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Purpose To provide clinical practice recommendations and generate a research agenda on mechanical ventilation and respiratory support in patients with acute brain injury (ABI). Methods An international consensus panel was convened including 29 clinician-scientists in intensive care medicine with expertise in acute respiratory failure, neurointensive care, or both, and two non-voting methodologists. The panel was divided into seven subgroups, each addressing a predefined clinical practice domain relevant to patients admitted to the intensive care unit (ICU) with ABI, defined as acute traumatic brain or cerebrovascular injury. The panel conducted systematic searches and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) method was used to evaluate evidence and formulate questions. A modified Delphi process was implemented with four rounds of voting in which panellists were asked to respond to questions (rounds 1-3) and then recommendation statements (final round). Strong recommendation, weak recommendation, or no recommendation were defined when > 85%, 75-85%, and < 75% of panellists, respectively, agreed with a statement. Results The GRADE rating was low, very low, or absent across domains. The consensus produced 36 statements (19 strong recommendations, 6 weak recommendations, 11 no recommendation) regarding airway management, non-invasive respiratory support, strategies for mechanical ventilation, rescue interventions for respiratory failure, ventilator liberation, and tracheostomy in brain-injured patients. Several knowledge gaps were identified to inform future research efforts. Conclusions This consensus provides guidance for the care of patients admitted to the ICU with ABI. Evidence was generally insufficient or lacking, and research is needed to demonstrate the feasibility, safety, and efficacy of different management approaches., Author(s): Chiara Robba [sup.1], Daniele Poole [sup.2], Molly McNett [sup.3], Karim Asehnoune [sup.4], Julian Bösel [sup.5] [sup.6], Nicolas Bruder [sup.7], Arturo Chieregato [sup.8], Raphael Cinotti [sup.9], Jacques Duranteau [sup.10], Sharon [...]

Byline: Laurence Vignaux (1), Didier Tassaux (1), Philippe Jolliet (1) Keywords: Mechanical ventilation; User-friendliness; Ergonomics Abstract: Objective To explore the user-friendliness and ergonomics of seven new generation intensive care ventilators. Design Prospective task-performing study. Setting Intensive care research laboratory, university hospital. Methods Ten physicians experienced in mechanical ventilation, but without prior knowledge of the ventilators, were asked to perform eight specific tasks [turning the ventilator on recognizing mode and parameters recognizing and setting alarms mode change finding and activating the pre-oxygenation function pressure support setting stand-by finding and activating non-invasive ventilation (NIV) mode]. The time needed for each task was compared to a reference time (by trained physiotherapist familiar with the devices). A time >180 s was considered a task failure. Results For each of the tests on the ventilators, all physicians' times were significantly higher than the reference time (P < 0.001). A mean of 13 +- 8 task failures (16%) was observed by the ventilator. The most frequently failed tasks were mode and parameter recognition, starting pressure support and finding the NIV mode. Least often failed tasks were turning on the pre-oxygenation function and alarm recognition and management. Overall, there was substantial heterogeneity between machines, some exhibiting better user-friendliness than others for certain tasks, but no ventilator was clearly better that the others on all points tested. Conclusions The present study adds to the available literature outlining the ergonomic shortcomings of mechanical ventilators. These results suggest that closer ties between end-users and manufacturers should be promoted, at an early development phase of these machines, based on the scientific evaluation of the cognitive processes involved by users in the clinical setting. Author Affiliation: (1) Service des soins intensifs, Hopital Cantonal Universitaire, 1211, Geneva 14, Switzerland Article History: Registration Date: 11/07/2009 Received Date: 30/12/2008 Accepted Date: 23/05/2009 Online Date: 29/07/2009 Article note: This study was presented in abstract form at the 2008 annual meeting of the European Society of Intensive Care Medicine (ESICM). This article is discussed in the editorial available at: doi: 10.1007/s00134-009-1581-6. Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1580-7) contains supplementary material, which is available to authorized users.

