Lung volume calculated from electrical impedance tomography in ICU patients at different PEEP levels.
OBJECTIVE
To study and compare the relationship between end-expiratory lung volume (EELV) and changes in end-expiratory lung impedance (EELI) measured with electrical impedance tomography (EIT) at the basal part of the lung at different PEEP levels in a mixed ICU population.


METHODS
End-expiratory lung volume, EELI and tidal impedance variation were determined at four PEEP levels (15-10-5-0 cm H2O) in 25 ventilated ICU patients. The tidal impedance variation and tidal volume at 5 cm H2O PEEP were used to calculate change in impedance per ml; this ratio was then used to calculate change in lung volume from change in EELI. To evaluate repeatability, EELV was measured in quadruplicate in five additional patients.


RESULTS
There was a significant but relatively low correlation (r = 0.79; R2 = 0.62) and moderate agreement (bias 194 ml, SD 323 ml) between DeltaEELV and change in lung volume calculated from the DeltaEELI. The ratio of tidal impedance variation and tidal volume differed between patients and also varied at different PEEP levels. Good agreement was found between repeated EELV measurements and washin/washout of a simulated nitrogen washout technique.


CONCLUSIONS
During a PEEP trial, the assumption of a linear relationship between change in global tidal impedance and tidal volume cannot be used to calculate EELV when impedance is measured at only one thoracic level just above the diaphragm.
Bikker
Ido G
IG
Department of Intensive Care Medicine, Room H602, Erasmus MC, Postbox 2040, 3000 CA Rotterdam, The Netherlands.
Leonhardt
Steffen
S
Bakker
Jan
J
Gommers
Diederik
D
D000368:Aged; D000369:Aged, 80 and over; D017097:Electric Impedance; D005260:Female; D005652:Functional Residual Capacity; D006801:Humans; D007362:Intensive Care Units; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000379:methods*; D012189:Retrospective Studies; D014054:Tomography