Mesenteric Ischemia

Etiology of Renal Artery Stenosis

Etiology

The predominant etiology is atherosclerotic renal artery stenosis (ARAS) (often proximal/ostial, frequently bilateral) in older patients with diffuse atherosclerosis (similar risk profile to 4Aneurysms and 10PAD). (Safian 2001) Fibromuscular dysplasia (FMD) is the next most common cause and typically affects the mid-to-distal renal artery with a “string of beads” appearance. (Gornik 2019)

Evaluation

• Establish clinical context: resistant hypertension, unexplained decline in renal function (especially after ACE inhibitor/ARB initiation), recurrent flash pulmonary edema, asymmetric kidney size, or widespread atherosclerosis. (Safian 2001)
• computed tomography angiography (CTA) or magnetic resonance angiography (MRA) defines anatomy and guides planning; consider contrast-sparing strategies in 11CKD. (Prince 2016)
• DUS can be used for screening and follow-up in experienced vascular labs (velocity criteria vary by lab and should be internally validated).

Medical therapy (first-line for most ARAS)

Most patients with ARAS should be treated with:

• Antihypertensive therapy (often including ACE inhibitor/ARB with careful creatinine/potassium monitoring, especially in bilateral disease/solitary kidney).
• High-intensity statin therapy and antiplatelet therapy consistent with systemic atherosclerotic disease prevention. (Aboyans 2017)📄

Revascularization (patient selection)

Routine stenting for ARAS does not improve composite cardiovascular/renal outcomes compared with optimal medical therapy in unselected patients in randomized trials. (Cooper 2014)📄 (Wheatley 2009)📄

Revascularization is generally reserved for high-risk phenotypes, including:

• Recurrent flash pulmonary edema or otherwise unexplained recurrent heart failure decompensation.
• Rapidly progressive renal dysfunction in the setting of bilateral severe stenosis or stenosis to a solitary functioning kidney.
• Truly refractory hypertension despite optimized multi-drug therapy. (Cooper 2014)📄 (Wheatley 2009)📄

FMD workup and management

Evaluation includes CTA/MRA demonstrating the classic “string of beads,” and one-time brain-to-pelvis screening to identify other FMD lesions and aneurysms. (Gornik 2019) For symptomatic renal FMD with resistant hypertension or complications (dissection/aneurysm), balloon angioplasty is preferred; stenting is reserved for angioplasty failure or flow-limiting dissection. (Gornik 2019)

Post-revascularization surveillance (renal interventions)

After renal angioplasty/stenting (ARAS or FMD), follow-up should include:

• Blood pressure control and medication requirements
• Renal function (creatinine/eGFR) and electrolytes
• DUS/CTA surveillance in selected patients to evaluate restenosis and to investigate recurrent hypertension or renal decline

A practical schedule is baseline imaging at ~1 month, then 6–12 months, then annually if stable, individualized to symptoms and renal function trajectory. (Gornik 2019) (Rutherford 2018)

Background

Scope and clinical importance

Mesenteric ischemia includes a spectrum of disorders caused by inadequate intestinal perfusion, classically categorized as:

• Acute mesenteric ischemia (AMI) (arterial embolism, arterial thrombosis, non-occlusive mesenteric ischemia (NOMI), and mesenteric venous thrombosis (MVT)). (Clair 2016) (Wahlgren 2025)
• Chronic mesenteric ischemia (CMI) due to progressive atherosclerotic stenosis/occlusion, typically involving the SMA ± celiac artery (CA) ± inferior mesenteric artery (IMA). (Bj 2017)📄 (Wahlgren 2025)

AMI remains a time-critical vascular emergency with substantial morbidity and mortality, and outcomes are driven by speed of diagnosis, restoration of perfusion, and bowel viability assessment. (Clair 2016) (Bj 2018)📄 AMI should be approached with the same urgency as 10PAD (systemic anticoagulation, rapid imaging, and revascularization when appropriate). (Bala 2017)📄

Diagnostic principle

In patients with suspected AMI, contrast-enhanced computed tomography angiography (CTA) is first-line and should not be delayed for laboratory confirmation; serum lactate may be normal early and typically rises late with transmural infarction. (Menke 2010)📄 (Brandt 2015)📄 (Wahlgren 2025)

Therapeutic principle

Management integrates:

