Bedside ultrasound after aortic surgery
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Early complications after aortic surgery, such as bleeding, vessel occlusion, and organ ischemia require quick and targeted diagnostics to reduce the morbidity and mortality. Ultrasound can be used for quick bedside diagnosis of vascular and organ complications.
The possibilities of color duplex and contrast-enhanced ultrasound for the detection of vascular and organ complications after aortic surgery are presented.
Vascular access complications, such as acute vessel occlusion, stenosis, dissection, bleeding, hematoma, and false aneurysms can be detected by color duplex ultrasound. The differentiation between hematoma and active bleeding is possible with contrast-enhanced ultrasound. Ultrasound contrast imaging enables the evaluation of hemodynamically relevant dissections and intraluminal thrombi. Furthermore, contrast-enhanced ultrasound enables the differential diagnostics of acute kidney failure and a differentiation between complete or partial organ ischemia.
The use of bedside ultrasound for quick detection of early complications after aortic surgery enables optimization of the perioperative management of complications. Further diagnostic and therapeutic interventions can be used in a targeted manner, if necessary. Unnecessary exposure to nephrotoxic radiopaque agents and X‑rays and the risks involved in transportation of critically ill patients can therefore be avoided.
KeywordsVascular diseases Early complications Bedside diagnostics Color duplex ultrasound (CDU) Contrast enhanced ultrasound (CEUS)
Bettseitiger Ultraschall nach Aorteneingriffen
Frühkomplikationen nach Aorteneingriffen wie Blutung, Gefäßverschluss oder Organischämie erfordern eine rasche und zielführende Diagnostik, um Morbidität und Mortalität zu senken. Der bettseitige Ultraschall kann zur schnellen Diagnostik bei Gefäß- und Organkomplikationen eingesetzt werden.
Es werden die Möglichkeiten der Farbduplex- und Kontrastmittelsonographie nach Aorteneingriffen zur Diagnostik bei Gefäß- und Organkomplikationen dargestellt.
Gefäßzugangskomplikation wie akuter Verschluss, Stenose, Dissektion, Blutung, Hämatom oder Aneurysma spurium lassen sich mittels Farbduplexsonographie diagnostizieren. Die Unterscheidung zwischen Hämatom und aktiver Blutung ist mittels Kontrastmittelsonographie möglich. Die Relevanz von Dissektionen oder intraluminalen Thromben kann durch die Ultraschallkontrastdarstellung eingeschätzt werden. Die Kontrastmittelsonographie ermöglicht ferner die Differenzialdiagnostik des akuten Nierenversagens sowie eine Unterscheidung zwischen kompletter und partieller Organischämie.
Der Einsatz des bettseitigen Ultraschalls zur schnellen Diagnostik bei Frühkomplikationen nach Aorteneingriffen ermöglicht eine Optimierung des perioperativen Komplikationsmanagements und damit die zielgerichtete Einleitung weiterer diagnostischer und therapeutischer Maßnahmen, wenn erforderlich. Eine unnötige, nephrotoxische Kontrastmittel- und Strahlenexposition sowie das Risiko des Transports von kritisch kranken Patienten können so vermieden werden.
SchlüsselwörterVaskuläre Erkrankungen Frühkomplikationen Bettseitge Diagnostik Farbduplexsonographie (FKDS) Kontrastmittelsonographie (CEUS)
Vessel and organ complications occur after both open and endovascular aortic surgery. These include vascular access complications, such as bleeding and acute ischemia in cases of occlusion or dissection and also hepatic, renal and intestinal ischemia. Rapid and targeted diagnostics are essential for avoidance of long-term damage and to reduce morbidity and mortality. Bedside color duplex and contrast-enhanced ultrasound can be used in the intensive care unit for rapid diagnosis of early complications after these interventions.
