Vascular access: care and monitoring of function

Lipectomy as an alternative for superficialization of autologous AVF in obese patients: experience of a referral center in Amazon

Background

The preferred vascular access for hemodialysis is a native arteriovenous fistula (AVF) because it offers the best results in the short and long terms, lower morbidity and mortality, and has additional advantages in relation to central venous catheters or arteriovenous grafts. However, obesity can present an additional challenge because of the barrier of subcutaneous cellular tissue covering the surface of the vein to be punctured.

Objectives

The authors review their experience with excision of subcutaneous tissue (lipectomy) overlying upper arm cephalic vein arteriovenous fistulas in obese patients.

Methods

Consecutive vascular access patients undergoing lipectomy for cannulation with difficult access because of vein depth were reviewed. Cephalic vein depth was measured by ultrasound in all cases.

Results

Twenty-two patients were reviewed (15 men and 7 women), with a mean body mass index of 34.0 kg/m2 (range: 28-40 kg/m2). Mean age was 58.4 years. The mean preoperative vein depth of 7.9 mm (range: 7.0-10.0 mm) was reduced to 4.7 mm (range: 3.0-6.0 mm) (P 0.01). The mean follow-up period for patients was 13.2 months. Four patients were lost to follow-up and four died during the period due to causes unrelated to vascular access.

Conclusions

Obesity should not be a limiting factor to creation of a native AVF, since lipectomy is a relatively simple option for superficialization, enabling functioning native and deep arteriovenous fistulas in obese patients.

A comparison of the Niagara and Medcomp catheters for continuous renal replacement therapy

PURPOSE

The choice of vascular access catheter may affect filter life during continuous renal replacement therapy (CRRT). In particular, differences in catheter design might affect the incidence of circuit clotting related to catheter malfunction.

DESIGN AND SETTING

Sequential controlled study in a tertiary, adult intensive care unit (ICU).

AIM

To compare circuit life when CRRT was performed with a Niagara catheter or a Medcomp catheter.

PATIENTS AND MEASUREMENTS

We studied 46 patients with acute kidney injury requiring CRRT, all delivered with catheters in the femoral position. We obtained information on age, gender, disease severity score [acute physiology and chronic health evaluation (APACHE II) and APACHE III], filter life, heparin dose per hour, daily systemic hemoglobin concentration, platelet count, international normalized ratio (INR), and activated partial thromboplastin time (APTT) during CRRT.

RESULTS

We studied 254 circuits in 46 patients. Of these, 26 patients (140 circuits) used the Niagara catheter and 20 patients (114 circuits) used the Medcomp catheter. Median circuit life in the two groups were 11 h and 7.3 h, respectively (p < 0.01). Patients using Medcomp catheters had a lower platelet count (p = 0.04) and a lower hemoglobin concentration (p = 0.01), but INR (p = 0.16), APTT (p = 0.46), anticoagulant treatment (p = 0.89), and heparin dose per hour (p = 0.24) were similar. After correcting for confounding variables by multivariable linear regression analysis, it was found that the choice of catheter is not an independent predictor of circuit life. On Kaplan-Meier survival analysis, circuit life was not significantly different between the two catheters (p = 0.87).

CONCLUSION

The choice of either the Niagara or Medcomp catheter does not appear to be a significant independent determinant of circuit life during CRRT.

A comparison of the Niagara™ and Dolphin® catheters for continuous renal replacement therapy

PURPOSE

The choice of vascular access catheter may affect filter life during continuous renal replacement therapy (CRRT); specifically, a new surface-modified catheter has been reported to possibly prevent thrombosis and catheter malfunction.

DESIGN AND SETTING

A sequential, controlled study in a tertiary ICU.

AIMS

To compare circuit life when CRRT was performed with a Bard®Niagara™ catheter or the surface-modified GamCath™ Dolphin® Protect 1320 catheter.

PATIENTS AND MEASUREMENTS

We studied 50 patients with acute kidney injury requiring CRRT, all delivered with catheters in the femoral position. We obtained information on age, gender, disease severity score (APACHE II and APACHE III), filter life, total heparin dose, hemoglobin concentration, platelet count, INR, and aPTT during CRRT.

RESULTS

We studied 341 circuits in 50 patients; 30 patients (140 circuits) used the Niagara and 20 patients (201 circuits) used the Dolphin catheter. Mean of circuit life in two groups was 14.9 hours and 13.1 hours, respectively (p=0.22). Patients using Niagara catheters had a more prolonged APTT (p<0.01) and lower platelet count (p=0.05), while heparin dose (p=0.22), and other anticoagulant treatment (p=0.73) were not significantly different. On Kaplan-Meier survival analysis, circuit life was not significant different between the two catheters (p=0.15).

