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Amino acid utilization during total parenteral nutrition in the surgical neonate
Amino Acid Utilization During Total Parenteral Nutrition in the Surgical Neonate By John B. Das and Robert M. Filler
I
N INFANTS
TOTAL PARENTERAL nutrition maintained with an infusate containing hypertonic glucose and a nitrogen source derived from a protein hydrolysate or crystalline amino acids usually results in satisfactory weight gains.’ These intravenous solutions supply essential amino acids and nonessential nitrogen together with adequate calories to induce rapid nitrogen retention.2 However, requirements of amino acids administered intravenously have yet to be established. The amino acid pattern of the commercially available crystalline amino acid solutions is based on adult oral requirements, while the pattern of amino acids in the protein hydrolysates is that of fibrin or casein. The quantity of amino acids supplied by the intravenous diets currently in use is in excess of that taken by the normal infant fed by mouth. The possibility that these imbalances or excesses could result in toxicity cannot be ignored. To evaluate amino acid utilization in neonates on these standard intravenous diets, amino acid intake, plasma amino acid levels, and amino acid excretion in urine, were studied in five neonates who required prolonged parenteral feeding after surgery. MATERIALS
AND
METHODS
Five neonates with omphalocele or gastroschisis in whom parenteral feeding was started on the first day of life were studied. Three of the infants were included in a previous report in which other metabolic data have been presented.’ The technical details of parenteral feeding have been described previously.’ The infusates used in this study were: (I) a fat-free mixture of 5% fibrin hydrolysate (Aminosol*) and anhydrous dextrose providing 5.6 g nitrogen and 940 calories per liter of infusate, and (2) a fatfree mixture of 8.5% crystalline amino acids (FreAminet) and dextrose providing 6.5 g nitrogen and 960 calories per liter of infusate. The amino acid compositions of the two infusates as determined in this laboratory are shown in Table I. Although the infused volume and caloric content were essentially the same for each infusate, the crystalline amino acid-dextrose solution supplied more nitrogen and amino acids than the fibrin hydrolysate-dextrose infusate. Daily requirements of all vitamins (except folic acid) and electrolytes were added to the infusate.’ The infants were given I25 ml infusate per kg per day through a central venous catheter
*Aminosol 5% in DS-W: Abbott Laboratories, North Chicago, Ill. t8.5% FreAmine: McGraw Laboratories, Glendale, Calif. From the Department of Surgery, Children’s Hospital Medical Center, and the Hantard Medical School, Boston, Mass. Presented before the Fourth Annual Meeting of The American Pediatric Surgical Association, Phoenix, Ark. April 12-14. 1973. Supported in part by USPHS Grant FRO0128 and 5SOl Fro5482-07. John B. Das, M.D., Ph.D.: Research Associate in Surgery. Children’s Hospital Medical Center: Principal Associate in Surgery, Harvard Medical School, Boston. Mass. Robert M. Filler, M.D.: Chief of Clinical Surgery, Children’s Hospital Medical Center: Associate Professor of Surgery. Children’s Hospital Medical Center, Harvard Medical School. Boston, Mass. Address for reprint requests: Robert M Filler, hf. D.. Department of Surgery, Children’s Hospital Medical Center and the Harvard Medical School, Boston, Mass. 02I IS. o I973 by Grune & Stratton, Inc. Journal of Pediatric Surgery. Vol. 8. No. 5 (October). 1973
793
DAS AND
794
Table 1. Daily Amino Acid Requirements of Aminosol-Dextrose
and Amino Acid Composition
and FreAmine-Dextrose
Mmlmum
Rqts. 1fi males per kg per day) Dally
lnfusates
pm&s/125
ml
AmmosolDextrose
FreAmmeDextrose
Lysine
704
738
Valine
898
582
1600
1143
1473
2410
1197
1740
Leucine lsoleucine
907
Methionine
302
Phenylalanine
545t
’
2375
636
1338
402
1305 1788
Threonine
730
178
Histldine
219
434
725
201
398
Tryptophane Argmine
230
648
Tryosine
360
0
Glycine
3707
12188
Alanine
1082
2955
Ornithine
50
+
Citrulline
16
0
Cystine
66
Serine Proline
FILLER
0
2146
2758
406
4394
*In presence of cystine. t In presence of tryosine.
