Low birthweight infants and total parenteral nutrition immediately after birth. I. Energy expenditure and respiratory quotient of ventilated and non-ventilated infants

Neonatal dysglycemia: a review of dysglycemia in relation to brain health and neurodevelopmental outcomes

Neonatal dysglycemia has been a longstanding interest of research in neonatology. Adverse outcomes from hypoglycemia were recognized early but are still being characterized. Premature infants additionally introduced and led the reflection on the importance of neonatal hyperglycemia. Cohorts of infants following neonatal encephalopathy provided further information about the impacts of hypoglycemia and, more recently, highlighted hyperglycemia as a central concern for this population. Innovative studies exposed the challenges of management of neonatal glycemic levels with a "u-shape" relationship between dysglycemia and adverse neurological outcomes. Lately, glycemic lability has been recognized as a key factor in adverse neurodevelopmental outcomes. Research and new technologies, such as MRI and continuous glucose monitoring, offered novel insight into neonatal dysglycemia. Combining clinical, physiological, and epidemiological data allowed the foundation of safe operational definitions, including initiation of treatment, to delineate neonatal hypoglycemia as ≤47 mg/dL, and >150-180 mg/dL for neonatal hyperglycemia. However, questions remain about the appropriate management of neonatal dysglycemia to optimize neurodevelopmental outcomes. Research collaborations and clinical trials with long-term follow-up and advanced use of evolving technologies will be necessary to continue to progress the fascinating world of neonatal dysglycemia and neurodevelopment outcomes. IMPACT STATEMENT: Safe operational definitions guide the initiation of treatment of neonatal hypoglycemia and hyperglycemia. Innovative studies exposed the challenges of neonatal glycemia management with a "u-shaped" relationship between dysglycemia and adverse neurological outcomes. The importance of glycemic lability is also being recognized. However, questions remain about the optimal management of neonatal dysglycemia to optimize neurodevelopmental outcomes. Research collaborations and clinical trials with long-term follow-up and advanced use of evolving technologies will be necessary to progress the fascinating world of neonatal dysglycemia and neurodevelopment outcomes.

Hyperglycemia and prematurity: a narrative review

Hyperglycemia is commonly encountered in extremely preterm newborns and physiologically can be attributed to immaturity in several biochemical pathways related to glucose metabolism. Although hyperglycemia is associated with a variety of adverse outcomes frequently described in this population, evidence for causality is lacking. Variations in definitions and treatment approaches have further complicated the understanding and implications of hyperglycemia on the immediate and long-term effects in preterm newborns. In this review, we describe the relationship between hyperglycemia and organ development, outcomes, treatment options, and potential gaps in knowledge that need further research. IMPACT: Hyperglycemia is common and less well described than hypoglycemia in extremely preterm newborns. Hyperglycemia can be attributed to immaturity in several cellular pathways involved in glucose metabolism in this age group. Hyperglycemia has been shown to be associated with a variety of adverse outcomes frequently described in this population; however, evidence for causality is lacking. Variations in definitions and treatment approaches have complicated the understanding and the implications of hyperglycemia on the immediate and long-term effects outcomes. This review describes the relationship between hyperglycemia and organ development, outcomes, treatment options, and potential gaps in knowledge that need further research.

Evolution of Resting Energy Expenditure, Respiratory Quotient, and Adiposity in Infants Recovering from Corrective Surgery of Major Congenital Gastrointestinal Tract Anomalies: A Cohort Study

This cohort study describes the evolution of resting energy expenditure (REE), respiratory quotient (RQ), and adiposity in infants recovering from corrective surgery of major congenital gastrointestinal tract anomalies. Energy and macronutrient intakes were assessed. The REE and RQ were assessed by indirect calorimetry, and fat mass index (FMI) was assessed by air displacement plethysmography. Longitudinal variations over time are described. Explanatory models for REE, RQ, and adiposity were obtained by multiple linear regression analysis. Twenty-nine infants were included, 15 born preterm and 14 at term, with median gestational age of 35.3 and 38.1 weeks and birth weight of 2304 g and 2935 g, respectively. In preterm infants, median REE varied between 55.7 and 67.4 Kcal/kg/d and median RQ increased from 0.70 to 0.86–0.92. In term infants, median REE varied between 57.3 and 67.9 Kcal/kg/d and median RQ increased from 0.63 to 0.84–0.88. Weight gain velocity was slower in term than preterm infants. FMI, assessed in a subset of 15 infants, varied between a median of 1.7 and 1.8 kg/m² at term age. This low adiposity may be related to poor energy balance, low fat intakes, and low RQ¸ that were frequently recorded in several follow-up periods.

