Metabolic acidosis resulting from intravenous alimentation mixtures containing synthetic amino acids

The evolution of nutritional care in preterm infants with a focus on the extreme preterm infant

The evolution of nutritional care in preterm infants, particularly those classified as extremely preterm, has undergone significant advancements in recent years. These infants, born at less than 28 weeks of gestation, face unique challenges related to their elevated nutrient requirements, underdeveloped organ systems and minimal reserves, posing a need for timely and specialised nutritional strategies. Historically, the nutritional management of preterm infants focussed on short-term goals to promote survival. In recent years, the focus has shifted to the quality of nutrient provision to optimise neurodevelopment and longer-term health outcomes. This review highlights the shift from a generalised nutritional approach to a robust, evidence-based approach for preterm infants, acknowledging the intricate interplay between nutrition, holistic care and developmental outcomes. As neonatal care continues to evolve, ongoing research will refine nutritional interventions, optimise growth and enhance the long-term health outcomes of these vulnerable infants.

A Review of Bicarbonate Use in Common Clinical Scenarios

BACKGROUND

The use of sodium bicarbonate to treat metabolic acidosis is intuitive, yet data suggest that not all patients benefit from this therapy.

OBJECTIVE

In this narrative review, we describe the physiology behind commonly encountered nontoxicologic causes of metabolic acidosis, highlight potential harm from the indiscriminate administration of sodium bicarbonate in certain scenarios, and provide evidence-based recommendations to assist emergency physicians in the rational use of sodium bicarbonate.

DISCUSSION

Sodium bicarbonate can be administered as a hypertonic push, as a resuscitation fluid, or as an infusion. Lactic acidosis and cardiac arrest are two common scenarios where there is limited benefit to routine use of sodium bicarbonate, although certain circumstances, such as patients with concomitant acute kidney injury and lactic acidosis may benefit from sodium bicarbonate. Patients with cardiac arrest secondary to sodium channel blockade or hyperkalemia also benefit from sodium bicarbonate therapy. Recent data suggest that the use of sodium bicarbonate in diabetic ketoacidosis does not confer improved patient outcomes and may cause harm in pediatric patients. Available evidence suggests that alkalinization of urine in rhabdomyolysis does not improve patient-centered outcomes. Finally, patients with a nongap acidosis benefit from sodium bicarbonate supplementation.

CONCLUSIONS

Empiric use of sodium bicarbonate in patients with nontoxicologic causes of metabolic acidosis is not warranted and likely does not improve patient-centered outcomes, except in select scenarios. Emergency physicians should reserve use of this medication to conditions with clear benefit to patients.

Implementation of nutrition practice improves growth velocity and weight gain in premature infants ≤ 1250 grams

BACKGROUND

The concept of parental nutritional care for premature infants has been applied and advanced over the past decade. This study compared the clinical outcomes before and after nutrition practice (NP) implementation and evaluated the effects of implementation on growth velocity and weight gain in premature infants.

METHODS

Descriptive data of premature infants (gestational age < 30 weeks; body weight ≤ 1250 g) born 4 years before and after NP implementation were retrospectively reviewed in a neonatal intensive care unit at a hospital in Taiwan. Nutrient intake, growth velocity, weight gain, and nutrition-related biochemical markers were compared at weeks 1, 2, and 4 after delivery.

RESULTS

A total of 77 premature infants were enrolled before NP implementation (non-NP group), whereas 89 were enrolled after implementation (NP group). The non-NP group consumed less fat and energy in week 1, and less protein, fat, and energy in weeks 2 and 4 compared with the NP group. Growth velocity was slower in the non-NP group. Fat intake was significantly positively correlated with body weight at week 4 in the non-NP group. However, protein and fat intake were significantly associated with body weight at week 1, fat and energy intakes were significantly associated with body weight at week 2, and fat intake was significantly associated with body weight at week 4 in the NP group.

CONCLUSION

These findings indicate that the NP implemented in this study is relatively safe and can improve growth velocity and body weight gain in premature infants.

The Impact of Intravenous Fluid Therapy on Acid-Base Status of Critically Ill Adults: A Stewart Approach-Based Perspective

One of the most important tasks of physicians working in intensive care units (ICUs) is to arrange intravenous fluid therapy. The primary indications of the need for intravenous fluid therapy in ICUs are in cases of resuscitation, maintenance, or replacement, but we also load intravenous fluid for purposes such as fluid creep (including drug dilution and keeping venous lines patent) as well as nutrition. However, in doing so, some facts are ignored or overlooked, resulting in an acid-base disturbance. Regardless of the type and content of the fluid entering the body through an intravenous route, it may impair the acid-base balance depending on the rate, volume, and duration of the administration. The mechanism involved in acid-base disturbances induced by intravenous fluid therapy is easier to understand with the help of the physical-chemical approach proposed by Canadian physiologist, Peter Stewart. It is possible to establish a quantitative link between fluid therapy and acid–base disturbance using the Stewart principles. However, it is not possible to accomplish this with the traditional approach; moreover, it may not be noticed sometimes due to the normalization of pH or standard base excess induced by compensatory mechanisms. The clinical significance of fluid-induced acid-base disturbances has not been completely clarified yet. Nevertheless, as fluid therapy may be the cause of unexplained acid-base disorders that may lead to confusion and elicit unnecessary investigation, more attention must be paid to understand this issue. Therefore, the aim of this paper is to address the effects of different types of fluid therapies on acid-base balance using the simplified perspective of Stewart principles. Overall, the paper intends to help recognize fluid-induced acid-base disturbance through bedside evaluation and choose an appropriate fluid by considering the acid-base status of a patient.

