Respiratory Quotient Changes in Full Term Newborn Infants Within 30 Hours from Birth Before Start of Milk Feeding

Respiratory quotient changes in full term newborn infants within 30 hours from birth before start of milk feeding

G Zoppi, A Luciano, M Cinquetti, S Graziani and M Bolognani

Chair of Paediatrics, University of Verona and Division of Paediatrics, Major City Hospital of Verona, Italy

Objective: To evaluate substrate utilization in full-term newborn infants, fed every 3±4 h with glucose 10% solution, within 30 h from birth. Design: Random. Setting: Full term newborn infants at the Paediatric Division City Major Hospital, Chair of Paediatrics, Verona University. Subjects: Forty-six newborn infants, 24 females and 22 males of 39 Æ 2 weeks gestational age. Methods: Oxygen consumption (VO2) and CO2 production (VCO2) were measured. Permitting the computation of the respiratory quotient (RQ), which expresses substrate oxidation, at 6 and 30 h from birth. An indirect calorimeter (Deltratrac TMII-MBM-200-DATEX) was used to measure components of energy-balance. Results: Energy expenditure calculated at 6 h was 8.130 (Æ1.5757) kJ=kg=h. At 30 h the value changed to 8.858 (Æ1.483) kJ=kg=h. Statistical evaluation (t-student) showed a signi®cant (P 0.000) variation in RQ values (6 h: RQ 0.94; 30 h: RQ 0.88). Conclusions: Respiratory quotient suggests an increase of energy derived from fat metabolism at 30 h from birth. Our data con®rm that early breast feeding or formula milk feeding could represent a physiological approach to nutritional regimen of the newborn infant. Sponsorship: University of Verona, Italy. Descriptors: respiratory quotient; newborn infant; indirect calorimetry; energy expenditure

