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Effect of inspired oxygen concentration on central venous oxygen saturation


A recent study has fuelled interest in the use of central venous oxygen saturation (SCVO2) as a target for resuscitation in early sepsis [1]. There has been no published study examining the effect of inspired oxygen concentration (FiO2) on SCVO2. We performed a study to examine the effect of increasing FiO2 on SCVO2.


We studied 20 stable critical care patients who had arterial and central venous lines in situ and who were not due to undergo any events that would affect their oxygen consumption or delivery. After consent was obtained, basal arterial and central venous gases were obtained. Their FiO2 was then increased to 1.0. After 30 min further arterial and central venous gases were taken and the patient's FiO2 was returned to baseline.


The mean baseline FiO2 was 0.35. The mean SaO2 increased from 97.5% (SD 1.6) to 99.5% (SD 0.6), mean increase 2% (95% CI 1.3–2.6, P < 0.001 [paired t test]). The mean SCVO2 increased significantly from 73.3% (SD 6.6) to 80.0% (SD 7.0), mean increase was 6.7% (95% CI 4.8–8.7, P < 0.001 [paired t test]).


This study has two implications. First, SCVO2 should be interpreted with knowledge of FiO2. Patients receiving high inspired oxygen concentrations may have elevated SCVO2 values leading to false reassurance. Second, in early resuscitation many of our strategies are aimed at increasing tissue oxygen delivery. We measure SCVO2 as a marker of oxygen extraction and thereby oxygen delivery. Our study showed that SCVO2 can be significantly increased by increasing FiO2, which implies better tissue oxygen delivery. Other investigators have shown that increasing FiO2 can increase tissue oxygen delivery in surgical patients [2] and in patients with traumatic brain injury [3]. It is possible that increasing FiO2 during the resuscitation of patients with sepsis may improve tissue oxygen delivery while other resuscitation is ongoing.


Increasing FiO2 significantly increased SCVO2 in our study.


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White, N., Jee, R. Effect of inspired oxygen concentration on central venous oxygen saturation. Crit Care 10 (Suppl 1), P237 (2006).

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