Avoiding Patient Harm With Parenteral Nutrition During Electrolyte Shortages

Purpose: We report a case of a patient with gastrointestinal dysmotility and substantial drainage losses who required parenteral nutrition (PN) and developed a non-anion gap metabolic acidosis secondary to a shortage of concurrent potassium acetate and sodium acetate PN additives. We describe how severe PN-associated metabolic consequences were averted during this acetate shortage. Summary: The patient with inability to swallow and significant weight loss was admitted to the hospital and given PN after failure to tolerate either gastric or jejunal feeding due to dysmotility and severe abdominal distension and discomfort. PN was initiated and the nasogastric and jejunal tubes were left to low intermittent suction or gravity drainage (average losses of 800 mL and 1600 mL daily, respectively) to reduce abdominal distension. The patient had been stable on PN for approximately 2 months prior to when a shortage in potassium acetate and sodium acetate occurred. As a result, potassium and sodium requirements had to be met with chloride and phosphate salts. The patient developed a non-anion gap metabolic acidosis after 11 days of acetate-free PN. Progression to severe acidemia was avoided by administration of sodium bicarbonate daily for 3 days and replacement of 0.9% sodium chloride supplemental intravenous fluid with lactated ringers solution. Conclusion: This case report illustrates that PN component shortages require clinicians to closely monitor patients who require PN. In addition, clinicians may need to use creative therapeutic strategies to avoid potential serious patient harm during PN component shortages.

Low- versus High-Dose and Early versus Late Parenteral Amino-Acid Administration in Very-Low-Birth-Weight Infants: A Systematic Review and Meta-Analysis

OBJECTIVES

Providing parenteral amino acids to very-low-birth-weight infants during the first weeks of life is critical for adequate growth and neurodevelopment. However, there is no consensus about what dose is appropriate or when to initiate supplementation. As a result, daily practice varies among neonatal intensive care units. The objective of our study was to determine the effects of early parenteral amino-acid supplementation (within 24 h of birth) versus later initiation and high dose (>3.0 g/kg/day) versus a lower dose on growth and morbidities.

METHODS

A systematic review and meta-analysis of publications identified by searching PubMed, EMBASE, and Cochrane databases was conducted. Randomized controlled studies were eligible if information on growth was available.

RESULTS

The search identified 14 studies. No differences were observed in growth or morbidity after early or high-dose amino-acid supplementation, but for several outcomes, meta-analysis was not possible due to study heterogeneity. Initiation of amino acids within the first 24 h of life appeared to be safe and well tolerated, and leads more rapidly to a positive nitrogen balance.

CONCLUSIONS

Administering a high dose (>3.0 g/kg/day) or an early dose (≤24 h) of parenteral amino acids is safe and well tolerated but does not offer significant benefits on growth. Further large-scale randomized controlled trials in preterm infants are needed to study the effects of early and high-dose amino acids on growth and morbidity more consistently and extensively.

Early optimal parenteral nutrition and metabolic acidosis in very preterm infants

BACKGROUND

It is currently recognized that an optimized nutritional approach, consisting of an early and substantial supply of protein and energy by parenteral route, may be beneficial for very low birth weight infants and recent guidelines endorse this strategy. However, the impact of the enhanced parenteral nutrition (PN) on acid-basic balance has never been investigated. The aim of the present study is to assess the effect of nutrient intake on acid-base homeostasis in a large population of preterm infants on PN.

METHODS

This observational study described the acid-base profile of very preterm infants (≤29 week's gestation) receiving PN during the first week of life. For this purpose three different cohorts of infants who received increasing (group 1 to group 3) nutritional intakes were considered. Nutrition data were recorded daily and correlated to acid-base data (pH, base excess, and lactate). The outcome measure to assess metabolic acidosis was the base excess (BE).

RESULTS

161 infants were included. 1127 daily nutritional records and 795 blood gas data were analyzed. The three groups were different with regard to nutritional intravenous intakes. Group 3 in particular had a higher mean intake of both amino acids (3.3 ± 0.8 g/kg/d) and lipids (2.8 ± 1.4 g/kg/d) during the first week of life. Metabolic acidosis was more severe in the group with the highest parenteral intake of amino acids and lipids: mean BE = -8.7 ± 3.4 (group 3); -6.4 ± 3.4 (group 2); -5.1 ± 3.0 (group 1)]. At the multivariate analysis the significant risk factors for metabolic acidosis were: gestational age, initial base excess, amino acid and lipid intravenous intakes.

DISCUSSION

Acid-base homeostasis was influenced by the nutritional intake. Earlier and higher intravenous amino acid and lipid intakes particularly increased the risk of metabolic acidosis. The nutritional tolerance was different depending on gestational age, and the smaller infants (24-26 week's gestation) displayed greater acidotic disequilibrium and a higher need of bicarbonate.

Biological Impact of Recent Guidelines on Parenteral Nutrition in Preterm Infants

OBJECTIVES

Recent guidelines for preterm neonates recommend early initiation of parenteral nutrition (PN) with high protein and relatively high caloric intake. This review considers whether these changes could influence homeostasis in very preterm infants during the first few postnatal weeks.

METHODS

This systematic review of relevant literature from searches of PubMed and recent guidelines was reviewed by investigators from several perinatal centers in France.

RESULTS

New recommendations for PN could be associated with metabolic acidosis via the increase in the amino acid ion gap, hyperchloremic acidosis, and ammonia acidosis. The introduction of high-intake amino acids soon after birth could induce hypophosphatemia and hypercalcemia, simulating a "repeat feeding-like syndrome" and could be prevented by the early intake of phosphorus, especially in preterm infants born after fetal growth restriction. Early high-dose amino acid infusions are relatively well tolerated in the preterm infant with regard to renal function. Additional studies, however, are warranted to determine markers of protein intolerance and to specify the optimal composition and amount of amino acid solutions.

CONCLUSIONS

Optimal PN following new guidelines in very preterm infants, despite their demonstrated benefits on growth, may induce adverse effects on ionic homeostasis. Clinicians should implement appropriate monitoring to prevent and/or correct them.

Metabolic acidosis during parenteral nutrition: Pathophysiological mechanisms

Total parenteral nutrition (TPN) is associated with metabolic complications including metabolic acidosis (MA), one of the main disorders of acid-base balance. The main causes involved in the appearance of MA during TPN administration are the metabolism of cationic amino acids and amino acids containing sulfuric acid (exogenous addition), the titratable acidity of the infused parenteral solution, the addition of acidificant agents (hydrochloric acid, acetic acid), thiamine deficiency, disruption of carbohydrate and lipid metabolic pathways and D-fructose administration. Moreover, hypophosphatemia that appears during TPN therapy contributes significantly to the maintenance of MA. This review describes in a comprehensive way the pathophysiological mechanisms involved in the appearance of MA induced by intravenous administration of TPN products most commonly used in critically ill-patients.

