Session SB1.5

Short-Term Variability of Oxygen Saturation (SO2) during Hemodialysis (HD) Is a Warning Parameter for Hypotension Appearance

E Mancini*, L Corazza, ML Soverini, DC Cannarile, S Cavalcanti,
S Cavani, A Fiorenzi, A Santoro

Hospital S. Orsola-Malpighi
Bologna, Italy

Arterial hypotension is a frequent problem complicating HD. Hypoxemia may be may be considered as a surrogate marker of hemodynamic instability. Continuous, non-invasive monitoring of SO2 during HD is now possible, by means of sensors measuring SO2 in blood entering the dialyzer. The aim of the present work was to analyze the short-term variability of SO2 correlated to conditions of hemodynamic instability during HD.
Twenty hypotension-prone patients where monitored during their HD sessions. SO2 signal was recorded from the Hemox sensor of the Formula 2000 (BellCo, Italy). Common hemodynamic parameters (blood pressure every 15 min, hypotension appearance) were collected. Data were analyzed off-line. Sessions with hypotension were classified as positive. SO2 time series was filtered (ft=0.1 Hz). SO2 data were extracted by shifting a 4-min long window (48 points, 1 min-step). Standard deviation (SD) was computed. In the positive sessions, SO2 variability analysis was truncated at hypotension onset. A critical threshold of 0.85% was fixed and positive session was predicted when SD exceeded this threshold. Overshoot time (OT) was computed.
Forty sessions were considered for analyses: on the basis of hypotension presence, 20 were classified as positive and 20 negative. The off-line overall prediction, based on the SO2 variability, was 88% (17/20 positive and 18/20 negative sessions). Notably, OT anticipated hypotension of 14±9 min. The positive likelihood ratio (sensitivity)/(1-specificity) was 8.5, indicating that SO2 variability index raises highly the likelihood of positive prediction.
Changes of intradialytic SO2 variability anticipate hypotension, likely as a result of the ups and downs of cardiac output and tissue perfusion. Continuous monitoring of SO2 variability may provide useful information to forecast the onset of hypotension. In this view, the study may pave the way to an automatic alarm system including SO2 changes as a warning variable, offering a chance for preventive manoeuvres to avoid hypotension.

(Abstract Control Number: 212)