[Update on point-of-care-based coagulation treatment : Systems, reagents, device-specific treatment algorithms]

Viscoelastic test (VET) procedures suitable for point-of-care (POC) testing are in widespread clinical use. Due to the expanded range of available devices and in particular due to the development of new test approaches and methods, the authors believe that an update of the current treatment algorithms is necessary. The aim of this article is to provide an overview of the currently available VET devices and the associated reagents. In addition, two treatment algorithms for the VET devices most commonly used in German-speaking countries are presented.

Population pharmacokinetic modeling of multiple-dose intravenous fosfomycin in critically ill patients during continuous venovenous hemodialysis

The aim of this study was to investigate the pharmacokinetics of multiple-dose intravenous (i.v.) fosfomycin in critically ill patients during continuous venovenous hemodialysis (CVVHD). Non-compartmental analysis and population pharmacokinetic modeling were used to simulate different dosing regimens. We evaluated 15 critically ill patients with renal insufficiency and CVVHD undergoing anti-infective treatment with fosfomycin in our ICU. Five grams of fosfomycin were administered for 120 min every 6 h. Plasma concentrations were determined with and without CVVHD. Pharmacokinetic analysis and simulations were performed using non-linear mixed effects modelling (NONMEM). A two-compartment model with renal and dialysis clearance was most accurate in describing the pharmacokinetics of i.v. fosfomycin during CVVHD. Population parameter estimates were 18.20 L and 20.80 L for the central and peripheral compartment volumes, and 0.26 L/h and 5.08 L/h for renal and intercompartmental clearance, respectively. Urinary creatinine clearance (CLCR) represented a considerable component of renal clearance. Central compartment volume increased over time after the first dose. For patients with CLCR > 50 (90) mL/min and CVVHD, dosage should be increased to ≥ 15 (16) grams of i.v. fosfomycin across three (four) daily doses. Individual CLCR must be considered when dosing i.v. fosfomycin in critically ill patients during CVVHD.

A randomized open label, parallel-group study to evaluate the hemodynamic effects of Cafedrine/Theodrenaline vs Noradrenaline in the treatment of intraoperative hypotension after induction of general anesthesia: the "HERO" study design and rationale

OBJECTIVE

Intraoperative arterial hypotension (IOH) is associated with poor patient outcome. This study aims to compare the hemodynamic effects of Cafedrine/Theodrenaline (C/T) and Noradrenaline (NA) for the treatment of hypotension in patients who develop IOH after anesthesia induction.

RESEARCH DESIGN AND METHODS

This is a national, randomized, parallel-group, multicenter, and open-label study. Adult patients (≥50 years, ASA-classification III-IV) who undergo elective surgery will be included. When IOH (MAP <70 mmHg) develops, C/T or NA will be given as a bolus injection ("bolus phase", 0-20 min after initial application) and subsequently as continuous infusion ("infusion phase", 21-40 min after initial application) to achieve MAP = 90 mmHg. Hemodynamic data are captured in real time by advanced hemodynamic monitoring.

RESULTS

Primary endpoints, i.e. the treatment-related difference in average mean arterial pressure (MAP) during the "infusion phase" and the treatment-related difference in average cardiac index during the "bolus phase" are assessed (fixed-sequence method). Non-inferiority of C/T compared to NA in achieving 90 mmHg (MAP) when applied as continuous infusion is hypothesized. In addition, superiority of C/T over NA, applied as bolus injection, in increasing cardiac index is postulated. It is estimated that 172 patients are required to establish statistical significance with a power of 90%. After adjusting for ineligibility and dropout rate, 220 patients will be screened.

CONCLUSION

This clinical trial will yield evidence for marketing authorization of C/T applied as continuous infusion. Additionally, the effects of C/T compared to NA on cardiac index will be assessed. First results of the "HERO"-study are expected in 2024. DRKS identifier: DRKS00028589. EudraCT identifier: 2021-001954-76.

Humidity and measurement of volatile propofol using MCC-IMS (EDMON)

The bedside Exhaled Drug MONitor - EDMON measures exhaled propofol in ppbv every minute based on multi-capillary column - ion mobility spectrometry (MCC-IMS). The MCC pre-separates gas samples, thereby reducing the influence of the high humidity in human breath. However, preliminary analyses identified substantial measurement deviations between dry and humid calibration standards. We therefore performed an analytical validation of the EDMON to evaluate the influence of humidity on measurement performance. A calibration gas generator was used to generate gaseous propofol standards measured by an EDMON device to assess linearity, precision, carry-over, resolution, and the influence of different levels of humidity at 100% and 1.7% (without additional) relative humidity (reference temperature: 37°C). EDMON measurements were roughly half the actual concentration without additional humidity and roughly halved again at 100% relative humidity. Standard concentrations and EDMON values correlated linearly at 100% relative humidity (R²=0.97). The measured values were stable over 100min with a variance ≤ 10% in over 96% of the measurements. Carry-over effects were low with 5% at 100% relative humidity after 5min of equilibration. EDMON measurement resolution at 100% relative humidity was 0.4 and 0.6 ppbv for standard concentrations of 3 ppbv and 41 ppbv. The influence of humidity on measurement performance was best described by a second-order polynomial function (R²≥0.99) with influence reaching a maximum at about 70% relative humidity. We conclude that EDMON measurements are strongly influenced by humidity and should therefore be corrected for sample humidity to obtain accurate estimates of exhaled propofol concentrations.

