Biomedical subjects

Alberto Magnasco

Publications and source records attributed to Alberto Magnasco.

6 recordsLinked to original sources

PubMed2006

Glucose infusion test (GIT) compared with the saline dilution technology in recirculation measurements.

BACKGROUND: Glucose infusion test (GIT) is a new method to measure vascular access recirculation (R) based on basal glucose increase in the arterial blood line after a 20% glucose bolus (5 ml) into the venous chamber. METHODS: We compared GIT with the ultrasound dilution method (HD01, Transonic Systems Inc., USA) in a circuit reproducing in vitro the phenomenon of R. We repeated the comparison in 162 chronic haemodialysis patients (133 fistulae, 17 central venous catheters, 12 prosthetic grafts). RESULTS: In vitro, we determined the timing for C2 sampling: QB 200 ml/min, C2 16-20 s; QB 300 ml/min, C2 13-17 s; QB 400 ml/min, C2 9-12 s. GIT showed no false positives nor false negatives (100% specificity and sensitivity) while HD01 did not recognize three cases with R=5% (91% sensitivity) and it yielded no false positive (100% specificity). The Bland-Altman analysis showed a bias of 0.2+/-1.3% and 1.3+/-2.9% for GIT and HD01, respectively. In vivo, only 16 out of 162 patients were found positive with both methods (GIT 13.5+/-13%; HD01 16.3+/-15%; P=NS) while three patients with minimal R (GIT 3.2%) were not recognized by HD01 although a low R peak was clearly evident and repeatable on the laptop plot. The Bland-Altman analysis showed an overall bias of 0.2+/-1.7% to the limits of agreement=-3.1 and 3.6% (n=162) and no correlation between the difference and the mean of positive tests. The pooled coefficient of variation of positive cases was 13.3 and 18.1% for GIT and HD01, respectively. DISCUSSION: Our in vitro study showed a good performance of GIT and its better sensitivity compared to HD01. These results were confirmed in vivo with only 3/162 discordant results due to a low R under the HD01 limit of detection (R=5%). In conclusion, the GIT proved to be a very accurate screening test for R, with a very low threshold of detection. In addition, it is simple, user-friendly and inexpensive.

Blood Circulation↗

PubMed2005

Efficacy prospective study of different frequencies of Epo administration by i.v. and s.c. routes in renal replacement therapy patients.

BACKGROUND: The problem of pure red cell aplasia (PRCA) prompted nephrologists to revert to a wider intravenous (i.v.) utilization of erythropoeitin (Epo). Once weekly i.v. Epo administration has been suggested to be as effective as the twice/thrice weekly i.v. dose. The aim of the present study was to test whether once weekly i.v. Epo administration is equally as cost-effective as once weekly subcutaneous (s.c.) and 2-3 times weekly i.v. administration. METHODS: We prospectively studied 41 patients (23 males, aged 28-82 years), on renal replacement therapy for 18-286 months, stabilized on twice or thrice weekly s.c. Epo-alpha (basal). The patients were treated for three consecutive 6 month periods with once weekly s.c. (OWSC), once weekly i.v. (OWIV) and twice/thrice weekly i.v. (TWIV) Epo-alpha. The initial dose for each period was equal to the final dose of the previous one; when necessary, the dose was adjusted according to DOQY guidelines. Iron, folic acid and vitamin B(12) supplementations were given throughout all the study periods. At the end of each of the four study periods, the following parameters were evaluated: haemoglobin, haematocrit, hypochromic red blood cells (RBCs), iron, serum ferritin, transferrin, folate, vitamin B(12), C-reactive protein (CRP), Kt/V, parathyroid hormone (PTH) and weekly dose of Epo-alpha. RESULTS: Thirty-three out of 41 enrolled patients completed the study (there were five deaths, two renal transplants and one transfer). No significant changes were observed as regards iron, serum ferritin, transferrin, folate, vitamin B(12), CRP, Kt/V or PTH level. Haemoglobin levels were not different at the end of the basal (11.7+/-1.21), OWSC (11.8+/-0.86) and TWIV (12.1+/-1.04) periods, while significantly lower levels were observed after the OWIV period (11.0+/-0.97, P<0.01). Weekly Epo consumption (Epo U/week/kg body weight/g haemoglobin) was: basal 11.57+/-5.96; OWSC 10.22+/-4.53; OWIV 15.99+/-7.7*(a); and TWIV 11.89+/-6.3*(a) (*P<0.01 vs basal; (a)P<0.01 vs OWSC). CONCLUSIONS: From our results, the OWIV schedule seems to have less efficacy in the control of anaemia of chronic renal failure patients on dialysis treatment than either OWSC or TWIV schedules.