1. Physiologic optimization (resuscitation, correction of shock/low flow, avoidance of excessive vasoconstriction). (Bala 2017)📄 (Bj 2018)📄
2. Systemic anticoagulation for most occlusive etiologies (unless contraindicated). (Wahlgren 2025) (Clair 2016)
3. Revascularization via endovascular, open, or hybrid approaches based on etiology, anatomy, and bowel status. (Wahlgren 2025) (Clair 2016)

For anticoagulation and longer-term management of MVT, see 12VTE. (Ortel 2020)📄

Evidence from randomized trials (CORAL, ASTRAL) and patient selection for renal artery stenting

The CORAL and ASTRAL randomized controlled trials demonstrated no improvement in composite cardiovascular or renal outcomes, or in blood pressure control, with routine renal artery stenting compared with optimal medical therapy alone in patients with atherosclerotic renal artery stenosis. Based on these findings, current practice reserves revascularization for high-risk phenotypes including recurrent flash pulmonary edema, rapidly progressive and otherwise unexplained decline in renal function in patients with bilateral severe stenosis or stenosis in a solitary kidney, and truly refractory hypertension despite optimal medical therapy. Medical management remains the cornerstone of treatment for most patients with atherosclerotic renal artery stenosis. (Cooper 2014)📄 (Wheatley 2009)📄

Fibromuscular dysplasia (FMD) comprehensive evaluation and longitudinal management

Fibromuscular dysplasia (FMD) requires comprehensive evaluation and long-term surveillance. Initial imaging with computed tomography angiography (CTA) or magnetic resonance angiography (MRA) of the affected vascular bed should be accompanied by a one-time brain-to-pelvis screening to identify other FMD lesions and associated aneurysms. Given the elevated risk of intracranial aneurysm in FMD patients, targeted screening of cerebral vessels is recommended.

Medical therapy forms the cornerstone of management for most patients. Aspirin at 75–100 mg daily is recommended unless contraindicated, combined with aggressive cardiovascular risk factor modification and smoking cessation. For patients with renal artery FMD complicated by resistant hypertension, medication intolerance, or dissection/aneurysm, revascularization with percutaneous transluminal balloon angioplasty is preferred over stenting except when dissection or angioplasty failure necessitates stent placement.

Women with FMD require specific counseling regarding pregnancy-related risks and should establish appropriate follow-up protocols. Following any revascularization procedure, duplex ultrasonography surveillance monitors treatment durability and disease progression (Gornik 2019).

Imaging and Contrast Strategies in CKD for Renal and Mesenteric Interventions

In patients with chronic kidney disease requiring renal or mesenteric vascular imaging, computed tomography angiography (CTA) should be used judiciously with pre-procedure hydration protocols to minimize contrast-induced nephropathy. Magnetic resonance angiography (MRA) may be considered if the risk-benefit ratio of gadolinium-based contrast is acceptable in the individual patient. During catheter-based angiography and intervention, iodinated contrast volume should be minimized, and carbon dioxide angiography may be employed when appropriate to reduce nephrotoxic contrast exposure. Serum creatinine should be monitored before and after procedures, and nephrotoxic medications should be held in the peri-procedural period when possible. (Prince 2016)

Etiology and Risk Factors

• Arterial embolism: heart (AF, mural thrombus), cardiac surgery, valve disease.
• Arterial thrombosis: on existing atherosclerotic stenosis.
• Non-occlusive mesenteric ischemia (NOMI): low flow states (shock, sepsis, vasoconstrictors).
• Mesenteric venous thrombosis (MVT): hypercoagulable states, intra-abdominal inflammation, pancreatitis, cirrhosis. Management follows 12VTE principles with anticoagulation.
• Risk factors: advanced age, cardiovascular disease, atrial fibrillation, hypotension, vasopressor therapy, renal dysfunction, diabetes, smoking.

Pathophysiology

• In AMI, sudden loss of arterial perfusion → intestinal ischemia, mucosal injury → transmural infarction if untreated. Bacterial translocation, sepsis.
• In NOMI, prolonged low perfusion → patchy ischemia without large vessel occlusion; severe morbidity.
• In CMI, chronic underperfusion leads to adaptation via collaterals, but when demand (after eating) increases, symptoms manifest. Progressive mucosal injury, malabsorption.
• In MVT, impaired venous outflow leads to congestion, edema, possibly infarction.

