Archived Comments for:
Impact of emergency intubation on central venous oxygen saturation in critically ill patients: a multicenter observational study
Possible explainations for a rise in ScvO2 following intubation
Paul Dean, East Lancashire Hospitals NHS Trust, Blackburn, UK
22 May 2009
Dear Sir
I read with interest Hernandez et al study into the effect on intubation on ScvO2. As they point out there remains some concern regarding the usefulness of ScvO2. They clearly demonstrate a statistical improvement in ScvO2 following intubation. The authors also report a statistically significant improvement in SaO2 following intubation. They claim the increase seen in ScvO2 is greater than that seen in SaO2. If we look at the oxygen dissociation curve, the ScvO2 values are situated on the steep part of the curve in comparison to the values of SaO2. A small increase in the partial pressure of oxygen will therefore produce a greater effect on ScvO2. At intubation 31 patients required vasopressor support; ephedrine or increases in norepinepherine. This would have followed a fluid bolus according to protocol design. The authors fail to mention whether they believe this has an impact on cardiac output and therefore improved ScvO2. Fluids and inotropes are recommended in the surviving sepsis campaign in those patients with a low ScvO2 in an attempt to improve its value. Interestingly the group who were excluded due to a delay in sampling, all failed to show any improvement in ScvO2, suggesting that the impact of intubation may be short lived, further supporting the premise that the processes around intubation rather than intubation may improve ScvO2. A further explanation for an improvement in ScvO2 may be the vasodilatory effect of induction of anaesthesia, this is difficult to isolate from intubation. In many patients, there is an increase in cardiac output during intubation as a consequence of sympathetic stimulation, could this alone account for the improved ScvO2?
This paper is interesting in that it generates many questions regarding the effect of induction of anaesthesia and intubation. Like the authors I would be sceptical in using intubation as a tool to improve ScvO2 especially as we are still debating its validity as a tool to direct resuscitation.
Critical Care
Possible explainations for a rise in ScvO2 following intubation
22 May 2009
Dear Sir
I read with interest Hernandez et al study into the effect on intubation on ScvO2. As they point out there remains some concern regarding the usefulness of ScvO2. They clearly demonstrate a statistical improvement in ScvO2 following intubation.
The authors also report a statistically significant improvement in SaO2 following intubation. They claim the increase seen in ScvO2 is greater than that seen in SaO2. If we look at the oxygen dissociation curve, the ScvO2 values are situated on the steep part of the curve in comparison to the values of SaO2. A small increase in the partial pressure of oxygen will therefore produce a greater effect on ScvO2.
At intubation 31 patients required vasopressor support; ephedrine or increases in norepinepherine. This would have followed a fluid bolus according to protocol design. The authors fail to mention whether they believe this has an impact on cardiac output and therefore improved ScvO2. Fluids and inotropes are recommended in the surviving sepsis campaign in those patients with a low ScvO2 in an attempt to improve its value.
Interestingly the group who were excluded due to a delay in sampling, all failed to show any improvement in ScvO2, suggesting that the impact of intubation may be short lived, further supporting the premise that the processes around intubation rather than intubation may improve ScvO2.
A further explanation for an improvement in ScvO2 may be the vasodilatory effect of induction of anaesthesia, this is difficult to isolate from intubation.
In many patients, there is an increase in cardiac output during intubation as a consequence of sympathetic stimulation, could this alone account for the improved ScvO2?
This paper is interesting in that it generates many questions regarding the effect of induction of anaesthesia and intubation. Like the authors I would be sceptical in using intubation as a tool to improve ScvO2 especially as we are still debating its validity as a tool to direct resuscitation.
Competing interests
I have no competing interests