatus and Candida species using ion mobility spectrometry - metabolic profiling by volatile organic compounds

Volatile metabolites of Aspergillus fumigatus and Candida species can be detected by gas chromatography/mass spectrometry (GC/MS). A multi‐capillary column – ion mobility spectrometer (MCC‐IMS) was used in this study to assess volatile organic compounds (VOCs) in the headspace above A. fumigatus and the four Candida species Candida albicans, Candida parapsilosis, Candida glabrata and Candida tropicalis in an innovative approach, validated for A. fumigatus and C. albicans by GC/MS analyses. For the detection of VOCs, a special stainless steel measurement chamber for the microbial cultures was used. The gas outlet was either attached to MCC‐IMS or to adsorption tubes (Tenax GR) for GC/MS measurements. Isoamyl alcohol, cyclohexanone, 3‐octanone and phenethylalcohol can be described as discriminating substances by means of GC/MS. With MCC‐IMS, the results for 3‐octanone and phenethylalcohol are concordant and additionally to GC/MS, ethanol and two further compounds (p_0642_1/p_683_1 and p_705_3) can be described. Isoamyl alcohol and cyclohexanone were not properly detectable with MCC‐IMS. The major advantage of the MCC‐IMS system is the feasibility of rapid analysis of complex gas mixtures without pre‐concentration or preparation of samples and regardless of water vapour content in an online setup. Discrimination of fungi on genus level of the investigated germs by volatile metabolic profile and therefore detection of VOC is feasible. However, a further discrimination on species level for Candida species was not possible.

Alignment of retention time obtained from multicapillary column gas chromatography used for VOC analysis with ion mobility spectrometry

Multicapillary column (MCC) ion mobility spectrometers (IMS) are increasingly in demand for medical diagnosis, biological applications and process control. In a MCC-IMS, volatile compounds are differentiated by specific retention time and ion mobility when rapid preseparation techniques are applied, e.g. for the analysis of complex and humid samples. Therefore, high accuracy in the determination of both parameters is required for reliable identification of the signals. The retention time in the MCC is the subject of the present investigation because, for such columns, small deviations in temperature and flow velocity may cause significant changes in retention time. Therefore, a universal correction procedure would be a helpful tool to increase the accuracy of the data obtained from a gas-chromatographic preseparation. Although the effect of the carrier gas flow velocity and temperature on retention time is not linear, it could be demonstrated that a linear alignment can compensate for the changes in retention time due to common minor deviations of both the carrier gas flow velocity and the column temperature around the MCC-IMS standard operation conditions. Therefore, an effective linear alignment procedure for the correction of those deviations has been developed from the analyses of defined gas mixtures under various experimental conditions. This procedure was then applied to data sets generated from real breath analyses obtained in clinical studies using different instruments at different measuring sites for validation. The variation in the retention time of known signals, especially for compounds with higher retention times, was significantly improved. The alignment of the retention time—an indispensable procedure to achieve a more precise identification of analytes—using the proposed method reduces the random error caused by small accidental deviations in column temperature and flow velocity significantly.

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.

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.

Detection and validation of volatile metabolic patterns over different strains of two human pathogenic bacteria during their growth in a complex medium using multi-capillary column-ion mobility spectrometry (MCC-IMS)

Headspace analyses over microbial cultures using multi-capillary column-ion mobility spectrometry (MCC-IMS) could lead to a faster, safe and cost-effective method for the identification of pathogens. Recent studies have shown that MCC-IMS allows identification of bacteria and fungi, but no information is available from when on during their growth a differentiation between bacteria is possible. Therefore, we analysed the headspace over human pathogenic reference strains of Escherichia coli and Pseudomonas aeruginosa at four time points during their growth in a complex fluid medium. In order to validate our findings and to answer the question if the results of one bacterial strain can be transferred to other strains of the same species, we also analysed the headspace over cultures from isolates of random clinical origin. We detected 19 different volatile organic compounds (VOCs) that appeared or changed their signal intensity during bacterial growth. These included six VOCs exclusively changing over E. coli cultures and seven exclusively changing over P. aeruginosa cultures. Most changes occurred in the late logarithmic or static growth phases. We did not find differences in timing or trends in signal intensity between VOC patterns of different strains of one species. Our results show that differentiation of human pathogenic bacteria by headspace analyses using MCC-IMS technology is best possible during the late phases of bacterial growth. Our findings also show that VOC patterns of a bacterial strain can be transferred to other strains of the same species.

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.

[Prewarming. Yesterday's luxury, today's minimum requirement].

Prewarming is a useful and effective measure to reduce perioperative hypothermia. Due to §23(3) of the German Infektionsschutzgesetz (Gesetz zur Verhütung und Bekämpfung von Infektionskrankheiten beim Menschen, Infection Act, act on protection and prevention of infectious diseases in man) and the recommendations of the Hospital Hygiene and Infection Prevention Committee of the Robert Koch Institute, implementation of prewarming is clearly recommended. There are several technically satisfactory and practicable devices available allowing prewarming on the normal hospital ward, in the preoperative holding area or in the induction room of the operating theater (OR) The implementation of prewarming requires additional equipment and training of staff. Using a locally adapted concept for the implementation of prewarming does not lead to inefficiency in the perioperative process. In contrast, the implementation can help to achieve stable arrival times for patients in the OR.