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Byline: J. Hinz (1), G. Hahn (1), P. Neumann (1), M. Sydow (2), P. Mohrenweiser (1), G. Hellige (1), H. Burchardi (1) Keywords: Thoracic electrical impedance tomography End-expiratory lung impedance change End-expiratory lung volume Abstract: Abstract Objective. The aim of the study was to investigate the effect of lung volume changes on end-expiratory lung impedance change (ELIC) in mechanically ventilated patients, since we hypothesized that ELIC may be a suitable parameter to monitor lung volume change at the bedside. Design. Clinical trial on patients requiring mechanical ventilation. Settings. Intensive care units of a university hospital. Patients. Ten mechanically ventilated patients were included in the study. Intervention. Patients were ventilated in volume-controlled mode with constant flow and respiratory rate. In order to induce changes in the end-expiratory lung volume (EELV), PEEP levels were increased from 0 mbar to 5 mbar, 10 mbar, and 15 mbar. At each PEEP level EELV was measured by an open-circuit nitrogen washout manoeuvre and ELIC was measured simultaneously using Electrical Impedance Tomography (EIT) with sixteen electrodes placed on the circumference of the thorax and connected with an EIT device. Cross-sectional electro-tomographic measurements of the thorax were performed at each PEEP level, and a modified Sheffield back-projection was used to reconstruct images of the lung impedance. ELIC was calculated as the average of the end-expiratory lung impedance change. Results. Increasing PEEP stepwise from 0 mbar to 15 mbar resulted in an linear increase of EELV and ELIC according to the equation: y =0.98 x --0.68, r .sup.2 =0.95. Conclusion. EIT is a simple bedside technique which enables monitor lung volume changes during ventilatory manoeuvres such as PEEP changes. Author Affiliation: (1) Department of Anaesthesiology, Emergency and Intensive Care Medicine, University of Gottingen, Robert-Koch-Str. 40, 37075 Gottingen, Germany (2) Department of Anaesthesiology and Intensive Care Medicine, St. Johannes-Hospital Dortmund, Germany Article History: Received Date: 20/12/2001 Accepted Date: 11/10/2002 Article note: Electronic Publication

Byline: M. Jegers (1), D. Edbrooke (2), C. Hibbert (3), D. Chalfin (4), H. Burchardi (5) Keywords: Intensive care medicine Cost definitions Cost categories Abstract: Objective. To define the different types of costs incurred in the care of critically ill patients and to describe some of the most commonly used methods for measuring and allocating these costs. Design. Literature review. Definitions for opportunity, direct and indirect, fixed, variable, marginal, and total costs are described and interpreted in the context of the critical care setting. Two main methods of costing are described: the 'top-down' and 'bottom-up' methods together with a number of cost proxies, such as the use of weighted hospital days, diagnosis-related groups, severity and activity scores, and effective costs per survivor. Conclusions. The assessment and allocation of costs to critically ill patients is complex and as a result of the different definitions and methods used, meaningful comparisons between studies are plagued with difficulty. When undertaking a study looking to measure costs, it is important to state: (a) the aim of the cost assessment study (b) the perspective (point of view) (c) the type of costs that need to be measured and (d) the time span of assessment. By being explicit about the rationale of the study and the methods used, it is hoped that the results of economic evaluations will be better understood, and hence implemented within the critical care setting. Author Affiliation: (1) Faculty of Economic, Social and Political Sciences, Microeconomics of the profit and non-profit sectors, Free University Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium (2) Medical Economics and Research Centre, Sheffield (MERCS), Intensive Care Unit, Royal Hallamshire Hospital, Sheffield, UK (3) Sheffield Health Economics Group, School of Health and Related Research, University of Sheffield, UK (4) Department of Emergency Medicine, Maimonides Medical Center, New York, USA (5) Centre of Anaesthesiology, Emergency and Intensive Care Medicine, University Hospital, Gottingen, Germany Article History: Received Date: 22/08/2001 Accepted Date: 22/02/2002 Article note: Electronic Publication