Systematic review of factors associated with energy expenditure in the critically ill

BACKGROUND AND AIMS

Indirect calorimetry is the reference standard for energy expenditure measurement. Predictive formulae that replace it are inaccurate. Our aim was to review the patient and clinical factors associated with energy expenditure in critically ill patients.

METHODS

We conducted a systematic review of the literature. Eligible studies were those reporting an evaluation of factors and energy expenditure. Energy expenditure and factor associations with p-values were extracted from each study, and each factor was classified as either significantly, indeterminantly, or not associated with energy expenditure. Regression coefficients were summarized as measures of central tendency and spread. Metanalysis was performed on correlations.

RESULTS

The search strategy yielded 8521 unique articles, 307 underwent full text review, and 103 articles were included. Most studies were in adults. There were 95 factors with 352 evaluations. Minute volume, weight, age, % body surface area burn, sedation, post burn day, and caloric intake were significantly associated with energy expenditure. Heart rate, fraction of inspired oxygen, respiratory rate, respiratory disease diagnosis, positive end expiratory pressure, intensive care unit days, C- reactive protein, and size were not associated with energy expenditure. Multiple factors (n = 37) were identified with an unclear relationship with energy expenditure and require further evaluation.

CONCLUSIONS

An important interval step in the development of accurate formulae for energy expenditure estimation is a better understanding of relationships between patient and clinical factors and energy expenditure. The review highlights the limitations of currently available data, and identifies important factors that are not included in current prediction formulae of the critically ill.

Higher versus lower amino acid intake in parenteral nutrition for newborn infants

BACKGROUND

Sick newborn and preterm infants frequently are not able to be fed enterally, necessitating parenteral fluid and nutrition. Potential benefits of higher parenteral amino acid (AA) intake for improved nitrogen balance, growth, and infant health may be outweighed by the infant's ability to utilise high intake of parenteral AA, especially in the days after birth.

OBJECTIVES

The primary objective is to determine whether higher versus lower intake of parenteral AA is associated with improved growth and disability-free survival in newborn infants receiving parenteral nutrition.Secondary objectives include determining whether:• higher versus lower starting or initial intake of amino acids is associated with improved growth and disability-free survival without side effects;• higher versus lower intake of amino acids at maximal intake is associated with improved growth and disability-free survival without side effects; and• increased amino acid intake should replace non-protein energy intake (glucose and lipid), should be added to non-protein energy intake, or should be provided simultaneously with non-protein energy intake.We conducted subgroup analyses to look for any differences in the effects of higher versus lower intake of amino acids according to gestational age, birth weight, age at commencement, and condition of the infant, or concomitant increases in fluid intake.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group to search the Cochrane Central Register of Controlled Trials (2 June 2017), MEDLINE (1966 to 2 June 2017), Embase (1980 to 2 June 2017), and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to 2 June 2017). We also searched clinical trials databases, conference proceedings, and citations of articles.

SELECTION CRITERIA

Randomised controlled trials of higher versus lower intake of AAs as parenteral nutrition in newborn infants. Comparisons of higher intake at commencement, at maximal intake, and at both commencement and maximal intake were performed.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials, assessed trial quality, and extracted data from included studies. We performed fixed-effect analyses and expressed treatment effects as mean difference (MD), risk ratio (RR), and risk difference (RD) with 95% confidence intervals (CIs) and assessed the quality of evidence using the GRADE approach.

