Torsten Meier

Protective ventilation using electrical impedance tomography

Dynamic thoracic EIT is capable of detecting changes of the ventilation distribution in the lung. Nevertheless, it has yet to become an established clinical tool. Therefore, it is necessary to consider application scenarios wherein fast and distinct changes of the tissue conductivities are to be found and also have a clear diagnostic significance. One such a scenario is the artificial ventilation of patients suffering from the acute respiratory distress syndrome (ARDS). New protective ventilation strategies involving recruitment manoeuvres are associated with noticeable shifts of body fluids and regional ventilation, which can quite easily be detected by EIT. The bedside assessment of these recruitment manoeuvres will help the attending physician to optimize treatment. Hence, we performed an animal study of lavage-induced lung failure and investigated if EIT is capable of qualitatively as well as quantitatively monitoring lung recruitment during a stepwise PEEP trial. Additionally, we integrated EIT into a fuzzy controller-based ventilation system which allows one to perform automated recruitment manoeuvres (open lung concept) based on online PaO2 measurements. We found that EIT is a useful tool to titrate the proper PEEP level after fully recruiting the lung. Furthermore, EIT seems to be able to determine the status of recruitment when combining it with other physiological parameters. These results suggest that EIT may play an important role in the individualization of protective ventilation strategies.

Discontinuous monitoring of propofol concentrations in expired alveolar gas and in arterial and venous plasma during artificial ventilation

Background: Analyzing propofol concentration in expired alveolar gas (cPA) may be considered as a convenient, noninvasive method to follow the propofol concentration in plasma (cPPL). In the current study, the authors established procedures to measure cPA and cPPL for the assessment of their relation in two animal models during anesthesia. Methods: Expired alveolar gas and mixed venous and arterial blood were simultaneously sampled during continuous application of propofol for general anesthesia to three goats and three pigs. Propofol infusion rates were varied to modify plasma concentrations. cPA, sampled cumulatively over several respiratory cycles, was quantified by thermal desorption gas chromatography–mass spectrometry. cPPL was determined using reversed phase high-performance liquid chromatography with fluorescence detection. Results: cPA ranged from 0 to 1.4 and from 0 to 22 parts per billion in goats and pigs, respectively, at cPPL of 0–8 &mgr;g/ml. The relation between cPA and cPPL was linear; however, the slopes of the regression lines varied between animals. Conclusion: Propofol can be quantified in expired alveolar gas. The results stress the role of marked species-specific variability.

Propofol concentration in exhaled air and arterial plasma in mechanically ventilated patients undergoing cardiac surgery

BACKGROUND Measuring propofol concentration in plasma (c(P)PL) and in exhaled alveolar gas (c(P)G) during constant infusion provides information about their respective time courses. In the present study, we compared these time courses in patients undergoing cardiac surgery from the beginning of propofol anaesthesia until eye opening upon awakening. METHODS The c(P)G was measured before, during, and after continuous infusion of propofol for general anaesthesia in 12 patients at two randomly allocated doses (3 or 6 mg kg(-1) h(-1)). Gas samples were collected on Tenax tubes. After thermodesorption, c(P)G was measured by gas chromatography mass spectrometry. Simultaneously with exhaled gas, arterial blood was sampled for measuring c(P)PL by reversed-phase high-performance liquid chromatography with fluorescence detection. In order to compare the time courses of c(P)PL and c(P)G as dimensionless values directly, each gas and plasma value was normalized by relating it to the corresponding value at the end of the initial infusion after 40 min. RESULTS The c(P)G ranged between 2.8 and 22.5 ppb, whereas the corresponding c(P)PL varied between 0.3 and 3.3 microg ml(-1). Normalized concentration values showed a delayed increase in c(P)G compared with c(P)PL under constant propofol infusion before the onset of cardiopulmonary bypass, and a delayed decrease after stopping the propofol at the end of anaesthesia. CONCLUSIONS Propofol can be measured in exhaled gas from the beginning until the end of propofol anaesthesia. The different time courses of c(P)PL and c(P)G have to be considered when interpreting c(P)G.