Early and late complications have to be expected after both open and endovascular aortic surgery. According to 2016 data from the German Institute for Vascular Medicine Healthcare Research (DIGG, Deutsches Institut für Gefäßmedizinische Gesundheitsforschung) of the German Society for Vascular Surgery and Vascular Medicine (DDG, Deutsche Gesellschaft für Gefäßchirurgie und Gefäßmedizin), the morbidity rate following endovascular aortic repair (EVAR) of symptom-free aortic aneurysms is 11.2%, compared to 29% after open surgery; the mortality is given as 1.0% and 4.1%, respectively . An increasing number of older and high-risk patients who would have been excluded from open surgery in the past nowadays receive treatment. The risk of potential perioperative complications is increasing as a consequence, as is in-hospital mortality (2.0% in patients aged over 80 years compared to 0.7% among those under 80 years after EVAR, versus 14.5% and 3.1%, respectively, after open surgery for symptom-free abdominal aortic aneurysms, AAA ). Adequate perioperative management is thus of paramount importance. Particularly in the case of early complications, rapid and targeted diagnostic measures are necessary to prevent long-term damage and reduce mortality.
Early complications after aortic interventions
Approximately 25% of patients with acute type B aortic dissection present with a complicated dissection. Such a situation is defined by the presence of malperfusion syndrome or hemodynamic instability . Malperfusion syndrome is described to occur at a frequency of approximately 10% in acute type B dissections. Clinical symptoms are often initially unclear . Computed tomography angiography (CTA) can reveal a true lumen collapse, intima flaps, or a delayed to absent contrast enhancement of the kidneys  but is not always unambiguous due to limitation of the results to generally just two phases (early and late phases).
After complex aortic interventions, patients are nearly always treated in the intensive care unit (ICU). In the case of perioperative complications, further diagnostic assessment with CTA or magnetic resonance imaging (MRI) requires patient transportation, which not only consumes personnel resources but also constitutes a risk for critically ill patients. Moreover, exposure to contrast agents can further exacerbate pre-existing renal insufficiency.
Color duplex and contrast-enhanced ultrasound have several advantages in this respect: the ultrasound examination can be performed at the bedside in the ICU, can be repeated as often as required, is not stressful for the patients, and has no nephrotoxicity.
Ultrasound can be used for bedside diagnostics
Using illustrative examples, the following article presents the possibilities of bedside ultrasound for rapid diagnosis of vessel and organ complications after aortic interventions and in patients with aortic dissection.
The use of B‑mode and color duplex ultrasound is possible with almost all modern ultrasound systems. For this two transducers of different penetration depths are required (sector or linear type probes). Contrast-enhanced ultrasound functions with system-specific software, which is nowadays available in all high-end systems of ultrasound manufacturers or can be retrofitted. Via a reduction in the acoustic power or so-called mechanical index (MI) of the transducer, the injected microbubbles of ultrasound contrast medium (SonoVue®, Bracco Imaging Deutschland GmbH, Konstanz, Germany, https://imaging.bracco.com) are excited but not destroyed. The microbubbles remain intravascular (blood pool agent) and are expelled in exhaled breath. This image is displayed as echo-rich blood flow on a black background .
Severe anaphylactic or anaphylactoid reactions occur at a frequency of 1:10,000. The cause is presumed to be complement activation via an interaction of the microbubbles with macrophages or basophils. Patients are thus required to give informed consent in non-emergency situations. SonoVue® must not be used together with dobutamine or in patients with a contraindication to dobutamine. Caution is advised in coronary thrombosis patients. SonoVue® is contraindicated in patients aged under 18 years and those with a known right-to-left shunt, severe pulmonary hypertension, uncontrolled systemic hypertension, or acute respiratory distress syndrome, as well as in pregnant and breastfeeding women (see SonoVue® product information). According to the current European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) guidelines from 2017, adequate experience and specialist user training is recommended for clinical use of contrast agent-enhanced ultrasound .