MAIN RESULTS

Thirty-two studies were eligible for inclusion. Six were short-term biochemical tolerance studies, one was in infants at > 35 weeks' gestation, one in term surgical newborns, and three yielding no usable data. The 21 remaining studies reported clinical outcomes in very preterm or low birth weight infants for inclusion in meta-analysis for this review.Higher AA intake had no effect on mortality before hospital discharge (typical RR 0.90, 95% CI 0.69 to 1.17; participants = 1407; studies = 14; I² = 0%; quality of evidence: low). Evidence was insufficient to show an effect on neurodevelopment and suggest no reported benefit (quality of evidence: very low). Higher AA intake was associated with a reduction in postnatal growth failure (< 10th centile) at discharge (typical RR 0.74, 95% CI 0.56 to 0.97; participants = 203; studies = 3; I² = 22%; typical RD -0.15, 95% CI -0.27 to -0.02; number needed to treat for an additional beneficial outcome (NNTB) 7, 95% CI 4 to 50; quality of evidence: very low). Subgroup analyses found reduced postnatal growth failure in infants that commenced on high amino acid intake (> 2 to ≤ 3 g/kg/day); that occurred with increased amino acid and non-protein caloric intake; that commenced on intake at < 24 hours' age; and that occurred with early lipid infusion.Higher AA intake was associated with a reduction in days needed to regain birth weight (MD -1.14, 95% CI -1.73 to -0.56; participants = 950; studies = 13; I² = 77%). Data show varying effects on growth parameters and no consistent effects on anthropometric z-scores at any time point, as well as increased growth in head circumference at discharge (MD 0.09 cm/week, 95% CI 0.06 to 0.13; participants = 315; studies = 4; I² = 90%; quality of evidence: very low).Higher AA intake was not associated with effects on days to full enteral feeds, late-onset sepsis, necrotising enterocolitis, chronic lung disease, any or severe intraventricular haemorrhage, or periventricular leukomalacia. Data show a reduction in retinopathy of prematurity (typical RR 0.44, 95% CI 0.21 to 0.93; participants = 269; studies = 4; I² = 31%; quality of evidence: very low) but no difference in severe retinopathy of prematurity.Higher AA intake was associated with an increase in positive protein balance and nitrogen balance. Potential biochemical intolerances were reported, including risk of abnormal blood urea nitrogen (typical RR 2.77, 95% CI 2.13 to 3.61; participants = 688; studies = 7; I² = 6%; typical RD 0.26, 95% CI 0.20 to 0.32; number needed to treat for an additional harmful outcome (NNTH) 4; 95% CI 3 to 5; quality of evidence: high). Higher amino acid intake in parenteral nutrition was associated with a reduction in hyperglycaemia (> 8.3 mmol/L) (typical RR 0.69, 95% CI 0.49 to 0.96; participants = 505; studies = 5; I² = 68%), although the incidence of hyperglycaemia treated with insulin was not different.

AUTHORS' CONCLUSIONS

Low-quality evidence suggests that higher AA intake in parenteral nutrition does not affect mortality. Very low-quality evidence suggests that higher AA intake reduces the incidence of postnatal growth failure. Evidence was insufficient to show an effect on neurodevelopment. Very low-quality evidence suggests that higher AA intake reduces retinopathy of prematurity but not severe retinopathy of prematurity. Higher AA intake was associated with potentially adverse biochemical effects resulting from excess amino acid load, including azotaemia. Adequately powered trials in very preterm infants are required to determine the optimal intake of AA and effects of caloric balance in parenteral nutrition on the brain and on neurodevelopment.

Impact of Nutrition on Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) remains a common morbidity of prematurity. Although the pathogenesis of BPD is recognized to be both multifactorial and complex, the role of nutrition in the pathophysiology of BPD is typically limited to management after a diagnosis has been made. Infants born small for gestational age and those who experience postnatal growth failure are more likely to have BPD. Therapies for lung disease, such as fluid restriction, diuretics, and corticosteroids, can negatively impact postnatal growth. Future research is needed to optimize nutritional strategies in the neonatal intensive care unit and following hospital discharge.

Assessing neonatal heat balance and physiological strain in newborn infants nursed under radiant warmers in intensive care with fentanyl sedation

PURPOSE

To assess heat balance status of newborn infants nursed under radiant warmers (RWs) during intensive care.

