Andreas Umgelter Wolfgang Reindl Michael Franzen Cosima Lenhardt Wolfgang Huber Roland M. Schmid
Renal resistive index and renal function before
and after paracentesis in patients
with hepatorenal syndrome and tense ascites
Received: 19 June 2008 Accepted: 17 August 2008
Published online: 18 September 2008 Ó Springer-Verlag 2008
A. Umgelter (
)
) W. Reindl W. Huber R. M. SchmidII. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Ismaninger Str. 22, 81675 Munich, Germany e-mail: andreas.umgelter@lrz.tu-muenchen. de Tel.: ?49-89-41402265 Fax: ?49-89-41404808 M. Franzen
Universita¨tsklinik fu¨r Medizin I, Paracelsus Universita¨t, Salzburg, Austria
C. Lenhardt
Klinik fu¨r Nieren-, Hochdruck-, und Rheumakrankheiten, Klinikum Schwabing, Sta¨dtisches Klinikum Mu¨nchen GmbH, Munich, Germany
Abstract Objective: To assess the effect of reducing intra-abdominal pressure (IAP) by paracentesis on renal resistive index (RI), hemody-namics and renal function. Design and setting: Uncontrolled trial in a university gastroenterological inten-sive care unit. Patients: Twelve spontaneously breathing cirrhotic patients with hepatorenal syndrome, tense ascites and a clinical indication for paracentesis.
Interven-tions: Paracentesis and substitution of albumin. Measurements and results: Hemodynamic variables were assessed by transpulmonary thermodilution, RI was determined by Doppler ultrasound of renal interlobar arteries. After paracentesis and albu-min substitution, there was a
significant decrease of IAP
(20 mmHg (19–22) to 12 mmHg (10– 13), systemic vascular resistance index (from 1,243 dyn s/cm5/m2 (1,095–1,745) to 939 dyn s/cm5/m2 (812–1,365); p = 0.005) and RI (from 0.848 (0.810–0.884) to 0.810 (0.780–0.826); p = 0.003). Arterial compliance increased from 1.33 mL/ mmHg (0.89–1.74) to 1.71 mL/ mmHg (1.21–2.12), pulse pressure index remained unchanged. Creati-nine clearance (ClCreat) increased significantly from 5 mL/min (0–28) to 9 mL/min (0–36) (p = 0.018) and urinary output from 12 mL/h (0–49) to 16 mL/h (0–64) (p = 0.043).
Conclusions: In patients with cir-rhosis, HRS and tense ascites, IAP may contribute to renal dysfunction. Reduction of IAP following paracen-tesis and albumin substitution may improve ClCreat, probably by improving renal blood flow as reflected by decreasing RI in Doppler ultrasound.
Keywords Hepatorenal syndrome Intra-abdominal hypertension Renal resistive index Paracentesis Ascites
Abbreviations
compa Arterial compliance CVP Central venous pressure CI Cardiac index
FG Filtration gradient GEDVI Global end-diastolic
volume index
HRS Hepatorenal syndrome IAH Intra-abdominal
hypertension
IAP Intra-abdominal pressure MAP Mean arterial pressure PPI Pulse pressure index RI Resistive index
RPP Renal perfusion pressure SVI Stroke volume index SVRI Systemic vascular
Introduction
According to the arterial vasodilation hypothesis, in cir-rhotic patients, renal failure may occur as a functional disorder secondary to splanchnic pooling of blood, reduced effective arterial volume and compensatory activation of vasopressor systems leading to renal vaso-constriction [1]. If it persists despite the correction of precipitating conditions and after plasma expansion, the term hepatorenal syndrome is applied [2].
Renal resistive index (RI) correlates with renal func-tion in a variety of kidney disorders [3] and increases along the clinical stages of cirrhotic renal dysfunction [4]. It has also been shown to increase with IAP in an animal model [5]. Intra-abdominal hypertension (IAH) affects kidney function [6] and is gaining growing attention as an important factor contributing to acute renal failure in critical care patients [7].
High values for RI predict the occurrence of HRS [8]. IAH due to tense ascites thus may reduce renal perfusion pressure and contribute to renal failure in cirrhotic patients with ascites [9].
