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Biomedical subjects

F A Gotch

Publications and source records attributed to F A Gotch.

72 records · Page 4Linked to original sources
PubMedDate not supplied

Evolution of the single-pool urea kinetic model.

Our interest in urea kinetic modeling (UKM) was stimulated some 30 years ago at the time of the advent of hollow fiber kidneys with greatly improved urea transport. This led to examination of the interaction between time and clearance in computing the dialysis dose. In early studies a fixed-volume single-pool UKM was used but this frequently gave spurious high volumes and led to the advent of the variable-volume single-pool model. The role of volume calculation in assessment of the delivered dialysis dose and the value of normalized protein catabolic rate (nPCR) calculation are reviewed. More recently quantification of double-pool effects has become simplified and now is widely used for UKM. The National Cooperative Dialysis Study (NCDS) resulted in the concept of dose quantification by Kt/V. This is reviewed, including the controversy surrounding interpretation of the NCDS. Currently there is great interest in more frequent dialysis, 4-6 days/week. The development of a new dose parameter, the standard Kt/V (stdKt/V), to enable quantitative comparison of dose with widely varying dose schedules is discussed.

Kinetics↗
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Kinetic modeling of continuous flow peritoneal dialysis.

Kinetic models have been derived for analysis of the effects on peritoneal urea clearance (Kp) of continuous single-pass flow of fresh peritoneal dialysate and continuous flow of peritoneal dialysate recirculating through an external dialyzer. Generalized solution of the models shows that both predict Kp to be a well-defined function of the peritoneal mass transfer coefficient (MTC) and the dialysance (D) of the external dialyzer, while the MTC is a function of the rate and distribution of dialysate flow. Thus the models should be useful to guide studies to optimize CFPD. Analysis of reported in vivo data indicate that with dialysate flow rate and D both in the range of 200 ml/min, MTC levels of 60-70 ml/min and Kp levels of 50 ml/min can be achieved. If the model predictions are verified in vivo, 8-hour overnight CFPD 6 nights/week could provide the average-size anephric patient a weekly stdKt/V of 3.2 which is competitive with daily hemodialysis. Kinetic modeling of ultrafiltration indicated ultrafiltration rates 0.2-0.3 L/hr should be achieved with 1.0-1.25% dextrose dialysate. The model shows average rates of glucose absorption can theoretically be reduced by 33% compared to CAPD with the same amount of fluid removal.

Absorption↗
PubMedDate not supplied

Single-pass continuous flow peritoneal dialysis using two catheters.

With a renewed interest in continuous flow peritoneal dialysis (CFPD), our standard practice of implanting a second catheter in those patients facing access failure provided us the opportunity to perform acute studies on CFPD in these patients, since it temporarily provided us with two catheters. Four patients were studied, with a total of five studies performed. A standard protocol was followed utilizing 1.5% dextrose solution, a 2 L fill, an inflow rate of 200 ml/min with a proportionate outflow for a 4-hour session. A full drain was performed at the end of the study. Our results provided us with a mean effective peritoneal clearance for urea (KpeU) and creatinine (KpeCr) of 40 ml/min and 28 ml/min, respectively, and a mean ultrafiltration rate (Qf) of 13.4 ml/min. Our average mass transfer coefficient (MTC) for urea was 40 ml/min, consistent with kinetic modeling and historical data. The Kpe, MTC, and Qf achieved are significantly higher than other investigators, which could possibly be explained by those obtained by two separate catheters resulting in adequate mixing of the dialysate. These clinical results provide a solid foundation for the future development of this PD modality.

Catheterization↗
PubMedDate not supplied

Clinical experience with continuous flow and flow-through peritoneal dialysis.

Concern over the inherent inefficiency of solute removal by conventional peritoneal dialysis (PD) has led to renewed interest in continuous flow PD (CFPD). We present clinical data from two experiences with CFPD. In the first, two catheters were used to recirculate a fixed intraperitoneal volume through an external circuit comprised of a standard hemodialysis system. The second patient had a dual-lumen PD catheter and was studied during two sessions of flow-through PD (FTPD) using sterile PD solution. Urea clearances with both techniques were around 30 ml/min, which is consistent with data reported in the literature. Significant streaming of dialysate from port to port within the peritoneal cavity limited clearances. CFPD offers a potentially safe and effective alternative to daily or nightly home hemodialysis.

Catheterization↗
PubMedDate not supplied

An analysis of thermal regulation in hemodialysis with one and three compartment models.