Clinical Presentation

• Acute: severe abdominal pain, often sudden; may have vomiting, diarrhea; pain out of proportion to physical examination initially. Signs of peritonitis later.
• Chronic: postprandial pain (“food fear”), weight loss, sometimes diarrhea, malnutrition. May have abdominal bruit, fear of eating.

Diagnostics

Diagnostic priorities (suspected AMI)

Do not delay imaging in patients with severe abdominal pain out of proportion, unexplained metabolic acidosis, new atrial fibrillation, recent cardiac surgery, or shock/vasopressor exposure. (Clair 2016) (Bala 2017)📄 (Wahlgren 2025)

First-line test

• computed tomography angiography (CTA) (arterial + portal venous phase) from diaphragm to pubis is the diagnostic test of choice, identifying arterial occlusion, venous thrombosis, bowel wall enhancement abnormalities, pneumatosis, and portal venous gas. (Wahlgren 2025)
• CTA diagnostic accuracy is high in meta-analysis (pooled sensitivity ~93%, specificity ~96%). (Menke 2010)📄

Laboratory tests (supportive, not exclusionary)

• Lactate, ABG/VBG, CBC, CMP, coagulation profile.
• Normal lactate does not exclude early AMI; rising lactate suggests advanced ischemia/infarction. (Brandt 2015)📄

Catheter angiography (DSA)

• Reserved for cases where CTA is equivocal and suspicion remains high, or when proceeding directly to endovascular therapy (thrombectomy/thrombolysis/stenting) or intra-arterial vasodilator infusion for NOMI. (Clair 2016) (Wahlgren 2025)
• See 3Chapter 3 for angiography fundamentals.

Diagnostic approach (suspected CMI)

CMI is a clinical-radiographic diagnosis: typical symptoms (postprandial pain, weight loss/food fear) plus hemodynamically significant mesenteric stenosis on cross-sectional imaging. (Clair 2016) (Bj 2017)📄 (Wahlgren 2025)

• CTA is the most commonly used first-line test for anatomic confirmation and treatment planning. (Wahlgren 2025)
• Duplex ultrasound (DUS) can be used for screening and follow-up in experienced labs but is limited by bowel gas and body habitus. (Moneta 1991)

Table 11.X. Imaging options in mesenteric ischemia

Treatment: Acute Mesenteric Ischemia

Immediate actions (first hour)

1. Resuscitate and optimize perfusion

• Aggressive volume resuscitation and correction of shock/low-flow states.
• Minimize vasoconstrictors when feasible; treat arrhythmias and low cardiac output. (Bala 2017)📄 (Bj 2018)📄

1. Anticoagulate early (when not contraindicated)

• Initiate systemic unfractionated heparin in most occlusive AMI (arterial embolus/thrombosis) and in MVT. (Clair 2016) (Wahlgren 2025)

1. Broad-spectrum antibiotics

• Treat/prevent bacterial translocation and sepsis in suspected bowel ischemia. (Bala 2017)📄 (Brandt 2015)📄

1. Urgent computed tomography angiography (CTA)

• Obtain contrast-enhanced CTA without delay to define etiology and bowel findings. (Menke 2010)📄 (Wahlgren 2025)

When to operate immediately

• Peritonitis, perforation, or frank necrosis on imaging → proceed to urgent laparotomy with resection of nonviable bowel and revascularization when appropriate. (Bala 2017)📄 (Wahlgren 2025)

Etiology-directed reperfusion strategies

• SMA embolism

• Options include open embolectomy or endovascular aspiration thrombectomy/thrombolysis in selected stable patients without peritonitis. (Clair 2016)

• SMA thrombosis on chronic atherosclerosis

• Often ostial/proximal disease; treat with endovascular stenting (antegrade) or hybrid approaches such as ROMS when antegrade access is challenging. (Clair 2016) (Wahlgren 2025)

• NOMI

• Treat the underlying shock/vasoconstriction; consider selective intra-arterial vasodilators in appropriate patients without peritonitis. (Bj 2018)📄 (Wahlgren 2025)

• MVT

• Immediate anticoagulation is first-line; invasive therapy is reserved for deterioration or peritonitis. See 12VTE. (Ortel 2020)📄 (Wahlgren 2025)

Bowel viability and staged management

• At laparotomy, resect only clearly necrotic bowel; preserve questionable segments and plan a second-look laparotomy in 24–48 hours when viability is uncertain or extensive ischemia was present. (Brandt 2015)📄 (Endean 2001)📄 (Wahlgren 2025)

Treatment: Chronic Mesenteric Ischemia

Functional tests such as gastric tonometry and mucosal perfusion assessment may serve as adjuncts in select centers, though current guidelines emphasize cross-sectional imaging as the primary diagnostic modality.

