Each hemoglobin molecule can carry 4 oxygen molecules. Normal value of SvO2 is 60% to 80%. If a subclavian catheter is used for this measure it is called ScvO2 and those normal values are 65% to 85%. For example, theorize that a normal person's blood was 100% saturated with oxygen at the start of its journey to the tissues after ejection from the heart. When the blood returns to the heart and we measure SvO2, our result is 75%. This means that the blood is still 75% saturated with oxygen and only 25% of the oxygen was utilized or needed while on the journey (or ¾ of the oxygen was utilized). Remember this is a normal person without any pathology. A good point to remember here is that venous blood is still saturated with oxygen. If someone had a sudden cardiac event that caused them to arrest, chest compressions are essential to get that oxygen to vital tissues. If a person is ill, we can expect variation in the SvO2 results.
• Oxygen demands are determined by the metabolic needs of the tissues
• Oxygen is extracted from the hemoglobin and used by the tissues.
• Normal SvO2 is 60% to 80%
• Normal ScvO2 is 65% to 85%
• Values vary slightly because of positioning of the different devices
SvO2 is oxygen saturation measured from a blood sample drawn from distal port of pulmonary artery catheter.
ScvO2 is oxygen saturation measured from a blood sample drawn from a central line placed in the subclavian or jugular vein.
Measures the end result of oxygen delivery and consumption at the tissue level.
• If at rest, SvO2 is measured at 75%, only 25% was extracted by the tissues. The remainder of O2 in the blood was returned to the heart unused by the tissues
• If at rest, SvO2 is measured at 95%. This indicates that the tissues are unable to extract oxygen from the blood and is a very grave sign
Since SvO2 is not routinely measured, one can make some assumptions about SvO2 by remembering the four variables.
1.Cardiac output: an effective pump is how oxygenated blood is delivered to the tissues. If cardiac output is decreased, oxygen delivery will be decreased. Cardiac output should be optimized using medications or fluids as indicated.
2.Oxygenation: the lungs supply the oxygen for the blood. If there are issues such as atelectasis, pneumonia, COPD, pulmonary embolism or other lung conditions, oxygen may not be present for the hemoglobin to carry. Vigorous pulmonary hygiene is essential after all surgery with coughing and deep breathing, incentive spirometers, and activity out of bed.
3. Hemoglobin: carries the oxygen. If the patient is bleeding or anemic, oxygen carrying capacity is reduced. The patient may need blood transfusion.
4. Oxygen consumption (workload): if the workload or demands increase, oxygenation will decrease. Fever, shivering, agitation, and pain are conditions that increase workload.
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Date last modified: January 7, 2013.
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