Renal dysfunction in hepatic disease: early identification with renal duplex Doppler US in patients who undergo liver transplantation

Peritransplant Renal Dysfunction in Liver Transplant Candidates

Renal function is intricately tied to Model for End-Stage Liver Disease score and overall prognosis among patients with cirrhosis. The estimation of glomerular filtration rate (GFR) and etiology of renal impairment are even more magnified among cirrhotic patients in the period surrounding liver transplantation. Novel biomarkers including cystatin C and urinary neutrophil gelatinase-associated lipocalin have been demonstrated to more accurately assess renal dysfunction and aid in the diagnosis of competing etiologies. Accurately identifying the severity and chronicity of renal dysfunction among transplant candidates is an imperative component with respect to stratifying patients toward simultaneous liver-kidney transplantation versus liver transplantation alone.

Renal Venous Doppler Study in Obstructive Uropathy

INTRODUCTION

Obstructive uropathy is very common cause of pain abdomen. Recognition of the cause of the pain and level of obstruction is the goal. Ultrasound is the primary modality used for detection and characterization of obstructive uropathy along with conventional radiographs. Obstructive uropathy in early stages can be difficult to diagnose using standard B-mode USG or arterial sensitive index.

AIM

The purpose of this study is to evaluate the diagnostic accuracy of renal venous doppler ultrasound in diagnosing acute obstructive uropathy either alone or in addition to arterial doppler study of inter lobar arteries. As there is limited literature available till date on Indian population regarding renal venous doppler in obstructive uropathy, this study can be useful.

MATERIALS AND METHODS

Fifty patients presenting with features suggestive of obstructive uropathy were studied and compared with non-obstructed kidney of the same patient. Fifty normal individuals were studied and taken as controls.

RESULTS

The mean venous impedance index on the obstructed side (0.26 ± 0.07) was less than the mean venous impedance index on the unobstructed side (0.41 ± 0.08) and was statistically highly significant. There was no statistically significant difference in mean arterial Resistivity Index (RI).

CONCLUSION

Thus renal venous doppler study is a reliable tool in diagnosing cases of acute obstructive uropathy. Though its use as single parameter to identify obstruction still needs further studies, it can be used in conjugation with b mode ultrasound and arterial Doppler to identify obstruction.

Kidney Failure and Liver Allocation: Current Practices and Potential Improvements

In February 2002, the United Network for Organ Sharing implemented a system for prioritizing candidates for liver transplantation that was based on the risk of 90-day mortality as determined by the Model for End-Stage Liver Disease (MELD) score. As the MELD score is driven in part by serum creatinine as a marker of kidney function, the prevalence of kidney dysfunction and failure in patients with end-stage liver disease at the time of listing and at transplantation has steadily risen. In this review, we discuss current practices in liver transplantation in patients with kidney dysfunction focusing briefly on the decision to perform simultaneous liver-kidney transplantation. We then discuss pitfalls to the current practices of liver transplantation in patients with kidney dysfunction. We conclude by discussing potential improvements to current practices including the use of the MELD-Na score, alternatives to creatinine and creatinine-based equation for estimating kidney function, and the use of intraoperative kidney replacement therapy during liver transplantation.

Challenges and Management of Liver Cirrhosis: Pathophysiology of Renal Dysfunction in Cirrhosis

Kidney dysfunction is a common complication of patients with advanced cirrhosis and is associated with poor prognosis. Patients with advanced cirrhosis show circulatory dysfunction characterized by reduced systemic vascular resistance due to splanchnic arterial vasodilation, which is caused by portal hypertension. The progressive reduction in systemic vascular resistance leads to effective arterial hypovolemia. In order to maintain arterial pressure within normal limits in this setting, there is activation of systemic vasoconstrictor systems, including the renin-angiotensin-aldosterone system, sympathetic nervous system and, in late stages, nonosmotic hypersecretion of vasopressin. Although these systems have positive effects in maintaining arterial pressure, they have a negative influence on kidney function, leading to the retention of sodium and solute-free water, and in late stages of the disease an intense kidney vasoconstriction develops, leading to decrease of the glomerular filtration rate and the development of hepatorenal syndrome (HRS). Moreover, bacterial translocation and the existence of a systemic inflammatory state in patients with advanced cirrhosis may play a role in the impairment of circulatory function. HRS is a unique cause of kidney failure of functional origin that develops in patients with cirrhosis. However, besides HRS, patients with cirrhosis may develop kidney failure due to other causes, including bacterial infections, prerenal kidney failure, shock, use of nephrotoxic drugs or intrinsic kidney diseases. Considering the existence of circulatory dysfunction and some degree of kidney vasoconstriction, patients with advanced cirrhosis have fragile kidney function and are susceptible to easily developing kidney failure associated with other complications of the disease, particularly bacterial infections and gastrointestinal bleeding.

