Abstract
Background
It is clinically relevant to predict outcomes in dogs with acute kidney injury (AKI) treated with haemodialysis. The aim of this study was to evaluate the prognostic value of contrast‐enhanced ultrasound (CEUS) and its role in discriminating between AKI and acute impairment associated with chronic kidney disease (AKI/CKD).
Methods
Dogs diagnosed with AKI or AKI/CKD were prospectively enrolled in the study. For all dogs, CEUS was performed at admission (T0). In addition, in haemodialysis‐treated dogs, it was performed after the first dialysis (T1) and 7 days (T7) and 30 days (T30) after admission.
Results
A total of 41 dogs were enrolled, of which 30 were treated with haemodialysis and 11 received medical therapy. No significant difference was found between CEUS values at T0 in surviving and non‐surviving patients after haemodialysis. A significant difference in cortical peak enhancement intensity (PI) values was found between T0, T1, T7 and T30, with the highest PI value at T0, a significant reduction at T1 and a progressive reduction in subsequent checks. There were no significant differences in CEUS parameters at T0 between patients with AKI and AKI/CKD.
Limitations
AKI aetiology was unknown in most cases, which limits the generalisability of the findings. Furthermore, the small sample size means that the statistical analysis is likely underpowered.
Conclusion
CEUS could be helpful in evaluating of the prognosis of dogs with AKI during haemodialysis.
Keywords: acute kidney injury, contrast‐enhanced ultrasound, dog, haemodialysis
INTRODUCTION
Acute kidney injury syndrome (AKI) encompasses a spectrum of diseases associated with sudden parenchymal and functional renal damage, most typically characterised by the inability of the kidneys to meet the body's excretory, metabolic and endocrine demands. 1 , 2 It is associated with a rapid decline in renal filtration, subsequent accumulation of uremic toxins and dysregulation of electrolyte and acid–base balance. 1 , 2 The mortality range in dogs with AKI is approximately 23.8–78.5%, as reported in studies including different aetiologies. 1 , 3 , 4 , 5
In dogs, AKI is the most common indication for haemodialysis. 2 , 6 In addition, haemodialysis can also be used to manage patients with acute impairment associated with chronic kidney disease (AKI/CKD). 6 The survival rate in AKI dogs treated with haemodialysis is between 48% and 50%. 7 , 8 , 9 Unfortunately, this therapy is expensive and may not be affordable for owners, especially due to the uncertainty of the prognosis. 8 For this reason, prognostic tools are needed to provide outcome predictions in dogs with AKI when management by haemodialysis is contemplated. 8
Multiple factors could determine the long‐term prognosis of dogs with AKI. 6 Some studies have identified some clinical variables (e.g., degree of AKI, respiratory complications, disseminated intravascular coagulation, urinary production) and haematobiochemical parameters (e.g., serum potassium level, serum creatinine concentration) as prognostic indicators 5 , 6 , 9 ; however, the prognostic value of contrast‐enhanced ultrasound (CEUS) in dogs with AKI has not yet been evaluated.
CEUS is a non‐invasive method used to study tissue perfusion, providing both qualitative and quantitative analysis. 10 , 11 The qualitative analysis consists of a subjective evaluation of the perfusion and evaluates the distribution of the contrast in the parenchyma; the quantitative analysis is more objective and is based on quantitative parameters of vascularisation, produced by a specific software program that transforms the brightness of the signal into an intensity/time curve. 10 , 11
A few clinical studies have been conducted to evaluate renal perfusion in dogs with AKI using the CEUS method, in which the authors were able to identify some significant changes in renal perfusion in pathological patients. 11 , 12 In human medicine, CEUS has been shown to be clinically useful in predicting renal outcomes in patients with AKI. 13
The aim of this study was to evaluate the possible prognostic value of renal CEUS in dogs treated with haemodialysis and its possible role in discriminating between AKI and AKI/CKD.