Adult↗

PubMed2004

Clinical validation of glucose pump test (GPT) compared with ultrasound dilution technology in arteriovenous graft surveillance.

BACKGROUND: Blood flow (Qa) measurements are an important step in the surveillance protocol of haemodialysis vascular access (VA). The glucose pump test (GPT) is a new test for Qa measurement based on the dilution of a constant glucose infusion. The aim of this study is to verify the clinical accuracy of GPT in a graft surveillance protocol with sequential Qa measurements. METHODS: In 30 chronic haemodialysis patients with graft, we compared monthly sequential Qa measurements performed with GPT in pre-dialysis and the ultrasound dilution technique (HD01 device Transonic Systems Inc., USA) during dialysis. The colour Doppler ultrasonography study (CDU) was our reference standard for the diagnosis of stenosis. The endpoints were the graft thrombosis or PTA treatment. RESULTS: According to the K/DOQI guidelines we could identify the thrombosis high-risk grafts when Qa was <600 ml/min or <1000 ml/min with a decrease >25% in serial Qa measurements. HD01 yielded 27 of 112 high-risk Qa measurements (21 Qa <600 ml/min; mean 406+/-145 ml/min; 6 deltaQa >25%; mean 43+/-7%). In 12 of 27 cases the CDU control did not show haemodynamically significant stenoses (false positive); 15 of 27 cases were confirmed high-risk accesses by CDU and did PTAs (HD01 specificity 86%). GPT yielded 14 of 112 high-risk Qa measurements (8 Qa <600 ml/min; mean 404+/-135 ml/min; 6 deltaQa >25%; mean 38+/-8%) and all had severe stenoses and underwent PTA treatments showing a GPT specificity of 100%. The CDU study allowed us to correctly assess the Qa negative cases. HD01 method had 10 false negative cases (treated or clotted grafts with a Qa >600 ml/min and deltaQa <25%) with a sensitivity of 60%, while GPT had 11 false negative cases with a sensitivity of 56%. The diagnostic accuracy tested with the ROC curves was similar with both tests (area under the curve was 0.762 and 0.752 with GPT and ultrasound dilution, respectively; P = 0.985). The diagnostic efficiency (percentage of grafts with agreement between test result and factual situation) was 90 and 80% (P = 0.056) for GPT and HD01, respectively. CONCLUSION: Compared with HD01, the GPT had a lower false positive rate and similar diagnostic accuracy and efficiency. The clinical implication is a smaller number of unnecessary, invasive procedures (angiographies or PTAs), without increasing the thrombosis risk. This study has shown that GPT is an accurate, quick and economic test for Qa monitoring.

Aged↗

PubMed2003

In vivo validation of glucose pump test for measurement of hemodialysis access flow.

BACKGROUND: The glucose pump test (GPT) is a recently introduced method of measuring hemodialysis access blood flow (Qa). A validation of GPT during dialysis has not yet been done, and performance characteristics of the method have not yet been fully analyzed. METHODS: The authors studied 33 patients (25 synthetic grafts, 8 autogenous arteriovenous fistulae). Qa measurements by ultrasound dilution (UD) and GPT were done in triplicate during dialysis. In GPT, a baseline blood sample (C(1)) was obtained, followed by infusion of a 10% glucose solution (C(i)) through the arterial needle into the access at 16 mL/min (Q(i)). After 11 seconds, a downstream blood sample (C(2)) was aspirated from the venous needle. C(1) and C(2) glucose were measured by glucometer. Qa was computed by the equation: Qa = Q(i)(C(i) - C(2))/(C(2) - C(1)). A model of the access vascular circuit was used to determine the influence of C(2) aspiration on the Qa measurement. RESULTS: Mean Qa was 1413 mL/min by UD versus 1,496 mL/min by GPT (P = 0.11). There was a strong linear correlation between the 2 methods (r = 0.905; P <0.001). The pooled coefficient of variation was 6.4% for UD and 9.6% for GPT. The circuit model showed that aspiration of C(2) causes an increase in Qa (DeltaQa) that depends on the aspiration rate (Q(ASP)) and fraction of resistance in the circuit that is downstream to the venous needle: DeltaQa = Q(ASP)(Downstream resistance)/(Total resistance). The model predicts the overestimate is approximately 62 mL/min for grafts and 120 mL/min for fistulae but may vary depending on the balance of resistances upstream and downstream to the venous needle. CONCLUSION: This study shows that GPT closely correlates with UD, and the method has adequate precision. GPT is an inexpensive method that may help make Qa measurements more widely available than previously possible.

