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Hypocalcaemia during plateletpheresis
Transfis. Sci. 1990; 11:217-221 Printed in Great Britain. All rights reserved
Copyright
0955-3886190 $3.00+0.00 @ 1990 Pergamon Press plc
Hypocalcaemia during Plateletpheresis Michael J. D. Cassid , MRCP*$ Lucille Woo B, RM, RNt Peter Jacobs, MD, PhDt
30min prior to the plasmapheresis: this is both inexpensive and well accepted by the majority of individuals undergoing the procedure. n
n Hypocalcaemia is a well recognized side-effect of citrate anticoagulation associated with plateletpheresis. In order to assess the frequency of this complication and to determine whether symptoms could be abolished with oral pretreatment of subjects with milk, calcium or vitamin D we prospectively evaluated total and ionizable serum volunteers calcium in healthy undergoing routine donor plateletpheresis. 39 subjects were divided into four groups. Group 1 consisted of 24 controls and received no pretreatment. The remaining patients were randomly allocated to Group 2 (n=5) who were pretreated with 200 mL pasteurized whole milk 30 min before the procedure, Group 3 (n=5) were pretreated with 1 g effervescent calcium dissolved in 200 mL water, and Group 4 (n=5) to whom 1 pg alphacalcidol was administered 4 h prior to the procedure. 7 of the individuals with no prior oral supplementation developed symptoms of hypocalcaemia, requiring intravenous calcium administration during the procedure, whereas none of the pretreated patients did (P= 0.0225). It is concluded that this unpleasant side effect, which occurs unpredictably, can be avoided by the administration of 200 mL of cow’s milk
INTRODUCTION Therapeutic plasma exchange is increasingly being used for an ever-expanding number of indications,* while closely allied procedures are employed to harvest platelet9 and granulocytes.3 Serious side effects are uncommon and fatal reactions extremely rare and attributed to cardiac arrhythmia.4 In this latter regard a distinction needs to be made between patients undergoing therapeutic procedures and otherwise healthy donors who volunteer to provide components in an apheresis programme. Minor side effects, such as peripheral and circumoral parasthesia due to hypocalcaemia, occur more commonly.5t6 These symptoms are of little clinical importance but can be distressing and may therefore affect the willingness of individuals who donate components. Of note is the association of silent and usually insignificant cardiac conduction disturbances, demonstrable on electrocardiography.7 The present study was designed to deflne biochemical changes in ionizable and total serum calcium levels, to correlate these with plasma citrate concentration, and to determine whether symptoms could be prevented by oral adminis-
Fmm the Universi of Cape Town Leukaemia Centre and the Departments or ‘MeLcine (Renal Unit) and tHaemato&, Groote Schun Hospital Cape Town, South Africa. *Presently Consultant Physician and Senior Lecturer, The ROY~ PoatSraduate Medical School, Hammenmith Hospitak Du Cane Road, London W12 OHS, England. Received 7/89; Accepted 3/90. 1s 11:z-E
217
218
Trunsfus. Sci. Vol. 11, No. 2
tration of fresh cows’ milk, a simple calcium salt, or 1a-hydroxycholecalciferol, each being given prior to the apheresis procedure.
METHODS Donors 39 normal healthy volunteers who fulfilled the American Association of Blood Banks’ criteria for participation in an apheresis programme, attending for routine platelet donation, agreed to enter this prospective study after having had the details fully explained to them. 24 of these individuals acted as controls. The remainder were randomly allocated to Group 2 (n=5) who received 200 mL of pasteurized whole milk 30min before the procedure; Group 3 (n=5) who were given 1 g of effervescent calcium (Calcium Sandoz, Basel, Switzerland) dissolved in 200 mL of water 30 min before the procedure; and Group 4, (n=5) with 1 ug of alphacalcidol (One Alpha, Leo Laboratories Ltd) 4 h before undergoing apheresis. The controls and study groups were comparable in terms of sex and age. These donors were not specifically matched for haematocrit and all had previously undergone plateletpheresis without a history of citrate-related side effects; none had previously been tried on any of these prophylactic measures. The symptomatic donors were not studied further and in subsequent procedures recurrence could be prevented by crossing over into one of the prophylactic treatment arms.
