Since the introduction of liver transplantation, the post-operative hepatic function assessment has been extensively studied. During the 1980s, this evaluation aimed mainly at detecting primary non function (PNF) (incidence up to 23%), which was considered to be an indication for retransplantation (reTX) [1,2]. Early graft dysfunction is now known to be irreversible (formerly PNF) or reversible (reversible poor function or RPF, i.e. not requiring reTX) but early differential diagnosis remains difficult. This confirms the need to search for indicators or functional tests of liver function, in order to appreciate the efficacy of cytoprotective supportive measures and the need for reTX. The ideal evaluation of graft function should be easy to perform and to interpret, reproducible, independent of hepatic blood flow and inexpensive (or at least cost-effective).
Several tests have been proposed for the assessment of metabolic activity [3–6] synthesis activity [7–10] and hepatic detoxification [11–15]. However, none have met the criteria of the ideal test, the hepatic blood flow being the most constant variable.
The aim of this study was to assess the lignocaine clearance test , associated with easily available biological indices, as an indicator in the early post-operative period of global graft function and of post-operative complications (PNF, vascular complications, acute rejection).
Patients and methods
During 1991 and 1992, 80 consecutive liver transplantations were performed in 71 patients. All the patients had the same surgical and anaesthetic management, antibiotic prophylaxis and immunosuppressive therapy. Pre-operative patient information was given according to local Ethical Committee requirements. They were included in this prospective study during their post-operative stay in a surgical intensive care unit. Demographic data are presented in Table 1.
The post-operative course was considered to be favourable (group F) if patients stayed less than 5 days in the intensive care unit (ICU) and were not readmitted during the following month. However, this group included those who suffered an acute rejection after day 5, because these patients were not readmitted to the ICU for their treatment. Indeed in these cases rejection was diagnosed by systematic biopsy without any elicitated clinical or biological signs.
The recorded complications (group C) were:
- Acute rejection was defined as the presence of inflammatory periportal infiltrates in the first liver biopsy performed routinely on the 7th post-operative day;
- PNF was defined as the absence of bile production, decreased blood clotting factors requiring FFP transfusion, a continuing rise in lactate levels and a rapid onset of hepato-renal syndrome. All the patients in this group had an emergency reTX;
- Vascular complications with consequences for hepatic blood flow diagnosed during early relaparotomy or at angiography;
- Pulmonary complications if leading to hypoxia (PaO2<8KPa) or prolonged ventilation (>3 days);
- Infection defined as the presence, in the cultures, of pathogenic micro-organisms during the first 5 days and requiring an antibiotic therapy.
Biological assessment was performed at regular intervals after graft revascularization (T1: +12 h, T2: +24 h, T3: +48 h, T4: +72 h) and included MEGX, prothrombin time (PTI), factor V (FVI), aminotransferases and bilirubin plasma concentrations.
Monoethylglycinexylidide (MEGX) measurements were performed 30 min after a BW lignocaine (Lig) 1 mg kg−1 intravenous (i.v.) bolus injection. In the case of a previous Lig injection, the residual MEGX level was determined on blood sampled just before Lig injection. Thus, measurements shown later are the differences between the basal and the post injection MEGX levels.
MEGX measurements were obtained by fluorescent polarization immunoassay (Abbott TDX system) with a convenient sensitivity between 11 and 250 μg L−1.
PTI and FVI were measured using routine methods (expressed as percentage of control).
Aminotransferases (ASAT, ALAT) were measured according to IFCC recommendations using a Technicon Dax 48 system to be suppressed.
Bilirubin level (μmol L−1) was determined by the method of Novros et al. on the same analyser, but this measurement could only be performed once daily.
The results concerning F and C groups were analysed by Anova and the data were expressed as means ± SD. The predictive values of various biological indices were calculated in a standard fashion. Threshold levels were determined according to the highest value of Younden's index.
The differences between complications were assessed using a two-way variance analysis. Thereafter, a step-by-step analysis determined the discriminant factor for a given complication. P<0.01 was considered significant.
The two groups were similar with regard to age, duration of surgery, haemodynamic responses at unclamping, initial diagnosis and Child Pugh's distribution (Table 1).
General data. The patient outcomes and type of complications are included in Table 1, in 3/4 of the cases the post-operative course was uneventful.
The global 1 year mortality rate was 12%. In the F group, three patients died (6% mortality) of peritonitis following a late anastomosis leak (their liver function remained satisfactory up until their complication). These three patients had a duodenopancreatectomy during transplantation. In group C, nine patients required to be retransplanted (four in the first 3 days, one on the 7th, four at a distance owing to chronic rejection) six patients died (30% mortality). No patient died during surgery.