utilizing a constant infusion pump. Three infants were maintained solely on the fibrin-hydrolysatedextrose solution, and one on the crystalline amino acid-dextrose solution; a fifth infant received the crystalline amino acid mixture for 8 days, followed by the fibrin hydrolysatedextrose solution (8 days). The infants were nursed in a metabolic incubator. All urine, gastric, and fecal outputs were collected in 24-hr pools. The micro-Kjeldahl method was used to determine the nitrogen content of the urine, fecal, and gastric drainage pools and of the infusate. At weekly intervals, plasma and urine concentrations of amino acids were determined by ion-exchange column chromatography. Heparinized blood samples were always taken at 9 a.m. to avoid changes due to circadian rhythms. The plasma was separated immediately and deproteinized with sulfosalicylic acid and stored at -20°C for less than 4 wk before analyses. The free amino acid composition of the urine pools and the infusates were also determined after preliminary treatment of the samples with sulfosalicylic acid. Routine laboratory techniques were employed for plasma and urine creatinine and urea nitrogen determinations. Creatinine clearances for the days on which amino acid analyses were done were calculated from the creatinine data on the timed collections of urine and blood. In the amino acid analysis of the plasma and urine, tryptophane was not assayed because of its binding to serum albumin and subsequent loss during the deproteinization step. In the chromatogram, the threonine peak could not be separated from the glutamine and asparagine peaks. In this study, the daily intake of amino acids was compared with the daily requirements recommended by Holt and Snyderman, and the plasma amino acid levels were compared to normals established by O’Brien, Ibbott, and Rodgerson. RESULTS
With the crystalline amino acid-dextrose solution, intakes of all Ifusates. essential amino acids were in excess of daily requirements with the exception of
AMINO
ACID UTILIZATION
IN SURGICAL
NEONATE
795
l
Fre Amine-dextrose
i Fig. 1. Quantities of essential amino acids provided daily by the Aminosoldextrose and FreAmine-dextrose infusates fed at 125 ml/kg/day. The height of each column represents the daily oral requirement of corresponding amino acid established by Holt and Snyderman for infants.3
Lyr
VOI
Leu
looI_
Met
Phe
Thr
His
Tryp
threonine (Fig. 1). This mixture also provided 12,000 pmoles of glycine per kg body weight per day. The fibrin hydrolysate-dextrose infusate was relatively deficient in valine, phenylalanine, and threonine. The quantity of methionine, leucine, and isoleucine infused with this mixture was in excess of daily recommended allowances, but less so than the quantity provided by the crystalline amino acid infusate. This mixture also provided less glycine (3700 pmole per kg per day) than the crystalline amino acid mixture. Plasma amino acids. The plasma levels of seven essential and two nonessential amino acids in four infants after 7 days of parenteral feeding are compared with “normal” plasma values4 in Fig. 2. Although there were variations between patients, several trends were apparent. Plasma levels of valine, isoleucine, methionine, phenylalanine, tyrosipe, and arginine were within normal limits. Moderate elevations of lysine and leucine were seen in three infants. The elevated plasma glycine levels were the most striking deviations from the normal range. Threonine, asparagine, and glutamine were measured together in the plasma aminograms, and were within normal limits in these four neonates. The variability in the plasma aminograms between individual infants is shown in Figs. 3 and 4. In one infant fed 10% dextrose in water, fibrin
Fig. 2. Plasma amino acid levels in four infants after 7 days of parenteral feeding with Aminosol-dextrose or FreAmine-dextrose. One infant was fed FreAmine and Aminosol sequentially. Each open box represents normal range of corresponding amino acid in 1 -wk-old infants: Plasma levels of nonessential amino acids not shown in figure were within normal limits.
DAS AND
Lys
Vd
Lcu
ISOL
Met
Phe
l’yr
Arq
Sty
FILLER
Fig. 3. Serial plasma amino acid levels in a 3.3-kg infant while being fed iv dextrose in water (second day of life), at the end of parenteral feeding (thirty-third day of life) ahd during oral feebing (fortieth day of life). In all periods, there was remarkable agreement between the individual amino acids which remained within normal limits.
hydrolysate-dextrose infusate, and Similac sequentially, the plasma aminograms were always within the normal range (Fig. 3). Figure 4 shows the plasma aminogram in a 1.6kg baby on the fibrin hydrolysate-dextrose infusate. Elevated plasma levels of lysine, valine, phenylalanine, and glycine were seen. Isoleucine, methionine, and tyrosine were present in trace amounts. This abnormal plasma amino acid pattern persisted even after the infant progressed to oral feedings with a milk-based formula. The eventual growth of the child, physical and mental, has been satisfactory. Amino acid excretion. In all infants, the quantity of essential amino acids found in the urine was less than 2% of that infused. In Table 2 are listed the daily intake and urinary outputs of selected amino acids in an infant maintained on 10% dextrose in water, crystalline amino acid-dextrose infusate, and fibrin hydrolysate-dextrose solution sequentially. These data show that the urinary excretion of amino acids was similar during the infusion of the. two nitrogenous infusates and dextrose in water. Nitrogen utilization. With the fibrin hydrolysate-dextrose mixture providing 0.71 g nitrogen per kg per day and the crystalline amino acid-dextrose providing 0.81 mg nitrogen per kg per day, average nitrogen retentions were
R 8.
