Nadine Hochhausen

Parameters derived from the pulmonary pressure-volume curve, but not the pressure-time curve, indicate recruitment in experimental lung injury

BACKGROUND:In acute lung injury, ventilation avoiding tidal hyperinflation and tidal recruitment has been proposed to prevent ventilator-associated lung injury. Information about dynamic recruitment may be obtained from the characteristics of pressure–volume (PV) curves or the profile of pressure–time (Paw-t) curves. METHODS:Six anesthetized pigs with lung lavage-induced acute lung injury were ventilated with lung-protective settings. We measured the effects of a standard recruitment maneuver on hysteresis area and ratio obtained from the PV curve and on the stress index obtained from the Paw-t curve and correlated this with aerated and nonaerated lung volumes as measured by multislice computed tomography. RESULTS:Hysteresis area and ratio correlated with aerated lung volume (r = 0.886). The recruitment maneuver resulted in an increase in aerated (+12%) and a decrease (−18%) in nonaerated lung. Hysteresis area correlated with alveolar recruitment, represented by an increase in aerated lung (r = 0.886) and a decrease in nonaerated lung (r = −0.829) during tidal ventilation. The stress index was always >1 and indicated tidal hyperinflation only. Values did not change after the recruitment maneuver and did not correlate with any other lung volume. CONCLUSIONS:Parameters derived from the PV curve may help in characterizing the lung aeration of the lung and in indicating recruitment. In the presence of lung-protective ventilator settings, the stress index derived from the Paw-t curve was not able to indicate recruitment.

Physiologic and biologic characteristics of three experimental models of acute lung injury in rats.

BACKGROUND: Strategies to attenuate ventilator-associated lung injury have been tested in various experimental methods of acute lung injury (ALI). Conclusions are often drawn from physiologic and biologic effects, but the influence of the model on these results is not known. Our aim in this study was to characterize frequently used models of experimental ALI. METHODS: Twenty Sprague Dawley rats were anesthetized and their lungs mechanically ventilated for 5 hours. Three models of ALI (surfactant washout, acid aspiration, and high tidal volume ventilation) were investigated with regard to hemodynamics, respiratory mechanics, gas exchange, lung pathology, and inflammatory reactions. Animals without ALI served as controls. RESULTS: Five animals in each group were analyzed. Dynamic compliance and PaO2/fraction of inspired oxygen ratio decreased by at least 50% in all groups after 1 hour. Whereas compliance remained decreased in all models, oxygenation returned to baseline values in the lavage group after 5 hours. Diffuse alveolar damage was worse in the high tidal volume model and was not different between the control and lavage animals. Interleukin-6 was increased in bronchoalveolar lavage fluid in the aspiration and high tidal volume models. CONCLUSIONS: Although comparable physiologic effects meeting acute respiratory distress syndrome criteria were achieved in all models, the biologic responses varied among lung injury models. The acid aspiration model created both respiratory and inflammatory responses typically seen in ALI; these data suggest that it may be the most clinically applicable model to study the intermediate-term effects of ventilator-associated lung injury in rats.

Effectiveness of nitric oxide during spontaneous breathing in experimental lung injury

ABSTRACT Inhaled nitric oxide (iNO) improves gas exchange in about 60% of patients with acute respiratory distress syndrome (ARDS). Recruitment of atelectatic lung areas may improve responsiveness and preservation of spontaneous breathing (SB) may cause recruitment. Accordingly, preservation of SB may improve effectiveness of iNO. To test this hypothesis, iNO was evaluated in experimental acute lung injury (ALI) during SB. In 24 pigs with ALI, effects of 10 ppm iNO were evaluated during controlled mechanical ventilation (CMV) and SB in random order. Preservation of SB was provided by 4 different modes: Unassisted SB was enabled by biphasic positive airway pressure (BIPAP), moderate inspiratory assist was provided by pressure support (PS) and volume-assured pressure support (VAPS), maximum assist was ensured by assist control (A/C). Statistical analysis did not reveal gas exchange improvements due to SB alone. Significant gas exchange improvements due to iNO were only achieved during unassisted SB with BIPAP (P <.05) but not during CMV or assisted SB. The authors conclude that effectiveness of iNO may be improved by unassisted SB during BIPAP but not by assisted SB. Thus combined iNO and unassisted SB is possibly most effective to improve gas exchange in severe hypoxemic ARDS.

