The Expanding Clinical Need for Venous Oximetry Monitoring
Venous oxygen saturation monitoring plays a significant role in the management of a wide range of patient populations, helping clinicians proactively manage patients prior to hemodynamic crisis rather than react to late indicators of instability.1 It has been clearly linked with improving outcomes in patients experiencing decreased cardiac output due to myocardial infarction, cardiac surgery, trauma or hemorrhagic shock, high-risk surgeries, and respiratory failure, in addition to its long-time association with early goal-directed therapy (EGDT) for sepsis identification and management (see Table 1).2,3,4,5,6,7
Accurate venous oximetry is key to understanding a patient’s true oxygenation status. Other objective measures used to assess the perfusion of organs and tissues—like mean arterial pressure, heart rate, urine output, and arterial oxygen saturation (SaO2 or SpO2)—can be normal in the presence of global tissue hypoxia and cannot rule out imbalances between oxygen supply and demand.1
Who Benefits from Continuous Venous Oximetry Monitoring?
Hemodynamic monitoring helps clinicians ensure adequate tissue perfusion and oxygenation. In the presence of critical illness or injury, the heart’s ability to respond may be limited. As a result, depleted tissue will draw oxygen from the venous oxygen reserve, which can lead to lactic acidosis and global tissue hypoxia.
In recent years, survival rates for acute myocardial infarction, trauma, stroke, and sepsis have improved through early identification of tissue oxygen imbalance using hemodynamic monitoring and tissue perfusion therapy. Early initiation of hemodynamic resuscitation has also been shown to improve mortality rates.8
SvO2 vs. ScvO2: What to Monitor?
Venous oxygenation measurements taken at the pulmonary artery are called mixed venous oxygen saturation, or SvO2, while measurements taken at the superior vena cava are called central venous oxygen saturation, or ScvO2.
When a patient is unable to generate cardiac output sufficient to meet the metabolic needs of the tissue, the tissue extracts greater amounts of oxygen, leaving less oxygen present in the venous blood. This is reflected as a decreasing SvO2 or ScvO2 level.
Conversely, when tissue does not extract the oxygen, both SvO2 and ScvO2 levels rise. Various studies have shown that there can be slight differences between ScvO2 and SvO2 values—with either measurement reading 5-6% higher or lower than the other based on patient acuity.9,10,11,12 However, the two have been shown to maintain a high correlation (see Figure 1).9 As a result, ScvO2 is accepted as an appropriate surrogate for SvO2.
Choosing the Most Accurate Venous Oximetry Technology
Venous oxygen saturation is measured using reflectance spectrophotometry, in which either two or three wavelengths of light are transmitted down a fiber optic filament in a catheter to the blood flowing past the catheter tip.
The current body of literature suggests multiple advantages of three-wavelength technology (TriOx®, ICU Medical, Inc. San Clemente, CA) over two-wavelength systems, including improved accuracy and the elimination of the need for routine calibration (see Figure 2). 14,15
The Move towards Less Invasive Venous Oximetry
Peripherally inserted central venous catheters (PICCs) have been safely used for many years to access the central venous circulation to administer fluids and facilitate blood draws. Because PICCs access the central venous circulation at the superior vena cava, they provide a less invasive avenue for venous oximetry.
Using a PICC avoids the complications associated with the direct neck puncture of the central venous circulation system with a CVC.16,17,18 and has been shown to have lower catheter-related bloodstream infection (CRBSI)19 and support a longer period of use.20
Because they can be inserted by trained nurses outside the operating room, PICCs reduce cost and decrease treatment delays common in busy operating or intensive care units,21 making them a more convenient, efficient, and cost-effective method to access ScvO2 levels.
The only PICC line with oximetry monitoring is the TriOx-PICC minimally invasive oximetry sensor (ICU Medical Inc., San Clemente CA), which uses three-wavelength oximetry technology to filter noise and artifact caused by cell orientation, vessel wall reflections, and changes in pH.
Venous oximetry has been established as a valuable method to monitor and maintain adequate tissue oxygenation and avoid hemodynamic crisis in critically ill and at-risk patients. ScvO2 has been shown to be a surrogate measurement for SvO2, reducing the reliance on invasive pulmonary artery catheterization. Its broad utility has been demonstrated across a variety of conditions—from cardiac care to trauma, respiratory failure and high-risk surgery—in addition to its origins in the treatment of sepsis.
The technology used to obtain venous oximetry measurements has evolved from pulmonary artery catheterization to less invasive central venous catheterization, with the goal of increasing patient safety, reducing costs, and minimizing procedure time. As the industry continues to migrate toward less invasive and more cost-effective patient monitoring trends, PICC line oximetry will continue to be a viable and efficient method for monitoring ScvO2.