MATERIALS AND METHODS
Study design and inclusion criteria
Dogs presented at the Veterinary Hospital of the Department of Veterinary Sciences of the University of Pisa between January 2020 and August 2022 were prospectively enrolled in the study. To be eligible for inclusion, dogs needed to have a diagnosis of prerenal or intrinsic AKI or AKI/CKD. The diagnosis was based on history, clinical and haematobiochemical findings, and abdominal ultrasound. AKI was diagnosed based on the acute onset of clinical signs consistent with AKI (e.g., anuria, oliguria, polyuria, vomiting, inappetence) and the International Renal Interest Society (IRIS) guidelines for the diagnosis of AKI. 14 Additionally, for the diagnosis of AKI/CKD, one or more of the following criteria were necessary to establish a diagnosis of CKD, as described by Dunaevich et al.: previous diagnosis of CKD based on persistently increased serum creatinine concentration, with a concurrent increase in serum creatinine concentration of greater than 25% above its previously documented baseline; and/or abdominal ultrasound findings compatible with CKD, including increased renal echogenicity, markedly decreased renal corticomedullary differentiation, decreased kidney size or asymmetry, and renal cysts or irregular renal contour. 5 The classification of AKI was carried out following the IRIS guidelines. 14
The dogs were divided into two groups according to the type of therapy they received: group A dogs were treated with haemodialysis and group B dogs received medical therapy. Group A was then divided into survivors and non‐survivors according to the outcome 30 days after the start of haemodialysis therapy. Dialysis therapy has been chosen as a treatment in cases of oliguria unresponsive to diuretics, overhydration, severe hyperkalaemia and severe uraemia unresponsive to medical therapies. However, due to its high cost, dialysis was not accepted by the owner in all the cases where it was suggested.
The following investigations were performed in each dog: physical examination, clinical laboratory analysis with complete blood count, serum biochemical profile (serum creatinine, urea, phosphate, total and ionised calcium, sodium, potassium, chloride, albumin, total protein), complete urinalysis, abdominal ultrasound and CEUS renal examination. In patients undergoing haemodialysis, whenever possible, CEUS examination was performed at admission before initiation of haemodialysis therapy (T0), 1 day after admission (after the first dialysis) (T1), 7 days after admission (T7) and 30 days after admission (T30). For dogs on medical management, CEUS was performed at the time of hospital admission (T0) only.
CEUS renal examination
The CEUS examination was performed by a single operator (C.P.) using a Canon Aplio CUS‐AA000 (Canon Medical Systems Europe) with a 6–8 MHz convex probe (PVT‐67487). The CEUS examination was carried out following the technique previously described by Mannucci et al. 11 The examination was performed on the left kidney, which is the most easily accessible and closest to the probe. 11 , 15 All the CEUS examinations were performed on non‐sedated dogs. All dogs were placed in right lateral recumbency and a longitudinal view of the left kidney was obtained. The system settings were optimised for contrast study with a mechanical index of 0.11–0.12, and the focus was positioned ventral to the renal caudal pole. Range power and gain compensation were adjusted so that the parenchyma fundamental signal was completely suppressed (gain between 70% and 77%, range power between 65% and 75%). An intravenous ultrasound contrast medium bolus (SonoVue, Bracco Imaging) was injected through a cephalic venous catheter at a dose of 0.03 mL/kg, followed by a 5 mL saline flush (0.9% NaCl). The timer was activated when the injection was initiated.
The kidney was scanned continuously for 90 seconds after the injection of the contrast medium, and the RAW data (good‐quality video clips) were stored digitally in the hard drive of the ultrasound machine. A subjective qualitative analysis was performed, and the following renal parenchyma perfusion stages were evaluated: arterial, cortical and medullary. For the arterial phase, the time from injection to the arrival of the contrast medium in the interlobar arteries was recorded; for the cortical phase, the time from injection to the maximum homogeneous enhancement of the cortex was recorded; and for the medullary phase, the time from injection to the maximum homogeneous enhancement of the medulla was recorded (Figure 1).
FIGURE 1.
Contrast‐enhanced ultrasonography images showing enhancement of the interlobar arteries (a), the renal cortex (b) and the renal medulla (c) of a dog with acute kidney injury
Three software programs integrated into the ultrasound machine [CHI kit (USHI‐AA550A, USHI‐AA550A/EL); CHI‐Q kit (USCQ‐AI900A, USCQ‐AI900/EL); Fitting Curve kits (USCQ‐AI901A, USCQ‐AI901A/EL)] were used for quantitative evaluation. Two regions of interest (ROIs) of equal area were drawn at similar levels and at similar depths on the renal parenchyma, one on the cortex and one on the medulla, avoiding interlobar and arcuate vessels and areas of non‐homogeneous enhancement (Figure 2).
