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Calculation of volumes for exchange transfusion
870
Editorial correspondence
Appropriate surveillance data including methods of administration of chloramphenicol in relation to aplastic anemia, and information regarding the number of persons at risk who received oral or parenteral preparations, are lacking. In addition, the pathogenesis of this condition is unknown. No valid scientific data are available to support the notion that the occurrence of aplastic anemia is related to the route of administration of chloramphenicol.
Larry K. Pickering, M.D. Thomas G. Cleary, M.D. Steve Kohl, M.D. University of Texas Health Science Center at Houston 6431 Fannin Houston, TX 77025 REFERENCES
1. Holt R: The bacterial degradation of chloramphenicol, Lancet 1:1259, 1967. 2. Yunis AA, and Bloomberg GR: Chloramphenicol toxicity: Clinical features and pathogenesis, Progr Hematol 4:138, 1967. 3. Best WR: Chloramphenicol-associated blood dyscrasias, JAMA 201:181, 1967. 4. Wallerstein RO, Coudit PK, Kasper CK, Brown JW, and Morrison FR: Statewide study of chloramphenicol therapy and fatal aplastic anemia, JAMA 208:2045, 1969. 5. Hans RJ: Letter, Parke, Davis and Company, Detroit, Michigan, September, 1975. 6. Rosenthan RL, and Blackman A: Bone marrow hypoplasia following use of chloramphenicol eye drops, JAMA 191:136, 1965.
Calculated lengths of umbilical catheters To the Editor: Rosenfeld et alI have presented well-documented prospective data on the use of a new graph for the placement of high umbilical artery lines in small as well as large neonates. The use of their technique is more simple than they anticipated. Their derived graph almost exactly describes the recommendation of Weaver and Ahlgren~ that the catheter be inserted one-third of the infant's total body length. In my experience, graphs are often misplaced when you need them most, so that remembering this "one-third rule" seems easier. I look forward to recommending to our house staff that they should expect 100% satisfactory placement with the one-third the total body length placement, provided that they measure the infants as carefully, and apply the same meticulous care in placing the catheters as did the authors of the Rosenfeld study.
Dale L. Phelps, M.ff. Division of Neonatology Department of Pediatrics Center for the Health Sciences University of California, Los Angeles Los Angeles, CA 90024
The Journal of Pediatrics November 1980
REFERENCES
1. Rosenfeld W, Biagtan J, Schaeffer H, Evans H, Flicker S, Salazar D, and Jhaveri R. A new graph for insertion of umbilical artery catheters, J PEmATR 96:735, 1980. 2. Weaver, R. and Ahlgren, E.: Umbilical artery catheterization in neonates, Am J Dis Child 122:499, 1971.
To the Editor: Dr. Phelps' observation that our recently reported graph for catheter insertion to Ts would follow the "one-third rule" described by Weaver and Ahlegren is a valid one. Although general rules can be helpful much of the time, the "one-third rule" can lead to problems in some instances. In the very premature neonate, in whom the margin of error is smaller, and total body lengths (TBLs) are often _< 36 cm, the line we developed for Ts and that described by the one-third rule begin to diverge. For example, a patient with a TBL of 30 cm would have a catheter inserted 8.5 cm by our graph and 10 cm by the one-third rule. In our nursery these very small patients constitute a large proportion of catheterizations. In 200 consecutively catheterized patients, 62 (31%) have had TBLs _< 36 cm and 9 (4.5%) _< 30 cm. Therefore although the one-third rule can be used as a general guide, the availability of the graph for insertion to T, would still be preferable, especially in patients ~< 36 cm TBL. Dr. Phelps' comments emphasizing the careful measurement of TBL and length of insertion are appreciated. In addition, the fact that all graphs described the distance of insertion from the umbilical ring, making the addition of the length of the umbilical stump and transected cord mandatory, should be stressed. The extra seconds needed to recheck these measurements will be rewarded with an increased rate of accuracy.
Warren Rosenfeld, M.D. Department of Pediatrics, Division of Newborn Medicine Jewish Hospital & Medical Center of Brooklyn The Downstate University School of Medicine 555 Prospect Place Brooklyn, N Y 11238
Calculation of volumes for exchange transfusion To the Editor: The method for calculating volumes for partial exchange transfusion offered by Berman et al, 1 while extremely accurate, is quite cumbersome. This point has elicited comment in these pages by Dr. Landaw, ~ but it seems to me that an essential point has been missed. Berman's method could be made less unwieldy without altering the results by simply reducing the family of "F" values to a single line. Although theoretically having a small effect, the "F" value has no actual effect on exchange volume so derived.