Resistive index and MELD-Na: nephrologic monitoring in cirrhotic patients awaiting liver transplantation

Renal dysfunction in cirrhotic patients is primarily related to disturbances in circulatory function. In decompensated cirrhosis, ascites and water retention are associated with development of dilutional hyponatremia. The arterial resistive index (RI) is a measure of resistance to arterial flow within the renal vascular bed. Hyponatremia is an independent predictor of mortality in patients with ascites. The aim of this study was to evaluate intrarenal RI in end-stage liver disease (ESLD) patients awaiting liver transplantation (LT) and its association with renal and hepatic function as assessed by Model for End-Stage Liver Disease (MELD) and MELD-Na scores. We evaluated 40 cirrhotic patients (23 males, 17 females) awaiting LT from January 2009 to January 2012. Twenty-six of the 40 patients (65%) showed a renal RI ≥ 0.70, the normal value according to standard reported evaluations. Patients with RI ≥ 0.70 showed significantly higher MELD and MELD-Na scores as well as greater higher serum creatinine and lower serum sodium concentrations compared with subject displaying RI <0.70. The most relevant result of our study was the strong association between elevated renal RI in ESLD patients and advanced liver dysfunction, as demonstrated by MELD and MELD-Na scores, hyponatremia, ascites, and acute renal failure episodes. In conclusion, this study suggested that intrarenal RI assessment should be considered in the clinical and nephrologic monitoring of cirrhotic patients awaiting LT.

Role of cystatin C and renal resistive index in assessment of renal function in patients with liver cirrhosis

AIM: To evaluate the clinical significance of cystatin C and renal resistive index for the determination of renal function in patients with liver cirrhosis.

METHODS: We conducted a study of 63 patients with liver cirrhosis. A control group comprised of 30 age and gender-matched healthy persons. Serum cystatin C was determined in all study subjects and renal Doppler ultrasonography was made. Estimated glomerular filtration rate from serum creatinine (GFR_Cr) and cystatin C (GFR_Cys) was calculated.

RESULTS: We confirmed significant differences in values of cystatin C between patients with different stages of liver cirrhosis according to Child-Pugh (P = 0.01), and a significant correlation with model of end stage liver disease (MELD) score (r_s = 0.527, P < 0.001). More patients with decreased glomerular filtration rate were identified based on GFR_Cys than on GFR_Cr (P < 0.001). Significantly higher renal resistive index was noted in Child-Pugh C than in A (P < 0.001) and B stage (P = 0.001). Also, a significant correlation between renal resistive index and MELD score was observed (r_s = 0.607, P < 0.001). Renal resistive index correlated significantly with cystatin C (r_s = 0.283, P = 0.028) and showed a negative correlation with GFR_Cys (r_s = -0.31, P = 0.016).

CONCLUSION: Cystatin C may be a more reliable marker for assessment of liver insufficiency. Additionally, cystatin C and renal resistive index represent sensitive indicators of renal dysfunction in patients with liver cirrhosis.

Doppler assessment of splanchnic arterial flow in patients with liver cirrhosis: correlation with ammonia plasma levels and MELD score

PURPOSE

To assess the clinical significance of blood flow velocity and resistance index (RI) in the visceral arteries of patients with liver cirrhosis with respect to plasma ammonia (NH3) level and liver function.

METHODS

We included 80 patients with liver cirrhosis (58 men) and 20 healthy controls (11 men). Duplex Doppler ultrasonography was used to assess flow velocity and RI in the hepatic (HA), right (RRA), and left renal (LRA), and splenic (SA) (LA) artery. Plasma NH3 was measured by biochemistry. Liver function was assessed by MELD score (model of end-stage liver disease).

RESULTS

HA, LRA, and SA systolic flow velocities were greater, whereas RRA diastolic velocity was lower in patients with liver cirrhosis than in controls RI was higher in LRA, RRA, SA, and HA in patients with liver cirrhosis than in controls. NH3 levels were significantly elevated in all patients with liver cirrhosis (p < 0.05) and significantly correlated with RI of RRA, LRA, and SA.

CONCLUSION

We found greater renal, hepatic, and LA RI in patients with liver cirrhosis than in healthy controls. The correlation we found between elevated renal artery RI (≥0.70) and MELD score emphasizes the risk of renal dysfunction during progression of liver cirrhosis.

Renal duplex sonographic evaluation of type 2 diabetic patients

OBJECTIVES

The purpose of this study was to evaluate the renal volume and intrarenal hemodynamics with duplex sonography in a group of diabetic patients with normal renal function in comparison to nondiabetic controls.

