B-mode ultrasound of the kidney, bladder and prostate is a basic tool in the assessment of both acute and chronic kidney injury. It is essential in the study of renal function deterioration in the absence of previous glomerular filtration data. It enables obstructive causes and, using colour Doppler, vascular causes to be confirmed or ruled out quickly and non-invasively for the patient.2,13 The nephrologist needs to be able to assess3 the presence and location of both kidneys, their size, symmetry and echo structure, dilation of the urinary tract, and the presence of masses, cysts or lithiasis. For the bladder, we need to be able to recognise the presence of exophytic lesions, diverticula and imprints on the bladder wall, as well as assess the wall's thickness. Inside the bladder, we have be able to recognise the presence of catheters or debris, as well as its filling volume. A full bladder and post-voiding examination should be performed to assess the presence of significant residue.

In the prostate, we have to be able to assess prostate size by measuring its three diameters in order to calculate the volume (Fig. 2).

Fig. 2.

Data to be collected in a renal, bladder and prostate ultrasound.

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The Doppler mode allows us to study intra- and extra-renal vessels, determine velocities for the diagnosis and follow-up of renal artery stenosis, and study vascular malformations, arterial or venous thrombosis and post-renal biopsy vascular complications.

Using colour Doppler (qualitative) we can assess the arterial and venous perfusion of the entire parenchyma, studying the renal artery and vein in all its sections. With spectral Doppler (quantitative) we can record the spectral wave of the vessel studied. From this record, we can make measurements of various parameters of vascular flow. In the indirect study, recordings are made of the intra-renal vessels, their morphology is analysed (e.g. to identify a "parvus et tardus" waveform, suggestive of stenosis), and the resistive, pulsatility and acceleration indices are calculated. The direct study (on the renal artery) is used to detect the presence of stenosis, measuring the velocities directly in the renal artery and in the aorta. The direct study is more complicated than the indirect one, as it is very difficult to visualise the renal artery in its entirety. In both the direct and indirect methods, a correct angle of insonation (angle between the ultrasound beam and the direction of blood flow) of a maximum of 60° is required for velocity measurements to be reliable (Fig. 3). Lastly, although in kidney transplantation the use of Doppler is mandatory, as there is a vascular anastomosis, in the native kidney there are only very specific indications (Fig. 4).

Fig. 3.

Renal Doppler ultrasound: key aspects.

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Fig. 4.

Renal Doppler ultrasound: indications in native kidney.

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Good vascular access (VA) is essential for the success of HD treatment, as it determines the quality of the dialysis, and complications can lead to high morbidity and mortality rates and increased healthcare costs.14

Preoperative mapping of the arterial and venous territory in the arms of patients who are candidates for VA, especially in patients with comorbidity, increases the rate of native VA and improves survival. Although arm mapping should be used in all patients, it is particularly necessary in cases where the habitual physical examination may be insufficient due to obesity, absent pulses, previous surgery, possible arterial disease (advanced age, diabetes, cardiovascular disease) or possible venous disease (multiple previous venous cannulation).

The examination includes grey-scale B-mode ultrasound followed by a Doppler scan. Both arterial and venous exploration is from the distal area, starting at the wrist, to the proximal area, ending at the subclavian and axillary veins.14

The clinical management of VA can be optimised by the nephrologist's use of Doppler, as it enables early diagnosis of VA problems that may go unnoticed, helping to determine the degree of therapeutic urgency15 and avoiding unnecessary aggressive tests. It is therefore essential that the nephrologist knows the theoretical principles and the practical application of VA ultrasound.

The nephrologist should perform serial Doppler scans of the VA (morphological surveillance and haemodynamic study)16,17 in order to detect significant stenosis,18 monitor non-significant stenosis,19 assess AVF maturation18 and diagnose various disorders, such as thrombosis,20 aneurysms and pseudoaneurysms,18,20 and personalise the treatment of steal syndrome21 or its cardiac impact.22–24

Cardiovascular (CV) disease is the leading cause of death in patients with chronic kidney disease (CKD), and the main culprit is atheromatosis. It is a chronic, progressive inflammatory process of the arteries, causing a thickening of the arterial intima-media layer until the formation of atheroma plaques (thickness >1.5 mm),25 and is accelerated by traditional CV risk factors (age, sex, hypertension, diabetes, dyslipidaemia, smoking, etc.) and non-traditional factors (in patients with CKD: uraemic toxins, oxidative stress, chronic inflammation, anaemia, etc.).26 Arterial ultrasound allows the direct and precise assessment of the damage caused by risk factors on the vascular wall, it being more accurate as it is not based solely on traditional CV risk factors and scores which are not validated in the population with CKD.27 For that reason it is recommended in several different clinical practice guidelines.28,29 The diagnosis of subclinical atheromatous disease will help to detect the population most at risk and allow us to act early to prevent progression and CV events.