Fig. 4. Plasma amino acid levels in a 1.6-kg baby during periods of Aminosol infusion and oral feeding. Abnormal pattern of amino acids essentially the same during either form of feeding.
AMINO
ACID UTILIZATION
Table 2.
IN SURGICAL
NEONATE
797
Daily Intake and Urinary Output of Selected Day 2
Ammo ac!d
Day 18 Amlnosol-Dextrose
FreAmme-Dextrose
D- 1 O/W
lnfusate
Amino Acids in Infant D.S.
Day 11
IV
(fimoles/kg/day)
I”
I”
Intake
intake
Lywx?
4
2355
7
736
Vallne
4
1540
4
563
7
Leucine
1
2130
1
1474
4
lsoleuclne
0
1686
0
1197
0
Methlonlne
+
1295
0
636
2
Phenylalanlne
9
1263
9
402
16
Tyrosine
2
0
3
360
7
Arglnlne
+
627
0
230
+
106
11777
98
3708
154
Glycme
12
Creatlnlne clearance (mVmidl.73
scI m)
37
38
35
278 mg <& 60 SD) per kg per day and 301 mg (& 47 SD) per kg per day for the two infusates, respectively. When the fibrin hydrolysate was infused, 56?; of the total infused nitrogen was excreted in the urine, with 58:/, of the total urinary nitrogen in the form of urea nitrogen. When the neonate was fed the crystalline amino acid-dextrose infusate, 48% of the total nitrogen infused was excreted in the urine, and the urea nitrogen constituted 74% of the total urinary nitrogen. When the infants were weaned to milk formulas (range of nitrogen intake: 0.4-0.5 g per kg per day), only 25% of the ingested nitrogen was excreted in the urine, and urea nitrogen constituted 47% of the total urinary nitrogen. Blood urea nitrogen. Average BUN was 12.4 mg/lOO ml (& 7.6 SD) in infants fed the fibrin hydrolysate-dextrose mixture; 2’1.7 mg/ 100 ml (+ 6.6 SD) in those receiving the crystalline amino acid-dextrose infusate; and 8.5/ 100 ml (‘t 3.1 SD) during periods of oral feeding with milk formulae. Endogenous creatinine clearance. The creatinine clearance values for the five neonates on the last day of parenteral feeding averaged 37 ml/min per 1.73 sq m (range: 32248), and proved normal maturation of neonatal renal function.’ DISCUSSION
The quantity of essential amino acids actually measured in both the fibrin hydrolysateedextrose and crystalline amino acid-dextrose mixtures was less than the amount calculated from the manufacturer’s specifications by as much as 30% to 40%. The glycine content of the fibrin hydrolysate-dextrose solution was found to be 60%. These inconsistencies were also noted by Stegink and Baker6 and by Ghadimi’ and co-workers. In spite of the high isoleucine and methionine contents of both infusates, the respective plasma levels were well within the normal range in all infants. In four term infants, the plasma phenylalanine to tyrosine ratio was near unity, (the ideal ratio), with both infusates even though the crystalline amino aciddextrose infusate contained negligible amounts of tyrosine. This demonstrates
798
DAS AND
FILLER
the ability of a term infant to convert phenylalanine to tyrosine. However, the failure to identify tyrosine in the plasma repeatedly in the face of high plasma phenylalanine levels in one infant (birth weight 1.6 kg) indicates that this conversion does not always occur. A similar metabolic conversion of methionine to cystine was probably responsible for the normal plasma levels of these two amino acids seen after the infusate of the crystalline amino acid-dextrose infusate which contains no cystine but is high in methionine. Normal growth and positive nitrogen balances were seen without excessive amino aciduria and clinical signs of toxicity in all infants maintained on these high nitrogenous diets with less than ideal amino acid patterns. However, some biochemical abnormalities were seen. Plasma lysine, leucine and glycine were consistently elevated. Blood and urine urea nitrogen values were elevated especially with the use of the crystalline amino acid infusate and probably resulted from the high nitrogen and glycine contents of these diets. A higher average positive nitrogen balance was noted in infants fed with crystalline amino acid-dextrose mixture than in those receiving the fibrin hydrolysate-dextrose infusate. However, this difference was not statistically significant. Compared to babies on oral diets in whom the magnitude of nitrogen retention is similar, the urine of infants fed intravenously contained larger quantities of nitrogen. This suggests that quantities of nitrogen given intravenously were in excess of needs. In infants on the crystalline ,amino aciddextrose infusate, the excess nitrogen was excreted mainly in the form of urea (urea nitrogen: 74% of urinary nitrogen). In infants receiving the fibrin hydrolysate-dextrose solution, urea excretion was (urea nitrogen: 58% of total urinary nitrogen), but nonutilizable small peptides (which make up one-third of the nitrogen content of the solution) contributed to the high urinary nitrogen. Our data suggest the need to modify the nitrogen and amino acid content of infusates currently used for parenteral feeding. These modifications can be expected to decrease the metabolic and excretory load on liver and kidneys, and minimize the need for certain amino acid transformations on the part of the neonate. Such innovations will be especially important for infants with low birth weight and premature infants, and others with impaired hepatic and/or renal function who require parenteral feeding.