METHODS

The renal volume and resistive index (RI) of segmental arteries were assessed by duplex sonography in 88 diabetic patients (44 male and 44 female; median age, 58 years [range, 37-69 years]) and 73 nondiabetic control participants (48 male and 25 female; median age, 53 years [range, 27-75 years]) without renal artery stenosis.

RESULTS

Both renal volume and RI values in the diabetic patients were significantly higher compared to the controls (mean volume ± SD: diabetic patients, 197.3 ± 47.6 mL; controls, 162.5 ± 35.2 mL; P < .0001; RI: diabetic patients, 0.70 ± 0.05; controls, 0.59 ± 0.06; P < .0001). Renal hypertrophy was present even in diabetic patients without proteinuria (renal volume: patients without proteinuria, 198.3 ± 45.9 mL; controls, 162.5 ± 35.2 mL; P < .005). Patients with higher RI values had significantly greater proteinuria (RI <0.75, 15.9 mg/g [range, 4.2-1718.9 mg/g]; RI >0.75, 37.9 mg/g [range, 11.34-2087.0 mg/g]; P < .02).

CONCLUSIONS

Changes in renal volume and hemodynamics are detectable on sonography in diabetic patients. Those changes are also present in patients without proteinuria or signs of renal atherosclerosis and with both normal and increased glomerular filtration rates. These results indicate a potential role of duplex sonography in the early identification of morphologic and hemodynamic renal changes in type 2 diabetic patients.

Intrarenal resistance index for the assessment of acute renal injury in a rat liver transplantation model

Background

Acute kidney injury (AKI) is a common complication after liver transplantation (LT) and associated with a high mortality. The renal resistive index (RI) is used to assess early renal function impairment in critical care patients. However, limited data are available concerning changes of renal RI and the development of AKI early after reperfusion. We approached to investigate the changes of renal RI and AKI after reperfusion in a rat liver transplantation model.

Methods

Rats were randomly divided into sham group or LT group. Ten rats in each group were used for the hemodynamic study and twenty for Doppler measurements during the procedure. Ten rats were sacrificed 30 min or 2 h after the reperfusion. We harvested kidneys, serum and urine for further analysis of the renal function.

Results

The intrarenal RI increased significantly in the anhepatic stage and decreased significantly after the reperfusion in the LT group compared with sham group (P < 0.05). AKI was seen after the reperfusion in the LT group. No correlation was noted between the RI and renal function parameters 30 min after reperfusion.

Conclusions

The intrarenal RI increased significantly during the anhepatic stage, and decreased significantly early after the reperfusion. Intrarenal RI was unable to assess renal function in a rat liver transplantation model.

LEFT ventricular function assessed by echocardiography in cirrhosis: relationship to systemic hemodynamics and renal dysfunction

BACKGROUND & AIMS

The current study aimed at assessing the potential role of cardiac abnormalities in the pathogenesis of circulatory and renal dysfunction in cirrhosis.

METHODS

One hundred and fifty-two patients (34 without ascites, 95 with ascites without renal failure and 21 with hepatorenal syndrome) were evaluated using Doppler echocardiography. In 102 patients, diastolic function was assessed by measuring parameters related to ventricular filling velocity, mitral annulus velocity and left atrial dimensions. Cardiopulmonary pressures were also measured by cardiac catheterization in 54 patients. In 50 additional patients, left ventricular myocardial strain was performed to estimate myocardial contractility and systolic function.

RESULTS

Grade 1 and 2 diastolic dysfunction was present in 41% and 16% of the patients, respectively. There was no patient with severe grade 3 diastolic dysfunction. Grade 2 diastolic dysfunction was associated with higher cardiopulmonary pressures but values were within the normal limits in all cases. Diastolic dysfunction directly correlated with liver failure but not with the degree of impairment in circulatory and renal function. The proportion of patients without or with grade 1 or 2 diastolic dysfunction was similar in patients with compensated cirrhosis, with ascites without renal failure or with hepatorenal syndrome despite marked differences in the degree of circulatory dysfunction, as indicated by plasma renin activity and noradrenaline concentration. The heart rate and systolic function were normal in all cases. There were no differences between patients without ascites, with ascites without renal failure or with HRS, despite marked differences in the activity of the renin-angiotensin system and sympathetic nervous system. These features indicate an impaired response of cardiac chronotropic and inotropic function to changes in systemic hemodynamics.

CONCLUSIONS

These data indicates that: (1) diastolic dysfunction is frequent in cirrhosis but in most cases it is of mild degree and does not increase the cardiopulmonary pressure to abnormal levels. This feature, which may be due to the central hypovolemia of cirrhosis, probably accounts for the lack of symptoms associated with this condition. (2) Diastolic dysfunction in cirrhosis is unrelated to circulatory dysfunction, ascites and HRS. (3) In cirrhosis, there is a lack of response of the left ventricular systolic and chronotropic function to peripheral arterial vasodilation and activation of the sympathetic nervous system and this feature is an important contributory factor to the progression of circulatory dysfunction and the pathogenesis of ascites and HRS.

