A prospective, randomized evaluation of the effect of silver impregnated subcutaneous cuffs for preventing tunneled chronic venous access catheter infections in cancer patients.

OBJECTIVE: This study was performed to evaluate the effect of a silver-impregnated cuff on the incidence of catheter-related bacteremia/fungemia or tunnel tract infection in cancer patients with chronic dual-lumen tunneled venous access catheters. SUMMARY BACKGROUND DATA: Infection is a frequent and potentially life-threatening complication of tunneled chronic cuffed silastic central venous access catheters in cancer patients. Recent experience with antimicrobial silver-impregnated cuffs placed on nontunneled percutaneously inserted central venous catheters suggests that such a cuff may render the catheter less prone to infection. METHODS: The authors prospectively randomized 200 cancer patients to receive either a dual-lumen 10 French tunneled cuffed silastic central venous access catheter or the same catheter with a second more proximal subcutaneous silver-impregnated cuff. All patients then were followed prospectively for infectious morbidity until the device was removed or the patient died. RESULTS: The hazard rate for infection/day (95% confidence limits) was 0.0022 (0.0015 to 0.0030) for standard catheters compared with 0.0027 (0.0019 to 0.0037) for catheters with silver-impregnated cuffs (p = not significant). Regression analysis of infection-free interval of both catheter types shows no difference over the lifetime of catheter as well as the over the first 48 days after insertion. CONCLUSIONS: The study indicated no effect of a silver-impregnated cuff in decreasing the incidence of catheter-related bacteremias/fungemias, tunnel infections, or the spectrum of causative microorganisms involved in cancer patients with tunneled chronic venous access catheters.     

Conversion of temporary hemodialysis catheters to tunneled hemodialysis catheters

PURPOSE: To determine the feasibility and clinical outcomes of conversion of temporary to tunneled hemodialysis catheters using the same venous insertion site. METHODS: Data from 42 patients with existing temporary hemodialysis catheters referred for placement of tunneled hemodialysis catheters were retrospectively reviewed. In these patients, the temporary catheter was exchanged for a peel-away sheath, and a tunneled catheter was inserted using the existing venous access site. Technical success, procedural complications, and clinical outcomes were evaluated. Hemodialysis records were reviewed to assess catheter patency during a 30-day follow-up period. RESULTS: The study group consisted of 20 males and 22 females (mean age: 58 years). All 42 temporary catheters were successfully converted to tunneled hemodialysis catheters without immediate procedure-related complications. Follow-up data were available for 32 patients (total: 3038; median 71 catheter days). Nine catheters were removed for infection, yielding a catheter infection rate of 0.30/100 catheter days; three catheters were removed for blood flow <200 ml/min. 13 patients had catheters removed when catheters were no longer needed. Three patients died with working catheters. The patency rate was 72% at 30 days, with four catheters functioning at the end of the study period. CONCLUSION: Conversion of a temporary hemodialysis catheter to a tunneled hemodialysis catheter using the same venous insertion site is a safe procedure that avoids complications associated with venotomy and allows conservation of other central venous access sites. Patency and infection rates in these catheters are comparable to several studies of catheter exchange and de novo placement of tunneled hemodialysis catheters.     

Hemodialysis catheter survival and complications in children and adolescents

. Venous catheters have become an indispensable form of hemodialysis access. We evaluated catheter performance as temporary and long-term access in children with end-stage renal disease (ESRD). We assessed the survival rates and causes of catheter failure in 78 catheters used for hemodialysis access in 23 pediatric patients (aged 10 months to 22 years) with ESRD over a 5-year period. Median survival was 31 days for 56 uncuffed catheters. One- and 2-month actuarial survival was 69% and 48%, respectively. Reasons for removal were: elective (39%), kinking (36%), trauma (11%), infection (7%), and other (5%). Smaller catheters (7 or 9 French) were more likely to be removed for kinking (P = 0.003). One-year actuarial survival for 22 cuffed catheters was 27%. Cuffed catheters were removed due to: infection (36%), kinking (14%), elective (9%), trauma (9%) and other (9%). Twelve catheters were removed for infection. Infection rates leading to removal were 0.58 and 0.71 per patient-year for uncuffed and cuffed catheters, respectively. Staphylococcus species were cultured most commonly. We conclude that uncuffed catheters function well for short-term hemodialysis access of up to 2 months’ duration and cuffed catheters are successful for long-term access in children and adolescents with ESRD. Received April 1, 1996; received in revised form and accepted August 1, 1996     