iess
SUMMARY
Amino acids, urea nitrogen, and creatinine in plasma and urine, and total urinary nitrogen were determined in five neonates during prolonged parenteral feeding. A fibrin hydrolysateedextrose or a crystalline amino acid-dextrose SOlution was infused for periods as long as 33 days. These solutions supplied essential amino acids and total nitrogen (mostly as glycine) in excess of that available to infants on oral diets. Despite weight gain, positive nitrogen balance, and the absence of excessive amino aciduria, several biochemical abnormalities were detected. Plasma lysine, leucine, and glycine were consistently elevated and in one low birth weight infant, plasma phenylalanine and valine were also markedly raised. The exces-
AMINO
ACID
UTILIZATION
IN SURGICAL
NEONATE
799
sive supply of glycine and nitrogen resulted in elevated urea levels in the blood and urine. The capacity to transform phenylalanine to tyrosine and methionine to cystine required by infants fed the tyrosine-cystine-free crystalline amino acid solution may be deficient in low birth weight premature infants and others with impaired liver function. These findings suggest that a more precise tailoring of the amino acid content of infusates for parenteral feeding is indicated. Such individually tailored solutions would decrease the metabolic and excretory load on the liver and kidneys. REFERENCES I. Filler RM, Eraklis AJ, Rubin VG, et al: Long-term parenteral nutrition in infants. N Engl J Med 281:589-594, 1969 2. Das JB, Filler RM, Rubin VG. et al: Intravenous dextrose-amino acid feeding: the metabolic response in the surgical neonate. J Pediatr Surg 5: I27- 135, 1970 3. Holt LE Jr, Snyderman SE: The amino acid requirements of infants. JAMA 175:lOC 103, 1961 4. O’Brien, D, Ibbott FA, Rodgerson DO: Laboratory Manual of Pediatric Microbio-
chemical Techniques (ed 2). New York, Harper & Row, 1968, p 35 5. Vesterdal J: The endocrine control of the water balance in the newborn. Biol Neonat 10:66-75, 1966 6. Stegink LD, Baker GL: Infusion of protein hydrolysates in the newborn infant: plasma amino acid concentrations. J Pediatr 78:595602,l971 7. Ghadimi H, Abaci F, Kumar S, et al: Biochemical aspects of intravenous alimentation. Pediatrics 48:955-965, 1971
Discussion Dr. D. Hays (Los AngelesJ: I can’t compare our data directly because we use a different protein source and my comments concern somewhat slightly older children. Nevertheless, the amino acid variations presented do raise a question. I assume that these levels were during infusion and during a steady-state flow. We have infused various solutions for complete parenteral nutrition for as long as 120 days with varying effects on amino acid levels. The point I want to make is simply that with all of these solutions, even the 6.7% synthetic amino acid solution, all of the levels returned to normal if the child was off the solution for 6 hr. Our high levels of methionine, I think, reflect either the high concentration used or the Amigen source which has added methionine. Again, our methionine levels returned within 6 hr to normal when the infusion ceased. Dr. J. Das (Boston): The blood samples were always taken at 9 a.m. to avoid changes due to circadian rhythm, and they were taken from a peripheral vein when the central venous line was still running. We were worried about the phenomenally low methionine and isoleucine levels which we saw in the plasma. These analyses were cross-checked by other laboratories outside of our hospital. Duplicate samples were analyzed, and we always came within 3Y;-5’?$ of each other. The infusates were also analyzed. We found that amino acid concentrations vary from lot to lot. We came out with 30%-40% less than what is stated as approximate content on the labels. This has been one of the problems, and so we resorted to analysis of the actual infusate the baby was getting. We are still unable to explain this decrease in plasma methionine levels. The urinary data do not show any excessive aminoaciduria either for methionine or isoleucine. The aminoaciduria was with respect to lysine, leucine, and glycine. Tubular reabsorption was about 80% even on the worst aminoaciduric day.