Quantification of exhaled propofol is not feasible during single-lung ventilation using double-lumen tubes: A multicenter prospective observational trial

BACKGROUND

Volatile propofol can be measured in exhaled air and correlates to plasma concentrations with a time delay. However, the effect of single-lung ventilation on exhaled propofol is unclear. Therefore, our goal was to evaluate exhaled propofol concentrations during single-lung compared to double-lung ventilation using double-lumen tubes.

METHODS

In a first step, we quantified adhesion of volatile propofol to the inner surface of double-lumen tubes during double- and single-lumen ventilation in vitro. In a second step, we enrolled 30 patients scheduled for lung surgery in two study centers. Anesthesia was provided with propofol and remifentanil. We utilized left-sided double-lumen tubes to separately ventilate each lung. Exhaled propofol concentrations were measured at 1-min intervals and plasma for propofol analyses was sampled every 20 min. To eliminate the influence of dosing on volatile propofol concentration, exhalation rate was normalized to plasma concentration.

RESULTS

In-vitro ventilation of double-lumen tubes resulted in increasing propofol concentrations at the distal end of the tube over time. In vitro clamping the bronchial lumen led to an even more pronounced increase (Δ AUC +62%) in propofol gas concentration over time. Normalized propofol exhalation during lung surgery was 31% higher during single-lung compared to double-lung ventilation.

CONCLUSION

During single-lung ventilation, propofol concentration in exhaled air, in contrast to our expectations, increased by approximately one third. However, this observation might not be affected by change in perfusion-ventilation during single-lung ventilation but rather arises from reduced propofol absorption on the inner surface area of the double-lumen tube. Thus, it is only possible to utilize exhaled propofol concentration to a limited extent during single-lung ventilation.

REGISTRATION OF CLINICAL TRIAL

DRKS-ID DRKS00014788 (www.drks.de).

Model-Based Analysis of SARS-CoV-2 Infections, Hospitalization and Outcome in Germany, the Federal States and Districts

The coronavirus disease 2019 (COVID-19) pandemic challenged many national health care systems, with hospitals reaching capacity limits of intensive care units (ICU). Thus, the estimation of acute local burden of ICUs is critical for appropriate management of health care resources. In this work, we applied non-linear mixed effects modeling to develop an epidemiological SARS-CoV-2 infection model for Germany, with its 16 federal states and 400 districts, that describes infections as well as COVID-19 inpatients, ICU patients with and without mechanical ventilation, recoveries, and fatalities during the first two waves of the pandemic until April 2021. Based on model analyses, covariates influencing the relation between infections and outcomes were explored. Non-pharmaceutical interventions imposed by governments were found to have a major impact on the spreading of SARS-CoV-2. Patient age and sex, the spread of variant B.1.1.7, and the testing strategy (number of tests performed weekly, rate of positive tests) affected the severity and outcome of recorded cases and could reduce the observed unexplained variability between the states. Modeling could reasonably link the discrepancies between fine-grained model simulations of the 400 German districts and the reported number of available ICU beds to coarse-grained COVID-19 patient distribution patterns within German regions.

Intravenous propofol, ketamine (ketofol) and rocuronium after sevoflurane induction provides long lasting anesthesia in ventilated rats

Rats are commonly used animals for laboratory experiments and many experiments require general anesthesia. However, the lack of published and reproducible intravenous anesthesia protocols for rats results in unnecessary animal use to establish new anesthesia techniques across institutions. We therefore developed an anesthesia protocol with propofol, ketamine, and rocuronium for mechanically ventilated rats, and evaluated vital parameters and plasma concentrations. 15 male Sprague-Dawley rats underwent inhalation induction with sevoflurane and tracheal, venous and arterial cannulation. After established venous access, sevoflurane was substituted by propofol and ketamine (ketofol). Rocuronium was added under mechanical ventilation for 7 h. Drug dosages were stepwise reduced to prevent accumulation. All animals survived the observation period and showed adequate depth of anesthesia. Mean arterial pressure and heart rate remained within normal ranges. Median propofol plasma concentrations remained stable: 1, 4, 7 h: 2.0 (interquartile range (IQR): 1.8–2.2), 2.1 (1.8–2.2), 1.8 (1.6–2.1) µg/ml, whereas median ketamine concentrations slightly differed after 7 h compared to 1 h: 1, 4, 7 h: 3.7 (IQR: 3.5–4.5), 3.8 (3.3–4.1), 3.8 (3.0–4.1) µg/ml. Median rocuronium plasma concentrations were lower after 4 and 7 h compared to 1 h: 1, 4, 7 h: 3.9 (IQR: 3.5–4.9), 3.2 (2.7–3.3), 3.0 (2.4–3.4) µg/ml. Our anesthesia protocol provides stable and reliable anesthesia in mechanically ventilated rats for several hours.