Dynamic evaluation of renal resistive index in normoalbuminuric patients with newly diagnosed hypertension or type 2 diabetes

AIM/HYPOTHESIS

Renal resistive index is a useful measure for quantifying alterations in renal blood flow. In the present study we evaluated resistive index at baseline and after vasodilation induced by nitroglycerine in normoalbuminuric patients with type 2 diabetes or essential hypertension, relating the values to indices of systemic vascular dysfunction.

METHODS

Newly diagnosed treatment-naïve type 2 diabetic (n = 32) and hypertensive patients (n = 49) were compared with 27 age- and sex-matched healthy controls. Renal resistive index was obtained by duplex ultrasound at baseline and after 25 μg sublingual nitroglycerine. Endothelium-dependent (flow-mediated dilation) and -independent (response to nitroglycerine) vasodilation in the brachial artery was assessed by computerised edge detection system. Carotid-femoral pulse-wave velocity and augmentation index were assessed by applanation tonometry. Nitrotyrosine levels, an index of oxidative stress, were also measured.

RESULTS

Resistive index was higher in diabetic than in hypertensive patients and controls (p < 0.001), while changes in resistive index induced by nitroglycerine were lower in hypertensive patients compared with controls (p < 0.01), and were further reduced in type 2 diabetic patients. Hypertensive and diabetic patients showed significantly increased arterial stiffness, nitrotyrosine levels and reduced endothelial function than controls (p < 0.05). Changes in resistive index induced by nitroglycerine were independently related to serum glucose, reactive hyperaemia and aortic pulse-wave velocity in the overall population.

CONCLUSIONS/INTERPRETATION

These results support the dynamic evaluation of renal resistive index as an early detector of renal vascular alterations in the presence of type 2 diabetes and hypertension, even before the onset of microalbuminuria.

The evaluation of renal function and disease in patients with cirrhosis

The MELD score has shown that, besides markers of liver function, serum creatinine has a strong prognostic value in cirrhosis. However, even though creatinine has a good prognostic value, it is an inaccurate marker of renal function in cirrhosis. Creatinine and creatinine-based equations tend to overestimate glomerular filtration rate (GFR), and creatinine clearance from timed urine collection also overestimates GFR. Hence, clearance of exogenous markers such as iohexol remains the only reliable method for assessing precisely GFR in cirrhosis. Whereas these investigations are limited by their costs and complexity, and they can hardly be repeated at short intervals, serum cystatin C could be an alternative, although it needs further validation. Accurate markers and/or specific equations are therefore still needed to assess GFR in cirrhotic patients. Pre-renal failure and hepatorenal syndrome (HRS) are the main causes of acute renal failure in cirrhosis. Both result from decreased renal blood flow and both can result in acute tubular necrosis. HRS is not always fully reversible with liver transplantation possibly due to underlying chronic kidney damage. A number of cirrhotic patients with acute renal failure may also have chronic kidney damage ("acute-on-chronic renal failure"); furthermore, cirrhotic patients frequently have co-morbidities such as diabetes that may result in chronic impairment in renal function. Since conventional urinary markers are biased in cirrhosis, a biopsy is the only way to document and quantify renal lesions; moreover, transvenous route should be preferred to percutaneous route. In candidates for transplantation, attention should therefore be focused on vascular lesions which may represent a risk factor for nephrotoxicities induced by calcineurin-inhibitors.

[Doppler US of the urinary system and renal vessels in normal and pathologic conditions]

The interest of Doppler ultrasound (US) in urinary tract investigation has dramatically increased during the past 10 years. It can provide useful diagnostic informations in pedicular and intrarenal vascular disorders, some medical nephropathies, in the assessment of renal tumors and urinary tract disorders including urolithiasis, acute obstruction and ureteral reflux. Recent technical improvements including the development of US contrast agents (microbubbles) have contributed to increase the diagnostic accuracy of the technique.

Increased renal vascular resistance in dogs with hepatic disease

Doppler ultrasound is a non-invasive technique that can be used to estimate vascular resistance by calculation of resistive index (RI) and pulsatility index (PI). Liver disease may increase renal RI and PI, and in humans with liver disease the indices are monitored to attain prognostic information. Systemic hypertension has been found in dogs with hepatic disease and is also related to increased renal vascular resistance in humans. The aim of this study was to examine renal vascular resistance increases in dogs with hepatic disease and to ascertain whether these may be related to blood pressure increases and biochemical parameters. Twenty dogs with hepatic disease were evaluated. The mean renal RI, PI, and systolic blood pressure were significantly higher than in normal animals. A positive correlation was found between the indices and alkaline phosphatase but not with systolic blood pressure. It is concluded that renal vascular resistance may increase in dogs with hepatic disease and in this study was above the limit value in 50% of the animals.

