The role of hepatic arterial Doppler ultrasound after liver transplantation: an 'audit cycle' evaluation

Tardus parvus waveforms in Doppler ultrasonography for hepatic artery stenosis after liver transplantation: can a new cut-off value guide the next step?

PURPOSE

Considering the high false-positive diagnosis of the tardus parvus waveform (TPW) in Doppler ultrasonography (DUS) for hepatic artery stenosis (HAS) after liver transplantation (LT), this study aimed to determine clinical features and new cut-off values to help guide treatment.

MATERIALS AND METHODS

This retrospective study was approved by an Institutional Review Board. A total of 171 LT recipients were included and underwent DUS and either computed tomography angiography or digital subtraction angiography with an interval < 4 weeks at least 1 month post-LT. The DUS of 69 patients exhibited TPW [defined as resistive index (RI) < 0.5 and systolic acceleration time (SAT) > 0.08 s]. A multilevel likelihood ratio (LR) analysis was used to explore new cut-off values for DUS. In addition, abnormal liver function was considered additional evidence (defined as any liver enzyme > 3-fold of the upper limit of normal level or 2-fold increased). The results were stratified into three categories, category 1 (subjects with traditional TPW), category 2 (subjects with traditional TPW and abnormal liver function), and category 3 (subjects with traditional TPW and abnormal liver function, or with new cut-off values), and the diagnostic performance of each category was analyzed.

RESULTS

The LR analysis revealed new cut-off values of RI < 0.4 (LR = 10.58) or SAT > 0.12 s (LR = 16.46). The false-positive rates for categories 2 and 3 were significantly lower (7.6% vs. 18.1%, P = 0.038; 1.9% vs. 18.1%, P < 0.001, respectively) than those for category 1, while the sensitivity for category 2 was significantly lower (41.8% vs. 74.6%, P < 0.001; 41.8% vs. 61.2%, P = 0.038, respectively) than that for categories 1 and 3.

CONCLUSION

Using either (1) RI < 0.4 or SAT > 0.12 s, or (2) traditional TPW (RI < 0.5 and SAT > 0.08 s) in the presence of abnormal liver functions as the DUS criteria for HAS will significantly decrease the false-positive rate compared to traditional TPW without a significant increase in the false-negative rate.

Doppler Parameters of the Hepatic Artery as Predictors of Graft Status in Pediatric Liver Transplantation

OBJECTIVE

The purpose of this article is to determine whether hepatic artery (HA) Doppler parameters can be used to predict pediatric liver graft status in the immediate postoperative (< 10 days) period and in the first year after transplant.

MATERIALS AND METHODS

A retrospective review of the liver transplant database was performed to review operative, clinical, laboratory, histopathologic, and ultrasound findings at three time points after surgery: 3 days, 3 months, and 1 year. The association between HA velocity and resistive index (RI) with graft status was assessed.

RESULTS

Of 120 children (54 girls and 66 boys; mean age, 3 years 2 months) enrolled, 70 had satisfactory graft status at the 1-year follow-up examination. HA velocity of 50-200 cm/s at 3 days was associated with normal graft status during the immediate postoperative period (p = 0.003), at 3 months (p = 0.0653), and at the 1-year follow-up examination (p = 0.0268). Vascular and biliary complications in the immediate postoperative period were more frequent at an HA velocity of 201-300 cm/s (p = 0.0024). There was a significant association between RI at 3 days and graft status in the immediate postoperative period (p = 0.0308), with an RI less than 0.5 associated with vascular complications (p = 0.0116).

CONCLUSION

An RI less than 0.5 is associated with vascular complications. An HA velocity of 50-200 cm/s and an RI of 0.5-0.8 are associated with normal graft status in children within the first year after transplant. Values outside this range, or in this range along with a constellation of other ultrasound findings and clinical status, support the initiation of additional more-specific investigations that may help in early treatment to prevent complications.

Hepatic arterial stenosis assessed with doppler US after liver transplantation: frequent false-positive diagnoses with tardus parvus waveform and value of adding optimal peak systolic velocity cutoff

PURPOSE

To evaluate the utility of the tardus parvus waveform of the hepatic artery at Doppler ultrasonography (US) in the diagnosis of hepatic arterial stenosis in liver transplant (LT) recipients and determine whether the accuracy of such a diagnosis is enhanced by including an optimal peak systolic velocity (PSV) cutoff.

