Doppler sonography in experimentally induced acute renal failure in rabbits. Resistive index versus serum creatinine levels

Duplex scan and histologic assessment of acute renal injury in a kidney-kidney crosstalk swine experimental model

OBJECTIVE

The objective of this study was to identify the effect of two left renal vasculature occlusion strategies on the duplex ultrasound-assessed rheology and histology of the contralateral kidney.

METHODS

Pigs were randomly assigned to one of two groups: left renal artery-only clamping (A group, n = 8) or left renal artery and vein clamping (AV group, n = 9). Bilateral renal parenchymal biopsy specimens were taken every 10 minutes for 90 minutes. Duplex ultrasound resistive index (RI) and pulsatility index (PI) were measured. Mixed models with normal distribution and first-order autoregressive correlation structure and generalized estimating equation models were used. Results are presented as adjusted means with standard errors, estimated proportions with standard errors, and line plots with 95% confidence intervals.

RESULTS

RI and PI increased in the nonischemic kidney. In A group animals, RI values increased significantly (P < .01) after 30 minutes of ischemia and PI increased significantly (P < .04) from 30 to 60 minutes of ischemia. The number of histologic abnormalities was higher in A group than in AV group biopsy specimens. The percentage of lesions increased significantly after 10 minutes in A group nonischemic kidneys (P < .02) and between 50 and 80 minutes in AV group nonischemic kidneys (P < .01).

CONCLUSIONS

Nonischemic kidneys were acutely affected by contralateral ischemia. Their function was more adversely affected by unilateral renal artery occlusion with preserved renal vein patency (A group).

Renal Doppler ultrasound: a new tool to assess renal perfusion in critical illness

Despite our increasing ability to support vital organs and resuscitate patients, the morbidity and mortality of acute kidney injury (AKI) remain high in the intensive care unit (ICU). The ability to predict the occurrence of AKI is crucial for the development of preventive strategies. Early diagnosis of AKI requires markers that are sensitive and easily applicable in clinical practice. The use of Doppler ultrasonography to assess renal perfusion is increasing in many kidney diseases and in the ICU. The Doppler-based renal resistive index, which is a simple, rapid, noninvasive, and repeatable marker, could be a promising tool to prematurely detect the patients most at risk of developing AKI in the ICU and to distinguish transient from persistent AKI. Moreover, the resistive index could also be useful to adjust preventive or therapeutic modalities for the kidney perfusion at the bedside. The recent progress in ultrasound with contrast-enhanced ultrasound gives the opportunity to assess not only the kidney macrocirculation but also the kidney microcirculation in the ICU.

The role of ultrasonography in the study of medical nephropathy

Diagnostic techniques in nephrology include clinical history, physical examination, laboratory tests, scintigraphy, diagnostic imaging techniques as well as renal biopsy. In kidney diseases, ultrasonography is used as a first-line imaging technique, and its role in medical nephropathy is to exclude urological pathologies, to differentiate between acute and chronic renal failure, to follow-up on the course of a disease, to guide needle biopsy, etc. Ultrasound images are useful at characterizing the pelvis, assessing renal dimensions and parenchymal echogenicity, sampling color-power Doppler signals and evaluating their characteristics and distribution as well as measuring parenchymal resistive index. Taken together, these data can provide useful clues to the diagnosis and help to reduce the number of possible differential diagnoses.

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.

Renal failure in septic shock: predictive value of Doppler-based renal arterial resistive index

OBJECTIVE

Because acute renal failure (ARF) is frequent in septic shock, an early marker of ARF could impact on management of such patients. High renal arterial resistive index (RI) is associated with parenchymatous renal failure. We assessed whether Doppler-measured RI on day 1 (D1) of septic shock can predict ARF.

DESIGN

Prospective descriptive clinical study.

SETTING

A 20-bed medical intensive care unit in a university hospital.

PATIENTS

All patients with septic shock, excluding those with chronic renal failure (serum creatinine >120 micromol/l).

MEASUREMENTS AND RESULTS

RI was determined during the first 24 h (D1) following vasopressor introduction, concomitant with recording of: age, SAPS II, mean arterial pressure, arterial lactate, catecholamine (dose and type), urine output and serum creatinine. ARF was diagnosed according to the RIFLE classification. RI measurement was possible for 35 of 37 included patients. On day 5 (D5), 17 patients were without ARF (RIFLE-0 or R) and 18 patients were classified as having ARF (RIFLE-I or F). On D1, RI was higher in these latter 18 patients (0.77+/-0.08 vs. 0.68+/-0.08, p<0.001). They also had higher SAPS II and arterial lactate concentration. RI >0.74 on D1 had a positive likelihood ratio of 3.3 (95% CI 1.1-35) for developing ARF on D5. RI correlated inversely with mean arterial pressure (rho=-0.48, p=0.006) but not with catecholamine type or dose or with lactate concentration.

