Research

Uneven distribution of ventilation in acute respiratory distress syndrome

Christian Rylander¹ , Ulf Tylén², Rauni Rossi-Norrlund³, Peter Herrmann⁴, Michael Quintel⁵ and Björn Bake⁶

¹Department of Anaesthesiology and Intensive Care, Sahlgrenska University Hospital, Göteborg, Sweden

²Professor, The Sahlgrenska Academy at Göteborg University, Department of Radiology, Sahlgrenska University Hospital, Göteborg, Sweden

³The Sahlgrenska Academy at Göteborg University, Department of Radiology, Sahlgrenska University Hospital, Göteborg, Sweden

⁴Engineer, Department of Anaesthesiology II – Intensive Care Medicine, Z.A.R.I., University Hospital Gottingen, Gottingen, Germany

⁵Professor, Department of Anaesthesiology II – Intensive Care Medicine, Z.A.R.I., University Hospital Gottingen, Gottingen, Germany

⁶Professor, The Sahlgrenska Academy at Göteborg University, Department of Pulmonary Medicine, Sahlgrenska University Hospital, Göteborg, Sweden

author email corresponding author email

Critical Care 2005, 9:R165-R171doi:10.1186/cc3058

Published:	21 February 2005

Abstract

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 (EELV_SF6), and the total gas volume, calculated from computed tomography images in the end-expiratory position (EELV_CT). 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

EELV_SF6 was 66% of EELV_CT, corresponding to a mean difference of 0.71 litre. EELV_SF6 and EELV_CT 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.