Renal ultrasonography in critically ill patients

Acute renal failure is a sudden and sustained decrease in the glomerular filtration rate associated with a loss of excretory function and the accumulation of metabolic waste products and water. It leads to an increase in serum urea and creatinine, usually with a decrease in urine output. Although routine surveillance of patients by means of laboratory examinations has been well defined, very little is known about renal imaging. Modern technology has provided a large number of sophisticated monitoring systems. Ultrasonography with color-Doppler study of the kidneys may be indicated as a possible monitor of renal perfusion. Ultrasonography is often used as the initial imaging procedure in the examination of patients with renal failure. Aside from excluding hydronephrosis, it is well recognized in characterizing the type of renal disease, especially in an acute setting. This article describes the use of ultrasound to achieve the proper diagnosis of acute renal diseases and to enable the appropriate and early assessment of these patients in intensive care units.

Impact of liver transplantation on renal function of patients with congenital hepatic fibrosis associated with autosomal recessive polycystic kidney disease

Congenital hepatic fibrosis (CHF) is an uncommon autosomal recessive malformation. It may be associated with extrahepatic manifestations such as polycystic kidney disease. The main consequence is portal hypertension and bleeding from varices. Despite liver transplantation as a therapeutic option for this patient, long-term impact of liver transplantation on renal functions of patients with autosomal recessive polycystic kidney disease with associated liver disease is not well known. In this study, we aimed to analyze the patient's renal function after liver transplantation by creatinine clearance, glomerular filtration rate, and renal resistive indexes. Between March 1997 and September 2002, three of 50 orthotopic liver transplantation (OLT) were performed because of CHF associated with ARPKD at Ege University Organ Transplantation and Research Center. Baseline immunosuppression consisted of prednisone and cyclosporine A (CSA). The mean follow-up of the patients was 2.1 yr. Blood urea and creatinine levels were decreased after operation in all patients and remained within the normal range at the sixth and 12th month, whereas the level of the third patient were increased at the 18th month. RRI values of patients were not found different at the sixth month whereas, RRI values of patients were decreased at the 12th month and remained unchanged at the 18th month of follow-up. During the study period hypertension developed in one patient at the 16th month and resolved with antihypertensive treatment and decreasing dosage of CSA. Kidney function has remained satisfactory in all of the patients despite the use of cyclosporine. OLT can provide good survival in patients with CHF associated with ARPKD.

Pediatric applications of abdominal vascular Doppler: Part II

Ultrasound is a remarkably powerful and versatile modality for pediatric imaging, without requiring exposure to radiation or sedatives. By providing information on blood flow, Doppler sonography can reveal details about normal physiology and disease processes not discernable from gray-scale anatomic images alone. In part I, the basics of hemodynamics and effects on the Doppler waveform were discussed, along with clinical applications in hepatic disease. In part II, the application of Doppler in renal disease and in conditions affecting the deep abdominal vessels are discussed. The role of ultrasound contrast agents in pediatric Doppler imaging is briefly reviewed.

Review article: pharmacological treatment of hepatorenal syndrome

Hepatorenal syndrome (HRS) is a common complication of advanced cirrhosis characterized not only by renal failure but also by marked alterations in systemic haemodynamics and activity of endogenous vasoactive systems. Renal failure is due to a severe vasoconstriction of the renal circulation. The pathogenesis of HRS is not completely understood but it is probably the result of extreme underfilling of the arterial circulation secondary to arterial vasodilation located in the splanchnic circulation. As well as the renal circulation, all other extrasplanchnic vascular beds appear to be vasoconstricted. The diagnosis of HRS is currently based on the exclusion of nonfunctional causes of renal failure; prognosis of patients with HRS is very poor. Liver transplantation is the best option in selected patients, but it is not always applicable as survival expectancy is short. Vasoconstrictor drugs with preferential effect on the splanchnic circulation (vasopressin analogues with a predominant V1 receptor effect, such as terlipressin--Glypressin) are very effective in improving renal function, with reversal of HRS being achieved in approximately two-thirds of patients. There is no agreement as to the terlipressin treatment regimen that is associated with a greater efficacy and lower incidence of side-effects. It appears that the administration of albumin together with terlipressin improves the therapeutic response rate. The impact of treatment on the natural course of HRS remains to be assessed in prospective investigations, but it seems that the reversal of HRS is associated with improved survival. Finally, treatment of patients with HRS with terlipressin before transplantation seems to improve post-transplantation outcome.