Vascular access complications
The use of B‑mode ultrasound enables rapid conclusions regarding hematomas (Fig. 1e) or lymphoceles in the region of access vessels. On detection of a large hematoma or pulsation, the possibility of active bleeding or false aneurysm must be considered (Fig. 1f, g). Not only the access vessel itself but also smaller branches may be affected (Fig. 1f). Typical for a false aneurysm is detection of to-and-fro flow in the aneurysm neck (Fig. 1g). To-and-fro flow may be absent in the aneurysm sack due to circulating currents. Depending on the size of the aneurysm and configuration of the neck, compression or an intervention, such as ultrasound-guided thrombin injection or surgery should be discussed.
Dissection and thromboses
Parametric imaging can ease evaluation
If the contrast agent enters the renal medulla normally but not the renal cortex, an acute cortical necrosis, such as in shock, hemorrhage or sepsis, may be present (Fig. 4e). Segmental renal infarctions appear as black areas in a kidney with otherwise normal temporal perfusion dynamics (Fig. 4f). In principle, kidney infarctions can also be visualized in color duplex (Fig. 4g) and B‑mode ultrasound; however, demonstration of missing vascularization in a kidney segment with color duplex ultrasound is significantly more difficult in obese and tachypneic patients with pain, and due to the Doppler artefact. In the early phase of the infarction, B‑mode ultrasound still reveals normal findings. The low echo demarcation of the infarction zone (Fig. 4h) is only visible hours later. Where doubt exists, the rapid and much more easily interpreted approach of contrast-enhanced ultrasound should be applied. Contrast-enhanced ultrasound is also able to distinguish between normally perfused sections of the intestine and bowel ischemia (Fig. 4i–j); however, contrast-enhanced ultrasound is currently not the preferred method for detection of intestinal ischemia and endoscopy or CTA is used in this scenario.
Aortic interventions carry a risk for various vessel, organ, and systemic complications . Knowledge of the specific complications associated with the different operative procedures is thus of vital importance. Particularly during the perioperative phase in the ICU, quick and targeted decisions must be made to reduce the perioperative morbidity and therefore also the mortality of these interventions .
The value of bedside ultrasound as a noninvasive, cost-effective, radiation-free diagnostic option has also been shown for other clinical intensive care scenarios, e. g., after liver transplantation . Highly important for these patients is the rapid diagnosis of stenoses, false aneurysms, thromboses, and dissections in the hepatic artery. Particularly contrast-enhanced ultrasound significantly improves visualization, while simultaneously enabling evaluation of perfusion in the liver parenchyma [3, 8]. A comparison between the diagnostic accuracy of contrast-enhanced ultrasound and that of a native CT examination in patients with kidney failure revealed correct characterization of liver, kidney, and intestinal pathologies in 96%, 89%, and 100% of cases for contrast-enhanced ultrasound versus 0%, 7%, and 18% for native CT, respectively . The diagnostic accuracy of contrast-enhanced ultrasound for diagnosing splenic artery complications after acute pancreatitis is given as 42%, leading to its description as a safe and effective method for increasing diagnostic certainty .
Color duplex ultrasound is the standard diagnostic method for detecting false aneurysms. Characteristic criteria are detection of circulating blood flow in a formation next to the artery and detection of an aneurysm neck with the typical to-and-fro flow (to-and-fro sign) . For blue toe syndrome, a frequent clinical manifestation of microembolisms, ultrasound has been described as the first-choice diagnostic procedure, enabling detection of the source of the embolism in over 90% of patients . In their 2012 study dedicated to diagnosis of vascular lesions in arteries of the lower extremities, Gabriel et al.  observed a diagnostic agreement between color duplex ultrasound and angiography in 94.6% of cases. Based on these results, color duplex ultrasound is to be viewed as being of equal value to angiography and CTA for vascular diagnostics of lower extremity arteries.