Implantation of permanent jugular catheters in patients on regular dialysis treatment: ten years' experience

Dual-lumen cuffed central venous catheter proved an important alternative vascular access compared to conventional arteriovenous (Cimino-Brescia) shunt in a selected group of patients on regular dialysis treatment. Typically, these catheters are used as bridging access, until fistula or graft is ready for use, or as permanent access when an arteriovenous fistula or graft is not planned (NKF-DOQI). We conducted a prospective study on IJV permanent catheter insertion and its related earlier and long-term complications. From February 1991 to February 2001 we inserted in 124 patients in end stage renal disease 135 cuffed catheters (130 in the right IJV and 5 in the left IJV), 92 of which were Permcath, 27 Vascath, and 16 Ash-Split. We performed the insertion of catheters by puncturing the IJV under ultrasonographic guid-ance in the lower side of the Sedillot triangle and checking the accurate position of the tip by endocavitary electrocardiography (EC-ECG). The duration of catheter use was from 60 to 1460 days, mean 345 days. The actuarial survival rate at 1 year was 82%, at 2 years 56%, at 3 years 42% and at 4 years 20%. The exit site infection and septicemia rates were 5.2 and 2.86 per 1000 catheter days respectively. Catheter sepsis was implicated in the death of three patients, all of whom had multiple medical problems. Several episodes of thrombosis (6% of dialyses) occurred which required urokinase treatment, and catheter replacement in 12 patients (9.6%). In 3 cases the catheters were displaced and correct repositioning was performed. Two catheters (Ash-Split) were replaced due to accidental damage of the external portion of catheters (alcoholic disinfectant). Catheter tip embolism occurred on one occasion during elective catheter exchange over guide-wire. One of the common problems encountered with cuffed tunneled catheters is poor blood flow, most often secondary to the formation of a fibrin sheath around the lumen. Even if we conducted a non-randomized study, in our experience, the higher rate of malfunctioning catheters was in the group with no anticoagulation therapy. Therefore, we suggest anticoagulation treatment in all patients wearing central vascular catheters with no contraindication. Just one year ago, we followed NKF-DOQI clinical practice guidelines for vascular access that indicated that for patients who have a primary AV fistula maturing, but need im-mediate hemodialysis, tunneled cuffed catheters are the access of choice and the preferred insertion site is the right IJV. Considering recent reports of permanent central venous stenosis or occlusion after IJV can-nulation, currently, our first choice is femoral vein cannulation with smooth silicone rubber catheters, tunneled if long-term utilization is needed (more the 3-4 weeks). In our opinion, the right IJV puncture is to be avoided as much as the venipuncture of arm veins suitable for vascular access placement, particularly the cephalic vein of the non-dominant arm. Our data confirm that permanent venous catheters might rep-resent an effective long-term vascular access for chronic hemodialysis, particularly for older patients with cardiovascular disease and for cancer patients.     

Conversion of temporary hemodialysis catheters to permanent hemodialysis catheters: a retrospective study of catheter exchange versus classic de novo placement

Many clinicians believe that de novo access is required when converting temporary hemodialysis (HD) catheters to long-term or permanent catheters. However, since vascular access sites are at a premium in the dialysis patient, it is important to preserve existing central venous catheters and conserve future access sites. In this retrospective study, data from 94 patients referred to interventional radiology for placement of long-term, tunneled HD catheters between July 2001 and September 2002 were reviewed. The study group consisted of 42 patients in whom the temporary catheter was exchanged for a peel-away sheath and a tunneled catheter inserted using the existing venous access site. The control group included 52 patients who received traditional de novo placement of permanent catheters. Based on available follow-up data, we report a 100% technical success rate, with 72% patency at 30 days in the study group (n = 32; mean age 58 years). By comparison, de novo catheter placement (n = 35; mean age 59 years) yielded a 100% technical success rate, with 83% patency at 30 days. The overall infection rate was 0.30 per 100 catheter-days (total 3036 catheter-days) and 0.36 per 100 catheter-days (total 3295 catheter-days), respectively (chi2 = 0.64, p > or = 0.05). There was no incidence of exit site infection, tunnel infection, or florid sepsis in either group. Likewise, no stenosis or bleeding complication was noted. Thus conversion of a temporary HD catheter to a tunneled catheter using the same venous insertion site is safe, does not increase the risk of infection, and allows conservation of other central venous access sites.     