MATERIALS AND METHODS

This retrospective study was institutional review board approved; the requirement for informed consent was waived. The authors identified 361 LT recipients (267 male, 94 female) who underwent Doppler US and either computed tomography (CT) or angiography, with an interval between these examinations of less than 1 week. At Doppler US, tardus parvus pattern was defined as a waveform with a resistive index (RI) of less than 0.5 and a systolic acceleration time longer than 0.08 second. At CT or angiography, patients were assigned to the hepatic arterial stenosis (≥50% vessel narrowing) or nonstenosis group. The capability of the tardus parvus pattern to facilitate the diagnosis of hepatic arterial stenosis was calculated. The difference in PSV between the true- and false-positive tardus parvus patterns was evaluated. Receiver operating characteristic (ROC) analysis was performed to determine the optimal cutoff PSV for diagnosing hepatic arterial stenosis. The capability of the tardus parvus pattern and an optimal PSV cutoff in the diagnosis of hepatic arterial stenosis was determined.

RESULTS

Sixty transplant recipients had the tardus parvus pattern at Doppler US. The sensitivity, specificity, and positive predictive value (PPV) of the tardus parvus pattern were 72% (23 of 32 LT recipients), 88.8% (292 of 329 LT recipients), and 38% (23 of 60 LT recipients), respectively. The false-positive rate was 11.2% (37 of 329 LT recipients). ROC analysis revealed an optimal PSV cutoff of less than or equal to 48 cm/sec for diagnosing hepatic arterial stenosis. The combination of the tardus parvus pattern and a PSV cutoff of less than or equal to 48 cm/sec improved specificity to 99.1% (326 of 329 LT recipients) and the PPV to 88% (22 of 25 LT recipients), thereby reducing the false-positive rate to 1% (three of 329 LT recipients) while slightly decreasing the sensitivity to 69% (22 of 32 LT recipients).

CONCLUSION

Use of the tardus parvus waveform of the hepatic artery resulted in a low PPV and a high false-positive rate. However, the combination of the tardus parvus pattern and an optimal PSV cutoff greatly improved the PPV and reduced the false-positive rate in the diagnosis of hepatic arterial stenosis.

Implantable sensor for blood flow monitoring after transplant surgery

A limited number of techniques are employed in clinical medicine for regional tissue perfusion assessment. These methods are marginally effective and are not well suited for implantation due to the inability to miniaturize the associated technologies. Consequently, no standardized techniques exist for real-time, continuous monitoring of organ perfusion following transplantation. In this paper, a brief overview of the relevant clinical techniques employed for regional tissue perfusion assessment is given with particular emphasis on post-surgical monitoring of transplanted organs. The ideal characteristics for a perfusion monitoring system are discussed and the development of a new, completely implanted local tissue monitoring system is summarized. <I>In vivo</I> and <I>in vitro</I> data are presented that establish the efficacy of this new technology, which is a photonics-based sensor system uniquely suited for continuous tissue monitoring and real-time data reporting. The suitablity of this sensor technology for miniaturization, which enables implantation for monitoring localized tissue perfusion, is discussed.

Hemodynamic changes on color Doppler flow imaging and intravenous contrast-enhanced ultrasound for assessing transplanted liver and early diagnosis of complications

The value of color Doppler flow imaging (CDFI) and intravenous contrast-enhanced ultrasound (CEUS) for assessing the transplanted liver and early diagnosing complications by examining hemodynamic changes was discussed. Seventy-five patients with orthotopic liver transplantation (OLT) underwent CDFI. The following parameters were measured: peak systolic velocity (PS), resistance index (RI) and Doppler perfusion index (DPI) of the hepatic artery (HA), time average velocity (TAV) of portal vein (PV) and velocity of hepatic vein (HV) in different stages postoperation. And 11 patients of them received CEUS. Thirty healthy subjects were enrolled as controls. The results showed that: (1) In 23 patients without obvious complications, TAV of PV within 15 days post-operation was significantly higher than in controls (P<0.05), PS and DPI of HA within 7 days postoperation were lower, but RI was higher than in controls (P<0.05); (2) When the hepatic artery thrombosis (HAT) occurred, PS and DPI of HA were obviously decreased, but TAV of PV significantly increased like a high saw-tooth wave; (3) While rejection occurred, both TAV of PV and PS of HA were decreased with the increase in RI of HA, and the triphasic wave of HV disappeared and displayed as saw-tooth wave; (4) The incidence of biliary complications in liver transplantation was increased when DPI was reduced; (5) Seven cases of hepatic carcinoma relapse after OLT demonstrated hyperecho in the arterial phase and hypoecho in the portal and later phase on CEUS; (6) In 2 cases of HA thrombus, there was no visualized enhancement in arterial phase of CEUS, but enhancement during the portal vein and parenchymal phase. It was concluded that the hemodynamic changes of PV, HA and HV in the transplanted liver are valuable for assessing the transplanted liver and early diagnosing complications on CDFI and CEUS.

