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Biomedical subjects

F Lopot

Publications and source records attributed to F Lopot.

46 records · Page 3Linked to original sources
PubMed1980

[Prediction of patient reaction to altering the dialysis schedule from 7 hours twice weekly to 4 hours 3 times a week].

The paper presents a computational study dealing with the patient's response to the change in dialysis time schedule from 7 hours twice a week to 4 hours thrice a week. The problem is treated in a purely mathematical way, based on a 3-pool model of the patient-artificial kidney system (one compartment represents patient's intracellular and extracellular volume, respectively, one compartment is reserved for description of the artificial kidney itself). The calculation was performed for two extreme values of intercompartmental permeability coefficient K and for two different values of dialysance of the dialyzer used. The results obtained are presented in form of graphs and tables and are in excellent accordance with the clinical results reported recently by Válek and co-workers.

Computers↗
PubMed1979

Pre-vs. post-dilutional hemofiltration.

The advantages and disadvantages of pre- and postdilution in hemofiltration are discussed, and formulae are derived for sieving coefficient, fractional clearance, and hemofiltration clearance. On the basis of these formulae the two methods are compared, and it is concluded that the present state of membranes is such that the postdilution method is more convenient and cheaper.

Blood↗
PubMedDate not supplied

Vascular access monitoring evaluated from automated recirculation measurement.

Vascular access quality monitoring by means of vascular access blood flow (QVA) evaluated from automated thermodilutional measurement of recirculation with reverse needle position is described. This method provides significant advantages over conventional methods based on simple monitoring of pressures in the extracorporeal circuit and/or measurement of recirculation with normal needle position. AQVA evaluation protocol was developed and introduced into the system of primary nursing. The QVA values were found independent of the extracorporeal blood flow used during the recirculation measurement. QVA values from below 200 ml/min to over 2 l/min were seen. In general, lower values were found in diabetics compared to non-diabetics and in females compared to males. While blood flow below 600 ml/min is considered risky for synthetic vascular grafts, native AV-fistulae seem to remain stable and patent at a flow of 400 ml/min or even below. The method is able to detect erroneous needle placement in looped grafts, stenosis between needles, and is also well suited for effective evaluation of success/failure of interventions on access.

Automation↗
PubMedDate not supplied

Vascular access quality monitoring.

Access dysfunction presents a risk for haemodialysis patients and is costly for health care providers. Regular vascular access quality (VAQ) monitoring enables the detection of adverse access conditions early allowing timely interventions, which will presumably be less invasive, more successful and cheaper. This paper reviews all currently used assessment parameters: dynamic and static pressures, recirculation and blood flow through the access--and analyses pros and cons of each of them. Based on this overview it is concluded that access flow monitoring should be the method of choice, possibly combined with monitoring of another parameter to further enlarge diagnostic possibilities of the monitoring. The VAQ monitoring system developed and used currently in the author's dialysis centre is briefly described as an example. The issue of access flow related to haemodynamics is briefly mentioned. With the introduction of any VAQ monitoring system, one has to acknowledge a change in structure of interventions and that the demand for surgical procedures decreases with a concurrent increase in percutaneous interventions.

Arteriovenous Shunt, Surgical↗
PubMedDate not supplied

Monitoring parameters of dialysis dose.

In order to deliver a specific dialysis dose (Kt/V) to all patients, their product Kt (urea clearance K multiplied by dialysis time t) should be individually adjusted according to total body water (V) of each patient. With dialysis time being fixed in most centres for organisational reasons, such individualization can be accomplished by individually set blood flow (QB). For a given t, the value of QB also defines the magnitude of the cumulative blood volume (VB = QB*t), i.e. the volume of blood perfused through the dialyser during the whole dialysis time. VB is displayed by every contemporary dialysis machine but not used. The aim of this work was to derive an easy to use approach to QB individualization based on patient's body weight and dialysis time to obtain a desired Kt/V value which would also be easy to check after dialysis by looking at the obtained VB value. Statistically significant correlation was found between the QB-based Kt/V estimation and Kt/V determined by the other two methods demonstrating practical feasibility of the novel approach. Kt/V values obtained with the QB prescribed according to patient's body weight tended to be better in females and patients with higher body mass index.

Aged↗
PubMedDate not supplied

Simple pressure measurement is not reliable in detection of access stenosis in native AV fistulas.

