Johannes Bickenbach

Comparison of electrical velocimetry and thermodilution techniques for the measurement of cardiac output

Aim:  To compare a new method of non‐invasive determination of cardiac output based on electrical velocimetry (EV‐CO) with invasive thermodilution methods.

Levosimendan but not norepinephrine improves microvascular oxygenation during experimental septic shock

Objective:To determine the effects of norepinephrine and levosimendan on microvascular perfusion and oxygenation in a rat model of septic shock. Design:Controlled laboratory animal study. Setting:Research laboratory in a university hospital. Subjects:Forty Sprague-Dawley rats. Interventions:Sepsis was induced in 32 animals by cecal ligation and puncture. Eight animals served as sham controls. Animals were randomly assigned to five groups: 1) fluid resuscitation (25 ml·kg−1·h−1), 2) fluid resuscitation plus norepinephrine (0.5 &mgr;g·kg−1·min−1), 3) fluid resuscitation plus levosimendan (0.3 &mgr;g·kg−1·min−1), 4) no treatment and 5) sham control. Measurements and Main Results:Microvascular perfusion was quantitated using sidestream darkfield imaging and microvascular oxygenation (&mgr;PO2) was assessed by oxygen-dependent quenching of phosphorescence. Measurements were obtained on the buccal mucosa at baseline and at hourly intervals thereafter. In parallel, cardiac output (CO) was recorded. After induction of sepsis microvascular perfusion and &mgr;PO2 were impaired early followed by significant decreases in CO. Although levosimendan and norepinephrine were equally effective in restoring CO, only treatment with levosimendan significantly improved &mgr;PO2 after 1 and 2 hours of treatment (9.7 ± 2.0 vs. 15.1 ± 2.6 and 16.0 ± 3.7 mmHg; p < 0.05). Microvascular perfusion was not significantly influenced by any of the treatment strategies. Conclusions:In this model, treatment with levosimendan and norepinephrine showed comparable effects in restoring CO and had no significant influence on microvascular perfusion. However, only levosimendan significantly improved &mgr;PO2, suggesting that a mechanism relatively independent of macrocirculatory hemodynamics and overall microvascular perfusion might account for these observations.

S-100 protein and neurohistopathologic changes in a porcine model of acute lung injury

Background: Survivors of acute respiratory distress syndrome exhibit neuropsychological sequelae that might be attributable to hippocampal damage. The authors sought to determine the effects of hypoxemia in a pig model of acute lung injury on the hippocampal region and the release of S-100 protein in comparison to a control group in which hypoxemia was induced by reducing the inspired oxygen fraction. Methods: Hypoxemia was induced in 14 female pigs by repeated lung lavages (lung injury group; n = 7) or by reducing the inspired oxygen fraction (hypoxia-only group; n = 7). Hemodynamic variables, gas exchange, and serum concentrations of S-100 protein were measured at baseline, after induction of acute lung injury, and subsequently for 12 h. Animals were euthanized, and the brains were removed for histopathologic examination. Results: Comparable blood gases were seen in both groups. Serum S-100 protein concentrations were comparable for both groups at baseline. At all other time points, S-100 concentrations were significantly higher in the lung injury group. Neuropathologic examination showed basophilic and shrunken neurons of the pyramidal cell layer in the hippocampal CA1 subregion of all pigs in the lung injury group. Few abnormalities were seen in the hypoxia-only group. Conclusions: The same degree of hypoxemia induced in a lavage model of acute lung injury results in greater brain damage assessed by S-100 protein and histopathologic findings when compared to a group in which hypoxemia at the same degree was induced by reducing the inspired oxygen fraction. This suggests that acute lung injury leads to neuropathologic changes independent of hypoxemia.

Low tidal volume ventilation in a porcine model of acute lung injury improves cerebral tissue oxygenation.

BACKGROUND:In study, we investigated the effects of different tidal volumes on cerebral tissue oxygenation and cerebral metabolism in a porcine model of acute lung injury (ALI). We hypothesized that mechanical ventilation with low tidal (LT) volumes improves cerebral tissue oxygenation and metabolism after experimentally induced ALI. METHODS:After inducing experimental ALI by surfactant depletion, we studied two conditions in 10 female pigs: 1) LT volume ventilation with 6 mL/kg body weight, and 2) high tidal (HT) volume ventilation with 12 mL/kg body weight. Variables of gas exchange, hemodynamic, continuous cerebral tissue oxygen tension (ptiO2), cerebral microdialysis, and systemic cytokines were analyzed. After induction of ALI, data were collected at 2, 4, and 8 h. The primary end point was the change in ptiO2. For group comparisons, a t-test was used. A value of <0.05 was considered to indicate statistical significance. RESULTS:At baseline and after induction of ALI, no differences between groups were found in ptiO2; however, ptiO2 was significantly lower in the HT group after 4 and 8 h. Pao2 and Paco2 showed no significant differences between the groups at all timepoints. Regarding cerebral microdialysis, a significantly higher level of extracellular lactate could be demonstrated after 2, 4, and 8 h in the HT group. The release of cytokines resulted in higher values for interleukin-6 and interleukin-8 in the HT group. CONCLUSION:Protective ventilation with LT yielded a significant improvement in cerebral tissue oxygenation and metabolism compared to HT ventilation in a porcine model of ALI. There was dissociation between arterial and cerebral tissue oxygenation. Cerebral oxygenation and metabolism might have possibly been impaired by a more distinctive inflammatory response in the HT group.