FIGURE 2.
Contrast‐enhanced ultrasonography images of the kidney of a dog with acute kidney injury showing the placement of the two rounded regions of interest that were used for quantitative evaluation of the images
The ROIs were held in place with the motion tracking option. The program calculated the average intensity of enhancement for each ROI. Intensity/time curves were generated, and the following perfusion parameters were calculated: peak enhancement intensity (PI), time to peak, mean transit time, wash‐in slope, area under the curve, wash‐in area under the curve and wash‐out area under the curve (Figure 3). Both qualitative and quantitative analyses were performed by a single observer (C.P.).
FIGURE 3.
Representative plot of a time–intensity curve generated from bolus administration of ultrasound contrast agent. The contrast agent intensity is represented by the solid line, with the intensity amplitude in arbitrary units (au) on the y‐axis and time on the x‐axis expressed in seconds (s). Also shown are the perfusion kinetic metrics of time to peak (TTP), wash‐in slope, wash‐in area under the curve (WiAUC), wash‐out area under the curve (WoAUC) and peak intensity (PI) that can be obtained from the curve. The area under the curve is estimated from the integral of the curve from time zero until complete wash‐out, and it is composed of the WiAUC and the WoAUC
Statistical analysis
The statistical analysis was performed by a single operator (C.P.) using commercially available statistical software (GraphPad Prism v. 9.0, GraphPad Software). First, the normality of the data was assessed using the Shapiro–Wilk test, and depending on their distribution, the data were expressed as median and range or mean ± standard deviation (SD). Fisher's exact test was used to compare the outcomes of AKI and AKI/CKD patients treated with haemodialysis.
To identify any significant differences in quantitative and qualitative CEUS parameter values at T0 between survivors and non‐survivors in group A, and between patients with AKI and AKI/CKD, the Kruskal–Wallis statistical test combined with the Dunn multiple comparison test was used. For survivors in group A, a repeated‐measures one‐way analysis of variance was used to identify any significant differences in quantitative and qualitative CEUS parameters between T0, T1, T7 and T30. For both survivors and non‐survivors in this group, a paired t‐test was used to assess any significant differences in quantitative and qualitative CEUS parameters between T0 and T1. Statistical significance was set at p < 0.05 for all analyses.
A post hoc power analysis based on the t‐test was performed to evaluate the analysis’ power for comparing the quantitative and qualitative parameters between survivors and non‐survivors. The result showed a power of 49.4%, which suggests the analysis is underpowered, given the small sample size. The power analysis was performed using G*Power (Ver. 3.1, Heinrich‐Heine‐Universität).
RESULTS
Study population
A total of 52 uraemic dogs meeting the inclusion criteria were initially selected. However, it was impossible to adequately assess the outcomes for 11 of these dogs because they were either discharged against medical advice or the owners declined haemodialysis for economic reasons and opted for euthanasia. These patients were excluded from the study. Thus, the final study population consisted of 41 dogs.
Group A (n = 30) consisted of 17 males and 13 females, including eight mixed breeds, three Jack Russell Terriers, two Labrador Retrievers, two English Setters, two Springer Spaniels and one of each of the following breeds: Bernese Mountain Dog, French Bracco, German Bracco, Cane Corso, Golden Retriever, Czechoslovakian Wolf, Maltese, German Shepherd Dog, Rottweiler, Schnauzer, Shar Pei, Italian Spinone and Spitz. The dogs in this group had a median age of 5.5 years (range: 0.33–15 years) and a median bodyweight of 20 kg (range: 2–53.4 kg). Group A included 20 dogs with AKI and 10 with AKI/CKD. Based on IRIS guidelines, AKI in these dogs was classified as follows: grade 3 (n = 1), grade 4 (n = 12) and grade 5 (n = 17).
Group B (n = 11) consisted of nine males and two females, including two Labrador Retrievers, two mixed breeds and one of each of the following breeds: Dachshund, Beagle, Border Collie, Breton, Jack Russell Terrier, German Shepherd Dog and Schnauzer. The dogs in this group had a median age of 7 years (range: 0.25–16 years) and a median bodyweight of 20.2 kg (range: 4.4–32.4 kg). Group B included four dogs with AKI and seven dogs with AKI/CKD. Based on IRIS guidelines, AKI in these dogs was classified as follows: grade 3 (n = 2), grade 4 (n = 5) and grade 5 (n = 4).
