Background: Open heart surgery with cardiopulmonary bypass (CPB) is associated with humoral and cellular activation, leading to organ dysfunction and an increased risk for infections in the postoperative period. The goal of our study was to investigate the effect of CPB on cellular immune system in children.

Methods: We conducted a prospective study to investigate the response of circulating lymphocytes and their subpopulations in a sample of 28 consecutive cyanotic or acyanotic children undergoing cardiac surgery. Peripheral blood samples were obtained preoperatively, and at 48 hours and three months postoperatively to study total lymphocyte count, T lymphocytes, and T-lymphocyte subsets.

Results: There were no differences between cyanotic and acyanotic cases with regard to T-cell and subset counts before and after surgery (p>0.05). Overall, total lymphocyte count and absolute total T lymphocyte (CD3+) and absolute T helper cell (CD4+) counts decreased significantly within 48 hours after CPB (p<0.05). T suppressor (CD8+) and natural killer cell (NKC) levels also decreased in the early period (p<0.05). These values increased to preoperative values three months after the operation (p<0.05). The CD4/CD8 ratio increased from 1.31 to 1.55 in the early postoperative period (p=0.002); however, it then decreased to 0.93 in the late postoperative period (p=0.001).

Conclusion: Significant decreases in absolute NKC count, total lymphocyte count, total T cells and their subsets in the early period of CPB may be due to an extravasation and/or T-cell activation during and after the operation, predisposing pediatric patients to a higher risk for infections.

Keywords : Cardiopulmonary bypass/adverse effects; child; immunity, cellular; lymphocyte activation; lymphocyte subsets; time factors