A one compartment model of heat kinetics in hemodialysis (HD) was formulated, solved for the body surface heat transfer coefficient, and used to analyze reported clinical data. The analysis showed a linear relationship between percent change in body surface (y) and fractional dialyzer (x) heat loss, such that y = -25 - 44X, p less than 0.001. Thus, when X = 0, surface heat loss decreases 25% and core temperature (T) rises, and X must equal 45% of heat production to stabilize core T during HD. A three compartment model predicts that skin clothing insulation will have to increase 2.5 times to avoid thermal discomfort when X = 45% of heat production. A theoretic mechanism for decreased symptomatic hypotension resulting from stabilization of core T is proposed.

Blood Pressure↗
PubMedDate not supplied

Measurement of blood access flow rate during hemodialysis from conductivity dialysance.

An on line clearance monitor automated for measurements of conductivity dialysance (Dcn) was used to measure blood access flow rate (cnQac) during hemodialysis. From mathematical analysis of transport, it was shown that cnQacc = [(Dcn*Decn)/(Dcn - Decn)] [1/bwf], where Dcn is measured with standard cocurrent flow of dialyzer blood (Qb) and Qac; Decn is measured with countercurrent Qb/Qac; and bwf is fractional blood water content. An identical equation was derived to measure Qac from urea dialysance (uQac, Du, Deu). In vitro studies showed excellent correlation between volumetric measurement of Qac (vQac) and cnQac, r = 0.98, n = 29, and between uQac and cnQac, r = 0.97, n = 28. In vivo studies showed comparable agreement between uQac and cnQacc, r = 0.97, n = 14. In two of the patients studied, there was unsuspected severe midgraft stenosis (no recirculation in cocurrent flow) with a Qac of 89 and 202 ml/min disclosed by both cnQac and uQac measurements. Mathematical analysis also showed that when Qb is greater than Qac and there is recirculation in cocurrent flow, the above equations always return the value Qac = Qb. An equation was derived to calculate cnQac without reversal of blood lines in this case, using Dcn calculated from the dialyzer transport coefficient and flow rates.

Blood Flow Velocity↗
PubMedDate not supplied

Theoretical considerations on molecular transport in dialysis and sorbent therapy for uremia.

The technology of uremic blood purification has grown rapidly over the past decade and has provided the clinician with a wide range of therapeutic options. These options involve mass transfer processes which may be primarily due to diffusion or convection, or a combination of both mechanisms. However, regardless of the mechanism of molecular transport, evaluation of the clinical utility of these therapies requires studies which provide sufficient data to solve the appropriate rate equations and to close mass balances. Data from the recent hemodialysis, peritoneal dialysis and sorbent literature are analyzed to show the magnitude of variability in both patient and therapy-related mass balance paramters for urea nitrogen (U) and middle molecules (MM) and to provide unambiguous comparisons for some of these therapies. A theoretical model is developed to describe sorbent-mediated gut elimination of solute as a first-order clearance limited by sorbent saturation. The model is used to analyze data in the literature on AL (OH)3 facilitated gut clearance of phosphate and indicates a gut P clearance of approximately 20 ml/min with maximum removal of approximately 800 mg P/24 hrs. Similar analysis of oxystarch indicated a gut U clearance of 2.5 ml/min and maximum removal of 1.5 gm/24 hrs.

Absorption↗
PubMedDate not supplied

The incident patient cohort study design with uncontrolled dose. Substantial over-estimation of mortality as a function of peritoneal dialysis dose?

In the Canada-USA (CANUSA) Study, the dialysis dose was neither randomized nor held constant, was measured at 6 month intervals, and the relative risk of mortality (R) was found to correlate linearly to mean values of weekly peritoneal plus renal urea clearance normalized to volume, (KprT/ V)m, ranging from 1.5 to 2.3. A risk/dose (R/D) function was derived for continuous ambulatory peritoneal dialysis from kinetic criteria for dose equivalency in hemodialysis (HD) and peritoneal dialysis (PD) and the HD R/D function. This PD R/D function was nonlinear with breakpoint from steep to shallow slope at (KprT/V)ud = 2.00, where ud refers to uniform single doses in contrast to mean doses with wide variances on the mean. The predicted decrease in renal urea clearance KrT/V per 6 months of CANUSA follow-up was computed from serial measured KrT/V in the Randomized Dialysis Prescription and Clinical Outcomes Study and showed it to be 0.21 +/- 0.34. The CANUSA (KprT/V)m values were corrected for the distributed values of 3 months decrements in KrT/V, and the population mortality risk at each (KprT/V)m dose level reported in CANUSA was computed from summation of the product of the R/D curve and fractional distribution of (KprT/V)ud values. From these calculations, the authors conclude that maximum (KprT/V)ud level achieved in CANUSA was 2.00, and the study does not define R/D response above this level.

Analysis of Variance↗