Common carotid artery diameter responds to intravenous volume expansion: an ultrasound observation

Background: In case of intravascular fluid depletion, large veins react to volume expansion with dilation. Little is known about the reaction of arterial vessels. We herein report on the effect of a standardized fluid bolus on the diameter of the common carotid artery (CCA) and its association with hemodynamic parameters, assessed in 20 mechanically ventilated patients after cardiac surgery. CCA was visualized using ultrasound, and the percentage increase in diastolic diameter was calculated by measuring before and after administration of crystalloid infusion solution. Invasive arterial blood pressure and pulse pressure variation (PPV) were assessed in parallel. Results: Median diastolic CCA diameter was 6.2 (Q(1)-Q(3): 5.4-7.1) mm, and it significantly increased to 6.7 (5.8-7.3) mm upon fluid administration [5.0 (1.9-10.5) % increase]. Mean arterial blood (MAP) pressure likewise increased from 68 (70-73) to 85 (71-100) mmHg, whereas PPV was significantly reduced from 17.6 (16.8-23.9) to 13.2 (6.7-18.1) %. There was a significant association between the change in CCA diameter and the hemodynamic response (delta-MAP: r = 0.53, delta-PPV: r = 0.56; p < 0.05). Furthermore, carotid diameter measured before volume expansion significantly correlated with the delta-PPV upon fluid administration (r = -0.5; p = 0.02). Conclusions: Diameter of the CCA increases in response to intravascular volume expansion. Additional studies on the interplay between carotid geometry and intravascular fluid status are necessary.