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CLINICAL TRANSPLANTATION

Intraoperative near-infrared spectroscopy for evaluating hepatic venous outflow in living-donor right lobe liver1

Ohdan, Hideki2; Mizunuma, Kazuyuki; Tashiro, Hirotaka; Tokita, Daisuke; Hara, Hidetaka; Onoe, Takashi; Ishiyama, Kohei; Shibata, Satoshi; Mitsuta, Hiroshi; Ochi, Makoto; Nakahara, Hideki; Itamoto, Toshiyuki; Asahara, Toshimasa

Author Information
doi: 10.1097/01.TP.0000074603.36553.BD
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Abstract

Living-donor liver transplantation (LDLT) has been developed as an important potential source of organs for treatment of children with acute and chronic liver disease. The feasibility of LDLT for adult patients has also been reported (1). However, liver grafts are small for adult-to-adult LDLT using a left lobe graft. Such small-for-size grafts in LDLT are sometimes insufficient to meet metabolic demands, resulting in a lower chance of survival. One solution to this problem is to use a right liver graft. Two surgical procedures for harvesting a right lobe have been reported: a right lobectomy with drainage of the right hepatic vein (RHV) alone (2–4), and an extended right lobectomy with both RHV and middle hepatic vein (MHV) drainage (5–7). In the case of the former procedure, which is widely applied because it is less invasive for donors, the need for drainage from the MHV tributaries has not yet been established. Venous outflow problems associated with deprivation of the MHV tributaries in LDLT using right lobes are uncommon (8–10) but are devastating when they occur (11,12). Even if a partial outflow disturbance does not result in graft dysfunction, venous congestion in LDLT is associated with disadvantages in postoperative liver volume regeneration (13). To prevent such venous outflow problems, a reliable method for evaluating the need for drainage from the MHV tributaries is currently desired.

Near-infrared spectroscopy (NIRS) enables nondestructive evaluation of hemoglobin (Hb) oxygenation and the redox state of cytochrome oxidase (Cyt.aa3) in living organ tissues (14–19). In the near-infrared (NIR) region (700–1,300 nm), light can penetrate deeply into biologic tissues over long distances, and the absorption intensity of NIR light depends on the level of Hb oxygenation, the redox state of Cyt.aa3, and the content of biologic pigments in the tissue (14,15). We applied NIRS for evaluation of venous outflow problems associated with the deprivation of the MHV tributaries in LDLT using right lobes.

PATIENTS AND METHODS

Patient Population

Fifteen consecutive patients who underwent adult-to-adult LDLT using a right lobe graft without the MHV from January 2001 to August 2002 at the Hiroshima University Hospital were enrolled in this study. The 15 patients included 11 men and 4 women, ranging in age from 27 to 66 years (mean±SD, 47±12 years). Graft weight and graft-to-recipient body weight ratio ranged from 480 to 790 g (mean, 621±81 g) and from 0.73% to 1.35% (mean, 0.93±0.19%), respectively. Original diseases of the patients are listed in Table 1. The graft donors were eight offspring, four siblings, and three spouses, with ages ranging from 19 to 54 years (mean, 32.2±9.01 years).

T1-9
Table 1:
Hepatic vein profile of right lobe liver grafts

Surgical Technique

Donor hepatectomy and the recipient transplantation procedure were performed as described previously with minor modifications. In brief, the right lobe, without the middle hepatic vein, was harvested from the donor as follows. An intraoperative ultrasonographic examination was performed for final identification of the anatomy of the hepatic veins and portal veins in addition to an intraoperative cholangiographic examination to determine the branching pattern of the bile ducts. Before parenchymal transection, the right lobe was mobilized and the short hepatic veins were transected. Parenchymal transection was performed on the right side of the MHV. During parenchymal transection, major right tributaries of the MHV were clamped using a vascular clip and transected. After hepatectomy, ex vivo perfusion of the right lobe graft was performed through the portal vein (PV). The initial perfusate was saline solution (500 mL) followed by University of Wisconsin solution (1,000 mL). During initial perfusion, real-time and continuous NIRS measurement was performed on the anterior segment of the right lobe graft to determine the kinetics of Hb washout from the hepatic tissue as described later.