Treatment: Mesenteric Venous Thrombosis

Diagnosis

• computed tomography angiography (CTA) with venous phase or MR venography demonstrates portal/mesenteric venous filling defects and bowel congestion/edema. (Wahlgren 2025)

Initial management

• Immediate therapeutic anticoagulation is the cornerstone of treatment, aligned with 12VTE principles. (Ortel 2020)📄 (Wahlgren 2025)
• Evaluate provoking factors (intra-abdominal inflammation, malignancy, thrombophilia) and tailor duration of anticoagulation accordingly. (Wahlgren 2025)

Escalation of care

• Consider catheter-directed thrombolysis/thrombectomy only in selected patients with clinical deterioration or extensive thrombosis despite anticoagulation and without contraindications. (Wahlgren 2025)

Acute Mesenteric Ischemia

Mesenteric venous thrombosis: Immediate anticoagulation is the cornerstone of therapy, following 12VTE management principles. In severe cases with clinical deterioration despite anticoagulation, catheter-directed thrombolysis or thrombectomy may be indicated. Surgical resection is reserved for patients with frankly infarcted bowel. (Wahlgren 2025)

Chronic Mesenteric Ischemia

Indication for treatment

• Revascularization is recommended for symptomatic CMI (postprandial pain with weight loss/food fear and confirmatory imaging), because untreated symptomatic disease risks progressive malnutrition and acute-on-chronic ischemic events. (Clair 2016) (Bj 2017)📄 (Wahlgren 2025)

Baseline therapy for all patients

• Aggressive atherosclerotic risk reduction (smoking cessation, blood pressure control, diabetes management).
• Antiplatelet therapy and high-intensity statin therapy are generally indicated in atherosclerotic CMI, consistent with systemic peripheral arterial disease (PAD) practice. (Aboyans 2017)📄
• Nutritional optimization (including short-term enteral/parenteral support in selected severely malnourished patients) should be considered before major open reconstruction when feasible. (Wahlgren 2025)

Revascularization options (endo-first vs open durability)

• Endovascular revascularization (angioplasty ± stent)

• Preferred first line in many patients due to lower perioperative morbidity and mortality in an older comorbid population. (Wahlgren 2025) (Freitas 2019)
  • Limitations: higher restenosis and reintervention rates; requires structured surveillance and readiness for reintervention. (Oderich 2013)📄 (Freitas 2019)

• Open surgical bypass

• Consider for younger/fit patients needing durable repair, long occlusions/unfavorable endovascular anatomy, or failed endovascular therapy. (Wahlgren 2025)
  • Provides superior long-term primary patency compared with endovascular approaches, at the expense of higher perioperative risk. (Huber 2010) (Freitas 2019)

Target vessel strategy

• The SMA is the primary target for symptom relief in most symptomatic patients; CA revascularization may be added based on anatomy, collateralization, and recurrence risk. (Clair 2016) (Wahlgren 2025)

Median Arcuate Ligament Syndrome

MALS is a diagnosis of exclusion after atherosclerotic CMI and other causes are ruled out. In carefully selected symptomatic patients with supportive imaging and hemodynamic findings, laparoscopic or open median arcuate ligament release can relieve extrinsic compression; adjunctive celiac artery stenting is considered only for residual fixed stenosis after adequate decompression (Jimenez 2012)📄.

