Catheter-directed foam sclerotherapy with tumescence of the great saphenous vein versus ultrasound-guided foam sclerotherapy: A randomized controlled trial

Guidelines for management of actual or suspected inadvertent intra-arterial injection of sclerosants

BACKGROUND

Inadvertent intra-arterial injection of sclerosants is an uncommon adverse event of both ultrasound-guided and direct vision sclerotherapy. This complication can result in significant tissue or limb loss and significant long-term morbidity.

OBJECTIVES

To provide recommendations for diagnosis and immediate management of an unintentional intra-arterial injection of sclerosing agents.

METHODS

An international and multidisciplinary expert panel representing the endorsing societies and relevant specialities reviewed the published biomedical, scientific and legal literature and developed the consensus-based recommendations.

RESULTS

Actual and suspected cases of an intra-arterial sclerosant injection should be immediately transferred to a facility with a vascular/interventional unit. Digital Subtraction Angiography (DSA) is the key investigation to confirm the diagnosis and help select the appropriate intra-arterial therapy for tissue ischaemia. Emergency endovascular intervention will be required to manage the risk of major limb ischaemia. This includes intra-arterial administration of vasodilators to reduce vasospasm, and anticoagulants and thrombolytic agents to mitigate thrombosis. Mechanical thrombectomy, other endovascular interventions and even open surgery may be required. Lumbar sympathetic block may be considered but has a high risk of bleeding. Systemic anti-inflammatory agents, anticoagulants, and platelet inhibitors and modifiers would complement the intra-arterial endovascular procedures. For risk of minor ischaemia, systemic oral anti-inflammatory agents, anticoagulants, vasodilators and antiplatelet treatments are recommended.

CONCLUSION

Inadvertent intra-arterial injection is an adverse event of both ultrasound-guided and direct vision sclerotherapy. Medical practitioners performing sclerotherapy must ensure completion of a course of formal training (specialty or subspecialty training, or equivalent recognition) in the management of venous and lymphatic disorders (phlebology), and be personally proficient in the use of duplex ultrasound in vascular (both arterial and venous) applications, to diagnose and provide image guidance to venous procedure. Expertise in diagnosis and immediate management of an intra-arterial injection is essential for all practitioners performing sclerotherapy.

Treatment of varicose great saphenous vein with endovenous laser alone or combined with eco-guided foam sclerotherapy: A randomized controlled trial

Objectives: This study compares Endovenous Laser Ablation (EVLA) alone versus combined with ultrasound-guided foam sclerotherapy (UGFS) for Great Saphenous Vein (GSV) insufficiency. Methods: Sixty patients were randomly allocated to EVLA or EVLA-UGFS groups which focused on GSV occlusion rates, complications, additional treatments, and quality of life (QoL) changes. Results: Among 55 participants, the EVLA group had higher 12-month occlusion rates (92.3% vs. 75.8%, p = 0.11). Nervous injury (NI) was rarer in EVLA-UGFS (3.4% vs. 23.1%, p = 0.04). No significant difference in other complication rates (p > 0.05). QoL improved in both groups (p < 0.001). EVLA-UGFS required more subsequent procedures (24.1% vs. 7.7%, p = 0.03). Conclusions: EVLA and EVLA-UGFS effectively treat GSV insufficiency, enhancing QoL. The combined method reduces NI risk but may require more follow-up procedures.

Is catheter-based foam sclerotherapy more effective than direct foam sclerotherapy when combined with high ligation for the treatment of primary great saphenous vein incompetence?

BACKGROUND

To retrospectively analyze the short-term outcomes of catheter-based versus direct foam sclerotherapy when combined with high ligation (HL) for the treatment of great saphenous vein (GSV) incompetence.

METHODS

From July 2018 to October 2019, a total of 82 lower limbs of 70 patients with GSV incompetence received HL combined with catheter-based foam sclerotherapy (CFS group) or direct foam sclerotherapy (DFS group) for GSV proximal trunk. Among them, 40 limbs of 36 patients were treated with CFS, and 42 limbs of 34 patients were treated with DFS. The occlusion of GSV proximal trunk was evaluated with venous duplex ultrasound examinations; Venous Clinical Severity Scores (VCSS) was used to assess clinical improvement; Aberdeen Varicose Veins Questionnaire (AVVQ) was used to assess quality-of-life scores; and Complications was used for the safety evaluation.

