C v O2 (and its components P v O2 and mixed venous oxygen saturation [Sv O2]) is decreased with decreases in CaO2 (ie, PaO2, SaO2 or hemoglobin), decreases in Q or increases in V O2. Note that an increase in V O2 with a proportional increase in Q does not affect C v O2. Also note that breathing 100% oxygen by persons with normal lung function does not affect C v O2 because increasing PaO2 affects CaO2 very little (ie, oxygen is very insoluble in blood and hemoglobin is nearly 100% saturated when breathing room air). In patients with abnormal lung function (eg, shunt), a decrease in Pv O2 may produce a decrease in PaO2.
Venous oximetry monitors S v O2 using a system incorporated into the pulmonary artery catheter (Figure 3). Light is reflected off red blood cells near the pulmonary artery catheter, and Sv O2 is determined as the ratio of transmitted to reflected light. Several commercial systems are available and differ in the number of reference wavelengths and detecting filaments. The clinical benefit of monitoring venous oximetry is unclear. This monitor is often not clinically useful due to imprecision in the measurement system and the nonspecific nature of Sv O2. Visit the best pharmacy giving you viagra professional canadian pharmacy and taking the best care of you.