- Hamilton MA, Cecconi M, Rhodes A. A Systematic Review and Meta-Analysis on the Use of Preemptive Hemodynamic Intervention to Improve Postoperative Outcomes in Moderate and High-Risk Surgical Patients. Anesth Analg 2011;112:1392–402.
- Astiz ME, Rackow EC, Kaufman B, Falk JL, Weil MH. Relationship of oxygen delivery and mixed venous oxygenation to lactic acidosis in patients with sepsis and acute myocardial infarction. Crit Care Med 1988, 16:655-658.
- Ander DS, Jaggi M, Rivers E, Rady MY, Levine TB, Levine AB, Masura J, Gryzbowski M. Undetected cardiogenic shock in patients with congestive heart failure presenting to the emergency department. Am J Cardiol 1998, 82:888-891.
- Scalea TM, Hartnett RW, Duncan AO, Atweh NA, Phillips TF, Sclafani SJ, Fuortes M, Shaftan GW. Central venous oxygen saturation: a useful clinical tool in trauma patients. J Trauma 1990, 30:1539-1543.
- Rady MY, Rivers EP, Martin GB, Smithline H, Appelton T, Nowak RM. Continuous central venous oximetry and shock index in the emergency department: use in the evaluation of clinical shock. Am J Emerg Med 1992, 10:538-541.
- Nakazawa K, Hikawa Y, Saitoh Y, et al. Usefulness of central venous oxygen saturation monitoring during cardiopulmonary resuscitation: a comparative case study with end-tidal carbon dioxide monitoring. Intensive Care Med. 1994; 20:450-451.
- Shoemaker WC, Appel PL, Kram HB. Role of oxygen debt in the development of organ failure sepsis, and death in high risk surgical patients. Chest 1992; 102:208–215
- Otero RM, Nguyen HB, Huang DT, et al. Early goal-directed therapy in severe sepsis and septic shock revisited: concepts, controversies, and contemporary findings. Chest 2006; 130(5):1579–95.
- Reinhart K, Rudolph T, Bredle D, et al. Comparison of Central-Venous to Mixed-Venous Oxygen Saturation During Changes in Oxygen Supply/Demand. Chest. 1989 Jun; 95(6):1216-1221.
- Shahbazi S, Khademi S, Shafa M, et al. Serum Lactate Is Not Correlated with Mixed or Central Venous Oxygen Saturation for Detecting Tissue Hypo Perfusion During Coronary Artery Bypass Graft Surgery: A Prospective Observational Study. Int Cardiovasc Res J.2013;7(4):130-134.
- Reinhart K, Huhn HJ, Hartog C, et al. Continuous central venous and pulmonary artery oxygen saturation monitoring in the critically ill. Intensive Care Med. 2004;30:1572-1578.
- Squara P. Central venous oxygenation: when physiology explains apparent discrepancies. Critical Care 2014, 18:579.
- Krafft P, Steltzer H, Hiesmayr M, Klimscha W, Hammerle AF.
- Mixed venous oxygen saturation in critically ill septic shock patients. The role of defined events. Chest 1993, 103:900-906.
- Rouby JJ, Poète P, Bodin L, Bourgeois JL, Arthaud M, Viars P. Three mixed venous saturation catheters in patients with circulatory shock and respiratory failure. Chest. 1990 Oct;98(4):954-8.
- Martin WE, Cheung PW, Johnson CC, Wong KC. Continuous monitoring of mixed venous oxygen saturation in man. Anesth Analg 1973; 52:784-93
- Maki DG, Kluger DM, Crnich CJ. The risk of bloodstream infection in adults with different intravascular devices: A systematic review of 200 published prospective studies. Mayo Clin Proc 2006; 81: 1159 – 71.
- O’Grady NP, Alexander M, Dellinger EP, et al. Guidelines for the prevention of intravascular catheter-related infections. MMWR Recomm Rep. 2002; 51(RR-10):1-29.
- Skiest DJ, Abbott M, Keiser P. Peripherally inserted central catheters in patients with AIDS are associated with a low infection rate. Clin Infect Diseases. 2000; 30:949-952.
- Carrico R, ed. APIC Text of Infection Control and Epidemiology, 2nd ed. Washington, DC: Association for Professionals in Infection Control and Epidemiology; 2005.
- Johansson E, Hammarskjöld F, Lundberg D, Arnlind MH. Advantages and disadvantages of peripherally inserted central venous catheters (PICC) compared to other central venous lines: a systematic review of the literature. Acta Oncol. 2013 Jun; 52(5):886-92.
- Oakley C, Wright E, Ream E. The experiences of patients and nurses with a nurse-led peripherally inserted central venous catheter line service. Eur J Oncol Nurs 2000; 4: 207 – 18.