Oxygenation correlates with lung aeration during unsupported spontaneous breathing in porcine lung collapse model

Introduction

We investigated whether oxygenation correlates with lung aeration during unsupported spontaneous breathing (SB) and mechanical ventilation (MV) in a porcine lung collapse model.

Methods

In 14 anesthetized supine piglets, lung collapse was induced by negative pressure application (NPA) to the endotracheal tube. Eight animals resumed SB 5 minutes after NPA, six animals were kept on MV at a respiratory rate and tidal volume corresponding to SB. Thoracic CTs and arterial blood gases were taken 2.5 and 30 minutes after NPA. Spearman rank correlation was used for testing; values are given as mean (95% CI).

Results

Thirty minutes after NPA the amount of lung tissue in collapsed regions was similar in both groups (MV: 40% (36 to 44), SB: 35% (26 to 43); P = 0.22). Resuming SB, PaO₂/FiO₂ improved significantly more with less amount of collapsed lung tissue 2.5 minutes after NPA (r = -0.87, P = 0.033). During SB a significant negative correlation between PaO₂/FiO₂ and the amount of collapsed lung tissue (r = -0.76, P = 0.038) was observed; no such correlation could be seen during MV (r = -0.3, P = 0.2) (Figure 1).

Figure 1

PaO ₂ /FiO ₂ plotted against the proportion of atelectatic lung tissue. Open circles, SB; solid circles, MV.

Conclusion

In porcine lung collapse PaO₂/FiO₂ correlates with lung aeration during unsupported SB, but not during MV at a similar breathing pattern. The less lung collapse the animals have, the more PaO₂/FiO₂ improves resuming SB.