Ultrasound also makes it possible to assess the burden of atheromatous disease (number of territories and plaque area), analyse the composition of the plaques (lipids, fibrous tissue, calcium) and assess progression. As it is a systemic disease, it is important to explore all the accessible arterial territories: carotid (common, bifurcation or bulb, internal and external), femoral (common and superficial) and aorta (at the level of the abdomen). Various studies have shown that the prevalence of atheromatosis in femoral arteries, in the absence of carotid involvement, is in the range of 17%–20%.30

Lung ultrasound is a non-invasive way to detect lung congestion. It is of great help in the management of renal patients with dyspnoea, even in early subclinical stages. It is very useful in the assessment and monitoring of the response to treatment, in the prevention of volume overload in hypovolaemic heart patients treated with fluid therapy, and in the diagnosis and follow-up of pneumonia.31,32 The diagnosis of volume overload is made by evaluating ultrasound artefacts with diagnostic value such as "lung rockets" (multiple B lines) or comet tail artefacts.33,34

Ultrasound is the best technique for the detection of pleural effusion; it is far superior to conventional radiology, as it is capable of detecting effusions of as little as 5 ml, compared to 150 ml in the posterior/anterior chest X-ray. The ultrasound pattern allows us to distinguish transudative from exudative. Lastly, ultrasound enables rapid detection of pneumothorax without the need to radiate the patient and with high reproducibility.

Transthoracic echocardiography is recognised for its utility in renal patients35 and nephrologists should know how to perform it at a basic level.

Essentially, they need to be able to recognise pericardial effusion and left ventricular hypertrophy, and to know how to calculate the ejection fraction. A low-frequency sector probe is required. The degree of inspiratory collapse of the inferior vena cava measured by ultrasound can help estimate patients' effective volume status and, in conjunction with the symptoms, be a support in decision-making for the management of fluid therapy.36

Ultrasound was the first imaging technique used to study the parathyroid glands. This is an easy technique for the nephrologist, with a quick and useful learning curve in the routine study of patients with secondary hyperparathyroidism, which provides great benefits and profitability.37 Using ultrasound, we can determine the number and location of the parathyroid hypertrophy in order to plan a parathyroidectomy. The assessment of the parathyroid mass (volume) is of important prognostic value, as any increase is associated with a poorer response to drug treatment.38 In some situations, ultrasound has been used to perform a chemical parathyroidectomy by intraglandular injection of alcohol/calcitriol.39

Ultrasound is highly useful in the implantation of the peritoneal catheter by the nephrologist, as it allows the systematic examination of the subcutaneous tissue, musculature and fascia of the rectus muscles, and the location of the epigastric artery to avoid the risk of laceration and of the parietal peritoneum and the peritoneal cavity. It also makes it possible to locate the intestinal loops to ensure they are not in the catheter's path and to rule out adhesions between them.40–42 Lastly, an ultrasound scan to assess the bladder before implantation of the peritoneal catheter can help to prevent perforation in patients with post-void residual volume, with these patients being catheterised, if necessary, to ensure complete bladder emptying. Abdominal ultrasound also helps us guide the insertion of the catheter between the layers of the peritoneum,43 observe how the infusion of peritoneal fluid separates the loops, and facilitate direction of the guide towards the pelvis,42 enabling correct placement of the catheter. It is important to use the ultrasound to identify the tip of the catheter in the pouch of Douglas before surgical closure at the end of the procedure.

In the post-implantation period, ultrasound in the hands of experienced personnel is very useful for assessing tunnel problems and complements other imaging techniques, such as plain X-ray or tomography, and can even sometimes replace them.44 Ultrasound is useful for checking for infection or peri-catheter abscesses,44,45 bleeding or haematoma post-mechanical traction or post-implantation of the catheter, extrusion of the peritoneal catheter, peri-catheter and peritoneal cavity leaks46 or catheter entrapment by omentum.47

Finally, ultrasound can also be used to determine the thickness of the peritoneal membrane and how it relates to the dialysis technique's effectiveness, possibly avoiding the need for future aggressive tests, such as peritoneal biopsy.48

Gastroparesis or slowed gastric emptying is a known complication of diseases such as diabetes or amyloidosis, and also postoperatively, such as after kidney transplantation. Gastric emptying time is reportedly lengthened in patients undergoing any of the three types of renal replacement therapy compared to healthy subjects.49 Gastroparesis can cause anorexia and malnutrition. It can be diagnosed by two-dimensional real-time ultrasound, taking dynamic images of gastric peristaltic activity and its effect on stomach emptying, and then calculating the total postprandial gastric volume.50

Ultrasound allows early detection of fatty liver, a highly prevalent disorder in the general population and also, therefore, in renal patients. The echogenicity of the healthy renal parenchyma is very similar to that of the healthy liver. In fatty liver, the liver is whiter (hyperechogenic) than the renal parenchyma.51 Although previously considered a benign condition, progression to liver fibrosis and even cirrhosis has been reported,52 owing to which these patients should be referred to Gastroenterology for assessment.