RESULTS

At day 7 post-operatively, complete occlusion of proximal trunk of the GSV was achieved in 92.5% legs of the CFS group and 71.4% of the DFS group (p = 0.014). Additionally, anterograde flow was found in 7.5% legs of the CFS group and 26.2% of the DFS group (p = 0.025). No significant differences in the occurrence of complications were observed between the two groups. The median follow-up was 285.5 days in the DFS group and 318 days in the CFS group (p = 0.140). VCSS and AVVQ reduction were significant in both CFS group and DFS group (5.3 ± 2.5, 5.5 ± 2.4, p < 0.001 for VCSS; 15.9 ± 8.0, 16.3 ± 8.6, p < 0.001 for AVVQ), but no significant difference were observed between two groups (p = 0.655 for VCSS, p = 0.934 for AVVQ).

CONCLUSIONS

Although the occlusion of great saphenous vein proximal trunk were different, two modalities result in similar clinical and quality-of-life improvements. DFS is a feasible alternative to CFS when combined with HL.

Sheath-Based Combined Foam Sclerotherapy to Promote Management of Extensive Insufficiency of the Great Saphenous Vein in Venous Ulcers

Background: Foam sclerotherapy is considered an acceptable method to treat great saphenous vein (GSV) insufficiency, promoting occlusion of its trunk and eradicating reflux. Various modalities and techniques have been described, varying form foam infusion through multiple short cannulae along the GSV to catheter-directed techniques in order to facilitate complete proximal GSV occlusion and improve technical and clinical success. Purpose: To present a modification of the sclerotherapy tehcnique where the presence of venous ulcers poses an extra challenge to the treatment of GSV treatment. Technique: We describe a technical proposal of single foam perfusion through a 11 cm 5F sheath placed at the knee level combined with simultaneous retrograde infusion below the knee. Perivenous tumescent segmental infiltration with cold normal saline at 4°C is applied initially to reduce the diameter in those GSV >6-7 mm. Conclusions: This combination avoids multiple vein cannulation in the GSV along the thigh as well as the need for antegrade infusion when GSV cannulation at the lower tibia is prohibited by a large ulcer area.

Customizing foam sclerotherapy of the great saphenous vein: A proposed algorithm to enhance technical efficacy

OBJECTIVES

The catheter-directed foam sclerotherapy (FS) and the suggested perivenous tumescent application for great saphenous vein (GSV) diameter reduction are suggested to improve technical and clinical results; yet, their use is reported rather indiscriminately. Our aim is to introduce an algorithm categorising the use of technical modalities accompanying ultrasound-guided FS of the GSV and present the technical efficacy of FS through a 5 F × 11  cm sheath placed at the knee level.

METHODS

Representative cases of GSV insufficiency were chosen to describe our methodology.

RESULTS

Sole sheath-directed FS can achieve complete GSV occlusion proximally at a level comparable to the catheter-directed technique. We apply perivenous 4°C cold tumescent to GSV >6 mm even in the standing position to ensure diameter reduction of the proximal GSV as close to the saphenofemoral junction. We use long catheters only to overcome large varicosities above the knee level that could otherwise compromise the adequate foam infusion from the sheath tip. When GSV insufficiency extends along the entire limb and severe skin lesions preclude the antegrade distal catheterisation, the sheath-directed FS in the thigh can be concomitantly combined with retrograde FS from catheterisation just below the knee.

CONCLUSIONS

A topology-oriented methodology with sheath-directed FS is technically feasible and avoids indiscriminate use of more complex modalities.

Treatment of Recurrent Symptomatic Saphenous Trunk Reflux with Catheter Directed Foam Sclerotherapy and Tumescent Anaesthesia

Objective

The aim was to assess short and midterm efficacy and safety of catheter directed foam sclerotherapy (CDFS) with tumescent anaesthesia in patients with recurrent symptomatic saphenous reflux.