I
N INFANTS
TOTAL PARENTERAL nutrition maintained with an infusate containing hypertonic glucose and a nitrogen source derived from a protein hydrolysate or crystalline amino acids usually results in satisfactory weight gains.’ These intravenous solutions supply essential amino acids and nonessential nitrogen together with adequate calories to induce rapid nitrogen retention.2 However, requirements of amino acids administered intravenously have yet to be established. The amino acid pattern of the commercially available crystalline amino acid solutions is based on adult oral requirements, while the pattern of amino acids in the protein hydrolysates is that of fibrin or casein. The quantity of amino acids supplied by the intravenous diets currently in use is in excess of that taken by the normal infant fed by mouth. The possibility that these imbalances or excesses could result in toxicity cannot be ignored. To evaluate amino acid utilization in neonates on these standard intravenous diets, amino acid intake, plasma amino acid levels, and amino acid excretion in urine, were studied in five neonates who required prolonged parenteral feeding after surgery. MATERIALS
AND
METHODS
Five neonates with omphalocele or gastroschisis in whom parenteral feeding was started on the first day of life were studied. Three of the infants were included in a previous report in which other metabolic data have been presented.’ The technical details of parenteral feeding have been described previously.’ The infusates used in this study were: (I) a fat-free mixture of 5% fibrin hydrolysate (Aminosol*) and anhydrous dextrose providing 5.6 g nitrogen and 940 calories per liter of infusate, and (2) a fatfree mixture of 8.5% crystalline amino acids (FreAminet) and dextrose providing 6.5 g nitrogen and 960 calories per liter of infusate. The amino acid compositions of the two infusates as determined in this laboratory are shown in Table I. Although the infused volume and caloric content were essentially the same for each infusate, the crystalline amino acid-dextrose solution supplied more nitrogen and amino acids than the fibrin hydrolysate-dextrose infusate. Daily requirements of all vitamins (except folic acid) and electrolytes were added to the infusate.’ The infants were given I25 ml infusate per kg per day through a central venous catheter
*Aminosol 5% in DS-W: Abbott Laboratories, North Chicago, Ill. t8.5% FreAmine: McGraw Laboratories, Glendale, Calif. From the Department of Surgery, Children’s Hospital Medical Center, and the Hantard Medical School, Boston, Mass. Presented before the Fourth Annual Meeting of The American Pediatric Surgical Association, Phoenix, Ark. April 12-14. 1973. Supported in part by USPHS Grant FRO0128 and 5SOl Fro5482-07. John B. Das, M.D., Ph.D.: Research Associate in Surgery. Children’s Hospital Medical Center: Principal Associate in Surgery, Harvard Medical School, Boston. Mass. Robert M. Filler, M.D.: Chief of Clinical Surgery, Children’s Hospital Medical Center: Associate Professor of Surgery. Children’s Hospital Medical Center, Harvard Medical School. Boston, Mass. Address for reprint requests: Robert M Filler, hf. D.. Department of Surgery, Children’s Hospital Medical Center and the Harvard Medical School, Boston, Mass. 02I IS. o I973 by Grune & Stratton, Inc. Journal of Pediatric Surgery. Vol. 8. No. 5 (October). 1973
793
DAS AND
794
Table 1. Daily Amino Acid Requirements of Aminosol-Dextrose
and Amino Acid Composition
and FreAmine-Dextrose
Mmlmum
Rqts. 1fi males per kg per day) Dally
lnfusates
pm&s/125
ml
AmmosolDextrose
FreAmmeDextrose
Lysine
704
738
Valine
898
582
1600
1143
1473
2410
1197
1740
Leucine lsoleucine
907
Methionine
302
Phenylalanine
545t
’
2375
636
1338
402
1305 1788
Threonine
730
178
Histldine
219
434
725
201
398
Tryptophane Argmine
230
648
Tryosine
360
0
Glycine
3707
12188
Alanine
1082
2955
Ornithine
50
+
Citrulline
16
0
Cystine
66
Serine Proline
FILLER
0
2146
2758
406
4394
*In presence of cystine. t In presence of tryosine.
