Chest
Volume 124, Issue 1, July 2003, Pages 314-322
Journal home page for Chest

Laboratory and Animal Investigations
Regional Ventilation by Electrical Impedance Tomography: A Comparison With Ventilation Scintigraphy in Pigs

https://doi.org/10.1378/chest.124.1.314Get rights and content

Study objective

The validation of electrical impedance tomography (EIT) for measuring regional ventilation distribution by comparing it with single photon emission CT (SPECT) scanning.

Design

Randomized, prospective animal study.

Settings

Animal laboratories and nuclear medicine laboratories at a university hospital.

Participants

Twelve anesthetized and mechanically ventilated pigs.

Interventions

Lung injury was induced by central venous injection of oleic acid. Then pigs were randomized to pressure-controlled mechanical ventilation, airway pressure-release ventilation, or spontaneous breathing.

Measurements and results

Ventilation distribution was assessed by EIT using cross-sectional electrotomographic measurements of the thorax, and simultaneously by single SPECT scanning with the inhalation of 99mTc-labeled carbon particles. For both methods, the evaluation of ventilation distribution was performed in the same transverse slice that was approximately 4 cm in thickness. The transverse slice then was divided into 20 coronal segments (going from the sternum to the spine). We compared the percentage of ventilation in each segment, normalized to the entire ventilation in the observed slice. Our data showed an excellent linear correlation between the ventilation distribution measured by SPECT scanning and EIT according to the following equation: y = 0.82x + 0.7 (R2 = 0.92; range, 0.86 to 0.97).

Conclusion

Based on these data, EIT seems to allow, at least in comparable states of lung injury, real-time monitoring of regional ventilation distribution at the bedside.

Section snippets

Study Protocol

After approval by the local animal ethics committee, 12 pigs of mixed breed (ie, Hampshire, Yorkshire, and Swedish country breed) [mean (± SD) weight, 30 ± 4 kg] were anesthetized and mechanically ventilated. Acute lung injury was induced in all pigs by IV injections of oleic acid (Apoteksbolaget; Go¨teborg, Sweden) that was suspended in 20 mL isotonic saline solution. The dosing of the oleic acid was guided by intermittently taken arterial blood samples in order to achieve a Pao2/fraction of

Results

Four pigs each were ventilated in the PCV, APRV, and CPAP modes, and the median values of the Pao2/Fio2 ratio were 176, 197, and 212 mm Hg, respectively. Respirator settings, blood gas data, and respiratory compliance are summarized in Table 1.

Discussion

EIT is a noninvasive technique with the potential to monitor regional ventilation distribution. Since its introduction, the hardware and software have been improved continuously.2324 Hahn and coworkers25 developed more advanced algorithms for the analysis of dynamic physiologic phenomena with low amplitudes than was initially supplied (Mark I or DAS-01P; Royal Hallamshire Hospital; Sheffield, UK). Thus, they introduced the f-EIT and the averaging technique.16 These improvements, together with

Conclusion

EIT data of regional ventilation correlated closely to ventilation distribution by SPECT scanning in a porcine, oleic acid-lung damage model. Whether breathing was spontaneous or mechanical had no effect on the relationship between EIT and SPECT scanning, and the severity of lung damage on a global or a regional level did not influence the relationship either. A slight overestimation of ventilation in well-ventilated areas and a slight underestimation in poorly ventilated areas was seen, but

References (32)

  • PW Kunst et al.

    Evaluation of electrical impedance tomography in the measurement of PEEP-induced changes in lung volume

    Chest

    (1999)
  • M Lichtwarck-Aschoff et al.

    Central venous pressure, pulmonary artery occlusion pressure, intrathoracic blood volume, and right ventricular end-diastolic volume as indicators of cardiac preload

    J Crit Care

    (1996)
  • DC Barber et al.

    Applied potential tomography

    J Phys [E]

    (1984)
  • A Adler et al.

    Monitoring changes in lung air and liquid volumes with electrical impedance tomography

    J Appl Physiol

    (1997)
  • I Frerichs et al.

    Monitoring perioperative changes in distribution of pulmonary ventilation by functional electrical impedance tomography

    Acta Anaesthesiol Scand

    (1998)
  • I Frerichs et al.

    Gravity-dependent phenomena in lung ventilation determined by functional EIT

    Physiol Meas

    (1996)
  • I Frerichs et al.

    Thoracic electrical impedance tomographic measurements during volume controlled ventilation-effects of tidal volume and positive end-expiratory pressure

    IEEE Trans Med Imaging

    (1999)
  • I Frerichs et al.

    Bestimmung der regionalen Ventilation bei einseitiger Lungenscha¨digung mittels funktioneller elektrischer Impedanztomographie

    Intensiv und Notfallbehandlung

    (1999)
  • I Frerichs et al.

    Monitoring regional lung ventilation by functional electrical impedance tomography during assisted ventilation

    Ann N Y Acad Sci

    (1999)
  • I Frerichs et al.

    Electrical impedance tomography in monitoring experimental lung injury

    Intensive Care Med

    (1998)
  • G Hahn et al.

    Determining local lung ventilation by functional electrical impedance tomography under clinical circumstances

    Biomed Tech (Berl)

    (1997)
  • G Hahn et al.

    Local mechanics of the lung tissue determined by functional EIT

    Physiol Meas

    (1996)
  • PW Kunst et al.

    Regional pressure volume curves by electrical impedance tomography in a model of acute lung injury

    Crit Care Med

    (2000)
  • PW Kunst et al.

    Ventilation and perfusion imaging by electrical impedance tomography: a comparison with radionuclide scanning

    Physiol Meas

    (1998)
  • PW Kunst et al.

    Influences of lung parenchyma density and thoracic fluid on ventilatory EIT measurements

    Physiol Meas

    (1998)
  • A Adler et al.

    Electrical impedance tomography can monitor dynamic hyperinflation in dogs

    J Appl Physiol

    (1998)
  • Cited by (0)

    This study was supported by grants from the Swedish Medical and Technical Research Councils (5315 and 299-2000-688), the Swedish Heart and Lung Foundation, and departmental funds.

    View full text