Hybrid and Endovascular Techniques

• Stenting: balloon-expandable stents are preferred for ostial/short proximal CA or SMA lesions to optimize radial strength and precise placement; self-expanding stents may be used in more distal or tortuous segments.
• Hybrid operations: examples include retrograde open mesenteric stenting (ROMS) for ostial SMA thrombosis in AMI and celiac artery stenting after MAL release in MALS.
• Thrombolysis: consider for selected embolic AMI without peritonitis and for severe mesenteric venous thrombosis with clinical deterioration despite anticoagulation. (Oderich 2013)📄 (Clair 2016) (Brandt 2015)📄

Follow-up

Ongoing monitoring for restenosis and symptom recurrence is essential after mesenteric revascularization, particularly following endovascular stenting where restenosis and reintervention are more common. (Oderich 2013)📄 (Freitas 2019)

Table 11.4. Surveillance after mesenteric revascularization

Duplex ultrasound thresholds (screening for significant restenosis)

• Validated criteria for native vessels suggest:
  • SMA PSV >275 cm/s
  • CA PSV >200 cm/s (Moneta 1991)

Interpretation after stenting should be lab- and protocol-specific; rising velocities plus recurrent symptoms should prompt CTA and consideration of reintervention. (Wahlgren 2025) (Oderich 2013)📄

Post-revascularization medical therapy

• Continue aggressive atherosclerotic risk reduction.
• Use antiplatelet and statin therapy consistent with systemic peripheral arterial disease (PAD) prevention strategies (individualize dual antiplatelet therapy after stenting per institutional practice and bleeding risk). (Aboyans 2017)📄 (Wahlgren 2025)

ESVS 2025 Guidelines

For mesenteric venous thrombosis (MVT), immediate anticoagulation is indicated, with low-molecular-weight heparin (LMWH) recommended as first-line therapy in the acute phase per the European Society for Vascular Surgery (ESVS) guidelines [@esvs2025; @esvs2025-editors]. Following the acute phase, direct oral anticoagulants (DOACs) may be considered as an alternative to vitamin K antagonists (VKAs) for long-term treatment in patients without malignancy or cirrhosis (Wahlgren 2025). Invasive therapy, including catheter-directed thrombolysis (CDT) or mechanical thrombectomy, should be considered in patients with clinical deterioration or signs of bowel ischemia despite anticoagulation (Wahlgren 2025). Evaluation for underlying provoking factors, including thrombophilia, malignancy, and specifically myeloproliferative neoplasms (MPN) via Janus kinase 2 (JAK2) mutation screening, is recommended (Wahlgren 2025). Anticoagulation is generally continued for at least 6 months, with extended or indefinite therapy considered for unprovoked MVT or persistent risk factors after individualized bleeding-risk assessment [@esvs2025; @esvs2025-editors].

Tables

Table 11.1. Acute Mesenteric Ischemia Classification and Management

Table 11.2. CMI Revascularization Strategy Selection

Table 11.3. Renal Artery Stenosis: Indications for Revascularization

SMA Embolism vs SMA Thrombosis in AMI: Clinical and Imaging Distinctions

Distinguishing SMA embolism from SMA thrombosis is critical for tailoring management in AMI.

SMA Embolism typically presents with sudden-onset severe abdominal pain in patients without prior intestinal angina. Computed tomography angiography (CTA) characteristically demonstrates an embolus lodged distal to the SMA origin, often sparing the proximal jejunal branches. Preferred revascularization strategies include open surgical embolectomy or, in hemodynamically stable patients, catheter-based aspiration thrombectomy or thrombolysis. (Clair 2016) (Endean 2001)📄

SMA Thrombosis usually occurs in patients with a history of postprandial pain and weight loss (suggesting preexisting CMI). CTA reveals an ostial or proximal SMA stenosis with acute occlusion. Preferred treatments include antegrade endovascular stenting when percutaneous access is feasible, or hybrid retrograde open mesenteric stenting (ROMS) when antegrade access is challenging. Open bypass grafting is reserved for cases where endovascular therapy fails or anatomy is unfavorable. (Clair 2016)

Regardless of the initial revascularization strategy, a liberal approach to second-look laparotomy at 24-48 hours is recommended to reassess bowel viability and extent of resection. (Brandt 2015)📄

CTA acquisition protocol and diagnostic performance for AMI

Optimal CT angiography for suspected AMI requires a multiphasic acquisition protocol including both arterial and portal venous phases with thin-collimation reconstruction, with imaging coverage extending from the diaphragm to the pubis. This protocol enables visualization of vascular occlusions, bowel wall enhancement patterns, pneumatosis, and portal venous gas.