CONCLUSION

Doppler-based determination of RI on D1 in septic shock patients may help identify those who will develop ARF.

Use of power Doppler ultrasound to monitor renal perfusion during burn shock

BACKGROUND

Renal cortical blood flow can be quantified by means of power Doppler ultrasound (PDUS) image analysis. We hypothesized that renal cortical perfusion, estimated by PDUS image intensity (PDUSII), would decrease during burn shock and improve during resuscitation in a porcine model.

METHODS

Eight anesthetized swine sustained a 75% scald injury. Resuscitation began 6h postburn. Renal cortical blood flow was measured directly using fluorescent microspheres (CORFLO), and was estimated noninvasively by PDUSII. PDUSII, CORFLO, and cardiopulmonary data were recorded every 2h.

RESULTS

PDUSII decreased significantly from preburn to postburn hour 6, and increased with resuscitation by hour 8. CORFLO correlated well with PDUS image intensity (n=48, r(2)=0.696) but poorly with urine output (n=48, r(2)=0.252).

CONCLUSION

PDUS in this study was superior to the urine output in assessing renal cortical microvascular blood flow during shock and resuscitation, and may be useful in the care of injured patients.

Dose-dependent toxicity of a commercially available demineralized bone matrix material

STUDY DESIGN

A relative risk assessment was performed to determine the safety of three commercially available Grafton demineralized bone matrix quantities used in athymic rats.

OBJECTIVE

To evaluate the possible dose-dependent adverse effects of a commercially available demineralized bone matrix containing glycerol.

SUMMARY OF BACKGROUND DATA

Commercially available Grafton demineralized bone matrix contains glycerol. The toxic effects of glycerol leading to acute renal failure have been documented. The toxicity of this glycerol-containing substance in higher doses has not been reported.

METHODS

Three doses of Grafton putty were implanted in the upper hind limb muscles of athymic nude rats. The rats were observed for adverse effects and early death. Histologic studies were performed.

RESULTS

All eight of the rats implanted with the highest dose of Grafton putty (0.008 mL/g) died, five of them within 12 hours of implantation and three in 48 to 72 hours. One rat with the intermediate dose (0.004 mL/g) died within 12 hours of implantation. By 72 hours after implantation, three of the six rats (50%) with the intermediate dose had died. All six of the rats receiving the lowest dose (0.002cc/g) survived. The median lethal dose of Grafton putty in athymic rats was estimated to be 0.00469 mL/g body weight. Histologic analysis of the animals that received the high dose showed acute tubular necrosis, probably secondary to rhabdomyolysis.

CONCLUSIONS

In athymic rats, large amounts of Grafton putty lead to death in a dose-dependent manner. Because the median lethal doses of Grafton putty (0.00469 mL/g) and glycerol (0.00442 mL/g) are comparable, a potential source of toxicity is the glycerol contained in the material. The results of this study suggest that high doses have the potential to cause acute renal failure. The authors suggest that clinical usage of Grafton putty in humans should be limited to no more than 2 mL/kg body weight of this material.

Differential diagnosis of prerenal azotemia from acute tubular necrosis and prediction of recovery by Doppler ultrasound

Acute renal failure (ARF) is a life-threatening disease that often causes multiple organ dysfunction. The accurate and rapid diagnosis of the cause of ARF is particularly important for selecting the appropriate therapy. Ultrasound Doppler is a noninvasive diagnostic method that has recently been introduced to clinical nephrology. We report the diagnostic value of Doppler ultrasound in differentiating acute tubular necrosis (ATN) from prerenal azotemia by comparing this study with the fractional excretion of sodium (FENa), renal failure index (RFI), and urinary/serum creatinine (Cr) ratio. Doppler ultrasound was able to differentiate prerenal azotemia from ATN, equivalent to FENa, RFI, and the urinary/serum Cr ratio. Doppler ultrasound does not require blood or urine samples and can be performed at the bedside. Of note, Doppler is unaffected by changes in Na or Cr in urine or serum after diuretics or hemodialysis. Furthermore, one can predict recovery from ATN by Doppler findings. Thus, we consider Doppler ultrasound an effective diagnostic tool in ARF.

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.