Effects of atelectatic areas on the surrounding lung tissue during mechanical ventilation in an experimental model of acute lung injury induced by lipopolysaccharide

Fonseca, Lídia Maria Carneiro; Reboredo, Maycon Moura; Lucinda, Leda Marília Fonseca; Fazza, Thaís Fernanda; Bergamini, Bruno Curty; Botelho, Mateus Pinto; Lopes, Gabriele Moura; Ferreira, Juliana Dias Nascimento; Carvalho, Erich Vidal; Pinheiro, Bruno Valle

doi:10.5935/2965-2774.20230190-en

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ORIGINAL ARTICLE • Crit. Care Sci. 35 (4) • Oct-Dec 2023 • https://doi.org/10.5935/2965-2774.20230190-en linkcopy

Effects of atelectatic areas on the surrounding lung tissue during mechanical ventilation in an experimental model of acute lung injury induced by lipopolysaccharide

Authorship SCIMAGO INSTITUTIONS RANKINGS

Objective: To assess the effect of atelectasis during mechanical ventilation on the periatelectatic and normal lung regions in a model of atelectasis in rats with acute lung injury induced by lipopolysaccharide.

Methods: Twenty-four rats were randomized into the following four groups, each with 6 animals: the Saline-Control Group, Lipopolysaccharide Control Group, Saline-Atelectasis Group, and Lipopolysaccharide Atelectasis Group. Acute lung injury was induced by intraperitoneal injection of lipopolysaccharide. After 24 hours, atelectasis was induced by bronchial blocking. The animals underwent mechanical ventilation for two hours with protective parameters, and respiratory mechanics were monitored during this period. Thereafter, histologic analyses of two regions of interest, periatelectatic areas and the normally-aerated lung contralateral to the atelectatic areas, were performed.

Results: The lung injury score was significantly higher in the Lipopolysaccharide Control Group (0.41 ± 0.13) than in the Saline Control Group (0.15 ± 0.51), p < 0.05. Periatelectatic regions showed higher lung injury scores than normally-aerated regions in both the Saline-Atelectasis (0.44 ± 0.06 x 0.27 ± 0.74 p < 0.05) and Lipopolysaccharide Atelectasis (0.56 ± 0.09 x 0.35 ± 0.04 p < 0.05) Groups. The lung injury score in the periatelectatic regions was higher in the Lipopolysaccharide Atelectasis Group (0.56 ± 0.09) than in the periatelectatic region of the Saline-Atelectasis Group (0.44 ± 0.06), p < 0.05.

Conclusion: Atelectasis may cause injury to the surrounding tissue after a period of mechanical ventilation with protective parameters. Its effect was more significant in previously injured lungs.

Keywords:
Acute respiratory distress syndrome; Respiration, artificial; Ventilator-induced lung injury; Pulmonary atelectasis; Lipopolysaccharides; Sepsis; Models, animal