Quantification of Volatile Acetone Oligomers Using Ion-Mobility Spectrometry

BACKGROUND

Volatile acetone is a potential biomarker that is elevated in various disease states. Measuring acetone in exhaled breath is complicated by the fact that the molecule might be present as both monomers and dimers, but in inconsistent ratios. Ignoring the molecular form leads to incorrect measured concentrations. Our first goal was to evaluate the monomer-dimer ratio in ambient air, critically ill patients, and rats. Our second goal was to confirm the accuracy of the combined (monomer and dimer) analysis by comparison to a reference calibration system.

METHODS

Volatile acetone intensities from exhaled air of ten intubated, critically ill patients, and ten ventilated Sprague-Dawley rats were recorded using ion-mobility spectrometry. Acetone concentrations in ambient air in an intensive care unit and in a laboratory were determined over 24 hours. The calibration reference was pure acetone vaporized by a gas generator at concentrations from 5 to 45 ppb_v (parts per billion by volume).

RESULTS

Acetone concentrations in ambient laboratory air were only slightly greater (5.6 ppb_v; 95% CI 5.1-6.2) than in ambient air in an intensive care unit (5.1 ppb_v; 95% CI 4.4-5.5; p < 0.001). Exhaled acetone concentrations were only slightly greater in rats (10.3 ppb_v; 95% CI 9.7-10.9) than in critically ill patients (9.5 ppb_v; 95% CI 7.9-11.1; p < 0.001). Vaporization yielded acetone monomers (1.3-5.3 mV) and dimers (1.4-621 mV). Acetone concentrations (ppb_v) and corresponding acetone monomer and dimer intensities (mV) revealed a high coefficient of determination (R ² = 0.96). The calibration curve for acetone concentration (ppb_v) and total acetone (monomers added to twice the dimers; mV) was described by the exponential growth 3-parameter model, with an R ² = 0.98.

CONCLUSION

The ratio of acetone monomer and dimer is inconsistent and varies in ambient air from place-to-place and across individual humans and rats. Monomers and dimers must therefore be considered when quantifying acetone. Combining the two accurately assesses total volatile acetone.

Volutrauma Increases Exhaled Pentanal in Rats: A Potential Breath Biomarker for Ventilator-Induced Lung Injury

BACKGROUND

Mechanical ventilation injures lungs, but there are currently no reliable methods for detecting early injury. We therefore evaluated whether exhaled pentanal, a lipid peroxidation product, might be a useful breath biomarker for stretch-induced lung injury in rats.

METHODS

A total of 150 male Sprague-Dawley rats were investigated in 2 substudies. The first randomly assigned 75 rats to 7 hours of mechanical ventilation at tidal volumes of 6, 8, 12, 16, and 20 mL·kg-1. The second included 75 rats. A reference group was ventilated at a tidal volume of 6 mL·kg-1 for 10 hours 4 interventional groups were ventilated at a tidal volume of 6 mL·kg-1 for 1 hour, and then for 0.5, 1, 2, or 3 hours at a tidal volume of 16 mL.kg-1 before returning to a tidal volume of 6 mL·kg-1 for additional 6 hours. Exhaled pentanal was monitored by multicapillary column-ion mobility spectrometry. The first substudy included cytokine and leukocyte measurements in blood and bronchoalveolar fluid, histological assessment of the proportion of alveolar space, and measurements of myeloperoxidase activity in lung tissue. The second substudy included measurements of pentanal in arterial blood plasma, cytokine and leukocyte concentrations in bronchoalveolar fluid, and cleaved caspase 3 in lung tissue.

RESULTS

Exhaled pentanal concentrations increased by only 0.5 ppb·h-1 (95% confidence interval [CI], 0.3-0.6) when rats were ventilated at 6 mL·kg-1. In contrast, exhaled pentanal concentrations increased substantially and roughly linearly at higher tidal volumes, up to 3.1 ppb·h-1 (95% CI, 2.3-3.8) at tidal volumes of 20 mL·kg-1. Exhaled pentanal increased at average rates between 1.0 ppb·h-1 (95% CI, 0.3-1.7) and 2.5 ppb·h-1 (95% CI, 1.4-3.6) after the onset of 16 mL·kg-1 tidal volumes and decreased rapidly by a median of 2 ppb (interquartile range [IQR], 0.9-3.2), corresponding to a 38% (IQR, 31-43) reduction when tidal volume returned to 6 mL·kg-1. Tidal volume, inspiratory pressure, and mechanical power were positively associated with pentanal exhalation. Exhaled and plasma pentanal were uncorrelated. Alveolar space decreased and inflammatory markers in bronchoalveolar lavage fluid increased in animals ventilated at high tidal volumes. Short, intermittent ventilation at high tidal volumes for up to 3 hours increased neither inflammatory markers in bronchoalveolar fluid nor the proportion of cleaved caspase 3 in lung tissue.