utilizing a constant infusion pump. Three infants were maintained solely on the fibrin-hydrolysatedextrose solution, and one on the crystalline amino acid-dextrose solution; a fifth infant received the crystalline amino acid mixture for 8 days, followed by the fibrin hydrolysatedextrose solution (8 days). The infants were nursed in a metabolic incubator. All urine, gastric, and fecal outputs were collected in 24-hr pools. The micro-Kjeldahl method was used to determine the nitrogen content of the urine, fecal, and gastric drainage pools and of the infusate. At weekly intervals, plasma and urine concentrations of amino acids were determined by ion-exchange column chromatography. Heparinized blood samples were always taken at 9 a.m. to avoid changes due to circadian rhythms. The plasma was separated immediately and deproteinized with sulfosalicylic acid and stored at -20°C for less than 4 wk before analyses. The free amino acid composition of the urine pools and the infusates were also determined after preliminary treatment of the samples with sulfosalicylic acid. Routine laboratory techniques were employed for plasma and urine creatinine and urea nitrogen determinations. Creatinine clearances for the days on which amino acid analyses were done were calculated from the creatinine data on the timed collections of urine and blood. In the amino acid analysis of the plasma and urine, tryptophane was not assayed because of its binding to serum albumin and subsequent loss during the deproteinization step. In the chromatogram, the threonine peak could not be separated from the glutamine and asparagine peaks. In this study, the daily intake of amino acids was compared with the daily requirements recommended by Holt and Snyderman, and the plasma amino acid levels were compared to normals established by O’Brien, Ibbott, and Rodgerson. RESULTS
With the crystalline amino acid-dextrose solution, intakes of all Ifusates. essential amino acids were in excess of daily requirements with the exception of
AMINO
ACID UTILIZATION
IN SURGICAL
NEONATE
795
l
Fre Amine-dextrose
i Fig. 1. Quantities of essential amino acids provided daily by the Aminosoldextrose and FreAmine-dextrose infusates fed at 125 ml/kg/day. The height of each column represents the daily oral requirement of corresponding amino acid established by Holt and Snyderman for infants.3
Lyr
VOI
Leu
looI_
Met
Phe
Thr
His
Tryp
threonine (Fig. 1). This mixture also provided 12,000 pmoles of glycine per kg body weight per day. The fibrin hydrolysate-dextrose infusate was relatively deficient in valine, phenylalanine, and threonine. The quantity of methionine, leucine, and isoleucine infused with this mixture was in excess of daily recommended allowances, but less so than the quantity provided by the crystalline amino acid infusate. This mixture also provided less glycine (3700 pmole per kg per day) than the crystalline amino acid mixture. Plasma amino acids. The plasma levels of seven essential and two nonessential amino acids in four infants after 7 days of parenteral feeding are compared with “normal” plasma values4 in Fig. 2. Although there were variations between patients, several trends were apparent. Plasma levels of valine, isoleucine, methionine, phenylalanine, tyrosipe, and arginine were within normal limits. Moderate elevations of lysine and leucine were seen in three infants. The elevated plasma glycine levels were the most striking deviations from the normal range. Threonine, asparagine, and glutamine were measured together in the plasma aminograms, and were within normal limits in these four neonates. The variability in the plasma aminograms between individual infants is shown in Figs. 3 and 4. In one infant fed 10% dextrose in water, fibrin
Fig. 2. Plasma amino acid levels in four infants after 7 days of parenteral feeding with Aminosol-dextrose or FreAmine-dextrose. One infant was fed FreAmine and Aminosol sequentially. Each open box represents normal range of corresponding amino acid in 1 -wk-old infants: Plasma levels of nonessential amino acids not shown in figure were within normal limits.
DAS AND
Lys
Vd
Lcu
ISOL
Met
Phe
l’yr
Arq
Sty
FILLER
Fig. 3. Serial plasma amino acid levels in a 3.3-kg infant while being fed iv dextrose in water (second day of life), at the end of parenteral feeding (thirty-third day of life) ahd during oral feebing (fortieth day of life). In all periods, there was remarkable agreement between the individual amino acids which remained within normal limits.
hydrolysate-dextrose infusate, and Similac sequentially, the plasma aminograms were always within the normal range (Fig. 3). Figure 4 shows the plasma aminogram in a 1.6kg baby on the fibrin hydrolysate-dextrose infusate. Elevated plasma levels of lysine, valine, phenylalanine, and glycine were seen. Isoleucine, methionine, and tyrosine were present in trace amounts. This abnormal plasma amino acid pattern persisted even after the infant progressed to oral feedings with a milk-based formula. The eventual growth of the child, physical and mental, has been satisfactory. Amino acid excretion. In all infants, the quantity of essential amino acids found in the urine was less than 2% of that infused. In Table 2 are listed the daily intake and urinary outputs of selected amino acids in an infant maintained on 10% dextrose in water, crystalline amino acid-dextrose infusate, and fibrin hydrolysate-dextrose solution sequentially. These data show that the urinary excretion of amino acids was similar during the infusion of the. two nitrogenous infusates and dextrose in water. Nitrogen utilization. With the fibrin hydrolysate-dextrose mixture providing 0.71 g nitrogen per kg per day and the crystalline amino acid-dextrose providing 0.81 mg nitrogen per kg per day, average nitrogen retentions were
R 8.