Pulmonary cytokine responses during mechanical ventilation of noninjured lungs with and without end-expiratory pressure.

BACKGROUND: Positive end-expiratory pressure (PEEP) during mechanical ventilation may impose different degrees of stress on healthy lungs. On the assumption that stress is reflected by cytokine production, we performed a translational study investigating the effect of PEEP on bronchoalveolar and systemic mediator levels in isolated perfused mouse lungs (IPL) and in patients with healthy lungs. METHODS: (Part I) IPL were ventilated with end-expiratory pressures of 0, 3, 6, or 10 cm H2O and end-inspiratory pressure (EIP) levels of 10 or 25 cm H2O. Interleukin (IL)-6 and macrophage inflammatory protein-2 concentrations in the venous effluate were monitored. (Part II) Patients (nonsmokers) scheduled for elective otorhinolaryngology surgery (duration >90 min) were randomized to receive either ventilation with zero end-expiratory pressure or PEEP (10 cm H2O). Mediators in bronchoalveolar lavage, nuclear factor &kgr;B, (NF-&kgr;B)-activation in alveolar macrophages and circulating systemic mediators were monitored. Control patients underwent bronchoalveolar lavage after intubation. RESULTS: In the IPL, mediator concentrations increased with increasing end-expiratory pressure at an EIP of 10 cm H2O, but decreased at 25 cm H2O EIP. In patients, bronchoalveolar IL-6, monocyte chemoattractant protein-1, and granulocyte monocyte-colony stimulating factor were increased by ventilation regardless of the PEEP level. IL-6 and IL-8 levels were moderately increased by PEEP but not zero end-expiratory pressure. Nuclear factor &kgr;B DNA binding activity in alveolar macrophages and systemic mediator levels did not change. CONCLUSIONS: On the basis of the premise that cytokine levels may indicate mechanical stress, our findings indicate that even low tidal volume ventilation causes some stress. PEEP is beneficial at high inspiratory pressure, but imposes moderate stress at low inspiratory pressure.

Effect of PEEP on regional ventilation during laparoscopic surgery monitored by electrical impedance tomography

Background: Anesthesia per se and pneumoperitoneum during laparoscopic surgery lead to atelectasis and impairment of oxygenation. We hypothesized that a ventilation with positive end‐expiratory pressure (PEEP) during general anesthesia and laparoscopic surgery leads to a more homogeneous ventilation distribution as determined by electrical impedance tomography (EIT). Furthermore, we supposed that PEEP ventilation in lung‐healthy patients would improve the parameters of oxygenation and respiratory compliance.

Risikofaktoren für Rückenschmerzen bei Kindern und Jugendlichen in Industrienationen

ZusammenfassungDie Ursache für die in den letzten Jahren zunehmende Prävalenz von Rückenschmerzen bei Kindern und Jugendlichen in entwickelten Industrienationen ist weitgehend unklar. Die Literaturübersicht umfasst publizierte Originalarbeiten in den Datenbanken PUBMED und MEDLINE im Zeitraum von 1985–2003 mit den Schlüsselwörtern „children or adolescents“ und „back pain“, in denen Rückenschmerzen bei 0- bis 18-jährigen Kindern untersucht wurden. Das Risiko, Rückenschmerzen zu erleiden, kann durch körperliche, behaviorale, emotionale und soziale Faktoren beeinflusst werden. Der Einfluss von körperlicher Aktivität, Sitzverhalten, Schulmobiliar, Haltung, Muskelstatus, Schultaschengewicht, Freizeitsport, Fernsehkonsum und Computergebrauch wurde neben Alter, Geschlecht und anthropometrischen Parametern als mögliche Einflussfaktoren zur Entwicklung und Chronifizierung von Rückenschmerzen untersucht. Zusammenhänge zwischen anhaltenden oder wiederkehrenden Rückenschmerzen in diesem Alter und psychosozialen Einflussfaktoren wurden aufgezeigt. Bisherige Untersuchungen zeigten keinen Zusammenhang zwischen radiologischen Veränderungen der Wirbelsäule und Rückenschmerzen in Adoleszenz oder Erwachsenenalter. Longitudinale epidemiologische Untersuchungen werden dringend benötigt, um den natürlichen Verlauf und Risikofaktoren, die im Langzeitverlauf wirksam werden, besser zu verstehen.AbstractFactors that have led to the increasing prevalence of back pain amongst children and adolescents living in industrialized nations are mostly unknown. The following literature review was aimed at determining the risk factors for back pain amongst children and adolescents. We searched both PUBMED and MEDLINE between the years 1985 and 2003 for the keywords “children or adolescents” and “back pain”. Only data published in original articles were used. The risk for suffering back pain is influenced by physical, behavioural, emotional and social factors. The effects of physical activity, sitting, muscle status, weight of schoolbags, exercise, television and computer use, as well as age and gender on the development of back pain in children and adolescents were examined. Associations between continuous or recurring back pain and psychosocial factors (lifestyle, emotional factors, social relationships) could be demonstrated. There was no relationship between changes of the spine seen by radiological tests and the development of chronic back pain. Longitudinal epidemiological studies are urgently needed to delineate the risk factors for the development as well as the natural history of chronic back pain in the young.