The dogs in both groups were divided according to the aetiology of their AKI: leptospirosis (n = 14), pyelonephritis (n = 2), contrast medium‐induced AKI due to iodinated contrast medium used for a CT scan, (n = 1), heat stroke (n = 1), vitamin D intoxication (n = 1), viper bite (n = 1), non‐steroidal anti‐inflammatory drug overdose (n = 1), septic shock (n = 1) and unknown cause (n = 16).
In group A, 10 dogs survived for at least 30 days after admission and 20 did not survive. The survivors comprised six dogs with AKI, of which one was classified as grade 3, two were categorised as grade 4 and two were categorised as grade 5, and four dogs with AKI/CKD, of which two were categorised as grade 4 and two were categorised as grade 5. The non‐survivors comprised 14 dogs with AKI, of which four were categorised as grade 4 and 10 were categorised as grade 5, and six dogs with AKI/CKD, of which four were categorised as grade 4 and two were categorised as grade 5. No significant difference in outcome was found between dogs with AKI and those with AKI/CKD (p = 0.69).
In group B, three dogs survived for at least 30 days after admission, of which one had AKI (grade 3) and two had AKI/CKD (grade 4). The remaining eight dogs did not survive, of which three had AKI (one classified as grade 4 and two classified as grade 5) and five had AKI/CKD (one classified as grade 3, two classified as grade 4 and two classified as grade 5).
CEUS renal examination
There were no significant differences in the qualitative and quantitative CEUS values obtained at the T0 assessment between the survivors and non‐survivors in group A (Tables 1 and 2).
TABLE 1.
Renal perfusion quantitative parameters in survivors (S) and non‐survivors (NS) in the group that underwent haemodialysis (group A), expressed as median and range
| S (n = 10) | NS (n = 20) | p‐Value | |
|---|---|---|---|
| CEUS cortical quantitative parameters | |||
| PI (au) | 8.7 (2.0–31.8) | 10.4 (2.8–66.0) | 0.99 |
| TTP (s) | 3.1 (0.9–9.4) | 3.1 (0.7–11.8) | 0.99 |
| mTT (s) | 9.3 (4.1–21.3) | 6.9 (1.9–17.7) | 0.99 |
| Wash‐in slope (au/s) | 6.0 (0.4–41.9) | 4.4 (0.5–23.5) | 0.99 |
| AUC (au x s) | 421.9 (40.5–920.4) | 200.5 (3.5–1497.0) | 0.99 |
| WiAUC (au x s) | 17.9 (3.6–377.6) | 19.0 (6.3–430.7) | 0.99 |
| WoAUC (au x s) | 263.7 (36.3–845.4) | 188.0 (31.3–1344.0) | 0.99 |
| CEUS medullary quantitative parameters | |||
| PI (au) | 3.9 (0.4–17.9) | 3.2 (0.9–16.3) | 0.99 |
| TTP (s) | 8.7 (3.4–13.8) | 5.9 (1.5–12.0) | 0.99 |
| mTT (s) | 27.7 (8.7–39.1) | 17.6 (3.6–41.8) | 0.99 |
| wash‐in slope (au/s) | 0.6 (0.1–3.0) | 0.8 (0.1–2.8) | 0.99 |
| AUC (au x s) | 211.4 (17.8–631.4) | 224.4 (38.9–702.8) | 0.99 |
| WiAUC (au x s) | 20.0 (17.8–631.4) | 9.6 (1.9–55.0) | 0.99 |
| WoAUC (au x s) | 194 (15.6–550.7) | 180.1 (33.3–620.8) | 0.99 |
Abbreviations: au, arbitrary units; AUC, area under the curve; CEUS, contrast‐enhanced ultrasound; mTT, mean transit time; PI, peak enhancement intensity; s, seconds; TTP, time to peak; Wash‐in slope, slope of the curve; WiAUC, wash‐in area under the curve; WoAUC, wash‐out area under the curve.
TABLE 2.
