Uneven distribution of ventilation in acute respiratory distress syndrome.
BACKGROUND
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.


CONCLUSIONS
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.
Rylander
Christian
C
Department of Anaesthesiology and Intensive Care, Sahlgrenska University Hospital, Göteborg, Sweden. christian.rylander@vgregion.se
Tylén
Ulf
U
Rossi-Norrlund
Rauni
R
Herrmann
Peter
P
Quintel
Michael
M
Bake
Björn
B
D000328:Adult; D003627:Data Interpretation, Statistical; D005652:Functional Residual Capacity; D006801:Humans; D007362:Intensive Care Units; D008962:Models, Theoretical; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy; D012129:Respiratory Function Tests; D012133:Respiratory Paralysis / Q000503:physiopathology; D013459:Sulfur Hexafluoride; D013990:Tidal Volume; D013997:Time Factors; D014057:Tomography, X-Ray Computed
D013459:Sulfur Hexafluoride