Vascular complications of kidney transplantation

1. Introduction

Vascular complications of kidney transplantation are relatively uncommon, but they are one of the most important causes of early graft loss.

Their seriousness lies in the fact that they can suddenly compromise renal perfusion, cause potentially life-threatening hemorrhage, or lead to progressive deterioration of graft function.

Unlike many immunologic or metabolic complications, some vascular complications are potentially correctable by urgent surgical or endovascular intervention.

The prognosis depends on four fundamental factors:

1. The mechanism of the vascular injury.
2. The extent and duration of the perfusion compromise.
3. The speed of diagnosis.
4. The possibility of effective treatment.

The importance of a multidisciplinary approach is emphasized, with the participation of urology, nephrology, vascular surgery, diagnostic imaging, and interventional radiology.

2. Classification of vascular complications

Complications can be classified by time of presentation, mechanism, and vascular territory.

Complication	Typical presentation	Main risk
Arterial thrombosis	Early	Infarction and graft loss
Venous thrombosis	Early	Congestion, hemorrhage, and infarction
Anastomotic hemorrhage	Immediate or early	Shock and graft compression
Pedicle torsion	Early, occasionally late	Interruption of perfusion
Renal artery stenosis	Months or years	Hypertension and graft dysfunction
Pseudoaneurysm	Variable	Rupture, hemorrhage, and infection
Arteriovenous fistula	Often after biopsy	Hematuria, bleeding, or hemodynamic changes
Iliac vascular injury	Intraoperative or postoperative	Lower limb ischemia or bleeding

The distinction between early and late is a guide only. A mechanical complication or a stenosis may appear outside its most frequent time window.

3. Prevention: preoperative vascular evaluation

Recipient evaluation

Patients with advanced chronic kidney disease frequently have atherosclerosis and vascular calcification, especially when diabetes, hypertension, cardiovascular disease, and prolonged exposure to dialysis are present.

The pretransplant vascular evaluation should answer three questions:

• Is there an adequate arterial territory to implant the graft?
• Is there a patent venous system that allows drainage?
• Can the anastomosis be performed without compromising circulation to the lower limb?

Medical history and physical examination

Investigate:

• Intermittent claudication.
• Peripheral arterial disease.
• Previous vascular surgeries.
• Deep vein thrombosis.
• Previous femoral catheters.
• Previous transplants.
• History of thrombophilia.
• Diabetes and cardiovascular disease.

The physical examination includes assessment of femoral and distal pulses, asymmetries, and signs of peripheral vascular disease. The presence of femoral pulses does not exclude significant iliac calcification.

Imaging studies

• Vascular Doppler ultrasound: allows assessment of patency, flow, and hemodynamic abnormalities of accessible vessels.
• Abdominal and pelvic CT: non-contrast CT can provide information on the distribution and severity of iliac calcifications.
• CT angiography: allows study of the lumen, stenoses, and arterial and venous anatomy, and planning of reconstructions when indicated.
• MR angiography: an alternative in selected situations, considering its limitations and the type of contrast.
• Arteriography: reserved for cases in which the anatomic evaluation or the possibility of intervention justifies an invasive study.

Patients with severe iliac calcification

A calcified iliac artery can make the following difficult:

• Vascular clamping.
• Arteriotomy.
• Creating a watertight anastomosis.
• Preservation of distal flow.
• Closing the anastomosis without causing stenosis.

In selected situations, endarterectomy, arterial reconstruction, use of another vascular territory, or strategies combined with vascular surgery may be required. The choice should be planned before surgery whenever possible.

4. Vascular evaluation of the graft and bench surgery

Bench surgery is a fundamental opportunity to recognize and correct problems before implanting the kidney.

Arterial evaluation

Identify:

• Number of renal arteries.
• Polar arteries.
• Injuries during retrieval.
• Atherosclerotic plaques.
• Intimal dissections.
• Stenoses.
• Arterial segments of insufficient length.
• Abnormalities of the aortic patch, if present.

Accessory arteries require planning according to their perfusion territory and caliber. Loss of a lower polar artery can affect ureteral perfusion, in addition to the renal parenchyma.

Venous evaluation

Assess:

• Length of the renal vein.
• Wall injuries.
• Venous branches.
• Thrombosis.
• Possibility of reconstruction.
• Relationship between the vein and the final position of the graft.

The right renal vein is usually shorter than the left. In right grafts from deceased donors, a venous extension with cava can be used when available. In living donors, extension or reconstruction strategies must be individualized.