Byline: H. Buscher (1), P. Valta (2), M. Sydow (1), K. Thies (1), H. Burchardi (1) Keywords: Key words Phrenic nerve stimulation; Work of breathing; Oesophageal pressure Abstract: Objective: Five commercially available oesophageal balloon catheters (OBCs) were tested to evaluate the accuracy in transmitting fast-changing pressure signals which can be observed, for example, during phrenic nerve stimulation.APSetting: Research laboratory of a university hospital.APMethod: The OBCs tested varied in length (900--1390 mm) and inner diameter (0.9--1.5 mm) as well as in balloon material [latex or polyvinyl-chloride (PVC)]. A 180-cm tube served as a control. A sudden pressure drop was generated by the explosion of a pressurized latex balloon. The time between the pressure drop and 75, 50, 25 and 10 % of the maximal pressure was measured.APResults: The time intervals required to transduce a pressure drop of 90 % varied between the different OBCs from 85 to 476 ms(control 32 ms). Transmission time was lower in OBCs with a larger inner diameter. Shortening the OBCs resulted in a further decrease in transmission time.APConclusion: The type of OBC used has an impact on signal processing. An OBCs with a short transmission time should be chosen, especially if fast pressure changes are to be evaluated such as during phrenic nerve stimulation. Author Affiliation: (1) Zentrum Anaesthesiologie, Rettungs- und Intensivmedizin, George-August Universitat Gottingen, Robert-Koch Strasse 40, D-37 075 Gottingen, Germany e-mail: hbusche@gwdg.de Tel.: + 49-5 51-39 29 95 Fax: + 49-5 51-39 86 76, DE (2) Surgical Hospital, Helsinki University Central Hospital, Helsinki, Finland, FI Article note: Received: 23 August 1999/Final revision received: 3 January 2000/Accepted: 1 February 2000

Byline: J. L. Vincent (1), H. Burchardi (2) Author Affiliation: (1) Department of Intensive Care, Erasme University Hospital, Route de Lennik 808, B-1070, Brussels, Belgium Tel.: 32 25 55 33 80, Fax: 32 25 55 45 55 email: jlvincen@ulb.ac.be, BE (2) Department of Anesthesiology and Intensive Care Medicine, Georg August University of Gottingen, Germany, DE Article note: Accepted: 15 October 1999

Byline: H. Wrigge (1), W. Golisch (2), J. Zinserling (1), M. Sydow (2), G. Almeling (2), H. Burchardi (2) Keywords: Key words Mechanical ventilation; Critical care; Chronic obstructive pulmonary disease; Patient-ventilator interaction; Proportional assist; Pressure support; Work of breathing physiology Abstract: Objective: To investigate the breathing pattern and the inspiratory work of breathing (WOB.sub.I) in patients with chronic obstructive pulmonary disease (COPD) assisted with proportional assist ventilation (PAV) and conventional pressure support ventilation (PSV). Design: Prospective controlled study. Setting: Intensive care unit of a university hospital. Patients: Thirteen COPD patients being weaned from mechanical ventilation. Interventions: All patients were breathing PSV and two different levels of PAV. Measurements and main results: During PAV (EVITA 2 prototype, Drager, Germany), the resistance of the endotracheal tube (R.sub.et) was completely compensated while the patients' resistive and elastic loads were compensated for by approximately 80 % and 50 % (PAV.sub.80 and PAV.sub.50), respectively. PSV was adjusted to match the same mean inspiratory pressure (Pinsp.sub.mean) as during PAV.sub.80. Airway pressure, esophageal pressure and gas flow were measured over a period of 5 min during each mode. Neuromuscular drive (P.sub.0.1) was determined by inspiratory occlusions. Mean tidal volume (V.sub.T) was not significantly different between the modes. However, the coefficient of variation of V.sub.T was 10 +- 4.%, 20 +- 13 % and 15 +- 8 % during PSV, PAV.sub.80 and PAV.sub.50, respectively. Respiratory rate (RR) and minute ventilation (V.sub.E) were significantly lower during PAV.sub.80 as compared with both other modes, but the differences did not exceed 10 %. PAV.sub.80 and PSV had comparable effects on WOB.sub.I and P.sub.0.1, whereas WOB.sub.I and P.sub.0.1 increased during PAV.sub.50 compared with both other modes. Conclusion: Mean values of breathing pattern did not differ by a large amount between the investigated modes. However, the higher variability of V.sub.T during PAV indicates an increased ability of the patients to control V.sub.T in response to alterations in respiratory demand. A reduction in assist during PAV.sub.50 resulted in an increase in WOB and indices of patient effort. Author Affiliation: (1) Klinik und Poliklinik fur Anaesthesiologie und Spezielle Intensivmedizin, Rheinische Friedrich-Wilhelms-Universitat Bonn, Sigmund-Freud-Strasse 25, D-53 105 Bonn, Germany e-mail: hwrigge@uni-bonn.de Tel.: + 49-2 28-2875586 Fax: + 49-2 28-2 87 67 54, DE (2) Zentrum Anaesthesiologie, Rettungs- und Intensivmedizin, Georg-August-Universitat, Robert-Koch-Strasse 40, D-37 075 Gottingen, Germany, DE Article note: Received: 21 October 1998 Final revision received: 23 March 1999 Accepted: 10 May 1999

