**5.2 Operative factors**

Lactic acidosis is often observed as being related to cardiac surgery with CPB, low output syndrome and hypoxemia, which usually show clinical evidence of poor tissue oxygen delivery. Early postoperative hyperlactatemia is seen in some children after surgical repair of CHD despite evidence of good cardiac output. Cardiac arrest or severe hypovolemia triggers anaerobic metabolism and hyperlactatemia, all of which can appear pre-, peri- or postoperatively due to the many cardiac or resuscitation problems found in pediatric patients with CHD.

Changes in lactate levels in post-cardiac surgery patients are not homogenous in nature, due to the fact that early hyperlactatemia and late hyperlactatemia differ in both risk profile and physiological rationale (O'Connor & Fraser, 2010).