Fig. 4. Plasma amino acid levels in a 1.6-kg baby during periods of Aminosol infusion and oral feeding. Abnormal pattern of amino acids essentially the same during either form of feeding.
AMINO
ACID UTILIZATION
Table 2.
IN SURGICAL
NEONATE
797
Daily Intake and Urinary Output of Selected Day 2
Ammo ac!d
Day 18 Amlnosol-Dextrose
FreAmme-Dextrose
D- 1 O/W
lnfusate
Amino Acids in Infant D.S.
Day 11
IV
(fimoles/kg/day)
I”
I”
Intake
intake
Lywx?
4
2355
7
736
Vallne
4
1540
4
563
7
Leucine
1
2130
1
1474
4
lsoleuclne
0
1686
0
1197
0
Methlonlne
+
1295
0
636
2
Phenylalanlne
9
1263
9
402
16
Tyrosine
2
0
3
360
7
Arglnlne
+
627
0
230
+
106
11777
98
3708
154
Glycme
12
Creatlnlne clearance (mVmidl.73
scI m)
37
38
35
278 mg <& 60 SD) per kg per day and 301 mg (& 47 SD) per kg per day for the two infusates, respectively. When the fibrin hydrolysate was infused, 56?; of the total infused nitrogen was excreted in the urine, with 58:/, of the total urinary nitrogen in the form of urea nitrogen. When the neonate was fed the crystalline amino acid-dextrose infusate, 48% of the total nitrogen infused was excreted in the urine, and the urea nitrogen constituted 74% of the total urinary nitrogen. When the infants were weaned to milk formulas (range of nitrogen intake: 0.4-0.5 g per kg per day), only 25% of the ingested nitrogen was excreted in the urine, and urea nitrogen constituted 47% of the total urinary nitrogen. Blood urea nitrogen. Average BUN was 12.4 mg/lOO ml (& 7.6 SD) in infants fed the fibrin hydrolysate-dextrose mixture; 2’1.7 mg/ 100 ml (+ 6.6 SD) in those receiving the crystalline amino acid-dextrose infusate; and 8.5/ 100 ml (‘t 3.1 SD) during periods of oral feeding with milk formulae. Endogenous creatinine clearance. The creatinine clearance values for the five neonates on the last day of parenteral feeding averaged 37 ml/min per 1.73 sq m (range: 32248), and proved normal maturation of neonatal renal function.’ DISCUSSION
The quantity of essential amino acids actually measured in both the fibrin hydrolysateedextrose and crystalline amino acid-dextrose mixtures was less than the amount calculated from the manufacturer’s specifications by as much as 30% to 40%. The glycine content of the fibrin hydrolysate-dextrose solution was found to be 60%. These inconsistencies were also noted by Stegink and Baker6 and by Ghadimi’ and co-workers. In spite of the high isoleucine and methionine contents of both infusates, the respective plasma levels were well within the normal range in all infants. In four term infants, the plasma phenylalanine to tyrosine ratio was near unity, (the ideal ratio), with both infusates even though the crystalline amino aciddextrose infusate contained negligible amounts of tyrosine. This demonstrates
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DAS AND
FILLER
the ability of a term infant to convert phenylalanine to tyrosine. However, the failure to identify tyrosine in the plasma repeatedly in the face of high plasma phenylalanine levels in one infant (birth weight 1.6 kg) indicates that this conversion does not always occur. A similar metabolic conversion of methionine to cystine was probably responsible for the normal plasma levels of these two amino acids seen after the infusate of the crystalline amino acid-dextrose infusate which contains no cystine but is high in methionine. Normal growth and positive nitrogen balances were seen without excessive amino aciduria and clinical signs of toxicity in all infants maintained on these high nitrogenous diets with less than ideal amino acid patterns. However, some biochemical abnormalities were seen. Plasma lysine, leucine and glycine were consistently elevated. Blood and urine urea nitrogen values were elevated especially with the use of the crystalline amino acid infusate and probably resulted from the high nitrogen and glycine contents of these diets. A higher average positive nitrogen balance was noted in infants fed with crystalline amino acid-dextrose mixture than in those receiving the fibrin hydrolysate-dextrose infusate. However, this difference was not statistically significant. Compared to babies on oral diets in whom the magnitude of nitrogen retention is similar, the urine of infants fed intravenously contained larger quantities of nitrogen. This suggests that quantities of nitrogen given intravenously were in excess of needs. In infants on the crystalline ,amino aciddextrose infusate, the excess nitrogen was excreted mainly in the form of urea (urea nitrogen: 74% of urinary nitrogen). In infants receiving the fibrin hydrolysate-dextrose solution, urea excretion was (urea nitrogen: 58% of total urinary nitrogen), but nonutilizable small peptides (which make up one-third of the nitrogen content of the solution) contributed to the high urinary nitrogen. Our data suggest the need to modify the nitrogen and amino acid content of infusates currently used for parenteral feeding. These modifications can be expected to decrease the metabolic and excretory load on liver and kidneys, and minimize the need for certain amino acid transformations on the part of the neonate. Such innovations will be especially important for infants with low birth weight and premature infants, and others with impaired hepatic and/or renal function who require parenteral feeding.