CONCLUSIONS

The Niagara and Dolphin catheters appear to be broadly equivalent in terms of their impact on circuit life.

Quality of care of vascular access in hemodialysis patients in a hemodialysis center in Iran

Because of the lack of study in the field of vascular access care for hemodialysis patients, an observational study was conducted on 110 patients undergoing chronic hemodialysis in the Isfahan's AliAsghar Hospital. Data were collected using a demographic questionnaire and a checklist related to vascular access care techniques. A total of 63 male and 47 female with an average of 40.02 months of hemodialysis were studied. In addition, 72 patients were under hemodialysis through arteriovenous fistula and 38 patients through subclavian catheters. The overall quality of care for vascular access site was moderate. Selecting an inappropriately high speed for the apparatus at the beginning of dialysis, needling of an aneurysm or needling near the fistula, and incomplete priming of the filter and the tubes were the most frequent inappropriate actions. Reinforcement of the nurses' continuing education programs and development of standard vascular access care protocols are recommended.

Time to move away from damage control strategy in hemodialysis vascular access management: a view from Saudi Arabia

For the last 40 years, most of the research and publications on hemodialysis access, has focused on the management of its complications e.g. thrombosis, infection, aneurysms. In other words, a damage control strategy. While this is undoubtedly an important part of access management, it is a deficient reactive strategy that does not enhance a better quality of life for patients or help reduce the burden on health care resources. To achieve these objectives, efforts should be directed at ways which provide a longer access life with fewer complications. Such an approach would save costs and reduce the suffering of the patient. In this paper we will focus on hemodialysis management in Saudi Arabia, describe the reasons for the current unsatisfactory situation, and highlight possible remedies.

Numerical and experimental study of blood flow through a patient-specific arteriovenous fistula used for hemodialysis

Arteriovenous fistula (AVF) pathologies related to blood flow necessitate valid calculation tools for local velocity and wall shear stress determination to overcome the clinical diagnostic limits. To illustrate this issue, a reconstructed patient-specific AVF was investigated, using computational fluid dynamics (CFDs) and particle image velocimetry (PIV). The aim of this study was to validate the methodology from medical images to numerical simulations of an AVF by comparing numerical and experimental data. Two numerical grids were presented with a refinement difference of a factor of four. A mold of the same volume was created and mounted on an experimental bench with similar boundary conditions. The patient's acquired echo D006Fppler flow waveform was injected at the arterial inlet. Experimental and numerical velocity vector cartography qualitatively produced similar flow fields. Quantification with a point-to-point approach thoroughly investigated the velocity profiles using the mean difference between both results. The finest mesh generated CFD results with a mean percentage of the difference in velocity magnitude, taking the PIV as reference, did not exceed 10%. At specific zones, the coarse mesh required adaptive meshing to improve fitting with experimental data. Meshing refinement was necessary to improve velocity accuracy at wide diameters and wall shear stress at narrow diameters. Provided that these criteria were properly respected, we show through this difficult example the validity of using CFD to properly describe flow patterns in image-based reconstructed blood vessels.

Avaliação da maturação das fístulas arteriovenosas para hemodiálise pelo eco-Doppler colorido

CONTEXTO: Quando se confecciona uma fístula arteriovenosa para hemodiálise (FAVH) autógena, é necessário que se aguarde a dilatação da veia em questão e o desenvolvimento de volume de fluxo mínimo, fenômeno chamado de maturação. Ainda hoje se discute qual o tempo necessário para ocorrer essa maturação. OBJETIVO: Avaliar a maturação de FAVH utilizando-se critérios ecográficos. MÉTODO: Entre maio de 2004 e 2005, 40 pacientes foram selecionados prospectivamente, sendo 23 homens (57,5%), com média de idade de 17,5±51,3 anos, com indicação de confecção de uma FAVH. Utilizou-se o aparelho Logic III® com transdutor de 10 MHz para a avaliação no pré-operatório e nos 7º, 14º, 21º e 28º dias de pós-operatório. Os critérios para a maturação após a cirurgia foram: veia com diâmetro médio maior que 4 mm e volume de fluxo maior que 400 mL/min. RESULTADOS: O diâmetro médio pré-operatório foi de 3,24±1,43 e 3,71±1,37 mm para fístulas de punho e de cotovelo, respectivamente. O diâmetro final foi de 5,01±0,87 mm para as FAVH de punho (p = 0,006) e de 6,15±1,16 mm para as FAVH de cotovelo (p = 0,95). O volume de fluxo no 7º dia pós-operatório foi de 493,63±257,49 mL/min e 976,33±332,90 mL/min para as FAVH de punho e cotovelo, respectivamente. Ao final do estudo, foi calculado o valor de 556,81±288,42 mL/min nas FAVH de punho (p < 0,05) e de 1031,62±614,812 mL/min nas FAVH de cotovelo. Baseados nos dois critérios, a maturação ocorreu em 57,1% das fístulas de punho e em 100% das fístulas de cotovelo após a 1ª semana. Após 4 semanas, 67,9% das fístulas de punho e 100% das fístulas de cotovelo apresentaram maturação. CONCLUSÃO: A maioria das FAVH de cotovelo apresentou diâmetro e fluxo adequados para punção logo após a 1ª semana de pós-operatório. Para as FAVH de punho, houve melhora progressiva dos padrões de maturação com o passar das semanas, sugerindo que essas FAVH devem ser puncionadas preferencialmente após a 4ª semana de pós-operatório.