CONCLUSIONS

Exhaled pentanal is a potential biomarker for early detection of ventilator-induced lung injury in rats.

Quantitative Determination of Fosfomycin in 10 μL of Plasma and Dialysate by Hydrophilic Interaction Liquid Chromatography Electrospray Ionization Mass Spectrometry

Fosfomycin is an antibiotic with a broad spectrum of activity against many multidrug-resistant bacterial strains. It is mainly excreted unchanged by the kidneys, and its half-life therefore depends on kidney function which varies considerably among individuals, and within individuals over time. Proper fosfomycin dosing thus depends on assaying blood concentration of the drug. We developed and validated a simple, sensitive and specific chromatography assay, which was coupled to electrospray ionization mass spectrometry for determination of fosfomycin. Separation of fosfomycin was based on the method of the hydrophilic interaction liquid chromatography; specifically, plasma and dialysate samples were acidified and the protein precipitated with acetonitrile. The calibration curves showed excellent coefficients of determination (R2 > 0.999) over the relevant concentration range of 25-700 μg/mL. Intraday precision was 1.1-1.2% and accuracy was -5.9% to 0.9% for quality control samples. Interday precision was 2.9-3.4% and accuracy was -3.7% to 5.5%. Extraction recovery was ≥87% and matrix effects ranged from 2.2% to 4.3%. After laboratory validation, the method was successfully applied to clinical samples.

Differential Response of Pentanal and Hexanal Exhalation to Supplemental Oxygen and Mechanical Ventilation in Rats

High inspired oxygen during mechanical ventilation may influence the exhalation of the previously proposed breath biomarkers pentanal and hexanal, and additionally induce systemic inflammation. We therefore investigated the effect of various concentrations of inspired oxygen on pentanal and hexanal exhalation and serum interleukin concentrations in 30 Sprague Dawley rats mechanically ventilated with 30, 60, or 93% inspired oxygen for 12 h. Pentanal exhalation did not differ as a function of inspired oxygen but increased by an average of 0.4 (95%CI: 0.3; 0.5) ppb per hour, with concentrations doubling from 3.8 (IQR: 2.8; 5.1) ppb at baseline to 7.3 (IQR: 5.0; 10.8) ppb after 12 h. Hexanal exhalation was slightly higher at 93% of inspired oxygen with an average difference of 0.09 (95%CI: 0.002; 0.172) ppb compared to 30%. Serum IL-6 did not differ by inspired oxygen, whereas IL-10 at 60% and 93% of inspired oxygen was greater than with 30%. Both interleukins increased over 12 h of mechanical ventilation at all oxygen concentrations. Mechanical ventilation at high inspired oxygen promotes pulmonary lipid peroxidation and systemic inflammation. However, the response of pentanal and hexanal exhalation varies, with pentanal increasing by mechanical ventilation, whereas hexanal increases by high inspired oxygen concentrations.

Treatment of intraoperative hypotension with cafedrine/theodrenaline versus ephedrine : A prospective, national, multicenter, non-interventional study-the HYPOTENS trial

BACKGROUND

Sympathomimetic drugs are a therapeutic cornerstone for the management of hypotensive states like intraoperative hypotension (IOH). While cafedrine/theodrenaline (C/T) is widely used in Germany to restore blood pressure in patients with IOH, more research is required to compare its effectiveness with alternatives such as ephedrine (E) that are more commonly available internationally.

METHODS

HYPOTENS (NCT02893241, DRKS00010740) was a prospective, national, multicenter, open-label, two-armed, non-interventional study that compared C/T with E for treatment of IOH. We describe a prospectively defined cohort of patients ≥50 years old with comorbidities undergoing general anesthesia induced with propofol and fentanyl. Primary objectives were to examine treatment precision, rapidity of onset and the ability to restore blood pressure without relevant increases in heart rate. Secondary endpoints were treatment satisfaction and the number of required additional boluses or other accompanying measures.

RESULTS

A total of 1496 patients were included in the per protocol analysis. Overall, effective stabilization of blood pressure was achieved with both C/T and E. Post-hoc analysis showed that blood pressure increase from baseline was more pronounced with C/T. Fewer additional boluses or other accompanying measures were required in the C/T arm. The incidence of tachycardia was comparable between groups. Post-hoc analysis showed that E produced dose-dependent elevated heart rate values. By contrast, heart rate remained stable in patients treated with C/T. Physicians reported a higher level of treatment satisfaction with C/T, with a higher proportion of anesthetists rating treatment precision and rapidity of onset as good or very good when compared with E.