Byline: Nectaria Xirouchaki (1), Eumorfia Kondili (1), Maria Klimathianaki (1), Dimitris Georgopoulos (1) Keywords: Ventilator settings; Sedatives; Analgesics; Vasoactive medications; Critically ill Abstract: Objectives The aim of this study was to compare the number of interventions (ventilator settings and sedatives, analgesics and vasoactive medication dose manipulations) between critically ill patients on proportional-assist ventilation with load-adjustable gain factors (PAV+) and those on pressure support (PS). Design Retrospective analysis of data from a previous randomized clinical trial. Methods A total of 208 patients who were mechanically ventilated on controlled modes and met criteria for assisted breathing were randomized to receive either PS (n = 100) or PAV+ (n = 108). Changes in ventilator settings and in the dose of sedatives, analgesics, and vasoactive medications were identified during the period in which the patients were ventilated either with PS (30.4 +- 17.4 h) or PAV+ (30.0 +- 18.1 h) and classified as changes to facilitate weaning (CFW) or changes to respond to deterioration (CD). Results The mean number of changes in ventilator settings was significantly higher with PS than that with PAV+ (10.7 +- 5.7 vs. 8.9 +- 4.6). With PS the proportion of these changes classified as CFW was significantly lower than that with PAV+ (59.8% vs. 69.2%). Dyssynchrony as a cause of CD was more likely to occur with PS than with PAV+ (42 vs. 3%). The mean number of changes in the dose of sedatives, analgesics, and vasoactive medications was higher with PS than with PAV+, the difference being significant only for sedatives (4.06 +- 3.8 vs. 2.82 +- 3.4). Conclusions Compared to PS, PAV+ is associated with fewer intervention in terms of ventilator settings and sedative dose changes. Author Affiliation: (1) Department of Intensive Care Medicine, University Hospital of Heraklion, Medical School, University of Crete, Heraklion, Crete, Greece Article History: Registration Date: 28/05/2009 Received Date: 19/03/2009 Accepted Date: 20/05/2009 Online Date: 16/06/2009 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1524-2) contains supplementary material, which is available to authorized users.

Byline: Jean Dellamonica (1,2,3), Bruno Louis (2,4), Aissam Lyazidi (1,2), Frederic Vargas (1,2), Laurent Brochard (1,2,4) Abstract: Objective Intrapulmonary percussive ventilation (IPV) is a form of high-frequency ventilation that can be superimposed on spontaneous breathing or conventional ventilation. Drawbacks include difficulties achieving adequate airway humidification and an inability to monitor delivered volumes and pressures, which may vary with patient characteristics. The objectives of this study were to assess various humidification set-ups, to measure intrapulmonary pressures and volumes resulting from IPV superimposed on a conventional driving ventilator (DV) and to test several ventilators regarding their ability to accept added IPV. Design Bench study in a test-lung set-up was used to measure humidification and the effects of adding IPV to a DV under various conditions of compliance, resistance, plateau and positive end-expiratory pressures. Then, five ventilators were tested in combination with IPV. Measurements and results Adequate humidification required a heated humidifier on the inspiratory line downstream of the IPV device. IPV increased end-inspiratory intrapulmonary pressures up to 10 cm[H.sub.2]O, increased delivered volumes up to 237 ml and generated intrinsic PEEP from 1.7 to 4.3 cm[H.sub.2]O when no PEEP was set on the DV. Intrinsic PEEP was lower or absent when PEEP was set on the DV. With most tested ventilators, IPV prevented reliable flow monitoring. Autotriggering and missing cycles were common and the PEEP effect varied across DVs. Conclusion Achieving adequate humidification with IPV requires a specific set-up. Superimposing IPV on standard ventilation can increase intrapulmonary pressures and tidal volumes importantly and interfere with the triggering sensors of the ventilator. These factors must be taken into account before clinical use. Author Affiliation: (1) Reanimation Medicale, AP-HP, Centre Hospitalier Albert Chenevier, Henri Mondor, Creteil, France (2) INSERM U 841, Creteil, France (3) Reanimation Medicale, CHU de Nice Hopital L'Archet, Nice Cedex, France (4) Universite Paris 12, Creteil, France Article History: Registration Date: 11/06/2008 Received Date: 20/10/2007 Accepted Date: 26/05/2008 Online Date: 01/07/2008 Article note: Electronic supplementary material The online version of this article (doi: 10.1007/s00134-008-1190-9) contains supplementary material, which is available to authorized users.