Renal perfusion qualitative parameters in survivors (S) and non‐survivors (NS) in the group that underwent haemodialysis (group A), expressed as median and range
| S (n = 10) | NS (n = 20) | p‐Value | |
|---|---|---|---|
| Arterial phase (s) | 7 (6–16) | 7 (4–12) | 0.99 |
| A–C T (s) | 3 (2–5) | 5 (3–9) | 0.99 |
| Cortical phase (s) | 10.5 (8–19) | 12 (8–16) | 0.99 |
| C–M T (s) | 8.5 (5–12) | 7 (4–9) | 0.99 |
| Medullary phase (s) | 18 (16–29) | 19 (14–25) | 0.99 |
Abbreviations: A–C T, time between the arterial phase and the cortical phase; C–M T, time between the cortical phase and the medullary phase; s, seconds.
Repeated CEUS renal examinations at T0, T1, T7 and T30 were performed in six of the 10 surviving dogs in group A. CEUS was not performed at T30 in the remaining four dogs, as their owners elected to continue the follow‐up with the referring veterinarian. In the surviving dogs with repeated CEUS examinations, no statistically significant differences in cortical and medullary quantitative and qualitative parameters were observed over time, except for the cortical PI. Cortical PI values exhibited a linear trend between T0 and T30, with the highest value at T0 and a progressive reduction at subsequent time points (Table 3). In addition, in surviving dogs, PI was significantly reduced at T1 compared to T0 (p = 0.04).
TABLE 3.
Peak enhancement intensity (PI) values (expressed as mean ± standard deviation) for repeated renal contrast‐enhanced ultrasound examinations performed in surviving (S) and non‐surviving (NS) dogs undergoing haemodialysis
| T0 | T1 | T7 | T30 | |
|---|---|---|---|---|
| S patients (n = 6) | ||||
| Cortical PI (au) | 18.33 ± 12.38 | 13.53 ± 10.02 | 9.22 ± 7.77 | 8.99 ± 8.43 |
| RM ANOVA p = 0.03; test for trend p = 0.002 | ||||
| NS patients (n = 12) | ||||
| Cortical PI (au) | 9.43 ± 8.69 | 9.83 ± 7.85 | ∖ | ∖ |
| Mann–Whitney test p = 0.94 | ||||
Note: CEUS examinations were carried out at admission before the start of therapy (T0), after the first dialysis (T1), 7 days after admission (T7), and 30 days after admission (T30).
Abbreviations: au, arbitrary units; RM ANOVA, repeated‐measures one‐way analysis of variance.
Of the non‐survivors in group A, eight died during the first haemodialysis, 10 died between Day 2 and Day 7 after admission, and two died between Day 7 and Day 30 after admission. For the 12 dogs that survived the first dialysis session, CEUS renal examinations were performed at T0 and T1, and only in two non‐survivors was the CEUS examination also performed at T7. No statistically significant differences in cortical and medullary qualitative and quantitative parameter values were found between T0 and T1 (Table 3).
In the non‐surviving dogs, the presumed causes of death were cardiopulmonary arrest in 10 patients, pulmonary complications in eight patients (pulmonary haemorrhage in five patients, ureamic pneumonia in two patients and aspiration pneumonia in one patient), acute pancreatitis in one patient, and sepsis and haemorrhagic diarrhoea in one patient.
In group B, eight of the 11 dogs died of complications related to the AKI. In most of the dogs in this group, medical therapy was undertaken because the owners declined haemodialysis, despite it being indicated.
Considering all dogs included in the study, there were no significant differences in quantitative and qualitative CEUS parameter values at T0 between patients with AKI and those with AKI/CKD (Tables 4 and 5).
TABLE 4.
