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. 2019 Mar 25;45(5):e20180067.
doi: 10.1590/1806-3713/e20180067.

Inflammatory lung injury in rabbits: effects of high-frequency oscillatory ventilation in the prone position

[Article in English, Portuguese]
Jose Roberto Fioretto  1 , Rafaelle Batistella Pires  2 , Susiane Oliveira Klefens  1 , Cilmery Suemi Kurokawa  1 , Mario Ferreira Carpi  1 , Rossano César Bonatto  1 , Marcos Aurélio Moraes  1 , Carlos Fernando Ronchi  1   3
Affiliations

Inflammatory lung injury in rabbits: effects of high-frequency oscillatory ventilation in the prone position

[Article in English, Portuguese]
Jose Roberto Fioretto et al. J Bras Pneumol. .

Abstract
in English, Portuguese

Objective: To compare the effects that prone and supine positioning during high-frequency oscillatory ventilation (HFOV) have on oxygenation and lung inflammation, histological injury, and oxidative stress in a rabbit model of acute lung injury (ALI).

Methods: Thirty male Norfolk white rabbits were induced to ALI by tracheal saline lavage (30 mL/kg, 38°C). The injury was induced during conventional mechanical ventilation, and ALI was considered confirmed when a PaO2/FiO2 ratio < 100 mmHg was reached. Rabbits were randomly divided into two groups: HFOV in the supine position (SP group, n = 15); and HFOV with prone positioning (PP group, n = 15). For HFOV, the mean airway pressure was initially set at 16 cmH2O. At 30, 60, and 90 min after the start of the HFOV protocol, the mean airway pressure was reduced to 14, 12, and 10 cmH2O, respectively. At 120 min, the animals were returned to or remained in the supine position for an extra 30 min. We evaluated oxygenation indices and histological lung injury scores, as well as TNF-α levels in BAL fluid and lung tissue.

Results: After ALI induction, all of the animals showed significant hypoxemia, decreased respiratory system compliance, decreased oxygenation, and increased mean airway pressure in comparison with the baseline values. There were no statistically significant differences between the two groups, at any of the time points evaluated, in terms of the PaO2 or oxygenation index. However, TNF-α levels in BAL fluid were significantly lower in the PP group than in the SP group, as were histological lung injury scores.

Conclusions: Prone positioning appears to attenuate inflammatory and histological lung injury during HFOV in rabbits with ALI.

Objetivo:: Comparar os efeitos das posições prona e supina durante ventilação oscilatória de alta frequência (VOAF) sobre oxigenação e inflamação pulmonar, lesão histológica e estresse oxidativo em um modelo de lesão pulmonar aguda (LPA) em coelhos.

Métodos:: Trinta coelhos Norfolk machos brancos foram submetidos à LPA por meio de lavagem traqueal com salina (30 ml/kg, 38°C). A lesão foi induzida durante a ventilação mecânica convencional, e a LPA foi considerada confirmada na presença de relação PaO2/FiO2 < 100 mmHg. Os coelhos foram aleatoriamente divididos em dois grupos: VOAF em posição supina (grupo PS, n = 15); e VOAF em posição prona (grupo PP, n = 15). Para a VOAF, a pressão média das vias aéreas foi inicialmente estabelecida em 16 cmH2O. No 30º, 60º e 90º min após o início do protocolo de VOAF, a pressão média das vias aéreas foi reduzida para 14, 12 e 10 cmH2O, respectivamente. No 120º min, os animais foram recolocados ou permaneceram na posição supina por mais 30 min. Foram avaliados os índices de oxigenação e escores histológicos de lesão pulmonar, bem como os níveis de TNF-α em lavado broncoalveolar e tecido pulmonar.

Resultados:: Após a indução da LPA, todos os animais apresentaram hipoxemia significativa, diminuição da complacência do sistema respiratório, diminuição da oxigenação e aumento da pressão média das vias aéreas em comparação aos valores basais. Não houve diferenças estatisticamente significativas entre os dois grupos, em nenhum dos momentos avaliados, quanto a PaO2 e índice de oxigenação. Entretanto, os níveis de TNF-α no lavado broncoalveolar foram significativamente menores no grupo PP que no grupo PS, assim como os escores histológicos de lesão pulmonar.

Conclusões:: A posição prona parece atenuar a lesão pulmonar inflamatória e histológica durante a VOAF em coelhos com LPA.

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Figures

Figure 1
Figure 1. Experimental protocol design. ALI: acute lung injury; and HFOV: high-frequency oscillatory ventilation. *Arterial blood gas analysis.
Figure 2
Figure 2. PaO2 and oxygenation indexa over time (A and B, respectively) in the experimental groups.b PP: prone position group (filled ovals); SP: supine position group (open ovals); T0: time zero; T30: 30 min; T60: 60 min; T90: 90 min; T120: 120 min; and T150: 150 min. aCalculated as [FiO2 × mean Paw] / PaO2 × 100. bValues expressed as mean ± SD. *p ≤ 0.05 vs. baseline.
Figure 3
Figure 3. TNF-α levels in BAL fluid (BALF) and lung tissue (A and B, respectively),a the latter comparing ventral and dorsal lung tissue samples, in the prone position (PP) and supine position (SP) groups. aValues expressed as mean ± SD. *p ≤ 0.05 vs. PP group. †p > 0.05 vs. dorsal lung tissue in the PP group. ‡p ≤ 0.05 vs. dorsal lung tissue in the SP group.
Figure 4
Figure 4. Histological lung injury scores in the supine position (SP) and prone position (PP) groups, including comparisons between scores for ventral and dorsal lung tissue samples.a,‡ aValues expressed as median (range). *p < 0.05 vs. ventral lung tissue (Mann-Whitney rank-sum test). †p < 0.05 vs. PP group (Mann-Whitney rank-sum test). ‡p > 0.05 for interactions among lung regions and positioning (Kruskal-Wallis ANOVA, followed by Dunn’s test).
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