Gemischtvenöse versus zentralvenöse Sauerstoffsättigung in der Intensivmedizin

Should We Monitor ScVO(2) in Critically Ill Patients?

Hemodynamic monitoring has become a real challenge in the intensive care unit. As an integrative parameter for oxygen supply/demand, venous oxygen saturation (SvO₂) provided by pulmonary artery catheterization is one of the most popular parameters to assess the adequacy of cardiac output. However, technical limitations and potential iatrogenic complications constitute important limits for a widespread use. Regular central venous catheters coupled with a fiberoptic lumen for central venous oxygen saturation (ScvO₂) monitoring have been proposed as a surrogate for SvO₂ monitoring. The purpose of the present article is to review the physiological backgrounds of circulation, the pathophysiology of circulatory failure and subsequent venous oxygen saturation alterations, and finally the merits and the limits of the use of ScvO₂ in different clinical situations.

Femoral-based central venous oxygen saturation is not a reliable substitute for subclavian/internal jugular-based central venous oxygen saturation in patients who are critically ill

BACKGROUND

Central venous oxygen saturation (Scv(O(2))) has been used as a surrogate marker for mixed venous oxygen saturation (Sv(O(2))). Femoral venous oxygen saturation (Sfv(O(2))) is sometimes used as a substitute for Scv(O(2)). The purpose of this study is to test the hypothesis that these values can be used interchangeably in a population of patients who are critically ill.

METHODS

We conducted a survey to assess the frequency of femoral line insertion during the initial treatment of patients who are critically ill. Scv(O(2)) vs Sfv(O(2)) STUDY: Patients with femoral and nonfemoral central venous catheters (CVCs) were included in this prospective study. Two sets of paired blood samples were drawn simultaneously from the femoral and nonfemoral CVCs. Blood samples were analyzed for oxygen saturation and lactate.

RESULTS

One hundred and fifty physicians responded to the survey. More than one-third of the physicians insert a femoral line at least 10% of the time during the initial treatment of patients who were critically ill. Scv(O(2)) vs Sfv(O(2)) STUDY: Thirty-nine patients were enrolled. The mean Scv(O(2)) and Sfv(O(2)) were 73.1% +/- 11.6% and 69.1% +/- 12.9%, respectively (P = .002), with a mean bias of 4.0% +/- 11.2% (95% limits of agreement: -18.4% to 26.4%). The mean serum lactate from the nonfemoral and femoral CVCs was 2.84 +/- 4.0 and 2.72 +/- 3.2, respectively (P = .15).

CONCLUSIONS

This study revealed a significant difference between paired samples of Scv(O(2)) and Sfv(O(2)). More than 50% of Scv(O(2)) and Sfv(O(2)) values diverged by > 5%. Sfv(O(2)) is not always a reliable substitute for Scv(O(2)) and should not routinely be used in protocols to help guide resuscitation.

[Venous oximetry: physiology and therapeutic implications]

OBJECTIVES

The aims of this review are to point out the determinants of oxygen saturation of the haemoglobin of mixed venous blood (SvO(2)), to specify the correlations existing between SvO(2) and central venous saturation in superior vena cava (ScvO(2)), to determine and finally to locate the current place of venous oximetry in clinical practice.

DATA SOURCES

A PubMed database research in English and French languages published until December 2006. The keywords were mixed venous blood oxygen saturation; oxygen consumption; oxygen delivery; oxygen extraction; tissue hypoxia; central venous oxygen saturation.

DATA EXTRACTION

Data in selected articles were reviewed, clinical and basic science research relevant information was extracted.

DATA SYNTHESIS

The SvO(2) reflects the peripheral extraction of oxygen (O(2)), O(2) delivery and consumption. Its value is related to four determinants: the O(2) consumption (VO(2)), cardiac flow (CF), haemoglobin level (Hb) and O(2) saturation of the haemoglobin of arterial blood (SaO(2)). ScvO(2) is more easily measurable than SvO(2). Under physiological conditions its value is 2 to 3% lower than that of SvO(2). In the critically ill patient, its value is 5% higher than that SvO(2). In most patients, changes in ScvO(2) values parallel those in SvO(2). The clinical interest of the monitoring of venous oximetry was underlined in cases of severe sepsis and septic shock, and during the perioperative period of major surgery.

CONCLUSION

The management of patients in critical states with therapeutic goals integrating the monitoring of venous oximetry may reduce the morbidity and mortality of patients undergoing major surgery or hospitalised in the intensive care unit.

Central venous oxygen saturation monitoring in the critically ill patient

In the initial treatment of a critically ill patient, blood pressure, heart rate, urine output, and central venous pressure guide resuscitative efforts. Despite normalization of these variables, global tissue hypoxia may still persist and has been implicated in the development of multiorgan failure and increased mortality. Definitive management includes intensive care unit admission, pulmonary artery catheterization using mixed venous oxygen saturation (SvO2), and hemodynamic optimization. In the absence of or before definitive management, hemodynamic optimization can be performed using central venous oxygen saturation (ScvO2) as a surrogate. The physiology, technology, clinical uses, and rationale for ScvO2 monitoring are reviewed, including issues regarding physiologic equivalence to SvO2. The clinical use of ScvO2 monitoring, evidence-based outcome implications, and limitations of ScvO2 monitoring will also be examined.

Central venous versus mixed venous oxygen content

Mixed venous oxygen content (commonly measured as oxygen saturation) is a highly relevant parameter in the monitoring of critically ill patients; unfortunately, its measurement requires catheterization of the pulmonary artery. Though less invasive, the central venous oxygen saturation is an unsatisfactory substitute, due to fluctuations in perfusion distribution and regional oxygen extraction in the course of illness. The present study examined the relation of oxygen contents in simultaneously withdrawn central venous and mixed venous blood samples from critically ill patients, in order to validate a hypothetical algorithm for the estimation of mixed venous oxygen content from a central venous sample: Although the proposed algorithm had a fairly high power of prediction, its merits in comparison to assuming simple proportionality between central venous and mixed venous oxygen content seemed marginal. However, as it is likely that the results so far are mathematically coupled, further prospective studies are necessary.