Intermittent vs Continuous Monitoring of ScvO2 in Sepsis

Discussion

The results of this study suggest that, when treating severe sepsis and septic shock, EGDT guided by intermittent monitoring of ScvO₂ is not inferior to continuous monitoring. Because we enrolled the patients with septic shock or sepsis with hypoperfusion consecutively, more patients with septic shock and lower MAP for initial 30 min were observed in the intermittent group. Although these differences could be associated with the faster transfer to ICU and the higher 6 h resuscitative fluid volume, the clinical outcomes did not differ significantly after intermittent compared with continuous monitoring of ScvO₂. To our knowledge, this is the first study to compare the efficacy of intermittent and continuous ScvO₂ monitoring in septic patients. The potential importance of these findings is suggested by a recent multicentre study performed by the SSC, which found that one-third of cases of sepsis originate in hospital wards and that patients with sepsis originating in the wards have a greater overall mortality rate compared with patients with sepsis originating in the emergency department or the ICU. The higher mortality of sepsis originate in wards and the importance of therapies given during first 6h extended the critical care skills beyond the ICU to all wards to ensure either timely ICU admission or support in the wards to avert ICU admissions. However, the application of the continuous monitoring of ScvO₂ is difficult in practice in patients whose sepsis originates in the general ward or emergency department because continuous monitoring requires critical care monitoring and a special central venous catheter, and is more expensive than intermittent monitoring.

To improve the outcomes of severe sepsis, the SSC recommends an international guideline-based performance programme comprising a 6 h resuscitation bundle and a 24 h management bundle. In the MOSAICS study, components of the resuscitation bundle (blood culture, broad spectrum antibiotics and central venous pressure ≥8 mm Hg) improved the survival of patients with severe sepsis. The same study also found that initial haemodynamic support with appropriate fluid treatment was important to the outcome of sepsis in Asian countries with resource limitations. ScvO₂ and lactic acid have been the key indicators used in the haemodynamic targets for quantitative resuscitation.

ScvO₂ as a surrogate for mixed venous oxygen saturation is related to the global oxygen supply-to-demand ratio in various clinical settings. Although the use of ScvO₂ to assess and manage patients is grounded in firm physiological principles, evidence is only now emerging that routine measurement of ScvO₂ affects or predicts the outcomes. The SSC Guidelines, endorse the elements of EGDT protocols, for resuscitation of septic shock patients. ScvO₂ is one of the core targets for EGDT in the treatment of septic shock. The shared elements in all of these protocols are as follows. First, resuscitation should be performed in a timely manner. Second, resuscitation must achieve a reasonable MAP so that a sufficient arterial pressure head is available to allow redistribution of the cardiac output to vital organs. Third, after these first goals have been achieved, the adequacy of oxygen delivery must be assessed. In many EGDT protocols, this need is addressed by measuring ScvO₂.

It is not clear whether central venous oxygen saturation must be measured continuously using a central venous oximetry catheter or whether intermittent measurements (eg, blood samples) suffice. The answer to this question depends on the clinical context. However, intermittent measurements increase workload, and can cause contamination of stopcocks and iatrogenic blood loss. In addition, the response time could be longer in intermittent monitoring, although the cost of equipment and laboratory tests would be lower than those for continuous monitoring. Therefore, reliable techniques for continuous monitoring of ScvO₂ are desirable. Continuous measurement may be helpful in a setting where clinically important minute-to-minute changes that would otherwise go undetected are possible. However, it is impossible to apply continuous measurement to all septic patients in Asian countries where medical resources and facilities are limited. In other settings where changes over a time span of hours need to be identified, intermittent measurements are often sufficient.

In our study, the amount of fluid resuscitation needed for the initial 6 h was greater in the intermittent group than in the continuous group. However, the EGDT goal achievement did not differ between the two groups.

The main limitation of our study is the relatively small number of patients, which gave limited statistical power and the heterogeneity of the two groups. Another important limitation of our study is that we could not validate the equality of all interventions given to both groups except for the ScvO₂ monitoring methods. It is likely that certain interventions such as fluid resuscitation of shock and appropriate antibiotic therapy are more important than others. In addition, our study was not blinded, which may have allowed unforeseen biases to influence the results. Finally, we cannot exclude that an education effect occurred as a result of our training of the nurses and physicians.

Our pilot study showed no difference in the achievement of the EGDT goals, patient outcomes and length of stay in patients with severe sepsis or septic shock between the intermittent and continuous monitoring groups of ScvO₂. A future, large randomised multicentre study is needed to confirm the clinical usefulness of intermittent ScvO₂ monitoring in other Asian countries.