A modeling approach to systemic oxygenation monitoring.

Grooth, H.J.S. de (2013) A modeling approach to systemic oxygenation monitoring. thesis, Medicine.

Text GroothHJSde.pdf Restricted to Registered users only Download (1MB)

Abstract

Introduction: Oxygenation of peripheral tissues is often disturbed in the critically ill or high risk surgical patient. The purpose of this study was to use continuous intraoperative data on cardiac index (CI, cardiac output divided by body surface area), thenar tissue oxygen saturation (StO2) and central venous oxygen saturation (ScvO2) to examine the relationship between these three variables in the operative setting. Subsequently we introduce a method for the development of an index of global tissue oxygenation (IO) to approximate ScvO2 by combining CI and StO2 in a mathematical model. We then test the predictive value of this index for static and dynamic agreement with ScvO2. Methods: In a secondary analysis of a prospective randomized trial, we used continuous intraoperative data on CI, thenar tissue StO2 and ScvO2 from 33 patients undergoing high-risk major elective surgery. The relationship between CI, StO2 and ScvO2 was analyzed on a between- and within-patient basis using regression on group means and random-effects generalized least squares (GLS) regression in multiple univariate and multivariate models. The parameter coefficients of the model IO were estimated using a generalized estimating equation (GEE) modeling procedure. IO was subsequently tested for static and trending agreement with ScvO2 using Bland-Altman analysis and Four-Quadrant plots. Results: Using multivariate random-effects GLS regression we found that StO2 is not influenced by the same underlying hemodynamic variables as ScvO2. More specifically, StO2 is not associated with CI (coef. = -0.68, p = 0.299), while ScvO2 is strongly associated with CI (coef. = 2.85, p = 0.000). CI is a better predictor of within-patient ScvO2 than between-patient ScvO2 (R2-within = 0.18, R2-between = 0.03) while StO2 is a better predictor of between-patient ScvO2 than within-patient ScvO2 (R2-within = 0.02, R2-between = 0.10). CI and StO2 were combined in a single model and its coefficients were estimating using GEE. The resulting index IO is a better predictor of ScvO2 than either CI or StO2 alone (R2-within = 0.23, R2-between = 0.10). Bland-Altman limits of agreement between IO and ScvO2 were 15.99% to -16.39%. Four-Quadrant trend concordance was 70% and 82% for 5-minute and 60-minute trends, respectively. Conclusion: Contrary to the notion of StO2 as a flow dependent variable, we found no association between StO2 and CI. This casts doubt on the usability of StO2 as a standalone non-invasive marker of systemic oxygenation. As for predicting ScvO2, CI was found to be strongly associated with ScvO2 on a within-patient basis but lacks predictive power in explaining between-patient differences. StO2, in contrast, was significantly associated with between-patient ScvO2 differences but does not follow within-patient ScvO2 variability. We hypothesize that StO2 is a gauge of microcirculatory functioning more than a measure of systemic oxygen balance. A model Index of Oxygenation (IO) based on CI and StO2 was found to be a better predictor of ScvO2 than either of the two standalone variables. The index IO could be put to use in situations where the clinician needs to (continuously) monitor systemic oxygen balance without a central venous or pulmonary artery catheter. Before clinical implementation, however, the model coefficients need to be estimated on a broader and larger dataset and validated under different clinical and pathological situations.

Item Type:	Thesis (Thesis)
Supervisor name:	Scheeren, prof. dr. T.W.L. and Beest, dr. P.A. van
Faculty:	Medical Sciences
Date Deposited:	25 Jun 2020 10:53
Last Modified:	25 Jun 2020 10:53
URI:	https://umcg.studenttheses.ub.rug.nl/id/eprint/1432

Actions (login required)

View Item