Arteriovenous Shunt, Surgical↗

PubMed2002

Glucose pump test: a new method for blood flow measurements.

BACKGROUND: A good test for monitoring blood flow (Q(a)) must be accurate, rapid and economical in order to allow frequent easy measurements. The glucose pump test (GPT) is based on a constant glucose infusion as a dilutional indicator of Q(a). METHODS: GPT protocol requires a constant glucose infusion, by a syringe pump, into the arterial needle and two blood withdrawals from the venous needle, one basal before the infusion (C(a1)), the other (C(a2)) 11 s after the start of the infusion. At the bedside we measure glucose on C(a1) and C(a2). Knowing the infused glucose concentration (C(i)) and the pump infusion rate (Q(i)) we can easily calculate Q(a)=Q(i)x(C(i)-C(a2))/(C(a2)-C(a1)). We verified the accuracy of this new method by comparing it with the in vitro results from a circuit reproducing vascular access circulation, and in vivo comparing GPT-Q(a) with Doppler ultrasound in pre-dialysis to the Transonic HD01-Q(a) during dialysis in 23 chronic haemodialysis patients. RESULTS: GPT-Q(a) values were highly correlated with the in vitro Q(a)=1.01 x GPT-Q(a)-16.6; r=0.94. There was agreement between the mean flow values of GPT and Doppler (927.5 and 927.1 ml/min, respectively; P=NS) while the mean value of HD01 was significantly lower (HD01-Q(a)=690 ml/min; P<0.001 vs GPT-Q(a) and Doppler-Q(a)). The regression analysis showed a good correlation between GPT and Transonic results (r=0.95; HD01-Q(a)=0.86 x GPT-Q(a)-111.9), while there was a significant difference between the two measurements (mean Delta 235+/-117 ml/min; range from 15 to 451 ml/min). This difference could be caused by the large haemodynamic variations (different blood pressure, cardiac output, circulating effective volume, haematocrit) between pre-dialysis and intra-dialysis and in addition by the counter current flow during the reversal blood lines Transonic measurements. CONCLUSIONS: GPT offers the advantage of a simple bedside procedure easily performed before dialysis: it does not interfere with the dialysis treatment and it is less intrusive for the patient as it does not involve reversal of the blood lines. The preliminary data indicate that our method could be a useful, simple and cheap test for monitoring access flow in every dialysis unit.

Blood Circulation↗

PubMedDate not supplied

Thresholds for significant decrease in hemodialysis access blood flow.

During hemodialysis access surveillance, referral for evaluation and correction of stenosis is based upon determination that a significant decrease in blood flow (Q) has occurred. However, criteria for determining when a decrease is statistically significant have not yet been established. In this study we established such criteria by analyzing Q variation with the glucose pump test (GPT). We took nine Q measurements in each of 25 patients (18 grafts, 7 fistulas) during three dialysis sessions within a 2-week period (predialysis and during hours 1 and 3). We determined thresholds that define a significant percentage decrease in Q (deltaQ) for various p values. In order to confirm the general applicability of these thresholds, we computed the average within-patient Q variation during the three sessions (computed as a coefficient of variation and referred to as short-term variation). We then determined the relative influences of biological (true) variation and analytical error on short-term variation. We found that deltaQ must be > 33% to be significant at p < 0.05, whereas the threshold is > 17% for p < 0.20. Measuring Q at uniform versus different times during the sessions did not significantly reduce these thresholds. We also found that biological variation was nearly as large as short-term Q variation, whereas analytical error contributed minimally to short-term variation. In conclusion, this study defines thresholds for a significant deltaQ that have wide application in determining access referral for evaluation and correction of stenosis. Selection of a particular threshold should consider the relative importance of avoiding thrombosis versus avoiding unnecessary procedures. If avoiding unnecessary procedures is a priority, then we recommend a threshold of > 33%. These thresholds apply to other methods of measuring Q, provided analytical error is significantly less than biological variation.

Arteriovenous Shunt, Surgical↗