Diagnosis of complicated outcome (F vs. C). For all biological indices, there was a significant difference at any time between the two groups (Table 2), moreover the predictive value for complicated outcome remains low (Table 3). The MEGX concentrations in those patients classified clinically as uncomplicated were normal as early as T1, long before normalization of standard liver function tests. Moreover MEGX values stayed stable for the first 3 days after transplantation.
Diagnosis of the type of complication. There are wide variations in biological indices for the type of complication (Table 4). Two-way analysis of variance was performed to detect differences between various complications. The initial failure can be distinguished from acute rejection, infection, vascular or pulmonary complications by an increase in bilirubin concentration as early as 24 h after unclamping. Acute rejection could be considered in case of an increase in ALAT 24 h after unclamping. Furthermore, the differences between vascular, infectious and respiratory complications are not significant.
Using step-by-step ascending regression analysis more precise data can be obtained. Thus, 24 h after surgery, FV and MEGX were found to be discriminators (r=0.59 at the first step for FV, r=0.69 at the second for FV and MEGX) for favourable outcome, ALAT (r=0.69) for acute rejection and bilirubin concentration for PNF (r=0.61). According to these findings, predictive values (sensitivity, specificity) were calculated combining the discriminant factor with one exploring another metabolic pathway (Table 5).
The occurrence of low MEGX values (<20 μg L−1) were identified in 11 patients. The four patients with PNF presented immediately with the lowest MEGX tests, all the MEGX values recorded in those patients up to retransplantation were below 20 μg L−1 with a median value of 4 μg L−1 (0–21). The other seven patients (two rejections, one hypoxia, two infections, two vascular complications) had an MEGX fall from normal or subnormal to low values with the occurrence of the complication.
The low MEGX test was transient in 6/7 cases, related to treatable clinical events and not necessarily accompanied by an alteration in standard liver function tests (4.6 cases).
One patient with caval thrombosis required transplantation on the 7th day because of severe ischaemic damage, the very low MEGX concentration preceding the increase in the aminotransferases remained until retransplantation.
MEGX formation by de-ethylation of lignocaine correlates well with CP450 III A4 activity, and thus might be a good indicator of hepatic oxidative metabolism. Moreover, phase 1 biotransformation reactions, generally dependent on CP450, have been shown to be the first altered in liver disease .
Oellerich et al. were the first to validate the MEGX test for the assessment of liver function . They confirmed this dynamic test to be cheap, quick, easy to perform and reproducible. Burdelski et al. then developed MEGX in liver transplantation, for the selection of organ donors . Thus, several of their prospective studies substantiate the value of the MEGX test compared with other criteria (bilirubin, PTI, aminotransferases activity, glutamate deshydrogenase and cholinesterase, indocyanine green clearance and galactose elimination capacity) for the evaluation of graft function [15,21,22]. Graft survival rate at day 120 is significantly higher if the MEGX test in the donor is over 90 μg L−1. According to MEGX formation, liver graft function is characterized as good: over 90 μg L−1, questionable: between 90–50 μg L−1 and poor under 50 μg L−1.
Another application of the MEGX test, suggested and verified by Oellerich and his team is the assessment of the degree of chronic liver disease and consequently the urgency for transplantation [24,25].
Among others, Gremse and Schroeder [26,27] have confirmed both these applications of the MEGX test.
The relevance of MEGX formation early after liver transplantation has not yet been explained. Oellerich mentions only that post-operative values are usually lower than in the donors [23,28]. Other teams have used this test for acute rejection diagnosis and treatment evaluation. Gremse and Schroeder first underlined the importance of MEGX formation after transplantation, with special emphasis on its sudden concentration fall if graft ischaemia or rejection occurs; this alteration precedes the rise in transaminases and bilirubin as well as the histological features of acute rejection, indicating that this may be a more sensitive index of hepatic function .
However, these authors mention that normal MEGX values are not achieved as quickly as are those in the other tests during efficient rejection treatment. In this study, in which no patients suffered a PNF, the relevance of MEGX after liver Tx was shown in the early detection of any event that could alter liver function .
Only Potter et al. had previously used the MEGX test to monitor hepatic function in liver transplantation recipients. They considered it to be an exciting investigation that showed that MEGX conentrations of less than 25 μg L−1 in the first 36 h after revascularization were predictive of greater morbidity and mortality. However, apparent discrepancies between very low MEGX concentrations and a normal course of the standard liver function tests were reported.