History of medical understanding and misunderstanding of Acid base balance

To establish how controversies in understanding acid base balance arose, the literature on acid base balance was reviewed from 1909, when Henderson described how the neutral reaction of blood is determined by carbonic and organic acids being in equilibrium with an excess of mineral bases over mineral acids. From 1914 to 1930, Van Slyke and others established our acid base principles. They recognised that carbonic acid converts into bicarbonate all non-volatile mineral bases not bound by mineral acids and determined therefore that bicarbonate represents the alkaline reserve of the body and should be a physiological constant. They showed that standard bicarbonate is a good measure of acidosis caused by increased production or decreased elimination of organic acids. However, they recognised that bicarbonate improved low plasma bicarbonate but not high urine acid excretion in diabetic ketoacidosis, and that increasing pCO2 caused chloride to shift into cells raising plasma titratable alkali. Both indicate that minerals influence pH. In 1945 Darrow showed that hyperchloraemic metabolic acidosis in preterm infants fed milk with 5.7 mmol of chloride and 2.0 mmol of sodium per 100 kcal was caused by retention of chloride in excess of sodium. Similar findings were made but not recognised in later studies of metabolic acidosis in preterm infants. Shohl in 1921 and Kildeberg in 1978 presented the theory that carbonic and organic acids are neutralised by mineral base, where mineral base is the excess of mineral cations over anions and organic acid is the difference between mineral base, bicarbonate and protein anion. The degree of metabolic acidosis measured as base excess is determined by deviation in both mineral base and organic acid from normal.

Initial nutritional management of the preterm infant

Postnatal nutrition has a large impact on long-term outcome of preterm infants. Evidence is accumulating showing even a relationship between nutrient supply in the first week of life and later cognitive development in extremely low birth weight infants. Since enteral nutrition is often not tolerated following birth, parenteral nutrition is necessary. Yet, optimal parenteral intakes of both energy and amino acids are not well established. Subsequently, many preterm infants fail to grow well, with long-term consequences. Early and high dose amino acid administration has been shown to be effective and safe in very low birth weight infants, but the effect of additional lipid administration needs to be defined.

Clinical utility of anion gap in deciphering acid-base disorders

The anion gap (AG) measurement is a very useful tool in the evaluation of patients with acid-base disorders. Once metabolic acidosis is identified, AG will provide the important first step in the differential diagnosis of disorders that either increase the AG and those that leave the AG unchanged. Delta gap is the comparison between change (delta) in the AG and the change (delta) in bicarbonate (HCO(3)(-)). Delta ratio, defined as delta AG:delta HCO(3)(-) is usually 1:1 in patients with an uncomplicated high AG acidosis. A value below 1:1 suggests a combined high and normal AG acidosis. A value above 2:1 suggests a combined metabolic alkalosis and a high AG acidosis. Urine AG (unmeasured anions-unmeasured cations) is an indirect estimate of the urine NH(4)(+) excretion. It is typically negative in patients with normal AG metabolic acidosis secondary to diarrhoea. Utilisation of AG calculations helps clinicians in identifying and treating acid-base disorders.

The Latent Risk of Acidosis in Commercially Available Total Parenteral Nutrition (TPN) Products: a Randomized Clinical Trial in Postoperative Patients

To evaluate the latent risk of acidosis in commercially available total parenteral nutrition (TPN) products, three types of commercially available TPN products were compared in postoperative patients. Sixty-four hospitalized patients with gastro-intestinal disease who undertook curative gastro intestinal resection were studied prospectively and administered with TPN solutions. Three types of commercially available TPN products were assigned randomly to eligible patients. Serial studies of blood acid-base status, serum electrolytes, and urinary acid-base status were conducted in the three groups administered with different TPN solutions. Patients received appropriate electrolytic solutions on the operation day and TPN solution from 2 to 7 days after operation. There were no differences among any of the serum electrolytes in the three groups. In one group, urinary pH decreased slightly and urinary net acid excretion (NAE) increased significantly after administration. This TPN product contains about 40 mEq/L of non-metabolizable acid to avoid the Maillard reaction that produces a complex of glucose and amino acids. Urinary NAE did not change in the other two groups. These TPN products do not use non-metabolizable acid to adjust pH. The present results suggest that the non-metabolizable acid may be a risk factor of metabolic acidosis.

Optimizing growth in the preterm infant

Most very low birth weight preterm infants experience postnatal growth failure in the neonatal ICU. In an attempt to minimize this phenomenon, the nutritional support of these infants has tended to become more aggressive in recent years and has become a focus of much study. Despite this attention, many questions remain unresolved. This article examines several of these issues, including the controversies regarding optimal postnatal growth velocity, early aggressive nutritional support, and the transition to enteral nutrition in preterm infants.

Iatrogenic malnutrition in neonatal intensive care units: urgent need to modify practice

BACKGROUND

Extrauterine growth retardation is a major clinical problem in very-low-birth-weight infants. Parenteral nutrition (PN) serves to achieve rapid maximal nutrition in early postnatal life. There is a lack of uniformity with regard to neonatal PN practice. The objective of this study is to ascertain current practice regarding neonatal PN prescription in the early postnatal period in the United Kingdom.

METHODS

A study questionnaire was e-mailed to neonatal pharmacists serving level 3 and major level 2 units in the United Kingdom between October 2005 and March 2006. Static numerical information regarding glucose, amino acids, and lipid prescription during the first 10 days of life was collected and compared with current recommendations.

