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Danielle L. Davison, MD; Lakhmir S. Chawla, MD; Michael G. Seneff, MD, FCCP
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From the George Washington University Medical Center, Department of Anesthesiology and Critical Care Medicine.

Correspondence to: Lakhmir S. Chawla, MD, Department of Anesthesiology and Critical Care Medicine, The George Washington University Medical Center, G-105, 901 23rd St NW, Washington DC 20037; e-mail: minkchawla@gmail.com


Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Dr Seneff receives consultant fees from Pfizer. Drs Davison and Chawla have reported that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2011 American College of Chest Physicians


Chest. 2011;139(6):1547. doi:10.1378/chest.11-0467
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To the Editor:

We thank Drs El-Rassi and Yazigi for their thoughtful comments regarding femoral-based central venous oxygen saturation (Svo2) and its potential use as a surrogate marker for central Svo2 to help guide resuscitation. Drs El-Rassi and Yazigi point out that the absolute margin of difference between central Svo2 and femoral Svo2 reported in our study1 is small (73.1% ±11.6% vs 69.1% ±12.9%, respectively; P = .002). Although the absolute difference is small, when considering the SD (SD ±11.6%) and large limits of agreement (18.4%-26.4%), the range of discrepancy is significant and clinically relevant.

As stated in our article, according to these findings, a central Svo2 of 70% corresponds to a femoral Svo2 range of 58.8% to 81.2%. A value of 58.8% would prompt the physician to optimize oxygen delivery by means of volume resuscitation, blood transfusion, or the initiation of inotropic agents. Yet, a value of 81.2% alone would not generate the same intervention. Thus, we believe that the femoral Svo2 cannot reliably be used to make clinical decisions or guide resuscitation. Svo2 values differ among organ systems because each organ extracts variable amounts of oxygen, particularly in states of physiologic stress. Absolute values of venous oxygenation, therefore, depend greatly on the site of measurement. It has been well established that the mixed Svo2 value obtained from the distal port of a pulmonary artery catheter reflects the venous return from both the upper and lower portions of the body and, therefore, is a marker of global tissue hypoxia.2 However, it is important to note that the standard femoral venous catheters are 20 cm in length. In the average-sized adult, the tip, and hence the venous sampling, is within the iliac vein and not in the inferior vena cava. Thus, Svo2 from the intraabdominal organs, including the liver, kidney, and splanchnic regions, is not necessarily sampled. A low femoral Svo2, therefore, may not necessarily reflect a redistribution of blood flow to indicate that global tissue hypoperfusion is present.

Future studies examining trends of femoral Svo2, particularly in patients in the early stages of shock, may produce more promising results, and we intend to conduct the same study in patients with shock. Based on our current study, we believe that femoral Svo2 cannot be used to reliably guide resuscitation. The topic of differences in regional blood flow and oxygen delivery is an interesting one and deserves further evaluation.

Davison DL, Chawla LS, Selassie L, et al. 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. Chest. 2010;1381:76-83. [CrossRef] [PubMed]
 
Kandel G, Aberman A. Mixed venous oxygen saturation. Its role in the assessment of the critically ill patient. Arch Intern Med. 1983;1437:1400-1402. [CrossRef] [PubMed]
 

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Davison DL, Chawla LS, Selassie L, et al. 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. Chest. 2010;1381:76-83. [CrossRef] [PubMed]
 
Kandel G, Aberman A. Mixed venous oxygen saturation. Its role in the assessment of the critically ill patient. Arch Intern Med. 1983;1437:1400-1402. [CrossRef] [PubMed]
 
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