The HIBA Index for ALPPS, Preliminary Results to Interpret With Caution

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To the Editor:
With interest we read the recent article by Serenari et al,1 who reported on the interstage assessment of remnant liver function in ALPPS using hepatobiliary scintigraphy (HBS). The authors conclude the newly developed HIBA index can assist in timing the second stage to avoid postoperative liver failure.
We welcome the increasing use of a dynamic functional test as hepatobiliary scintigraphy to assist in the decision to proceed with major liver resection and specifically in ALPPS, to time the second stage. We recently have shown in a rabbit model that resembles ALPPS, that liver function measured with HBS lags behind increase in liver volume after portal vein embolization combined with parenchymal transection.2 Therefore, the accurate predictive value of HBS in the current report of Serenari et al is encouraging and warrants further implementation of HBS in the setting of ALPPS.
However, the current report is based on a total of 20 patients who underwent HBS of a total of 39 ALPPS cases at 1 single center. Of these 20 patients, only 4 developed liver failure according to at least one of the ISGLS, 50–50, or bilirubin > 7 mg/dL liver failure criteria, and only 1 patient died perioperatively. The current series is limited and contains a selection of ALPPS patients at a single center with substantial ALPPS experience. Therefore, the results might not be applicable to all the ALPPS patients at the analyzing center, and especially not to the ALPPS series worldwide, which contains a large variety of patients in both high and low volume centers with differing mortality rates.3,4
The 100% sensitivity and 100% negative predictive value for liver failure using all 3 mentioned parameters warrants further caution, as it was based on only 4 patients with liver failure and these predictive values will most likely never be reproduced as we experienced in our own series with HBS. In addition, the authors state a 100% negative predictive cutoff value of 1.69%/min/m2 based on the Amsterdam calculations which is far below our previously set 2.69%/min/m2.5
Although encouraging and promising, the present results should be interpreted with caution as the set cutoffs might be insufficient for the entire ALPPS experience and only be applicable to a selected patient cohort at a center with major experience in ALPPS. Nevertheless, we encourage implementation of HBS in ALPPS in order to time the second stage, as volume of the future liver remnant overestimates function. The authors call for caution and recommend including volume, age, tumor type, and interstage complications in clinical decision making. Nevertheless, we feel extra caution regarding the proposed cutoff should be exercised while future, larger studies should more accurately determine the minimal liver function to safely complete the second stage of ALPPS.
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