Byline: Fabien G. Eyal (1,2), Charles R. Hamm (2), James C. Parker (3) Keywords: Ventilator-induced lung injury; Volutrauma; Barotrauma; Macrophages; Clodronate; Inflammation Abstract: Objective Alveolar macrophages are the sentinel cell for activation of the inflammatory cascade when the lung is exposed to noxious stimuli. We investigated the role of macrophages in mechanical lung injury by comparing the effect of high-volume mechanical ventilation with or without prior depletion of macrophages. Design and setting Randomized sham-controlled animal study in anesthetized rats. Methods Lung injury was induced by 15a-min of mechanical ventilation (intermittent positive pressure ventilation) using high peak pressures and zero end-expiratory pressure. The mean tidal volume was 40a-+-a-0.7a-ml/kg. One group of animals was killed immediately after this period of volutrauma (HV), while in a second group normoventilation was continued for 2a-h at a tidal volume less than 10a-ml/kg (HV-LV). One-half of the animals were depleted of alveolar macrophages by pretreatment with intratracheal liposomal clodronate (C[L.sub.2]MDP). Measurements Arterial blood gas, blood pressure. After kill: lung static pressure volume curves, bronchoalveolar fluid concentration for protein, macrophage inflammatory protein 2, tumor necrosis factor [alpha], and wet/dry lung weight ratio (W/D). Results During HV and HV+LV oxygenation, lung compliance, and alveolar stability were better preserved in animals pretreated with C[L.sub.2]MDP. In both groups W/D ratio was significantly greater in ventilated than in nonventilated animals (4.5a-+-a-0.6), but the increase in W/D was significantly less in C[L.sub.2]MDP treated HV and HV-LV groups (6.1a-+-a-0.4, 6.6a-+-a-0.6) than in the similarly ventilated nontreated groups (8.7a-+-a-0.2 and 9.2a-+-a-0.5). Conclusions Alveolar macrophages participate in the early phase of ventilator-induced lung injury. Author Affiliation: (1) Department of Pediatrics, Children's and Women's Hospital, University of South Alabama, 1700 Center Street, 36604, Mobile, AL, USA (2) Department of Pediatrics, University of South Alabama, Mobile, AL, USA (3) Department of Physiology, University of South Alabama, Mobile, AL, USA Article History: Registration Date: 04/04/2007 Received Date: 23/06/2006 Accepted Date: 26/03/2007 Online Date: 28/04/2007 Article note: This research was performed at the University of South Alabama, Mobile, AL.