Volume 97 Number 5
Editorial correspondence
However, it would still be necessary to consult a graph each time one wished to perform the procedure; the same is true of Dr. Landaw's method. It would be preferable, by far, to employ a method simple enough to be performed from memory, posing no crises when graphs or complicated formulas are not at hand. The following is an approximation of the exact formula, but is accurate to about 1 to 2% provided that exchange aliquots do not exceed 10% of blood volume (i.e., "F" values __. 0.10). An error of this magnitude is no greater than that introduced by interpolation on the Berman graph, as anyone who has attempted to use it will know. I have employed this method for a number of years with results as predictable as those of Berman et al. It requires only a knowledge of the basic principle of incremental exchange transfusion. desired A Hct Voxchao~o -X blood volume Het increment =
H~ -- H i
H d - (Hf + H,)/2
• blood volume
From a teaching standpoint, this method has the great advantage of reinforcing understanding of the principle each time it is used, thus facilitating the ability to perform the procedure in any situation, with no special aids. From a practical standpoint, in a busy neonatal intensive care unit (NICU) with numerous harried housestaff and busy attending physicians, it is much simpler than methods employing graphs and tables. In the already complex world of the NICU, shouldn't we make every possible attempt to simplify without loss of efficiency?
David H. Levine, M.D. Perinatal Research Fellow Nuffield Institute for Medical Research Headley Way, Headington Oxford OX3 9DS England
REFERENCES 1. Berman B, Krieger A, and Naiman JL: A new method for calculating volumes of blood required for partial exchange transfusion, J P~DIAXR 94:86, 1979. 2. Landaw EM: Volume estimation for partial exchange transfusion (letter), J PEDIATR 95:491, 1979.
Reply To the Editor: Dr. Levine presents in a more accessible form the same formula used by Nieberg and Stockman, 1 which I discussed in my letter? I agree that it yields excellent approximations in the usual clinical range for partial exchange transusions. However, I repeat the caution that moderate ( > 10%) to large errors underestimating the required exchange volume will appear when this formula is used for a greater than 70% replacement of the patient's blood volume (e.g., an exchange volume a little more than the blood volume). Of course this is well outside the range of partial exchanges for which Levine's formula is intended. Both my approximation and the method of Berman et aP are valid for multiple volume as well as partial exchanges. In
871
principle, our formulas could even be used for estimating the large volumes needed in the exchange transfusion treatment of severe poisoning. The terms Hf, Hi, and Hd would apply, respectively, to the final, initial, and donor blood concentrations of the toxin (Ha = 0 presumably), but one would have to augment the estimated patient's blood volume by any equilibrating extravascular volume in which the toxin also distributes. Elliot M. Landaw, M.D. Departments of Biomathematics and Pediatrics UCLA School of Medicine Los Angeles, CA 90024 REFERENCES 1. Nieberg PI, and Stockman JA: Rapid correction of anemia with partial exchange transfusion, Am J Dis Child 131:60, 1977. 2. Landaw EM: Volume estimation for partial exchange transfusion (letter), J PEDIATR 95:490, 1979. 3. Berman B, Krieger A, and Naiman JL: A new method for calculating volumes o f blood required for partial exchange transfusion, J PED1ATR 94:86, 1979.
Screening for metabolic disease To the Editor: In a recent article in T~E JOURNAL, Paul, Naylor, and Guthrie 1 describe a new method which uses urine for screening for metabolic disease in neonates. From an epidemiologic perspective, the test meets most of the requirements necessary for a valid screening procedure, i.e., it makes it possible to identify both diseased (sensitivity) and non-diseased (specificity) individuals in a population. However, as a routine screening procedure it has as a major d r a w b a c k - a n extremely low yield, and consequently, a low cost/benefit ratio as compared to that observed for routine screening of neonates' blood for the detection of treatable inherited metabolic disorders? The authors give two reasons for doing such urine screening: the inability to detect certain metabolic disorders using blood from neonates, and the potential for not identifying an infant with an inherited metabolic defect because the normal length of hospital stay for a neonate does not allow enough time for the evidence of the defect to become detectable. Disorders not detectable by screening blood of neonates that are detectable by screening urine and that also have clinical significance, such as methylmalonic acidemia and argininosuccinic acidemia, generally have incidences in the newborn population of between 1:100,000 and 1:700,000, based on results of urine screening of neonates in Massachusetts? Screening programs and procedures cannot be justified given such low frequencies. At an estimated $0.49/specimen, the cost of screening 100,000 neonates is $49,000, and the probability'of detecting a diseased infant based on these frequencies is quite low. In response to the second reason for doing urine screening, a study of the necessity for a follow-up blood specimen for phenylketonuria (PKU) screening' concluded that the major reason for not detecting neonates with
Editorial correspondence
Appropriate surveillance data including methods of administration of chloramphenicol in relation to aplastic anemia, and information regarding the number of persons at risk who received oral or parenteral preparations, are lacking. In addition, the pathogenesis of this condition is unknown. No valid scientific data are available to support the notion that the occurrence of aplastic anemia is related to the route of administration of chloramphenicol.