Byline: A. Brauer (1), H. Wrigge (2), J. Kersten (1), J. Rathgeber (1), W. Weyland (1), H. Burchardi (1) Keywords: Key words Accidental hypothermia; Rewarming strategy; Critical care; Extracorporeal circulation Abstract: Objective: To study a rewarming strategy for patients with severe accidental hypothermia using a simple veno-venous bypass in combination with a convective air warmer. Setting: Eighteen beds in a university hospital intensive care unit. Patients: Four adults admitted with a core temperature less than 30 degC. Hypothermia was caused by alcoholic intoxication in three patients and by drug overdose in one patient. Measurements and main results: All patients were rewarmed by a veno-venous bypass and in three cases a convective air warmer was also used. At a bypass flow rate of 100--300 ml/min the mean increase in core temperature was 1.15 degC/h (Range: 1.1--1.2 degC/h). One patient died 2 days after rewarming as a consequence of a reactivated pancreatitis. The other three patients survived without neurological sequelae. Conclusion: This rewarming technique seems safe and effective and allowed the controlled rewarming of our patients who suffered from severe accidental hypothermia Author Affiliation: (1) Dept. of Anesthesiology, Emergency and Intensive Care Medicine, University of Gottingen, Robert-Koch-Strasse 40, D-37 075 Gottingen, Germany e-mail: abraeue@gwdg.de Tel. + 49--551--39--8826 Fax + 49--551--39--8676, DE (2) Dept. of Anesthesiology and Intensive Care Medicine, University of Bonn, Germany, DE Article note: Received: 15 September 1998 Final revision received: 4 January 1999 Accepted: 11 February 1999

Byline: H. Wrigge (1), M. Sydow (1), J. Zinserling (2), P. Neumann (1), J. Hinz (1), H. Burchardi (1) Keywords: Key words Aged; Functional residual capacity; Lung volume measurement; Mechanical ventilation; Critical care; Chronic obstructive pulmonary disease; Acute lung injury Abstract: Objective: Validation of an open-circuit multibreath nitrogen washout technique (MBNW) for measurement of functional residual capacity (FRC). The accuracy of FRC measurement with and without continuous viscosity correction of mass spectrometer delay time (T.sub.D) relative to gas flow signal and the influence of baseline FIO.sub.2 was investigated. Design: Laboratory study and measurements in mechanically ventilated patients. Setting: Experimental laboratory and anesthesiological intensive care unit of a university hospital. Patients: 16 postoperative patients with normal pulmonary function (NORM), 8 patients with acute lung injury (ALI) and 6 patients with chronic obstructive pulmonary disease (COPD) were included. Interventions: Change of FIO.sub.2 from baseline to 1.0. Measurements and main results: FRC was determined by MBNW using continuous viscosity correction of T.sub.D (T.sub.Ddyn), a constant T.sub.D based on the viscosity of a calibration gas mixture (T.sub.D0) and a constant T.sub.D referring to the mean viscosity between onset and end of MBNW (T.sub.Dmean). Using T.sub.Ddyn, the mean deviation between 15 measurements of three different lung model FRCs (FRC.sub.measured) and absolute volumes (FRC.sub.model) was 0.2 %. For baseline FIO.sub.2 ranging from 0.21 to 0.8, the mean deviation between FRC.sub.measured and FRC.sub.model was -0.8 %. However, depending on baseline FIO.sub.2, the calculation of FRC using T.sub.Dmean and T.sub.D0 increased the mean deviation between FRC.sub.measured and FRC.sub.model to 2--4 % and 8--12 %, respectively. In patients (n = 30) the average repeatability coefficient was 6.0 %. FRC determinations with T.sub.Dmean and T.sub.D0 were 0.8--13.3 % and 4.2--23.9 % (median 2.7 % and 8.7 %) smaller than those calculated with T.sub.Ddyn. Conclusion: A dynamic viscosity correction of T.sub.D improves the accuracy of FRC determinations by MBNW considerably, when gas concentrations are measured in a sidestream. If dynamic T.sub.D correction cannot be performed, the use of constant T.sub.Dmean might be suitable. However, in patient measurements this can cause an FRC underestimation of up to 13 %. Author Affiliation: (1) Zentrum Anaesthesiologie, Rettungs- u. Intensivmedizin, Robert-Koch-Str. 40, D-37075 Gottingen, Germany Tel.: +49-5 51-39-88 26 Fax: +49-5 51-39-86 76 email: hwrigge@gwdg.de, DE (2) Klinik u. Poliklinik fur Anaesthesiologie u. Spezielle Intensivmedizin, Rheinische Friedrich-Wilhelms-Universitat, Siegmund-Freud-Strasse 25, D-53105 Bonn, Germany, DE Article note: Received: 29 August 1997 Accepted: 11 March 1998