With ultrasound, we can easily detect gallbladder sludge and gallstones, whether asymptomatic or complicated with cholecystitis, if we know how to recognise their ultrasound signs.

Percutaneous renal biopsy (PRB) is one of the main procedures in the diagnosis of many different disorders, both of native and transplanted kidneys, and is currently the most widely used interventional technique in Nephrology departments.53 With PRB not being free of complications,54 the use of ultrasound when performing the procedure led to a clear reduction in post-biopsy complications, ranging from 10% to 15% of all patients biopsied using other procedures, to 4% to 6% after the introduction of ultrasound-guided PRB.55

We can differentiate between three uses of ultrasound in renal biopsy:

• •

  Dummy run to assess structure, characteristics of the kidney, access difficulties and possible contraindications to performing the biopsy (e.g. single kidney).

• •

  Performing the PRB per se, with ultrasound enabling the exact puncture point to be chosen, the visualisation of the needle inside the kidney throughout the procedure, and the structures to avoid such as colon, large vessels or renal cysts.

• •

  And afterwards, to detect possible complications, such as bleeding, haematoma, arteriovenous or arteriocalyceal fistulas and pseudoaneurysms,56,57 even at the patient's bedside.

When the nephrologist is able to perform the PRB, this affords them autonomy and reduces the hospital stay by not having to depend on other departments. Acquiring skills in ultrasound-guided PRB requires specific training, experience and mastery in the morphological analysis of the healthy kidney and its pathological variables, and in the use of the Doppler mode for the analysis of post-biopsy vascular complications.

Implantation of a catheter in a central vein with subcutaneous tunnelling is a valid alternative in various clinical situations requiring VA for HD, such as contraindication for an AVF, patients awaiting an AVF, or patients with an AVF, but not sufficiently developed to be used.

For the implantation of a catheter in a central vein, whether tunnelled or not, the AV Guidelines recommend ultrasound-guided puncture rather than implantation by anatomical reference 18, as ultrasound identifies the position of each vessel and its anatomical relationship, and reduces the risk of unwanted puncture of other adjacent vascular structures or the pneumothorax. It also enables detection of thrombosis, which would rule out the vessel for catheter implantation. In short, the use of ultrasound makes catheterisation easier, quicker and safer, and reduces both the likelihood of complications58,59 and the costs.60 Ultrasound-guided puncture is ideal for cannulation of the jugular vein. However, for cannulation of the subclavian vein, the ultrasound view is limited by the interposition of the clavicle. For the implantation of a tunnelled catheter into a central, internal jugular or subclavian vein, it is recommended that after the puncture and the introduction of the guidewire the position of the guidewire be checked by radioscopy to confirm that the intravascular end is lodged in the right place, and to avoid catheter dysfunction owing to malpositioning. 18 Radioscopy also facilitates the identification of thrombosis or stenosis in central veins with the use of contrast, helping to rule out the affected vessel. Radioscopic confirmation is not considered necessary if the catheter is implanted in the femoral vein.

As already discussed in the "Ultrasound in peritoneal dialysis" section, ultrasound will be very useful in peritoneal catheter implantation in order to optimise placement, avoid complications such as puncture of the epigastric artery or intestinal loops, and to confirm the exact position.

Puncture of the AVF can be difficult due to poor maturation, small diameter, juxta-anastomotic stenosis or, around the puncture site, proximity to arteries or nerves, existence of collaterals, previous unsuccessful punctures with haematomas, or even not knowing the direction of cannulation in the case of deep AVF. The characteristics of the HD programme population, with a progressive increase in age and vascular comorbidity, have led to an increase in this type of puncture with extra difficulties.

To counteract these difficulties, Doppler ultrasound performed at the patient's bedside by the nephrologist and/or haemodialysis unit nurse can increase the sensitivity of early detection of abnormalities, resulting in reduced morbidity and mortality rates.61–63 Doppler provides information on the patency, flow, depth and diameter of the vessel when performing the targeted puncture,64,65 and allows the path of the needle to be tracked within the vessel.66–70 This last aspect is essential, as it allows the needle to be repositioned during the HD session if necessary.

Although there are limited studies on the utility of Doppler ultrasound for ultrasound-guided puncture of the VA, its recent incorporation into routine clinical practice has shown that it can reduce the number of punctures, facilitate cannulation in difficult-to-access AVF, and reduce patient discomfort deriving from the puncture. It is therefore necessary to include strategies aimed at training professionals in this specific area.71