In patients requiring mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ARDS), tidal volume reduction decreases mortality, but the mechanisms of the protective effect have not been tully explored. To test the hypothesis that alveolar macrophage activation is an early and critical event in the initiation of ventilator-induced lung injury (VILI), rats were ventilated with high tidal volume (H[V.sup.T]) for 10 min to 4 h. Alveolar macrophage counts in bronchoalveolar lavage (BAL) fluid decreased 45% by 20 min of H[V.sub.T] (P < 0.05) consistent with activation-associated adhesion. Depletion of alveolar macrophages in vivo with liposomal clodronate significantly decreased permeability and pulmonary edema following 4 h of H[V.sub.t] (P < 0.05). BAL fluid from rats exposed to 20 min of H[V.sub.t] increased nitric oxide synthase activity nearly threefold in naive primary alveolar macrophages (P < 0.05) indicating that soluble factors present in the air spaces contribute to macrophage activation in VILI. Media from cocultures of alveolar epithelial cell monolayers and alveolar macrophages exposed to 30 rain of stretch in vitro also significantly increased nitrite production in naive macrophages (P < 0.05), but media from stretched alveolar epithelial cells or primary alveolar macrophages alone did not, suggesting alveolar epithelial cell-macrophage interaction was required for the subsequent macrophage activation observed. These data demonstrate that injurious mechanical ventilation rapidly activates alveolar macrophages and that alveolar macrophages play an important role in the initial pathogenesis of VILI. alveolar epithelial barrier function; ventilator-associated lung injury; acute lung injury; acute respiratory distress syndrome

Previous animal studies have identified a role for activation of innate immunity in the pathogenesis of ventilator-associated lung injury. These studies have used large tidal volume ventilation to study the effect of alveolar overdistension on induction of inflammatory pathways. We hypothesized an alternative mechanism for the pathogenesis of lung injury in which moderate tidal volume ventilation does not independently cause clinical inflammation but rather interacts with innate immune activation by bacterial products, resulting in an enhanced inflammatory response. We measured cytokine expression and lung injury in normal and lipopolysaccharide (LPS)-treated anesthetized rabbits randomized to either spontaneous respiration or mechanical ventilation. Outcome parameters were analyzed by two-way factorial analysis of variance to identify synergism between ventilation and systemic LPS. Mechanical ventilation alone resulted in minimal cytokine expression in the lung but did enhance LPS-induced expression of tumor necrosis factor-[alpha], the CXC chemokines interleukin-8 and growth-related protein-[alpha] and the CC chemokine monocyte chemoattractant protein-1. Increased mRNA expression and activation of the transcription factors nuclear factor-[kappa]B and activator protein-I accompanied the cytokine responses. We conclude that moderate volume ventilation strategies augment the innate immune response to bacterial products in the lung and may play a role in the development of acute lung injury in patients with sepsis. acute lung injury; innate immunity; transcription factor-1; nuclear factor-[kappa]B

Byline: Carolina A. M. Schurink (1), Christianne A. Van Nieuwenhoven (1), Jan A. Jacobs (1), Maja Rozenberg-Arska (1), Hans C. A. Joore (1), Erik Buskens (1), Andy I. M. Hoepelman (1), Marc J. M. Bonten (1) Keywords: Clinical pulmonary infection score; Ventilator-associated pneumonia; Intensive care unit; Inter-observer variability; Diagnosis Abstract: Objective Although quantitative microbiological cultures of samples obtained by bronchoscopy are considered the most specific tool for diagnosing ventilator-associated pneumonia, this labor-intensive invasive technique is not widely used. The Clinical Pulmonary Infection Score (CPIS), a diagnostic algorithm that relies on easily available clinical, radiographic, and microbiological criteria, could be an attractive alternative for diagnosing ventilator-associated pneumonia. Initially, the CPIS scoring system was validated upon 40 