Lactate Levels as Predictors of the Relationship between Oxygen Delivery and Consumption in ARDS: Discussion (2)


19 Jan 2013

Lactate Levels as Predictors of the Relationship between Oxygen Delivery and Consumption in ARDS: Discussion (2)In several studies of patients with ARDS, a much greater proportion of patients exhibited supply-dependent behavior when compared to the proportion in our study; for example, more than 90 percent of the patients studied by Danek et al and by Powers et al exhibited changes in Vo2 that corresponded to changes in Do2; in our population, only 54 percent (14) of the patients in the normal lactate group and 81 percent (26) of the patients in the increased lactate group exhibited these changes. We speculate on the mechanism for these differences. Danek et al and Powers et al may have included groups of patients with more advanced ARDS or underlying sepsis, patients more likely to exhibit a supply-dependent response or to develop signs of an oxygen debt; however, lactate levels or other markers of oxygen debt were not reported in these studies. We speculate that the use of PEEP to manipulate Do2 may have accounted in part for the findings reported in these studies; PEEP may be an intervention that is more frequently characterized by a supply-dependent Vo2 response than the other interventions used in our study. buy ampicillin

Implementation of PEEP may, for example, independently change systemic oxygen demands, resulting in a change in Vo2 coincident to but not directly related to the resultant change in Do2; for example, PEEP-induced hemodynamic changes may result in increased cardiac work and increased myocardial oxygen consumption. Positive end-expiratory pressure has been shown to alter the distribution of systemic perfusion, which could lead to regional supply dependency; however, by separately analyzing patients in our series who received an increase in PEEP, we continued to find that a substantial proportion nevertheless demonstrated supply-independent behavior. Subsets of these patients with and without lactic acidosis continued to exhibit contrasting patterns of oxygen utilization.

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