PURPOSE: Rapid prediction of the effect of volume expansion (VE) is crucial in hemodynamically unstable patients on mechanical ventilation. While accurate, both radial artery pulse pressure variation (ΔPP) and changes of aortic blood flow peak velocity (ΔVPeakAo) have limitations that make them impractical as point-of-care tools. In this study, we sought to determine whether respiratory changes in the brachial artery blood flow velocity (VPeakBA) as measured by Internal Medicine residents using a hand-carried ultrasound (HCU) could provide an accurate corollary to ΔPP in mechanically ventilated patients.
METHODS: Thirty mechanically ventilated patients with pre-existing radial artery catheters admitted to the intensive care unit (ICU) at the University of Chicago Hospital were enrolled in the study. All patients passively received volume control ventilation with a tidal volume of at least 8 cc/kg ideal body weight for the duration of the study. The brachial artery Doppler signal was recorded and analyzed over a 30-second interval by Internal Medicine residents using a SonoSite TITAN HCU device. A simultaneous recording of the contra lateral arm radial artery pulse wave and corresponding telemetry strip was analyzed by a critical care physician blinded to both the ΔVPeakBA results and clinical status of the patient. When available, a CVP measurement was obtained. The correlation between ΔVPeakBA, ΔPP, and CVP was determined using the Pearson correlation coefficient.
RESULTS: An adequate Doppler signal was obtained in all 30 patients. The intra-observer variability for the technique was 1.2% (+/-1.2%). The brachial artery ΔVPeak correlated well with the radial artery ΔPP (r=0.84). The mean variance between ΔPP and ΔVPeakBA was 1.0% (+/-3.87%). A poor correlation existed between the CVP and both ΔVPeakBA (r=-0.21) and ΔPP (r=-0.16).
CONCLUSION: The HCU Doppler assessment of the brachial artery ΔVPeak as performed by Internal Medicine residents is a rapid, non-invasive bedside correlate to ΔPP.
CLINICAL IMPLICATIONS: The ΔVPeakBA may prove useful as a point-of-care tool for the prediction of volume responsiveness in mechanically ventilated ICU and emergency room patients.
DISCLOSURE: J. Matthew Brennan, None.