Risk factors for back pain in children and adolescents

ZusammenfassungDie Ursache für die in den letzten Jahren zunehmende Prävalenz von Rückenschmerzen bei Kindern und Jugendlichen in entwickelten Industrienationen ist weitgehend unklar. Die Literaturübersicht umfasst publizierte Originalarbeiten in den Datenbanken PUBMED und MEDLINE im Zeitraum von 1985–2003 mit den Schlüsselwörtern „children or adolescents“ und „back pain“, in denen Rückenschmerzen bei 0- bis 18-jährigen Kindern untersucht wurden. Das Risiko, Rückenschmerzen zu erleiden, kann durch körperliche, behaviorale, emotionale und soziale Faktoren beeinflusst werden. Der Einfluss von körperlicher Aktivität, Sitzverhalten, Schulmobiliar, Haltung, Muskelstatus, Schultaschengewicht, Freizeitsport, Fernsehkonsum und Computergebrauch wurde neben Alter, Geschlecht und anthropometrischen Parametern als mögliche Einflussfaktoren zur Entwicklung und Chronifizierung von Rückenschmerzen untersucht. Zusammenhänge zwischen anhaltenden oder wiederkehrenden Rückenschmerzen in diesem Alter und psychosozialen Einflussfaktoren wurden aufgezeigt. Bisherige Untersuchungen zeigten keinen Zusammenhang zwischen radiologischen Veränderungen der Wirbelsäule und Rückenschmerzen in Adoleszenz oder Erwachsenenalter. Longitudinale epidemiologische Untersuchungen werden dringend benötigt, um den natürlichen Verlauf und Risikofaktoren, die im Langzeitverlauf wirksam werden, besser zu verstehen.AbstractFactors that have led to the increasing prevalence of back pain amongst children and adolescents living in industrialized nations are mostly unknown. The following literature review was aimed at determining the risk factors for back pain amongst children and adolescents. We searched both PUBMED and MEDLINE between the years 1985 and 2003 for the keywords “children or adolescents” and “back pain”. Only data published in original articles were used. The risk for suffering back pain is influenced by physical, behavioural, emotional and social factors. The effects of physical activity, sitting, muscle status, weight of schoolbags, exercise, television and computer use, as well as age and gender on the development of back pain in children and adolescents were examined. Associations between continuous or recurring back pain and psychosocial factors (lifestyle, emotional factors, social relationships) could be demonstrated. There was no relationship between changes of the spine seen by radiological tests and the development of chronic back pain. Longitudinal epidemiological studies are urgently needed to delineate the risk factors for the development as well as the natural history of chronic back pain in the young.