iess
SUMMARY
Amino acids, urea nitrogen, and creatinine in plasma and urine, and total urinary nitrogen were determined in five neonates during prolonged parenteral feeding. A fibrin hydrolysateedextrose or a crystalline amino acid-dextrose SOlution was infused for periods as long as 33 days. These solutions supplied essential amino acids and total nitrogen (mostly as glycine) in excess of that available to infants on oral diets. Despite weight gain, positive nitrogen balance, and the absence of excessive amino aciduria, several biochemical abnormalities were detected. Plasma lysine, leucine, and glycine were consistently elevated and in one low birth weight infant, plasma phenylalanine and valine were also markedly raised. The exces-
AMINO
ACID
UTILIZATION
IN SURGICAL
NEONATE
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sive supply of glycine and nitrogen resulted in elevated urea levels in the blood and urine. The capacity to transform phenylalanine to tyrosine and methionine to cystine required by infants fed the tyrosine-cystine-free crystalline amino acid solution may be deficient in low birth weight premature infants and others with impaired liver function. These findings suggest that a more precise tailoring of the amino acid content of infusates for parenteral feeding is indicated. Such individually tailored solutions would decrease the metabolic and excretory load on the liver and kidneys. REFERENCES I. Filler RM, Eraklis AJ, Rubin VG, et al: Long-term parenteral nutrition in infants. N Engl J Med 281:589-594, 1969 2. Das JB, Filler RM, Rubin VG. et al: Intravenous dextrose-amino acid feeding: the metabolic response in the surgical neonate. J Pediatr Surg 5: I27- 135, 1970 3. Holt LE Jr, Snyderman SE: The amino acid requirements of infants. JAMA 175:lOC 103, 1961 4. O’Brien, D, Ibbott FA, Rodgerson DO: Laboratory Manual of Pediatric Microbio-
chemical Techniques (ed 2). New York, Harper & Row, 1968, p 35 5. Vesterdal J: The endocrine control of the water balance in the newborn. Biol Neonat 10:66-75, 1966 6. Stegink LD, Baker GL: Infusion of protein hydrolysates in the newborn infant: plasma amino acid concentrations. J Pediatr 78:595602,l971 7. Ghadimi H, Abaci F, Kumar S, et al: Biochemical aspects of intravenous alimentation. Pediatrics 48:955-965, 1971
Discussion Dr. D. Hays (Los AngelesJ: I can’t compare our data directly because we use a different protein source and my comments concern somewhat slightly older children. Nevertheless, the amino acid variations presented do raise a question. I assume that these levels were during infusion and during a steady-state flow. We have infused various solutions for complete parenteral nutrition for as long as 120 days with varying effects on amino acid levels. The point I want to make is simply that with all of these solutions, even the 6.7% synthetic amino acid solution, all of the levels returned to normal if the child was off the solution for 6 hr. Our high levels of methionine, I think, reflect either the high concentration used or the Amigen source which has added methionine. Again, our methionine levels returned within 6 hr to normal when the infusion ceased. Dr. J. Das (Boston): The blood samples were always taken at 9 a.m. to avoid changes due to circadian rhythm, and they were taken from a peripheral vein when the central venous line was still running. We were worried about the phenomenally low methionine and isoleucine levels which we saw in the plasma. These analyses were cross-checked by other laboratories outside of our hospital. Duplicate samples were analyzed, and we always came within 3Y;-5’?$ of each other. The infusates were also analyzed. We found that amino acid concentrations vary from lot to lot. We came out with 30%-40% less than what is stated as approximate content on the labels. This has been one of the problems, and so we resorted to analysis of the actual infusate the baby was getting. We are still unable to explain this decrease in plasma methionine levels. The urinary data do not show any excessive aminoaciduria either for methionine or isoleucine. The aminoaciduria was with respect to lysine, leucine, and glycine. Tubular reabsorption was about 80% even on the worst aminoaciduric day.