Byline: M. Mohr (1), L. Englisch (1), A. Roth (1), H. Burchardi (1), S. Zielmann (1) Keywords: Key words Critical illness polyneuropathy; Sepsis; Multiple organ failure; Immunoglobulin Abstract: Objective: The evaluation of incidences and relating factors of severe persisting critical illness polyneuropathy (CIP) in survivors of multiple organ failure (MOF). Design: Prospective study with an entry period of 24 months. Electrophysiological studies for the diagnosis of CIP were performed 1 or 2 days before the patients were discharged from the intensive care unit (ICU). Factors which might have been related to the development of CIP were identified by a retrospective chart analysis. Setting: The interdisciplinary ICU of a university hospital. Patients: Thirty-three patients who survived MOF. Sixteen of these critically ill patients developed severe sepsis due to nosocomial infections with gram-negative bacteria. Results: In seven survivors of MOF and sepsis typical electrophysiological features of CIP, like spontaneous fibrillations and low compound muscle action potentials, were detectable at the time of discharge from the ICU. Seventeen patients with MOF following multiple trauma who developed no sepsis, and nine survivors of MOF with sepsis showed no signs of persisting CIP at the end of their ICU stay. Chart analysis revealed that eight survivors of MOF with sepsis and without the development of CIP had been treated with intravenous immunoglobulin (IVIG) with a dosage of 0.3 g/kg per day for 3 days immediately (within 24 h) after the diagnosis of sepsis. Four out of seven patients with MOF and sepsis who developed CIP were transferred to our ICU after the onset of sepsis and had not received IVIG treatment. The IVIG treatment in three patients was delayed for more than 24 h after the diagnosis of sepsis and was then omitted. Obviously not related to the development of CIP were aminoglycoside antibiotics, steroids, nutritional disturbances and episodes of hypotension or hypoxia. Neuromuscular blocking agents were not used during intensive care treatment. Conclusions: A high incidence of severe CIP persisting until the day of discharge from the ICU was related to gram-negative sepsis but not to MOF alone. Retrospective chart analysis suggested that early application of IVIG may prevent or mitigate this severe complication. However, these results have to be confirmed in a prospective, placebo-controlled study. Author Affiliation: (1) Department of Anaesthesiology, Critical Care and Emergency Medicine, University of Goettingen, Robert-Koch-Strasse 40, D-37075 Goettingen, Germany FAX: + 49 (5 51) 398 676 e-mail: mmohr@gwdg.de, DE Article note: Received: 22 April 1997 Accepted: 17 September 1997

Byline: H. Burchardi (1) Author Affiliation: (1) Zentrum Anaesthesiologie, Rettungs- und Intensivmedizin, University Hospital, Robert-Koch-Strasse 40, 37075 Gottingen, Germany Article History: Received Date: 04/06/2002 Accepted Date: 05/06/2002 Article note: Electronic Publication

Byline: H. Burchardi (1) Author Affiliation: (1) Department of Anaesthesiology, Emergency and Intensive Care Medicine, University of Gottingen, Robert-Koch-Strasse 40, D-37 075 Gottingen, Germany, DE Article note: Received: 14 September 1998 Accepted: 14 September 1998