Mixed venous O2 saturation and fluid responsiveness after cardiac or major vascular surgery

Arjan N Kuiper,Ronald J Trof,Ab Johan Groeneveld

doi:10.1186/1749-8090-8-189

Abstract

BackgroundIt is unclear if and how SvO2 can serve as an indicator of fluid responsiveness in patients after cardiac or major vascular surgery.MethodsThis was a substudy of a randomized single-blinded clinical trial reported earlier on critically ill patients with clinical hypovolemia after cardiac or major vascular surgery. Colloid fluid loading was done for 90 min, guided by changes in pulmonary artery occlusion pressure (PAOP) or central venous pressure (CVP). Fluid responsiveness was defined as ≥15% increase in cardiac index (CI). Hemodynamics, including transpulmonary dilution-derived global end-diastolic volume index (GEDVI) and global ejection fraction (GEF), were measured and blood samples taken.ResultsWhereas baseline SvO2 (>70% in 68% of patients) did not differ, the SvO2 increased in patients responding to fluid loading (≥15% in CI in n = 26) versus those not responding (n = 11; P = 0.03). The increase in GEDVI was also greater in responders (P = 0.005). The area under the receiver operating characteristic curve for fluid responsiveness of changes in SvO2 was 0.73 (P = 0.007), with an optimal cutoff of 2%, and of those in GEDVI 0.82 (P < 0.001), while the areas did not differ. However, the value of SvO2 increases to reflect CI increases with fluid loading was greatest when GEF was ≤20% (in 53% of patients).ConclusionsAn increase in SvO2 ≥2%, irrespective of a relatively high baseline value, can thus be used as a monitor of fluid responsiveness in clinically hypovolemic patients after cardiac or major vascular surgery, particularly in those with systolic cardiac dysfunction. Fluid responsiveness concurs with increased tissue O2 delivery.

Highlights

It is unclear if and how O2 saturation in mixed venous blood (SvO2) can serve as an indicator of fluid responsiveness in patients after cardiac or major vascular surgery
Study population Twenty-six (70%) of 37 patients were responders according to cardiac index (CI) and 23 (62%) according to Stroke volume index (SVI) increase ≥15%
O2-related variables and fluid responsiveness, dependent on systolic cardiac function Baseline CI and SVI were lower in responders

Summary

Introduction

It is unclear if and how SvO2 can serve as an indicator of fluid responsiveness in patients after cardiac or major vascular surgery. Since relatively low mixed venous O2 saturations (SvO2) are associated with postoperative complications, (continuous) monitoring has been used to optimize cardiac output and O2 delivery relative to tissue needs (O2 consumption) after (cardiovascular) surgery. To this end fluids, red cell concentrates and vasoactive drugs have been infused to improve patient outcomes [1,2,3,9,10,11,12]. Giraud et al [20] suggested that in cardiac patients SvO2 changes are useful monitors of fluid responsiveness, but the role of cardiac function was unclear This may be important since impaired function and a relatively low cardiac output may diminish fluid responsiveness. A normal SvO2 may not exclude fluid responsiveness, if, as in healthy volunteers and septic patients, the heart operates in the steep part of its function curve even when meeting tissue demands, but this is expected to only minimally increase SvO2 [19,21]

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