Quantitative renal perfusion parameters at admission in dogs with acute kidney injury (AKI) and those with acute impairment associated with chronic kidney disease (AKI/CKD), expressed as median and range
| AKI (n = 24) | AKI/CKD (n = 17) | p‐Value | |
|---|---|---|---|
| CEUS cortical quantitative parameters | |||
| PI (au) | 9.6 (1.8–66.0) | 9.2 (0.9–54.4) | 0.99 |
| TTP (s) | 3.2 (0.7–4.5) | 3.8 (0.9–14.9) | 0.99 |
| mTT (s) | 6.9 (2.3–17.9) | 8.2 (1.9–29.0) | 0.99 |
| Wash‐in slope (au/s) | 5.2 (0.5–23.5) | 2.8 (0.2–41.9) | 0.99 |
| AUC (au x s) | 238.0 (3.5–1497.0) | 218.5 (45.2–1292.0) | 0.99 |
| WiAUC (au x s) | 15.7 (3.6–430.7) | 19.0 (3.3–377.6) | 0.99 |
| WoAUC (au x s) | 204.9 (31.3–1344.0) | 197.8 (41.9–1111.) | 0.99 |
| CEUS medullary quantitative parameters | |||
| PI (au) | 3.8 (0.11–17.9) | 3.2 (0.8–15.6) | 0.99 |
| TTP (s) | 6.2 (1.6–11.6) | 7.0 (1.5–17.4) | 0.99 |
| mTT (s) | 22.9 (8.0–72.5) | 19.6 (3.6–32.0) | 0.99 |
| Wash‐in slope (au/s) | 0.8 (0.1–4.4) | 0.6 (0.1–9.8) | 0.99 |
| AUC (au x s) | 211.1 (17.8–908.8) | 130.1 (26.7–688.1) | 0.99 |
| WiAUC (au x s) | 17.0 (1.9–82) | 13.11 (4.1–173.3) | 0.99 |
| WoAUC (au x s) | 195.7 (15.6–846.2) | 116.2 (22.6–514.8) | 0.99 |
Abbreviations: au, arbitrary units; AUC, area under the curve; CEUS, contrast‐enhanced ultrasound; PI, peak enhancement intensity; mTT, mean transit time; s, seconds; TTP, time to peak; Wash‐in slope, slope of the curve; WiAUC, wash‐in area under the curve; WoAUC, wash‐out area under the curve.
TABLE 5.
Qualitative renal perfusion parameters at admission in dogs with acute kidney injury (AKI) and those with acute impairment associated with chronic kidney disease (AKI/CKD), expressed as median and range
| AKI (n = 24) | AKI/CKD (n = 17) | p‐Value | |
|---|---|---|---|
| Arterial phase (s) | 8 (4–16) | 7.5 (4–12) | 0.99 |
| A–C T (s) | 5 (2–9) | 4 (2–9) | 0.99 |
| Cortical phase (s) | 14 (6–19) | 12 (7–19) | 0.99 |
| C–M T (s) | 7 (4–12) | 7 (4–12) | 0.99 |
| Medullary phase (s) | 21 (13–29) | 19 (11–26) | 0.99 |
Abbreviations: A–C T, time between the arterial phase and the cortical phase; C–M T, time between the cortical phase and the medullary phase; s, seconds.
DISCUSSION
In dogs with AKI undergoing haemodialysis, the described survival rate is around 50%, and it would be advisable to identify prognostic tools to provide a prediction of the outcome of these patients. 7 , 8 , 9 In our study, 33.3% of dogs treated with haemodialysis survived for at least 30 days after admission. The aetiology of AKI in our patients was variable and often unknown; this factor could possibly explain the difference in the survival rate between our study and the other studies where the survival rate was evaluated. Indeed, AKI aetiologies might vary between different geographical areas, possibly influencing outcomes. 16
CEUS proved to be a safe and easy‐to‐use method for the study of renal perfusion in dogs with acute renal impairment. The examination was performed in awake patients, without the need for sedation. No adverse effects were reported, confirming the safety of the method. 17
In our patients undergoing haemodialysis (group A), no significant differences in quantitative and qualitative perfusion parameters were found between survivors and non‐survivors at T0. Therefore, in our cohort of dogs, CEUS examination before the start of haemodialysis did not seem able to predict survival. However, considering instead the repeated CEUS examinations that were carried out in individual patients, the cortical PI was significantly reduced at T1 compared to T0 in survivors, and was significantly reduced at subsequent time points in these dogs. In contrast, there were no significant differences in cortical PI between T0 and T1 in non‐survivors. The cortical PI represents the maximum value of intensity reached in the renal cortex during the CEUS examination compared to the mean value of the baseline intensity. 10 Our finding could be due to the microcirculatory dysfunctions that developed during AKI. First, some studies have shown that during septic AKI, a redistribution of flow from the renal medulla to the renal cortex can develop, with a significant degree of medullary deoxygenation. 18 , 19 , 20 During AKI, vasoconstriction of glomerular afferent arterioles and increased vascular resistance in the kidneys may develop secondary to numerous factors, such as severe inflammation. The activation of inflammatory processes influenced by the factors released by the cells of the damaged proximal tubules and by the adhesion of damaged endothelial cells is of fundamental importance in this process. 21 Finally, leukocytes can interfere with renal blood flow by secreting vasoactive factors or physically contributing to flow disruption. 21
It is possible that similar mechanisms developed in our patients, and that these determined a significant modification of cortical PI between T0 and T1 in surviving dogs. Based on our results, it is likely that the cortical PI has partially modified from T0 to T1 in surviving dogs to result in a significant reduction in PI, which has not been observed in non‐survivors. This significant difference between survivors and non‐survivors may be secondary to the severity of the initial damage and its persistence before the start of therapy, depending on when the patient was referred to our veterinary hospital.
