To evaluate the interrater reliability and parallel forms reliability of transcutaneous Doppler ultrasonography (TCDU) and impedance cardiography (ICG) in clinically and hemodynamically stable emergency department patients.
We enrolled 30 emergency department patients over a 2-day period. Patients had three consecutive simultaneously blinded measurements of stroke volume (SV) and heart rate (HR) recorded by TCDU (USCOM) and ICG (Cardiodynamics). Two physicians, with basic familiarity but no clinical experience with either device recorded three measurements of SV and HR on each device. Intraclass correlation coefficients (ICC), mixed linear models for repeated measures, and Bland–Altman plots were used to assess interrater reliability and nature of relationships between measures from the devices (parallel forms reliability).
The ICC for TCDU was 0.96 for HR and 0.95 for SV, whereas the ICC for ICG was 0.93 for HR and 0.98 for SV. The device HR estimates were significantly related (P<0.0001 for all slopes) for all phases, but SV failed to reach significance following the first 50 trials [t(94.2)=2.72, P=0.0077]. Although HR estimates were within reasonable clinical tolerances (bias 0.5%, limits of agreement −15.4 to 16.4%) SV disagreement was concerning (bias 3.8%, limits of agreement −58 to 66%).
Both TCDU and ICG have fair interrater reliability of SV independent of operator experience. A statistically significant relationship exists between the two devices but this does not produce predictable values in SV. Over time comparative results become less biased but remain limited by a great degree of variability.