Optimizing PEEP by Electrical Impedance Tomography in a Porcine Animal Model of ARDS

BACKGROUND: Mechanical ventilation is necessary in diverse clinical circumstances. Especially in the context of ARDS, so-called protective ventilation strategies must be followed. It is already known that PEEP might enhance oxygenation in ARDS. However, determining the optimal PEEP settings in clinical routines is challenging. Electrical impedance tomography (EIT) is a promising technique with which to adjust ventilator settings. We investigated whether the combination of different EIT parameters, namely the global inhomogeneity and hyperdistension indices, may lead to a feasible and safe PEEP setting. METHODS: ARDS was induced by a double-hit approach in 18 pigs weighing, on average, 34.8 ± 3.97 kg. First, a surfactant washout was conducted; second, the tidal volume was increased to 20 mL/kg body weight, triggering a ventilator-induced lung injury. Subsequently, pigs were randomized to either the EIT or control groups, followed by an observation time of 24 h. In the control group, PEEP was set according to the ARDS network table. In the EIT group, a PEEP trial was conducted to determine an appropriate PEEP. At defined time points, hemodynamic measures, ventilation parameters, and EIT recordings, as well as blood samples, were taken. After euthanization, lungs were removed for subsequent histopathological and cytological examination. RESULTS: The combination of PEEP and FIO2 differed between groups, although respiratory compliance, gas exchange, and histopathological examinations, as well as hemodynamics, did not show any statistical differences between the EIT and control groups. However, in the control group, the PEEP/FIO2 settings followed the given coupling; in the EIT group, divergent individual combinations of PEEP and FIO2 ranges occurred. CONCLUSIONS: PEEP setting by EIT facilitates a more individual ventilation therapy. However, in our relatively short ARDS observation period of 24 h, no significant differences appeared in common clinical parameters compared with a control group.

Improved electrode positions for local impedance measurements in the lung : a simulation study

Impedance spectroscopy can be used to analyze the dielectric properties of various materials. In the biomedical domain, it is used as bioimpedance spectroscopy (BIS) to analyze the composition of body tissue. Being a non-invasive, real-time capable technique, it is a promising modality, especially in the field of lung monitoring. Unfortunately, up to now, BIS does not provide any regional lung information as the electrodes are usually placed in hand-to-hand or transthoracic configurations. Even though transthoracic electrode configurations are in general capable of monitoring the lung, no focusing to specific regions is achieved. In order to resolve this issue, we use a finite element model (FEM) of the human body to study the effect of different electrode configurations on measured BIS data. We present evaluation results and show suitable electrode configurations for eight lung regions. We show that, using these optimized configurations, BIS measurements can be focused to desired regions allowing local lung analysis.

Heutige Möglichkeiten der Telemedizin in der Anästhesiologie

Because of an ageing population and a relative lack of professionals, the German health system is under great pressure. In rural regions in particular, anesthesiology is also affected - nursing staff, anesthetists, intensive care physicians, and emergency physicians often have to be supported by freelancers from other regions and from abroad - at least periodically. In addition to the increasing number of treatments, the potential quality of therapy is also increasing owing to progress in medical research. Against this background the need for resources is increasing to ensure the optimal quality of treatment. This applies to all clinical disciplines, including all sections of anesthesiology - especially in economically underdeveloped regions where highly qualified experts are lacking. In various cases it is not the physical attendance or manual skills of experts that is primarily requested on-site, but rather their medical expertise and experience. Therefore, telemedicine systems are suitable for closing these gaps very effectively and efficiently. In the various anesthesiological sub-sections the number of scientific papers published to date varies. For anesthesia and pain therapy only a few telemedical applications or concepts have been reported in the literature. However, in tele-intensive care medicine and tele-emergency medicine several national and international research projects have successfully been carried out, leading to established routine systems in some cases.

