The present study demonstrates a significant reduction of pulmonary function in the early postoperative period of OPCAB surgery, regardless of the technique employed. There is clear evidence that postoperative pulmonary dysfunction of varying degrees is an inevitable consequence of cardiac surgery [2, 3, 13]. A number of factors appear to contribute to pulmonary function abnormalities including general anesthesia, median sternotomy, surgical injury and cardiopulmonary bypass [3, 14]. General anesthesia combined with prolonged supine positioning results in an upward displacement of the diaphragm, and a shift in blood volume to the abdomen from the thorax, with consequent ventilation-perfusion mismatch . Sternotomy itself may decrease chest wall compliance and interfere with sternal stability [2, 3]. The cardiopulmonary bypass additionally causes lung injury and a delay in pulmonary recovery [15–17]. Lung injury has been largely attributed to higher degree of acute systemic and pulmonary inflammatory response [17, 18].
Internal thoracic artery (ITA) has become the conduit of choice for myocardial revascularization because of its superior patency rate, reduced cardiac events and increased long-term survival compared with saphenous vein grafting . However, reports have demonstrated that ITA harvesting during a CABG is an adjunctive factor for further impairment of postoperative pulmonary function, and may increase the risk of pleuropulmonary complications [2, 3, 13]. Previous reports attributed the postoperative poor lung function to pleurotomy followed by chest tube insertion and additional trauma to the chest wall during dissection of ITA graft [2, 5, 19, 20].
Gullu et al  recommended averting routine pleura opening, as preservation of pleural integrity during ITA harvesting had positive beneficial effect on pulmonary function, pain decrease and lowered the rate of postoperative pleural effusions and atelectasis.
We have previously shown that even avoiding the systemic inflammatory response syndrome and pulmonary injury associated to cardiopulmonary bypass (i.e., OPCAB surgery), patients undergoing pleurotomy and intercostal space drain placement presented a larger decrease of the FVC and FEV1, oxygenation, and gas exchange in comparison to patients with intact pleura in the early postoperative period .
Additionally, pleural integrity is reportedly associated with other further advantages, such as a less incidence of pleuropulmonary alteration [4, 5, 21], reduced orotracheal intubation time [7, 19, 20] and lower pain score [5–7]. These findings associated to the enhanced preservation of the pulmonary function appear to be, at least in part, responsible for the shorter hospital stay found in patients with intact pleura [7, 19, 20].
Greater pulmonary dysfunction, increased rates of atelectasis and pleural effusion in patients undergoing to pleurotomy with an intercostal pleural drain reflects the greater degree of chest wall trauma [5, 7, 20, 22]. Typically, pleural tube insertion through the intercostals space is associated with significant patient discomfort in the early postoperative period . The friction of the drain between the ribs leads to painful sensations caused by costal periosteum and parietal pleura irritation [23, 24]. The patient responds with chest wall immobilization and superficial respiratory movements, restricting deep breaths until drain removal, intensifying pulmonary capacities and volumes decreases [7, 22]. All of these factors lead to a negative impact on mobilization and pulmonary toilet and increase the risk of respiratory complications in the postoperative period [4, 22–24].
Evidence indicates that the degree of pulmonary dysfunction in the presence of pleurotomy depends on the insertion site of the pleural drain. Hagl et al  showed that subxyphoid insertion of the pleural drain leads to a significantly lower impairment of pulmonary function and less pain than intercostal insertion in the early postoperative period, similar results were demonstrated in patients undergoing OPCAB .
Technical questions concerning the pleural opening with subxyphoid chest drain insertion, compared to the maintenance of pleural integrity and its influence on postoperative pulmonary function have not been addressed to date. Therefore the main question is: "Does subxyphoid insertion of the pleura drain generate similar effects on pulmonary function when compared to the maintenance of pleural integrity?".
In the present study, no significant differences on pulmonary function parameters (FVC and FEV1), oxygenation and shunt fraction between the two groups were found during the early postoperative period. Our study also demonstrated that when subxyphoid site for drain insertion was used, the pain score was similar to the pleural integrity maintenance. Furthermore, mechanical ventilation time, incidence of atelectasis, pleural effusion and postoperative hospital stay were similar when compared the intact pleura to the pleural drain in subxyphoid position. Most likely, these outcomes resulted from the minimized chest wall trauma influenced by the change of the pleural drainage site to the subxyphoid position.
A large body of evidence demonstrates that preservation of pleural integrity during harvesting the ITA graft is associated to lower degrees of pulmonary dysfunction. The present study showed that even in the presence of pleurotomy, shifting the drain pleural insertion site to the subxyphoid position may constitute an excellent alternative technique to preserve the chest wall and decrease impairment in pulmonary function, as compared to intact pleura. This finding might be important for patients with impaired pulmonary function like chronic obstructive pulmonary disease and also those who are at risk of postoperative respiratory complication. Additionally, this information could be of relevant interest when both pleura are entered and bilateral drainage of pleural cavities becomes necessary.
Therefore, the original findings of this study suggest that in the presence of pleurotomy, placement of pleural drain in subxyphoid position may represent a clear advantage to decrease trauma to the chest wall and minimize pulmonary dysfunction in the early postoperative period.
Although the impact of comparative direct or indirect costs between groups has not been assessed, our results showed no significant difference in clinical outcomes, such as, mechanical ventilation time, incidence of the atelectasis and pleural effusion and hospital stay.