For the recipient, the implantation was performed after total hepatectomy. The middle and left hepatic veins were closed, and then the graft RHV was anastomosed to the RHV of the recipient in an end-to-end fashion. After end-to-end anastomosis of the graft right PV to the right PV of the recipient, the graft was reperfused before microsurgical reconstruction of the hepatic artery (HA) (end-to-end anastomosis of the HA of the graft to the right HA of the recipient). The bile duct of the graft liver was anastomosed in an end-to-end fashion to the common or right hepatic bile duct of the recipient. All recipients continuously received intravenous injection of prostaglandin E1 (0.01 μg/kg/min) during surgery and for 24 hr after surgery. Levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and serum bilirubin were measured as indexes of liver function. The initial immunosuppressive regimen consisted of tacrolimus and steroids. Computed tomographic (CT) scans and Doppler ultrasonography were routinely performed.

Intraoperative NIRS

During the course of harvesting and implantation, in vivo NIRS measurements were performed on both the anterior and posterior segments of the liver grafts to determine Hb and Cyt.aa3 content in the hepatic tissues as indicators of congestion and redox state (Fig. 1A). In addition, during initial ex vivo perfusion, continuous NIRS measurement was performed on the anterior segment of the right lobe graft to determine the kinetics of Hb washout from the hepatic tissue (Fig. 1B). NIRS measurement was carried out as follows. NIR reflectance was measured with a multichannel photodetector (MCPD-2000; Otsuka Electronics, Osaka, Japan) connected to a personal computer (PC-9801FS; NEC, Tokyo, Japan). NIR light from a halogen lamp at 300 W was directed through a flexible bundle of quartz optical fibers to the liver, and the reflected light was conveyed through another bundle to a spectrophotometer. The tips of the two fiber bundles were fixed at a position approximately 1 cm above the liver, and the distance between the two probes was approximately 1 cm. The reflected light was measured sequentially in the range of 700 to 1,000 nm, with an interval of 2 nm. The sampling time for each scan was 4 sec. The difference between the spectrum from the liver immediately after laparotomy of the donor and that from the liver shortly before closure of the recipient’s abdomen (Fig. 1A) and the difference between the spectrum from the liver just before initial ex vivo perfusion and that from the liver during ex vivo perfusion (Fig. 1B) were calculated every 2 nm. The difference between the spectra was analyzed by a curve-fitting technique based on the least-squares method using standard spectra of purified oxyhemoglobin, deoxyhemoglobin, oxidized Cyt.aa3, and water. The five components were fitted with the following equation: MATH where OD(λ), L(λ), and e1–5(λ) are optical density, mean light path length, and extinction coefficient of each component at a wavelength of λ, respectively. The relative changes in each component were determined using this multicomponent analysis calculated on the basis of singular value decomposition (20). The changes in total Hb content were calculated by adding the changes in oxyhemoglobin and deoxyhemoglobin.

F1-9
Figure 1:
Block diagram of NIRS for determining Hb and Cyt.aa3 content in hepatic grafts. NIR, near-infrared; RPV, right portal vein; RHV, right hepatic vein; MHV, middle hepatic vein. NIRS was performed on the anterior or posterior hepatic segment immediately after laparotomy of the donor and on the anterior or posterior hepatic segment shortly before closure of the recipient’s abdomen (A) and on the anterior segment during ex vivo perfusion (B).

Statistical Analysis

Statistical analysis was performed using Student t test. Differences at P <0.05 were considered significant.

RESULTS

Patients

Thirteen of the 15 patients did not incur fatal complications within 1 month after LDLT, but one patient (patient 2) died of multiple organ failure caused by perforation of the stomach and rupture of the HA at postoperative day (POD) 16, and one patient (patient 6) suffered from sepsis from POD 14 and died on POD 30.