METHODS

Heat balance, thermal status and primary indicators of physiological strain were concurrently measured in 14 newborns nursed under RWs for 105 min. Metabolic heat production (M), evaporative heat loss (E), convective (C) and conductive heat flow (K), rectal temperature (T re) and mean skin temperatures (T sk) were measured continuously. The rate of radiant heat required for heat balance (R req) and the rate of radiant heat provided (R prov) were derived. The rate of body heat storage (S) was calculated using a two-compartment model of 'core' (T re) and 'shell' (T sk) temperatures.

RESULTS

Mean M, E, C and K were 10.5 ± 2.7 W, 5.8 ± 1.1 W, 6.2 ± 0.8 W and 0.1 ± 0.1 W, respectively. Mean R prov (1.7 ± 2.6 W) and R req (1.7 ± 2.7 W) were similar (p > 0.05). However, while the resultant mean change in body heat content after 105 min was negligible (-0.1 ± 3.7 kJ), acute time-dependent changes in S were evidenced by a mean positive heat storage component of +6.4 ± 2.6 kJ and a mean negative heat storage component of -6.5 ± 3.7 kJ. Accordingly, large fluctuations in both T re and T sk occurred that were actively induced by changes in RW output. Nonetheless, no active physiological responses (heart rate, breathing frequency and mean arterial pressure) to these bouts of heating and cooling were observed.

CONCLUSIONS

RWs maintain net heat balance over a prolonged period, but actively induce acute bouts of heat imbalance that cause rapid changes in T re and T sk. Transient bouts of heat storage do not exacerbate physiological strain, but could in the longer term.

Standardised neonatal parenteral nutrition formulations - an Australasian group consensus 2012

Standardised parenteral nutrition formulations are routinely used in the neonatal intensive care units in Australia and New Zealand. In 2010, a multidisciplinary group was formed to achieve a consensus on the formulations acceptable to majority of the neonatal intensive care units. Literature review was undertaken for each nutrient and recommendations were developed in a series of meetings held between November 2010 and April 2011. Three standard and 2 optional amino acid/dextrose formulations and one lipid emulsion were agreed by majority participants in the consensus. This has a potential to standardise neonatal parenteral nutrition guidelines, reduce costs and prescription errors.

Measuring energy expenditure in clinical populations: rewards and challenges

The measurement of energy expenditure (EE) is recommended as an important component of comprehensive clinical nutrition assessments in patients with altered metabolic states, who failed to respond to nutrition support and with critical illness that require individualized nutrition support. There is evidence that EE is variable in patients with metabolic diseases, such as chronic renal disease, cirrhosis, HIV, cancer cachexia, cystic fibrosis and patients under intensive care. By using appropriate techniques and interpretations of basal or resting EE, clinicians can facilitate the adequate nutrition support with minimum negative impacts from under- or overfeeding in these patients. This review is based on our current understanding of the different components of EE and the techniques to measure them, and to re-examine advances and challenges to determine energy needs in clinical populations with more focuses on the obese, pediatric and elderly patients. In addition, technological advances have expanded the choices of market-available equipments for assessing EE, which also bring specific challenges and rewards in selecting the right equipment with specific performance criteria. Lastly, analytical considerations of interpreting the results of EE in the context of changing body composition are presented and discussed.

Dynamic coordination of macronutrient balance during infant growth: insights from a mathematical model

BACKGROUND

Complex dynamic changes in body composition, dietary intake, energy expenditure, and macronutrient oxidation occur during infant growth. Although previous investigators have focused on energy requirements for normal growth, little is known about the dynamic coordination of macronutrient balance.

OBJECTIVE

Our objective was to develop a mathematical model of the dynamic relations between diet, macronutrient oxidation, and energy expenditure during normal infant growth.

DESIGN

We developed a mathematical model that integrates longitudinal data on changes of body composition and carbon dioxide production determined with the doubly labeled water method to calculate both energy intake requirements and macronutrient oxidation rates during normal infant growth.

