Estimating the rapid haemodynamic effects of passive leg raising in critically ill patients using bioreactance

Abstract

Background: Rapid detection of changes in cardiac index (CI) in real time using minimally invasive monitors may be of clinical benefit. We tested whether the Starling-SV bioreactance device, which averages CI over a short 8 s period, could assess the effects of passive leg raising (PLR), a clinical test that is recommended to assess fluid responsiveness during septic shock.

Methods: In 32 critically ill patients, we measured CI by transpulmonary thermodilution (PiCCO2, CI_td), pulse contour analysis (PiCCO2, CI_Pulse), and the Starling-SV device (CI_Starling) at baseline. CI_Pulse and CI_Starling were measured again at the end of a PLR test. In the 13 patients with a positive PLR test, CI_td, CI_Pulse, and CI_Starling were measured before and after a 500 ml saline infusion. The primary outcome was relative changes from baseline measurements in CI_td, CI_Pulse, and CI_Starling. Secondary outcomes compared absolute values measured by each method.

Results: Relative changes in CI_Pulse and CI_td were significantly correlated (r=0.82; n=45; P<0.001), with an 89% concordance rate (n=45 paired measurements). Relative changes in CI_Starling and CI_td were also significantly correlated (r=0.59; n=45; P<0.001) with a 78% concordance rate. For absolute measures of CI (n=77 paired measurements), the bias between CI_Pulse and CI_td was 0.01 L min^-1 m^-2 (limits of agreement, -0.49 and 0.51 L min^-1 m^-2; 15% percentage error). Bias between CI_Starling and CI_td was 0.03 L min^-1 m^-2 (limits of agreement, -1.61 and 1.67 L min^-1 m^-2; 48% percentage error).

Conclusions: In critically ill patients, a non-invasive bioreactance device with a shorter averaging period assessed a passive leg raising test with reasonable accuracy.

Keywords: cardiac output; equipment; measurement; measurement techniques; monitors.