CONCLUSION

Neither drug was superior in restoring blood pressure levels; however, post-hoc analyses suggested that treatment is more goal-orientated and easier to control with C/T. Heart rate was shown to be more stable with C/T and fewer additional interventions were required to restore blood pressure, which could have contributed to the increased treatment satisfaction reported by anesthetists using C/T.

Exhaled Propofol Concentrations Correlate With Plasma and Brain Tissue Concentrations in Rats

BACKGROUND

Propofol can be measured in exhaled gas. Exhaled and plasma propofol concentrations correlate well, but the relationship with tissue concentrations remains unknown. We thus evaluated the relationship between exhaled, plasma, and various tissue propofol concentrations. Because the drug acts in the brain, we focused on the relationship between exhaled and brain tissue propofol concentrations.

METHODS

Thirty-six male Sprague-Dawley rats were anesthetized with propofol, ketamine, and rocuronium for 6 hours. Animals were randomly assigned to propofol infusions at 20, 40, or 60 mg·kg·h (n = 12 per group). Exhaled propofol concentrations were measured at 15-minute intervals by multicapillary column-ion mobility spectrometry. Arterial blood samples, 110 µL each, were collected 15, 30, and 45 minutes, and 1, 2, 4, and 6 hours after the propofol infusion started. Propofol concentrations were measured in brain, lung, liver, kidney, muscle, and fat tissue after 6 hours. The last exhaled and plasma concentrations were used for linear regression analyses with tissue concentrations.

RESULTS

The correlation of exhaled versus plasma concentrations (R = 0.71) was comparable to the correlation of exhaled versus brain tissue concentrations (R = 0.75) at the end of the study. In contrast, correlations between plasma and lung and between lung and exhaled propofol concentrations were poor. Less than a part-per-thousand of propofol was exhaled over 6 hours.

CONCLUSIONS

Exhaled propofol concentrations correlate reasonably well with brain tissue and plasma concentrations in rats, and may thus be useful to estimate anesthetic drug effect. The equilibration between plasma propofol and exhaled gas is apparently independent of lung tissue concentration. Only a tiny fraction of administered propofol is eliminated via the lungs, and exhaled quantities thus have negligible influence on plasma concentrations.

Changes in volatile organic compounds provoked by lipopolysaccharide- or alpha toxin-induced inflammation in ventilated rats

Inflammation may alter volatile organic compounds (VOCs) in exhaled breath. We therefore used ion mobility spectrometry (IMS) to evaluate exhaled breath components in two non-infectious inflammatory models. Fifty male Sprague Dawley rats were anesthetized and ventilated for 24 h. Five treatments were randomly assigned: (1) lipopolysaccharide low dose [5 mg/kg]; (2) lipopolysaccharide high dose [10 mg/kg]; (3) alpha toxin low dose [40 µg/kg]; (4) alpha toxin high dose [80 µg/kg]; and, (5) NaCl 0.9% as control group. Gas was sampled from the expiratory line of the ventilator every 20 min and analyzed with IMS combined with a multi-capillary column. VOCs were identified by comparison with an established database. Survival analysis was performed by log-rank test, other analyses by one-way or paired ANOVA-tests and post-hoc analysis according to Holm-Sidak. Rats given NaCl and low-dose alpha toxin survived 24 h. The median survival time in alpha toxin high-dose group was 23 (95%-confidence interval (CI): 21, 24) h. In contrast, the median survival time in rats given high-dose lipopolysaccharide was 12 (95% CI: 9, 14) and only 13 (95% CI: 10, 16) h in those given high-dose lipopolysaccharide. 73 different VOCs were detected, of which 35 were observed only in the rats, 38 could be found both in the blank measurements of ventilator air and in the exhaled air of the rats. Forty-nine of the VOCs were identifiable from a registry of compounds. Exhaled volatile compounds were comparable in each group before injection of lipopolysaccharide and alpha toxin. In the LPS groups, 1-pentanol increased and 2-propanol decreased. After alpha toxin treatment, 1-butanol and 1-pentanol increased whereas butanal and isopropylamine decreased. Induction of a non-infectious systemic inflammation (niSI) by lipopolysaccharide and alpha toxin changes VOCs in exhaled breath. Exhalome analysis may help identify niSI.

Residual volatile anesthetics after workstation preparation and activated charcoal filtration

BACKGROUND

Volatile anesthetics potentially trigger malignant hyperthermia crises in susceptible patients. We therefore aimed to identify preparation procedures for the Draeger Primus that minimize residual concentrations of desflurane and sevoflurane with and without activated charcoal filtration.

METHODS

A Draeger Primus test workstation was primed with 7% desflurane or 2.5% sevoflurane for 2 hours. Residual anesthetic concentrations were evaluated with five preparation procedures, three fresh gas flow rates, and three distinct applications of activated charcoal filters. Finally, non-exchangeable and autoclaved parts of the workstation were tested for residual emission of volatile anesthetics. Concentrations were measured by multicapillary column-ion mobility spectrometry with limits of detection/quantification being <1 part per billion (ppb) for desflurane and <2.5 ppb for sevoflurane.