Dialysekatheter

In cases of sudden deterioration of renal function or failure of an existing arteriovenous (AV) access, large bore central venous catheters are needed for emergency access for hemodialysis. In terms of complication and patency rates, tunneled long-term catheters are superior to non-tunneled catheters even after 2 weeks. They can usually be inserted under local anesthesia in an outpatient setting. There are several different catheter types and designs. Main complications are infection and central venous stenosis whereby the latter is common after subclavian catheters and can lead to loss of ipsilateral AV access. Long-term catheters should be part of an individual vascular access concept to ensure short dwell times.     

Vascular access and increased risk of death among hemodialysis patients

BACKGROUND: Hemodialysis with a venous catheter increases the risk of infection. The extent to which venous catheters are associated with an increased risk of death among hemodialysis patients has not been extensively studied. METHODS: We conducted a retrospective cohort study of 7497 prevalent hemodialysis patients to assess the association between dialysis with a venous catheter and risk of death due to all causes and to infection. RESULTS: A tunneled cuffed catheter was used for access in 12% of the patients and non-cuffed, not tunneled catheter in 2%. Younger age (P = 0.0005), black race (P = 0.0022), female gender (P = 0.0004), short duration since starting dialysis (P = 0.0003) and impaired functional status (P = 0.0001) were independently associated with increased use of catheter access. The proportion of patients who died was higher among those who were dialyzed with a non-cuffed (16.8%) or cuffed (15.2%) catheter compared to those dialyzed with either a graft (9.1%) or a fistula (7.3%; P < 0.001). The proportion of deaths due to infection was higher among patients dialyzed with a catheter (3.4%) compared to those dialyzed with either a graft (1.2%) or a fistula (0.8%; P < 0.001). The adjusted odds ratio (95% CI) for all-cause and infection-related death among patients dialyzed with a catheter was 1.4 (1.1, 1.9) and 3.0 (1.4, 6.6), respectively, compared to those with an arteriovenous (AV) fistula. CONCLUSION: Venous catheters are associated with an increased risk of all-cause and infection-related mortality among hemodialysis patients.     

Complications of catheters: tunneled and nontunneled

Central venous catheters for hemodialysis remain an indispensable modality of vascular access in the United States. Despite strong recommendations by the NKF-KDOQI guidelines to reduce the dependence on catheters, > 80% of all patients initiate hemodialysis using a central venous catheter. Although the tunneled dialysis catheters have some advantages, their disadvantages are many and often dwarf the miniscule advantages. This review is intended to discuss the complications--both acute and chronic--related to the use of tunneled dialysis catheters for hemodialysis access.     

Polyurethane Catheters for Long-Term Hemodialysis Access

Abstract: Chronic hemodialysis patients with failed native fistulas and/or synthetic arteriovenous grafts are usually dialyzed via surgically placed silicone jugular catheters such as the PermCath (Quinton, Seattle, WA, U.S.A.). We report a successful experience with the use of double lumen polyurethane central venous catheters placed percutaneously. Catheters with poor flows were replaced over a guidewire at the bedside. Eleven long-term hemodialysis patients failed arteriovenous access, 9 of them having had multiple attempts at fistulas and/or grafts. Seven of these patients had also failed peritoneal dialysis. They were dialyzed with polyurethane catheters for a mean of 681 ± 280 days (range 282–1150 days), requiring a mean of 3.4 ± 0.4 new venous punctures and 8.2 ± 1.5 catheter changes over a guidewire over that period of time. Actuarial patient survival was 50% at 2 years, and mean urea reduction during dialysis was 64.2 ± 1.7%. The septicemia rate was only 1.2 episodes per 1,000 catheter-days, but about 20% of patients experienced central venous occlusion, attributable to the use of subclavian catheter placement in 82% of the sites. The success of this technique and its elimination of the need for urokinase, radiologic interventions, and surgical placement warrant its consideration as an acceptable form of long-term vascular access, provided jugular placement allows reduced central venous occlusion rates.     

