The online version of this article (doi:10.1186/1471-2253-14-64) contains supplementary material, which is available to authorized users.
The laboratory where the experiments were performed received a fund from Maquet Critical Care AB, Solna, Sweden to partially cover the material costs. Mats Wallin, Magnus Hallbäck work at the Research Development Department of the Maquet, Solna, Sweden and they established the theoretical bases of the ELV measurement technique based on capnodynamics. Walid Habre received a research grant from Maquet Solna, Sweden for acting as consultant in the respiratory developments.
GA and TZ carried out the experiments and the preliminary data analyses. FP coordinated the various experimental approaches, and contributed to their design and to the manuscript preparation. MW and MH participated in the design of the study and in the interpretation of ELV measurements. WH conducted the design of the study and had a major role in drafting the manuscript. All authors have read and approved the final manuscript.
Bedside assessment of lung volume in clinical practice is crucial to adapt ventilation strategy. We compared bedside measures of lung volume by helium multiple-breath washout technique (EELVMBW,He) and effective lung volume based on capnodynamics (ELV) to those assessed from spiral chest CT scans (EELVCT) under different PEEP levels in control and surfactant-depleted lungs.
Lung volume was assessed in anaesthetized mechanically ventilated rabbits successively by measuring i) ELV by analyzing CO2 elimination traces during the application of periods of 5 consecutive alterations in inspiratory/expiratory ratio (1:2 to 1.5:1), ii) measuring EELVMBW,He by using helium as a tracer gas, and iii) EELVCT from CT scan images by computing the normalized lung density. All measurements were performed at PEEP of 0, 3 and 9 cmH2O in random order under control condition and following surfactant depletion by whole lung lavage.
Variables obtained with all techniques followed sensitively the lung volume changes with PEEP. Excellent correlation and close agreement was observed between EELVMBW,He and EELVCT (r = 0.93, p < 0.0001). ELV overestimated EELVMBW,He and EELVCT in normal lungs, whereas this difference was not evidenced following surfactant depletion. These findings resulted in somewhat diminished but still significant correlations between ELV and EELVCT (r = 0.58, p < 0.001) or EELVMBW,He (0.76, p < 0.001) and moderate agreements.
Lung volume assessed with bedside techniques allow the monitoring of the changes in the lung aeration with PEEP both in normal lungs and in a model of acute lung injury. Under stable pulmonary haemodynamic condition, ELV allows continuous lung volume monitoring, whereas EELVMBW,He offers a more accurate estimation, but intermittently.
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- Lung volume assessments in normal and surfactant depleted lungs: agreement between bedside techniques and CT imaging
- BioMed Central
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