„Meet the AIX-PERTs...“

ZusammenfassungHintergrundDer berechtigte Anspruch, notwendige Fertigkeiten der Notfallversorgung von jedem Arzt erwarten zu können, und ein steigendes öffentliches Interesse an der Qualität ärztlicher Leistungen erfordern eine größere Gewichtung dieser Lerninhalte im Medizinstudium.MethodenIm Rahmen der seit dem 1.10.2003 gültigen neuen Approbationsordnung für Ärzte beschloss die medizinische Fakultät der RWTH Aachen zum Wintersemester 2003 einen „Modellstudiengang Medizin“ zu starten. Praktische Fertigkeiten der zukünftigen Mediziner sollen durch interdisziplinäre Vermittlung organsystembezogener Inhalte verbessert werden.ErgebnisUnter Einbindung von problemorientiertem Lernen wurde mit AIX-PERT (Aix-la-Chapelle Program for Emergency Medical Care and Resuscitation Training) ein multidisziplinäres Konzept zur Studiumseinführung entwickelt und evaluiert, das definierte Kernlernziele zur notfallmedizinischen Versorgung beinhaltet.SchlussfolgerungDie Evaluationsergebnisse demonstrieren die Akzeptanz von AIX-PERT und sind Basis longitudinaler Implementierung relevanter notfallmedizinischer Inhalte in das neue Curriculum.AbstractBackgroundExtensive knowledge and skills in the basics of emergency medical care are of paramount importance for every physician and should therefore be an integral part of medical education.MethodsRegulations for medical licensure in Germany were revised by the administrative authorities in 2002 and as a consequence the Medical Faculty of the University of Aachen (Germany) decided to start the Medical Reform Curriculum Aachen. A multidisciplinary, problem-oriented and organ-related approach to medical education replaces the classical discrimination between basic and clinical sciences.ResultsWith AIX-PERT (AIX-la-Chapelle Program for Emergency medical care and Resuscitation Training), a program consisting of problem-based learning sessions was developed for introduction to the first year students. Defined teaching objectives in emergency medicine are now incorporated in undergraduate medical education.ConclusionThe extremely positive evaluation of the new approach encouraged us to promote AIX-PERT further. In the future the effects of success of this approach will be assessed by longitudinal studies of skills and knowledge during the continuing curriculum.

The intuitive use of laryngeal airway tools by first year medical students

BackgroundProviding a secured airway is of paramount importance in cardiopulmonary resuscitation. Although intubating the trachea is yet seen as gold standard, this technique is still reserved to experienced healthcare professionals. Compared to bag-valve facemask ventilation, however, the insertion of a laryngeal mask airway offers the opportunity to ventilate the patient effectively and can also be placed easily by lay responders. Obviously, it might be inserted without detailed background knowledge.The purpose of the study was to investigate the intuitive use of airway devices by first-year medical students as well as the effect of a simple, but well-directed training programme. Retention of skills was re-evaluated six months thereafter.MethodsThe insertion of a LMA-Classic and a LMA-Fastrach performed by inexperienced medical students was compared in an airway model. The improvement on their performance after a training programme of overall two hours was examined afterwards.ResultsPrior to any instruction, mean time to correct placement was 55.5 ± 29.6 s for the LMA-Classic and 38.1 ± 24.9 s for the LMA-Fastrach. Following training, time to correct placement decreased significantly with 22.9 ± 13.5 s for the LMA-Classic and 22.9 ± 19.0 s for the LMA-Fastrach, respectively (p < 0.05). After six months, the results are comparable prior (55.6 ± 29.9 vs 43.1 ± 34.7 s) and after a further training period (23.5 ± 13.2 vs 26.6 ± 21.6, p < 0.05).ConclusionUntrained laypersons are able to use different airway devices in a manikin and may therefore provide a secured airway even without having any detailed background knowledge about the tool. Minimal theoretical instruction and practical skill training can improve their performance significantly. However, refreshment of knowledge seems justified after six months.

["Meet the AIX-PERTs." Emergency medical care at the beginning of the medical reform curriculum in Aachen].