quantitative cultures of bronchoalveolar lavage fluid from 28 patients, and only few other studies have evaluated this scoring system since then. Therefore, little is known about the accuracy of this score. Design We compared the scores of a slightly adjusted CPIS with results from quantitative cultures of bronchoalveolar lavage fluid in 99 consecutive patients with suspicion of ventilator-associated pneumonia, using growth of aY=10.sup.4 cfu/ml in bronchoalveolar lavage fluid as a cut-off for diagnosing ventilator-associated pneumonia. In addition, the CPIS were calculated for 52 patients by two different intensivists to determine the inter-observer variability. Results Ventilator-associated pneumonia was diagnosed in 69 (69.6%) patients. When using a CPIS >5 as diagnostic cutoff, the sensitivity of the score was 83% and its specificity was 17%. The area under the Receiver Operating Characteristic curve was 0.55. The level of agreement for prospectively measured Clinical Pulmonary Infection Score (a$?6 and >6) was poor (kappa =0.16). Conclusions When compared to quantitative cultures of bronchoalveolar lavage fluid, the CPIS has a low sensitivity and specificity for diagnosing ventilator-associated pneumonia with considerable inter-observer variability. Author Affiliation: (1) Department of Medicine, Division of Acute Medicine and Infectious Diseases, Eijkman-Winkler Laboratory for Microbiology , Julius Centre for Health Sciences and Primary Health Care, University Hospital Maastricht, University Medical Centre Utrecht and Department of Medical Microbiology, PO Box 85500, HP F02.1263508 GA , Utrecht, The Netherlands Article History: Received Date: 06/02/2003 Accepted Date: 19/08/2003 Online Date: 18/10/2003

Byline: J.-C. Richard (1), A. Carlucci (1), L. Breton (1), N. Langlais (1), S. Jaber (1), S. Maggiore (1), S. Fougere (1), A. Harf (1), L. Brochard (1) Keywords: Demand-valve Pressure support ventilation Work of breathing Trigger Abstract: Abstract Objective. The new generations of intensive care ventilators tend to be more innovative and sophisticated than previous ones, but little is known about their respective performance for delivering pressure support ventilation (PSV) and how they compare to previous generations. Design. Active lung model bench test. Apparatus. Twenty-two commercially available ventilators classified into three categories: new generation ventilators (after 1993, n=7), previous generation (before 1993, n=6), and recent piston or turbine-based ventilators (n=9). Measurements and results. During PSV, the unloading efficacy of the assistance depends on the ventilator's ability to meet inspiratory flow demand. Three levels of flow (0.1 l/s, 0.6 l/s, and 1.2 l/s) were used to simulate inspiratory demand and the net area of the inspiratory airway pressure-time trace was calculated over the first 0.3 s, 0.5 s, and 1 s (Area .sub.0.3, Area .sub.0.5, and Area .sub.tot) with three levels of PSV (5 cm[H.sub.2]O, 10 cm[H.sub.2]O, and 15 cm[H.sub.2]O). To assess the respective role of pressure support delivery and triggering function, triggering sensitivity was assessed independently by measuring the time delay (TD .sub.tg) and the pressure fall (I Paw .sub.tg) with two levels of inspiratory drive. All the new generation ventilators exhibited significantly better results than most of the previous generation ventilators regarding Area .sub.0.3 and TD .sub.tg, indicating large improvements in terms of triggering and pressurisation. Conclusion. Regarding PSV and trigger performance, the new generation ventilators -- but also some piston and turbine-based ventilators -- outperform most of previous generation ventilators. Author Affiliation: (1) Assistance Publique -- Hopital de Paris, and the Groupe de Travail des respiratuers de l'AP-HP, Paris, France (2) Intensive Care Unit, Paris 12 Universite and INSERM U 492, Henri Mondor Hospital, Creteil (3) Department of Physiology, Paris 12 Universite, and INSERM U 492, Henri Mondor Hospital, Creteil, France (4) DIREQ, Paris 12 Universite and INSERM U 492, Henri Mondor Hospital, Creteil, France Article History: Received Date: 12/12/2001 Accepted Date: 18/03/2002 Article note: Electronic Publication