RESULTS

The calculated fat oxidation rate was initially <20 kcal x kg(-1) x d(-1), despite the consumption of >60 kcal x kg(-1) x d(-1) of dietary fat. This discrepancy was maintained until approximately 6 mo, after which fat intake was only slightly greater than fat oxidation. Nonfat oxidation closely followed nonfat dietary intake for the duration of the period studied. Model calculations of the energy intake requirements for normal growth were slightly lower than previous estimates. The calculations were robust to variations of body weight, body composition, and diet composition input data, but depended sensitively on variations of carbon dioxide production data.

CONCLUSIONS

Our model presents a dynamic picture of how macronutrient oxidation adapts in concert with dietary changes and energy expenditure to give rise to normal tissue deposition. The model integrates a variety of data in a self-consistent way, simulating the complex metabolic adaptations occurring during normal growth while extracting important physiologic information from the data that would otherwise be unavailable.

Energy requirements

The determination of the appropriate energy and nutritional requirements of a newborn infant requires a clear goal of the energy and other compounds to be administered, valid methods to measure energy balance and body composition, and knowledge of the neonatal metabolic capacities. Providing an appropriate amount of energy to newborn infants remains a challenge considering the great number of newborn infants who suffer in-hospital growth retardation. The energy requirements of a newborn infant are influenced by several factors - basal metabolism, growth, energy expenditure, and energy losses - which change continuously during development. Calculating the energy requirements of preterm infants is subject to error if general recommendations are applied without recognition of the large variation in factors that influence, for example, energy expenditure. Therefore, energy recommendations should be individualized and preferably based on measurements of energy expenditure. In particular, extremely low birth-weight and very low birth-weight infants are prone to develop negative energy and nutrient balances, due to low energy intake, low energy reserves and high energy demands. Early energy accretion is not only essential for growth but also influences neurodevelopmental outcome and physical health in the long term, thereby underlining the importance of adequate neonatal nutrition.

Validation of the direct nasopharyngeal sampling method for collection of expired air in preterm neonates

In clinical studies, the oxidation of 13C-labeled substrates to 13CO2 and the measurement of the appearance of excess 13CO2 in expiratory air has progressed to an increasingly common method as it is noninvasive and lacks the radiation exposure associated with the use of 14C. The collection of respiratory CO2 currently used occurs via trapping of CO2 in sodium hydroxide (trapping method), sometimes in conjunction with indirect calorimetry. The aim of the present study was to determine the accuracy of our direct nasopharyngeal sampling method for the collection of breath samples in preterm infants compared with the currently used trapping method. We present a method that simplifies the collection of breath samples in preterm infants. Seven preterm infants with a gestational age of 26-29 wk were studied on different postnatal days (range, 8-52 d) while receiving full enteral feeding. A primed constant 3-h intragastric infusion of [13C]bicarbonate was given, and breath samples were collected by means of direct nasopharyngeal sampling and by a sodium hydroxide trap simultaneously. Breath CO2 isotopic enrichments rose rapidly to reach a plateau by 120 min with <5% variation of plateau in both methods. 13CO2 breath isotopic enrichments obtained by the direct nasopharyngeal sampling method correlated highly (r2 = 0.933; p < 0.0001) with the trapping method. The Bland-Altman analysis showed no significant variability between the two methods and demonstrated that the 95% confidence interval is within +/- 4.68 delta per thousand. These findings validate the simple method of direct nasopharyngeal sampling of expired air in neonates.

Longitudinal study of energy expenditure in preterm neonates <30 weeks' gestation during the first three postnatal weeks

OBJECTIVES

The objective of this study was to measure energy expenditure (EE) in a contemporary population of preterm neonates <30 weeks' gestation.

STUDY DESIGN

Prospective longitudinal cohort study in 26 consecutive preterm neonates (gestational age, 27 weeks [23-29] [median, range]; birth weight, 980 g [554-1592]). EE was measured by indirect calorimetry on postnatal days 1, 3, 5, 10, and 21. Data on body weight, energy intake, and medical therapy were prospectively collected.

