Prostacyclin in Septic Shock: Discussion

Prostacyclin in Septic Shock: DiscussionWe believe that the higher baseline levels of D02 in our patients are at least in part responsible for the differences in V02 with prostacyclin infusion between the present study and the previous ones. It has been demonstrated that supranormal levels of D02 improved survival rate in a variety of critically ill patients, possibly by improvement of tissue oxygenation A supranormal D02 does not guarantee a concomitant increase in V02 or higher survival rate 2 which may explain our high mortality rate, 87 percent. At our D02 levels closer to 800 ml/min/m2, near the value found by Mohsenifar et al to be needed for the V02 to become independent of D02 in ARDS, we found neither the substantial increase in V02 nor the increase in O2 extraction that Bihari et al reported from a much lower baseline D02 of 375 (nonsurvivors) or 420 ml/min/m2 (survivors). A “pathological” O2 supply dependency at suboptimal
O2 deliveries has been shown after other therapies such as volume loading and inotropes.’ The initial D02 in the present study was about 22 percent higher than in the study of Pittet et al and 15 percent higher than in the study of Radermacher et al. In using PGI2 as an “O2 flux” test, the pattern which appears to be emerging is that the greater the initial D02 the less the effect of PGI2 on V02. Prostacyclin did not predict mortality by O2 supply dependency. Health and care mall add comment The only evidence we saw for an increase in V02 (7 percent by the indirect Fick method) still fell below the value of about 10 percent established by a recent consensus conference as the threshold for clinically relevant improvement in V02. Two possible conclusions from the present findings are (1) a covert whole-body O2 debt did not exist in these patients, perhaps due to the aggressive resuscitation, or (2) if an O2 debt persisted at these high D02 levels, PGI2 did not have a detectable effect on global O2 uptake. The first concept is supported by the fact that 11 of the 15 patients had normal blood lactate levels, and in the remaining 4 it was only slightly elevated. High arterial blood lactate concentration is a marker of tissue anaerobiosis and has been correlated with systemic oxygen debt. In most of the shock studies in which abnormal O2 supply dependency has been demonstrated, blood lactate levels were markedly elevated. The patients in our study with moderately elevated lactate levels, if anything, had slightly smaller increase in D02 after PGI2 infusion compared with the patients with normal lactate levels.

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