The present study investigates changes in renal resis-tive index, hemodynamic parameters and renal function in response to paracentesis and albumin infusion.
Patients and methods
After approval of our institutional ethics committee, consecutive patients with advanced cirrhosis treated for acute conditions in our intensive care unit were included if they had acute renal failure (serum creati-nine [ 133 lmol/L) with normal serum creaticreati-nine values during the past 2 weeks before enrolment, persistent ascites and a clinical indication for paracentesis. Patients had to fulfill the major criteria for hepatorenal syndrome established by the international ascites club in 1994 [10]. Exclusion criteria were pre-existing renal disease, current hemorrhage or infection, portal vein thrombosis, use of beta-blockers, diuretics or nephrotoxic drugs during 5 days preceding enrolment, septic shock, use of vaso-pressors or proteinuria [ 500 mg/dL. Paracentesis was performed once in each patient.
Measurements of intra-abdominal pressure (IAP)
The IAP was measured intraperitoneally during paracen-tesis using an 8 Charrie`re Teflon catheter connected to a measuring gauge, as traditionally used for measurements of central venous pressure (CVP). Patency of the system was ascertained by observing respiratory modulations of the fluid level in the measuring gauge and the zero-point was set at the mid-axillary line. Readings were done at
end-expiration. Renal perfusion pressure (RPP) and filtration gradient (FG) were calculated as RPP = (MAP -IAP); FG = (MAP - 2IAP).
Doppler measurements
Color-Doppler examinations and calculations of RI were performed using a Logiq 400 scanner and a 3.5-MHZ convex probe (Kranzbu¨hler, Solingen, Germany). Dopp-ler signals were obtained from interlobar arteries along the border of medullar pyramids. RI was determined according to the following formula: (peak systolic fre-quency shift - minimum diastolic frefre-quency shift)/peak systolic frequency shift. Three consecutive measurements at the upper, middle and lower pole of the organ were averaged. All Doppler examinations were done by one examiner (AU), blinded to the results of hemodynamic and IAP measurements.
Hemodynamic measurements
We used a commercially available system (PiCCO, PUL-SION Medical Systems, Munich, Germany), which works as described elsewhere [11]. Measurements were done in triplicate and averaged. Arterial compliance (compa) was calculated as compa= stroke volume/(RRsys - RRdia) and pulse pressure index (PPI) as (RRsys - RRdia)/ RRsys.
Study protocol (Fig. 1)
Urine was collected over 6 h for the determination of urinary output (UO) creatinine and urea nitrogen. There-after, hemodynamic parameters were assessed by transpulmonary thermodilution, blood was drawn for routine biochemistry, and RI was determined by Doppler ultrasound of the kidneys. Paracentesis was done by an infra-umbilical approach. After 1 h, paracentesis was terminated and measurements were repeated. Afterwards, patients received 200 mL of 20% human albumin solution over 30 min. After another 30 min, hemodynamic and Doppler investigations were repeated. Collections of urine were continued for another 6 h and biochemical investi-gations repeated thereafter.
Statistical analysis
Data are presented as median and 1st and 3rd quartiles and the Wilcoxon test was used for paired comparisons. All baseline parameters were examined for correlations using Spearman’s rank correlation coefficient. Significance was
assumed for p values\0.05. Calculations were done with SPSS 13 for Mac.
Results
Patients’ characteristics
Twelve patients were included between August 2007 and December 2007. At baseline, there was a correlation between CVP and creatinine clearance (ClCreat) (r = 0.739, p = 0.006) as well as between IAP and CVP (r = 770, p = 0.043) and a negative correlation between mean arterial pressure (MAP) and RI (r = -0.712, p = 0.009). A correlation between GEDVI and ClCreat failed to be significant (r = 0.563, p = 0.056). There were no other correlations between hemodynamic vari-ables and indicators of renal function or between any other of these and RI or IAP.
Hemodynamic changes, changes of renal Doppler indices and parameters of renal function
Values before and after paracentesis and albumin substi-tution, respectively, are presented in Tables1,2and3. A median of 5.3 L (4.8–6.5) of ascites was removed.
