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Monitoring dead space during recruitment and PEEP titration in an experimental model
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Physiology.
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2006 (English)In: Intensive Care Medicine, ISSN 0342-4642, E-ISSN 1432-1238, Vol. 32, no 11, 1863-1871 p.Article in journal (Refereed) Published
Abstract [en]

Objective: To test the usefulness of dead space for determining open-lung PEEP, the lowest PEEP that prevents lung collapse after a lung recruitment maneuver. Design: Prospective animal study. Setting: Department of Clinical Physiology, University of Uppsala, Sweden. Subjects: Eight lung-lavaged pigs. Interventions: Animals were ventilated using constant flow mode with VT of 6 ml/kg, respiratory rate of 30 bpm, inspiratory-to-expiratory ratio of 1 : 2, and FiO(2) of 1. Baseline measurements were performed at 6 cmH(2)O of PEEP. PEEP was increased in steps of 6 cmH(2)O from 6 to 24 cmH(2)O. Recruitment maneuver was achieved within 2 min at pressure levels of 60/30 cmH(2)O for Peak/PEEP. PEEP was decreased from 24 to 6 cmH(2)O in steps of 2 cmH(2)O and then to 0 cmH(2)O. Each PEEP step was maintained for 10 min. Measurements and results: Alveolar dead space (VDalv), the ratio of alveolar dead space to alveolar tidal volume (VDalv/VTalv), and the arterial to end-tidal PCO2 difference (Pa-ETCO2) showed a good correlation with PaO2, normally aerated areas, and non-aerated CT areas in all animals (minimum-maximum r(2) = 0.83-0.99; p < 0.01). Lung collapse (non-aerated tissue > 5%) started at 12 cmH(2)O PEEP; hence, open-lung PEEP was established at 14 cmH(2)O. The receiver operating characteristics curve demonstrated a high specificity and sensitivity of VDalv (0.89 and 0.90), VDalv/VTalv (0.82 and 1.00), and Pa-ETCO2 (0.93 and 0.95) for detecting lung collapse. Conclusions: Monitoring of dead space was useful for detecting lung collapse and for establishing open-lung PEEP after a recruitment maneuver.

Place, publisher, year, edition, pages
2006. Vol. 32, no 11, 1863-1871 p.
Keyword [en]
dead space, lung recruitment, SBT-CO2, atelectasis, oxygenation, PEEP
National Category
Medical and Health Sciences
URN: urn:nbn:se:uu:diva-96744DOI: 10.1007/s00134-006-0371-7ISI: 000241453400030PubMedID: 17047925OAI: oai:DiVA.org:uu-96744DiVA: diva2:171422
Available from: 2008-02-20 Created: 2008-02-20 Last updated: 2011-05-19Bibliographically approved
In thesis
1. Titrating Open Lung PEEP in Acute Lung Injury: A clinical method based on changes in dynamic compliance
Open this publication in new window or tab >>Titrating Open Lung PEEP in Acute Lung Injury: A clinical method based on changes in dynamic compliance
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The recognition that supportive mechanical ventilation can also damage the lung, the so called ventilation induced lung injury (VILI), has revived the more than 40 year long debate on the optimal level of PEEP to be used. It is established that the prevention of VILI improves patient outcome and that PEEP exerts protective effects by preventing unstable diseased alveoli from collapsing. Therefore, the term “open lung PEEP” (OL-PEEP) has been introduced as the end-expiratory pressure that keeps the lung open after its collapse has been eliminated by an active lung recruitment manoeuvre. The determination of such an optimal level of PEEP under clinical circumstances is difficult and remains to be investigated.

The aim of this study was to investigate the usefulness of breath by breath monitoring of dynamic compliance (Cdyn) as a clinical means to identify OL-PEEP at the bedside and to demonstrate the improvement in lung function resulting from its application.

In a porcine lung lavage model of acute lung injury PEEP at maximum Cdyn during a decremental PEEP trial after full lung recruitment was related to the onset of lung collapse and OL-PEEP could be found 2 cmH2O above this level Ventilation at OL-PEEP was associated with improved gas exchange, efficiency of ventilation, lung mechanics and less than 5% collapse on CT scans. In addition, dead space, especially its portion related to alveolar gas changed characteristically during recruitment, PEEP titration and collapse thereby helping to identify OL-PEEP.

The beneficial effects of OL-PEEP on lung function and mechanics was demonstrated in a porcine model of VILI. OL-PEEP improved lung function and mechanics when compared to lower or higher levels prior to or after lung recruitment. By using electrical impedance tomography it could be shown that PEEPs within the range of 14 to 22 cmH2O resulted in a similar redistribution of both ventilation and perfusion to the dorsal regions of the lung. OL-PEEP resulted in the best regional and global matching of ventilation and perfusion explaining the drastic improvements in gas exchange. Also regional compliance was greatly improved in the lower half of the lung as compared to all other situations.

In ARDS patients OL-PEEP could be identified applying the same protocol. The physiological changes described could now be reproduced and maintained during a four hours study ventilation period in real patients at four study centres.

In conclusion, the usefulness of dynamic compliance for identifying open lung PEEP during a decremental PEEP trial was demonstrated under experimental and clinical conditions. This PEEP should then be used as an essential part of any lung protective ventilation strategy. The impact of ventilating ARDS patients according to the principles described in these studies on outcome are currently being evaluated in an international randomized controlled trial.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 52 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 313
PEEP, open lung, recruitment, dead space, electrical impedance tomography, ARDS.
National Category
Clinical Science
urn:nbn:se:uu:diva-8460 (URN)978-91-554-7093-7 (ISBN)
Public defence
2008-03-13, Enghoffsalen, University Hospital Entrance 50, Uppsala, 13:00
Available from: 2008-02-20 Created: 2008-02-20Bibliographically approved

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