Pulmonary artery perfusion versus no pulmonary per-fusion during cardiopulmonary bypass

During conventional cardiopulmonary bypass (CPB) there is no active perfusion of the pulmonary circulation and the mechanical ventilation is ceased leaving the lungs exposed to warm ischemia.
 
Pulmonary dysfunction is seen in varying degrees after major surgery, but more severe in cardiac surgery patients probably due to the effects of CPB. The evidence for effect and safety are limited, but active pulmonary artery perfusion during CPB could be beneficial for the patients' postoperative oxygenation.
Our aim was in a randomised clinical trial to assess primarily the effect of pulmonary artery perfusion during CPB on postoperative oxygenation in patients diagnosed with chronic obstructive pulmonary disease (COPD), secondarily to assess other possible benefits and harms. Furthermore, we wanted in a systematic review with meta-analyses of all randomised clinical trials to investigate the pooled effects of pulmonary artery perfusion during CPB. 
We planned and conducted a randomised, partly blinded, clinical trial assigning cardiac surgery patients diagnosed with COPD to receive pulmonary artery perfusion with oxygenated blood or histidine-tryptophan-ketoglutarate (HTK) solution compared to no pulmonary perfusion during CPB. The primary outcome was the oxygenation index measured during and after surgery. Secondary outcomes were intubation time, serious adverse events, days alive outside the intensive care unit and outside the hospital, 30- and 90-days mortality. 
Secondly, we conducted a systematic review of randomised clinical trials comparing benefits and harms of using pulmonary artery perfusion versus no pulmonary perfusion during CPB pooling results in meta-analyses and trial sequential analyses (TSA).
 
Of the 90 randomised patients 89 were included in analysis of the primary outcome, the inverse oxygenation index, measured at a single time point 21 hours after CPB start and longitudinally 1, 3, 5, 7, and 21 hours after CPB start. At 21 hours, patients randomised to pulmonary artery perfusion with oxygenated blood had a higher inverse oxygenation index compared to patients randomised to no pulmonary perfusion during CPB (mean difference (MD) 0.94; 95% confidence interval (CI), 0.05 to 1.83; P=0.04). The inverse oxygenation index was also significantly higher at 21 hours after CPB start (MD 0.99; CI, 0.29 to 1.69; P=0.007), and longitudinally (P=0.009), for patients receiving pulmonary artery perfusion with oxygenated blood compared to pulmonary artery perfusion with HTK solution. This corresponds to a PaO₂ difference of 23 mmHg with a median FiO₂ of 0.32. We found no additional significant differences for the remaining comparisons of the inverse oxygenation index neither for any of the secondary outcomes. 
The systematic review identified 4 trials with a total of 210 patients. In meta-analyses pulmonary artery perfusion with blood versus no pulmonary perfusion during CPB was not associated with relative risk of death (1.7; 95% CI, 0.4 to 6.9; 210 patients in three trials with high and one trial with low risk of bias), serious adverse events (1.2; 95% CI, 0.8 to 1.8; 180 patients in two trials with high and one trial with low risk of bias) or intubation time (-0.4 hours; 95% CI, -1.1 to 0.4; 176 patients in three trials with high and one trial with low risk of bias). TSA on mortality, serious adverse events, and PaO₂/FiO₂ ratio showed that required information sizes have not been reached, but pulmonary artery perfusion with blood was associated with a higher PaO₂/FiO₂ ratio (27.8 mmHg; 95% CI, 5.7 to 50.0 mmHg; 119 patients in two trials with high and one trial with low risk of bias). TSA on intubation time showed that the boundary for lack of superiority (futility) was crossed refuting a shorten intubation time of 1.5 hours or more. 
Our trial provided additional knowledge about the use of pulmonary artery perfusion during CPB in cardiac surgery patients with COPD, and improved oxygenation for patients receiving pulmonary artery perfusion with oxygenated blood. Pulmonary artery perfusion with HTK solution did not result in an improved oxygenation. In line with this, the systematic review including data from additional trials showed a possible association between pulmonary artery perfusion with blood and improved oxygenation, but no significant associations with mortality, serious adverse events or intubation time. However, all data are too sparse to be conclusive.