Liver graft hyperperfusion in the early postoperative period promotes hepatic regeneration 2 weeks after living donor liver transplantation: A prospective observational cohort study

Abstract

Hepatic regeneration is essential to meet the metabolic demands of partial liver grafts following living donor liver transplantation (LDLT). Hepatic regeneration is promoted by portal hyperperfusion of partial grafts, which produces shear stress on the sinusoidal endothelium. Hepatic regeneration is difficult to assess within the first 2 weeks after LDLT as the size of liver graft could be overestimated in the presence of postsurgical graft edema. In this study, we evaluated the effects of graft hyperperfusion on the rate of hepatic regeneration 2 weeks after LDLT by measuring hepatic hemodynamic parameters. Thirty-six patients undergoing LDLT were enrolled in this study. Hepatic hemodynamic parameters including peak portal venous flow velocity (PVV) were measured using spectral Doppler ultrasonography on postoperative day 1. Subsequently, we calculated the ratio of each velocity to 100 g of the initial graft weight (GW) obtained immediately after graft retrieval on the day of LDLT. Ratios of GW to recipient weight (GRWR) and to standard liver volume (GW/SLV) were also obtained. The hepatic regeneration rate was defined as the ratio of the regenerated volume measured using computed tomographic volumetry at postoperative week 2 to the initial GW. Correlations of the hemodynamic parameters, GRWR, and GW/SLV with the hepatic regeneration rate were assessed using a linear regression analysis. The liver grafts regenerated to approximately 1.7 times their initial GW (1.7 ± 0.3 [mean ± standard deviation]). PVV/100 g of GW (r = 0.224, β1 [slope coefficient] = 2.105, P = 0.004) and velocities of the hepatic artery and vein per 100 g of GW positively correlated with the hepatic regeneration rate, whereas GRWR (r = 0.407, β1 = -81.149, P < 0.001) and GW/SLV (r = 0.541, β1 = -2.184, P < 0.001) negatively correlated with the hepatic regeneration rate. Graft hyperperfusion demonstrated by increased hepatic vascular velocities and a small-sized graft in the early postoperative period contributes to hepatic regeneration 2 weeks after LDLT.

Figure 1

Measurement of PVV (A), PSV and EDV (B), and HVV (C) using spectral Doppler ultrasonography 1 day after living donor liver transplantation. RI is calculated by (PSV–EDV)/PSV. EDV = end diastolic velocity of the hepatic artery, HVV = peak hepatic venous flow velocity, PSV = peak systolic velocity of the hepatic artery, PVV = peak portal venous flow velocity, RI = resistive index.

Figure 2

Measurement of one (7785 mm³) of the cross-sectional areas from the liver graft, which regenerated 2 weeks after living donor liver transplantation, by manual contour tracing of the hepatic contours. The volume of liver graft is calculated by multiplying sum of the cross-sectional areas of the liver graft by the slice thickness (3 mm).

Figure 3

Positive correlations of PVV/GW (A), PSV/GW (B), EDV/GW (C), and HVV/GW (D) on postoperative day 1 with the hepatic regeneration rate at postoperative week 2. EDV/GW = end diastolic velocity of the hepatic artery per 100 g of the initial graft weight, HVV/GW = peak hepatic venous flow velocity per 100 g of the initial graft weight, PSV/GW = peak systolic velocity of the hepatic artery per 100 g of the initial graft weight, PVV/GW = peak portal venous flow velocity per 100 g of the initial graft weight. Initial graft weight: The liver graft weight measured immediately after its retrieval. Hepatic regeneration rate: The ratio of the liver graft weight measured at postoperative week 2 to the initial graft weight.

Figure 4

Negative correlations of GRWR (A) and GW/SLV (B) with the hepatic regeneration rate at postoperative week 2. GRWR = graft-to-recipient weight ratio representing the ratio of initial graft weight (the liver graft weight measured immediately after its retrieval) to recipient's weight, GW/SLV = graft-to-standard liver volume ratio representing the ratio of initial graft weight to standard liver volume (=706.2 × body surface area (m²) + 2.4 where body surface area (m²) = body weight (kg)^0.425 × body height (cm)^0.725 × 0.007184).^[14]