Larry K. Pickering, M.D. Thomas G. Cleary, M.D. Steve Kohl, M.D. University of Texas Health Science Center at Houston 6431 Fannin Houston, TX 77025 REFERENCES
1. Holt R: The bacterial degradation of chloramphenicol, Lancet 1:1259, 1967. 2. Yunis AA, and Bloomberg GR: Chloramphenicol toxicity: Clinical features and pathogenesis, Progr Hematol 4:138, 1967. 3. Best WR: Chloramphenicol-associated blood dyscrasias, JAMA 201:181, 1967. 4. Wallerstein RO, Coudit PK, Kasper CK, Brown JW, and Morrison FR: Statewide study of chloramphenicol therapy and fatal aplastic anemia, JAMA 208:2045, 1969. 5. Hans RJ: Letter, Parke, Davis and Company, Detroit, Michigan, September, 1975. 6. Rosenthan RL, and Blackman A: Bone marrow hypoplasia following use of chloramphenicol eye drops, JAMA 191:136, 1965.
Calculated lengths of umbilical catheters To the Editor: Rosenfeld et alI have presented well-documented prospective data on the use of a new graph for the placement of high umbilical artery lines in small as well as large neonates. The use of their technique is more simple than they anticipated. Their derived graph almost exactly describes the recommendation of Weaver and Ahlgren~ that the catheter be inserted one-third of the infant's total body length. In my experience, graphs are often misplaced when you need them most, so that remembering this "one-third rule" seems easier. I look forward to recommending to our house staff that they should expect 100% satisfactory placement with the one-third the total body length placement, provided that they measure the infants as carefully, and apply the same meticulous care in placing the catheters as did the authors of the Rosenfeld study.
Dale L. Phelps, M.ff. Division of Neonatology Department of Pediatrics Center for the Health Sciences University of California, Los Angeles Los Angeles, CA 90024
The Journal of Pediatrics November 1980
REFERENCES
1. Rosenfeld W, Biagtan J, Schaeffer H, Evans H, Flicker S, Salazar D, and Jhaveri R. A new graph for insertion of umbilical artery catheters, J PEmATR 96:735, 1980. 2. Weaver, R. and Ahlgren, E.: Umbilical artery catheterization in neonates, Am J Dis Child 122:499, 1971.
To the Editor: Dr. Phelps' observation that our recently reported graph for catheter insertion to Ts would follow the "one-third rule" described by Weaver and Ahlegren is a valid one. Although general rules can be helpful much of the time, the "one-third rule" can lead to problems in some instances. In the very premature neonate, in whom the margin of error is smaller, and total body lengths (TBLs) are often _< 36 cm, the line we developed for Ts and that described by the one-third rule begin to diverge. For example, a patient with a TBL of 30 cm would have a catheter inserted 8.5 cm by our graph and 10 cm by the one-third rule. In our nursery these very small patients constitute a large proportion of catheterizations. In 200 consecutively catheterized patients, 62 (31%) have had TBLs _< 36 cm and 9 (4.5%) _< 30 cm. Therefore although the one-third rule can be used as a general guide, the availability of the graph for insertion to T, would still be preferable, especially in patients ~< 36 cm TBL. Dr. Phelps' comments emphasizing the careful measurement of TBL and length of insertion are appreciated. In addition, the fact that all graphs described the distance of insertion from the umbilical ring, making the addition of the length of the umbilical stump and transected cord mandatory, should be stressed. The extra seconds needed to recheck these measurements will be rewarded with an increased rate of accuracy.
Warren Rosenfeld, M.D. Department of Pediatrics, Division of Newborn Medicine Jewish Hospital & Medical Center of Brooklyn The Downstate University School of Medicine 555 Prospect Place Brooklyn, N Y 11238
Calculation of volumes for exchange transfusion To the Editor: The method for calculating volumes for partial exchange transfusion offered by Berman et al, 1 while extremely accurate, is quite cumbersome. This point has elicited comment in these pages by Dr. Landaw, ~ but it seems to me that an essential point has been missed. Berman's method could be made less unwieldy without altering the results by simply reducing the family of "F" values to a single line. Although theoretically having a small effect, the "F" value has no actual effect on exchange volume so derived.