Diagnostic performance of computed tomography angiography (CTA) for AMI is excellent, with pooled sensitivity of approximately 93% and specificity of 96% in meta-analyses (Menke 2010)📄. Importantly, normal serum lactate levels do not exclude early AMI, as lactate elevation is a late finding typically indicating transmural bowel infarction (Brandt 2015)📄. Therefore, clinical suspicion should guide imaging even when initial laboratory studies are unremarkable.

NOMI-specific management (hemodynamics and intra-arterial vasodilators)

Management of non-occlusive mesenteric ischemia (NOMI) differs fundamentally from occlusive forms of AMI, focusing on hemodynamic optimization rather than mechanical revascularization. Treatment priorities include:

1. Hemodynamic correction: Promptly reverse systemic low-flow states through volume resuscitation and optimization of cardiac output.
2. Vasopressor minimization: Discontinue or minimize vasoconstrictive agents when clinically feasible.
3. Selective vasodilator therapy: In patients without peritonitis, consider selective intra-arterial vasodilator infusion (e.g., papaverine) via catheter directed into the SMA to reverse mesenteric vasoconstriction.
4. Conservative surgical approach: If laparotomy is required, resect only frankly necrotic bowel segments, leaving marginally viable bowel in situ. A planned second-look laparotomy at 24-48 hours allows reassessment after hemodynamic stabilization and vasodilator therapy. (Brandt 2015)📄 (Clair 2016)

CMI target vessel strategy and outcomes (endo vs open)

Target vessel selection and revascularization strategy are critical decisions in CMI management. The superior mesenteric artery (SMA) is the principal target for symptom relief, as it supplies the midgut and has the most consistent correlation with clinical symptoms. In most symptomatic patients, revascularization of the SMA alone provides adequate symptom resolution, though some advocate for multi-vessel revascularization to improve long-term durability (Clair 2016).

Endovascular revascularization (angioplasty with stenting) offers lower perioperative morbidity and mortality compared to open surgery, with technical success rates exceeding 95% and perioperative mortality typically less than 5% (Oderich 2013)📄. However, restenosis and reintervention rates are higher, ranging from 20-40% at 3-5 years, necessitating ongoing surveillance.

Open surgical bypass (typically using supraceliac aorta as inflow with antegrade bypass to the SMA and/or celiac artery) carries higher perioperative risk, with mortality rates of 5-15%, but demonstrates superior long-term patency, with primary patency rates of 70-90% at 5 years (Huber 2010). Systematic reviews confirm these trade-offs: endovascular therapy provides safer initial treatment with acceptable intermediate-term outcomes, while open surgery offers more durable long-term results in appropriately selected patients (Freitas 2019).

Bowel viability assessment and second-look policy in AMI

Assessment of bowel viability after revascularization remains challenging despite successful restoration of arterial flow. The guiding principle is to resect only frankly necrotic bowel at the initial operation, preserving all segments of questionable viability.

Intraoperative adjuncts to assess perfusion include Doppler examination of antimesenteric bowel wall vessels, assessment of serosal color and peristalsis, and in some centers, fluorescence angiography with intravenous indocyanine green. Despite these tools, determination of ultimate viability is often impossible at the initial laparotomy (Endean 2001)📄.

Therefore, a planned second-look laparotomy at 24-48 hours is recommended in all cases where bowel viability remains equivocal after initial revascularization and resection. This approach allows marginally ischemic bowel to declare itself as either viable or necrotic after a period of restoration of perfusion, minimizing the extent of bowel resection while ensuring adequate débridement of nonviable tissue (Brandt 2015)📄.

Duplex ultrasound thresholds and role in surveillance after mesenteric stenting

Duplex ultrasound serves as a noninvasive surveillance tool after mesenteric revascularization, though its role is limited by technical challenges including bowel gas interference and operator dependency. Validated velocity criteria for hemodynamically significant (≥70%) stenosis have been established for both the celiac artery (peak systolic velocity >200 cm/s) and the superior mesenteric artery (peak systolic velocity >275 cm/s) (Moneta 1991).

In centers with expertise in mesenteric duplex examination, this modality is useful for surveillance after both open bypass and endovascular stenting, allowing detection of restenosis before symptom recurrence (Oderich 2013)📄. However, given the technical limitations, many centers rely primarily on CT angiography for postintervention surveillance, reserving duplex for interval monitoring between computed tomography angiography (CTA) studies or when contrast administration is contraindicated.