Effects of different fluid management on lung and kidney during pressure-controlled and pressure-support ventilation in experimental acute lung injury

Abstract

Optimal fluid management is critical during mechanical ventilation to mitigate lung damage. Under normovolemia and protective ventilation, pulmonary tensile stress during pressure-support ventilation (PSV) results in comparable lung protection to compressive stress during pressure-controlled ventilation (PCV) in experimental acute lung injury (ALI). It is not yet known whether tensile stress can lead to comparable protection to compressive stress in ALI under a liberal fluid strategy (LF). A conservative fluid strategy (CF) was compared with LF during PSV and PCV on lungs and kidneys in an established model of ALI. Twenty-eight male Wistar rats received endotoxin intratracheally. After 24 h, they were treated with CF (minimum volume of Ringer's lactate to maintain normovolemia and mean arterial pressure ≥70 mmHg) or LF (~4 times higher than CF) combined with PSV or PCV (V_T = 6 ml/kg, PEEP = 3 cmH₂ O) for 1 h. Nonventilated animals (n = 4) were used for molecular biology analyses. CF-PSV compared with LF-PSV: (1) decreased the diffuse alveolar damage score (10 [7.8-12] vs. 25 [23-31.5], p = 0.006), mainly due to edema in axial and alveolar parenchyma; (2) increased birefringence for occludin and claudin-4 in lung tissue and expression of zonula-occludens-1 and metalloproteinase-9 in lung. LF compared with CF reduced neutrophil gelatinase-associated lipocalin and interleukin-6 expression in the kidneys in PSV and PCV. In conclusion, CF compared with LF combined with PSV yielded less lung epithelial cell damage in the current model of ALI. However, LF compared with CF resulted in less kidney injury markers, regardless of the ventilatory strategy.

Keywords: acute lung injury; fluid therapy; hemodynamics; immunofluorescence; immunohistochemistry; molecular biology; pressure-support ventilation.

FIGURE 1

Experimental design and temporal evolution. (a) Experimental design. The CF regimen was defined as the minimal amount of Ringer's lactate to maintain mean arterial pressure (MAP) ≥70 mmHg. The LF regimen was defined as ~4–5 times higher fluids than in the CF groups. (b) Temporal evolution. CF, conservative fluid; Echo, echocardiography; FiO₂, inspired fraction of oxygen; i.v., intravenous; LF, liberal fluid; MV, mechanical ventilation; PEEP, positive end‐expiratory pressure; V_T, tidal volume.

FIGURE 2

DAD score and immunohistochemistry for occludin. (a) Representative images of histologic sections of alveolar pulmonary parenchyma (alveolar sacs and ducts, alveoli, and associated capillary loops) and perivascular sections (intra‐acinar arteries) stained by hematoxylin‐eosin and immunohistochemistry for occludin at high magnification. The intra‐acinar artery sections of CF‐PCV demonstrate discrete cuff‐shaped perivascular edema (double blue arrowheads) coincident with prominent expression of occludin by the endothelial cells of the artery (blue arrowheads). A similar immunophenotypic pattern of occludin was found in CF‐PSV and LF‐PCV, except for slightly cuff‐shaped perivascular edema (blue arrowheads) and mild inflammatory cells (blue square). In contrast, the LF‐PSV alveolar parenchyma exhibited almost absence of occludin in the endothelium of capillary loops (blue arrows). (b) Boxplot of occludin quantification in lung tissue. p = 0.026. (c) DAD score. **, means different from CF‐PSV (p < 0.01); #, vs LF‐PCV (p < 0.05). Alv, alveoli; art, artery; CF, conservative fluid therapy; DAD, diffuse alveolar damage; ed, edema; LF, liberal fluid therapy; PCV, pressure‐controlled ventilation; PSV, pressure‐support ventilation.

FIGURE 3

Immunofluorescence of occludin and vimentin. Histologic sections (×400) of the axial and alveolar staining for immunofluorescence to occludin and vimentin divided by groups (CF‐PCV, CF‐PSV, LF‐PCV, and LF‐PSV). The arrows indicate the endothelial cells of the bronchiolar and alveolar capillaries expressing occludin [nuclei in blue, 4′,6‐diamidino‐2‐phenylindole (DAPI); connective tissue in green; vimentin; bronchiolar vessels and alveolar capillaries in red; occludin and colocation, blue‐orange‐red]. (a) DAPI (nuclei in blue) in axial parenchyma in CF‐PCV. (b,f) Vimentin in axial parenchyma in CF‐PCV. (d) merge of DAPI, vimentin and occludin in axial parenchyma in CF‐PCV. (e) DAPI (nuclei in blue) in alveolar parenchyma in CFPCV. (f) Vimentin in alveolar parenchyma in CF‐PCV. (h) Merge of DAPI, vimentin and occludin in alveolar parenchyma in CF‐PCV. (i) DAPI (nuclei in blue) in axial parenchyma in CF‐PSV. (j) Vimentin in axial parenchyma in CF‐PSV. (l) Merge of DAPI, vimentin and occludin in alveolar parenchyma in CF‐PCV. (m) DAPI (nuclei in blue) in alveolar parenchyma in CF‐PSV. (n) vimentin inalveolar parenchyma in CF‐PSV. (p) Merge of DAPI, vimentin and occludin in alveolar parenchyma in CF‐PSV. The CF‐PCV parenchyma (C and G) presents intense red birefringence of occludin in dilated lymphatics and blood vessels around the bronchiolar mucosa and along the capillary alveoli (simple white arrows). CF‐PSV and LF‐PCV (K, O, C2, and G2) present a similar pattern of birefringence for occludin (red) in endothelial cells of the lymphatics and blood vessels (double white arrows), as well as along capillaries of the alveolar septa (single white arrows). In contrast, LF‐PSV (K2 and O2) has almost no birefringence of occludin in the endothelium of the lymphatics and blood vessels, as well as along capillaries of the alveolar septa, with prominent oedema in this group (*). Br, bronchioles; Alv, alveoli; Ve, blood vessels; Cap, capillaries. White double arrows, connective tissue around bronchiolar vessels and alveolar capillaries. Simple white arrows, expression of occludin by endothelial cells of bronchiolar vessels and alveolar capillaries; white arrowhead, colocation of vimentin and occludin; *, peribronchiolar and alveolar cuff.

FIGURE 4

Molecular biology of lung and kidney. Gene expression of ZO‐1 and MMP‐9 in lung tissue; and KIM‐1, NGAL, and IL‐6 in kidney tissue. Boxplots represent the median and interquartile range of 6 animals per group. Comparisons were done by Kruskal–Wallis test followed by Dunn's multiple comparisons test (p < 0.05). CF, conservative fluid therapy; IL‐6, interleukin‐6; KIM‐1, kidney injury molecule 1; LF, liberal fluid therapy; MMP‐9, metalloproteinase‐9; NGAL, neutrophilic gelatinase‐associated lipocalin; PCV, pressure‐controlled ventilation; PSV, pressure‐support ventilation; ZO‐1, zona occludens‐1; *, depicting the differences between groups (p < 0.05).