RESULTS

Fifty-two (81%) units responded to the questionnaire; 4 units were excluded for incomplete data. Twenty-six units (54%) initiated PN on day 1. Full PN was achieved by the median age of 6 days. Twelve units (25%) achieved full PN only by day 7 or later. Maximum median amino acids were 2.9 g/kg/d. Only 13 units (27%) prescribed >/=3 g/kg/d, and 2 prescribed more than 3.5 g/kg/d. Nineteen units (39%) initiated lipids on day 1. Eleven units (23%) delayed lipids until day 3, and 2 units delayed lipids until day 4. In comparison to the recommended intake of calories and amino acids, the current median prescription would result in a cumulative deficit over the first 10 days of 420 kcal/kg and 11.9 g/kg, respectively.

CONCLUSIONS

Our study suggests diverse practice with regard to neonatal PN prescription in the United Kingdom. Current neonatal PN practice entails a significant calorie and protein deficit during early postnatal life and warrants further review.

Parenteral amino acid and metabolic acidosis in premature infants

BACKGROUND

Aggressive parenteral nutrition (PN) including amino acids is recommended for low-birth-weight infants to prevent energy and protein deficit. Their impact on acid-base homeostasis has not been examined.

METHODS

We investigated the impact of dose and duration of parenteral amino acids, with cysteine, on acid-base parameters in 122 low-birth-weight infants. Premature infants <or=32 weeks, <or=1850 g, and receiving parenteral amino acids at 1.5 g/kg/d for an extended period (>24 hours), or 3 g/kg/d for a short (5 hour), extended (24 hour), or prolonged (3-5 days) duration were included in the study. Data were obtained at age 0-3 days (n = 43) or, when clinically stable, age 3-5 days (n = 49). Data from 30 infants, matched for birth weight and gestational age, receiving PN during the first 5 days after birth were also obtained. Acidosis was defined as pH <7.25.

RESULTS

Acidosis was evident in all infants between 2 and 5 days after birth. Infants with large patent ductus arteriosus (PDA) exhibited significantly (p < .05) lower pH early, had higher blood urea nitrogen levels (26 +/- 9 vs 18 + 8 mg/dL; p < .05), and had greater weight loss ( approximately 17% of birth weight) when compared with infants without PDA. Gestational age, weight loss, and patent ductus arteriosus accounted for 65% of variance in acidosis.

CONCLUSIONS

Low-birth-weight infants develop metabolic acidosis between 2 and 5 days after birth, irrespective of dose and duration of parenteral amino acid administration. Careful management of parenteral fluids and comorbidities may lower the incidence of acidosis and promote protein accretion.

Protein metabolism in preterm infants with particular reference to intrauterine growth restriction

There is growing evidence that neonatal and long-term morbidity in preterm infants, particularly those born before 32 weeks' gestation, can be modified by attained growth rate in the neonatal period. Guidelines for optimal growth and the nutritional intakes, particular of protein, required to achieve this are not well defined. Due to delays in postnatal feeding and a lack of energy stores developed in the last trimester of pregnancy, preterm infants often suffer early postnatal catabolism until feeding is established. There are indications that infants born with intrauterine growth restriction have perturbations in protein metabolism. Therefore, they may have different protein requirements than appropriate for gestational age infants. This review summarises what is known about protein requirements and metabolism in the fetus and preterm infant, with particular emphasis on the distinct requirements of the growth-restricted infant.

Biochemical homeostasis and body growth are reliable end points in clinical nutrition trials

Studies of biochemical homeostasis and/or body growth have been included as outcome variables in most nutrition trials in paediatric patients. Moreover, these outcome variables have provided important insights into the nutrient requirements of infants and children, and continue to do so. Examples of the value of such studies in improving parenteral nutrition, in defining essential fatty acid metabolism and requirements of infants and in defining the protein and energy needs of low-birth-weight infants are discussed. Data from such studies have helped to define the mechanism of metabolic acidosis and hyperammonaemia associated with the use of early crystalline amino acid mixture and, hence, how to prevent these disorders. Such studies have allowed the development of parenteral amino acid mixtures that circumvent grossly abnormal plasma concentrations of most amino acids and appear to be utilized more efficiently. These studies have also helped define micronutrient requirements, including requirements for several such nutrients that had not been previously recognized as essential (e.g. Cr, Se, Mo, α-linolenic acid). Studies of body growth have been particularly valuable in defining the nutritional requirements of low-birth-weight infants. Finally, studies of metabolic homeostasis coupled with more sophisticated metabolic studies have provided considerable insight into the metabolism of the essential fatty acids, linoleic acid (18:2n-6) and α-linolenic acid (18:3n-3). Although such studies have not defined the amount of the longer-chain PUFA synthesized from each of these essential fatty acids, i.e. arachidonic acid (20:4n-6) and DHA (22:6n-3), they have shown that the rates of conversion are extremely variable from infant to infant, suggesting a possible explanation of why some studies show developmental advantages from intake of these fatty acids while others do not.

Safety and efficacy of early amino acids in preterm <28 weeks gestation: prospective observational comparison

OBJECTIVE

To assess the safety and efficacy of early amino acid (AA) administration in preterm neonates <28 weeks gestational age.

STUDY DESIGN

Prospective data collection for 1 year for the late AA group (AA started at 12-30 h) and for another year with practice change to early AA administration (immediately after stabilization).

RESULTS

Time of initiation of AA differed (early group 4+/-3 h vs late group 20+/-6 h; P<0.001). There were no statistically significant differences in the incidence of clinically significant metabolic acidosis. Blood urea at 24 h was higher in the early AA group. No significant differences in growth rate or neonatal outcomes were identified. Days to regain birth weight and sepsis were lower in the early AA group.

CONCLUSIONS

Early AA administration was not associated with any clinically significant adverse effects; it was associated with reduction in the incidence of sepsis and marginally effective in reducing time to regain birth weight.

Amino acid administration to premature infants directly after birth

OBJECTIVES

To test the hypothesis that the administration of 2.4 g amino acids (AA)/(kg.d) to very low birth weight infants is safe and results in a positive nitrogen balance.

