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Laboratory and Animal InvestigationsRegional Ventilation by Electrical Impedance Tomography: A Comparison With Ventilation Scintigraphy in Pigs
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
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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.