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Nathan W Levin

Publications and source records attributed to Nathan W Levin.

84 records · Page 5Linked to original sources
PubMed2002

Noninvasive transcutaneous access flow measurement before and after hemodialysis: impact of hematocrit and blood pressure.

BACKGROUND/AIMS: The dialysis outcome is strongly affected by the function of the vascular access. It has been suggested that access clotting may be related to increased hematocrit (Hct) or excessive ultrafiltration during dialysis. The present study was designed to evaluate the changes of vascular access flow during hemodialysis in 18 end-stage renal disease patients with native arteriovenous fistulas and the possible correlations with Hct and mean arterial pressure (MAP). METHODS: We utilized a noninvasive vascular access flow measurement technique, based on a transcutaneous optical sensor, to evaluate the flow in the access before and after a single hemodialysis session. At the beginning and at the end of the session, the blood flow was measured noninvasively, placing the sensor approximately 2 in from the point of insertion of the arterial needle. At the same time, Hct and MAP were measured directly. All patients were on hemodialysis for more than 3 months. RESULTS: There was a significant increase in Hct, likely due to ultrafiltration and consequent hemoconcentration, from the beginning to the end of the dialysis session. In detail, the Hct increased from 32.6 +/- 1.9 to 35.4 +/- 1.8% (p < 0.001), while the MAP did not present significant variations. The blood flow did not show significant variations, increasing from 780 +/- 312 to 919 +/- 411 ml/min after the session. Because of the stability of the MAP, we could dissociate the effects of the Hct from those of the MAP on blood flow variations. CONCLUSION: Our study suggests that the blood flow in native fistulas is not affected by the acute rise in Hct due to ultrafiltration during hemodialysis. The transcutaneous access flow measurement technique appears to be reliable and accurate, and it could represent an important diagnostic tool.

Arteriovenous Fistula↗
PubMed2001

Association of elevated serum PO(4), Ca x PO(4) product, and parathyroid hormone with cardiac mortality risk in chronic hemodialysis patients.

Hyperphosphatemia is highly prevalent among patients with end-stage renal disease (ESRD) and is associated with increased mortality risk in hemodialysis (HD) patients. The mechanism through which this mortality risk is mediated is unclear. Data from two national random samples of HD patients (n = 12,833) was used to test the hypothesis that elevated serum PO(4) contributes mainly to cardiac causes of death. During a 2-yr follow-up, the cause-specific relative risk (RR) of death for patients was analyzed separately for several categories of cause of death, including coronary artery disease (CAD), sudden death, and other cardiac causes, cerebrovascular and infection. Cox regression models were fit for each of the eight cause of death categories, adjusting for patient demographics and non-cardiovascular comorbid conditions. Time at risk for each cause-specific model was censored at death that resulted from any of the other causes. Higher mortality risk was seen for patients in the high PO(4) group (>6.5mg/dl) compared with the lower PO(4) group (< or =6.5mg/dl) for death resulting from CAD (RR 1.41; P < 0.0005), sudden death (RR 1.20; P < 0.01), infection (RR 1.20; P < 0.05), and unknown causes (RR 1.25; P < 0.05). Patients in the high PO(4) group also had non-significantly increased RR of death from other cardiac and cerebrovascular causes of death. The RR of sudden death was also strongly associated with elevated Ca x PO(4) product (RR 1.07 per 10 mg(2)/dl(2); P < 0.005) and serum parathyroid hormone levels greater than 495 pg/ml (RR 1.25; P < 0.05). This study identifies strong relationships between elevated serum PO(4), Ca x PO(4) product, and parathyroid hormone and cardiac causes of death in HD patients, especially deaths resulting from CAD and sudden death. More vigorous measures to reduce the prevalence of these factors in HD patients may result in improved survival.

Adult↗
PubMedDate not supplied

Surveillance of fistula function by frequent recirculation measurements during high efficiency dialysis.

Native fistulae are assumed to remain patent even with low access flows and are likely to cause access recirculation in high efficiency treatments done with high extracorporeal blood flows. We tested whether frequent recirculation measurements could be used to identify fistulae at risk to fail because of low access flow. High efficiency hemodialysis was delivered by 2008H machines equipped with blood temperature monitors (BTM) to measure recirculation within the first hour of every hemodialysis treatment. Access flow was measured when two consecutive BTM recirculation measurements exceeded a threshold of 15%. If access flow was < 500 ml/min, patients were referred for fistula revision. Eighty patients with native AV fistulae were studied for a period of 6 months. Nine of 11 interventions performed during the whole observation period were triggered by a BTM recirculation above the threshold. Two fistulae thrombosed in spite of a BTM recirculation below the threshold. One fistula with a BTM recirculation above the threshold had an access flow of 1,550 ml/min and was not referred for revision. BTM recirculation to detect fistulae for revision is sensitive (81.8%) and specific (98.6%) in the presence of cardiopulmonary recirculation and can be done with minimum intervention and without loss of efficient treatment time.

Adult↗
PubMedDate not supplied

On-line clearance: a useful tool for monitoring the effectiveness of the reuse procedure.

