Accuracy of continuous central venous oxygen saturation monitoring in patients undergoing cardiac surgery

Optimization of the target strategy of perioperative infusion therapy based on monitoring data of central hemodynamics in order to prevent complications

Enhanced Recovery After Surgery (ERAS) protocols are increasingly used in the perioperative period around the world. The concept of goal-directed fluid therapy (GDT) is a key element of the ERAS protocols. Inadequate perioperative infusion therapy can lead to a number of complications, including the development of an infectious process, namely surgical site infections, pneumonia, urinary tract infections. Optimal infusion therapy is difficult to achieve with standard parameters (e.g., heart rate, blood pressure, central venous pressure), so there are various methods of monitoring central hemodynamics - from invasive, minimally invasive to non-invasive. The latter are increasingly used in clinical practice. The current evidence base shows that perioperative management, specifically the use of GDT guided by real-time, continuous hemodynamic monitoring, helps clinicians maintain a patient's optimal fluid balance. The manuscript presents the analytical data, which describe the benefits and basic principles of perioperative targeted infusion therapy based on central hemodynamic parameters to reduce the risk of complications.

[Haemodynamic monitoring in sepsis and septic shock]

Cardiovascular disturbances associated with sepsis cause hypoperfusion situations, which will negatively impact these patients' prognosis. The aim of haemodynamic monitoring is to guide the detection and correction of this hypoperfusion, and assist in decision making in optimising oxygen transport to tissues, primarily by manipulating cardiac output. This review seeks to summarise the different parameters of haemodynamic monitoring, the objectives of resuscitation, the physiological parameters, and the tools available to us for appropriate cardiac output manipulation.

Accuracy, Precision, and Trending Ability of Perioperative Central Venous Oxygen Saturation Compared to Mixed Venous Oxygen Saturation in Unselected Cardiac Surgical Patients

OBJECTIVE

To determine whether central venous oxygen saturation (ScvO₂) measurements could be used interchangeably with mixed venous oxygen saturation (SvO₂) measurements in adult cardiac surgery patients.

DESIGN

A single-center prospective observational study.

SETTING

A university hospital.

PARTICIPANTS

Eighty-five adult patients undergoing cardiac surgery.

INTERVENTIONS

The study authors compared the oxygen saturations in 590 pairs of venous blood samples drawn from the pulmonary artery catheter (PAC) at three different time points during surgery and four different time points in the intensive care unit. They compared samples obtained from the distal pulmonary artery line (SvO₂) to those drawn from the proximal central venous line of the PAC (ScvO₂) with the Bland-Altman test and the four-quadrant method.

MEASUREMENTS AND MAIN RESULTS

The mean bias between SvO₂ and ScvO₂ was -1.9 (95% confidence interval [CI], -2.3 to -1.5) and the limits of agreement (LOA) were -11.5 to 7.6 (95% CI, -12.5 to -10.7 and 6.8-8.5, respectively). The percentage error (PE) was 13.2%. Based on the four-quadrant plot, only 50% of the measurement pairs were in agreement, indicating deficient trending ability.

CONCLUSION

ScvO₂ values showed acceptable accuracy as the mean bias was low. The precision was inadequate; although the PE was acceptable, the LOA were wide. Trending ability was inadequate. The authors cannot recommend the use of ScvO₂ values interchangeably with SvO₂ measurements in the management of adult cardiac surgery patients.

Do ScvO2 variations induced by passive leg raising predict fluid responsiveness? A prospective study

OBJECTIVE

The present study investigates whether ScvO2 variations induced by passive leg raising (PLR) are able to predict fluid responsiveness (FR) in mechanically ventilated patients.

DESIGN

A monocentric prospective clinical study.

SETTING

An intensive care division in a tertiary hospital.

PATIENTS

The inclusion criteria were elective postoperative cardiac surgery patients who were over 18 years old, deeply sedated, mechanically ventilated and needed volume expansion (VE). Fluid responders (R) were defined as patients who increased their left ventricular outflow tract velocity time integral (VTI) ≥15% after VE.

INTERVENTION

In patients included in this study, continuous ScvO2  monitoring (CeVOX device, Pulsion Medical Systems) and VTI (transthoracic echocardiography) were measured simultaneously before and during a PLR test and before and after VE (with 500 ml of saline).

MEASUREMENTS AND MAIN RESULTS

Thirty-three consecutive patients were included in this study. In 15 patients with a positive PLR test (increase in VTI ≥15%), ScvO2 increased during PLR by 9 ± 4%. In the 18 patients with a negative PLR test, ScvO2 did not significantly change during PLR. VE increased ScvO2 by 9 ± 6% and 2 ± 4% in responders and nonresponders, respectively. If ScvO2 increased by >4% during the PLR test, then a positive VTI response (≥15%) was diagnosed with a sensitivity of 93% (68-99%) and a specificity of 94% (63-99%) (Area under the receiver operating characteristic curve 0.92 ± 0.58, p < 0.05). Moreover, ScvO2 variations were able to distinguish responders to VE from nonresponders to VE with a sensitivity of 87% (68-99%) and a specificity of 89% (63-99%) (Area under the receiver operating characteristic curve 0.89 ± 0.07, p < 0.05).

