Published in:
01-12-2016 | Letter to the Editor
Reply: Hepatic Hemodynamic Changes Following Stepwise Liver Resection (Golriz et al. J Gastrointest Surg (2016) 20:587-594)
Published in: Journal of Gastrointestinal Surgery | Issue 12/2016
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We read with interest the comments by Mohkam et al. on our article entitled “Hepatic hemodynamic changes following stepwise liver resection” published in the Journal of Gastrointestinal Surgery.1 The following points were unclear to Mohkam et al. which we explain below:
1.
Transhepatic flow variations and modulation following extended liver resection:
Small for size and flow (SFSF) syndrome is one of the most challenging issues in extended hepatectomy.2 The role of transhepatic flow (THF) in this regard has been discussed many times during the last decades.3 – 5 However, to our knowledge, there is no experimental big animal study and no clinical evaluation that shows the correlation of the remnant liver volume (RLV) and THF during a stepwise liver resection. Moreover, the available studies are either mainly focused on the partial liver transplantation or a modulation method.3 , 5 – 10
2.
Portal vein pressure changes following extended hepatectomy:
Reviewing the literature shows that the left lateral and left and right medial lobes make up about 75 % of the liver volume in porcine model.11 , 12 Our findings that the portal vein pressure (PVP) increases following resection of 75 % of the liver are in line with those of Wang et al.12 and Xia et al.11 The non-significant increase of the PVP in the study of Darnis et al.13 may be due to small number of the animals (n = 7) or missed data (the presented value of HVPG in this study is not equal with PVP minus IVCP).
3.
Hemodynamic stability following 75 % liver resection:
Referring to the Figure 3 of our study, Mohkam et al. concluded that the animals were unstable following 75 % liver resection. We must clarify that the labels of heart rate and pressure are mistakenly reversed in this figure in the final version, while they were correct in the first submitted draft (the values of the right vertical axis are heart rates and the left ones are pressure). Regardless of this labeling error, since it is statistically not possible to discuss the significance of mean arterial pressure (MAP) changes only based on our figure, we present the data in this regard: MAP before 75 % resection = 54.4 ± 3.6 mmHg, MAP after 75 % resection = 48.1 ± 4.2 mmHg, p = 0.06. Therefore, the animals were stable during our study.
4.
Hepatic venous pressure gradient (HVPG) in our study:
The HVPG was not calculated because the values of the hepatic vein pressure (HVP) were almost unchanged during our study (6.2 ± 0.9 to 6.5 ± 0.9, p = 0.7). Calculating the HVPG in our study shows again a significant rise after 75 % liver resection (HVPG before resection = 5.8 ± 1.4 mmHg, HVPG after 75 % resection = 9.6 ± 0.8, p = 0.01). The flaw of the conclusion of Mohkam et al. about our results is comparing the HVPG value after 75 % resection with the value after 50 % resection instead of the baseline value. Moreover, it is important to know that an HVPG value of 6–9 mmHg is known as preclinical sinusoidal portal hypertension.14
5.
Portal vein resistance (PVR):
PVR plays an important role in explaining the lack of correlation between PVP and portal vein flow (PVF). However, it is known that hepatic compliance depends mainly on the underlying diseases of the liver such as cirrhosis, fibrosis, etc.15 Therefore, the role of PVR in development of SFSF should be interpreted with caution. Along with this, in the results of two recent studies performed by the Mohkam et al.13 , 16, the PVR following 70 and 90 % liver resection changed neither significantly nor had the same trend after 90 % resection.
6.
Small for size and flow (SFSF) in porcine model:
SFSF is a clinical syndrome which cannot be diagnosed, confirmed, or ruled out considering only one aspect. In experimental settings, it has often been shown that resection of 90 % of the liver causes nonreversible hepatic failure and does not lead to SFSF.11 , 12 Moreover, a combination of PVF >250 ml/min/100 g and remnant liver volume (RLV) <25 % has been considered as a prerequisite for SFSF.2 , 4 However, in porcine model, this can only be confirmed in a long-term follow-up with clinical, laboratory, and histopathological evaluations. Interestingly, in both studies of Darnis et al.13 and Mohkam et al.16, the PVF levels following 75 % resection exceeded 250 ml/min/100 g, and it is quite likely that the animals would have developed SFSF syndrome if a long-term follow-up had taken place.