Aphetesis Procedure
Using a vein-to-vein closed circuit, a dual channel and disposable lines, apheresis procedures were carried out on the Cobe 2997 cell separator, as previously described for platelets,2 in which 3.8% sodium citrate was infused at an anticoagulantto-venous whole blood ratio of 1:7.5, with flow rates between 35 and 45 mL/ min. Collection of platelet-rich plasma
took place over 9Omin at a rate of 3 mL/min, with a final volume of 250 mL.
Biochemical
Measurements
Blood was drawn without venous occlusion prior to the apheresis procedure, and at three 30min intervals thereafter. Ionizable calcium was measured using a Radiometer 1CA 1 and total calcium using standard antoanalyzer techniques in all patients (normal range for our laboratory: ionizable calcium I. I1.2 mmol/L, total calcium 2.12.6mmoVL). Serum citrate level was measured at the same time intervals in 5 donors using a potassium permanganate titration technique.
RESULTS The donors consisted of 8 females and 3 1 males, with a median age of 33 yr (range 24-55). Of the 24 controls 7 developed symptomatic hypocalcaemia during the procedure. The features consisted of circumoral and peripheral paresthesia and a feeling of coldness. The time of onset of these symptoms varied from 25 to 90 min and was rapidly relieved by IO mL of 10% intravenous calcium gluconate. The mean ionizable calcium in this group at the onset of symptoms was 0.72 + 0.25mmol/L. This was lower than the ionizable calcium levels in asymptomatic controls at 30 min (0.90 * 0.13 mmoll L), 60min (0.86 + O.O5mmol/L) and 90 min (0.85 f 0.05 mmol/L), which did not reach statistical significance. None of the 39 volunteers developed low magnesium levels. No subjects receiving oral pretreatment with either milk, effervescent calcium or alphacalcidol developed symptoms (P=O.O225; Fisher’s exact test). No symptoms of hypocalcaemia developed in the remaining 17 control individuals or in any of the patients making up the three treatment groups. Ionized calcium fell uniformly and to the
Hypocalcaemia during Plateletpheresis
hypothesis is in keeping with the rising citrate levels from a mean pretreatment level of 0.1 mmol/L to a mean in excess of 1 mmol/L (range 0.48-0.96), which was achieved within 30 min of commencing the procedure and remained constant throughout the infusion (Fig. 1). The sodium citrate flow rate was constant throughout the procedure and maintained an anticoagulant-to-venous whole blood ratio of 1: 7.5; predictably, there was no significant difference in citrate concentration when this was correlated with the size of the donor. At the same time, the total serum calcium remained unchanged. Neither milk, oral calcium nor vitamin D prevented a reduction in ionized calcium for the plateletpheresis procedure described and this fall was remarkably constant between the asymptomatic controls and the three treatment groups.
same extent in all these groups during the procedure (Table 1) and the percentage of ionized to total calcium also decreased (Fig. 1; Table 2), suggesting that this was due to increased amounts of calcium-complex being formed. This
3
0
60
30 TIME
219
90
IN MNUTES
Figure 1. Calcium and citrate kinetics during plasma exchange. The ratio of ionized/ total calcium expressed as a percentage and plotted against duration of plateletpheresis. Corresponding values for plasma citrate levels are shown in mmol/L. Each point represents mean + SEM. ---------Citrate; asymptomatic controls (21= 17);
DISCUSSION
Calcium is found in the circulation in three main forms, with approximately 50% being free or ionized, 40% bound to protein, which is mainly albumin, and
.......... pasteurized whole milk (n=5); la-hyclroxycholecalciferol II(n=5); - - - - - - effervescent calcium (Sandoz)(n=5).