STUDY DESIGN

We conducted a randomized, clinical trial. Preterm infants with birth weights <1500 g received either glucose and 2.4 g AA/(kg.d) from birth onward (n=66) or solely glucose during the first day with a stepwise increase in AA intake to 2.4 g AA/(kg.d) on day 3 (n=69). Blood gas analysis was performed daily during the first 6 postnatal days; blood urea nitrogen levels were determined on days 2, 4, and 6; AA plasma concentrations and nitrogen balances were determined on days 2 and 4. Student t tests, Mann-Whitney tests, and chi2 tests were performed to compare groups.

RESULTS

Infants supplemented with AA had no major adverse side effects. Their blood urea nitrogen levels were higher, nitrogen balance turned positive upon AA administration, and more AA concentrations were within reference ranges.

CONCLUSIONS

High-dose AA administration to very low birth weight infants can be introduced safely from birth onward and results in an anabolic state.

A survey of neonatal parenteral nutrition design practices in North Carolina

BACKGROUND

Parenteral nutrition is an important component of postnatal hospital care for very-low-birth-weight infants (VLBW; birth weight < or =1500 g). Designing and preparing parenteral nutrition for VLBW infants is a complicated process requiring many nutrition decisions and mathematical computations, a process most medical centers have developed independently. The goal of this project was to examine the nutrition design practices and resources of regional neonatal intensive care units (NICUs).

METHODS

In depth interviews were conducted with neonatal nutrition health-care providers at eight medium to large NICUs in North Carolina to describe the patient population, the nutrition support staff, nutrition decision-making procedures and resources, the design of parenteral nutrition, and problems with parenteral nutrition design and preparation.

RESULTS

The eight centers reported an average of 182 VLBW infant admissions and prepared 4810 parenteral nutrition orders per year. Five centers employed experienced neonatal nutrition staff to offer decision support. Six centers used paper parenteral nutrition order forms, all of which provided some decision guidance such as a recommended ordering dose range. Self-reported medical mistakes included incorrect parenteral nutrition additive dilutions and incorrect supplementation of parenteral nutrition additives.

CONCLUSIONS

Most NICUs offered nutrition resource personnel and used paper parenteral nutrition order forms, which offered a wide range of decision guidance. About half the reported medical errors could be addressed using electronic parenteral nutrition design; however, a broader, more general approach to the entire design and administration system would reduce more errors. Last, as development of electronic neonatal nutrition resources in the clinical arena progresses, standards for recording neonatal nutrition content, and evaluating the effect of decision support need to be identified.

Metabolic acidosis in the intensive care unit

Metabolic acidosis is a common occurrence in critically ill patients. Understanding the pathological mechanisms underlying the generation of protons will enable the clinician to quickly recognize these disorders and establish an acceptable treatment strategy. This article presents a logical approach to metabolic acidosis.

Increased parenteral amino acid administration to extremely low-birth-weight infants during early postnatal life

BACKGROUND

Early administration of parenteral amino acids to infants with extremely low birth weight (birth weight < or = 1,000 g) has been encouraged to foster growth. However, excessive intravenous intake of amino acids may cause metabolic acidosis and uremia in extremely low birth weight infants. The hypothesis for this study was that extremely low birth weight infants would tolerate slightly increased early postnatal parenteral amino acid administration and benefit.

METHODS

The peak daily parenteral amino acid dosage was increased from 3 g/kg (standard group) to 4 g/kg (modified group). The corrected parenteral amino acid dosage was computed to account for enteral protein intake and keep the combined daily intravenous amino acid and enteral protein intake at or below 3 g . kg -1 . d -1 in the standard group and 4 g . kg -1 . d -1 in the modified group. The primary outcome measure was plasma bicarbonate concentration as an indicator of acid-base status. Data were collected for patient demographics, nutritional intake, serum bicarbonate and serum urea nitrogen concentrations, and outcome.

RESULTS

The corrected parenteral amino acid intake of the modified group was 16% greater at postnatal week 1 (3.30 +/- 0.83 g . kg -1 . d -1; mean, +/-1 SD) and 18% greater (3.86 +/- 0.94 g . kg -1 . d -1 ) at postnatal week 2 than the parenteral amino acid intake of the standard group. In the modified group, the mean serum bicarbonate concentration was 19.1 +/- 1.8 mEq/dL at week 1 and 23.9 +/- 2.9 mEq/dL at week 2, with no difference between the groups. At week 1, serum urea nitrogen concentrations were the same in both groups. The mean serum urea nitrogen concentration of the modified group at postnatal week 2 (18.2 +/- 8.8 mg/dL) was unchanged from postnatal week 1, but was greater than that of the standard group at postnatal week 2. Weight gain was the same in both groups. Corrected parenteral amino acid intake at postnatal week 1 correlated directly with weight gain from birth to postnatal week 2 ( P < 0.03) in both groups.

CONCLUSIONS

Infants with extremely low birth weight tolerated parenteral amino acid intake of approximately 4 g . kg -1 . d -1. Mild increases of mean serum urea nitrogen concentration and mean weight gain were associated with increased parenteral amino acid administration without significant acidosis.

Acid load during total parenteral nutrition: comparison of hydrochloric acid and acetic acid on plasma acid-base balance

The effects of hydrochloric acid and acetic acid on the plasma acid-base balance were investigated in four rabbits receiving parenteral nutrition. Hyperchloremic metabolic acidosis was observed only in the animals receiving total parenteral nutrition (TPN) whose pH was adjusted with hydrochloric acid. The observed acidosis was due to an excess of hydrogen ions with chloride ions as judged by the plasma-base excess and urinary net-acid excess and not by the infusion of solution having a high titratable acidity. The hydrogen ion released from the acetic acid added to TPN is consumed by the metabolism of the acetate ion and thus does not contribute to the net hydrogen-ion load. A reduction in the chloride load by using acetic acid to adjust the pH of the TPN solution when it is formulated can be safely achieved and prevents acidosis.

