Nitric Oxide Administration During Pediatric Cardiopulmonary Bypass Surgery to Prevent Platelet activation-a Single Center Pilot Study

Open heart surgery requires the use of a CPB circuit. As blood flows across the artificial surfaces of the CPB circuit, platelets are consumed (1). The investigators recently completed a prospective observational trial of neonates undergoing cardiac surgery requiring CPB. In this trial the investigators demonstrated a dramatic decrease in platelet count from baseline to intraoperatively. The platelet count rebounded with transfusion and normalized by the time of admission to the cardiac intensive care unit (CICU). Despite prophylactic transfusion of blood products to all patients, 41% experienced excessive postoperative bleeding (defined in terms of chest tube output and need for reoperation).

Further investigation by Dr. Debra Newman in her lab at the Blood Research Institute delineated the platelet defect associated with CPB in the neonates more clearly. Dr. Newman found a significant decrease in the platelet responsiveness to thrombin receptor activating protein (TRAP), thromboxane A2 analog (U46619), and collagen-related peptide (CRP). Further analysis revealed that the effect of CPB on platelet responsiveness to TRAP and U46619 is likely dependent on its effect on platelet count, whereas CPB affects platelet responsiveness to CRP independently of platelet count.

In children, postoperative blood loss and transfusion of blood products has been shown to contribute significantly to the morbidity and mortality of surgeries that require CPB (2, 3). In addition to the need for blood product replacement, the activation of platelets contributes to the intense inflammatory reaction seen in surgeries requiring CPB (4). Patients with a less intense inflammatory response post-operatively generally do better with less morbidity (5).

The oxygenator membrane surface of the CPB pump is a large contributor to the surface area of CPB circuit. As a major contributor to the surface area of the circuit and the location of the gas interface, the oxygenator is a significant contributor to the hemostatic and inflammatory stimulus of CPB. Advances in oxygenator technology have modified the surface to prevent interaction with the blood, but no artificial surface has been found to be as inert as the natural endothelium of the vasculature (5).

A major mechanism by which endothelial surfaces inhibit activation of platelets is by producing nitric oxide (6). Nitric oxide is lipophilic and traverses cellular membranes where it acts on intracellular signaling pathways in platelets to prevent platelet activation and aggregation (7). The artificial surface of the CPB pump does not produce nitric oxide and hence is devoid of this potent inhibitor of platelet activation.