CONCLUSIONS

ScvO2 variation induced by PLR is a reliable, minimally invasive parameter for predicting FR at the postoperative cardiac surgery bedside of mechanically ventilated, critically ill patients.

Accuracy and precision of ScvO2 measured with the CeVOX-device: A prospective study in patients with a wide variation of ScvO2-values

INTRODUCTION

Central-venous oxygen saturation (ScvO2) is a key parameter of hemodynamic monitoring and has been suggested as therapeutic goal for resuscitation. Several devices offer continuous monitoring features. The CeVOX-device (Pulsion Medical Systems) uses a fibre-optic probe inserted through a conventional central-venous catheter (CVC) to obtain continuous ScvO2.

OBJECTIVES

Since there is a lack of studies validating the CeVOX, we prospectively analyzed data from 24 patients with CeVOX-monitoring. To increase the yield of lower ScvO2-values, 12 patients were equipped with a femoral CVC.

METHODS

During the 8h study period ScvO2_CeVOX was documented immediately before withdrawal of blood to measure ScvO2 by blood gas analysis (ScvO2_BGA) 6min, 1h, 4h, 5h and 8h after the initial calibration. No further calibrations were performed.

RESULTS

In patients with jugular CVC (primary endpoint; 60 measurements), bias, lower and upper limits of agreement (LLOA; ULOA) and percentage error (PE) of the estimate of ScvO2 (ScvO2_CeVOX_jug) were acceptable with 0.45%, -13.0%, 13.9% and 16.6%, respectively. As supposed, ScvO2 was lower in the femoral compared to the jugular measurements (69.5±10.7 vs. 79.4±5.8%; p<0.001). While the bias (0.64%) was still acceptable, LLOA (-23.8%), ULOA (25.0%) and PE (34.5%) were substantially higher for femoral assessment of ScvO2 by the CeVOX (ScvO2_CeVOX_fem). Analysis of the entire data-pool with jugular as well as femoral CVCs allowed for a multivariate analysis which demonstrated that the position of the CVC per se was not independently associated with the bias ScvO2_CeVOX-ScvO2_BGA. The amount of the bias |ScvO2_CeVOX-ScvO2_BGA| was independently associated with the amount of the change of ScvO2_CeVOX compared to the initial calibration to ScvO2_BGA_baseline (|ScvO2_CeVOX-ScvO2_BGA_baseline|) as well as with low values of ScvO2_BGA_baseline. Furthermore, increasing time to the initial calibration was associated to the amount of the bias with borderline significance. A statistical model based on |ScvO2_CeVOX-ScvO2_BGA_baseline| and "time to last calibration" derived from an evaluation dataset (80 of 120 datasets, 16 of 24) provided a ROC-AUC of 0.903 to predict an amount of the bias |ScvO2_CeVOX-ScvO2_BGA| ≥5% in an independent validation group (40 datasets of 8 patients).

CONCLUSION

These findings suggest that the CeVOX device is capable to detect stability or instability of ScvO2_BGA. ScvO2_CeVOX accurately estimates ScvO2_BGA in case of stable values. However, intermittent measurement of ScvO2_BGA and re-calibration should be performed in case of substantial changes in ScvO2_CeVOX compared to baseline. Therefore, continuous measurement of ScvO2 with the CeVOX cannot replace ScvO2_BGA in instable patients. On the other hand, CeVOX might be useful for the monitoring of stable patients as a pre-test tool for more differentiated monitoring in case of changes in ScvO2_CeVOX.

Implications of the nutrition transition for vitamin D intake and status in Aboriginal groups in the Canadian Arctic

Aboriginal Canadians have low intakes of vitamin D and are shifting away from consumption of traditional foods. Higher body mass index, skin pigmentation, and geographic latitude of residence further predispose Canadian Aboriginal populations to low vitamin D status. Low vitamin D status could compromise bone health and other health outcomes. Studies assessing vitamin D status of different Aboriginal groups are limited. The aim of this review is to examine the literature on vitamin D status and intakes of Canadian Aboriginal populations living in the Arctic. PubMed was searched for relevant articles published from 1983 to 2013. The prevalence of 25-hydroxy vitamin D deficiency ranged from 13.9% to 76.0% among children and adults in the summer. Furthermore, mean vitamin D intakes among all age groups were below the estimated average requirement. As vitamin D deficiency has been recently associated with chronic diseases, and Aboriginal populations living in the Arctic are at high risk for low vitamin D status, their vitamin D status should be assessed regularly across seasons.