Overfeeding macronutrients to critically ill adults: metabolic complications

Metabolic complications from overfeeding critically ill patients are serious and sometimes fatal. Nutrition care is best provided through repeated evaluation of patients' responses to feeding. Nutrition support may need to be modified over time to maintain metabolic stability and promote recovery. This article describes the etiology of 10 metabolic complications of overfeeding. Guidelines for recommending macronutrients are discussed, as are factors that could increase the risk of overfeeding. Patients who are very small, very large, or very old are particularly vulnerable to overfeeding. Overfeeding protein has led to azotemia, hypertonic dehydration, and metabolic acidosis. Excessive carbohydrate infusion has resulted in hyperglycemia, hypertriglyceridemia, and hepatic steatosis. High-fat infusions have caused hypertriglyceridemia and fat-overload syndrome. Hypercapnia and refeeding syndrome have also been caused by aggressive overfeeding. Dietitians can prevent or curtail the metabolic complications of overfeeding by identifying patients at risk, providing adequate assessment, coordinating interdisciplinary care plans, and delivering timely and appropriate monitoring and intervention. Dietitians need to document complications, interventions, and the outcomes of their clinical care to evaluate the appropriateness of existing nutrition guidelines.

Metabolic acidosis

Metabolic acidosis is a pathophysiologic state that is associated with serious morbidities and mortality. The diagnosis of metabolic acidosis is perplexing for novice and expert advanced practice nurses for many reasons. Its differential diagnosis is broad and includes common and rare, complex disease. The diagnosis of metabolic acidosis is also difficult because it is frequently associated with mixed, acid-base disorders. Its clinical manifestations are often nonspecific or subclinical, which means that its diagnosis is made from laboratory and other diagnostic tests. Timely diagnosis of metabolic acidosis is needed to institute appropriate therapy to avoid negative physiologic effects.

Acid-base disorders in medicine

The practice of internal medicine involves daily exposure to abnormalities of acid-base balance. A wide variety of disease states either predispose patients to develop these conditions or lead to the use of medications that alter renal, gastrointestinal, or pulmonary function and secondarily alter acid-base balance. In addition, primary acid-base disease follows specific forms of renal tubular dysfunction (renal tubular acidosis). We review the acid-base physiologic functions of the kidney and gastrointestinal tract and the current understanding of acid-base pathophysiologic conditions. This includes a review of whole animal and renal tubular physiologic characteristics and a discussion of the current knowledge of the molecular biology of acid-base transport. We stress an approach to diagnosis that relies on knowledge of acid-base physiologic function, and we include discussion of the appropriate treatment of each disorder considered. Finally, we include a discussion of the effects of acidosis and alkalosis on human physiologic functions.

The kidney in acid-base balance

The practitioner's approach to the pediatric patient with metabolic acidosis begins with calculation of the serum anion gap, which allows the clinician to place the patient in one of two categories of acid-base disturbance: a normal anion gap acidosis or high anion gap acidosis. Likewise, the patient with metabolic alkalosis can be categorized by urinary chloride concentration and the response to chloride replenishment as either chloride-responsive or chloride-resistant. The disease states associated with each category are reviewed in this article.

Immediate commencement of amino acid supplementation in preterm infants: effect on serum amino acid concentrations and protein kinetics on the first day of life

To determine whether the general reluctance to begin amino acid administration to preterm infants from birth onward might lead to loss of lean body mass and impairment of growth, we measured amino acid levels and protein kinetics in 18 preterm infants. Nine infants received amino acids (1.15 +/- 0.06 gm.kg-1.day-1) and glucose (6.05 +/- 1.58 gm.kg-1.day-1), whereas the other nine infants received only glucose (6.48 +/- 1.30 gm.kg-1.day-1) from birth onward. Protein kinetics on the first postnatal day were measured with a stable isotope dilution technique with [1-13C]leucine as a tracer. No statistically significant differences were noted in blood pH, base excess, urea concentration, or glucose levels. Both total amino acid concentration and total essential amino acid concentration were significantly lower and were below the reference range in the nonsupplemented group. Plasma amino acid levels of five essential amino acids (methionine, cystine, isoleucine, leucine, arginine) were below the reference range in the nonsupplemented group, whereas only cystine was below the reference range in the supplemented group. Nitrogen retention was improved significantly by the administration of amino acids (-110 +/- 44 mg nitrogen per kilogram per day in the glucose-only group vs +10 +/- 127 mg nitrogen per kilogram per day in the group given glucose and amino acids; p = 0.001); leucine oxidation was not significantly increased in the supplemented group (41 +/- 13 mumol.kg-1.hr-1 vs 46 +/- 16 mumol.kg-1.hr-1). Leucine balance also improved significantly (-41 +/- 13 mumol.kg-1.hr-1 vs -8 +/- 16 mumol.kg-1.hr-1; p = 0.01) because of a combination of an increased amount of leucine being used for protein synthesis and a lower amount of leucine coming from protein breakdown. Plasma cystine concentration, the only amino acid below the reference range in the supplemented group, was highly predictive for protein synthesis in that group. We conclude that the administration of amino acids to preterm infants from birth onward seems safe and prevents the loss of protein mass.

Low birthweight infants and total parenteral nutrition immediately after birth. II. Randomised study of biochemical tolerance of intravenous glucose, amino acids, and lipid

This randomised study aimed to compare the biochemical tolerance of three parenteral regimens administered during the first 48 hours of life. Twenty nine infants were randomised to either: (a) glucose 10%; (b) glucose 10%/amino acids; (c) glucose 10%/amino acids/lipid. Blood samples for plasma amino acid profiles, cholesterol, and triglyceride concentrations were taken on arrival in the neonatal unit and again between 36 and 48 hours of life. Arterial or capillary blood gas analysis and blood glucose estimates were performed routinely during the first 48 hours of life. There was a sharp decline in plasma amino acid concentrations in the group following (a) compared with the two groups following (b) and (c) regimens. In all groups plasma triglyceride and cholesterol were not significantly different before and after 48 hours of lipid infusion. Peak mean (SE) bilirubin concentrations (203 (12) v 181 (19) v 220 (20) mumol/l) and the need for phototherapy (nine v eight v five infants) were similar for each of the groups. Hypoglycaemia occurred most frequently during the (b) regimen and least commonly in the (c) group. There are potential health gains from giving parenteral nutrition to low birthweight infants immediately after birth, and this study indicates that restriction of nutritional intake immediately after birth in preterm infants may cause significant metabolic disturbance. This can be prevented by starting a regimen of intravenous amino acids and lipid immediately after birth.

