Research
Uneven distribution of ventilation in acute respiratory distress syndrome
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* Corresponding author: Christian Rylander christian.rylander@vgregion.se
1 Department of Anaesthesiology and Intensive Care, Sahlgrenska University Hospital, Göteborg, Sweden
2 Professor, The Sahlgrenska Academy at Göteborg University, Department of Radiology, Sahlgrenska University Hospital, Göteborg, Sweden
3 The Sahlgrenska Academy at Göteborg University, Department of Radiology, Sahlgrenska University Hospital, Göteborg, Sweden
4 Engineer, Department of Anaesthesiology II – Intensive Care Medicine, Z.A.R.I., University Hospital Gottingen, Gottingen, Germany
5 Professor, Department of Anaesthesiology II – Intensive Care Medicine, Z.A.R.I., University Hospital Gottingen, Gottingen, Germany
6 Professor, The Sahlgrenska Academy at Göteborg University, Department of Pulmonary Medicine, Sahlgrenska University Hospital, Göteborg, Sweden
Critical Care 2005, 9:R165-R171 doi:10.1186/cc3058
Published: 21 February 2005Abstract
Introduction
The aim of this study was to assess the volume of gas being poorly ventilated or non-ventilated within the lungs of patients treated with mechanical ventilation and suffering from acute respiratory distress syndrome (ARDS).
Methods
A prospective, descriptive study was performed of 25 sedated and paralysed ARDS patients, mechanically ventilated with a positive end-expiratory pressure (PEEP) of 5 cmH2O in a multidisciplinary intensive care unit of a tertiary university hospital. The volume of poorly ventilated or non-ventilated gas was assumed to correspond to a difference between the ventilated gas volume, determined as the end-expiratory lung volume by rebreathing of sulphur hexafluoride (EELVSF6), and the total gas volume, calculated from computed tomography images in the end-expiratory position (EELVCT). The methods used were validated by similar measurements in 20 healthy subjects in whom no poorly ventilated or non-ventilated gas is expected to be found.
Results
EELVSF6 was 66% of EELVCT, corresponding to a mean difference of 0.71 litre. EELVSF6 and EELVCT were significantly correlated (r2 = 0.72; P < 0.001). In the healthy subjects, the two methods yielded almost identical results.
Conclusion
About one-third of the total pulmonary gas volume seems poorly ventilated or non-ventilated in sedated and paralysed ARDS patients when mechanically ventilated with a PEEP of 5 cmH2O. Uneven distribution of ventilation due to airway closure and/or obstruction is likely to be involved.