RESULTS

The best preparation procedure included a flushing period of 10 minutes between removal and replacement of all parts of the ventilator circuit which immediately produced residual concentrations <5 ppm. A fresh gas flow of 10 L/minute reduced residual concentration as effectively as 18 L/minute, whereas flows of 1 or 5 L/minute slowed washout. Use of activated charcoal filters immediately reduced and maintained residual concentrations <5 ppm for up to 24 hours irrespective of previous workstation preparation. The fresh gas hose, circle system, and ventilator diaphragm emitted traces of volatile anesthetics.

CONCLUSION

In elective cases, presumably safe concentrations can be obtained by a 10-minute flush at ≥10 L/minute between removal and replacement all components of the airway circuit. For emergencies, we recommend using an activated charcoal filter.

Volatile organic compounds in head and neck squamous cell carcinoma-An in vitro pilot study

Owing to the lack of specific symptoms, diagnosis of head and neck squamous cell carcinoma (HNSCC) may be delayed. We evaluated volatile organic compounds in tumor samples from patients suffering from HNSCC and tested the hypothesis that there is a characteristic altered composition in the headspace of HNSCC compared with control samples from the same patient with normal squamous epithelium. These results provide the basis for future noninvasive breath analysis in HNSCC. Headspace air of suspected tumor and contralateral control samples in 20 patients were analyzed using ion-mobility spectrometry. Squamous cell carcinoma was diagnosed in 16 patients. In total, we observed 93 different signals in headspace measurements. Squamous cell carcinomas revealed significantly higher levels of volatile cyclohexanol (0.54 ppb_v , 25th to 75th percentiles 0.35-0.86) compared with healthy squamous epithelium (0.24 ppb_v , 25th to 75th percentiles 0.12-0.3; p < 0.001). In conclusion, head and neck squamous cell carcinoma emitted significantly higher levels of volatile cyclohexanol in headspace compared with normal squamous epithelium. These findings form the basis for future breath analysis for diagnosis, therapy control and the follow-up of HNSSC to improve therapy and aftercare.

Developments to monitor the exhalome in organ failure in critically ill patients-a look into the future

Critically ill patients typically need some kind of functional organ support or replacement. Cardiopulmonary and renal replacement therapies are well established measures in intensive care units. However, there are also inherent risks associated with these treatments. The appropriate and timely commencement, maintenance and termination of organ replacement procedures currently use weak surrogates as decision support in clinical practice. A more reasonable application of extracorporeal organ support can be expected to potentially lower adverse events and save costs in healthcare systems, if a precise online monitoring was available. The analysis of the exhalome offers great opportunities to detect circulatory, pulmonary, and renal failure in critically ill patients. Volatile organic compounds and exhalation patterns are associated with a series of metabolic disorders and may be key to indicate the appropriate time point for initiation, maintenance and termination of organ support technologies. It may thus be expected that mortality, infection risk, replacement therapy days, and medical costs of intensive care treatment may possibly be reduced using exhalome analysis for control of organ replacement therapies in the distant future.

[Remifentanil up2date - Part 2]

Remifentanil is a short-acting opioid of high analgetic potency and superior controllability. It is widely used in day-case surgery, procedural sedation, for reduction of recovery-times and obstetrics and whenever excellent controllability of opioid effects is needed. Especially in combination with propofol it is used for target controlled infusion (TCI). The second part of the article shows the differences between groups of patients regarding the use of remifentanil.

Volatile organic compounds in ventilated critical care patients: a systematic evaluation of cofactors

Background

Expired gas (exhalome) analysis of ventilated critical ill patients can be used for drug monitoring and biomarker diagnostics. However, it remains unclear to what extent volatile organic compounds are present in gases from intensive care ventilators, gas cylinders, central hospital gas supplies, and ambient air. We therefore systematically evaluated background volatiles in inspired gas and their influence on the exhalome.

Methods

We used multi-capillary column ion-mobility spectrometry (MCC-IMS) breath analysis in five mechanically ventilated critical care patients, each over a period of 12 h. We also evaluated volatile organic compounds in inspired gas provided by intensive care ventilators, in compressed air and oxygen from the central gas supply and cylinders, and in the ambient air of an intensive care unit. Volatiles detectable in both inspired and exhaled gas with patient-to-inspired gas ratios < 5 were defined as contaminating compounds.

Results

A total of 76 unique MCC-IMS signals were detected, with 39 being identified volatile compounds: 73 signals were from the exhalome, 12 were identified in inspired gas from critical care ventilators, and 34 were from ambient air. Five volatile compounds were identified from the central gas supply, four from compressed air, and 17 from compressed oxygen. We observed seven contaminating volatiles with patient-to-inspired gas ratios < 5, thus representing exogenous signals of sufficient magnitude that might potentially be mistaken for exhaled biomarkers.