Hepatorenal syndrome

Hepatorenal syndrome (HRS) is a common complication of advanced cirrhosis, characterised by renal failure and major disturbances in circulatory function. Renal failure is caused by intense vasoconstriction of the renal circulation. The syndrome is probably the final consequence of extreme underfilling of the arterial circulation secondary to arterial vasodilatation in the splanchnic vascular bed. As well as the renal circulation, most extrasplanchnic vascular beds are vasoconstricted. The diagnosis of HRS is currently based on the exclusion of other causes of renal failure. The prognosis is very poor, particularly when there is rapidly progressive renal failure (type 1). Liver transplantation is the best option in patients without contraindications to the procedure, but it is not always possible owing to the short survival expectancy. Therapies introduced during the past few years, such as vasoconstrictor drugs (vasopressin analogues, alpha-adrenergic agonists) or the transjugular intrahepatic portosystemic shunt, are effective in improving renal function. Nevertheless, liver transplantation should still be done in suitable patients even after improvement of renal function because the outcome of HRS is poor. Finally, recent findings suggest that the risk of developing HRS in the setting of spontaneous bacterial peritonitis may be reduced by the administration of albumin together with antibiotic therapy, and that of HRS occurring in severe alcoholic hepatitis can be lowered by administration of pentoxifylline. Although these findings need to be confirmed, these two strategies represent innovative approaches to lower the frequency of HRS in clinical practice.

Pathophysiology of renal disease associated with liver disorders: implications for liver transplantation. Part I

Renal and hepatic function are often intertwined through both the existence of associated primary organ diseases and hemodynamic interrelationships. This connection occasionally results in the chronic failure of both organs, necessitating combined liver-kidney transplantation (LKT). Since 1988, more than 850 patients in the United States have received such transplants, with patient survival somewhat less than that for patients receiving either organ alone. Patients with renal failure caused by acute injury or hepatorenal syndrome have classically not been included as candidates for combined transplantation because of the reversibility of renal dysfunction after liver transplantation. However, the rate and duration of renal failure before liver transplantation is increasing in association with prolonged waiting list times. Thus, the issue of acquired permanent renal damage in the setting of hepatic failure continues to confront the transplant community. The following article and its sequel (Part II, to be published in vol 8, no 3 of this journal) attempt to review the problem of primary and secondary renal disease in patients with end-stage liver disease, elements involved in renal disease progression and recovery, the impact of renal disease on liver transplant outcome, and results of combined LKT; outline the steps in the pretransplantation renal evaluation; and provide the beginnings of an algorithm for making the decision for combined LKT.

Correlation between renal vascular resistance, pulse pressure, and the resistive index in isolated perfused rabbit kidneys

PURPOSE

To assess the effect of acute changes in renal vascular resistance (RVR) and pulse pressure on the resistive index (RI) measured by using Doppler ultrasonography (US).

MATERIALS AND METHODS

Rabbit kidneys were perfused by using a pulsatile perfusion system in which RVR, systolic and diastolic pulse pressures, and pulse kinetics were controlled and monitored while simultaneously measuring the RI.

RESULTS

When RVR was increased fivefold with phenylephrine hydrochloride, the RI increased only slightly (from 0.45 at baseline up to 0.50). There was a virtually linear relationship between the RI and the pulse pressure index ([systolic pressure-diastolic pressure]/systolic pressure) in the range of 0.30-0.80. The RI was not affected by the pulse rate or fraction of time that systolic pressure was applied during the pulse cycle.

CONCLUSION

Contrary to conventional teaching, which is based on theoretic considerations, the RI is not readily affected by acute changes in RVR. This indicates a need to reconsider the conventional explanations used to explain increases in RI that are frequently found in patients with renal disease or ureteral obstruction.

Renal dysfunction in liver cirrhosis: renal duplex Doppler US vs. scintigraphy for early identification

A diagnostic tool to detect early renal dysfunction before it becomes irreversible would be useful in cirrhosis. This study was carried out to evaluate the role of Doppler sonography and Tc-99m DTPA renography in the detection of early renal dysfunction in patients with different grades of liver cirrhosis. Renal arteries of 43 patients with cirrhosis and normal renal function tests were compared with 15 age and gender matched normal subjects as a control group using colour Doppler sonography and Tc-99m DTPA scintigraphy. The patients were categorized into three groups, A (14), B (14) and C (15), according to a modified Child's classification that assesses the severity of liver cirrhosis. Doppler results revealed a highly significant increase in both the pulsatility and resistive indices in groups B and C compared with either group A patients or control subjects and in group C compared with group B (P < 0.001) in the main renal arteries as well as in the interlobar and arcuate arteries. Insignificant differences were observed between group A and controls (PI: control 0.96+/-0.08, group A 0.95+/-0.07, group B 1.26+/-0.06, group C 1.48+/-0.06; RI: control 0.57+/-0.02, group A 0.58+/-0.02, group B 0.66+/-0.01, group C 0.72+/-0.02). Abnormal renograms in the form of delayed appearance (34+/-14.6 s), diminished blood flow bilaterally with prolonged secretory (12+/-4.5 min) and excretory phases (> 30 min) and poor response to intravenous frusemide were only observed in group C patients. Radionuclide computed glomerular filtration rate was within the normal range in patients of group A (81+/-9.5 ml/min) and group B (78+/-8.4 ml/min) and reduced only in patients of group C (34+/-14.5 ml/min). Thus Doppler sonography can detect an increase in renal vascular resistance in patients with moderately severe cirrhosis (Child grade B) when renography was normal. We conclude that Doppler sonography can be used for earlier identification of cirrhotic patients with a higher risk of impending renal failure earlier than renography and may also be used to guide therapeutic approaches.