Over the whole study period, GEDVI significantly increased (p = 0.002), as did SVI (p = 0.004), CI (p = 0.002) and compa(p = 0.003). Decreases of systemic vascular resistance (SVRI, p = 0.005), HR (p = 0.016), and RI (p = 0.003) were significant. Excretion of urine increased from 12 mL/h (0–49) to 16 mL/h (0–64) (p = 0.043) and ClCreat from 5 mL/h (0–28) to 9 (0–36) (p = 0.018). Fractional excretion of sodium (FeNa) was calculated for non-anuric patients (n = 7). Its increase
from 0.3% (0.1–0.4) to 0.4% (0.3–0.6) missed the level of significance (p = 0.068).
Discussion
The results of transpulmonary thermodilution measure-ments in our patients are consistent with the hypothesis of arterial vasodilation and reduced central blood volume in portal hypertension. All patients had received goal directed fluid therapy and CVP was within the normal range. GEDVI, however, was low.
After paracentesis, there was an increase in CI and a decrease in SVRI, however the latter only reached the level of significance after albumin infusion. Increasing CI after paracentesis has been attributed to improved venous return and right ventricular filling, as impingement of the elevated diaphragm on the right heart is reduced [12]. However, we did not find any change in GEDVI after paracentesis, whereas CVP even decreased, probably due to the reduction of IAP. The augmented SVI despite unchanged GEDVI indicates diminished end-systolic volume due to reduced afterload.
Renal Doppler indices have been used to analyze renal hemodynamics for a long time [3]. Initial enthusiasm for
Fig. 1 Schematic representation of the study protocol
Table 1 Patients’ baseline characteristics
Age (years) 59 (40–64)
Gender (m/f) 8/4
Cause of cirrhosis 10
Alcohol 2
Alcohol and hepatitis C
Listed for transplantation 4 Hepatocellular carcinoma 2 Cause of ICU admission
Encephalopathy III°/IV° 4 Acute renal failure 4
Sepsis 2 Pneumonia 1 Gastrointestinal hemorrhage 1 MELD-score 33 (24–37) Child-Pugh-score 12 (11–13) SOFA-score 10 (9–13) Urinary output (mL/h) 12 (0–50) Serum creatinine (lmol/L) 256 (139–385) ClCreat (mL/min) 5 (0–28) FeNa (%) 0.3 (0.1–0.4) Serum sodium (mmol/L) 132 (128–134) Serum albumin (g/L) 28 (23–30) Hematocrit (%) 25 (23–29) ASAT (U/L) 112 (70–195) ALAT (U/L) 38 (29–49) Data presented as median (25th–75th percentile)
MELD model of end-stage liver disease; SOFA sequential organ-failure assessment; ClCreat creatinine clearance; FeNa fractional excretion of sodium; ASAT aspartate-aminotransferase; ALAT ala-nine-aminotransferase
the method gave way to disillusionment as several studies failed to reproduce earlier promising results [13–16]. Whereas originally it had been assumed that RI would vary linearly with changes in renal vascular resistance, subsequent experimental research has shown that major factors influencing RI are vascular compliance and pulse pressure index [17,18].
In our study, initial values for RI were elevated compared to published data for normal volunteers [19]. They were also higher than values previously reported for patients with refractory ascites [4] or patients developing hepatorenal failure [8], possibly because the of more advanced kidney failure in our patients. After the com-bined intervention of paracentesis and albumin infusion, we found a pronounced decrease in RI occurring during paracentesis but not during albumin substitution, with a
concomitant increase in UO and ClCreat. Any decrease in RI may be the consequence of either decreasing arterial compliance, reduced pulse pressures, diminished vascular resistance, increasing heart rate or a combination of these factors [3]. There were no changes in pulse pressure during our study, but total arterial compliance, expressed as stroke volume per pulse pressure, did increase, possibly as a consequence of reduced intra-abdominal and retro-peritoneal pressures. According to experimental findings, however, increased vascular compliance would have been associated with increasing values for RI [17].
Increasing heart rate by increasing the pacing-fre-quency of an electric pacemaker has also been found to decrease renal RI [20]. In our patients, heart rate decreased significantly during paracentesis. This may have blunted the observed decrease in RI.