Methods

This was a prospective observational study (February 2018 to February 2019) including 21 consecutive patients referred with recurrent symptomatic varicose veins. Standing duplex ultrasound (DUS) with saphenous vein diameter measurement 3 cm from the terminal valve was performed pre-operatively. All the patients were operated on under local anaesthesia. By ultrasound guided puncture a hydrophilic 0.035″ guidewire and 5F Berenstein catheter were inserted through a 5F introducer sheath. Peri-saphenous tumescent anaesthesia (PSTA) was performed under ultrasound guidance. Sclerosant foam was prepared with sodium tetradecyl sulphate 3% or polidocanol 3% using the Tessari method. Concomitant phlebectomies were performed in 52%. Clinical evaluation and DUS were performed pre- and post-operatively at one week, six months, and 12 months.

Results

There were 11 men and 10 women (median age 52 years; interquartile range [IQR] 43 – 61). The great saphenous vein was treated in 18 patients. The median vein diameter was 6.8 mm (IQR 4.7 – 8.9). Previous procedures were Cure conservatrice et Hemodynamique de l'Insuffisance Veineuse en Ambulatoire (CHIVA), mechanochemical ablation, thermal ablation, and cyanoacrylate closure. The distribution of the clinical class (Clinical Etiology Anatomy Pathophysiology [CEAP] classification) was 16 C2, three C3, and two C4 limbs. Immediate technical success was 100%. There were no complications in the early post-operative period. The median follow up was eight months (IQR 5 – 10). The occlusion rate demonstrated by DUS was 100% (21/21) at one week, 100% (21/21) at six months, and 86% (18/21) at 12 months. The median post-procedural vein diameter at one week, six months, and 12 months was 4.8 mm (IQR 3.9 – 6), 4.3 mm (IQR 3.5 – 5.5), and 4 mm (IQR 3 – 4.9), respectively.

Conclusion

Combination CDFS with PSTA achieves good short and medium term venous occlusion rates, associated with few complications in patients with recurrent symptomatic saphenous reflux.

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The objective was to assess short and midterm efficacy and safety of catheter directed foam sclerotherapy with tumescent anaesthesia in patients with recurrent symptomatic saphenous trunk reflux.

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Ultrasound guided foam sclerotherapy is the endovenous modality with the highest recanalisation rate compared with other techniques when treating patients with primary superficial venous reflux. Although the combination of catheter directed foam sclerotherapy with tumescent perivenous anaesthesia is a more complex procedure, this modification can increase the probability of success in terms of vein occlusion for patients with recurrent symptomatic saphenous reflux.

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An occlusion rate 86% at 12 months is reported, but the “reflux free” ratio accounts for 95%. No relevant complications occurred in the early post-operative period. Patients did not report any neurological, pulmonary, or cardiac symptoms intra-operatively, or in the following hours or days.

Injection sclerotherapy for varicose veins

BACKGROUND

Varicose veins are enlarged and tortuous veins, affecting up to one-third of the world's population. They can be a cause of chronic venous insufficiency, which is characterised by oedema, pigmentation, eczema, lipodermatosclerosis, atrophie blanche, and healed or active venous ulcers. Injection sclerotherapy (liquid or foam) is widely used for treatment of varicose veins aiming to transform the varicose veins into a fibrous cord. However, there is limited evidence regarding its effectiveness and safety, especially in patients with more severe disease. This is the second update of the review first published in 2002.

OBJECTIVES

To assess the effectiveness and safety of injection sclerotherapy for the treatment of varicose veins.