Byline: G. Zanetta (1), D. Robert (1), C. Guerin (1) Keywords: Bench study Portable ventilators Transporting ICU patients Abstract: Objectives: To evaluate portable ventilators. Design and settings: Bench study. Materials and methods: Five portable ventilators used for transporting ICU patients [Osiris 1, (ventilator a), Osiris 2, (ventilator b), Oxylog 1000, (ventilator c), Oxylog 2000, (ventilator d), AXR1a, (ventilator e)] and three ICU ventilators which can be used for this purpose [Horus, (ventilator f), T-Bird, (ventilator g), and SV 300, (ventilator h)] were compared using a test lung regarding: 1) their capability to maintain set tidal volumes (V.sub.T) of 300 ml, 500 ml, and 800 ml under a normal condition A [resistance (R) 5 cm[H.sub.2]O/l/s and compliance (C) 100 ml/cmH.sub.20] and two abnormal conditions B (R 20--C 30) and C (R 50--C 100) 2) trapped volume (expired [V.sub.T ]relative to inspired [V.sub.T ]at 0.7 s, 1 s, and 1.4 s), an estimate of the expiratory resistance of both circuit and valve and 3) the triggering system assessed from the measurements of It, IP for two inspiratory efforts at a PEEP of 0 cmH.sub.20 and 5 cmH.sub.20 in ventilators b, d, f, g, and h. Flow and airway pressure were measured with an independent physiologic recording system. Results: 1) V.sub.T. For ventilators a--h, the mean+-SD changes of a set [V.sub.T ]of 300 ml were --2.6+-0.2%, --9.7+-0.2%, 0+-0%, --6.1+-0.2%, 1.0+-0.3%, --2.1+-1.7%, 0.3+-0%, and --1.3+-0.1% (P Author Affiliation: (1) Service de Reanimation Medicale et Assistance Respiratoire, Hopital de la Croix Rousse, 103 grande rue de la Croix-Rousse, 69004 Lyon, France Article History: Received Date: 21/06/2001 Accepted Date: 14/01/2002 Article note: Electronic Publication

Byline: Silvio Sibilla (1), Stefano Tredici (1), Giuliana Porro (1), Manuela Irace (1), Massimiliano Guglielmi (1), Gabriella Nicolini (2), Giovanni Tredici (2), Franco Valenza (1), Luciano Gattinoni (1) Keywords: Ventilator-induced lung injury Respiratory system elastance Abstract: Objective: We hypothesized that a 50% increase in respiratory system elastance (Ers) would indicate similar degree of lung damage (equi-damage, ED), independently of ventilation strategy. Design and setting: A prospective, randomized animal laboratory investigation at a university hospital laboratory. Subjects: 35 anesthetized, paralyzed, mechanically ventilated male Sprague-Dawley rats. Interventions: Each rat was ventilated with a different combination of tidal volume, positive end-expiratory pressure, and inspired fraction of oxygen. Ers was determined throughout the experiment the studies were interrupted when Ers reached 150% (ED) of its baseline value, or after 5 h. Measurements and results. Lung wet to dry weight ratio (W/D) was assessed. Morphological damage of the lung was scored on a grading of perivascular edema, hemorrhage, and breaks in the alveolar septa to obtain a total injury score. Twenty-four rats achieved an Ers of 150%: nine within 1 h (class 1), nine in 1--2 h (class 2), and six in 2--5 h (class 3). Eleven rats did not reach the target 50% increase in Ers (class 4). W/D was higher in rats that reached the target than in those that did not. W/D did not differ among rats that reached ED. Similarly, the total injury score did not differ among classes 1--3 but was higher than class 4. Conclusions: In the setting of VILI a 50% increase in Ers corresponds to an equal level of lung damage, irrespective of ventilatory setting and time of ventilation. Author Affiliation: (1) Istituto di Anestesia e Rianimazione, Ospedale Maggiore di Milano, IRCCS, Via F. Sforza n. 35, 20122 Milan, Italy (2) Dipartimento di Neuroscienze e Tecnologie Biomediche, Universita' di Milano Bicocca, Monza, Italy Article History: Received Date: 04/04/2001 Accepted Date: 12/11/2001 Article note: Electronic Publication