Dynamic arterial and venous pressures (PA, PV) are used as the simplest tools to assess vascular access quality (VAQ). An increased PV over three consecutive dialyses is believed to indicate a stenosis, a rule devised for synthetic grafts (AVG) but not adequately validated for AV fistulas (AVF). In this study dynamic PV and static intra-access pressure (calculated by means of the simplified formula PIA=(PA+PV)/2) changes were evaluated in 46 accesses in which balloon angioplasty had to eventually be performed. The whole group consisted of 30 forearm AVF, 5 upper arm AVF and 11 AVG. Pressures were compared in each patient at a time of satisfactory access flow (QVA) and immediately before the angioplasty and pressure difference over that period (deltaPV, deltaPIA) evaluated. Despite a significant drop in QVA over the follow-up interval in both AVF and AVG, the mean deltaPV and deltaPIA in AVF were only several mm Hg and the chosen threshold limit of 20 mmHg was exceeded in approximately 10% of patients only. The results in the AVG group were, however, very different: The mean deltaPV and deltaPIA were close to 20 mmHg and almost 60% of patients in the AVG group exceeded this limit. Evaluation of PIA did not improve stenosis detection in either group. It is concluded that PV and/or PIA monitoring may be useful to detect a stenosis in AVG but not in AVF.

Angioplasty, Balloon↗
PubMedDate not supplied

Comparison of different techniques of hemodialysis vascular access flow evaluation.

Measurement of vascular access flow (QVA) has been suggested as a method of choice for vascular access quality (VAQ) monitoring. Besides traditional duplex Doppler, a number of bedside methods based mostly on the Krivitski principle of QVA evaluation from recirculation at reversed needles (RX), have been developed. This work compares ultrasonic dilution (UD), taken as a reference, HD01, Transonic Systems; duplex Doppler (DD); thermodilution (TD), BTM, Fresenius; optodilutional RX measurement (ORX), Critline III, R-mode, HemaMetrics; direct optodilutional QVA evaluation from jumpwise changes in ultrafiltration rate at both normal and reversed needles connection (OABF), Critline III, ABF-mode; and direct transcutaneous optodilutional QVA evaluation (TQA), Critline III TQA. Firstly, reproducibility of each method was assessed by duplicate measurement at unchanged conditions. This was followed by paired measurement with each method performed at controlled change in relevant measurement condition (two different extracorporeal blood flows in UD and TD, changed sensor position in TQA). Finally paired measurements by each method and the reference method performed at identical conditions were evaluated to assess accuracy of each method. The simple Krivitski formula QVA= QB(1-RX)/RX was used wherever manual QVA calculation was needed. Very high reproducibility was seen in UD, both for measurement at the same extra corporeal blood flow (QB) (correlation coefficient of duplicate measurement r= 0.9702, n= 58) and for measurement at two different QB (r= 0.9735, n= 24), justifying its current status of a reference method in QVA evaluation. Slightly lower reproducibility of TD measurement at the same QB (r= 0.9197, n= 40) and at two different QB (r= 0.8508, n= 168) can be easily overcome by duplicate measurement with averaging. High correlation of TD vs. UD (r= 0.9543, n= 54) makes TD a viable clinical alternative in QVA evaluation. Consistently different QVA obtained at two different QB should prompt closer investigation of anatomical conditions of the access. Use of the simple Krivitski formula in TD (which measures total recirculation, i.e. sum of access recirculation and cardiopulmonary recirculation) brings about underestimation of QVA, which progressively increases from QVA of about 600 ml/min up. Good correlation, although with significant scatter (r= 0.8691, n= 27) was found between the DD- and UD-based QVA. By far the worst reproducibility at the same QB from among the investigated methods was found in ORX (0.6430, n= 23). Also the correlation of ORX vs. UD was lower than in other methods (r= 0.702, n=33) and general overestimation of QVA by about 25% was noted. Correlation of OABF vs. UD (r= 0.6957, n= 26) was slightly better than that of ORX and it gave less overestimated values. The TQA method showed very high reproducibility (r= 0.9712, n= 85), however only for unchanged sensor position. Correlation of QVA measured at two different sensor positions was much worse (r= 0.7255, n= 22). Correspondence of TQA vs. UD was satisfactory (r= 0.8077, n= 36). Skilled and experienced operators are a must with this method.

Journal Article↗
PubMedDate not supplied

Clinical use of continuous blood volume monitoring.

Our department has been using continuous blood volume monitoring (Critline instrument, In-line Diagnostics, Riverdale, USA) for over two years now. First during research on sodium concentration control in haemodialysis (HD), later in the project on assessment and control of hydration in HD patients.

Blood Volume↗