**3.2 Secondary (type A)**

Secondary hyperlactatemia is due to poor tissue perfusion and the body-buffering mechanisms are not able to compensate for the decreasing pH (Smith et al., 2001). This is the common post-cardiac surgery type of hyperlactatemia. The most frequent cause for secondary hyperlactatemia is the hypoperfusion and tissue hypoxia that are associated with significant cardiopulmonary compromise. Either systemic or regional hypoperfusion may result in hyperlactatemia (Mizock & Falk, 1992). The major causes of secondary hyperlactatemia are shock (cardiogenic, septic, hypovolemic), regional hypoperfusion (limb, mesenteric ischemia), severe hypoxemia, severe anemia, carbon monoxide poisoning, and severe respiratory acidosis (asthma) (Juneja et al., 2011; Mizock, 1989).

The relationship between regional oxyhemoglobin saturation (rS02) and lactate is exponential in nature, as demonstrated in a study which aimed to determine whether there is a relationship between rS02 measured at various body locations by near-infrared spectroscopy and blood lactate level in children after cardiac surgery (Chakravarti et al., 2009).