RESULTS

EE increased from 121 +/- 25 kJ/kg per day (29 +/- 6 kcal/kg per day) (mean +/- SD) on day 1 to 222 +/- 25 kJ/kg per day (53 +/- 6 kcal/kg per day) on day 21. An energy deficit occurred only on day 1. EE was closely related to energy intake: For each additional kJ given, EE increased by 0.3 kJ (r = 0.789, P <.0001). Neonates with a birth weight <1000 g did not have a more pronounced energy deficit than the heavier neonates. EE during nasal continuous positive airway pressure in the first postnatal week was 25% lower than during spontaneous respiration.

CONCLUSIONS

EE could be predicted from energy intake with acceptable accuracy in preterm neonates <30 weeks' gestation during the first 3 postnatal weeks. There was no prolonged energy deficit.

Normal value of resting energy expenditure in healthy neonates

OBJECTIVE

We investigated the value of resting energy expenditure (REE) in healthy neonates and evaluated the impact factors on REE.

METHODS

One hundred eighty healthy neonates (95 boys and 85 girls) with birth weights above 2500 g were measured by indirect calorimetry, and the effect of birth weight evaluated. Measured and predicted REEs were compared, and the effects of sex and delivery method on REE were examined in 154 newborn infants with birth weights of approximately 2500 to 4000 g.

RESULTS

Birth weight had a significant effect on REE. There was a negative relation between REE and birth weight (r = -0.289). The REEs of newborn infants weighing more than 4000 g were statistically lower than those of infants weighing 2500 to 4000 g (44.5 +/- 5.9 versus 48.3 +/- 6.1 kcal x kg(-1) x d(-1), P = 0.01). The measured and predicted REEs of 154 newborn infants were 48.3 +/- 6.1 and 54.1 +/- 1.1 kcal x kg(-1) x d(-1), respectively. There was a significant difference between the two values. Sex and delivery methods had no effect on REE in healthy neonates.

CONCLUSIONS

The value from the predicted equation is not suitable for neonatal energy supplementation in clinical practice. The normal REE value for healthy neonates with birth weights of 2500 to 4000 g is 48.3 +/- 6.1 kcal x kg(-1) x d(-1).

Effect of sepsis syndrome on neonatal oxygen consumption and energy expenditure

OBJECTIVE

To evaluate oxygen consumption (VO2), carbon dioxide production, and energy expenditure (EE) in full-term neonates with early-onset neonatal septicemia daily for 7 days beginning at the day of clinical diagnosis of sepsis.

METHODS

A total of 17 spontaneously breathing full-term neonates, 10 with clinical signs of sepsis and 7 healthy neonates (control group), were enrolled in the study. Age at first study day was 3 +/- 0.9 days in both groups. Sepsis syndrome was defined as a systemic response to a bacterial infection with clinical signs of infection, elevated values of interleukins 6 and 8 and C-reactive protein, and abnormal white blood cell count and positive blood cultures (9 group B streptococci, 1 Escherichia coli). Measurements of VO2 and carbon dioxide production were performed daily for 7 days by means of indirect calorimetry.

RESULTS

In the septic infants, VO2 and EE were increased by about 20% at days 1 to 3 and by 15% at day 4 when compared with the controls. From days 1 to 3, EE averaged 57 +/- 3 kcal/kg/d in the septic neonates and 47 +/- 2 kcal/kg/d in the controls. At day 4, EE was 55 +/- 2 and 47 +/- 2 kcal/kg/d, respectively. Energy intake was about the same in both groups, whereas weight gain during the 7 study days was significantly lower in the sick patients than in the control group (19 +/- 2 g/d vs 33 +/- 9 g/d and 5.4 +/- 0.5 g/kg/d vs 9.4 +/- 2.6 g/kg/d, respectively). Increased EE was associated with increased heart rate (126 +/- 4 vs 112 +/- 4 min(-1) at day 1) and respiratory rate (56 +/- 6 vs 40 +/- 4 min(-1) at day 1). There were no differences in rectal temperature (37.3 +/- 0.4 degrees C vs 37.4 +/- 0.2 degrees C), skin temperature (36.5 +/- 0.4 degrees C vs 36.6 +/- 0.3 degrees C), and oxygen saturation (96 +/- 3% vs 96 +/- 3%) between the 2 groups.

CONCLUSIONS

Neonates with sepsis syndrome have elevated VO2 and EE values that could explain impaired growth during the illness period and may make the infants vulnerable to insufficient calorie supply during the acute phase of septic disease.

