• S Kárason, S Søndergaard, S Lundin, and O Stenqvist.
• Department of Anaesthesia and Intensive Care, Sahlgrenska University Hospital, 413 45 Göteborg, Sweden. sigge.karason@molndal.mail.telia.com
• Intensive Care Med. 2001 Aug 1;27(8):1328-39.

ObjectiveWe present a concept of on-line, manoeuvre-free monitoring of respiratory mechanics during dynamic conditions, displaying calculated alveolar pressure/volume curves continuously and separating lung and chest wall mechanics.DesignProspective observational study.SettingIntensive care unit of a university hospital.PatientsTen ventilator-treated patients with acute lung injury.InterventionsDifferent positive end-expiratory pressure (PEEP) and tidal volumes, low flow inflation.Measurements And ResultsPreviously validated methods were used to present a single-value dynostatic compliance for the whole breath and a dynostatic volume-dependent initial, middle and final compliance within the breath. A high individual variation of respiratory mechanics was observed. Reproducibility of repeated measurements was satisfactory (coefficients of variations for dynostatic volume-dependent compliance: < or =9.2% for total respiratory system, < or =18% for lung). Volume-dependent compliance showed a statistically significant pattern of successively decreasing compliance from the initial segment through the middle and final parts within each breath at all respiratory settings. This pattern became more prominent with increasing PEEP and tidal volume, indicating a greater distension of alveoli. No lower inflection point (LIP) was seen in patients with respiratory rate 20/min and PEEP at 4 cmH2O. A trial with low flow inflation in four of the patients showed formation of a LIP in three of them and an upper inflection in one.ConclusionsThe monitoring concept revealed a constant pattern of successively decreasing compliance within each breath, which became more prominent with increasing PEEP and tidal volume. The monitoring concept offers a simple and reliable method of monitoring respiratory mechanics during ongoing ventilator treatment.

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