Two previous studies have investigated the diagnostic value of renal CEUS in dogs with AKI. 11 , 12 The first study, conducted by Mannucci et al., included dogs with different AKI aetiologies, including leptospirosis, pyelonephritis and grape toxicity. The findings revealed that pathological patients exhibited a higher cortical PI than healthy patients, although this disparity did not reach statistical significance. 11 In the second study, by Gasser et al., exclusively dogs with septic AKI secondary to pyometra were included (n = 20). In these patients, the cortical PI was significantly lower than in the healthy group. 12 In human medicine, it is described that the vascular perfusion within the renal cortex starts to decline during the early stages of AKI, resulting in reduced renal perfusion. 22 However, it is important to note that our study comprised patients referred for dialysis therapy from other veterinary facilities, and they were typically in an advanced stage of AKI. Consequently, the persistence of AKI in our study's patients might have led to modifications in kidney perfusion that might not necessarily manifest as a reduction in cortical PI. Additionally, the aetiology of AKI could potentially influence alterations in perfusion throughout the course of the condition.
Regarding the evaluation of renal perfusion in patients with AKI and AKI/CKD, no significant differences in quantitative and qualitative perfusion parameters were found between the two groups. This finding could indicate that, in patients with AKI/CKD, the perfusion changes detectable with CEUS are not significantly influenced by the parenchymal changes that occur during CKD. 23
However, our study has some limitations. First, the injection of contrast medium was done manually, and not using a pump and an infusion syringe. However, while manual injection has the potential to be less accurate in contrast medium infusion, the manual injection method has been used in most published studies. 11 , 12 Second, the AKI aetiology in most of the cases included was unknown. Different aetiologies can result in different renal histological and vascular modifications, and this may have influenced our results. Further studies are needed to investigate the prognostic value of CEUS for specific aetiologies of AKI. Finally, the small sample population and the small number of surviving patients included in the study mean that the statistical analysis is likely underpowered. Therefore, the findings should be interpreted cautiously.
In conclusion, repeated CEUS examinations could be a useful prognostic tool for dogs with AKI undergoing haemodialysis. However, it is not possible to differentiate between patients with AKI and those with AKI/CKD by CEUS examination.
AUTHOR CONTRIBUTIONS
Caterina Puccinelli: Conceptualisation; methodology; software; formal analysis; investigation; data curation; writing—original draft preparation; writing—review and editing. Ilaria Lippi: Conceptualisation; investigation; writing—review and editing. Tina Pelligra: Methodology; validation; data curation; writing—review and editing. Simonetta Citi: Conceptualisation; methodology; software; formal analysis; investigation; data curation; writing—review and editing; supervision and project administration. All authors have read and agreed to the published version of the manuscript.
CONFLICT OF INTEREST STATEMENT
The authors declare they have no conflicts of interest.
ETHICS STATEMENT
The research protocol was approved by the Institutional Animal Care and Use Committee of the University of Pisa (permission number: 14/2020).
FUNDING INFORMATION
This research received no external funding.
ACKNOWLEDGEMENTS
The authors thank Federica Pardini for her contribution to realising Figure 3.
Puccinelli C, Lippi I, Pelligra T, Citi S. Prognostic value of contrast‐enhanced ultrasound in dogs with acute renal injury treated with haemodialysis. Vet Rec. 2025;e4959. 10.1002/vetr.4959
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.