Conclusions

Volatile organic compounds can be present in gas from central hospital supplies, compressed gas tanks, and ventilators. Accurate assessment of the exhalome in critical care patients thus requires frequent profiling of inspired gases and appropriate normalisation of the expired signals.

Adhesion of volatile propofol to breathing circuit tubing

Propofol in exhaled breath can be measured and may provide a real-time estimate of plasma concentration. However, propofol is absorbed in plastic tubing, thus estimates may fail to reflect lung/blood concentration if expired gas is not extracted directly from the endotracheal tube. We evaluated exhaled propofol in five ventilated ICU patients who were sedated with propofol. Exhaled propofol was measured once per minute using ion mobility spectrometry. Exhaled air was sampled directly from the endotracheal tube and at the ventilator end of the expiratory side of the anesthetic circuit. The circuit was disconnected from the patient and propofol was washed out with a separate clean ventilator. Propofol molecules, which discharged from the expiratory portion of the breathing circuit, were measured for up to 60 h. We also determined whether propofol passes through the plastic of breathing circuits. A total of 984 data pairs (presented as median values, with 95% confidence interval), consisting of both concentrations were collected. The concentration of propofol sampled near the patient was always substantially higher, at 10.4 [10.25-10.55] versus 5.73 [5.66-5.88] ppb (p < 0.001). The reduction in concentration over the breathing circuit tubing was 4.58 [4.48-4.68] ppb, 3.46 [3.21-3.73] in the first hour, 4.05 [3.77-4.34] in the second hour, and 4.01 [3.36-4.40] in the third hour. Out-gassing propofol from the breathing circuit remained at 2.8 ppb after 60 h of washing out. Diffusion through the plastic was not observed. Volatile propofol binds or adsorbs to the plastic of a breathing circuit with saturation kinetics. The bond is reversible so propofol can be washed out from the plastic. Our data confirm earlier findings that accurate measurements of volatile propofol require exhaled air to be sampled as close as possible to the patient.

[Remifentanil Up2date - Part 1]

Remifentanil is a short-acting opioid of high analgetic potency and superior controllability. It is widely used in day-case surgery, procedural sedation, for reduction of recovery-times and obstetrics and whenever excellent controllability of opioid effects is needed. Especially in combination with Propofol it is used for target-controlled infusion (TCI). The first part of the article provides readers with information about historical aspects, pharmacological characteristics, effects and side effects of remifentanil.

Validation of liquid and gaseous calibration techniques for quantification of propofol in breath with sorbent tube Thermal Desorption System GC-MS

Plasma concentrations of intravenous drugs cannot currently be evaluated in real time to guide clinical dosing. However, a system for estimating plasma concentration of the anesthetic propofol from exhaled breath may soon be available. Developing reliable calibration and analytical validation techniques is thus necessary. We therefore compared the established sorbent tube liquid injection technique with a gas injection procedure using a reference gas generator. We then quantified propofol with Tenax sorbent tubes in combination with gas-chromatography coupled mass spectrometry in the breath of 15 patients (101 measurements). Over the clinically relevant concentration range from 10 to 50 ppb_v, coefficient of determination was 0.995 for gas calibration; and over the range from 10 to 100ng, coefficient of determination was 0.996 for liquid calibration. A regression comparing gas to liquid calibration had a coefficient of determination of 0.89; slope 1.05±0.01 (standard deviation). The limit of detection was 0.74ng and the lower limit of quantification was 1.12ng for liquid; the limit of detection was 0.90 ppb_v and the lower limit of quantification was 1.36 ppb_v for gas. Loaded sorbent tubes were stable for at least 14days without significant propofol loss as determined with either method. Measurements from liquid or gas samples were comparably suitable for evaluation of patient breath samples.

Adherence of volatile propofol to various types of plastic tubing

Propofol is an intravenous anesthetic. Currently, it is not possible to routinely measure blood concentration of the drug in real time. However, multi-capillary column ion-mobility spectrometry of exhaled gas can estimate blood propofol concentration. Unfortunately, adhesion of volatile propofol on plastic materials complicates measurements. Therefore, it is necessary to consider the extent to which volatile propofol adheres to various plastics used in sampling tubing. Perfluoralkoxy (PFA), polytetrafluorethylene (PTFE), polyurethane (PUR), silicone, and Tygon tubing were investigated in an experimental setting using a calibration gas generator (HovaCAL). Propofol gas was measured for one hour at 26 °C, 50 °C, and 90 °C tubing temperature. Test tubing segments were then flushed with N₂ to quantify desorption. PUR and Tygon sample tubing absorbed all volatile propofol. The silicone tubing reached the maximum propofol concentration after 119 min which was 29 min after propofol gas exposure stopped. The use of PFA or PTFE tubing produced comparable and reasonably accurate propofol measurements. The desaturation time for the PFA was 10 min shorter at 26 °C than for PTFE. PFA tubing thus seems most suitable for measurement of volatile propofol, with PTFE as an alternative.