Introduction et al, 1981). Many of these studies, however, were con- ducted in infants fed different amounts of a single formula, During the years 1977±1989 metabolic and endocrine while others included on measurements of energy and interrelations during adaptation to the postnatal life of the nitrogen balances. new-born infant were extensively investigated by Aynsley- In other words, we still need to draw practical conclu- Green (1982, 1989) and (Zoppi et al, 1982). sions on the nutritional and clinical management of the Such studies were carried out by means of blood new-born infant during the hours immediately following determinations of glucose and several hormones. What birth. In our study we used a no-invasive method: indirect still remains to be fully explained is the clinical signi®- calorimetry, an important technique for measuring oxygen cance of hormone level variations in the blood. The ®rst consumption (VO ), carbon dioxide consumption (VCO ), feed of human milk given to term infants 4±6 h after birth 2 2 energy expenditure (EE). Respiratory quotient (RQ) com- has been found to cause an increase in blood glucose, puted as the ratio of VCO to VO was determined. The RQ plasma insulin, growth hormone, gastrin and glucagon 2 2 provide us with a very important metabolic indicator: its concentrations without affecting the levels of pancreatic value expresses the oxidised substrate. A reduction in the glucagon (Ansley-Green et al, 1977; Bloom et al, 1978). RQ value indicates that carbohydrate metabolism decreases The composition of the feed also affects the endocrine progressively with a shift towards the utilization of other response: therefore, a ®rst feed of dextrose though causing substrates such as proteins and particularly fats. We should similar increases in insulin, gastrin and glucose to those recall, in fact, that for carbohydrates RQ CO :O 6: seen after milk, does not stimulate enteroglucagon secre- 2 2 6 1, whereas for fats RQ is less than 1 (RQ CO : tion (Bloom et al, 1978; Ansley-Green et al, 1979). In 2 O 114: 163 0.7). contrast to infants born at term, the ®rst feed of human milk 2 When mother's milk feeding is impossible, a solution of given to preterm infants (28±33 weeks of gestation) 3±6 h glucose 10% (10 ml every 3 h) is the most common after birth causes no changes in the circulating concentra- feeding in the 24±36 h from birth. tion of any of the metabolites or hormones measured (Lucas et al, 1978). Several other studies suggest that the amount of protein deposited is closely related to protein Subjects and methods intake and that the amount of fat deposited is closely Forty-six normal healthy new-born infants (24 F, 22 M), related to energy intake (Reichman et al, 1981; Chessex with 39 Æ 2 weeks gestational age and 3.323 g (Æ0.3 s.d.) birth-weight, were recruited for the study. APGAR score was in normal range. None of the infants had medical Correspondence: Prof G Zoppi, Director, Chair of Paediatrics, Division of Paediatrics, Major City Hospital, Piazzale Stefani 1, 37126 Verona, Italy. problems, and none was receiving medication other than Received 11 July 1997; revised 10 January 1998; accepted 31 January vitamins at the time of investigation. Newborn infants 1998 enrolled in this study did not receive breast milk, either Respiratory quotient changes in full term newborn infants G Zoppi et al 361 because mothers did not produce milk or because mothers Table 1 Characteristics of study population and components of energy did not want to, for personal problems. The infants were balance examined asleep, 2 h after glucose 10% solution feeding. Study 1 (6 h) Study 2 (30 h) P value Body temperature (rectal and axillary) was in the neutral range. During the 30 h of survey the children were orally No. 46 46 Ð fed with glucose solution (10%), 10 ml every 3 h. A Age (weeks) 39 Æ 239Æ 2Ð commercially available indirect calorimeter was used Body weight (g) 3.323 (Æ0.367) 3.074 (Æ0.339) 0.000 VO (ml/kg/min) 6.660 (Æ1.244) 7.422 (Æ1.241) 0.424 (model: Deltratrac TM II-MBM-200-DATEX Division 2 VCO2 (ml/kg/min) 6.305 (Æ1.259) 6.532 (Æ1.091) 0.349 Instrumentarium Corp., Helsinki, Finland). It consists of a RQ 0.947 (Æ0.068) 0.882 (Æ0.046) 0.000 differential paramagnetic oxygen analyser, with automati- EE measured (kj/kg/h) 8.130 (Æ1.575) 8.858 (Æ1.483) 0.012 cally compensated baseline draft, an infrared CO sensor, 2 Values represent mean Æ s.d. and a constant ¯ow generator. The O2 and CO2 analysers have a resolution of 0.01%. Every minute a mean value for the O2 and CO2 concentrations was calculated. The ¯ow generator produces a ¯ow of 700 L=min, reduced by built- normal neurological function. The increased ratio between in ¯ow restrictor elements to 42, 12, and 3 L=min. Before cerebral mass and body weight in the new-born infant each experiment the gas analysers were calibrated using a needs a high glucose consumption. The opinion that the high precision calibration gas (5% CO2 and 95% O2, Datex newborn infant's brain is more resistant to effects of Division Instrumentarium Corp.). hypoglycaemia than the adult brain is no longer acceptable, A round transparent plastic canopy with a capacity of for asymptomatic