Byline: M. Nishimura (1), O. Honda (2), N. Tomiyama (2), T. Johkoh (2), K. Kagawa (3), T. Nishida (4) Keywords: Mechanical ventilation Lung injury Body position Abstract: Objective: To ascertain whether the locations of ventilator-induced lung injury (VILI) are influenced by body position. Design: Randomized prospective short-term study. Setting: Animal laboratory at a university school of medicine. Interventions: Twelve white rabbits were mechanically ventilated in IMV mode with an infant ventilator (V.I.P. Bird, Bird Products, Palm Springs, Calif., USA). Based on the results of a preliminary study to determine the ventilator settings at which the lungs of rabbits were injured within 5 h in the supine position, the ventilator was set at [F.sub.I]O.sub.2 0.21, at a rate of 30/min, T.sub.I 0.6 s, peak inspiratory pressure 30 cm [H.sub.2]O, inspiratory flow 10 l/min with no applied positive end-expiratory pressure (PEEP). Six of the animals were tested in the supine position and the other six in the prone position. Respiratory gases were measured and CT scanning was performed every 30 min. The animals were ventilated for 5 h or until pulmonary parenchymal opacification was detected. The lungs were divided into three areas from apex to base and three levels from ventral to dorsal, and the location of opacification was ascribed according to this scheme. After the experiment, the lungs were excised and examined histologically. Measurements and results: Parenchymal opacification occurred mainly in the dorsal lung areas. The time from the beginning of ventilation to the appearance of lung damage was 60--120 min in the supine (S) group, and 60--270 min in the prone (P) group, and it was significantly longer in the prone group (P Author Affiliation: (1) Intensive Care Unit, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565--0871, Japan (2) Department of Radiology, Osaka University Medical School, 1-1 Yamadaoka, Suita, Osaka 565-0871, Japan (3) Department of Anesthesiology, National Cardiovascular Center, 5-7-1 Fujishiro-dai, Suita City, Osaka 565-0873, Japan (4) Department of Anesthesia, Nakatsu-Saiseikai Hospital, 2-10-39 Shibata, Kita-ku, Osaka 530-0012, Japan Article History: Received Date: 03/01/2000 Accepted Date: 03/08/2000 Article note: Final revision received: 1 August 2000 Electronic Publication

Byline: W. Stahl (1), P. Radermacher (1), E. Calzia (1) Keywords: Key words Hyperbaric oxygen therapy; Ventilator; Airway resistance; Gas density Abstract: Objective: To evaluate the function of four currently available, not specifically modified time-cycled ICU ventilators (EVITA 4, Oxylog 2000 HBO and Microvent from Dragerwerk, Germany and Servo 900C, Siemens-Elema, Sweden) under hyperbaric conditions using volume-controlled ventilation (VCV) and, if available, pressure-controlled ventilation (PCV).APDesign: All ventilators were studied on an electromechanical lung simulator consisting of a motor driven bellows (LS 1500, Dragerwerk, Germany) at normobaric (1 bar) and hyperbaric ambient pressures (1.3, 1.6, 1.9, 2.8 bar). Servo 900C and Microvent were additionally tested at 6 bar.APSettings: Hyperbaric chamber.APMeasurements and results: During VCV the tidal volume (V.sub.T) was set at 750 ml at normobaric conditions prior to starting hyperbaric exposure. During PCV the same V.sub.T setting was achieved by adjusting the inspiratory pressure level. At each ambient pressure we registered airway pressure (measured inside the bellows) and flow (derived from the linear displacement of the bellows) for a period of 1 min. From these data we calculated off-line V.sub.T, inspiratory airway peak and plateau pressure (P.sub.peak and P.sub.plateau) and, during PCV only, peak inspiratory flow (V.sub.max) and the time delay between onset of and peak inspiratory flow (V.sub.delay). During VCV inspiratory flow and, consequently, V.sub.T consistently decreased with increasing ambient pressure. In contrast, during PCV V.sub.T remained stable at each condition despite a slight decrease in V.sub.max.APConclusions: Whenever available, PCV should be preferentially used during hyperbaric oxygen therapy due to the stability of ventilator functioning. Based on the specific ventilator properties at increasing ambient pressures, appropriate corrections should be possible which will allow the safe use of ICU ventilators even during VCV. Author Affiliation: (1) Department of Anesthesiology, University Hospital Ulm, Section APV, Parkstrasse 11, D-89073 Ulm, Germany e-mail: Peter.Radermacher@medizin. uni-ulm.de Tel.: + 49-7 31-5 02 51 40 Fax: + 49-7 31-5 02 51 43, DE Article note: Received: 14 June 1999/Final revision received: 18 November 1999/Accepted: 20 January 2000