Influence of disease state on oxygen transport in newborn piglets

Optimally, oxygen delivery (DO2) should be sufficient to provide for adequate oxygen consumption (VO2) while avoiding O2 toxicity. Physiologically a critical level of DO2 has been described, below which decreases in oxygen supply begin to impair VO2, leading to venous hypercarbia and tissue acidosis. We predicted that this critical level would be influenced by factors such as underlying disease state and oxygen needs. Newborn piglets were exposed either to hypoxia (n = 6) or to group-B beta-hemolytic streptococcal sepsis (n = 6). Hemodynamic parameters were measured; DO2 and VO2 were calculated and compared within and between the groups. 'Critical DO2' was defined as the point at which decreases in DO2 began to produce concomitant decreases in VO2. This was observed at 9 ml/kg/min in hypoxic vs. 21 ml/kg/min in septic piglets. The 'critical Vsat' was defined as the venous O2 saturation beyond which tissue acidosis, as defined by base excess, developed. 'Critical VsatS' were 17% for hypoxic vs. 21% for septic animals. In summary, septic newborn piglets had higher critical DO2 and critical Vsat than hypoxic piglets, implying that they became oxygen supply dependent and developed tissue acidosis at higher levels of DO2 and Vsat, respectively.