Inhaled NO as an Anti-inflammatory and Anti-reperfusion Agent in Infants and Children Undergoing Cardiopulmonary Bypass

Overview

Each year, there are over 400,000 cardiac surgical operations performed in the United States; of which 10,000 are performed on children. These operations are made possible by the use of the heart-lung bypass machine, also known as cardiopulmonary bypass. This machine allows for the body to be supported while the heart is repaired. While this machine has been life saving, it has risks and can lead to a variety of complications. One such complication results from the fact that the patient's blood is exposed to the foreign material of the machine, such as plastic tubing. In nearly all cases of cardiac surgery, this leads to a whole body response in the patient following the operation. This response, inflammation, is characterized by alterations in the function of the heart and lungs, fever, fluid retention, and bleeding disorders in the postoperative period. While this is usually temporary and self limiting, significant morbidity occurs in approximately 1-2% of cases where this inflammatory response is present. Additionally, children appear to be more susceptible to this response. This can lead to significant postoperative complications that are not associated with the actually surgical procedure performed on the heart. The exact cause of this response is not fully understood. However, it is important to understand the triggers, timing, and pattern of this complex inflammatory response in order to modify or arrest it. Unlike other situations associated with this type of whole-body inflammatory reaction such as trauma or overwhelming infection, cardiac surgical teams have the advantage of knowing when the trigger will occur (i.e. during the cardiac operation) and hence have the opportunity for preemptive intervention in an effort to minimize the response. One such effort is the focus of this proposal. Nitric oxide (NO) is a gas that has been used for years in the treatment of lung disease in infants. It has been life saving and safe. Recently, it has been investigated for its anti-inflammatory effects outside the lungs. We propose delivering NO to the source of the greatest inflammation in cardiac surgery, the cardiopulmonary bypass machine. It is our intention to show that in doing so; we can minimize the inflammation found in the first 24 hours following cardiac surgery in children. If we are correct, the reduction of this inflammation will result in less damage to other organs of the child's body and improved outcome following surgery.

I. Hypothesis Treatment of children during surgery employing cardiopulmonary bypass with inhaled, exogenous nitric oxide (iNO) delivered to the cardiopulmonary bypass circuit will: 1. Modulate ischemia/reperfusion injury 2. Influence endothelial dysfunction 3. Ameliorate the bypass-triggered systemic inflammatory response II. Specific Aims Three specific aims will test this hypothesis: Delivery of iNO to the cardiopulmonary bypass circuit will result in a decrease in: 1. Measures of end-organ dysfunction often associated with CPB; pulmonary function, cardiac injury markers, serum creatinine, and neurologic injury markers. 2. Measures of inflammatory response, specifically IL-6 and TNFa via its antioxidant properties. 3. Platelet activation and aggregation leading to reduced transfusion requirements. III. Introduction and Background * Cardiopulmonary bypass leads to ischemia/reperfusion injury. One of the mediators of this injury is oxygen radical production. NO is known to bind oxygen radical species. * Cardiopulmonary bypass leads to endothelial dysfunction. This is mediated through cell-free hemoglobin binding endogenous NO, as seen in sickle cell disease. * Both of these factors, separately and in combination, perpetuate the inflammatory response triggered by CPB. NO affects this response by interfering with this process. Additionally, NO is known to affect neutrophil chemotaxis as well as platelet activation and aggregation, both of which further amplify the inflammatory response. IV. Basic Protocol Experimental Design In a prospective, randomized, controlled, blinded pilot trial we will compare 20 ppm of iNO delivered to the CPB circuit. Our study will target children undergoing cardiopulmonary bypass (CPB) for surgery for the correction of transposition of great arteries (TGA) and Tetralogy of Fallot (TOF). Subjects Inclusion Undergoing repair of TGA and TOF \< 16 years of age Exclusion Age \> 16 years of age Pregnancy Known bleeding disorder Treatment Protocol Following informed consent, blood will be drawn pre-operatively for baseline characteristics (methemoglobin, venous saturation, CBC, S100, gene expression profiles, BNP, cTnI, IL-6, IL-8, lactate, TNFalpha)\[Table, Blood sample for Study\]. Intra-operatively we will use a standardized anesthetic protocol unless contraindicated by specific patient clinical characteristics. Intraoperative measurements will include: aortic cross clamp time, and total cardiopulmonary bypass time. Intraoperative hemodynamic measurements will include: mean systemic blood pressure (MAP), central venous pressure, right atrial pressure pulmonary artery pressure, and pulmonary capillary wedge pressure (when available). Blood samples will be drawn following CPB upon arrival to the ICU and will be analyzed as above. Repeat blood samples for each will be drawn again after 12, 24, and 48 hours. Patients will be followed to the time of discharge. Ventilator settings, length of ICU and hospital stay will be recorded. All measurements in both groups will be the same. Time points will be referenced from the time of admission to the PICU for both groups.