Oxygen Extraction Ratio (OER) as a Measurement of Hemodialysis (HD) Induced Tissue Hypoxia: A Pilot Study

Abstract

HD tissue hypoxia associates with organ dysfunctions. OER, the ratio between SaO2 and central-venous-oxygen-saturation, could estimate oxygen requirements during sessions, but no data are available. We evaluated OER behavior in 20 HD patients with permanent central venous catheter (CVC) as vascular access. Pre-HD OER (33.6 ± 1.4%; M ± SE) was higher than normal (range 20–30%). HD sessions increased OER to 39.2 ± 1.5% (M ± SE; p < 0.05) by 30′ and to 47.4 ± 1.5% (M ± SE; p < 0.001) by end of treatment (delta 40%). During HD sessions of the long and short interdialytic intervals, OER values overlapped, suggesting no influence of patient’s hydration status shifts. OER increased (p < 0.05) after 30′ of isolated HD (zero ultrafiltration), but not during isolated ultrafiltration (zero dialysate flow), suggesting a role for blood-membrane-dialysate interaction, independent of volume reduction. In ten patients, individual variability of pre-HD OER was low and repeatable (maximum calculated difference over time 6.6%), and negatively correlated with HD-induced OER increments (r = 0.860; p < 0.005), suggesting a decline in the adaptive response along with resting OER increments. In 30 prevalent patients, adjusted multivariate analysis showed that pre-HD OER (HR = 0.88, CI 0.79–0.99, p = 0.028) and percent HD-induced OER (HR = 1.04, CI 1.01–1.08, p = 0.015) were both associated with mortality, with threshold values respectively <32% and >40%. In HD patients with CVC as vascular access, OER is a cheap, easily measurable and repeatable parameter useful to assess intradialytic hypoxia, and a potential biomarker of HD related stress and morbidity, helpful to recognize patients at increased risk of mortality.

Oxygen Extraction Ratio to Identify Patients at Increased Risk of Intradialytic Hypotension.

“…1). This is in perfect agreement with the available evidence (15) of HD related hypoxic stress which is not sensed by the patients and is not detected by commonly available parameters like BP and HR (5,6,15,25,26,27). Therefore, ∆OER seems to offer a prompt and direct measurement of the hypoxic stress produced by HD and could thus represent a useful tool to identify more fragile patients.…”

“…Since OER measurement is handy in dialysis patients with central venous catheter (CVC), we recently evaluated it before and during HD sessions in a pilot study. We demonstrated that patients showing lower resting pre-HD OER values (< 32%) and/or greater OER increments (∆OER >40%) after HD had higher mortality rate (15). Also, in this same work, we could appreciate that OER values are rather stable and repeatable in the single patient, thus pointing to its potential usefulness to describe the hemodynamic capacity of a patient.…”

“…Also, in a next future, we need to know how much resting values of OER are stable over time in the individual patient. Our data from a previous study (15) suggest a significant stability in the short term; however, we need to characterize how much resting and HD induced changes in OER are affected by occasional or chronic clinical events.…”

“…At variance, during each HD session the rapid hemodynamic changes produced by dialysis inevitably induce an acute hypoxic stress that in some patients become clinically relevant thus representing a further burden to the cardiovascular system. These episodes are secondary to reduced cardiac output with the eventual low oxygen delivery and increased parenchymal tissues demand (5,15). Both ultrafiltration rate and the dialytic procedure per se can lead to parenchymal stress responsible for IDH (15,20,21,22,23,24).…”

Quantile contours and allometric modelling for risk classification of abnormal ratios with an application to asymmetric growth-restriction in preterm infants

“…A low input volume indicates atrial insufficiency, a low output volume ventricular insufficiency, and a low ratio might be associated to heart failure in several respects (e.g., decline of the contractile function). The list goes on with the albumin-to-globulin ratio (liver insufficiency, immunodeficiency, auto-immunity, infection, cancer); calciumto-albumin ratio (malnutrition); albumin-to-creatinine ratio (kidney disease); cortisol-to-cortisone ratio (cardiovascular risk); calcitriol-to-calcifediol ratio (renal efficiency); 50 oxigen extration ratio (haemodialysis efficacy); metabolite ratios (type 2 diabetes); 51 and stable isotope ratios (diet). 52 The first component d 1 (major axis) is the direction with maximal variance and its equation can expressed as 34…”