Table 1. Ionized Calcium in the Controls and Three Study Groups Measured 90 min from Commencement of Plateletpheresis
at 0 30, 60 and
Time Asymptomatic controls (n = 17) Milk (n=5) Calcium Sandoz (n=S) Alphacalcidol (n=5)
0
30
60
90
1.12(0.04) l.ll(O.02) 1.13(0.02) l.lO(O.02)
0.90(0.13) 0.93(0.04) 0.93(0.03) 0.94(0.05)
0.86(0.05) 0.90(0.61)
O.SS(O.05) 0.88(0.06)
Results expressed as mean (+ SD) Table 2. The Percentage and Ratio of Ionized Calcium to Total Serum Calcium in the Controls and Three Study Groups Measured at 0, 30, 60 and 90min from Commencement of
Plateletnheresis Time
% Asymptomatic controls (n = 17) Milk (n=5) Calcium Sandoz (n=5) Alphacalcidol (n=5) Results expressed as mean (+ SD)
48.4 47.3 49.0 48.6
0 Ratio 2.2 2.3 1.5 3.1
%
30 Ratio
39.6 41.0 40.3 42.6
5.2 2.1 2.6 4.4
%
60 Ratio
38.5 38.9 37.3 39.4
2.0 2.9 3.2 3.4
%
90 Ratio
38.1 38.4 37.1 38.4
2.6 2.6 3.4 4.0
220
Trunsfis.
Sci.
Vol. 11, No. 2
10% complexed to circulating anions. Citrate-containing anticoagulants exert their effect primarily by forming a complex with the ionized calcium, this may result in hypocalcaemic symptoms and is dependent upon the concentration of citrate, the cumulative dose and rate of its infusion.U In the present study total citrate doses were under 700 mL and there was a fall in both the ionized calcium and the Ca2+ and Ca total ratio in all participants. Symptoms of hypocalcaemia developed in almost one third (29%) of the control group. It is recognized that the citrate dose of 5.07 mg/mL is higher than some of the other methods described, where between 2.00 and 2.75 mg are used. It is possible that with reduced dose the incidence of symptoms may decrease further. Nevertheless, while these subjective findings are not of a serious nature, they are distressing to the donor. It is therefore important to try to prevent their occurrence. The use of half strength acid-citrate-dextrose has been shown to be of benefit,’ as has supplementing the replacement solutions with calcium gluconate. The latter approach is only applicable when heparin is used as the anticoagulant.9 To see these data in perspective, particularly with the increasing use of automated plateletpheresis where lesser amounts of citrate may be infused, it is likely that in the latter circumstances symptoms may be less common but, nevertheless, intravenous calcium is, on occasions, still necessary. Thus, while the incidence of symptoms for any particular method needs to be defined, relatively simple measures such as oral pretreatment with milk, effervescent calcium or alphacalcido1 can prevent even a low incidence of symptomatic hypocalcaemia. It is noteworthy that no difference was demonstrable between those individuals receiving milk, calcium supplements or lahydroxycholecalciferol on the level of ionized calcium and those controls who did not develop symptoms, and, furthermore, the calcium levels between the three treatment groups were comparable. As hypocalcaemic and symptoms of
hypocalcaemia are based on dose delivered per min per L blood volume and the total time of delivery, the absence of symptoms could be explained by the low flow rates of citrate, which averaged 4.6 mL/min. It is concluded that since each of these three options were equivalent in preventing hypocalcaemic symptoms it would be reasonable to offer all individuals undergoing apheresis procedures, where citrate is used as the anticoagulant, a glass of milk immediately prior to the exchange procedure. Should lactose intolerance be present, calcium salts could be used, although they would be marginally more expensive, whereas 1 ahydroxycholecalciferol has the disadvantage of requiring ingestion 4 h before the procedure. This simple practice is an inexpensive means of avoiding troublesome symptoms due to hypocalcaemia in apheresis donors.