Prospective evaluation of regional oxygen saturation to estimate central venous saturation in sepsis

Current treatment guidelines for sepsis claim an early goal-directed hemodynamic optimization including fluid resuscitation, use of vasopressors and inotropic agents. We investigated the correlation between the prominent treatment goal central venous saturation (ScvO2) and the frontal and the thenar regional oxygen saturation (rSO2) measured by near infrared spectroscopy. Secondary, we examined the value of ScvO2, lactate levels and rSO2 as surrogate markers of an impaired tissue oxygenation for outcome prediction in sepsis. This prospective, observational study was performed at the surgical intensive care unit of the University Hospital Giessen. A total of 50 patients with sepsis, severe sepsis or septic shock were included. ScvO2, rSO2 and lactate were measured at sepsis diagnosis (baseline), 24 and 48 h, thereafter. We investigated the predictive value of frontal and thenar rSO2 for a decreased SvcO2 under 70%. For survivor and non-survivors ScvO2, rSO2 and lactate were analysed. Patients with ScvO2 >70% showed a trend to higher levels of fontal rSO2 (62.81 ± 8.06 vs. 53.54 ± 15.48; p = 0.058). ROC-analysis revealed a minor prediction of a decreased ScvO2 by frontal rSO2 levels at baseline (AUC = 0.687; 95% CI 0.511-0.863; p = 0.047). Combined measurements of lactate and ScvO2 showed significantly elevated mortality for patients with ScvO2 ≥70% and lactate levels ≥2.5 mmol/l (log rank test p = 0.004). In the group with ScvO2 <70% and lactate levels <2.5 mmol/l no patients died during the observation period. Frontal rSO2 correlates with ScvO2 but both frontal and thenar rSO2 do not exactly discriminate between patients with high or low ScvO2 in sepsis. The combination of elevated lactate >2.5 mmol/l and ScvO2 >70 % is highly associated with poor outcome in ICU patients with sepsis, severe sepsis and septic shock.

Use of central venous oxygen saturation to guide therapy

The use of pulmonary artery catheters has diminished, so that other technologies are emerging. Central venous oxygen saturation measurement (ScvO₂) as a surrogate for mixed venous oxygen saturation measurement (SvO₂) is simple and clinically accessible. To maximize the clinical utility of ScvO₂ (or SvO₂) measurement, it is useful to review what the measurement means in a physiologic context,how the measurement is made, important limitations, and how this measurement may be helpful in common clinical scenarios. Compared with cardiac output measurement, SvO₂ is more directly related to tissue oxygenation. Furthermore,when tissue oxygenation is a clinical concern, SvO₂ is less prone to error compared with cardiac output, where small measurement errors may lead to larger errors in interpreting adequacy of oxygen delivery. ScvO₂ should be measured from the tip of a central venous catheter placed close to, or within, the right atrium to reduce measurement error. Correct clinical interpretation of SvO₂, or its properly measured ScvO₂ surrogate, can be used to (1) estimate cardiac output using the Fick equation, (2) better understand whether a patient's oxygen delivery is adequate to meet their oxygen demands, (3) help guide clinical practice, particularly when resuscitating patients using validated early goal directed therapy treatment protocols, (4) understand and treat arterial hypoxemia, and (5) rapidly estimate shunt fraction (venous admixture).

In-vitro evaluation of the PediaSat continuous central venous oxygenation monitoring system

BACKGROUND AND OBJECTIVE

In-vitro performance of the PediaSat system for continuous monitoring of central venous oxygen saturation by spectrophotometry has been evaluated.

METHODS

PediaSat continuous fibre-optic oximetry catheters were inserted in a black testing chamber, connected with an extracorporeal circuit and filled with human whole blood. Oxygen inflow into the cardiopulmonary bypass system was varied, and the testing chamber was perfused with blood flow of 1000 ml min(-1). Oxygen saturation values measured by PediaSat (S PediaSat O2) were compared with cooximetry (S CO-OX O2) values from simultaneously taken blood samples by Bland-Altman and simple regression analyses.

RESULTS

Fifty data pairs were obtained. S PediaSat O2 and S CO-OX O2 values ranged between 28-98 and 24.9-99.5%, respectively. Correlation between S PediSat O2 and S CO-OX O2 was high with an r2 value equal to 0.96 (P < 0.0001). Overall, S PediaSat O2 only slightly overestimated S CO-OX O2 (mean bias +2.9%), and limits of agreement (+/-2 SD of bias) were acceptable (-6.8/+12.6%). Sensitivity and specificity of the first differences of S PediaSat O2 and S CO-OX O2 were 1.0 and 0.92, respectively. Subgroup analysis of S CO-OX O2 values below 70% resulted in an overestimation by S PediaSat O2, with a mean bias of +5.2% and limits of agreement of -4.7 and +15.1%.

CONCLUSION

The current version of the PediaSat system does not reliably reflect S CO-OX O2 values below 70%, but it seems to be a useful tool providing an accurate trend of continuous central venous oxygen saturation.