Prospective evaluation of a Dacron cuffed hemodialysis catheter for prolonged use

Double lumen subclavian venous hemodialysis catheters are in wide use in the United States to provide temporary vascular access. The disadvantages of these catheters include a high infection rate and short use-life (2 to 3 weeks). We evaluated a felt cuffed tunnelled jugular venous hemodialysis catheter (PermCath) to determine its ability to overcome these shortcomings and compared it with standard noncuffed double lumen dialysis catheters. Eighty PermCaths were inserted during this prospective study in patients needing temporary vascular access in excess of 1 month. Median use-life of these catheters was 8 weeks with a use range of 3 weeks to 5.4 months. Only four functioning catheters failed before elective removal. Despite the prolonged use-life there was only one episode of catheter mediated bacteremia. Seven catheters (9%) failed to function immediately after insertion. These failures were caused by catheter kinking in the region of the felt cuff. Thrombosis of the catheter lumen was the most frequent complication (137 episodes) but resolved in over 95% of the instances with urokinase instillation. Exit site infections (23 instances) were successfully treated conservatively. We conclude that the PermCath (Quinton Instrument Co, Seattle) is a safe and reliable new device with a low complication rate and a longer use-life than standard subclavian dialysis catheters. This longer use-life allows more time for maturation of primary arteriovenous (AV) fistulas and Tenckhoff peritoneal dialysis catheters, and provides time for the healing of infected vascular access grafts. Its primary disadvantage is the need for surgical insertion.     

Hemodialysis catheters and ports

Percutaneous placement of cuffed tunneled catheters for hemodialysis access has become a firmly established method of providing vascular access to patients with end-stage renal disease. Considerable evidence supports the right internal jugular vein as the preferred site for catheter insertion. The use of real-time imaging using both ultrasound and fluoroscopy permits simple, safe, and effective placement of the catheter for hemodialysis. The use of these imaging techniques has significantly reduced the number of and severity of complications associated with catheter placement. A specific method of placement is described including variations for specific catheter types. The new subcutaneous port as an alternative to the cuffed tunneled catheter appears to provide another option for vascular access; preliminary data suggests higher flow rates and lower infection rates compared with externalized cuffed tunneled catheters. Finally, the criteria for obtaining training and proficiency in placement of cuffed tunneled catheters are outlined.     

Comparison of antimicrobial impregnation with tunneling of long-term central venous catheters: a randomized controlled trial

OBJECTIVE: We sought to compare the impact of antimicrobial impregnation to that of tunneling of long-term central venous catheters on the rates of catheter colonization and catheter-related bloodstream infection. SUMMARY BACKGROUND DATA: Tunneling of catheters constitutes a standard of care for preventing infections associated with long-term vascular access. Although antimicrobial coating of short-term central venous catheters has been demonstrated to protect against catheter-related bloodstream infection, the applicability of this preventive approach to long-term vascular access has not been established. METHODS: A prospective, randomized clinical trial in 7 university-affiliated hospitals of adult patients who required a vascular access for > or = 2 weeks. Patients were randomized to receive a silicone central venous catheter that was either impregnated with minocycline and rifampin or tunneled. The occurrence of catheter colonization and catheter-related bloodstream infection was determined. RESULTS: Of a total of 351 inserted catheters, 346 (186 antimicrobial-impregnated and 160 tunneled) were analyzed for catheter-related bloodstream infection. Clinical characteristics were comparable in the 2 study groups, but the antimicrobial-impregnated catheters remained in place for a shorter period of time (mean, 30.2 versus 43.8 days). Antimicrobial-impregnated catheters were as likely to be colonized as tunneled catheters (7.9 versus 6.3 per 1000 catheter-days). Bloodstream infection was 4 times less likely to originate from antimicrobial-impregnated than from tunneled catheters (0.36 versus 1.43 per 1000 catheter-days). CONCLUSIONS: Antimicrobial impregnation of long-term central venous catheters may help obviate the need for tunneling of catheters.     