Electrical impedance tomography: changes in distribution of pulmonary ventilation during laparoscopic surgery in a porcine model

BackgroundBecause of the creation of a pneumoperitoneum, impairment of ventilation is a common side-effect during laparoscopic surgery. Electrical impedance tomography (EIT) is a method with the potential for becoming a tool to quantify these alterations during surgery. We have studied the change of regional ventilation during and after laparoscopic surgery with EIT and compared the diagnostic findings with computed tomography (CT) scans in a porcine study.Materials and methodsAfter approval by the local animal ethics committee, six pigs were included in the study. Two laparoscopic operations were performed [colon resection (n=3) and fundoplicatio (n=3)]. The EIT measurements (6th parasternal intercostal space) were continuously recorded by an EIT prototype (EIT Evaluation Kit, Dräger Medical, Lübeck, Germany). To verify ventilatory alterations detected by EIT, a CT scan was performed postoperatively.ResultsVentilation with defined tidal volumes was significantly correlated to EIT measurements (r2=0.99). After creation of the pneumoperitoneum, lung compliance typically decreased, which agreed well with an alteration of the distribution of pulmonary ventilation measured by EIT. Elevation of positive end-inspiratory pressure reopened non-aerated lung areas and showed a recovery of the regional ventilation measured by EIT. Additionally, we could detect pulmonary complications by EIT monitoring as verified by CT scans postoperatively.ConclusionEIT monitoring can be used as a continuous non-invasive intraoperative monitor of ventilation to detect regional changes of ventilation and pulmonary complications during laparoscopic surgery. These EIT findings indicate that surgeons and anesthetists may eventually be able to optimize ventilation directly in the operating theatre.

[Reduction of chronic pain for non-postherpetic peripheral neuropathies after topical treatment with a lidocaine patch].

INTRODUCTION To clarify whether the therapeutic indication for a lidocaine patch to treat postherpetic neuralgia can be extended to include other focal peripheral neuropathic pain syndromes, we performed a subgroup analysis of a placebo-controlled, double-blind randomized study. METHODS The study included 16 patients with focal peripheral painful neuropathies of non-herpetic origin, pain intensity > or =40 mm (VAS), and a stable pain medication. The patients received either the lidocaine patch 5% for 1 week or a placebo patch for 12 h daily according to a crossover design. Persistent pain, mechanical allodynia, and adverse events were assessed daily by the patients. Additionally, the pain perception test, the list of physical complaints, the depression test, and the health-related quality of life (SF-36) were used. Of the enrolled patients, 12 were statistically analyzed. RESULTS Persistent pain was reduced by the lidocaine patch almost significantly and allodynia was reduced significantly in comparison to the placebo patch. Scores for physical complaints improved significantly with the lidocaine patch. Only mild focal skin irritations occurred. CONCLUSIONS As an adjuvant medication, the lidocaine patch is effective and safe for reducing chronic pain and physical complaints in focal non-herpetic neuropathies.

Reduktion chronischer Schmerzen bei nichtpostherpetischen peripheren Neuropathien nach topischer Behandlung mit Lidocainpflaster

INTRODUCTION To clarify whether the therapeutic indication for a lidocaine patch to treat postherpetic neuralgia can be extended to include other focal peripheral neuropathic pain syndromes, we performed a subgroup analysis of a placebo-controlled, double-blind randomized study. METHODS The study included 16 patients with focal peripheral painful neuropathies of non-herpetic origin, pain intensity > or =40 mm (VAS), and a stable pain medication. The patients received either the lidocaine patch 5% for 1 week or a placebo patch for 12 h daily according to a crossover design. Persistent pain, mechanical allodynia, and adverse events were assessed daily by the patients. Additionally, the pain perception test, the list of physical complaints, the depression test, and the health-related quality of life (SF-36) were used. Of the enrolled patients, 12 were statistically analyzed. RESULTS Persistent pain was reduced by the lidocaine patch almost significantly and allodynia was reduced significantly in comparison to the placebo patch. Scores for physical complaints improved significantly with the lidocaine patch. Only mild focal skin irritations occurred. CONCLUSIONS As an adjuvant medication, the lidocaine patch is effective and safe for reducing chronic pain and physical complaints in focal non-herpetic neuropathies.