Reprocessing of a dialyzer for repeated use in the same patient is widely practiced. The dialyzer fiber bundle volume (FBV) is monitored as an indicator of the dialyzer's suitability for continued use, with standards for reprocessed dialyzers requiring a FBV of greater than 80% of a new dialyzer to be maintained. We have used on-line measurement of clearance of sodium (OLC module, Fresenius Medical Care, Walnut Creek, CA) to assess small molecule clearance changes during and between treatments for a group of 29 chronic hemodialysis patients who reused high flux polysulfone dialyzers (F80, Fresenius Medical Care, Lexington, MA) reprocessed using citric acid and heat (95 degrees C). Data pertaining to the initial, 5th, 10th, and 15th uses were analyzed and showed that, within a single dialysis session, there was a trend for the clearance to reduce throughout the treatment (p < 0.001). Overall, there was also a trend for clearances to decline with increasing number of reuses (p < 0.008). Changes in FBV occurred, but such changes remained within the guidelines suggested by standards. It is concluded that on-line clearance measurements provide a simple noninvasive method to monitor dialyzer performance over each use and between uses.

Aged↗
PubMedDate not supplied

Nitric oxide and hemodialysis.

Nitric oxide (NO), previously thought of as a noxious gas, is now recognized as an important mediator of vascular responsiveness. Soon after its discovery, it was realized that the actions of NO are similar to the previously described endothelium-derived relaxing factor (EDRF). It is synthesized in the vascular endothelium utilizing the enzyme nitric oxide synthase (NOS) and diffuses in the adjacent vascular media, where it has a vasodilatory action. Opposing actions of NO and vasoconstrictor agents (such as endothelin-1, angiotensin IotaIota, and others) maintain the vascular tone of the renal arteries. The same balance at the level of the macula densa maintains glomerular filtration rate (GFR) during varying levels of salt excretion. Lack of NO can result in disruption of this fine balance, with resultant vasoconstriction and disease progression, hypertension, and accelerated atherosclerosis. In addition, hypertension may result from positive salt balance that occurs when macula densa NOS is inhibited. While most investigators report low levels of NO in uremic subjects, the levels in hemodialysis (HD) patients have not been characterized adequately. This is primarily because HD patients are exposed to both stimulatory and inhibitory factors for NO synthesis. Retention of inhibitors of NOS tends to decrease NO levels, whereas production of NO will be increased by cytokines generated during blood-dialyzer interaction. There is less disagreement, however, over the finding of elevated levels in those with dialyzer reactions and dialysis-induced hypotension. Recent developments in the isolation of inducible and constitutive forms of NOS makes understanding of its pathophysiologic effects more complete. Newer treatment directed at inhibiting only the inducible forms of NOS (sparing the constitutive forms) may soon be found useful for the treatment and prevention of hypotension and dialyzer reactions in HD patients.

Citrulline↗
PubMedDate not supplied

C-reactive protein and end-stage renal disease.

The significance of CRP and inflammation has increased over time, especially in the end-stage renal disease (ESRD) population. From a simple marker it now appears that CRP is an active participant in pro-atherosclerotic phenomenon including local pro-inflammatory and thrombotic events. Studies in the general population indicate the usefulness of CRP in prognostication and in monitoring response to therapy. The clinical usefulness of CRP monitoring in chronic kidney disease (CKD) and especially in ESRD deserves closer study. In the meantime, the utility of CRP measurements for monitoring and treatment is on a case-by-case basis. Management of traditional cardiovascular risk factors should be considered. In the interest of optimizing therapy it is prudent to use biocompatible membranes and ultrapure water. A careful search for infectious processes in dialysis patients is recommended, with special attention to vascular access sites, periodontitis, gastritis, and other potentially chronic or covert infections. ACE-inhibitor use should be maximized in all eligible CKD patients. The data on the use of statins in ESRD have been generally positive but await further validation. Individualized use for selected patients is probably beneficial.

Anemia↗
PubMedDate not supplied

Uremic toxins: a new focus on an old subject.

The uremic syndrome is characterized by an accumulation of uremic toxins due to inadequate kidney function. The European Uremic Toxin (EUTox) Work Group has listed 90 compounds considered to be uremic toxins. Sixty-eight have a molecular weight less than 500 Da, 12 exceed 12,000 Da, and 10 have a molecular weight between 500 and 12,000 Da. Twenty-five solutes (28%) are protein bound. The kinetics of urea removal is not representative of other molecules such as protein-bound solutes or the middle molecules, making Kt/V misleading. Clearances of urea, even in well-dialyzed patients, amount to only one-sixth of physiological clearance. In contrast to native kidney function, the removal of uremic toxins in dialysis is achieved by a one-step membrane-based process and is intermittent. The resulting sawtooth plasma concentrations of uremic toxins contrast with the continuous function of native kidneys, which provides constant solute clearances and mass removal rates. Our increasing knowledge of uremic toxins will help guide future treatment strategies to remove them.

Albumins↗
PubMedDate not supplied

Interdialytic weight gain: implications in hemodialysis patients.

Interdialytic weight gain (IDWG) is an easily measurable parameter in the dialysis unit, routinely assessed at the beginning of the dialysis session. It is used along with clinical symptoms and signs and predialysis blood pressure readings to make decisions regarding the amount of fluid removal during a dialysis session. IDWG is also used as a basis for fluid and salt intake recommendations. However, advising fluid and salt restriction based solely on IDWG may not be appropriate because of its status as a nutritional indicator, as well. Very few studies have been designed to determine the direct effect of IDWG on morbidity and mortality. Any such effect is confounded by residual renal function and various comorbidities, the effects of which might be difficult to separate from those of IDWG. Most attempts to control IDWG have concentrated on requiring patients to reduce fluid and dietary salt intake. Although there does not seem to be a consensus at this point, it is likely that within the lower values of IDWG (less than 5.7% of dry weight), tighter control of fluid and salt intake might not be warranted since these values may reflect higher protein and calorie intake, indicating better nutritional status.

Adult↗