Relationship between Caliber of MHV Tributaries and Graft Congestion

The 15 cases were divided into three groups according to the caliber of the major MHV tributaries in the right lobe grafts: the small group (<4 mm) (n=4), the intermediate group (4–7 mm) (n=5), and the large group (>7 mm) (n=6) (Table 1). Congestion in the graft livers was estimated as an increase in tissue Hb content (i.e., the difference between Hb content in the liver immediately after laparotomy of the donor and that in the liver shortly before closure of the recipient’s abdomen). After implantation, congestion was observed in both the anterior and posterior segments regardless of the caliber of the MHV tributaries (Fig. 2A). However, the congestion in the anterior segment was more severe than that in the posterior segment in the intermediate and large groups. The large group included two cases with extraordinarily severe congestion in the anterior segment (patients 4 and 15), resulting in a large standard deviation. The increase in Hb content reflected the increase in oxyhemoglobin rather than that in deoxyhemoglobin (Fig. 2B and C). No significant changes in oxidized Cyt.aa3 (Fig. 2D) were seen in either of the segments in the small and intermediate groups, indicating a well-preserved mitochondrial redox state. However, two cases with severe congestion in the large group showed reduction in oxidized Cyt.aa3 in the anterior segment.

F2-9
Figure 2:
Relationship between caliber of MHV tributaries and hepatic graft oxygen metabolism after LDLT. The 15 patients were divided into three groups according to the caliber of the major MHV tributaries in the right lobe graft. The difference between NIR spectra from the liver immediately after laparotomy of the donor and those from the liver shortly before closure of the recipient’s abdomen was analyzed to determine the changes in Hb and Cyt.aa3 content. On each anterior or posterior hepatic segment, three to five points were measured in each case, and the averages represent an individual’s data. Congestion and mitochondrial redox in the liver grafts were estimated as changes in tissue Hb and Cyt.aa3 content, respectively. Average±SEM of changes in total Hb (A), oxyhemoglobin (B), deoxyhemoglobin (C), and oxidized Cyt.aa3 (D) content in the anterior segment (▪) and the posterior segment (□) for the individual groups are shown (*P <0.05).

If the right lobe graft is deprived of the MHV tributaries and the PV and HA inflow and the RHV outflow are adequate, anterior segment congestion after transplantation might depend on the venous collaterals between the MHV and the RHV in a right lobe graft. To estimate the significance of venous collaterals in a right lobe graft before implantation, NIRS measurement was performed on the anterior segment of the right lobe graft to quantify tissue content of Hb during initial ex vivo perfusion. Representative kinetics of Hb washout from the anterior segment calculated by NIRS is shown in (Figure 3A). In most cases, tissue content of Hb was decreased by ex vivo flushing and became constant within 180 sec. However, Hb content in the anterior segment remained high even after ex vivo flushing in some cases in the large group, demonstrating poor venous collaterals. (Figure 3B) shows the relationship between the remaining Hb content at 180 sec after initial flushing and the extent of postoperative congestion (ΔHb) in the anterior segment. They were significantly correlated, indicating that postoperative congestion can be predicted by NIRS during initial perfusion.

F3-9
Figure 3:
(A) Representative kinetics of Hb washout in the anterior segment of the right lobe graft during ex vivo perfusion. The value at each time point represents percentage of total change in Hb (difference between 0 and 180 sec) in the posterior segment. Patients 13 and 11: rapid release of Hb was seen when the hepatic vein drainage was sufficient. Patients 12 and 4: Hb remained in the right anterior segment even after perfusion. In patient 4, Hb washout was greatly impaired, indicating lack of functional collaterals between the MHV tributaries and the RHV. (B) Relationship between the remaining Hb content after initial flushing and the extent of postoperative congestion in the anterior segment. During initial ex vivo perfusion, continuous NIRS measurement was performed on the anterior segment of the right lobe graft to determine the kinetics of Hb washout from the hepatic tissue. The extent of postoperative congestion (ΔHb) in the anterior segment was significantly correlated with the tissue content of remaining Hb in that segment after ex vivo perfusion (at 180 sec after initial flushing).