Volume 97 Number 5
Editorial correspondence
However, it would still be necessary to consult a graph each time one wished to perform the procedure; the same is true of Dr. Landaw's method. It would be preferable, by far, to employ a method simple enough to be performed from memory, posing no crises when graphs or complicated formulas are not at hand. The following is an approximation of the exact formula, but is accurate to about 1 to 2% provided that exchange aliquots do not exceed 10% of blood volume (i.e., "F" values __. 0.10). An error of this magnitude is no greater than that introduced by interpolation on the Berman graph, as anyone who has attempted to use it will know. I have employed this method for a number of years with results as predictable as those of Berman et al. It requires only a knowledge of the basic principle of incremental exchange transfusion. desired A Hct Voxchao~o -X blood volume Het increment =
H~ -- H i
H d - (Hf + H,)/2
• blood volume
From a teaching standpoint, this method has the great advantage of reinforcing understanding of the principle each time it is used, thus facilitating the ability to perform the procedure in any situation, with no special aids. From a practical standpoint, in a busy neonatal intensive care unit (NICU) with numerous harried housestaff and busy attending physicians, it is much simpler than methods employing graphs and tables. In the already complex world of the NICU, shouldn't we make every possible attempt to simplify without loss of efficiency?
David H. Levine, M.D. Perinatal Research Fellow Nuffield Institute for Medical Research Headley Way, Headington Oxford OX3 9DS England
REFERENCES 1. Berman B, Krieger A, and Naiman JL: A new method for calculating volumes of blood required for partial exchange transfusion, J P~DIAXR 94:86, 1979. 2. Landaw EM: Volume estimation for partial exchange transfusion (letter), J PEDIATR 95:491, 1979.
Reply To the Editor: Dr. Levine presents in a more accessible form the same formula used by Nieberg and Stockman, 1 which I discussed in my letter? I agree that it yields excellent approximations in the usual clinical range for partial exchange transusions. However, I repeat the caution that moderate ( > 10%) to large errors underestimating the required exchange volume will appear when this formula is used for a greater than 70% replacement of the patient's blood volume (e.g., an exchange volume a little more than the blood volume). Of course this is well outside the range of partial exchanges for which Levine's formula is intended. Both my approximation and the method of Berman et aP are valid for multiple volume as well as partial exchanges. In
871
principle, our formulas could even be used for estimating the large volumes needed in the exchange transfusion treatment of severe poisoning. The terms Hf, Hi, and Hd would apply, respectively, to the final, initial, and donor blood concentrations of the toxin (Ha = 0 presumably), but one would have to augment the estimated patient's blood volume by any equilibrating extravascular volume in which the toxin also distributes. Elliot M. Landaw, M.D. Departments of Biomathematics and Pediatrics UCLA School of Medicine Los Angeles, CA 90024 REFERENCES 1. Nieberg PI, and Stockman JA: Rapid correction of anemia with partial exchange transfusion, Am J Dis Child 131:60, 1977. 2. Landaw EM: Volume estimation for partial exchange transfusion (letter), J PEDIATR 95:490, 1979. 3. Berman B, Krieger A, and Naiman JL: A new method for calculating volumes o f blood required for partial exchange transfusion, J PED1ATR 94:86, 1979.
Screening for metabolic disease To the Editor: In a recent article in T~E JOURNAL, Paul, Naylor, and Guthrie 1 describe a new method which uses urine for screening for metabolic disease in neonates. From an epidemiologic perspective, the test meets most of the requirements necessary for a valid screening procedure, i.e., it makes it possible to identify both diseased (sensitivity) and non-diseased (specificity) individuals in a population. However, as a routine screening procedure it has as a major d r a w b a c k - a n extremely low yield, and consequently, a low cost/benefit ratio as compared to that observed for routine screening of neonates' blood for the detection of treatable inherited metabolic disorders? The authors give two reasons for doing such urine screening: the inability to detect certain metabolic disorders using blood from neonates, and the potential for not identifying an infant with an inherited metabolic defect because the normal length of hospital stay for a neonate does not allow enough time for the evidence of the defect to become detectable. Disorders not detectable by screening blood of neonates that are detectable by screening urine and that also have clinical significance, such as methylmalonic acidemia and argininosuccinic acidemia, generally have incidences in the newborn population of between 1:100,000 and 1:700,000, based on results of urine screening of neonates in Massachusetts? Screening programs and procedures cannot be justified given such low frequencies. At an estimated $0.49/specimen, the cost of screening 100,000 neonates is $49,000, and the probability'of detecting a diseased infant based on these frequencies is quite low. In response to the second reason for doing urine screening, a study of the necessity for a follow-up blood specimen for phenylketonuria (PKU) screening' concluded that the major reason for not detecting neonates with