Acknowledgements Supported by the University of Cape Town Leukaemia Centre and Staff Research (Foote) Fund, the Nellie Atkinson Trust, the Medical Research Council, and the National CancerAssociation. We thank Dr Peter Berman and Mrs Lucille Human for determination of plasma citrate levels, and [ackie Davies for help with preparation of the manuscript and its typing.
REFERENCES 1. Nose Y, Malchesky PS, Smith JW, Krakauer RS (eds): Plasmapheresis: Therapeutic Applications and New Techniques. New York, Raven Press, 1983.
2. Bond R, Wood L, Jacobs P, Kemoff LM: Platelet collection using the IBM 2997 cell separator. / Clin Apheresis 1985; 2:258-261.
3. Wood L, Hester JP, Jacobs P: The function and structure of granulocytes collected using the IBM 2997 separator. I Clin Apheresis 1985; 2:190-194.
4. Ludbrook J, Wyrm V: Citrate intoxication. A clinical and experimental study. Br Med J 1958; ii:523-528. 5. Bongiovanni MB, Strauss JE, Ziselman EM, Wurzel HA: Parathyroid response during therapeutic plasma exchange. Transfusion 1983; 23~535-536.
Hypocalcaemia during Plateletpheresis 221 6. Hester JP, Ayyar R: Anticoagulation and electrolytes. 1 Clin Apheresis 1984; 2:4151. 7. Olson PR, Cox C, McCullough J: Laboratory and clinical effects of the infusion of ACD solution during plateletpheresis. VOXSang 1977; 33:79-87. 8. Committee on Standards: American
Association of Blood Banks, in Holland PV, Schmidt PJ (eds): Standards for Blood Banks and Transfusion Services, 12th edn, 1987. 9. Buskard NA, Varghese Z, Wills MR: Correction of hypocalcaemic symptoms during plasma exchange. Lancet 1976; ii:344--345.
Copyright
0955-3886190 $3.00+0.00 @ 1990 Pergamon Press plc
Hypocalcaemia during Plateletpheresis Michael J. D. Cassid , MRCP*$ Lucille Woo B, RM, RNt Peter Jacobs, MD, PhDt
30min prior to the plasmapheresis: this is both inexpensive and well accepted by the majority of individuals undergoing the procedure. n
n Hypocalcaemia is a well recognized side-effect of citrate anticoagulation associated with plateletpheresis. In order to assess the frequency of this complication and to determine whether symptoms could be abolished with oral pretreatment of subjects with milk, calcium or vitamin D we prospectively evaluated total and ionizable serum volunteers calcium in healthy undergoing routine donor plateletpheresis. 39 subjects were divided into four groups. Group 1 consisted of 24 controls and received no pretreatment. The remaining patients were randomly allocated to Group 2 (n=5) who were pretreated with 200 mL pasteurized whole milk 30 min before the procedure, Group 3 (n=5) were pretreated with 1 g effervescent calcium dissolved in 200 mL water, and Group 4 (n=5) to whom 1 pg alphacalcidol was administered 4 h prior to the procedure. 7 of the individuals with no prior oral supplementation developed symptoms of hypocalcaemia, requiring intravenous calcium administration during the procedure, whereas none of the pretreated patients did (P= 0.0225). It is concluded that this unpleasant side effect, which occurs unpredictably, can be avoided by the administration of 200 mL of cow’s milk
INTRODUCTION Therapeutic plasma exchange is increasingly being used for an ever-expanding number of indications,* while closely allied procedures are employed to harvest platelet9 and granulocytes.3 Serious side effects are uncommon and fatal reactions extremely rare and attributed to cardiac arrhythmia.4 In this latter regard a distinction needs to be made between patients undergoing therapeutic procedures and otherwise healthy donors who volunteer to provide components in an apheresis programme. Minor side effects, such as peripheral and circumoral parasthesia due to hypocalcaemia, occur more commonly.5t6 These symptoms are of little clinical importance but can be distressing and may therefore affect the willingness of individuals who donate components. Of note is the association of silent and usually insignificant cardiac conduction disturbances, demonstrable on electrocardiography.7 The present study was designed to deflne biochemical changes in ionizable and total serum calcium levels, to correlate these with plasma citrate concentration, and to determine whether symptoms could be prevented by oral adminis-
Fmm the Universi of Cape Town Leukaemia Centre and the Departments or ‘MeLcine (Renal Unit) and tHaemato&, Groote Schun Hospital Cape Town, South Africa. *Presently Consultant Physician and Senior Lecturer, The ROY~ PoatSraduate Medical School, Hammenmith Hospitak Du Cane Road, London W12 OHS, England. Received 7/89; Accepted 3/90. 1s 11:z-E
217
218
Trunsfus. Sci. Vol. 11, No. 2
tration of fresh cows’ milk, a simple calcium salt, or 1a-hydroxycholecalciferol, each being given prior to the apheresis procedure.
