Central venous oxygen saturation (ScvO2) is a useful therapeutic target in septic shock. ScvO2 is an indirect index of the balance between oxygen supply and demand, thus in critically ill patients a fall in ScvO2 reflects a decrease in tissue oxygenation. ScvO2 depends on arterial oxygen saturation, oxygen consumption, cardiac output and hemoglobin. The aim of the study was to evaluate events of tissue oxygenation impairment that could be unrecognized by simple blood gas analysis, by continuously monitoring ScvO2 and to establish whether peripheral oxygen saturation (SpO2), mean arterial pressure (MAP), heart rate (HR), and central venous pressure (CVP) could predict LowScvO2 events.


Ventilated critically ill patients requiring a central venous catheter (CVC) for clinical use were enrolled. Continuous ScvO2 monitoring was obtained by a fiberoptic sensor inserted in the CVC and recorded for 72 hours with SpO2, HR, MAP and CVP. LowScvO2 events were defined as ScvO2 < 65% maintained for at least 5 minutes.


Thirty-seven patients (24 males) were enrolled. The mean clinical characteristics at admission to intensive care were: age 59 ± 16 years, BMI 26.1 ± 4.5 kg/m2, SAPS II 40 ± 13 (on 33 patients), PaO2/FiO2 206 ± 79, MAP 80 ± 13 mmHg, HR 92 ± 21 bpm, CVP 12 ± 3 mmHg, Hb 10.6 ± 1.9 g/dl. Continuous monitoring analysis detected 147 LowScvO2 events in 15 patients; while central venous blood gas analysis identified only nine LowScvO2 events in eight patients (6%). Table 1 summarizes patients' variables according to three ScvO2 ranges. SpO2, HR, MAP and CVP were not correlated with LowScvO2 events. Most patients had long periods of ScvO2 > 75 (supranormal ScvO2).

Table 1 Patients' variables according to ScvO2 range


Continuous ScvO2 monitoring showed that most events of poor tissue oxygenation are relatively common, are not recognized by extemporary central venous blood gas analysis and are not mirrored by changes in SpO2, HR, MAP or CVP.