2Bristol Heart Institute Bristol University, UK
Pulmonary Abnormalities after Cardiopulmonary Bypass: Beneficial Effects of Low Frequency Mechanical Ventilation during Bypass
1)Department of Biological Regulation and Regenerative Surgery, Graduate School of Medicine, Nippon Medical School
2)Bristol Heart Institute Bristol University, UK
Pulmonary injury is a common complication of cardiac surgery. Numerous studies have been shown that cardiopulmonary bypass (CPB) is associated with significant inflammatory response, ischemia and reperfusion injury, histopatological changes such as pulmonary edema and atelectasis, and endothelial dysfunction of the pulmonary vessels. However, current surgical practice includes no strategy for active lung protection, because after the start of CPB, the lungs are disconnected from the mechanical ventilator and are left collapsed for the entire duration of CPB. We investigated the efficacy of low-frequency ventilation (LFV) and continuous positive airway pressure (CPAP) during CPB to reduce post-CPB lung injury.
Our experimental study was performed in 18 Yorkshire pigs subjected to 120 minutes of CPB (1 hour of cardioplegic arrest) followed by 90 minutes of recovery. Six pigs served as controls with the endotracheal tube open to the atmosphere during CPB. The remaining 12 pigs were divided into 2 groups of 6: during CPB 1 pig in each group received CPAP of 5 cm H2O, and the other 5 pigs received LFV (5 breaths/minute) with air (21% oxygen) at a tidal volume of 8 to 10 mL/kg. Lung tissue biopsy and broncoalveolor lavage samples were obtained serially for measurement of adenine nucleotides (ATP, ADP, AMP), lactate, DNA levels, and histology. Hemodynamic data and arterial blood gases were also collected throughout the study.
In LFV pigs improvements in PO2 and A-aDO2 after CPB were significantly greater than in the no protection group. The CPAP pigs did not show significant deterioration in PCO2 after CPB (p=0.08), although the PO2 level was similar to that in the no protection group.
Lung injury was observed as atelectasis and pulmonary edema on light microscopy and type I cell edema and microvilli diminutions of type II cells on electronic microscopy. In LFV pigs, there was significantly less derangement on all pathological examinations during and after CPB than in the no protection pigs. CPAP also brought improvements in pathological changes to some extent. although the benefits were less than with LFV.
Ischemic changes appeared as increased DNA levels in bronchoalveolor lavage fluid, decreased total adenine nucleotide levels, and increased lactate levels in lung tissue. The LFV pigs showed less derangement in these variables than did the control group. CPAP seemed to provide some benefits for these changes during CPB, but these benefits did not reach the level of statistical significance.
In summary LFV during CPB reduces tissue metabolic and histopathological damage in the lungs and is associated with improved postoperative gas exchange in an experimental pig model. The mode of action of this technique is probably a reduction in ischemic changes and the prevention of atelectasis.
ϊγεγο 2010; 6(3), 118-126
cardiopulmonary bypass, lung injury, ventilation, continuous positive airway pressure
Hajime Imura, MD, Department of Cardiovascular Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku Tokyo 113-8602, Japan