Reconstruction of multiple arteries

The options include:

• Independent arterial anastomoses.
• Reconstruction of arteries onto a common trunk.
• Side-to-side anastomosis between selected arteries.
• Use of vascular patches.
• Reconstructions with vascular grafts in complex cases.

The decision depends on the anatomy and on the risk of producing an anastomosis that is too narrow, long, or angulated.

Principles of a safe vascular anastomosis

• Preserve the integrity of the intima.
• Avoid excessive traction.
• Maintain an adequate diameter.
• Avoid twisting.
• Avoid major caliber discrepancies without technical adaptation.
• Check the flow before finishing.
• Verify the final position of the graft.

5. Diagnosis of vascular complications

Clinical presentation

Suspicion should arise in the presence of:

• Sudden oliguria or anuria.
• Unexpected deterioration of renal function.
• Pain or swelling over the graft.
• Hematuria.
• Hypotension.
• Drop in hemoglobin.
• Hard-to-control hypertension.
• Lower limb edema.
• Signs of peripheral ischemia.

None of these findings is specific on its own. In the immediate postoperative period, hypovolemia, catheter obstruction, acute tubular necrosis, rejection, urologic complications, and pharmacologic causes must also be considered.

Graft Doppler ultrasound

Doppler ultrasound is the fundamental initial study when a vascular complication is suspected. It allows assessment of arterial and venous perfusion, as well as the characteristics of the parenchyma and the presence of collections.

Arterial evaluation: proximal and distal iliac artery, arterial anastomosis, main renal artery, accessory arteries if present, intrarenal branches, and distribution of cortical flow.

Venous evaluation: renal vein, venous anastomosis, iliac vein, patency and direction of flow, and signs of parenchymal congestion.

Resistance index

It is calculated as:

RI = (peak systolic V − end-diastolic V) / peak systolic V

The resistance index reflects characteristics of intrarenal flow, but it is not specific for rejection, thrombosis, or stenosis. It can be altered by systemic, hemodynamic, and parenchymal factors.

Interpretation of Doppler patterns

Finding	Possible interpretation
Absence of intrarenal arterial flow	Arterial thrombosis, mechanical interruption, or technical problem
Absence of venous flow	Venous thrombosis or severe obstruction of drainage
Reversed arterial diastolic flow	Extreme vascular resistance; consider venous thrombosis, compression, or other causes
Focally elevated velocity with turbulence	Suspected arterial stenosis
Distal tardus-parvus flow	Suggests significant proximal stenosis
High-velocity turbulent flow in a focal lesion	Possible arteriovenous fistula
Lesion with bidirectional yin-yang flow	Suggests pseudoaneurysm

These patterns require joint interpretation with the clinical picture, the surgical technique, and the rest of the workup.

Complementary studies

• CT angiography: useful for studying vascular anatomy, stenoses, thromboses, pseudoaneurysms, and relationships with neighboring structures.
• MR angiography: an alternative in selected cases.
• Catheter angiography: allows lesions to be defined and, at times, treated during the same procedure.
• Venography: may be used when complex venous obstruction is suspected.

The choice must balance urgency, the patient's condition, graft function, and the possibility of immediate treatment.

6. Graft renal artery thrombosis

Definition and importance

This is thrombotic occlusion of the main artery or one of its branches, with partial or complete interruption of graft perfusion. Thrombosis of the main artery can cause irreversible loss of the kidney in a short period. It is predominantly an early complication, although it can present late in particular situations.

Etiology and risk factors

Technical factors

• Pedicle torsion.
• Arterial kinking.
• Stenotic anastomosis.
• Intimal injury.
• Arterial dissection.
• Suture that compromises the lumen.
• Extrinsic compression.
• Problems in multiple arterial reconstructions.

Graft and recipient factors

• Atherosclerosis.
• Small vessels.
• Coagulation disorders.
• Prothrombotic states.
• Prolonged hypotension.
• Insufficient perfusion.
• Factors associated with the donor and ischemia time.

Not all factors have the same level of evidence, nor do they by themselves imply an indication for anticoagulation.

Clinical presentation

The classic presentation is: initially functioning graft → sudden decrease in urine output → anuria → functional deterioration.

In a graft with delayed function, the absence of urine output can make recognition difficult. In these cases, Doppler and flow assessment become more important.

Diagnosis

Doppler ultrasound may show absence of flow in the main artery or in the parenchyma. It is essential to rule out technical errors in the study and to recognize whether multiple arteries are present. Anatomic confirmation can be obtained with CT angiography or angiography when it does not delay a necessary intervention.