Relationship between Caliber of MHV Tributaries and Liver Faction

Serum levels of AST, ALT, and bilirubin after LDLT were measured as indexes of liver function. Those parameters were not significantly different among the groups, but two cases with severe congestion showed transient but marked elevation of AST and ALT levels in the first week after LDLT (Fig. 4).

F4-9
Figure 4:
Relationship between caliber of the MHV tributaries and liver function. Serum levels of bilirubin (A), AST (B), and ALT (C) after LDLT were measured as indexes of liver function. Number of patients in each group: small MHV tributaries (<4 mm) (n=3), intermediate MHV tributaries (4–7 mm) (n=4), and large MHV tributaries (>7 mm) (n=6). Patients 2 and 6 were excluded from this analysis because of postoperative complications (stomach perforation and HA rupture at POD 16 and sepsis after POD 14, respectively).

Computed Tomographic Scan and Doppler Ultrasound Examinations

Computed Tomographic (CT) scan examination after LDLT generally revealed no remarkable graft congestion in the small and intermediate groups (Fig. 5A). In some of the cases in the intermediate and large groups, venous drainage from the right anterior segment lagged behind that from the posterior segment by 2 to 4 weeks after surgery (Fig. 5B). However, this time lag in MHV tributary drainage gradually improved (Fig. 5C). In such cases, reverse flow in the proximal-to-peripheral direction in the tributaries was observed by color Doppler ultrasound examination (Fig. 5E), suggesting growth of intrahepatic collaterals between the MHV tributaries and the RHV. In the case with the most severe congestion, as determined by intraoperative NIRS, a perfusion defect was seen in the anterior segment on a CT scan 2 weeks after LDLT (Fig. 5D). This circulatory impediment was persistent, causing atrophy of the anterior segment. However, compensatory hypertrophy of the posterior segment saved this patient (not shown).

F5-9
Figure 5:
CT scan and Doppler ultrasound findings after LDLT. (A) Patient 13 (MHV tributary <4 mm) at 2 weeks after LDLT. There was no remarkable graft congestion. (B) Patient 12 (>7 mm MHV tributary) at 2 weeks after LDLT. Venous drainage from the right anterior segment lagged behind that from the posterior segment. (C) Patient 12 at 4 weeks after LDLT. Time lag of the MHV tributary drainage had improved. (D) Patient 4 (>7 mm MHV tributary) at 2 weeks after LDLT. A perfusion defect was seen in the anterior segment. (E) Reverse flow in the proximal-to-peripheral direction in the MHV tributary of patient 12 was observed by color Doppler ultrasound examination (at 4 weeks after LDLT). (arrow) An intrahepatic communicating vein draining into the RHV.

DISCUSSION

In hepatectomy for LDLT, it is practically impossible to maintain complete venous drainage in both the right and left lobes, because the MHV can be preserved on only one side. Poor venous outflow can result in engorgement and graft failure (11,12). However, many authors have reported that the right liver graft showed good function without reconstruction of the MHV tributaries (3,4,9,21,22). One possible explanation for these good results is that drainage flow from the anterior segment to the posterior segment of a right lobe graft is established by means of intrahepatic PV and then into the RHV (23). Another possible explanation is that intrahepatic communication between the MHV tributaries and the RHV contributes to the prevention of congestion of the anterior segment (24). If such vein communications are significant in the right lobe graft, reconstruction of the MHV tributaries might not be required for adequate hepatic venous drainage. The necessity for reconstruction of the MHV tributaries or the inferior right hepatic vein is currently judged by the caliber of such vessels (3,11). Information on the presence or absence of hepatic segmental congestion after temporarily clamping the corresponding vein during donor surgery is also useful (9). Recent studies have demonstrated that concomitant temporary clamping of the HA is also useful for diagnosis of venous congestion of the liver, because the hepatofugal area is discolored under these conditions (10,25). Such methods would provide a gross extent but not a quantitative degree of hepatic engorgement. As a more objective method for predicting hepatic vein drainage problems, we have used NIRS, which enables nondestructive and continuous evaluation of Hb and Cyt.aa3 content in living organ tissues (16–18).

