The effects of increasing levels of PEEP on inflammation markers and oxygenation in rats with unilateral lung injury

Introduction

The effects of PEEP on inflammation and oxygenation during acute lung injury are not well known. Accordingly, we investigated the effect of different PEEP levels on local and systemic parameters of lung injury and inflammatory response in a unilateral in vivo lung injury model.

Methods

Male Wistar rats (350 g) underwent left-sided lung injury using endobronchial instillation of 0.4 ml HCl (pH 1) (study group) or endobronchial instillation of 0.1 ml NaCl 0.9% (placebo group). Twenty-four hours after treatment the rats were anesthetized, and intravascular catheters inserted for fluid infusion and hemodynamic monitoring. A tracheostomy was performed and the rats were ventilated for 4 hours with tidal volume of 6 ml/kg body weight and randomly assigned to ZEEP, PEEP = 5 cmH₂O or PEEP = 10 cmH₂O groups. Oxygenation was measured every 30 min and left and right lung lavage was performed lung after 4 hours of ventilation for cell and protein determination. An ANOVA was used for statistical analysis.

Results and conclusion

PaO₂ was higher in the PEEP groups as in the ZEEP groups. Protein and neutrophils in lung lavage fluid of both sides were higher in injured as in placebo rats. Increasing PEEP levels reduced neutrophil count in lavage fluid of the damaged lung in a dose dependent manner. PEEP increases oxygenation and decreased neutrophil infiltration in this model of lung injury.

Table.

	Lung injury with HCl			Controls
	ZEEP	PEEP5	PEEP10	ZEEP	PEEP5	PEEP10
PaO2 after 4 h vent. (mmHg)*	127 ± 26	193 ± 4	203 ± 10	138 ± 14	215 ± 10	197 ± 13
Protein left lung (mg/l)**	2841 ± 146	2867 ± 253	1970 ± 300	80 ± 11	62 ± 17	72 ± 17
Protein right lung (mg/l)***	343 ± 69	212 ± 69	195 ± 43	69 ± 7	85 ± 13	92 ± 10
Neutrophils left lung (ml-1)**	4082 ± 503	2634 ± 530	1744 ± 453	158 ± 77	157 ± 34	85 ± 29
Neutrophils right lung (ml-1)***	456 ± 98	449 ± 147	335 ± 148	155 ± 33	214 ± 56	185 ± 58

Mean ± SEM; Protein and neutrophils: in lavage fluid. ^*P < 0.05 for effects of PEEP; ^**P < 0.05 for effects of group, PEEP and interaction; ^***P < 0.05 for effects of group.