Treatment

Graft arterial thrombosis is an emergency. The chances of salvage depend on the duration of ischemia, the mechanism, and the viability of the parenchyma. The options include:

• Urgent surgical exploration.
• Thrombectomy.
• Revision or reconstruction of the anastomosis.
• Correction of torsion or kinking.
• Endovascular treatment in selected cases.
• Thromboaspiration or catheter-directed thrombolysis, depending on the scenario and bleeding risk.

There is no single strategy applicable to all patients. Thrombolysis immediately after major surgery carries a significant risk of bleeding, so it requires individualized evaluation. If there is irreversible infarction of the graft, a graft nephrectomy may be necessary.

Prevention

• Anastomosis without stenosis.
• Preservation of the intima.
• Adequate pedicle length.
• Correct positioning.
• Avoid hypotension and hypoperfusion.
• Verify flow after reperfusion and with the graft in its final position.

7. Graft renal vein thrombosis

Pathophysiology

Venous thrombosis prevents drainage of the graft, increasing intrarenal venous pressure. This causes congestion, edema, increased vascular resistance, and progressive reduction of arterial perfusion. It can progress rapidly to hemorrhagic infarction.

Predisposing factors

• Pedicle torsion.
• Venous kinking.
• Stenotic venous anastomosis.
• Short renal vein.
• Compression by hematoma or collection.
• Iliac thrombosis.
• Prothrombotic states.
• Flow abnormalities due to graft position.

Clinical presentation

It may manifest as:

• Sudden anuria or oliguria.
• Swelling of the graft.
• Pain over the iliac fossa.
• Hematuria.
• Acute functional deterioration.

At times the picture is difficult to distinguish clinically from arterial thrombosis.

Doppler findings

• No detectable venous flow.
• Increased graft size.
• High-resistance arterial flow.
• Absent or reversed diastolic flow.

Reversal of arterial diastolic flow is an important finding, but it is not exclusive to venous thrombosis. Extrinsic compression, torsion, or pedicle abnormalities must also be sought.

Treatment

Acute venous thrombosis requires urgent evaluation for salvage. The following may be considered:

• Surgical exploration.
• Correction of torsion or compression.
• Venous thrombectomy.
• Revision of the anastomosis.
• Selected endovascular treatment.
• Treatment of an associated iliac thrombosis.

The chance of recovering the graft depends on the degree of congestion and the time elapsed. When there is irreversible hemorrhagic infarction, graft nephrectomy may be required.

Differences from arterial thrombosis

Characteristic	Arterial thrombosis	Venous thrombosis
Mechanism	Interruption of blood supply	Interruption of drainage
Urine output	Sudden decrease or anuria	Sudden decrease or anuria
Arterial Doppler	Absence of flow if complete occlusion	High-resistance flow; possible diastolic reversal
Venous Doppler	May be secondarily altered	Absence of venous flow
Parenchyma	Ischemia/infarction	Congestion and hemorrhagic infarction
Treatment	Urgent revascularization when viable	Urgent restoration of drainage when viable

8. Transplant renal artery stenosis (TRAS)

Graft renal artery stenosis (Transplant Renal Artery Stenosis, TRAS) is one of the most relevant late vascular complications and a potentially reversible cause of hypertension and renal dysfunction. Unlike complete arterial thrombosis, its presentation is usually progressive, although it can cause relatively rapid deterioration.

Pathophysiology

Reduction of arterial caliber lowers distal perfusion pressure. When the stenosis is hemodynamically significant, it can activate the renin-angiotensin-aldosterone system, promoting arterial hypertension and sodium retention. It can also reduce glomerular filtration, especially if renal perfusion depends critically on flow through the lesion. Not every anatomic stenosis has functional repercussions.

Location and mechanisms

• Anastomotic site: related to technical factors, caliber discrepancy, scar fibrosis, or intimal injury.
• Donor renal artery: may be related to preexisting atherosclerotic disease, procurement injuries, or abnormalities of the reconstruction.
• Proximal iliac artery: an injury to the recipient vessel can compromise graft perfusion without a true stenosis of the transplanted renal artery itself.
• Kinked segments: an excessively long artery or an unfavorable graft position can cause functional narrowing.

Clinical manifestations

It should be suspected in the presence of:

• New-onset or hard-to-control hypertension.
• Progressive rise in creatinine without an evident cause.
• Functional deterioration associated with changes in antihypertensive treatment.
• Volume overload or pulmonary edema in severe situations.
• Vascular bruit over the graft, although its absence does not rule out stenosis.

