Influence of respiration and portal pressure on transabdominal duplex Doppler ultrasound measurement of portal blood flow: a porcine model for experimental studies

Transit time ultrasound perivascular flow probe technology is superior to MR imaging on hepatic blood flow measurement in a porcine model

BACKGROUND

The hepatic hemodynamics is an essential parameter in surgical planning as well as in various disease processes. The transit time ultrasound (TTUS) perivascular flow probe technology is widely used in clinical practice to evaluate the hepatic inflow, yet invasive. The phase-contrast-MRI (PC-MRI) is not invasive and potentially applicable in assessing the hepatic blood flow. In the present study, we compared the hepatic inflow rates using the PC-MRI and the TTUS probe, and evaluated their predictive value of post-hepatectomy adverse events.

METHODS

Eighteen large white pigs were anaesthetized for PC-MRI and approximately 75% hepatic resection was performed under a unified protocol. The blood flow was measured in the hepatic artery (Qha), the portal vein (Qpv), and the aorta above the celiac trunk (Qca) using PC-MRI, and was compared to the TTUS probe. The Bland-Altman method was conducted and a partial least squares regression (PLS) model was implemented.

RESULTS

The mean Qpv measured in PC-MRI was 0.55 ± 0.12 L/min, and in the TTUS probe was 0.74 ± 0.17 L/min. Qca was 1.40 ± 0.47 L/min in the PC-MRI and 2.00 ± 0.60 L/min in the TTUS probe. Qha was 0.17 ± 0.10 L/min in the PC-MRI, and 0.13 ± 0.06 L/min in the TTUS probe. The Bland-Altman method revealed that the estimated bias of Qca in the PC-MRI was 32% (95% CI: -49% to 15%); Qha 17% (95% CI: -15% to 51%); and Qpv 40% (95% CI: -62% to 18%). The TTUS probe had a higher weight in predicting adverse outcomes after 75% resection compared to the PC-MRI (β= 0.35 and 0.43 vs β = 0.22 and 0.07, for tissue changes and premature death, respectively).

CONCLUSIONS

There is a tendency of the PC-MRI to underestimate the flow measured by the TTUS probes. The TTUS probe measures are more predictive of relevant post-hepatectomy outcomes.

Portal Vein Pressure Change Predicts Posthepatectomy Liver Failure Following Right Lobectomy

The aim of this study was to evaluate the usefulness of intraoperative portal venous pressure (PVP) as a predictor of posthepatectomy liver failure (PHLF). Hepatic functional reserve is typically evaluated by using parameters such as albumin level, platelet count, prothrombin activity level, or indocyanine green retention rate at 15 minutes. Low hepatic functional reserve can enhance the risk of PHLF. We retrospectively analyzed the outcomes of 35 patients who underwent right lobectomy and intraoperative PVP measurements between April 2004 and August 2012. According to preoperative prediction scores, all patients were within a safe limit for right lobectomy. The patients were grouped into uncomplicated (n = 22) and PHLF (n = 13) groups by postoperative course. PHLF was defined as grade B or C according to International Study Group of Liver Surgery criteria. Patient background, intraoperative bleeding, operative time, and PVP elevation after hepatectomy (ΔPVP) grade were compared between the groups. No cases of in-hospital death occurred. Univariate analysis revealed significant differences in preoperative white blood counts, intraoperative bleeding, and ΔPVP between the groups (P < 0.05). The ΔPVP was an independent risk factor on multivariate analysis. A ΔPVP >3 cmH2O was associated with PHLF at 69.2% sensitivity and 90.9% specificity. Following right lobectomy, a ΔPVP >3 cmH2O indicates a risk of PHLF and warrants careful postoperative management.

Duplex Doppler ultrasound examination of the portal venous system: an emerging novel technique for the estimation of portal vein pressure

PURPOSE

Measurement of portal venous pressure in patients with portal hypertension is important to assess efficacy of beta blockers in patients with esophageal varices. Currently, the gold standard for measurement of portal venous pressure is the estimation of hepatic venous pressure gradient (HVPG). Being an invasive technique, serial measurements of HVPG are not feasible in clinical practice. In this respect, duplex Doppler ultrasound (DDUS) examination is an upcoming non-invasive technique for the estimation of portal venous and splanchnic hemodynamics. The aim of the present review is to analyze the current literature focusing on how the two techniques compare to each other in terms of assessing the portal pressure and assessing pitfalls in the current technique.

RESULTS

Duplex Doppler ultrasound (DDUS) currently has limitations in measuring the portal pressure in a non-invasive way. Hemodynamic venous and arterial indices measured on DDUS correlate with the HVPG. The technique has been refined, however, there is no uniform surrogate marker that can be used in clinical practice.

CONCLUSIONS

More studies are needed in order to remove the shortcomings in the current technique. The target is to be able to measure the actual portal pressure or at least derive an ideal venous or arterial hemodynamic surrogate marker having close correlation with the HVPG.

The measurement of liver blood flow: a review of experimental and clinical methods

Changes in hepatic blood flow reflect adaptive responses of the liver to injury, regeneration, and the development of disease states. The measurement of hepatic blood flow is, however, technically challenging and although theoretically useful has not become routine in clinical work. The different techniques that have been developed for quantitative measurement of hepatic blood flow require careful interpretation of the results obtained but are frequently applied without careful considerations of their technical limitations. In particular, many noninvasive techniques depend on good hepatocellular function and are thus irrelevant under most clinical conditions. Many other potentially useful techniques are poorly validated and standardized and there is a need for further research into smethodology. This review summarizes the salient technical features of the different techniques for quantitative measurement of hepatic blood flow. The techniques are divided into invasive, minimally invasive, and noninvasive categories and the relevance of each technique to both routine clinical application or research is discussed.