SEARCH METHODS

For this update, the Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, AMED, CINAHL, and LILACS databases, and the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registries, on 20 July 2021.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) (including cluster-randomised trials and first phase cross-over studies) that used injection sclerotherapy for the treatment of varicose veins.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed, selected and extracted data. Disagreements were cross-checked by a third review author. We used Cochrane's Risk of bias tool to assess the risk of bias. The outcomes of interest were cosmetic appearance, complications, residual varicose veins, quality of life (QoL), persistence of symptoms, and recurrent varicose veins. We calculated risk ratios (RRs) or mean difference (MD) with 95% confidence intervals (CIs). We used the worst-case-scenario for dichotomous data imputation for intention-to-treat analyses. For continuous outcomes, we used the 'last-observation-carried-forward' for data imputation if there was balanced loss to follow-up. We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included 23 new RCTs for this update, bringing the total to 28 studies involving 4278 participants. The studies differed in their design, and in which sclerotherapy method, agent or concentration was used. None of the included RCTs compared sclerotherapy to no intervention or to any pharmacological therapy. The certainty of the evidence was downgraded for risk of bias, low number of studies providing information for each outcome, low number of participants, clinical differences between the study participants, and wide CIs. Sclerotherapy versus placebo Foam sclerotherapy may improve cosmetic appearance as measured by IPR-V (independent photography review - visible varicose veins scores) compared to placebo (polidocanol 1%: mean difference (MD) -0.76, 95% CI -0.91 to -0.60; 2 studies, 223 participants; very low-certainty evidence); however, deep vein thrombosis (DVT) rates may be slightly increased in this intervention group (RR 5.10, 95% CI 1.30 to 20.01; 3 studies, 302 participants; very low-certainty evidence). Residual varicose vein rates may be decreased following polidocanol 1% compared to placebo (RR 0.19, 95% CI 0.13 to 0.29; 2 studies, 225 participants; very low-certainty evidence). Following polidocanol 1% use, there may be a possible improvement in QoL as assessed using the VEINES-QOL/Sym questionnaire (MD 12.41, 95% CI 9.56 to 15.26; 3 studies, 299 participants; very low-certainty evidence), and possible improvement in varicose vein symptoms as assessed using the Venous Clinical Severity Score (VCSS) (MD -3.25, 95% CI -3.90 to -2.60; 2 studies, 223 participants; low-certainty evidence). Recurrent varicose veins were not reported for this comparison. Foam sclerotherapy versus foam sclerotherapy with different concentrations Three individual RCTs reported no evidence of a difference in cosmetic appearance after comparing different concentrations of the intervention; data could not be pooled for two of the three studies (RR 1.11, 95% CI 0.84 to 1.47; 1 study, 80 participants; very low-certainty evidence). Similarly, there was no clear difference in rates of thromboembolic complications when comparing one foam concentration with another (RR 1.47, 95% CI 0.41 to 5.33; 3 studies, 371 participants; very low-certainty evidence). Three RCTs investigating higher concentrations of polidocanol foam indicated the rate of residual varicose veins may be slightly decreased in the polidocanol 3% foam group compared to 1% (RR 0.67, 95% CI 0.43 to 1.04; 3 studies, 371 participants; moderate-certainty evidence). No clear improvement in QoL was detected. Two RCTs reported improved VCSS scores with increasing concentrations of foam. Persistence of symptoms were not reported for this comparison. There was no clear difference in recurrent varicose vein rates (RR 0.91, 95% CI 0.62 to 1.32; 1 study, 148 participants; low-certainty evidence). Foam sclerotherapy versus liquid sclerotherapy One RCT reported on cosmetic appearance with no evidence of a difference between foam or liquid sclerotherapy (patient satisfaction scale MD 0.2, 95% CI -0.27 to 0.67; 1 study, 126 participants; very low-certainty evidence). None of the RCTs investigated thromboembolic complications, QoL or persistence of symptoms. Six studies individually showed there may be a benefit to polidocanol 3% foam over liquid sclerotherapy in reducing residual varicose vein rate; pooling data from two studies showed a RR of 0.51, with 95% CI 0.41 to 0.65; 203 participants; very low-certainty evidence. One study reported no clear difference in recurrent varicose vein rates when comparing sodium tetradecyl sulphate (STS) foam or liquid (RR 1.10, 95% CI 0.86 to 1.42; 1 study, 286 participants; very low-certainty evidence). Sclerotherapy versus sclerotherapy with different substances Four RCTs compared sclerotherapy versus sclerotherapy with any other substance. We were unable to combine the data due to heterogeneity or assess the certainty of the evidence due to insufficient data.

