Study objectives: A new noninvasive practical technique
called electrical impedance tomography (EIT) was examined for the
measurement of alveolar recruitment.
Prospective clinical study.
Setting: ICU of a general
Patients: Acute respiratory failure (ARF)
Measurements: The ventilation-induced
impedance changes (VICs) of the nondependent and the dependent part of
the lung were determined by EIT as a measure of tidal volume
distribution. By the use of an impedance ratio (IR), defined as the VIC
of the nondependent part of the lung divided by the VIC of the
dependent part of the lung, the ventilation performances in both parts
of the lung were compared to each other.
Between patients, the VIC of the nondependent part of the lung was
significantly lower in the patients with a level of positive
end-expiratory pressure (PEEP) of > 10 cm H2O than in
patients with a PEEP of < 5 cm H2O (p < 0.05). A
significantly lower IR (± SD) was found in the group with PEEP of>
10 cm H2O than in the group with PEEP between 0 and 5
cm H2O (1.28 ± 0.58 vs 2.99 ± 1.24, respectively;
p < 0.01). In individual patients, the VIC of the whole lung
increased when the PEEP level was increased. The VICs of the
nondependent part of the lung and of the dependent part of the lung
showed significant increases at a PEEP of 10 cm H2O
compared to a PEEP of 0 cm H2O (p < 0.05). Also the IR
decreased in individual patients when the PEEP was increased; a
significant decrease was found at 10 cm H2O compared to 0
cm H2O (1.67 ± 1.24 vs 2.23 ± 1.47, respectively;
p < 0.05).
Conclusions: The decrease in IR
indicates an increase in VIC in the dependent part of the lung above
the nondependent part of the lung. The increase in VIC can be regarded
as an increase in lung volume, implying alveolar recruitment in the
dependent part of the lung. The same results also have been shown in
earlier reports by CT scan. Since EIT is far more practical than CT
scanning and also is a bedside method, EIT might help in the adjustment
of ventilator settings in ARF patients.