ZusammenfassungHintergrundDer berechtigte Anspruch, notwendige Fertigkeiten der Notfallversorgung von jedem Arzt erwarten zu können, und ein steigendes öffentliches Interesse an der Qualität ärztlicher Leistungen erfordern eine größere Gewichtung dieser Lerninhalte im Medizinstudium.MethodenIm Rahmen der seit dem 1.10.2003 gültigen neuen Approbationsordnung für Ärzte beschloss die medizinische Fakultät der RWTH Aachen zum Wintersemester 2003 einen „Modellstudiengang Medizin“ zu starten. Praktische Fertigkeiten der zukünftigen Mediziner sollen durch interdisziplinäre Vermittlung organsystembezogener Inhalte verbessert werden.ErgebnisUnter Einbindung von problemorientiertem Lernen wurde mit AIX-PERT (Aix-la-Chapelle Program for Emergency Medical Care and Resuscitation Training) ein multidisziplinäres Konzept zur Studiumseinführung entwickelt und evaluiert, das definierte Kernlernziele zur notfallmedizinischen Versorgung beinhaltet.SchlussfolgerungDie Evaluationsergebnisse demonstrieren die Akzeptanz von AIX-PERT und sind Basis longitudinaler Implementierung relevanter notfallmedizinischer Inhalte in das neue Curriculum.AbstractBackgroundExtensive knowledge and skills in the basics of emergency medical care are of paramount importance for every physician and should therefore be an integral part of medical education.MethodsRegulations for medical licensure in Germany were revised by the administrative authorities in 2002 and as a consequence the Medical Faculty of the University of Aachen (Germany) decided to start the Medical Reform Curriculum Aachen. A multidisciplinary, problem-oriented and organ-related approach to medical education replaces the classical discrimination between basic and clinical sciences.ResultsWith AIX-PERT (AIX-la-Chapelle Program for Emergency medical care and Resuscitation Training), a program consisting of problem-based learning sessions was developed for introduction to the first year students. Defined teaching objectives in emergency medicine are now incorporated in undergraduate medical education.ConclusionThe extremely positive evaluation of the new approach encouraged us to promote AIX-PERT further. In the future the effects of success of this approach will be assessed by longitudinal studies of skills and knowledge during the continuing curriculum.

Analysis of regional compliance in a porcine model of acute lung injury

Lung protective ventilation in acute lung injury (ALI) focuses on using low tidal volumes and adequate levels of positive end-expiratory pressure (PEEP). Identifying optimal pressure is difficult because pressure-volume (PV) relations differ regionally. Precise analysis demands local measurements of pressures and related alveolar morphologies. In a porcine model of surfactant depletion (n=24), we combined measuring static pressures with endoscopic microscopy and electrical impedance tomography (EIT) to examine regional PV loops and morphologic heterogeneities between healthy (control group; CON) and ALI lungs ventilated with low (LVT) or high tidal volumes (HVT). Quantification included indices for microscopy (Volume Air Index (VAI), Heterogeneity and Circularity Index), EIT analysis and calculation of regional compliances due to generated PV loops. We found that: (1) VAI decreased in lower lobe after ALI, (2) electrical impedance decreased in dorsal regions and (3) PV loops differed regionally. Further studies should prove the potentials of these techniques on individual respiratory settings and clinical outcome.

In vivo microscopy in a porcine model of acute lung injury.

Regional inhomogeneity and alveolar mechanics in a porcine model of acute lung injury (ALI) was evaluated using confocal laser scanning microscopy (CLSM). CLSM was performed through thoracic windows of the upper and lower lobes. Image quantification was conducted by use of a volume air index (VAI). Twelve anesthetized, mechanically ventilated pigs were randomized to non-injury (control group, n = 6) or ALI induced by surfactant depletion (ALI group, n = 6). CLSM was performed at baseline, after 1 h at 5 mbar and after 2 h at 15 mbar positive end-expiratory pressure (PEEP). Haemodynamics, respiratory mechanics and calculation of pulmonary ventilation-perfusion distribution by MIGET were determined. At baseline, VAI was not different. In the upper lobes, VAI significantly decreased in ALI compared to control group, with no changes after PEEP application. In the lower lobes, VAI significantly decreased in ALI compared to control group. Incremental PEEP significantly increased VAI in ALI, but not in control group. Haemodynamics were significantly compromised in the ALI group. A significant deterioration in oxygenation and ventilation-perfusion distribution could be seen being restored after PEEP adjustment. The VAI may help to assess regional inhomogeneity of the acutely injured lung.

Neurological outcome after experimental lung injury.

We examined the influences of acute lung injury and hypoxia on neurological outcome. Functional performance was assessed using a neurocognitive test and a neurologic deficit score (NDS) five days before. On experimental day, mechanically ventilated pigs were randomized to hypoxia only (HO group, n=5) or to acute lung injury (ALI group, n=5). Hemodynamics, respiratory mechanics, systemic cytokines and further physiologic variables were obtained at baseline, at the time of ALI, 2, 4 and 8h thereafter. Subsequently, injured lungs were recruited and animals weaned from the ventilator. Neurocognitive testing was re-examined for five days. Then, brains were harvested for neurohistopathology. After the experiment, neurocognitive performance was significantly worsened and the NDS increased in the ALI group. Histopathology revealed no significant differences. Oxygenation was comparable between groups although significantly higher inspiratory pressures occured after ALI. Cytokines showed a trend towards higher levels after ALI. Neurocognitive compromise after ALI seems due to a more pronounced inflammatory response and complex mechanical ventilation.