Resistance index in mediastinal lymph nodes: a feasibility study

OBJECTIVE

The purpose of this study was to determine the range of Doppler ultrasonographic measurements of the resistance index in presumed normal mediastinal lymph node arteries.

METHODS

Consecutive patients referred for bronchoscopy for various indications and normal CT findings in the mediastinum were included. The resistance index (RI) in mediastinal lymph node arteries was examined with Color Doppler ultrasonography. The peak systolic velocity (PSV) and the end-diastolic velocity were measured, which allowed for calculation of the resistance indices in different lymph node stations and in each lymph node artery.

RESULTS

Eighty-nine patients (32 female; 57 male; mean age, 42.2 years) were examined, and of these, 50 patients (24 female; 36 male; mean age, 44.7 years) had measurable RIs. PSV and ESV were measured in all visible nodes (n = 196) and an interpretable value was obtained in 127 nodes (2.5 nodes per patient.). The median PSV was 15.6 cm/s (range, 8.9-23.2 cm/s, SD +/- 2.6, 25-75% percentile 13.8-17.5), and the median end-diastolic velocity was 5.8 cm/s (range, 3.6-11.4 cm/s, SD 1.15 cm/s, 25-75% percentile 5.1-6.3). The median RI values for arteries were 0.63 (range, 0.52-0.75, SD 0.04, 25-75% percentile 0.6-0.64) respectively. The Doppler measurements lasted on average 4.3 minutes and no complications were seen.

CONCLUSION

Color Doppler ultrasonography allows for quantification of velocities like PSV and ESV in mediastinal lymph node arteries, which in turn allow calculation of a resistance index. Knowledge of the resistance index's normal range (which describes the resistance of the blood flow within the lumen of the lymph node artery) may be a useful adjunct to the ultrasonic assessment of the mediastinum.

Clinical outcomes from hepatic artery stenting in liver transplantation

Hepatic artery stenosis after liver transplantation may affect liver function and result in hepatic artery thrombosis. Surgical reconstruction has been the first choice for treatment. Interventional radiologic technique can be used, but there is no report on long-term outcome. The aim of this paper is to assess current outcome and complications of hepatic artery stenting. Twenty-six adult patients were stented for hepatic artery stenosis between 1998 and 2003. Nine patients had previous surgical reconstruction for hepatic artery stenosis. Seventeen patients suffered newly developed hepatic artery stenosis. Three patients were retransplanted. After stenting, the patients were followed by Doppler ultrasound at day 1, 1 month, and 6 months. Angiography was scheduled in 6 months. Four patients died within 2 months. The other 22 patients were followed for mean 31 +/- 14 months (8-71 months). One of 22 patients died from renal failure 2 years later. Twelve patients' hepatic arteries looked normal after stenting. Restenosis was seen in 8 patients (36%). Other complications were artery thrombosis (n = 1) and long segment stricture (n = 1). In 2 patients (25%) restenosis resulted in thrombosis. Six of the 8 patients who developed recurrent stenosis were successfully treated interventionally: restent (n = 5) and balloon dilation (n = 3). However, 3 patients (38%) restenosed. Kaplan-Meier complication-free survival was 54% at 1 year after stenting. In conclusion, hepatic artery stenting is a viable treatment for hepatic artery stenosis with reasonable results. Stenting is useful as adjuvant treatment after surgical revision.

Early Postoperative Hepatic Sonography as a Predictor of Vascular and Biliary Complications in Adult Orthotopic Liver Transplant Patients

OBJECTIVE

Our objective was to quantitatively assess the value of early posttransplantation hepatic artery resistive indexes in predicting vascular and nonvascular complications in adult orthotopic liver transplant (OLT) patients.

