Effect of mechanical ventilation with different tidal volumes on pulmonary surfactant in dogs during cardiopulmonary resuscitation

Abstract

Objective To observe the effects of mechanical ventilation with different tidal volumes (Vt) on the pulmonary surfactant in dogs during cardiopulmonary resuscitation (CPR) and discuss the strategy of mechanical ventilation for CPR.Methods A total of 24 healthy,adult and mongrel canines were randomly (random number) divided into three groups,namely control group (A),low Vt group (B) and high Vt group (C).Canines without ventricular fibrillation in group A were not supported with mechanical ventilation,while canines in group B and group C were induced to get ventricular fibrillation (VF) with pacing catheter inserted through right external carotid vein into the right ventricle.CPR was initiated with mechanical ventilation with different Vt for 6 hours after ventricular fibrillation.The Vt set in group B was 6 ml/kg body weight and Vt set in group C was 20 ml/kg body weight.The arterial blood gas analyses were tested in different intervals.The levels of phosphatidylchline in bronchia alveolus lavage fluid (BALF) was assayed with high performance liquid chromatography (HPLC).The ratio of wet and dry weight and the morphological change scores of lung tissue were calculated.Results After ventricular fibrillation,pH,PaO2 in both groups B and C decreased and PaCO2 increased in comparison with those before VF (P ＜ 0.05),while pH,PaO2 and PaCO2 were improved after mechanical ventilation.These was statistical difference in PaCO2 between group B and group C 2 h after mechanical ventilation (P ＜ 0.05).There was difference in HCO3-between group B and group C 6 h after ROSC.The rate of successful restoration of spontaneous circulation (ROSC) and the 72 h survival rate were 75％ and 50％ respectively in group B,and 62.5％ and 40％ respectively in group C.There were no statistically different between two groups (P ＞ 0.05).The levels of phosphatidylchline in BALF of group B and C greatly decreased compared with the group A (All P ＜0.01),while phosphatidylcholine detected in the group C decreased much more than that in the group B (P ＜0.01).The W/D ratio and morphological change scores in the group C were higher than those in the group B (P ＜ 0.01).Conclusion Low tidal volume ventilation can reduce the loss of pulmonary surfactant and mitigate pulmonary injury.Therefore it may be a protective ventilation strategy after resuscitation. Key words: Cardiopulmonary resuscitation; Mechanical ventilation ; Tidal volumes ; Lung injury ; Pulmonary surfactant