Comparison of alteplase and heparin in maintaining the patency of paediatric central venous haemodialysis lines: a randomised controlled trial

OBJECTIVES

To determine whether the tissue plasminogen activator, alteplase, is more effective than heparin in preventing blood clots developing in children's haemodialysis central lines between dialysis sessions.

DESIGN

A prospective double-blind, within-patient multiperiod cross-over controlled trial of instilling a "lock" of either heparin 5000 U/ml or alteplase 1 mg/ml into the central lines of two children haemodialysed twice weekly, and seven dialysed thrice weekly, over 10 weeks.

SETTING

A UK paediatric nephrology unit.

MAIN OUTCOME MEASURES

Weight of blood clot aspirated from the line at the start of the next dialysis session.

RESULTS

The odds of a clot forming was 2.4 times greater with heparin than alteplase (95% CI 1.4 to 4.0; p = 0.001), and when present they were 1.9 times heavier (31 vs 15 mg; 95% CI 1.5 to 2.4; p<0.0005). There was no effect of inter-dialytic interval. One child required an alteplase infusion to clear a blocked line following a heparin lock. We subsequently changed our routine locks from heparin to alteplase. Comparing the year before and after that change, the incidence of blocked lines requiring an alteplase or urokinase infusion fell from 2.7 to 1.2 per child (p<0.03), and the need for surgical replacements from 0.7 to nil (p<0.02).

CONCLUSION

Alteplase is significantly more effective than heparin in preventing clot formation in central haemodialysis lines. This reduces morbidity and improves preservation of central venous access. It is more expensive, though relatively economic if packaged into syringes and stored frozen until needed, but reduces the costs of unblocking or replacing clotted lines.

Association of clinic vascular access monitoring practices with clinical outcomes in hemodialysis patients

BACKGROUND

Early identification of access dysfunctions may be associated with improved patient outcomes. We examined whether patient outcomes were associated with vascular access monitoring practices in an incident dialysis cohort.

METHODS

We conducted a national prospective cohort study and analyzed 363 hemodialysis patients who had a first permanent vascular access (arteriovenous fistula or graft) by 6 months after the start of dialysis. Multivariate methods were used to examine associations between monitoring practices and 6-month Kt/V (reaching Kt/V >/=1.2), access intervention, access failure, and 2-year septicemia and all-cause hospitalization and mortality.

RESULTS

Patients who received monitoring weekly or more often (49%) were more likely to have an access intervention (adjusted RH = 1.40, 95% CI, 1.07-1.84) than those who received monitoring less frequently. Additionally, patients treated at clinics that reported performing regular access monitoring (80% of patients) were less likely to be hospitalized for septicemia (IRR = 0.35, 95% CI, 0.21-0.61) or for any cause (IRR = 0.77, 95% CI, 0.60-0.99). There were no statistically significant differences between patients exposed to different vascular access monitoring practices in access failure, achievement of Kt/V, or survival.

CONCLUSION

Frequent monitoring of dialysis access may initially increase the number of interventions but is beneficial to longer-term outcomes, including septicemia-related and all-cause hospitalization.