Effect of changes in inspired oxygen tension on indexes of oxygenation in ventilated neonates

OBJECTIVE

Several indexes are used to quantify the severity of hypoxemia, including the arterial to alveolar oxygen ratio (a/APO(2)), the alveolar-arterial difference P(a-a)o(2), the ratio Pao(2)/Fio(2), and the oxygenation index (OI = mean airway pressure x Pao(2)/Fio(2)). This study was carried out to test how stable these indexes are when small changes in Fio(2) are made in ventilated neonates.

DESIGN

Open prospective clinical study.

SETTING

Level III neonatal intensive care unit of a teaching hospital.

PATIENTS

Forty studies were performed in 31 clinically stable ventilated neonates (median birth weight, 1450 g; median gestation, 30.6 wks), monitored by transcutaneous Pao(2)-oxygen saturation (Sao(2)).

INTERVENTIONS

If hyper- or hypoxemia without derangements of Paco(2) or pH were detected in a blood sample taken from an indwelling arterial catheter, Fio(2) was changed (median change, 0.05; range, -0.3 to 0.25) and another arterial blood sample was obtained 26-83 mins (median, 42) after. The indexes were calculated in the two blood samples, and for each index the changes between baseline and the value after Fio(2) change were analyzed.

MEASUREMENTS AND MAIN RESULTS

Median baseline P(a-a)o(2) was 211.7 torr, median a/APO(2) was 0.24, median Pao(2)/Fio(2) was 161 torr, and median OI was 6.14. After the Fio(2) change, the coefficients of variation (sd/mean) were calculated, and they were 27.5%, 23.8%, 24.5%, and 31.6% for P(a-a)o(2), a/APO(2), Pao(2)/Fio(2), and OI, respectively. Changes in the value of each index were correlated to changes in Fio(2), indicating a dependency on Fio(2). When data were analyzed as "high Fio(2)" (approximate Sao(2) 95%) vs. "low Fio(2)" (approximate Sao(2) 90%), differences were statistically significant for all indexes except for a/APO(2).

CONCLUSIONS

All the indexes tested showed a dependency on the value of Fio(2): increasing Fio(2) spuriously made neonates appear less hypoxemic. The a/APO(2) appeared to perform better than other indexes in this study, with a lower variability and a lower oxygen dependency.

Measurement of carbon dioxide production in very low birth weight babies

BACKGROUND

CO2 production is most commonly measured by using indirect calorimetry to quantify elimination of CO(2) in breath (VCO2). An alternative is to measure the rate at which CO2 appears in the body pool (RaCO2) by infusing a (13)C labelled bicarbonate tracer. VCO2 and RaCO2 generally differ but are related by c, a factor that adjusts for the incomplete recovery of infused tracer in the breath. The literature relating to human studies cites a wide range of values for c but the only neonatal study to determine c empirically estimated a mean value of 0.77.

AIM

To estimate fractional recovery rate, c, in very low birthweight babies, and assess the feasibility of using the isotopic technique to measure CO2 production during mechanical ventilation.

METHOD

Eleven spontaneously breathing, continuously fed, very low birthweight infants (median birth weight 1060 g, median gestational age 29 weeks) were studied.

RESULTS

Mean (SD) VCO2 was 9.0 (2.0) ml/min (standard temperature and pressure dry, STPD) and mean (SD) RaCO2 was 9.6 (2.1) ml/min (STPD). The mean (SD) value of c was estimated as 0.95 (0.13). The 95% confidence intervals of the mean were 0.87-1.03.

CONCLUSIONS

The results emphasise the importance of measuring c for a given study population rather than assuming a value based on adult studies. The close approximation of RaCO2 and VCO2 in this group of babies implies that the labelled bicarbonate infusion technique could be used to measure simply CO2 production during mechanical ventilation.

Energy expenditure in critically ill children

OBJECTIVES

To measure energy expenditure in critically ill children and compare it with the energy expenditure predicted by recommended formulas, and relate the measured energy expenditure to nutritional and clinical indices.

DESIGN

A prospective, clinical study.