Respiratory measurements by group	Time after start of protocol			p value
Respiratory measurements by group	Baseline	60 minutes	120 minutes	Group	Time	Interaction
V_T /kg (mL/kg)
SAL-C	7.9 ± 0.2	7.7 ± 0.3	7.7 ± 0.4	NS	NS	NS
SAL-AT	7.6 ± 0.4	7.6 ± 0.5	7.8 ± 0.7
LPS-C	7.6 ± 0.3	7.7 ± 0.5	7.7 ± 0.2
LPS-AT	7.8 ± 0.3	7.5 ± 0.4	7.5 ± 1.3
RR (bpm)
SAL-C	76.3 ± 0.8	76.6 ± 0.7	76.6 ± 0.7	NS	NS	NS
SAL-AT	76.0 ± 1.1	76.1 ± 1.6	76.3 ± 0.9
LPS-C	75.8 ± 0.9	76.1 ± 0.8	76.0 ± 0.8
LPS-AT	7.4 ± 0.4	76.4 ± 1.0	76.1 ± 0.8
Ppeak (cmH₂O)
SAL-C	10.8 ± 1.0	11.0 ± 0.8	11.4 ± 0.8	NS	< 0.01	NS
SAL-AT	11.4 ± 0.7	11.7 ± 1.3	12.1 ± 1.3†
LPS-C	10.3 ± 0.4	10.7 ± 1.0	10.5 ± 0.7
LPS-AT	11.9 ± 1.3†	12.7 ± 0.7*†	13.2 ± 0.5*†
PEEP (cmH₂O)
SAL-C	3.8 ± 0.4	3.6 ± 0.4	3.6 ± 0.3	NS	NS	NS
SAL-AT	3.6 ± 0.3	3.6 ± 0.1	3.5 ± 0.1
LPS-C	3.9 ± 0.9	3.9 ± 0.4	3.8 ± 0.6
LPS-AT	3.9 ± 0.8	3.9 ± 0.9	3.9 ± 0.8
Ers (cm H₂O/l)
SAL-C	2.4 ± 0.4	2.6 ± 0.4 ‡	2.8 ± 0.4 §‡	0.017	< 0.01	NS
SAL-AT	2.9 ± 0.5	3.1 ± 0.6 ‡	3.4 ± 0.7 §‡
LPS-C	2.3 ± 0.2	2.5 ± 0.3 ‡	2.6 ± 0.3 §‡
LPS-AT	3.1 ± 0.6	3.4 ± 0.5*† ‡	3.6 ± 0.5*† §‡
Rrs (cmH₂O/l/s)
SAL-C	0.10 ± 0.01	0.09 ± 0.00	0.10 ± 0.03	NS	NS	NS
SAL-AT	0.11 ± 0.02	0.10 ± 0.02	0.10 ± 0.02
LPS-C	0.12 ± 0.05	0.15 ± 0.10	0.11 ± 0.39
LPS-AT	0.12 ± 0.03	0.15 ± 0.07	0.18 ± 0.13
Volume of fluids infused (mL)
SAL-C			3.71 ± 0.87	NS
SAL-AT			3.22 ± 0.58
LPS-C			3.03 ± 0.41
LPS-AT			3.62 ± 0.58

	Groups
	SAL-C	LPS-C	SAL-AT		LPS-AT
	SAL-C	LPS-C	Normally-aerated	Periatelectatic	Normally-aerated	Periatelectatic
Overall score	0.15 ± 0.51	0.41 ± 0.13*	0.27 ± 0.74	0.44 ± 0.06†	0.35 ± 0.04	0.56 ± 0.09†‡
Alveolar neutrophils	0 (0.75)	3.00 (8.75)	2.50 (4.00)	7.00 (5,75)†	3.00 (3.25)	12.50 (7.00)†
Interstitial neutrophils	9.33 ± 2.33	19.50 (1.75)*	14.00 ± 2.44	17.83 ± 1.16†	18.83 ± 1.47	19.16 ± 1.16
Proteinaceous debris	2.00 (1.50)	6.66 ± 3.55	1.50 (1.50)	6.00 (8.75)†	3.00 (1.75)	7.00 (4.25)†
Hyaline membrane	00	00	00	00	00	00
Septal thickening	0.00 (0.25)	1.83 ± 3.12	0.00 (0.25)	0.00 (1.00)	0.50 (1.25)	2.50 ± (6.25)

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[1] V_T - tidal volume; SAL-C - Saline-Control Group; NS - not significant; LPS-C - Lipopolysaccharide Control Group; SAL-AT - Saline-Atelectasis Group; LPS-AT - Lipopolysaccharide Atelectasis Group; RR - respiratory rate; Ppeak - peak airway pressure; PEEP - positive end-expiratory pressure; Ers - elastance of the respiratory system; Rrs - resistance of the respiratory system.

[TFN1] ^*
p < 0.05 compared to Saline-Control Group; † p < 0.05 compared to Lipopolysaccharide Control Group; ‡ p < 0.05 compared to baseline of the same group; § p < 0.05 compared to 60 minutes of the same group. Data are expressed as the mean ± standard deviation.