MATERIALS AND METHODS

Between 1999 and 2001, 110 consecutive adults received grafts. Doppler sonographic graft evaluations measured main, right, and left resistive indexes within 24 to 48 hr after surgery (normal resistive index cutoff, 0.6). Clinical, operative, procedural, and radiologic reports were reviewed for vascular and biliary complications. Frequency, Student's t test, logistic, and regression statistical analyses were performed.

RESULTS

even patients (6.4%) had vascular complications, including two (1.8%) hepatic artery and two (1.8%) hepatic vein stenoses, one (0.9%) hepatic vein thrombosis, two (1.8%) portal vein thromboses, and one (0.9%) thrombosis and two (1.8%) stenoses of the inferior vena cava (IVC). In 19 patients (17.3%), biliary complications included anastomotic strictures and leaks 1 week to 18 months after transplantation. In 11 patients (10%), sonographically large hematomas required surgical evacuation. In grafts with vascular complications or large hematomas, the mean early posttransplant main, right, and left indexes were significantly lower (< or = 0.6) than without these complications (p < 0.01). In grafts with and without biliary complications, mean early posttransplant main, right, and left indexes did not differ significantly.

CONCLUSION

In adult OLT patients, low early posttransplant hepatic artery resistive indexes were sensitive (100%) and specific (80%) predictors for vascular complications (e.g., hepatic artery, portal vein, hepatic vein, and IVC) but not for biliary complications. All patients with indexes less than 0.6 within 24-48 hr after surgery should be monitored closely for vascular complications.

Microbubble ultrasound contrast in the assessment of hepatic artery patency following liver transplantation: role in reducing frequency of hepatic artery arteriography

We prospectively evaluated the role of microbubble ultrasound contrast for detection of hepatic artery thrombosis following liver transplantation. The hepatic artery of adult liver transplant recipients with suspected thrombosis on surveillance Doppler ultrasound (US) were re-examined by a second observer. In patients with no hepatic spectral Doppler signal the microbubble contrast agent Levovist was used. The presence or absence of flow following microbubble contrast was evaluated against arteriography or repeated Doppler US findings. A total of 794 surveillance Doppler US examinations were performed in 231 patients. Hepatic artery flow was demonstrated in 759 of 794 (95.6%) examinations. Microbubble ultrasound contrast was administered in 31 patients (35 studies) with suspected hepatic artery thrombosis. Following microbubble US contrast the hepatic artery could not be demonstrated in 13 of 35 (37.1%) studies (12 patients). Eight patients had arteriography: there was hepatic artery thrombosis in 7 patients and 1 patient had a patent, highly attenuated artery. Detection of a patent hepatic artery increased from 759 of 794 (95.6%) to 781 of 794 (98.4%) with the addition of microbubble contrast. Upon independent reading of the data, the degree of operator confidence in the assessment of the hepatic artery patency prior to microbubble contrast was 4.7 (CI 1.92-7.5) but rose to 8.45 (CI 7.06-9.84) following microbubble contrast ( p<0.0001). In 22 of 35 (62.9%) of studies arteriography could potentially have been avoided. Ultrasound microbubble contrast media may reduce the need for invasive arteriography in the assessment of suspected hepatic artery thrombosis.

Doppler evaluation of arterial complications of adult orthotopic liver transplantation

PURPOSE

The aim of this study was to analyze the role of the resistance index (RI), systolic acceleration time (SAT), and spectral waveform's morphologic characteristics in the sonographic evaluation of the hepatic artery for early detection of stenosis or thrombosis after orthotopic liver transplantation.

METHODS

Arterial Doppler sonograms of 174 transplanted livers in 150 patients were analyzed for presence or absence of blood flow, RI, SAT, and peak systolic velocity. A qualitative evaluation of the spectral waveform morphologic characteristics was also made. In patients who had had abnormal findings on sonography, we compared those results with results obtained on multislice helical CT or angiography.

RESULTS

At least 1 of the Doppler criteria for hepatic artery stenosis or thrombosis was identified in 25 of the transplants. The findings on multislice helical CT, angiography, or both confirmed the diagnosis of stenosis or thrombosis in 20 of the 25 cases: in 9 of 10 cases of absent hepatic arterial blood flow, 5 of 9 with an RI lower than 0.5, 6 of 7 cases with an SAT longer than 0.08 second, 10 of 11 cases of changes to a tardus-parvus-like spectral waveform, and in the 1 case of a peak systolic velocity greater than 2 m/second.