METHODS Donors 39 normal healthy volunteers who fulfilled the American Association of Blood Banks’ criteria for participation in an apheresis programme, attending for routine platelet donation, agreed to enter this prospective study after having had the details fully explained to them. 24 of these individuals acted as controls. The remainder were randomly allocated to Group 2 (n=5) who received 200 mL of pasteurized whole milk 30min before the procedure; Group 3 (n=5) who were given 1 g of effervescent calcium (Calcium Sandoz, Basel, Switzerland) dissolved in 200 mL of water 30 min before the procedure; and Group 4, (n=5) with 1 ug of alphacalcidol (One Alpha, Leo Laboratories Ltd) 4 h before undergoing apheresis. The controls and study groups were comparable in terms of sex and age. These donors were not specifically matched for haematocrit and all had previously undergone plateletpheresis without a history of citrate-related side effects; none had previously been tried on any of these prophylactic measures. The symptomatic donors were not studied further and in subsequent procedures recurrence could be prevented by crossing over into one of the prophylactic treatment arms.
Aphetesis Procedure
Using a vein-to-vein closed circuit, a dual channel and disposable lines, apheresis procedures were carried out on the Cobe 2997 cell separator, as previously described for platelets,2 in which 3.8% sodium citrate was infused at an anticoagulantto-venous whole blood ratio of 1:7.5, with flow rates between 35 and 45 mL/ min. Collection of platelet-rich plasma
took place over 9Omin at a rate of 3 mL/min, with a final volume of 250 mL.
Biochemical
Measurements
Blood was drawn without venous occlusion prior to the apheresis procedure, and at three 30min intervals thereafter. Ionizable calcium was measured using a Radiometer 1CA 1 and total calcium using standard antoanalyzer techniques in all patients (normal range for our laboratory: ionizable calcium I. I1.2 mmol/L, total calcium 2.12.6mmoVL). Serum citrate level was measured at the same time intervals in 5 donors using a potassium permanganate titration technique.