Central venous dialysis access: experience with a dual-lumen, silicone rubber catheter

The central venous dialysis catheter has gained wide acceptance for short-term hemodialysis with the realization of the need to spare peripheral extremity vessels for the creation of more durable internal arteriovenous fistulas. The Hemocath (Quinton Instrument Co., Seattle, Wash.), a soft, silicone rubber, double-lumen central venous dialysis catheter, was introduced as a permanent access device in 1984. A prospective evaluation of 53 catheters placed in 51 patients over a 9-month period is presented. Forty-nine catheters were placed for temporary access and four were placed for permanent access. All 53 catheters were discontinued after functioning an average of 63.9 days (range, 5 to 324 days). No major complications occurred during insertion or on dialysis. One catheter fragmented during removal and was retrieved in the operating room. Infection led to the removal of 17 catheters (34.7%). Thrombosis occurred in 11 catheters and was the cause of removal in two (4.1%). Excluding the two catheters that functioned at the time of the patient's deaths and those placed for permanent access, 91.5% of the catheters performed successfully as temporary accesses devices until permanent access sites were available for use. The catheter provided reliable, relatively safe, and easily maintained central venous access for hemodialysis.     

Percutaneous, non-surgical placement of tunneled, cuffed, external jugular hemodialysis catheters: a case report

The right internal jugular vein is widely accepted as the vessel of choice for placement of long-term central venous catheters for hemodialysis. As vascular access sites become progressively depleted, alternate anatomic locations for access must be sought. We describe a non-surgical (fluoroscopy assisted, percutaneous) technique for placement of external jugular, tunneled, cuffed hemodialysis catheters, and provide long-term blood flow and dialysis adequacy data for EJV catheters.     

An alternative approach to the central circulation from above the diaphragm

This is a review of a new fluoroscopically guided safe technique to place tunneled cuffed hemodialysis (HD) catheters via the supraclavicular location. Right supraclavicular catheters were placed in 12 patients who had no patent internal jugular veins. The placements were all successful and without serious complications. Over the 2 years of follow-up, two episodes of thrombosis/stenosis (16.7%) resulted in catheter removal. The rate of infection was 8%, or one episode in 1204 patient-days. The average length of use was 111 days. The average rate of blood flow was 354 cc/min. The right supraclavicular approach for tunneled HD catheters is safe and compares favorably to the internal jugular approach for patients with limited access options.     

A modified supraclavicular approach for central venous catheterization by manipulation of ventilation in ventilated patients

Background: Because of overuse and multiple implantations of hemodialysis catheters through internal jugular or subclavian vein (SCV) in patients with chronic hemodialysis, these veins often become stenotic or occlude, therefore necessitating alternative access. We introduce a new technique in ventilated patients for placement of tunneled cuffed chronic hemodialysis catheter: modified supraclavicular approach by cease of ventilation. Methods: Patients who received implantation of the tunneled cuffed chronic hemodialysis catheters by supraclavicular approach were collected from February 2003 to July 2005. Right subclavian, right innominate or left SCVs were accessed through the supraclavicular approach for catheter insertion. The procedures were performed by certificated anesthesiologists. The following parameters were recorded: co‐morbidities, laboratory examinations before the procedure, method for catheterization, duration of procedure, complications related to catheterization and long‐term outcome of hemodialysis catheters. Results: Eleven catheters were inserted in nine patients (two patients received twice) by supraclavicular approach during this period. All patients were mechanically ventilated and these catheters (seven at right and four at left) were implanted using the modified supraclavicular approach with lung deflation during venipuncture, advance of guidewire, and insertion of catheter. There were no procedural complications. The average duration of whole procedure was 36.6 minutes (30–45 minutes) and the mean catheter survival days were 62.1 days (13–152 days). The estimated duration was <1 minute of each period of lung deflation. There were no desaturation or pneumothorax during the whole procedure. Conclusion: The modified supraclavicular approach with lung deflation for tunneled cuffed chronic hemodialysis catheter in ventilated patients is at least as effective as traditional approach and can be easily performed by surgeons as well as experienced physicians. Based on the results, this simplified technique using lung deflation may be particularly useful to decrease procedural complications.     