Using the NIRS system, we confirmed congestion in both the anterior and posterior segments after implantation. This finding is consistent with the results of our previous study showing transient congestion after rat liver transplantation (16). The congestion in the anterior segment tended to be more severe than that in the posterior segment in the grafted hepatic right lobe with significant MHV tributaries (>4 mm), reflecting the deprivation of the tributaries. In contrast, it was shown in a previous study that the anterior segment of the right loge graft was susceptible to ischemia rather than to congestion after LDLT (9). In that study, an NIRS system similar to that used in our study was used, and it was demonstrated that Hb content in the anterior segments after implantation was lower than before hepatic transection in donors. Ischemia of the grafted liver is thought to be associated with ischemia-reperfusion–induced disturbance of sinusoidal microcirculation, at least in the early phase after implantation, probably masking hepatic venous outflow insufficiency. To attenuate such microcirculatory disturbance, recipients routinely received prostaglandin E1 during implantation surgery in the present study. This might explain why graft congestion occurred even early after implantation in our patients. Thus, it seems difficult to evaluate only venous outflow problems in vivo, because hepatic hemodynamics is complexly influenced by inflow (portohepatic artery blood supply), sinusoidal microcirculation, and hepatic vein outflow. NIRS measurement of remaining tissue Hb during ex vivo flushing probably has the advantage of minimizing effects of factors other than venous outflow. Such NIRS measurement enabled accurate prediction of hepatic hemostasis caused by deprivation of the MHV tributaries, indicating that this method is useful for determining whether MHV tributaries should be reconstructed. In this study, two recipients of liver graft with high Hb residue even after ex vivo flushing (patients 4 and 15 in the large group), who showed impairment of mitochondrial respiration and significant increase in serum transaminase levels, would be appropriate candidates for reconstruction of MHV tributaries.

Congestion of a liver graft results not only from venous outflow insufficiency but might also be exacerbated by portal hypertension. Particularly in cases with marginal communicating veins, portal pressure after grafting might be an important factor for deciding whether to reconstruct MHV tributaries in a right liver graft. Because the present series, in which portal pressure after the LDLT (at the end of recipient surgery) was between 13 and 16 mm Hg in all cases (data not shown), did not allow us to analyze this issue, further studies are needed.

When in vivo spectroscopy is applied to living tissues, the field of view of scanning should be taken into account. It has been established that the “mean light pathlength,” labeled “field of view,” in in vivo NIRS is four- to sixfold greater than the distance between the transmitting and receiving optical bundles when those are vertically applied to the scanned tissues and the intensity of the light source is adequate (26). In our NIRS system, the distance between the transmitting and receiving optical bundles was 1 cm; thus, the mean light pathlength, spectrophotometric view, was theoretically 4 to 6 cm, suggesting that several-point scanning might be sufficient to quantitatively represent the state of venous congestion in a subsegment of the liver graft. However, this method did not enable accurate determination of the venocongestive areas in the liver grafts. To compensate for this defect, visualization of the venocongestive area by temporary clamping of the corresponding vein and the HA during donor surgery (25) would be helpful.

CONCLUSION

Intraoperative NIRS enabled quantification of the extent of congestion and the influence of the oxygenation state of right lobe liver grafts by determining changes in tissue content of oxyhemoglobin, deoxyhemoglobin, and oxidized and reduced Cyt.aa3. In addition, by determining the kinetics of Hb washout of the right hepatic lobe graft during ex vivo perfusion, NIRS enabled prediction of such a venous outflow problem before implantation.

Acknowledgment.

The authors thank Yuka Tanaka for expert secretarial assistance.

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