RESULTS The donors consisted of 8 females and 3 1 males, with a median age of 33 yr (range 24-55). Of the 24 controls 7 developed symptomatic hypocalcaemia during the procedure. The features consisted of circumoral and peripheral paresthesia and a feeling of coldness. The time of onset of these symptoms varied from 25 to 90 min and was rapidly relieved by IO mL of 10% intravenous calcium gluconate. The mean ionizable calcium in this group at the onset of symptoms was 0.72 + 0.25mmol/L. This was lower than the ionizable calcium levels in asymptomatic controls at 30 min (0.90 * 0.13 mmoll L), 60min (0.86 + O.O5mmol/L) and 90 min (0.85 f 0.05 mmol/L), which did not reach statistical significance. None of the 39 volunteers developed low magnesium levels. No subjects receiving oral pretreatment with either milk, effervescent calcium or alphacalcidol developed symptoms (P=O.O225; Fisher’s exact test). No symptoms of hypocalcaemia developed in the remaining 17 control individuals or in any of the patients making up the three treatment groups. Ionized calcium fell uniformly and to the
Hypocalcaemia during Plateletpheresis
hypothesis is in keeping with the rising citrate levels from a mean pretreatment level of 0.1 mmol/L to a mean in excess of 1 mmol/L (range 0.48-0.96), which was achieved within 30 min of commencing the procedure and remained constant throughout the infusion (Fig. 1). The sodium citrate flow rate was constant throughout the procedure and maintained an anticoagulant-to-venous whole blood ratio of 1: 7.5; predictably, there was no significant difference in citrate concentration when this was correlated with the size of the donor. At the same time, the total serum calcium remained unchanged. Neither milk, oral calcium nor vitamin D prevented a reduction in ionized calcium for the plateletpheresis procedure described and this fall was remarkably constant between the asymptomatic controls and the three treatment groups.
same extent in all these groups during the procedure (Table 1) and the percentage of ionized to total calcium also decreased (Fig. 1; Table 2), suggesting that this was due to increased amounts of calcium-complex being formed. This
3
0
60
30 TIME
219
90
IN MNUTES
Figure 1. Calcium and citrate kinetics during plasma exchange. The ratio of ionized/ total calcium expressed as a percentage and plotted against duration of plateletpheresis. Corresponding values for plasma citrate levels are shown in mmol/L. Each point represents mean + SEM. ---------Citrate; asymptomatic controls (21= 17);
DISCUSSION
Calcium is found in the circulation in three main forms, with approximately 50% being free or ionized, 40% bound to protein, which is mainly albumin, and
.......... pasteurized whole milk (n=5); la-hyclroxycholecalciferol II(n=5); - - - - - - effervescent calcium (Sandoz)(n=5).
Table 1. Ionized Calcium in the Controls and Three Study Groups Measured 90 min from Commencement of Plateletpheresis
at 0 30, 60 and
Time Asymptomatic controls (n = 17) Milk (n=5) Calcium Sandoz (n=S) Alphacalcidol (n=5)
0
30
60
90
1.12(0.04) l.ll(O.02) 1.13(0.02) l.lO(O.02)
0.90(0.13) 0.93(0.04) 0.93(0.03) 0.94(0.05)
0.86(0.05) 0.90(0.61)
O.SS(O.05) 0.88(0.06)
Results expressed as mean (+ SD) Table 2. The Percentage and Ratio of Ionized Calcium to Total Serum Calcium in the Controls and Three Study Groups Measured at 0, 30, 60 and 90min from Commencement of
Plateletnheresis Time
% Asymptomatic controls (n = 17) Milk (n=5) Calcium Sandoz (n=5) Alphacalcidol (n=5) Results expressed as mean (+ SD)
48.4 47.3 49.0 48.6
0 Ratio 2.2 2.3 1.5 3.1
%
30 Ratio
39.6 41.0 40.3 42.6
5.2 2.1 2.6 4.4
%
60 Ratio
38.5 38.9 37.3 39.4
2.0 2.9 3.2 3.4
%
90 Ratio
38.1 38.4 37.1 38.4
2.6 2.6 3.4 4.0
220
Trunsfis.
Sci.