AUTHORS' CONCLUSIONS

There is a very low to low-certainty evidence that, compared to placebo, sclerotherapy is an effective and safe treatment for varicose veins concerning cosmetic appearance, residual varicose veins, QoL, and persistence of symptoms. Rates of DVT may be slightly increased and there were no data concerning recurrent varicose veins. There was limited or no evidence for one concentration of foam compared to another; foam compared to liquid sclerotherapy; foam compared to any other substance; or one technique compared to another. There is a need for high-quality trials using standardised sclerosant doses, with clearly defined core outcome sets, and measurement time points to increase the certainty of the evidence.

Interventions for great saphenous vein incompetence

BACKGROUND

Great saphenous vein (GSV) incompetence, causing varicose veins and venous insufficiency, makes up the majority of lower-limb superficial venous diseases. Treatment options for GSV incompetence include surgery (also known as high ligation and stripping), laser and radiofrequency ablation, and ultrasound-guided foam sclerotherapy. Newer treatments include cyanoacrylate glue, mechanochemical ablation, and endovenous steam ablation. These techniques avoid the need for a general anaesthetic, and may result in fewer complications and improved quality of life (QoL). These treatments should be compared to inform decisions on treatment for varicosities in the GSV. This is an update of a Cochrane Review first published in 2011.

OBJECTIVES

To assess the effects of endovenous laser ablation (EVLA), radiofrequency ablation (RFA), endovenous steam ablation (EVSA), ultrasound-guided foam sclerotherapy (UGFS), cyanoacrylate glue, mechanochemical ablation (MOCA) and high ligation and stripping (HL/S) for the treatment of varicosities of the great saphenous vein (GSV).

SEARCH METHODS

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, CINAHL, and AMED databases, and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 2 November 2020. We undertook reference checking to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) treating participants for varicosities of the GSV using EVLA, RFA, EVSA, UGFS, cyanoacrylate glue, MOCA or HL/S. Key outcomes of interest are technical success, recurrence, complications and QoL.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials, applied Cochrane's risk of bias tool, and extracted data. We calculated odds ratios (ORs) with 95% confidence intervals (CIs) and assessed the certainty of evidence using GRADE.

MAIN RESULTS

We identified 11 new RCTs for this update. Therefore, we included 24 RCTs with 5135 participants. Duration of follow-up ranged from five weeks to eight years. Five comparisons included single trials. For comparisons with more than one trial, we could only pool data for 'technical success' and 'recurrence' due to heterogeneity in outcome definitions and time points reported. All trials had some risk of bias concerns. Here we report the clinically most relevant comparisons. EVLA versus RFA Technical success was comparable up to five years (OR 0.98, 95% CI 0.41 to 2.38; 5 studies, 780 participants; moderate-certainty evidence); over five years, there was no evidence of a difference (OR 0.85, 95% CI 0.30 to 2.41; 1 study, 291 participants; low-certainty evidence). One study reported recurrence, showing no clear difference at three years (OR 1.53, 95% CI 0.78 to 2.99; 291 participants; low-certainty evidence), but a benefit for RFA may be seen at five years (OR 2.77, 95% CI 1.52 to 5.06; 291 participants; low-certainty evidence). EVLA versus UGFS Technical success may be better in EVLA participants up to five years (OR 6.13, 95% CI 0.98 to 38.27; 3 studies, 588 participants; low-certainty evidence), and over five years (OR 6.47, 95% CI 2.60 to 16.10; 3 studies, 534 participants; low-certainty evidence). There was no clear difference in recurrence up to three years and at five years (OR 0.68, 95% CI 0.20 to 2.36; 2 studies, 443 participants; and OR 1.08, 95% CI 0.40 to 2.87; 2 studies, 418 participants; very low-certainty evidence, respectively). EVLA versus HL/S Technical success may be better in EVLA participants up to five years (OR 2.31, 95% CI 1.27 to 4.23; 6 studies, 1051 participants; low-certainty evidence). No clear difference in technical success was seen at five years and beyond (OR 0.93, 95% CI 0.57 to 1.50; 5 studies, 874 participants; low-certainty evidence). Recurrence was comparable within three years and at 5 years (OR 0.78, 95% CI 0.47 to 1.29; 7 studies, 1459 participants; and OR 1.09, 95% CI 0.68 to 1.76; 7 studies, 1267 participants; moderate-certainty evidence, respectively). RFA versus MOCA There was no clear difference in technical success (OR 1.76, 95% CI 0.06 to 54.15; 3 studies, 435 participants; low-certainty evidence), or recurrence (OR 1.00, 95% CI 0.21 to 4.81; 3 studies, 389 participants; low-certainty evidence). Long-term data are not available. RFA versus HL/S No clear difference in technical success was detected up to five years (OR 5.71, 95% CI 0.64 to 50.81; 2 studies, 318 participants; low-certainty evidence); over five years, there was no evidence of a difference (OR 0.88, 95% CI 0.29 to 2.69; 1 study, 289 participants; low-certainty evidence). No clear difference in recurrence was detected up to three years (OR 0.93, 95% CI 0.58 to 1.51; 4 studies, 546 participants; moderate-certainty evidence); but a possible long-term benefit for RFA was seen (OR 0.41, 95% CI 0.22 to 0.75; 1 study, 289 participants; low-certainty evidence). UGFS versus HL/S Meta-analysis showed a possible benefit for HL/S compared with UGFS in technical success up to five years (OR 0.32, 95% CI 0.11 to 0.94; 4 studies, 954 participants; low-certainty evidence), and over five years (OR 0.09, 95% CI 0.03 to 0.30; 3 studies, 525 participants; moderate-certainty evidence). No clear difference was detected in recurrence up to three years (OR 1.81, 95% CI 0.87 to 3.77; 3 studies, 822 participants; low-certainty evidence), and after five years (OR 1.24, 95% CI 0.57 to 2.71; 3 studies, 639 participants; low-certainty evidence). Complications were generally low for all interventions, but due to different definitions and time points, we were unable to draw conclusions (very-low certainty evidence). Similarly, most studies evaluated QoL but used different questionnaires at variable time points. Rates of QoL improvement were comparable between interventions at follow-up (moderate-certainty evidence).