TRAS should be included in the differential diagnosis alongside rejection, calcineurin inhibitor toxicity, urinary obstruction, recurrence of kidney disease, and other causes.

Diagnosis by Doppler ultrasound

Doppler is usually the first study. The parameters of interest include:

• Peak systolic velocity in the renal artery.
• Focal flow acceleration.
• Velocity ratio between the suspicious segment and the reference segment.
• Poststenotic turbulence.
• Distal tardus-parvus pattern.
• Intrarenal acceleration time.

A peak systolic velocity above approximately 200–300 cm/s may raise suspicion, but there is no single universal cutoff. Velocities can be elevated by tortuosity, kinking, insonation angle, high flow, or characteristics of the anastomosis. For this reason it is important not to diagnose TRAS on a single number alone.

Confirmatory studies

CT angiography or MR angiography can provide anatomic information. Catheter angiography allows the lesion to be defined and treatment to be considered in the same procedure. In lesions of uncertain significance, hemodynamic assessment may be useful when available.

Treatment

• Stenosis without significant clinical repercussions: follow-up, blood pressure control, and monitoring of renal function, according to the characteristics of the lesion.
• Stenosis with refractory hypertension or attributable functional deterioration: consider revascularization by percutaneous angioplasty, with or without stenting, according to anatomy, mechanism, and results.
• Complex lesion, endovascular failure, or uncorrectable mechanical problem: evaluate surgical reconstruction at an experienced center.

Percutaneous angioplasty is usually a first-line option for appropriate lesions. A stent may be especially useful in cases of elastic recoil, dissection, recurrent stenosis, or certain anastomotic lesions, but its placement is not mandatory in all cases.

Risks of endovascular treatment

• Arterial dissection.
• Rupture.
• Thrombosis.
• Distal embolization.
• Restenosis.
• Vascular access complications.
• Contrast-associated kidney injury.

9. Vascular hemorrhage in kidney transplantation

Hemorrhagic complications can simultaneously compromise the stability of the recipient and the perfusion of the graft.

Intraoperative hemorrhage

It can originate from:

• Arterial anastomosis.
• Venous anastomosis.
• Unligated vascular branches.
• Injuries to the iliac vessels.
• Dissection surfaces.
• Injuries to the renal parenchyma.

Evaluation during reperfusion. Once the clamps are removed, hemostasis of both anastomoses must be verified. A distinction should be made between bleeding from a suture point and a more significant technical defect. Graft perfusion and distal circulation of the lower limb should also be assessed.

Early postoperative hemorrhage

It may manifest as:

• Hypotension.
• Tachycardia.
• Drop in hemoglobin.
• Increased bloody drain output.
• Distension or pain of the iliac fossa.
• Decreased urine output.
• Perigraft hematoma.

Significant bleeding requires assessment of hemodynamic stability, need for resuscitation, and probable source. Ultrasound can detect hematomas; CT angiography can identify active bleeding in sufficiently stable patients. With persistent instability or suspected major surgical hemorrhage, urgent exploration may be necessary.

Compressive hematoma of the graft

A hematoma can cause dysfunction by compressing the parenchyma or the vascular pedicle. In certain situations, a phenomenon similar to Page kidney can occur, with increased intrarenal pressure, decreased perfusion, and hypertension. Doppler may show flow abnormalities and increased resistance.

The decision to evacuate a hematoma depends on its repercussions, course, and clinical context. Not all hematomas require intervention.

Late hemorrhage

Late hemorrhage should prompt consideration of:

• Pseudoaneurysm.
• Vascular infection.
• Arterial erosion.
• Post-biopsy injuries.
• Arteriovenous fistulas.
• Abnormalities of the anastomosis.

10. Pseudoaneurysms in kidney transplantation

Definition

A pseudoaneurysm is a lesion of the vascular wall in which blood is contained by adjacent tissues, without retaining all the normal layers of the artery. It can be located within the graft or outside it.

Intrarenal pseudoaneurysm

It is frequently related to percutaneous procedures, especially biopsies. It can be asymptomatic and detected incidentally. Other presentations include hematuria, pain, anemia, or functional deterioration.

Extrarenal pseudoaneurysm

It can appear in relation to the arterial anastomosis or injuries to recipient vessels. The possibility of infection must be especially considered. An infected anastomotic pseudoaneurysm represents a high-risk situation because of the possibility of rupture.

Diagnosis

Doppler may show turbulent flow within the lesion and the characteristic bidirectional flow pattern. CT angiography or angiography allows definition of:

• Size.
• Location.
• Neck of the pseudoaneurysm.
• Relationship to the anastomosis.
• Arteries involved.
• Possibility of treatment.

