Comparison of filtration to continuous-flow centrifugation for plasma exchange

Optimizing management of replacement fluids for therapeutic plasma exchange: Use of an automated mathematical model to predict post-procedure fibrinogen and antithrombin levels in high-risk patients

BACKGROUND

Therapeutic plasma exchange (TPE) utilizes an extracorporeal circuit to remove pathologic proteins causing serious illness. When processing a patient's entire blood volume through an extracorporeal circuit, proteins responsible for maintaining hemostatic system homeostasis can reach critically low levels if replacement fluid types and volumes are not carefully titrated, which may increase complications.

METHODS

The charts from 27 patients undergoing 46 TPE procedures were reviewed to evaluate the accuracy of our predictive mathematical model, utilizing the following patient information: weight, hematocrit, pre- and post-TPE factor levels (fibrinogen, n = 46, and antithrombin, n = 23), process volume and volumes of fluids (eg, plasma, albumin, and normal saline) administered during TPE and adverse events during and after TPE.

RESULTS

Altogether, 25% of patients experienced minor adverse events that resolved spontaneously or with management. There were no bleeding or thrombotic complications. The mean difference between predicted and measured post-TPE fibrinogen concentrations was -0.29 mg/dL (SD ±23.0, range -59 to 37), while percent difference between measured and predicted fibrinogen concentration was 0.94% (SD ±10.8, range of -22 to 19). The mean difference between predicted and measured post-TPE antithrombin concentrations were 0.89% activity (SD ±10.0, range -23 to 14), while mean percent difference between predicted and measured antithrombin concentrations was 3.87% (SD ±14.5, range -25 to 38).

CONCLUSIONS

Our model reliably predicts post-TPE fibrinogen and antithrombin concentrations, and may help optimize patient management and attenuate complications.

Membrane and centrifugal therapeutic plasma exchange: practical difficulties in anticoagulating the extracorporeal circuit

Therapeutic plasma exchange (TPE) is a well-established treatment modality for nephrology patients, using two conventional methods: membrane (mTPE) or centrifugal TPE (cTPE). Although the efficacy of both treatments has been described, there are few reports that compare these methodologies. Here we describe three nephrology patients who were treated with both mTPE and cTPE. The mTPE method, but not the cTPE method, was associated with persistent difficulty anticoagulating the extracorporeal circuit in all three patients. In mTPE procedures, the doses of heparin bolus and infusion rate were important determinants of whether the circuit clotted. With a heparin bolus at or below 2000 IU, clotting occurred in 67% of treatments, dropping to 25% with a bolus of >2000 IU. Likewise, a heparin infusion rate during the procedure was indicative of clotting. With a maintenance infusion of <2000 IU/h, most circuits clotted. No clotting was observed during cTPE procedures using acid citrate dextrose formula A solution as an anticoagulant of the extracorporeal circuit. Overall, difficulties maintaining the extracorporeal circuit in mTPE required the use of additional disposable sets, high doses of heparin and nursing time. In addition, mTPE procedures took longer to perform than cTPE.

Plasmapheresis: technique and complications

Plasmapheresis has been used in an increasing number of diverse conditions over the past 15 years, and patients on intensive care units are sometimes so treated. This article reviews the principles, different techniques and refinements available, including the more specific methods of antibody removal, such as immunoadsorption. The vascular access, anticoagulation, choice of fluid replacement and monitoring requirements are discussed. The reported possible complications of plasmapheresis, relating both to the practical aspects of the procedure and to the effects of plasma removal and the replacement fluids, are reviewed.

