**3.9 Blood loss and coagulation**

172 Special Topics in Cardiac Surgery

undergone cardiac surgery are prone to develop atelectasis. Theoretically, this may be

Most of the authors addressing this question, found that postoperative ventilation times were longer for patients who underwent CCABG than for those who underwent OPCAB. There is good evidence from a meta-analysis for a lower incidence of chest infections and shorter postoperative need for ventilator assistance after OPCAB (21), although one study of low-risk patients contradicts this finding (23). Most of these studies may be biased by the fact that the staff members deciding the time when the patients should be weaned from the ventilator were not blinded with regard to the type of operation that had been performed. On the other hand, evidence is strengthened by the fact that the one study in which the staff was indeed blinded

In two trials, patients with chronic obstructive pulmonary disease were studied specifically. In one of these studies, a significantly higher postoperative decrease in lung function was found among post-CCABG patients (62). In the other study, a shorter time to extubation and shorter stay in intensive care unit was found among OPCAB patients (63). Also, in a study of patients with recent myocardial infarction, a shorter ventilation time was documented for

It has been suggested, that the mechanism behind impaired lung function after CCABG was changes in alveolar gas exchange as a result of increased interstitial oedema. This effect has, however, been specifically addressed by several studies finding that this effect is comparable in OPCAB and CCABG-patients and most significant during the first few postoperative hours (23, 42, 64-65).In a randomized comparison of patients with single- and double-vessel disease, a significantly higher veno-arterial shunting was found after cardiopulmonary by-pass (23). It is still unknown whether this result can be generalized to patients with triple vessel disease where the OPCAB-technique is complicated by the need

There is evidence from a single, large, randomized trial that the risk of gastro-intestinal complications - including ischaemic bowel, hepatic failure, gastric bleeding, perforated duodenal ulcer, acute cholecystitis, and acute pancreatitis - is higher after CCABG than after OPCAB (66). This study, however, excluded patients needing grafts to the circumflex territory. This selection can be expected to favour OPCAB. Other, larger, randomized trials

A generalized inflammatory response is activated by any sort of surgery, but is aggravated by cardio-pulmonary by-pass. The blood–air interface and the contact between the blood and the artificial surfaces of the CPB circuit play important roles. Cooling and heating as well as ischemia and reperfusion of the myocardium are other factors that tend to activate a

The inflammatory response includes both humoral and cellular elements. Randomized comparisons between CCABG and OPCAB shows the CCABG patients to have increased serum-levels of a multitude of different substances including tumor necrosis factor-alpha, interleukins 6 and 8, selectin, c-reactive protein, intracellular adhesion molecule – 1, and vascular endothelial growth factor (39,67-72). Also, the expression of a scavenger molecule on monocytes is significantly higher in "on-pump" patients (73). It has been proposed that

either do not find this difference or do not report this endpoint (6-7, 12-14).

prevented by OPCAB where the lungs are continuously ventilated.

OPCAB-patients compared to CCABG-patients (32).

to manipulate the heart.

**3.8 Inflammatory response** 

systemic inflammatory response.

**3.7 Gastro-intestinal complications** 

also found a shorter postoperative need of ventilation in the OPCAB group (12).

Transfusions have been shown to be associated with substantial incremental increases in risks of mortality and morbidity for patients undergoing cardiac surgery. There is good evidence from a number of large, randomized trials that blood loss and need for transfusions is lower after OPCAB than after CCABG (7,15, 24, 45, 74-76). This finding is often explained by the activation and subsequent deactivation of platelets and humoral coagulation factors by the non-biological surfaces of the cardiopulmonary by-pass circuit. The alpha granules of the platelets are being depleted and the platelet count is reduced by dilution. Also fibrinolytic cascades are activated.

Some characteristics of the study protocols may, however, influence these results. Typically, different protocols for heparinization and reversion with protamine are used for the study groups, increasing bleeding tendency in the CCABG-groups. In addition, some studies apply a fixed value of haematocrit as an indication for transfusion. Because of dilution caused by the priming volume of the cardiopulmonary by-pass circuit this will increase the risk of transfusion in the CCABG-group compared to the OPCAB-group, even if this dilution were better treated using diuretics.
