How do regional blood flow rates measured by arterial Doppler vary during hemorrhagic shock? An experimental study in anesthetized piglets

Hemorrhagic shock induces compensatory vasoconstriction that may affect arterial territories differently. Regional blood flow (RBF) can be assessed using Doppler ultrasound with the time-averaged mean velocity (TAMV). The primary objective was to describe changes in RBF among the carotid, femoral, superior mesenteric and renal arterial territories across blood depletion during controlled hemorrhagic shock in anesthetized piglets. Anesthetized and mechanically ventilated piglets underwent controlled blood withdrawal at 2 mL·kg⁻¹·min⁻¹ until a mean arterial pressure of 40 mmHg was reached. At baseline and after each 5-mL·kg⁻¹ depletion step, VTI was measured in the carotid, femoral, superior mesenteric and renal arteries. TAMV was calculated as VTI × HR / 60 and normalized to each animal’s baseline value. TAMV was analyzed using linear mixed-effects models with a subject-specific random intercept. Fixed effects were assessed using type III analysis of variance and reported as F statistics with Satterthwaite-approximated degrees of freedom. Pairwise comparisons were adjusted for multiple testing by Holm method. Seventeen piglets were analyzed, with a median blood withdrawal of 38 [34; 42] mL·kg⁻¹. Median carotid, femoral, renal and mesenteric TAMV values and their interquartile ranges were 16 [14; 20], 23 [15; 29], 26 [19; 42] and 55 [40; 66] cm·s⁻¹ at T0; 19 [15; 24], 25 [19; 38], 25 [17; 30] and 44 [36; 53] cm·s⁻¹ at 10 mL·kg⁻¹; 17 [14; 24], 26 [22; 40], 26 [18; 34] and 41 [38; 48] cm·s⁻¹ at 20 mL·kg⁻¹; 21 [16; 22], 25 [19; 32], 23 [19; 31] and 41 [36; 51] cm·s⁻¹ at 30 mL·kg⁻¹; and 20 [17; 22], 27 [25; 30], 16 [14; 16] and 48 [39; 59] cm·s⁻¹ at 40 mL·kg⁻¹, respectively. Overall territorial comparisons were F (3, 109) = 17.14 ( p < 0.01) at T0 and F (3, 109) = 18.92 ( p < 0.01) at T1. Within-territory analyses were F (8, 93) = 1.69 (Holm-adjusted p = 0.34) for the carotid territory, F (8, 91) = 2.10 (Holm-adjusted p = 0.18) for the femoral territory, F (8, 76) = 1.02 (Holm-adjusted p = 0.43) for the mesenteric territory, and F (8, 96) = 1.55 (Holm-adjusted p = 0.34) for the renal territory. The depletion step-by-territory interaction was F (24, 393) = 0.85 ( p = 0.68). The variations in RBF assessed by Doppler appeared to be heterogeneous across different territories, with carotid blood flow remaining preserved, although the study’s statistical power was insufficient to confirm this difference.