Interobserver and interequipment variability of hepatic, splenic, and renal arterial Doppler resistance indices in normal subjects and patients with cirrhosis

BACKGROUND/AIMS

Doppler arterial resistance indices are used to evaluate alterations in arterial hemodynamics in the liver, spleen, and kidney. The purpose of this study was to determine the interobserver and interequipment variability of hepatic, splenic, and renal arterial Doppler resistance indices, and the influence of a cooperative training program of the operators on the reproducibility of the results.

METHODS

In the first part of the study, hepatic (PI-L, RI-L), splenic (PI-S, RI-S), and renal (PI-K, RI-K) pulsatility and resistive indices were measured by echo-color-Doppler in eight control subjects and ten patients with cirrhosis by three operators using three different machines. In the second part of the study, measurements were taken by the three operators in nine controls and nine patients with cirrhosis, after cooperative training, with a single machine.

RESULTS

Significant interobserver variability was present for all parameters except RI-L. Significant interequipment variability was present for all parameters except PI-S and RI-S. Only 0-3% of variance was equipment- or operator-related, while 58-72% was patient-related. Hepatic and renal coefficients of variation were similar in patients with cirrhosis and controls, while splenic coefficients of variation were higher in patients with cirrhosis than in controls. After training, differences among operators disappeared for all variables except RI-K, and the operator-related component of variance nearly disappeared for all parameters.

CONCLUSIONS

Hepatic, splenic, and renal arterial resistance indices show small but significant interobserver and interequipment variability. Interobserver variability can be decreased to non-significant levels by a common training program. Thus, these indices can be widely applied to the study of arterial circulation in these organs.

Duplex doppler estimation of intrarenal pourcelot resistive index in dogs and cats with renal disease

In human beings, intrarenal blood flow impedance, expressed as the resistive index (RI) and obtained by duplex Doppler ultrasonography, has been used to aid in diagnosis and prognosis of renal failure. Higher than normal values for RI were obtained in 3 of 4 dogs with acute tubular necrosis (ATN) and in 5 of 10 dogs with glomerulonephrosis (GN). Normalization of RI was observed in 2 dogs with ATN evaluated serially during treatment. Increased RI values were obtained in 9 of 10 cats with nonobstructive renal disease and in 2 of 5 cats with obstructive renal disease. Normalization of RI was observed in 3 cats with renal failure in which treatment was effective (1 with obstruction; 2 with nonobstructive disease). The magnitude of increase in RI did not correlate with the magnitude of concurrent renal dysfunction. These results suggest that duplex Doppler evaluation of intrarenal RI is more useful as an ancillary diagnostic technique in azotemic dogs with ATN than in those with GN and in azotemic dogs with nonobstructive than in those with obstructive disease.

Ascites and renal functional abnormalities in cirrhosis. Pathogenesis and treatment

In the past few years, there have been important advances in the field of pathogenesis and management of ascites and hepatorenal syndrome in cirrhosis. A new pathogenic theory of ascites and renal dysfunction in cirrhosis has been presented and previously ill-defined conditions, such as refractory ascites and hepatorenal syndrome, have been defined precisely. The link between the diseased liver and the disturbances in renal function and vasoactive systems is not completely known, but a large body of evidence indicates that it consists of a circulatory dysfunction that affects mainly the arterial circulation and is characterized by an inability to maintain an effective arterial blood volume within normal limits. The research on the mechanisms of this circulatory dysfunction will give valuable information in the design of more pathophysiologically oriented therapeutic approaches to the management of ascites.