Effects of a high protein intake on renal acid excretion in bodybuilders

Bodybuilders often prefer a high protein diet to achieve maximum skeletal muscle hypertrophy. In this study the effect of a high protein diet on renal acid load and renal handling of proton excretion was studied comparing dietary intake and urinary ionograms in 37 male bodybuilders and 20 young male adults. Energy intake (+ 7%), protein intake (128 vs 88 g/d/1.73 m2), and renal net acid excretion (95 vs 64 mmol/d/1.73 m2) were higher in the bodybuilders than in the controls, however, urine-pH was only slightly lower (5.83 vs 6.12). In the bodybuilders renal ammonium excretion was higher at any given value of urine pH than in the controls. In a regression analysis protein intake proved to be an independent factor modulating the ratio between urine-pH and renal ammonium excretion. The concomitant increase of renal net acid excretion and maximum renal acid excretion capacity in periods of high protein intake appears to be a highly effective response of the kidney to a specific food intake leaving a large renal surplus capacity for an additional renal acid load.

Amino acid solutions for premature neonates during the first week of life: the role of N-acetyl-L-cysteine and N-acetyl-L-tyrosine

Tyrosine and cyst(e)ine are amino acids that are thought to be essential for preterm neonates. These amino acids have low stability (cyst(e)ine) or low solubility (tyrosine) and are therefore usually present only in small amounts in amino acid solutions. Acetylation improves the stability and solubility of amino acids, facilitating a higher concentration in the solution. We compared three commercially available amino acid solutions, Aminovenös-N-päd 10%, Vaminolact 6.5%, and Primène 10%, administered to 20 low-birth-weight neonates on total parenteral nutrition from postnatal day 2 onward. Aminovenös-N-päd 10% contains acetylated tyrosine and acetylated cysteine; the other solutions do not contain acetylated amino acids and differ in the amount of tyrosine and cysteine added. On postnatal day 7, plasma amino acids were measured together with urinary excretion of amino acids and the total nitrogen excretion; 38% of the intake of N-acetyl-L-tyrosine and 53% of the intake of N-acetyl-L-cysteine were excreted in urine. Plasma levels of N-acetyl-L-tyrosine (331 +/- 74 mumol/L) and N-acetyl-L-cysteine (18 +/- 29 mumol/L) were higher than those of tyrosine (105 +/- 108 mumol/L) and cystine (11 +/- 9 mumol/L), respectively. Plasma tyrosine levels in the groups receiving small amounts of tyrosine remained just below the reference range. We show a linear correlation of plasma cystine with the intake of cysteine (r = .75, p = 0.01), but not with N-acetyl-L-cysteine. The estimated intake of cysteine should be 500 mumol.kg-1.d-1 in order to obtain levels comparable with those shown in normal term, breast-fed neonates. Nitrogen retention did not differ among the three groups (247 to 273 mg.kg-1.d-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Parenteral nutrition-related bone disease

Parenteral nutrition (PN)-related bone disease remains a problem in patients of all ages. Understanding of the pathogenesis of PN-related bone disease is complicated by the effect of underlying illnesses, therapeutic interventions, and pre-existing nutrition deficiencies before the initiation of PN therapy. Interrelation of various nutrients, for example, calcium, phosphorus, and vitamin D, in their effects on bone mineralization, demands simultaneous assessment of the role of multiple nutrients and increases the difficulty in defining the role of a single nutrient in the development of bone disease. However, recent reports indicate that there exist a number of factors important in the development of PN-related bone disease and some factors such as increased mineral requirement are unique to growing infants whereas other factors such as aluminum toxicity may be common to both adult and pediatric populations. Nonnutritional factors, including chronic use of potent loop diuretics and altered acid-base status, can affect urine mineral loss, cell metabolism, and bone mineralization, particularly in small, preterm infants. Current evidence indicates that the cause of PN-related bone disease is multifactorial, and the prevention of PN-related bone disease awaits better delineation of the exact sequence of pathogenic events.

Retrospective approach to explain growth retardation and urolithiasis in a child with long-term nutritional acid loading

An infant with phenylketonuria unintentionally received a highly acidic low phenylalanine diet for 29 months. Temporary growth retardation and urolithiasis were observed, probably as direct effects of chronic acid loading. Caries at the age of 6 years may be a late consequence. This case report shows that chronic dietary acid load may cause serious side effects.

Priapism in a patient treated with total parenteral nutrition

Venous thrombosis is a common complication of total parenteral nutrition. We report a case of priapism in a 40-year-old man after administration of total parenteral nutrition for chronic idiopathic intestinal pseudo-obstruction. The patient received glucose, amino acids, and 20% fat emulsion; 12 hours after administration, the patient complained of a persistent, painful penile erection lasting 5 hours. Bilateral corpora cavernosa spongiosum shunts achieved immediate and sustained detumescence, but the patient remained impotent. There was no history of penile or pelvic trauma, hemoglobinopathy, coagulopathy, venous thrombosis, or leukemia. The medical literature describes seven other cases of priapism related to total parenteral nutrition. All of the patients received 20% fat emulsion; two patients developed priapism during the weekly infusion of fat emulsion. Among the multiple factors that can favor thrombosis and therefore priapism during total parenteral nutrition, fat infusion appears to be the most important. Three different mechanisms have been postulated: increase in blood coagulability, effects on red blood cells, and fat embolism. In this patient, platelet function was estimated in vivo by the levels of antiheparin platelet factor 4 and beta-thromboglobulin. These two parameters were both elevated before 20% lipid emulsion and were even higher after the 20% fat-emulsion infusion. Therefore, even if a direct thromboplastic effect is possible, 20% fat emulsion increases platelet activity, which was already high in our patient, and thereby favors priapism.

