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Serum lactate poorly predicts central venous oxygen saturation in critically ill patients: a retrospective cohort study.

ABSTRACT:

Background

Serum lactate and central venous oxygen saturation (ScvO₂) are commonly used and commonly recommended as markers of tissue oxygenation in shock states. Medical literature has both explicitly stated and implied that the two biomarkers are interchangeable in the management of patients with shock. However, there have been relatively few direct comparisons of these tests in clinical circumstances, and the relationship between them is uncertain. The objective of our study was to evaluate whether simultaneous or near-simultaneous measurements of lactate and ScvO₂ reveal a consistent relationship between these two biomarkers.

Methods

A retrospective cohort study was conducted in an urban, academic US hospital. All adults in ICUs between March 2007 and March 2017 who had a lactate measurement and ScvO₂ or mixed venous oxygen saturation (SvO₂) measurement made +/- 1 h from the lactate were included. Linear and non-linear correlations of ScvO₂ and lactate were assessed in a variety of shock states.

Results

Two thousand sixty-two patients were included. Lactate and ScvO₂ correlated poorly (r ² = 0.0041, p = 0.0019). This was true for patients with ScvO₂ ≤ 65% (r ² = 0.0431, p < 0.001), patients with normal kidney and liver function (r ² = 0.0517, p < 0.001), and septic shock patients (r ² = 0.0037, p = 0.17). For patients with an O₂ extraction ratio ≥ 50%, lactate and ScvO₂ were strongly correlated (r ² = 0.93, p = 0.0019), but these patients represented only 2.8% of patients in whom the ratio could be calculated.

Conclusions

Lactate can predict ScvO₂ when patients are at or below the critical oxygen delivery threshold, but relatively few shock patients meet this criterion. In the overall population of critically ill patients, serum lactate predicts ScvO₂ poorly, even after controlling for factors that may affect lactate production. Lactate and ScvO₂ should not be assumed to be interchangeable markers of tissue oxygenation/perfusion.

SUBMITTER: Bisarya R

PROVIDER: S-EPMC6728973 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundCentral venous oxygen saturation (ScvO2) is often used to help to guide resuscitation of critically ill patients. The standard gold technique for ScvO2 measurement is the co-oximetry (Co-oximetry_ScvO2), which is usually incorporated in most recent blood gas analyzers. However, in some hospitals, those machines are not available and only calculated ScvO2 (Calc_ScvO2) is provided. Therefore, we aimed to investigate the agreement between Co-oximetry_ScvO2 and Calc_ScvO2 in a general population of critically ill patients and septic shock patients.MethodsA total of 100 patients with a central venous catheter were included in the study. One hundred central venous blood samples were collected and analyzed using the same point-of-care blood gas analyzer, which provides both the calculated and measured ScvO2 values. Bland and Altman plot, intra-class correlation coefficient (ICC), and Cohen's Kappa coefficient were used to assess the agreement between Co-oximetry_ScvO2 and Calc_ScvO2. Multiple linear regression analysis was performed to investigate the independent explanatory variables of the difference between Co-oximetry_ScvO2 and Calc_ScvO2.ResultsIn all population, Bland and Altman's analysis showed poor agreement (+4.5 [-7.1, +16.1]%) between the two techniques. The ICC was 0.754 [(95% CI: 0.393-0.880), P< 0.001], and the Cohen's Kappa coefficient, after categorizing the two variables into two groups using a cutoff value of 70%, was 0.470 (P <0.001). In septic shock patients (49%), Bland and Altman's analysis also showed poor agreement (+5.6 [-6.7 to 17.8]%). The ICC was 0.720 [95% CI: 0.222-0.881], and the Cohen's Kappa coefficient was 0.501 (P <0.001). Four independent variables (PcvO2, Co-oximetry_ScvO2, venous pH, and Hb) were found to be associated with the difference between the measured and calculated ScvO2 (adjusted R2 = 0.8, P<0.001), with PcvO2 being the main independent explanatory variable because of its highest absolute standardized coefficient. The area under the receiver operator characteristic curves (AUC) of PcvO2 to predict Co-oximetry_ScvO2 ? 70% was 0.911 [95% CI: 0.837-0.959], in all patients, and 0.903 [95% CI: 0.784-0.969], in septic shock patients. The best cutoff value was ? 36 mmHg (sensitivity, 88%; specificity, 83%), in all patients, and ? 35 mmHg (sensitivity, 94%; specificity, 71%) in septic shock patients.ConclusionsThe discrepancy between the measured and calculated ScvO2 is clinically not acceptable. We do not recommend the use of calculated ScvO2 to guide resuscitation in critically ill patients. In situations where the Co-oximetry technique is not available, relying on PcvO2 to predict the measured ScvO2 value above or below 70% could be an option.

Project description:ContextGoal-directed resuscitation for severe sepsis and septic shock has been reported to reduce mortality when applied in the emergency department.ObjectiveTo test the hypothesis of noninferiority between lactate clearance and central venous oxygen saturation (ScvO2) as goals of early sepsis resuscitation.Design, setting, and patientsMulticenter randomized, noninferiority trial involving patients with severe sepsis and evidence of hypoperfusion or septic shock who were admitted to the emergency department from January 2007 to January 2009 at 1 of 3 participating US urban hospitals.InterventionsWe randomly assigned patients to 1 of 2 resuscitation protocols. The ScvO2 group was resuscitated to normalize central venous pressure, mean arterial pressure, and ScvO2 of at least 70%; and the lactate clearance group was resuscitated to normalize central venous pressure, mean arterial pressure, and lactate clearance of at least 10%. The study protocol was continued until all goals were achieved or for up to 6 hours. Clinicians who subsequently assumed the care of the patients were blinded to the treatment assignment.Main outcome measureThe primary outcome was absolute in-hospital mortality rate; the noninferiority threshold was set at Delta equal to -10%.ResultsOf the 300 patients enrolled, 150 were assigned to each group and patients were well matched by demographic, comorbidities, and physiological features. There were no differences in treatments administered during the initial 72 hours of hospitalization. Thirty-four patients (23%) in the ScvO2 group died while in the hospital (95% confidence interval [CI], 17%-30%) compared with 25 (17%; 95% CI, 11%-24%) in the lactate clearance group. This observed difference between mortality rates did not reach the predefined -10% threshold (intent-to-treat analysis: 95% CI for the 6% difference, -3% to 15%). There were no differences in treatment-related adverse events between the groups.ConclusionAmong patients with septic shock who were treated to normalize central venous and mean arterial pressure, additional management to normalize lactate clearance compared with management to normalize ScvO2 did not result in significantly different in-hospital mortality.Trial registrationclinicaltrials.gov Identifier: NCT00372502.