hypoglycaemia has been shown to be 2540 mL (diameter 24 cm) covered the infant's head and associated with deep neurological dysfunction in new-born chest. The sampling ¯ow used for the sampling of the infants (Koh et al, 1988). expired air was 12 L=min, with an air inlet in one side wall Studies evaluating the adaptation of new-born infants to and an air outlet leading to the gas analysers in the opposite enteral feeding have shown that milk feeding is capable of side wall. This canopy is commercially available for use on causing a cyclic increase in blood glucose concentrations, the new-born infant (Datex Division Instrumentarium thereby maintaining normoglycaemia and signi®cant Corp.). Canopy was used to provide the best patient's increases in plasma hormones. Impressive differences compatibility, also some observations suggested a varia- between breast-fed and formula-fed preterm and full-term bility of measurements using the canopy, face mask or head infants have been documented (Calvert et al, 1985). More- hood (Bauer et al, 1997). over discontinuous milk-feeding represents an important DeltatracTM II-MBM-200 measured oxygen consump- stimulus for intestinal hormone production, suggesting the tion (VO2), carbonic dioxide production (VCO2) and then it importance of enteral feeding for a normal development of was calculated the respiratory quotient (RQ) and energy intestinal function in postnatal life (Dunn et al, 1988). expenditure (EE) kJ=kg=h. The patient remained under the Our study evaluated oxygen consumption (VO2) and canopy for half an hour, with parameters measured every carbonic dioxide production (VCO2) and calculated respira- minute. The artifacts automatically relieved by the machine tory quotient (RQ: VO2=VCO2 ratio), and energy expendi- were eliminated and therefore not considered in the mean ture (EE). EE (kJ=kg=h) increased from 6 h to 30 h values of each parameter. Measurements were made at 6 (P 0.012). The increase in metabolic rate in the early and 30 h from birth. For each measured parameter, mean postnatal period appears to be a consequence of the energy value and standard deviation were calculated, after which cost of tissue synthesis. This increase may be accounted for statistical evaluation of data variation between 6 and 30 h by the fact that EE is an expression of metabolically active was accomplished using the t-student test. Informed par- tissue, or Fat-Free Mass (FFM) and not of Fat Mass (FM). ental consent was obtained before infants were recruited. This would mean that a loss of fat mass occurs from 6 h to 30 h with the result that the drop in weight does not reduce EE, but, on the contrary, increases it. In fact, EE=weight Results (kg) increases, since the total weight drops as a result of the The energy expenditure calculated at 6 h was 8.130 reduction in FM. The utilization of fat depots is con®rmed (Æ1.575) kJ=kg=h. At 30 h the value changed to 8.858 by the change in RQ values. Measurements, obtained at 6 (Æ1.483). and 30 h from birth, demonstrated a signi®cant variation in Oxygen consumption and carbonic dioxide production the respiratory quotient (P 0.000) between 6 h were slightly higher during the second control. The respira- (RQ 0.94) and 30 h (RQ 0.88). It is well known that tory quotient, 0.94 Æ 0.06 at 6 h, decreased to 0.88 Æ 0.04 RQ value expresses substrate oxidation. Low RQ values after 24 h (30 h). This variation in RQ was statistically indicate lipid substrate utilisation and, if RQ < 0.70 signi®cant (P < 0.000). Data referring to characteristics of expresses ketogenesis, RQ close to 1 is indicative of study population and components of energy balance with glucose substrate oxidation, while RQ > 1 shows conver- mean value, s.d. and statistical analysis are reported in sion of glucose to lipids. Table 1. We observed a reduction of the RQ value, demonstrating a rapid consumption of glucidic substrate, and an increase of fat metabolism. Fat oxidation occurs when there is a Discussion difference between total energy expenditure and the oxida- Metabolism and nutrition are the two most important tion of proteins and carbohydrates (Flatt, 1993). Carbohy- processes in the new-born infant's adaptation to extra- drate and protein oxidation, in fact, correspond roughly to uterine life. Normoglycaemia and intermittent feeding their intake, whereas fat oxidation is not proportional to and fasting represent the essential changes of extrauterine intake (Flatt et al, 1985; Schultz et al, 1989). life. Glucose represents an important substrate of cerebral Little glycogen is stored in newborn infants (0.45±0.9% metabolism and its continuous supply is indispensable for of body weight) (Lusk, 1961; Schulze et al, 1981), and the Respiratory quotient changes in full term newborn infants G Zoppi et al 362 energy expended in storing metabolisable energy as fat has Bloom SR, Aynsley-Green A & Lucas A (1978): Hormonal response to been estimated to be 0.36 kcal per kcal energy stored as fat ®rst feeding in neonates. J. Pediatr. 93, 900±901. Calvert SA, Soltesz G, Jenkins PA, Harris D, Newman C, Adrian TE, (Van Es, 1977; Harvey & Tobin, 1983). 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