Further targeted diagnostic procedures can be initiated
After aortic interventions, many questions related to vascular access complications, including hematomas, active and peripheral bleeding, venous thromboses in the legs or organ ischemia, can be answered with B‑mode, color duplex, and contrast-enhanced ultrasound in the ICU. Where necessary, further targeted diagnostic or therapeutic measures can then be initiated.
This is of particular importance for the differential diagnoses of acute kidney failure, since it is vital to distinguish between prerenal and intrarenal kidney failure. The risk of contrast agent-induced nephropathy with acute kidney failure is as high as 6.7% after EVAR . Since average contrast agent volumes for infrarenal aortic stent graft implantation of 50–100 ml have been described , renewed administration of iodine-based contrast agent for early postoperative CTA can further increase the risk of contrast agent-induced kidney failure. In this scenario, contrast-enhanced ultrasound is significantly better suited to diagnosis of organ infarction than B‑mode  or color duplex ultrasound . In two studies from 2006 and 2017, a suspected diagnosis of organ ischemia could be made in 25% of patients using B‑mode ultrasound , organ ischemia could be diagnosed by color duplex ultrasound in 28%  and organ ischemia could be clearly demonstrated by contrast-enhanced ultrasound in 83% with the remaining 17% of findings stated to be consistent with organ ischemia . A differentiation between renal infarction and cortical ischemia was possible, which was not possible with color duplex ultrasound . Moreover, contrast-enhanced ultrasound could also distinguish between cystic and solid kidney pathologies and classify the cysts according to the Bosniak system .
In patients with aortic dissection, two or more phase CTA does not always permit adequate evaluation of whether a hemodynamically relevant true-lumen collapse with subsequent organ underperfusion is present; however, continuous observation with contrast-enhanced ultrasound enables imaging of both the true and the false lumen, as well as evaluation of organ perfusion. A 3C recommendation (evidence level 3, recommendation grade C) for evaluation of dissection of the aorta and its primary branches by contrast-enhanced ultrasound is contained in the current EFSUMB guidelines from 2017 .
The highest evidence level (1a) and the highest grade of recommendation (A) for vascular contrast agent-enhanced ultrasound remain unchanged for detection and classification of endoleaks during follow-up after endovascular aortic repair . This is generally not of central importance for management of perioperative complications and only relevant after endovascular repair of a ruptured aneurysm. Suspected diagnoses that are currently hardly applicable to evaluation by ultrasound, e. g., acute cerebral ischemia or cerebral hemorrhage and also fulminant pulmonary artery embolisms, continue to require rapid CTA or MRI diagnostics.
In summary, bedside ultrasound after aortic interventions serves to optimize perioperative complications management and thus targeted use of further diagnostic and therapeutic measures. Unnecessary exposure to contrast agent or radiation can be avoided, as can the risk of transporting critically ill patients.
Early complications after aortic interventions are vascular access complications, bleeding, and organ and systemic complications.
Rapid and targeted diagnostic procedures are necessary to reduce perioperative morbidity and mortality of these interventions.
Color duplex and contrast-enhanced ultrasound enable rapid bedside diagnosis of vessel and organ complications after aortic interventions as well as an estimation of the hemodynamic relevance of an aortic dissection.
The differentiation between hematoma and active bleeding as well as between acute kidney failure and complete or partial organ ischemia is possible with ultrasound contrast imaging.
Where necessary, further diagnostic and therapeutic measures can be initiated in a targeted manner, and unnecessary exposure to contrast agents and radiation as well as the risk of transporting critically ill patients can be avoided.
Compliance with ethical guidelines
Conflict of interest
W. Schierling received travelling expenses from von Bracco Imaging Deutschland GmbH. K. Pfister received travelling expenses and advisor fees from Bracco Imaging Deutschland GmbH. I. Göcze, H. Apfelbeck, K. Oikonomou and P.M. Kasprzak declare that they have no competing interests.
This article does not contain any studies with human participants or animals performed by any of the authors.
The supplement containing this article is not sponsored by industry.
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