The effect of serial therapeutic plasmapheresis on platelet count, coagulation factors, plasma immunoglobulin, and complement levels

One hundred therapeutic plasmaphereses were carried out at biweekly intervals in seven patients, without morbidity or mortality, using the IBM 2997 blood fraction separator. In standardised procedures, 1.5 times the calculated plasma volume was replaced with an electrolyte solution containing 4% salt-free human albumin. Anticoagulation was achieved using a whole venous blood to acid-citrate dextrose ratio of 11 to 1. Median flow rates, plasma collection, and procedure times were respectively 40 ml/minute, 20 ml/minute, and 3 hours. Haemoglobin and total white cell counts were not significantly affected by the procedures. In contrast, platelet count, fibrinogen, immunoglobulin levels, total haemolytic complement, as well as C3 and C4 fractions fell, and the prothrombin and partial thromboplastin times were lengthened by the exchanges. All these measurements had returned to normal within 24 hours, apart from the fibrinogen, which took between 48 and 72 hours, and the immunoglobulin level, which required 35 days to return to baseline. In a further patient, more detailed studies (n = 13) were carried out to characterise the behaviour of antithrombin III and factor VIII. Both levels were markedly reduced immediately following the procedure and, like fibrinogen, had returned to normal within 48 hours. These data indicate that in an isovolemic plasmapheresis there was a transient but rapidly reversible effect on all the factors studied, with fibrinogen level, antithrombin III, and factor VIII returning more slowly to normal than the others, and immunoglobulin levels responding the slowest. None of these changes was associated with clinically significant haemostatic abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

The epipodophyllotoxin VP16-213 in combination chemotherapy for adults with acute nonlymphoblastic leukaemia

A total of 232 previously untreated adults with acute nonlymphoblastic leukaemia were consecutively entered into four successive studies. In the first, complete remission rates and survival were inferior to a group treated on the same regimen in London, suggesting population differences, possibly on the basis of late referral and poor nutritional status. In the second study the addition of the epipodophyllotoxin VP16-213 to conventional doses of doxorubicin and cytosine arabinoside improved complete remission rate and median duration of survival. In the third study this induction programme was unchanged and short duration of intensification was compared with an extended period, but no statistically significant difference was demonstrated. In the fourth study, which is currently active, the role of the epipodophyllotoxin VP16-213 (Cape Town Regimen/CTR III) was compared with the same two agents in combination with thioguanine (DAT), but to date no difference in remission rate or survival is evident. Four conclusions are supported by data from these studies. First, the addition of VP16-213 to doxorubicin and cytosine arabinoside improves complete remission rate, prolongs median duration of complete remission and survival, with shortening of the time taken to achieve this status in our population. Second, evidence to date shows no advantage for the DAT programme containing thioguanine over CTR III in which this latter agent is replaced by the epipodophyllotoxin VP16-213. Third, there is no statistically significant difference in survival once patients have achieved complete remission following randomisation to receive 6 months in comparison with 15 months of intensification therapy. Finally, of the previously described prognostic factors, only response to initial chemotherapy has proved significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclophosphamide-related intravascular haemolysis during continuous-flow plasma exchange

The plasma of a patient being prepared for allogeneic bone marrow transplantation was found to be severely lymphocytotoxic to donor cells. Three isovolaemic plasma exchanges carried out using a continuous-flow technique were required to reduce this titre to undetectable levels. Neither these procedures nor pretransplantation conditioning of the patient with 60 mg/kg or cyclophosphamide on two consecutive days resulted in overt haemolysis. However, a single identical plasmapheresis 12 hours after completing the second dose of the alkylating agent resulted in profound intravascular haemolysis requiring red cell transfusion. Subsequent studies in five patients receiving the same cyclophosphamide regimen demonstrated that red cell life span, when measured with radiochromium, was reduced from a normal of 25-35 days to a median of 11.5 days. Further studies in the same five patients carried out simultaneously demonstrated that red cell fragility, when assessed in vitro with osmotic or mechanical stress, was marginally increased but became clearly abnormal in only one individual. These doses of cyclophosphamide may result in accelerated but subclinical red cell destruction, and plasma exchange in this period may be associated with rapid intravascular haemolysis. This complication should now be added to the list of those that can occur when plasmapheresis is required in this specific clinical situation.