Previously , we insisted on the interpretation of the first MEGX level (12 h after graft vascularization) but also of its evolution during the first 3 post-operative days (Fig. 1) discriminating between the complicated patients those with PNF (early MEGX <20 μg L−1, with values decreasing even further until reTx), those with hypoxia, early acute rejection or vascular complication (sudden decrease in MEGX formation after initial values >60 μg L−1) and those with low functional recovery, characterized by a minimal initial value (40–60 μg L−1) with a rather slow upward course. When hypoxia or ischaemia are rapidly recognized and corrected, MEGX tests return to normal values, but in the case of acute rejection, treatment has a much slower effect on MEGX formation. We have already noted the increased sensitivity but the low specificity of this test . MEGX formation in groups F and C, in this study remain different from the first sampling time (T1) through the whole study period. The lowest MEGX synthesis was found in one patient with PNF, in all the patients, it correlated well with the severity of graft disease.
The high sensitivity is linked with the fact that the MEGX test decreases sharply in the event of an hypoxic insult (circulatory failure or ischaemia) to the liver [24,31,32]. It is well established that lignocaine clearance depends on liver blood flow and the metabolizing capacity of CP450 III A. CP450 activity is readily altered by liver hypoxia [31,33]. The MEGX test could be the most reliable and rapid marker of hypoxic liver injury, along with hepatic oxygen consumption and ATP content .
The lack of specificity of MEGX test explains why some authors emphasize the possibility of good graft function with low MEGX formation [35–37]. This phenomenon is better understood because the wide inter individual variability of CP450 III A activity is known, differentiating good and poor metabolizers [38,39]. In the case of liver Tx, it is important to detect these poor metabolizers, they need less Cyclosporine, in order to avoid overdose and toxicity [38,40,41]. Moreover, several agents administered during and after surgery, metabolized by this type of cytochrome, can compete with each other (alfentanil, propofol, sufentanil, erythromycin), other drugs may act as cytochrome inhibitors (ketoconazole, cimetidine, ranitidine, omeprazol) or inducers (rifampicin, phenobarbital and phenytoin) . This may explain some drug interactions and possibly the decreased MEGX production during a prolonged ICU stay . This low specificity, combined with all the known and unknown factors independent of liver function, applies to almost all dynamic liver function tests. Thus, arterial ketone body ratio (AKBR), another commonly used test, depends on glucose and fatty acid administration , and becomes useless following retransplantation because of the complex metabolic deficits and therapies .
On the whole the MEGX test appears in our experience to be very useful, and several situations can be schematically described.
- In all cases in which the MEGX values are satisfactory (above 60 μg L−1), the initial evolution is uncomplicated; 1 year survival is nearly 100% even if some conventional liver function tests are altered. The association of a good MEGX test with altered conventional tests seems to reflect graft injury during removal, cold ischaemia or reperfusion but without compromise of the liver graft function.
- An abnormal MEGX test can be associated with normal conventional liver function tests; either we are dealing with poor CP450 III A activity or with a complication without serious repercussions on the liver function (infection, hypoxia). On each occasion when reduced CP450 III A activity was suspected Cyclosporine values were considerably increased, necessitating reduced CycloA administration [45,46]. An explanation for an abnormal MEGX test was found in all these situations.
- Concomitant alterations in MEGX and conventional tests always reflected graft injury. The degree in MEGX test alteration is best linked with the degree of liver disease. A persisting MEGX formation below 20 μg L−1 was synonymous with retransplantation. Furthermore in case of later follow-up complication MEGX test modification preceded the changes in the conventional liver function tests, justifying therapeutic and diagnostic attitudes.
This led us to combine two tests, which assess independent metabolical pathways to improve the predictive value of the post transplantation course for these patients. The value of this had already been shown by Foster in a particular case of PNF diagnosis by the combination of ASAT and F VIII, or bile production and F VIII or ASAT . For Gubernatis et al. the association of a low liver oxygen consumption and a low AKBR has the best predictive value of irreversible graft injury .
The combination of two well selected independent tests allows one to predict not only a short term favourable outcome, but also to suspect with a high degree of predictive value a PNF or an acute rejection [5,47] and to treat these conditions early. In daily practice, the main problem is to distinguish acute rejection from primary non function (PNF). As with some recent studies, the present data emphasize that the increase in ASAT predicts acute rejection [48–50], unlike previous reports basing the diagnosis on cholestasis.
MEGX measurement allows a rapid determination of liver graft function and appears to be an early indicator for outcome. It can easily predict an uncomplicated post-operative course, 24 h after unclamping when values are in excess of 60 μg L−1. If this level is maintained for the first 3 days, no serious complication need be feared. Low MEGX formation must be considered with conventional liver function tests. Only in combination with an altered biochemical test does it reflect a graft injury. Severe liver graft dysfunction associates the lowest MEGX values and the highest bilirubin concentration. Acute rejection can be evoked in the presence of cytolysis with resulting MEGX test alteration.
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