Treatment

It depends on location, size, growth, symptoms, risk of rupture, and presence of infection. The options may include:

• Observation in small, stable, selected lesions.
• Endovascular embolization of intrarenal lesions.
• Covered stent in appropriate anatomies.
• Surgical vascular reconstruction.
• Graft nephrectomy in cases of vascular destruction, uncontrollable infection, or nonviable graft.

11. Arteriovenous fistulas of the graft

Definition

These are abnormal communications between an artery and a vein, generally acquired. In the renal graft, a frequent cause is percutaneous biopsy.

Presentation

Many small fistulas are asymptomatic and may close spontaneously. Others can cause:

• Hematuria.
• Hemodynamic changes.
• Bleeding.
• Functional deterioration.
• Hypertension or circulatory overload in high-flow lesions, which are uncommon.

Diagnosis

Doppler may show:

• High-velocity turbulent flow.
• Focal alteration of the vascular pattern.
• Arterialization of venous flow.
• Decreased resistance in the feeding artery.

Treatment

Small, asymptomatic, stable lesions can be observed. Symptomatic, persistent, high-flow lesions, or those associated with significant hemorrhage, may require selective embolization. The goal is to exclude the abnormal communication while preserving as much functioning parenchyma as possible.

12. Torsion and kinking of the vascular pedicle

This complication deserves special attention because it can cause severe vascular obstruction without a primary thrombosis.

Mechanism

Rotation of the graft on its pedicle can compress or twist the renal artery and vein. It can occur in intraperitoneal grafts or in those with excessive mobility. Kinking can also result from excessive vessel length or an unfavorable position of the kidney.

Manifestations

• Sudden decrease in urine output.
• Functional deterioration.
• Abdominal pain or pain over the graft.
• Perfusion abnormalities on Doppler.

Diagnosis and treatment

Doppler may show arterial and venous abnormalities that mimic thrombosis. Suspicion should increase when there is a relationship with changes in position or a predisposing anatomy.

Torsion with acute vascular compromise requires immediate surgical assessment. Treatment consists of correcting the position of the graft, evaluating viability, and preventing a new torsion by fixation when appropriate.

This complication is seen particularly in intraperitoneal transplants, including certain simultaneous kidney-pancreas transplants.

13. Vascular complications in the recipient

The evaluation should not be limited to the graft vessels. The procedure can also affect the recipient's iliac vascular axis.

Iliac artery dissection or thrombosis

It can result from intimal injury, clamping, severe atherosclerosis, or anastomotic problems. It should be suspected in the presence of:

• Decreased or absent distal pulses.
• Coldness of the lower limb.
• Pain.
• Sensory or motor changes.
• Decreased arterial flow on Doppler.

Acute lower limb ischemia is a vascular emergency.

Iliac vein thrombosis

It can compromise drainage of the graft and the lower limb. Presentation may include unilateral edema, pain, venous flow abnormalities, and graft deterioration. Treatment depends on the extent, mechanism, time course, and bleeding risk.

Importance of previous femoral catheters

Patients with multiple femoral vascular accesses may have venous stenoses or occlusions. This history should be factored into planning the implant site.

Algorithm A. Sudden anuria in the immediate postoperative period

Sudden anuria or oliguria after transplant → immediate, simultaneous evaluation: hemodynamics · Foley catheter patency · labs · urgent Doppler · notify the transplant team.

• Suspected vascular compromise (absent flow, venous obstruction, torsion, or severely impaired perfusion) → activate immediate surgical or endovascular rescue according to mechanism and viability.
• Preserved vascular perfusion → investigate hypovolemia, urinary obstruction, tubular dysfunction, rejection, and other causes, and proceed with targeted treatment.

An apparently normal Doppler does not exclude all complications. If clinical suspicion remains high, the evaluation should be broadened.

Algorithm B. Hypertension and late functional deterioration

Resistant hypertension and/or rising creatinine → evaluate common causes and perform a graft Doppler. Is significant arterial stenosis suspected?

• No / uncertain finding → investigate alternative causes and consider follow-up or additional studies depending on suspicion.
• Yes → define the anatomy and hemodynamic significance. Consider angiography and revascularization if clinically indicated.

Algorithm C. Bleeding after transplant

Suspected bleeding → assess hemodynamic stability and resuscitate.

• Persistent instability → urgent control of the bleeding; consider surgical exploration or immediate intervention depending on the scenario.
• Stability → ultrasound and/or CT angiography to locate the hematoma, active bleeding, or vascular injury; targeted treatment.