Imaging properties of high aspect ratio absorption gratings for use in preclinical x-ray grating interferometry

X-ray grating interferometry is one among various methods that allow extracting the so-called phase and visibility contrasts in addition to the well-known transmission images. Crucial to achieving a high image quality are the absorption gratings employed. Here, we present an in-depth analysis of how the grating type and lamella heights influence the final images. Benchmarking gratings of two different designs, we show that a frequently used proxy for image quality, a grating's so-called visibility, is insufficient to predict contrast-to-noise ratios (CNRs). Presenting scans from an excised rat lung, we demonstrate that the CNRs obtained for transmission and visibility images anti-correlate. This is explained by the stronger attenuation implied by gratings that are engineered to provide high visibilities by means of an increased lamella height. We show that even the visibility contrast can suffer from this effect when the associated reduced photon flux on the detector is not outweighed by a corresponding gain in visibility. Resulting in an inevitable trade-off between the quality of the two contrasts, the question of how an optimal grating should be designed can hence only be answered in terms of Pareto optimality.

Two different approaches for pharmacokinetic modeling of exhaled drug concentrations

Online measurement of drug concentrations in patient's breath is a promising approach for individualized dosage. A direct transfer from breath- to blood-concentrations is not possible. Measured exhaled concentrations are following the blood-concentration with a delay in non-steady-state situations. Therefore, it is necessary to integrate the breath-concentration into a pharmacological model. Two different approaches for pharmacokinetic modelling are presented. Usually a 3-compartment model is used for pharmacokinetic calculations of blood concentrations. This 3-compartment model is extended with a 2-compartment model based on the first compartment of the 3-compartment model and a new lung compartment. The second approach is to calculate a time delay of changes in the concentration of the first compartment to describe the lung-concentration. Exemplarily both approaches are used for modelling of exhaled propofol. Based on time series of exhaled propofol measurements using an ion-mobility-spectrometer every minute for 346 min a correlation of calculated plasma and the breath concentration was used for modelling to deliver R(2) = 0.99 interdependencies. Including the time delay modelling approach the new compartment coefficient k(e0lung) was calculated to k(e0lung) = 0.27 min(-1) with R(2) = 0.96. The described models are not limited to propofol. They could be used for any kind of drugs, which are measurable in patient's breath.

[Basic algorithm for Point-of-Care based hemotherapy: perioperative treatment of coagulopathic patients]

During perioperative treatment of coagulopathic patients the so-called Point-of-Care (POC) analyses enable more rapidly available and more comprehensive hemostatic analyses compared to routinely performed conventional coagulation testing, such as activated partial thromboplastin time (aPTT), international normalized ratio (INR), fibrinogen concentration and platelet count. In this review article a hemotherapy algorithm is presented which is based on viscoelastic and aggregometric POC measurements. The algorithm was designed double sided and consists of a general and a special part. The general part contains boxes and fields for sociodemographic data and gives general recommendations for coagulation management and therapy specifications for particular patient collectives and presents proposals for emergency reversal of anticoagulation therapy. The special part refers to basic physiological conditions for hemostasis and asks for measurement results of clot initiation, clot firmness, clot stability and platelet function analyses. Reference values were defined for each parameter and therapeutic options are presented. In cases of persistent coagulopathy despite algorithm-conform therapy, the algorithm could be run through once again. Finally, the algorithm presents therapeutic options for an ultima ratio therapy approach.

Sample transport by pneumatic tube system alters results of multiple electrode aggregometry but not rotational thromboelastometry

Pneumatic tube systems (PTS) present a convenient way for blood sample transport in medical facilities. Associated preanalytical interference in various tests is largely unknown. Implementing point-of-care coagulation management at our institution, we investigated multiple electrode aggregometry (MEA) and rotational thromboelastometry (ROTEM) after PTS transportation. Whole blood samples from patients undergoing general or trauma surgery were analysed by MEA after collection (baseline, '0 × PTS') and sent on a predefined PTS track (n = 12). MEA was repeated after samples travelled the track 4 ('4 × PTS'), 8 ('8 × PTS') and 12 times ('12 × PTS') and compared with stationary controls analysed at the same time. Samples for ROTEM (n = 6) were analysed after collection and travelling the track 12 times. An acceleration detector recorded g-forces on the PTS track. At '0 × PTS' no significant differences in MEA results were detected. Values were significantly lower for transported samples compared with controls ('4 × PTS' to '12 × PTS', p < 0.001). Furthermore, MEA results of PTS samples were significantly decreased for '4 × PTS' to '12 × PTS' compared to baseline (p < 0.001). Except for the clotting time in EXTEM PTS transport did not significantly alter results for investigated ROTEM parameters, compared with baseline and stationary controls. Acceleration detector readout revealed alternating g-forces between -6.3 and +5.9 during transport. PTS transport caused invalid results in MEA while only one ROTEM parameter was found to be affected in this study. Variable acceleration during transport provides a potential reason for platelet activation. The authors recommend sample transport by hand or the device to be placed patient-side when MEA is performed.