Lactate and acid base changes in the critically ill

Abstract

Metabolic acidosis and hyperlactataemia are important, independent findings in acute illness, and the combination of these abnormalities carries a grave prognosis. Despite this there is still controversy about the most appropriate therapy of lactic acidosis, and the relationship of commonly used acid base measurements to blood lactate levels. This paper details studies in shock and multiple organ failure examining these issues. Shocked patients were studied during catecholamine therapy and showed improvements in acidosis and hyperlactataemia in conjunction with cardiorespiratory improvement. This supports a beneficial role for these agents in appropriately monitored, volume resuscitated and oxygenated patients with shock and lactic acidosis. Assessment of differences in mixed venous and arterial acid base status was performed in 32 patients. The relationship of blood lactate to acid base measurements was examined. There were no significant differences in [H+], [HCO3] or base excess. There was no significant correlation between any of these in arterial or mixed venous samples and arterial whole blood lactate. Mixed venous PCO2 was significantly higher than arterial PCO2. Haemodynamic, oxygen transport and acid base changes were documented in eight patients with multiple organ failure being treated by intermittent high volume haemofiltration (Gambro AK10 system) with lactate buffered replacement fluid PCO2 (Gambro haemofiltrasol). Cardiac output and oxygen delivery fell significantly during therapy but blood pressure was maintained by an increase in systemic vascular resistance as we have shown previously. Serious acid base derangements were not seen. Significant hyperlactataemia was present throughout haemofiltration as a result of the infusion of replacement fluid containing 45 mmol/l lactate. The only alterations in acid base status were transient falls in arterial bicarbonate and base excess at one hour.