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Oxygenation index, an indicator of optimal distending pressure during high-frequency oscillatory ventilation?
Huibert R van Genderingen1, Johannus A van Vught, Jos R C Jansen
1Department of Clinical Physics & Informatics, Vrije Universiteit Medical Center, PO Box 7057,1007 MB Amsterdam, The Netherlands. hr.genderingen@VUmc.nl
Objective:
To test the hypothesis that, during high-frequency oscillatory ventilation (HFOV) of pigs with acute lung injury, the oxygenation index (OI = Paw*FIO(2)*100/PaO(2)) is minimal at the lowest continuous distending pressure (Paw), where the physiological shunt fraction is below 0.1 (Paw(optimal)).
Design And Setting:
Prospective, observational study in a university research laboratory.
Subjects:
Eight Yorkshire pigs weighing 12.0+/-0.5 kg, with lung injury induced by lung lavage.
Interventions:
After initiation of HFOV, the pigs were subjected to a stepwise increase of Paw to obtain under-inflation, optimal inflation and over-distension of the lungs (inflation) in series, followed by a similar decrease of Paw (deflation).
Measurements And Results:
At each Paw level, the OI and physiological shunt fraction were determined. The OI reached a minimum of 6.2+/-1.4 at Paw 30+/-4 cmH(2)O during inflation and a minimum of 2.4+/-0.3 at Paw 13+/-2 cmH(2)O during deflation. Paw(optimal) was 32+/-6 cmH(2)O on the inflation limb and 14+/-2 cmH(2)O on the deflation limb. The difference between the Paw at minimal OI and Paw(optimal) was -1.9+/-4.2 cmH(2)O (NS) during inflation and -1.5+/-1.6 cmH(2)O (p<0.05) during deflation. In 15 out of the 16 comparisons, the difference in Paw was within one step (+/-3 cmH(2)O).
Conclusion:
The minimal OI is indicative for the Paw where oxygenation is optimal during HFOV in surfactant-depleted pigs.