SETTING

Tertiary care pediatric intensive care unit in a university children's hospital.

PATIENTS

A total of 37 patients with critical illness who were mechanically ventilated for > or =24 hrs were studied.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Chronic protein-energy malnutrition (CPEM) and acute protein-energy malnutrition were defined by the Waterlow's stages and fat and protein stores were classified as defined by Frisancho, Ryan, and Martinez. Severity of illness was assessed by the Pediatric Risk of Mortality Score, the Therapeutic Intervention Scoring System, and indices of organ failure. Oxygen consumption, carbon dioxide production, and the respiratory quotient were measured by indirect calorimetry, and energy expenditure (MEE) was calculated using the modified Weir formula. Resting energy expenditure (PBMR), predicted energy expenditure, and caloric intake were calculated using recommended formulas. A total of 77 measurements were made in 37 children. MEE was significantly lower than PBMR as estimated by all equations except the Talbot equations. MEE was significantly lower than predicted energy expenditure and the recommended daily allowances. On the first day, the MEE/PBMR ratio was <0.9 in 56.8%, 0.9-1.1 in 21.6%, and >1.1 in 21.6% of patients. MEE did not differ significantly among disease groups or between medical and surgical patients. There was no difference in MEE with or without neuromuscular blockade. MEE was lower in the presence of multiple organ system failure (MOSF) (1019 + 166 kcal/m2 without MOSF vs. 862 + 241 with MOSF; p = .025). A total of 21% had CPEM and 8.1% had acute protein-energy malnutrition. Multivariate stepwise regression analysis showed that the protein intake, midarm muscle area, midarm fat area, the use of vasoactive agents, and sedation correlated with MEE (p < .05). With CPEM, MEE was correlated to the severity of illness (p < .05). Patients at risk for protein stores depletion (midarm muscle areas 1 and 2) had a higher incidence of MOSF compared with nutritionally normal children (p < .05), whereas patients with fat stores depletion (midarm fat area 2) had a higher probability of death (50% vs. 6%, respectively).

CONCLUSIONS

Recommended daily allowances and energy expenditure predicted by using a stress-related correction to the resting energy expenditure grossly overestimate MEE. MEE is close to PBMR and in many patients, it is lower than PBMR. MEE that is lower than PBMR is associated with a higher morbidity. Nutritional repletion should thus be based on MEE to avoid the problems of over- or underfeeding.

Low birthweight infants and total parenteral nutrition immediately after birth. III. Randomised study of energy substrate utilisation, nitrogen balance, and carbon dioxide production

This study aimed to investigate energy substrate utilisation and nitrogen balance in low birthweight infants receiving total parenteral nutrition during the first days of life, and in particular, to determine the effect of two different glucose intakes on carbon dioxide production. Twenty infants (mean (SE) birthweight 1314 (65) g, mean (SE) gestation 30.9 (0.4) weeks) were recruited to the study. Immediately after birth they were randomised to a carbohydrate intake of 8 g/kg/day (5.5 mg/kg/minute) or 12 g/kg/day (8.3 mg/kg/minute). After 24 hours they were changed to the alternative regimen which was continued for a further 24 hours. Fat and protein intakes were kept constant throughout the study. Indirect calorimetry was performed during each of the regimens, urine was collected for urinary nitrogen, and substrate utilisation calculated for 12 infants. The carbohydrate utilisation rate was increased during the higher carbohydrate intake. Lipid utilisation rates were significantly different, with net lipid synthesis occurring during high carbohydrate intake. Protein utilisation rates were not influenced by the different carbohydrate intakes. The mean plasma glucose concentration was higher during the high carbohydrate intake but the mean highest and lowest values were not significantly different during the two study periods. A plasma glucose below 2.6 mmol/l was recorded more frequently during the low glucose intake (9/20 v 5/20). Capillary PCO2 values measured during high and low glucose intakes were similar (5.9 (0.2) v 6.2 (0.3) kPa. Carbon dioxide production rates were increased during the higher carbohydrate intake but the differences were not significant. Similarly, there was no significant difference in the respiratory quotients (RQ), oxygen consumption, or energy expenditure during the two study periods.