Development of a “Thermal-Associated Pain Index” score using infrared-thermography for objective pain assessment

Without any doubt, research in biomedical engineering and anesthesiology achieved diverse ground-breaking successes for the sake of patient safety and for optimization of medical treatment in the last decades. Particularly anesthesia has become increasingly comfortable and safer due to new monitoring devices and further techniques. However, assessment of pain still relies on self-reporting of the patient using a Numeric Rating Scale ranging from 0 to 10. Obviously, this method suffers from severe restraints when unconscious, anesthetized or uncooperative subjects or children are involved as patients. Furthermore, no continuous monitoring is available so that features like alerting telemetry are lacking. Several scientific groups and companies searched intensively for procedures to measure pain objectively. Skin conductance, heart rate variability and peripheral perfusion, among others, were used to develop new algorithms and devices. Up to date, none of these devices succeeded to enter in clinical routine. In this project, we used infrared thermography (IRT) to analyze facial expressions and further thermal-associated phenomena that are visible in recorded IRT sequences such as lacrimation and perspiration. By means of clinical observations, a number of IRT features were predefined that were expected to correlate with pain. The combination of those features led to the so-called “Thermal-Associated Pain Intensity” (TAPI) after normalization and transformation. The TAPI correlates significantly with the NRS and achieves a sensitivity of above 0.75 to detect pain.

Current capabilities of telemedicine in anaesthesiology

Because of an ageing population and a relative lack of professionals, the German health system is under great pressure. In rural regions in particular, anesthesiology is also affected - nursing staff, anesthetists, intensive care physicians, and emergency physicians often have to be supported by freelancers from other regions and from abroad - at least periodically. In addition to the increasing number of treatments, the potential quality of therapy is also increasing owing to progress in medical research. Against this background the need for resources is increasing to ensure the optimal quality of treatment. This applies to all clinical disciplines, including all sections of anesthesiology - especially in economically underdeveloped regions where highly qualified experts are lacking. In various cases it is not the physical attendance or manual skills of experts that is primarily requested on-site, but rather their medical expertise and experience. Therefore, telemedicine systems are suitable for closing these gaps very effectively and efficiently. In the various anesthesiological sub-sections the number of scientific papers published to date varies. For anesthesia and pain therapy only a few telemedical applications or concepts have been reported in the literature. However, in tele-intensive care medicine and tele-emergency medicine several national and international research projects have successfully been carried out, leading to established routine systems in some cases.

Estimating Respiratory Rate in Post-Anesthesia Care Unit Patients Using Infrared Thermography: An Observational Study

The post-anesthesia care unit (PACU) is the central hub for recovery after surgery, especially when the surgery is performed under general anesthesia. Aside from clinical aspects, respiratory impairment is one of the major causes of morbidity and affected recovery in the PACU and should therefore be monitored. In previous studies, infrared thermography was applied to assess the breathing rate (BR) of healthy volunteers. Here, the transferability of published methods for postoperative patients in the PACU was examined. Video recordings of 28 patients were acquired using a long-wave infrared camera, and analyzed offline. For validation purposes, BRs derived from body surface electrocardiography were measured simultaneously. In general, a close agreement between the two techniques (r = 0.607, p = 0.002 upon arrival, and r = 0.849, p < 0.001 upon discharge from the PACU) was obtained. In conclusion, the algorithm was demonstrated to be feasible and reliable under these challenging conditions.

Lung Pathologies analyzed with Multi-Frequency Electrical Impedance Tomography: Pilot Animal Study

In critically ill patients, correct diagnosis of lung disease is essential for successful therapy. Therefore, this study investigated whether new multi-frequency electrical impedance tomography (mfEIT) can detect, monitor and differentiate between pathologies associated with the acute respiratory distress syndrome (ARDS). For this pilot study, 12 pigs were randomized into an ARDS (bronchoalveolar lavage) group (n = 7) and a healthy control group (n = 5). Animals were monitored by means of mfEIT. In addition to functional images, a new impaired-ventilation (rImpVent) index was developed and frequency-difference images were computed and analyzed. Amplitude functional images revealed only small differences between the groups. However, phase functional images were of greater importance in distinguishing between lung pathologies. Correlation images showed substantial differences between the two groups. The new rImpVent index achieved high sensitivity (91%) and specificity (92%) in detecting PaO2/FiO2 ≤ 200 mmHg. mfEIT was able to detect lung edema, differentiate this from atelectasis, and also monitor their progress over time in terms of global and regional differences.