Thermography and colour duplex ultrasound assessments of arterio-venous fistula function in renal patients

Vascular and clinical assessments of arterio-venous fistula (AVF) function and access are important in patients undergoing or preparing to undergo renal dialysis. Objective assessment techniques include colour duplex ultrasound and more recently medical infrared thermography. Ideally, these should help assess problems relating to fistula failure or to vascular steal from the hand which can result from excessive fistula blood flow. The clinical value of thermography, as yet, has not been assessed for this patient group. The aims of this study were therefore to investigate the relationships between thermography skin temperature measurement and (a) quantitative ultrasound measurement of AVF blood flow, and (b) qualitative clinical assessment of vascular steal from the hands. Fifteen adult patients underwent thermal imaging of the upper limbs, colour duplex ultrasound to derive AVF blood flow from brachial artery blood flow measurements, and a clinical evaluation for vascular steal. Temperature measurements were extracted from the thermograms, including bilateral arm and hand (Fistula -- Non-Fistula) differences, for comparison with derived AVF blood flow and steal grading. Derived AVF blood flow ranged from 30 to 1,950 ml min(-1), with a mean rate close to one litre per minute. Thermography detected the warmer superficial veins in proximity to the patent fistulas, with bilateral differences in fistula region skin temperature correlated with derived AVF blood flow (using maximum temperature measurements the correlation was +0.71 [p < 0.01]; and using mean temperature measurements the correlation was +0.56 [p < 0.05]). When thermography measurements were compared with the clinical assessment of steal the mean hand temperature differences separated steal from non-steal patients with an accuracy of greater than 90%. In summary, we have now demonstrated the potential clinical value of medical infrared thermography for assessing AVF function in renal patients.

Vascular access survival and morbidity on daily dialysis: a comparative analysis of home and limited care haemodialysis

BACKGROUND

Concerns about vascular access failure may have limited the widespread use of daily haemodialysis (DHD). We assessed the incidence and type of vascular access complications during DHD and other schedules, both at home and on limited care haemodialysis.

METHODS

All patients were treated in a limited care and home haemodialysis unit with a stable caregiver team (November 1998-November 2002). Vascular access failure, surgical treatment, angioplasty and declotting were studied alone or in combination by univariate and multivariate models. We analysed the effects of age, sex, comorbidity, previous vascular events, schedule, setting of treatment (home, limited care), dialysis follow-up, vascular access (native vs prosthetic, first vs subsequent) and setting of vascular access creation. 'Intention to treat' and 'per protocol' analyses were performed.

RESULTS

In 2160 patient-months (home dialysis: DHD 400 months, non-DHD 655 months; limited care: DHD 208 months; non-DHD 897 months), 57 adverse events occurred (27 failures), in which 30 were at home (nine DHD) and 27 were in limited care (five DHD). The probability of remaining free from adverse events at 6 and 12 months was 89% and 80% on DHD and 79% and 76% on other schedules ('intention to treat'). Univariate analyses revealed a significant difference for the setting of the vascular access creation (lower risk of vascular access complications in our centre) and sex (male sex was protective). Logistic regression and Cox analyses confirmed the role for the setting of the vascular access creation.

CONCLUSIONS

Although DHD did not appear as a risk factor for vascular access morbidity or failure at home or in a limited care centre setting, the setting of vascular access creation may influence its success.

Clinical and Doppler ultrasonography data of a polyurethane vascular access graft for haemodialysis: a prospective study

BACKGROUND

Absence of a permanent vascular access in most patients starting haemodialysis remains a cause of high morbidity and costs. This study obtained new clinical and colour Doppler ultrasound (CDU) data of a polyurethane vascular access graft (PVAG) proposing early post-operative cannulation.

METHODS

Baseline characteristics were determined in 15 patients and the PVAGs were evaluated prospectively including first cannulation, patency and complications. CDU was used post-operatively and after 1 year for assessing graft morphology and access blood flow.

RESULTS

PVAGs were cannulated at a median of 4 days post-operatively. The 1-year primary patency of the PVAG was 66.7%. During the 15 months observation three grafts thrombosed, one was replaced because of infection and one because of ischaemia. CDU measurements at the feeding brachial artery revealed a mean initial access volume flow of 773+/-89 ml/min, being significantly higher in patients without thrombosis compared to patients with thrombotic events (930+/-90 vs 375+/-143 ml/min, P<0.05). The initial inability to directly monitor PVAGs by CDU changed at sites of frequent centesis, where Doppler signals and luminal morphology could be evaluated in the follow up examination.

CONCLUSIONS

The PVAG offers early access for urgent haemodialysis. CDU for access volume flow measurement at the feeding brachial artery contributes to predict access thrombosis. Direct non-invasive graft imaging is limited and the ultrasonographical changes in the polyurethane material enabling graft monitoring after repeated cannulation might indicate an injury of the graft with increased risk for access failure.