AUTHORS' CONCLUSIONS

Our conclusions are limited due to the relatively small number of studies for each comparison and differences in outcome definitions and time points reported. Technical success was comparable between most modalities. EVLA may offer improved technical success compared to UGFS or HL/S. HL/S may have improved technical success compared to UGFS. No evidence of a difference was detected in recurrence, except for a possible long-term benefit for RFA compared to EVLA or HL/S. Studies which provide more evidence on the breadth of treatments are needed. Future trials should seek to standardise clinical terminology of outcome measures and the time points at which they are measured.

Catheter-directed foam sclerotherapy, an alternative to ultrasound-guided foam sclerotherapy for varicose vein treatment: A systematic review and meta-analysis

PURPOSE

Catheter-directed foam sclerotherapy is a new addition to the treatment modalities available for varicose veins. As a modification of ultrasound-guided foam sclerotherapy, catheter-directed foam sclerotherapy has been purported to offer higher complete ablation rates and an improved safety profile. The aim of this study is to appraise the current literature on the outcomes of catheter-directed foam sclerotherapy compared to ultrasound-guided foam sclerotherapy in chronic venous insufficiency.

METHODS

The review of the literature was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Data from studies that reported the outcomes of catheter-directed foam sclerotherapy and ultrasound-guided foam sclerotherapy were extracted, to determine the pooled proportion of complete ablation rates, using a random effect meta-analysis model.

RESULTS

A total of 62 studies, involving 3689 patients, were included in the systematic review. Higher rates of complete ablation were reported in catheter-directed foam sclerotherapy compared to ultrasound-guided foam sclerotherapy during the short- and medium-term follow-ups (Relative Risk = 1.06, Relative Risk = 1.15, Relative Risk = 1.19, p < 0.05). Fewer major and minor complications were also reported in patients who underwent catheter-directed foam sclerotherapy (Relative Risk = 0.23, Relative Risk= 0.43-0.76, p < 0.05).

CONCLUSION

Catheter-directed foam sclerotherapy has been demonstrated to have many advantages over ultrasound-guided foam sclerotherapy, offering superior complete ablation rates in the short-, medium- and long-term follow-ups. It also has a better safety profile, conferring a lower risk of major and minor complications. The conclusions should however be viewed in the context of significant limitations imposed by limited study data.