Table 2 Hemodynamic, clinical and Doppler parameters before and after paracentesis
Before paracentesis After paracentesis p
IAP (mmHg) 20 (19–22) 12 (10–13) 0.002 RPP (mmHg) 57 (52–71) 63 (59–72) 0.025 FG (mmHg) 38 (31–46) 51 (47–62) 0.002 CVP (mmHg) 14 (11–16) 11 (9–14) 0.041 GEDVI (mL/m2) (n 680–800) 660 (540–748) 700 (565–725) 0.814 CI (L/min/m2) (n 3–5) 4.12 (3.13–5.03) 4.49 (3.40–5.26) 0.041 SVI (mL/m2) (n = 40–60) 48 (41–54) 55 (43–63) 0.016 HR (bpm) 101 (85–116) 91 (80–101) 0.026 SVRI (dyn s/cm5/m2) (n 1,700–2,400) 1,243 (1,095–1,745) 1,058 (987–1,337) 0.131 compa(mL/mmHg) 1.33 (0.89–1.74) 1.49 (1.05–1.81) 0.071 MAP (mmHg) 77 (72–96) 77(69–85) 0.023 PPI 0.53 (0.47–0.57) 0.53 (0.51–0.58) 0.032 RI 0.848 (0.810–0.884) 0.807 (0.770–0.844) 0.002 Data presented as median (25th–75th percentile)
IAP intra-abdominal pressure; RPP renal perfusion pressure; FG filtration gradient; CVP central venous pressure; GEDVI global end-diastolic volume index; CI cardiac index; SVI stroke volume
index; HR heart rate; SVRI systemic vascular resistance index; compaarterial compliance; MAP mean arterial pressure; PPI pulse
pressure index; RI renal resistive index
Table 3 Hemodynamic and Doppler parameters after paracentesis but before albumin infusion and after albumin infusion After paracentesis,
before albumin infusion
After albumin infusion p CVP (mmHg) 11 (9–14) 14 (11–15) 0.144 GEDVI (mL/m2) 700 (565–725) 740 (653–800) 0.004 CI (L/min/m2) 4.49 (3.40–5.26) 4.55 (3.66–5.70) 0.019 SVI (mL/m2) 55 (43–63) 59 (50–65) 0.010 HR (bpm) 91 (80–101) 91 (68–106) 0.594 SVRI (dyn s/cm5/m2) 1058 (987–1,337) 939 (812–1,365) 0.050 compa(mL/mmHg) 1.49 (1.05–1.81) 1.71 (1.21–2.12) 0.002 MAP (mmHg) 77 (69–85) 77 (67–83) 0.455 PPI 0.53 (0.51–0.58) 0.51 (0.45–0.54) 0.002 RI 0.807 (0.770–0.844) 0.810 (0.780–0.826) 0.784 Data presented as median (25th–75th percentile)
CVP central venous pressure; GEDVI global end-diastolic volume index; CI cardiac index; SVI stroke volume index; HR heart rate;
SVRI systemic vascular resistance index; compa arterial
compli-ance; MAP mean arterial pressure; PPI pulse pressure index; RI renal resistive index
Thus, even if we cannot exclude an influence of changes in compliance and HR on the RI measured in our study, the finding of decreasing RI despite increasing compliance and decreasing HR may be interpreted as indicating reduced renal vascular resistance. This result mirrors that of a recent study on RI in a porcine model of IAH. With only minor changes in MAP over the study period (and increases in renal perfusion pressure), reduced resistance would also imply increased renal blood flow, which is consistent with our finding of improved renal function after paracentesis and albumin substitution.
The most important limitation of our study is the lack of a control group. Thus, causal relations between the interventions and the observed hemodynamic, clinical and ultrasound findings may not be inferred. A further
limitation is the fact that the ultrasound examiner could not be blinded to the occurrence of paracentesis, as the change in the amount of ascites is easily recognizable on renal ultrasound.
In conclusion, our study suggests that Doppler ultra-sound may be a valuable tool in assessing changes in renal perfusion caused by IAH. After paracentesis and albumin substitution we observed a reduction in RI sug-gestive of increased renal blood flow and accompanied by an increase in ClCreat and UO.
Conflict of interest statement A. Umgelter and W. Huber have been invited speakers for Pulsion Medical Systems, Munich, Ger-many. The other authors declare no conflict of interest.
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