Vascular screening prior to placement of tunnelled and cuffed hemodialysis catheters

Purpose: To demonstrate the importance of venous vascular screening before the placement of tunneled and cuffed hemodialysis catheters in patients requiring hemodialysis prior to placement and/or maturation of an arteriovenous fistula (AVF) or graft (AVG). Methods: Between October 1998 and March 2000, all patients requiring hemodialysis access placement were prospectively evaluated with duplex ultrasound for status of upper extremity vessels and central veins prior to selection of a permanent access site. When interim tunneled and cuffed hemodialysis catheters were required, they were placed on the side contralateral to proposed AVF/AVG placement. No catheters were placed without initial vascular screening. The study group was compared to historical controls during a similar period (April 1997 through September 1998) when no vascular screening was performed. Results: During the study period, 234 screening duplex ultrasound examinations were performed in 244 patients. Ten patients required no screening prior to access site placement. Overall, 353 catheters were placed, 243 (69%) on the right side and 110 (31%) on the left side. During the control period, 394 catheters were placed in 255 patients, 306 (78%) right-sided and 88 (22%) left-sided. The increase in left-sided catheters with ultrasound screening and careful planning for future access sites was significant (p<0.01). Conclusion: Vascular-screening-directed catheter placement significantly alters the side of catheter placement when compared to a management protocol without prior screening. Such screening helps identify the side of permanent access placement, while directing interim catheters to the contralateral side such that central veins may be preserved for permanent access.     

Bacterial meningitis--complication from a dialysis catheter

Various infective complications associated with dialysis catheter infection have been reported in the literature previously. We report a case of a hemodialysis patient presented with confusion and dysarthria secondary to Staphylococcus aureus septicemia and meningitis originating from a tunneled catheter used for providing dialysis. Blood cultures from the periphery, central venous catheter and culture of the line tip grew methicillin-sensitive Staphylococcus aureus. Lumbar puncture after CT brain confirmed Staphylococcus aureus. He was treated with high dose of an appropriate parenteral antibiotic and also removal of the infected line. In spite of optimal treatment, he died 15 days following his admission. The ideal option will be to use a definitive access like a fistula or AV graft, but in practice a significant proportion of hemodialysis patients is dialyzed with temporary or tunneled catheters all over the world, and infection poses a serious threat to dialysis patients resulting in significant mortality and morbidity. In patients with dialysis catheter-related sepsis, removal of the infected catheters and appropriate antibiotic treatment will prevent serious metastatic complications. Planning definitive access well ahead in chronic kidney disease patients and minimizing the use of temporary access is the only way forward.     

Treatment of dialysis catheter infections in 2004

Hemodialysis catheter associated infections are a major source of morbidity and mortality in end stage renal disease patients. There is disagreement about the management of catheter infections, particularly concerning the removal of potentially infected tunneled dialysis catheters. A dialysis catheter should generally be removed when an infection involves a temporary hemodialysis catheter, a septic patient, a patient with a tunnel tract infection, or a patient with evidence of a metastatic infectious complication. In treating stable patients with clinically mild catheter associated bacteremia, parenteral antibiotics alone have a low success rate in eliminating the infection. Antibiotic locks are an emerging strategy for treating these patients, but at present higher rates of success and lower costs are achieved by exchanging the catheter over a guidewire. Antibiotic lock solutions, antibiotic coated catheters, and totally implantable dialysis access systems may play a large role in prevention of catheter associated infections in the future; however, further randomized controlled trials of these strategies are needed. Future efforts should concentrate on limiting the use of traditional tunneled cuffed hemodialysis catheters by early referral to vascular surgery for the creation of an arterio-venous fistula.     

Use of a subclavian venous catheter for short- and long-term hemodialysis in children

Vascular access for hemodialysis in children poses problems not encountered in adults because of the small size of the vessels available. The increasing use of peritoneal dialysis has created a large number of patients who need prompt access for hemodialysis for days to weeks during episodes of peritonitis. There are also occasional patients who have exhausted available fistula sites and still require hemodialysis. To address these problems, we designed a series of catheters for insertion in the subclavian vein. The catheters are stiffer than the Hickman type catheter to allow for higher flow rates without collapse. Seventy-five catheters were implanted in 58 patients with a mean age of 14 years. Twelve catheters were inserted in ten children for long-term (over 3 months) access; they have been in place for a mean of 259 days and used for a mean of 64 dialyses. In two children, the catheter has been the sole site for hemodialysis for over a year. Fifty-eight catheters were implanted in 43 patients for short-term hemodialysis. They were in place for a mean of 29 days and used for a mean of 13 dialyses. The major complications encountered were clotting of the catheter and migration out of position. Four catheters were removed because of infection. These new catheters provide effective hemodialysis for children as small as 7 kg with an acceptable morbidity rate and may be used for extended periods of time if necessary.