Vol. 11, No. 2
10% complexed to circulating anions. Citrate-containing anticoagulants exert their effect primarily by forming a complex with the ionized calcium, this may result in hypocalcaemic symptoms and is dependent upon the concentration of citrate, the cumulative dose and rate of its infusion.U In the present study total citrate doses were under 700 mL and there was a fall in both the ionized calcium and the Ca2+ and Ca total ratio in all participants. Symptoms of hypocalcaemia developed in almost one third (29%) of the control group. It is recognized that the citrate dose of 5.07 mg/mL is higher than some of the other methods described, where between 2.00 and 2.75 mg are used. It is possible that with reduced dose the incidence of symptoms may decrease further. Nevertheless, while these subjective findings are not of a serious nature, they are distressing to the donor. It is therefore important to try to prevent their occurrence. The use of half strength acid-citrate-dextrose has been shown to be of benefit,’ as has supplementing the replacement solutions with calcium gluconate. The latter approach is only applicable when heparin is used as the anticoagulant.9 To see these data in perspective, particularly with the increasing use of automated plateletpheresis where lesser amounts of citrate may be infused, it is likely that in the latter circumstances symptoms may be less common but, nevertheless, intravenous calcium is, on occasions, still necessary. Thus, while the incidence of symptoms for any particular method needs to be defined, relatively simple measures such as oral pretreatment with milk, effervescent calcium or alphacalcido1 can prevent even a low incidence of symptomatic hypocalcaemia. It is noteworthy that no difference was demonstrable between those individuals receiving milk, calcium supplements or lahydroxycholecalciferol on the level of ionized calcium and those controls who did not develop symptoms, and, furthermore, the calcium levels between the three treatment groups were comparable. As hypocalcaemic and symptoms of
hypocalcaemia are based on dose delivered per min per L blood volume and the total time of delivery, the absence of symptoms could be explained by the low flow rates of citrate, which averaged 4.6 mL/min. It is concluded that since each of these three options were equivalent in preventing hypocalcaemic symptoms it would be reasonable to offer all individuals undergoing apheresis procedures, where citrate is used as the anticoagulant, a glass of milk immediately prior to the exchange procedure. Should lactose intolerance be present, calcium salts could be used, although they would be marginally more expensive, whereas 1 ahydroxycholecalciferol has the disadvantage of requiring ingestion 4 h before the procedure. This simple practice is an inexpensive means of avoiding troublesome symptoms due to hypocalcaemia in apheresis donors.
Acknowledgements Supported by the University of Cape Town Leukaemia Centre and Staff Research (Foote) Fund, the Nellie Atkinson Trust, the Medical Research Council, and the National CancerAssociation. We thank Dr Peter Berman and Mrs Lucille Human for determination of plasma citrate levels, and [ackie Davies for help with preparation of the manuscript and its typing.
REFERENCES 1. Nose Y, Malchesky PS, Smith JW, Krakauer RS (eds): Plasmapheresis: Therapeutic Applications and New Techniques. New York, Raven Press, 1983.
2. Bond R, Wood L, Jacobs P, Kemoff LM: Platelet collection using the IBM 2997 cell separator. / Clin Apheresis 1985; 2:258-261.
3. Wood L, Hester JP, Jacobs P: The function and structure of granulocytes collected using the IBM 2997 separator. I Clin Apheresis 1985; 2:190-194.
4. Ludbrook J, Wyrm V: Citrate intoxication. A clinical and experimental study. Br Med J 1958; ii:523-528. 5. Bongiovanni MB, Strauss JE, Ziselman EM, Wurzel HA: Parathyroid response during therapeutic plasma exchange. Transfusion 1983; 23~535-536.
Hypocalcaemia during Plateletpheresis 221 6. Hester JP, Ayyar R: Anticoagulation and electrolytes. 1 Clin Apheresis 1984; 2:4151. 7. Olson PR, Cox C, McCullough J: Laboratory and clinical effects of the infusion of ACD solution during plateletpheresis. VOXSang 1977; 33:79-87. 8. Committee on Standards: American
Association of Blood Banks, in Holland PV, Schmidt PJ (eds): Standards for Blood Banks and Transfusion Services, 12th edn, 1987. 9. Buskard NA, Varghese Z, Wills MR: Correction of hypocalcaemic symptoms during plasma exchange. Lancet 1976; ii:344--345.