Acid-base state of the preterm infant and the formulation of intravenous feeding solutions

An acidic intravenous source of phosphorus (Addiphos) was compared with dipotassium hydrogen phosphate in 25 preterm infants to study acid-base state. Eight infants were given either Addiphos or dipotassium hydrogen phosphate alternately for 48 hour periods and similar amounts of calcium and phosphorus were delivered. There were no significant differences in calcium and phosphorus intake, calcium and phosphate plasma concentrations, or acid-base state between study periods on the two solutions. Seventeen infants were given the two solutions alternately for 72 hour periods; Addiphos was used to increase the amounts of calcium and phosphorus being delivered. Calcium and phosphorus intake was decreased on dipotassium hydrogen phosphate, but Addiphos significantly increased calcium and phosphorus intake and plasma calcium and phosphate concentrations. It also lowered the pH of the urine and raised the titratable acidity. Acid-base state, however, was not significantly different. It is therefore possible to increase intake of calcium and phosphorus in preterm infants without causing a significant metabolic acidosis.

Early parenteral feeding of amino acids

Serial 24 hour balance studies of nitrogen and energy were carried out over 10 days in two groups of ventilator dependent preterm infants, of comparable weight and gestational age. In one group (n = 10) a parenteral amino acid source (Vamin 9) was started within 24 hours of birth, and in the other group (n = 11) it was not started until 72 hours. The feeding protocol was otherwise identical. The nitrogen intake (286 compared with 21 mg/kg/day), energy intake (188 compared with 151 kJ), and nitrogen retention (120 compared with -133 mg/kg/day), were all significantly higher during the first three days of life in the group in which the amino acid solution was started early. There were no differences by 7-10 days. The early introduction of amino acids improves the early nutritional state of sick preterm infants.

Mineral balance studies in sick preterm intravenously fed infants during the first week after birth. A guide to fluid therapy

Mineral balance studies were performed in 61 sick preterm infants given parenteral fluids only. Their gestational ages varied from 24 to 35 weeks, and 50 required mechanical ventilation. Two consecutive balance studies were performed; the first from admission to 48 hours in all babies given maintenance fluids of 10% Dextrose, and the second from 48 hours to 7 days in those babies given intravenous feeding (IVN). At the beginning and end of each balance period, the baby was weighed and an arterial blood sample taken for blood gases, electrolyte, urea, creatinine and protein determinations. During the balance period all urine was collected and analysed for electrolyte, urea, and creatinine composition, and all fluid intake was recorded. The balance of a mineral was calculated as the difference between parenteral intake and urine output. Infants requiring IVN were allocated alternatively to regimen X or regimen Y, which had the same calcium content of 9.5 mmol/L, but different phosphate contents, regimen X containing 7.3 mmol/L and regimen Y 11.6 mmol/L. In those infants requiring prolonged IVN, 12-24 hour balance studies were performed at weekly intervals after day 10. 1. Phosphate deficiency developed in infants given regimen X, who had higher urine calcium excretion, lower percentage calcium retention and lower plasma phosphate levels than those given regimen Y. These differences were apparent by day 7 and persisted after day 10. In infants given regimen Y, mean calcium retention from admission to day 7 was 3.9 mmol/kg, and after day 10 was 0.9 mmol/kg/day. 2. In the first 48 hours, urine output and creatinine clearance varied widely and were lower in infants with higher oxygen requirements at 48 hours. Ten babies had severe oliguria with outputs less than 10 mL/kg/day. Creatinine clearance was directly related to gestational age, mean arterial blood pressure, and plasma protein concentrations on admission. After 48 hours, urine output and creatinine clearance increased considerably. 3. In the first 48 hours, metabolic acidosis was produced by increased plasma non-protein metabolisable acid concentrations, which were associated with low creatinine clearances, and were thought to be due to lactic acid accumulation in response to decreased tissue perfusion. At 7 days, metabolic acidosis was of similar severity but was produced by decreased plasma non-metabolisable base concentrations, caused by increased urine loss of net base, and not directly by IVN.(ABSTRACT TRUNCATED AT 400 WORDS)

D-lactate and metabolic bone disease in patients receiving long-term parenteral nutrition

D-lactate accumulates in some patients with malabsorption who continue oral intake of carbohydrate leading to a clinical syndrome of acidosis and encephalopathy. To assess the possibility that D-lactate contributes to acidosis and/or metabolic bone disease in patients with malabsorption receiving long-term parenteral nutrition yet maintaining oral intake, D-lactate levels in serum and urine were measured in 14 long-term parenteral nutrition subjects (average duration of support 74 months) and 27 control subjects. Significant elevations in both serum and urine D-lactate were found in only two parenteral nutrition subjects. Both subjects with elevated D-lactate levels had bone pain, x-ray evidence of fractures, and biopsy evidence of osteomalacia. These studies suggest that D-lactate accumulation may be a heretofore unappreciated metabolic abnormality associated with metabolic bone disease and acidosis in patients with malabsorption who are supported by long-term parenteral nutrition.

Neonatal metabolic acidosis: effect of chloride from normal saline flushes

Metabolic Acidosis is a reported complication of total parenteral nutrition (TPN). A large number of infants receiving TPN in an NICU were noted to have metabolic acidosis. We evaluated the effect of lowering the chloride intake on the incidence of metabolic acidosis in low birth weight (LBW) infants on TPN. Standard TPN solutions were adjusted to provide about 2-3 mEq/kg/day chloride instead of 5-7 mEq/kg/day provided previously. Most infants on TPN received approximately another 1-3 mEq/kg/day from intravenous and arterial line flushes with normal saline. Ten infants who had been on the original TPN solutions were compared to 10 infants who were on the revised TPN solutions. Serum pH, bicarbonate, and base deficit were used to measure acidosis. Medical records were reviewed for the number of days the infants had abnormal values. Serum chloride levels were also recorded. While similar in gestational age, birth weight, age during study period, days on TPN, and days on orally supplemented parenteral nutrition, the group with higher chloride intake had significantly more days of metabolic acidosis. They also had significantly higher serum chlorides. It is concluded that a total chloride load in excess of 6 mEq/kg/day in LBW infants receiving TPN is associated with more metabolic acidosis. Also, if saline is used for clearing of intravenous and arterial lines, standard TPN solutions should be formulated with consideration of the total chloride load.