Pathophysiology, complications, and treatment of ascites

In the past few years, there have been important advances in the field of pathogenesis and management of ascites and spontaneous bacterial peritonitis in cirrhosis. A new pathogenic theory of ascites and renal dysfunction in cirrhosis has been presented, and previously ill-defined conditions, such as refractory ascites and hepatorenal syndrome, have been defined precisely. The reintroduction of therapeutic paracentesis has modified markedly the way in which patients hospitalized for ascites are treated. The use of potent and safe antibiotics has improved the resolution rate and survival of patients with spontaneous bacterial peritonitis, and the use of oral antibiotics will simplify the management of this condition in the near future. Finally, prophylactic antibiotic regimens represent a major step forward in the prevention of spontaneous bacterial peritonitis in subsets of cirrhotic patients with a great risk of developing this complication.

Doppler ultrasound of the kidney

Conventional ultrasound of the kidney is used commonly to depict structural abnormalities. It is limited, however, by a lack of functional and vascular information. Doppler sonography can reduce this limitation of standard sonography quickly and noninvasively. Doppler examinations, although not difficult, must be done property to obtain useful data. Information regarding the presence and direction of flow in renal vessels can be obtained. Vascular stenosis can be identified by several Doppler criteria, although the role of Doppler as a screening measure remains controversial. Assessment of vascular resistance is possible from Doppler waveform analysis, using parameters such as the resistive index. These data may provide hemodynamic and predictive information regarding a dilated collecting system identified by conventional ultrasound. Analysis of the resistive index also may provide helpful clinical information in nonobstructive renal disease. In certain clinical settings, such analysis provides diagnostic data not readily available with other clinical and laboratory assessment methods. Pharmacologically stimulated renal Doppler examinations may lead to even greater benefits in the future. This article reviews renal Doppler ultrasound, including the physiological basis for Doppler examination, the technical principles of renal Doppler sonography, and the clinical applications of Doppler findings.

Duplex Doppler estimation of Pourcelot resistive index in arcuate arteries of sedated normal cats

Renal failure is an important cause of morbidity and mortality in feline patients. In human patients, intrarenal blood flow values obtained with duplex Doppler ultrasonography have been used to aid in the diagnosis and prognosis of renal failure. The purpose of this report is to present values for resistance to intrarenal blood flow in normal cats, derived by duplex Doppler ultrasonography. Ten mature clinically healthy conditioned domestic shorthaired cats were screened for normal renal anatomy and function by CBC, serum biochemical profile, urinalysis, urine protein/creatinine ratio, endogenous creatinine clearance, and renal B-mode ultrasonography; and for normal systemic blood pressure with Doppler pressure cuff measurement. Subsequently, the cats were sedated with ketamine hydrochloride, and values for mean intrarenal (arcuate artery) resistance to blood flow were determined by duplex Doppler ultrasonography, and expressed as the Pourcelot resistive index, a ratio of systolic to diastolic flow commonly used in duplex Doppler sonography in human patients. After duplex Doppler sonographic examination, histological normalcy of the kidneys was verified by evaluation of ultrasound-guided percutaneous renal biopsy. Based on the obtained resistive indices, 95% confidence intervals for normal values were calculated as follows: left kidney, 0.52 to 0.60; right kidney, 0.55 to 0.63. No statistically significant difference was noted between the values obtained for the right versus the left kidney.

Renal duplex Doppler ultrasonography: a noninvasive predictor of kidney dysfunction and hepatorenal failure in liver disease

Hepatorenal failure, a well-recognized complication of established liver disease, is characterized by early renal hemodynamic changes (vasoconstriction) before clinically recognized kidney disease. This renal vasoconstriction (increased renal vascular resistance) should be detectable noninvasively by Doppler ultrasonography. We studied whether renal Doppler ultrasonography detects abnormalities in patients with nonazotemic liver disease and its prognostic value for subsequent kidney status. We observed by renal Doppler ultrasonography 180 patients who had liver disease without azotemia. A simple parameter, resistive index, was derived for each subject on the basis of Doppler waveform analysis. Traditional parameters used to assess patients with liver disease were also recorded at the time of Doppler ultrasonography. Subsequent kidney outcomes were kidney dysfunction (doubling of initial creatinine level to 1.5 mg/dl [133 mumol/L]) or more and the presence or absence of the hepatorenal syndrome. Abnormal results of Doppler examinations (elevated resistive index) were seen in 76 (42%) of the 180 patients. Kidney dysfunction developed in 55% (42/76) of the patients with an elevated resistive index and 6% (6/104) of those with normal results of Doppler study (p < 0.00005). Hepatorenal syndrome developed in 26% (20/76) of subjects with an elevated resistive index and 1% (1/104) of those with a normal resistive index (p < 0.00005). Cox regression analysis identified resistive index as a significant independent predictor of subsequent hepatorenal syndrome (p < 0.00005) and kidney dysfunction (p < 0.00005). Renal duplex Doppler ultrasonography can noninvasively identify a subgroup of nonazotemic patients with liver disease that is at significantly higher risk for subsequent development of kidney dysfunction and the hepatorenal syndrome.