CONCLUSIONS

The most accurate indicator of hepatic arterial stenosis or thrombosis was a change in the spectral waveform to a tardus-parvus pattern, with 91% sensitivity and 99.1% specificity. Among the other parameters, an increase of the SAT value (> 0.08 second), when associated with the morphologic modification of the systolic peak, is a more reliable parameter than the RI for early detection of artery stenosis, especially when the type of anastomosis is unknown.

Hepatic artery thrombosis after adult liver transplantation

The incidence, clinical presentation, therapeutic options, and outcome of hepatic artery thrombosis (HAT) were analyzed in a series of 1,192 consecutive adult orthotopic liver transplantations (OLTs). HAT after OLT was observed in 30 cases, resulting in an incidence of 2.5%. The incidence of HAT increased 5.76-fold when the donor hepatic artery was reconstructed with an interposition graft to the supraceliac aorta (P <.05). Early HAT (within the first 30 days after OLT) occurred in 14 of these patients (46.7%), whereas in 16 patients (53.3%), HAT occurred beyond 30 days post-OLT. Clinical presentation of HAT ranged from an increase in serum transaminase levels with or without cholestasis to liver abscess and biliary complications, including cholangitis, bile duct stenosis or necrosis, to liver dysfunction and failure. Impairment of graft function was observed in patients with early HAT, whereas biliary tract destruction was seen more often in patients with late HAT. In only 1 patient was HAT clinically asymptomatic. Therapy consisted of recombinant plasminogen lysis with hepaticojejunostomy, liver abscess drainage, endoscopy or surveillance, and surgical thrombectomy. In 14 of 30 patients (46.7%), the occurrence of HAT required re-OLT. Nine patients with HAT died during follow-up; however, only 4 of these deaths were related to HAT, resulting in a mortality rate of 13.3%. Our results indicate that HAT is a rare but serious complication after OLT, requiring re-OLT in almost 50% of patients. In particular, conservative treatment modalities may significantly prolong graft survival, thus postponing re-OLT.

Changes in hepatic perfusion after administration of hydroxyethyl starch in intensive care patients assessed using color-coded Doppler sonography

Using color-coded Doppler sonography (CCDS), changes in the resistance index of the hepatic artery (HA-RI) and in the velocities of the hepatic artery, portal and splenic vein (HA-V, PV-V, SV-V) were measured after administration of hydroxyethyl starch (HES) in 50 intensive care patients. PV-V and SV-V increased, whereas HA-V and HA-RI remained unchanged. CCDS is suitable to assess liver perfusion in intensive care patients. Since HES enhances splanchnic perfusion, its application improves hepatic perfusion in intensive care patients.

Correlation between intraoperative blood flows and hepatic artery strictures in liver transplantation

Hepatic artery strictures (HASs) may be a source of morbidity and mortality in liver transplant recipients. This study evaluated the potential correlation between intraoperative arterial and venous blood flows measured after implantation of the liver allograft and the occurrence of postoperative HASs requiring repair. Prospectively collected data from 1,038 patients with complete data sets who underwent initial orthotopic liver transplantations between December 1984 and December 1999 were used. Electromagnetic flow measurements were routinely obtained in these cases. Hepatic artery and portal vein patency were reassessed routinely according to our protocol in the first postoperative day by Doppler ultrasound. When considered hemodynamically significant, strictures were corrected. There was a 6.2% incidence (n = 64) of hepatic artery stenosis in our transplant population. When considered as a whole, the hepatic artery stenosis group had lower intraoperative flow volumes than transplant recipients who did not develop strictures (mean flows, 452 v 518 mL/min, respectively; P =.025). The hepatic artery stenosis group also had lower intraoperative portal vein flows compared with the group without hepatic artery stenosis (1.80 v 2.11 L/min, respectively; P =.0043). Strictures were less frequent among transplant recipients with cryptogenic cirrhosis. We did not observe differences among the groups for retransplantation or patient and graft survival. In our series, there was a 6.2% incidence of postoperative HASs. We observed a significant association between intraoperative hepatic artery and portal vein flows and postoperative HASs.