16: Continuous Venous Oxygen Saturation Monitoring

PROCEDURE 16


Continuous Venous Oxygen Saturation Monitoring





PREREQUISITE NURSING KNOWLEDGE




• Anatomy and physiology of the cardiopulmonary system should be understood.


• Physiologic principles related to invasive hemodynamic monitoring should be understood.


• Technical aspects of central line placement and pressure monitoring should be understood.


• Technical aspects of pulmonary artery (PA) pressure monitoring should be understood.


• Physiologic concepts of oxygen delivery, oxygen demand, and tissue oxygen consumption should be understood.


• The percent of venous oxygen saturation as measured in the PA (SVO2) is flow weighted and represents a true mixing of all venous blood: inferior vena cava (IVC), superior vena cava (SVC), and coronary sinus.


• Clinically, SVO2 provides an index of overall oxygen balance because it is a reflection of the dynamic relationship between the patient’s oxygen delivery (DO2) and oxygen consumption (VO2). Whenever a threat to the oxygen balance occurs, the body’s primary compensatory mechanisms are to increase oxygen delivery by increasing cardiac output or to increase oxygen extraction at the tissue level.


• In a critically ill patient, if cardiac output is limited, increased extraction occurs to meet the demand for oxygen at the tissue level. The result is a decreased level of oxygen returning to the heart and a lower SVO2 measurement. Many factors can affect the requirements for oxygen and subsequently SVO2 (Table 16-1).2,6,8,13



• SVO2 does not correlate directly with any of the determinants of oxygen delivery or oxygen consumption. Because a critically ill patient is in a dynamic state with rapidly changing oxygen demand and oxygen consumption, SVO2 must be viewed in the light of these changing determinants and considered an index of oxygen balance.1,2,6,8,13


• A normal SVO2 generally is considered to be 60% to 80%,2,8 and a clinically significant change in SVO2 (5% to 10%) can be an early indicator of physiologic instability.2,8 SVO2 values of less than 60% may result from either inadequate oxygen delivery or excess oxygen consumption. SVO2 monitoring is used in critically ill patients for earlier detection of oxygenation instability than that obtained through traditional PA monitoring.2,6,8,13


• The percent of venous oxygen saturation as measured in the superior vena cava (ScVO2) reflects the mixing of venous blood from the superior half of the body. It does not include blood from the IVC and coronary sinus. ScVO2, right atrium (RA), and SVO2 do not correlate absolutely. ScVO2 does trend with SVO2 in a variety of hemodynamic states. In normal conditions, ScVO2 is slightly less than the RA oxygen saturation and lower than SVO2. In septic or shock states, ScVO2 is higher than SVO2, with a difference that ranges from 5% to 7% and up to 18% in severe shock. This difference is in part because of a redistribution of blood flow caused by the various pathophysiologies. Therefore, ScVO2 overestimates SVO2 in shock conditions; a low ScVO2 likely indicates an even lower SVO2.4,911


• Small French size and shorter oximetry catheters have pediatric patient applications for assessment of venous saturation.9


• Some common proper setup and maintenance steps for the catheters and bedside computer or module are necessary for accurate monitoring of both ScVO2 and SVO2.


• Continuous venous saturation monitoring is performed with a three-component system (Fig. 16-1)2,57:

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Jun 4, 2016 | Posted by in CRITICAL CARE | Comments Off on 16: Continuous Venous Oxygen Saturation Monitoring

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