William W. Hay

Nutritionally Mediated Placental Growth Restriction in the Growing Adolescent: Consequences for the Fetus

Abstract Human adolescent pregnancy is characterized by poor pregnancy outcome; the risks of spontaneous miscarriage, prematurity, and low birth weight are particularly acute in girls who are still growing at the time of conception. Studies using a highly controlled sheep paradigm demonstrate that, in growing adolescents who are overnourished throughout pregnancy, growth of the placenta is impaired, resulting in a decrease in lamb birth weight relative to control-fed adolescents of equivalent age. Rapid maternal growth is also associated with increased spontaneous abortion rates in late gestation and a reduction in gestation length. Nutritionally sensitive hormones of the maternal somatotrophic axis may orchestrate nutrient partitioning in this paradigm and the particular role of growth hormone is discussed. At midgestation, the placentae of rapidly growing dams exhibit less proliferation in the fetal trophectoderm and reduced placental mRNA expression of a range of angiogenic factors. These changes occur before differences in placental size are apparent but may impact on subsequent vascularity. By late pregnancy, placental mass in the rapidly growing versus the control dams is reduced by approximately 45%; the fetuses display asymmetric growth restriction and are hypoxic and hypoglycemic. These growth-restricted pregnancies are associated with major reductions in absolute uterine and umbilical blood flows, leading to attenuated fetal oxygen, glucose, and amino acid uptakes. Placental glucose transport capacity is markedly reduced in the rapidly growing dams but is normal when expressed on a weight-specific placental basis. Thus, it is the small size of the placenta per se rather than alterations in its nutrient metabolism or transfer capacity that is the major limitation to fetal growth in the growing adolescent sheep. Information obtained from this highly controlled paradigm is clearly relevant to the clinical management of human adolescent pregnancies. In addition, the paradigm provides a robust model of placental growth restriction that replicates many of the key features of human intrauterine growth restriction per se.

Reliability of Conventional and New Pulse Oximetry in Neonatal Patients

OBJECTIVES: Pulse oximetry is widely used in the NICU, but clinicians often distrust the displayed values during patient motion, i.e., questionable oxygen saturation (SpO2) and pulse rate (PR) values. Masimo Corporation (Irvine, CA) has developed pulse oximetry with claims of resistance to sources of interference. To test this premise, we compared the performance of the Masimo SET pulse oximeter to a conventional device, Nellcor N-200, and then with three other new-generation pulse oximeters, Nellcor N-395, Novametrix MARS, and Philips Viridia 24C.STUDY DESIGN: We studied 26 nonsedated NICU infants who were on supplemental oxygen and/or mechanical ventilation. ECG heart rate (HR) from a bedside monitor and SpO2 and PR from the two pulse oximeters were captured by a PC for a total of 156 hours. The ECG HR and pulse oximeter spectral waveform were analyzed at alarms for hypoxemia (SpO2≤85%) and/or bradycardia (HR≤80 bpm). We then compared the performance of the Masimo SET to three other new-generation pulse oximeters, Agilent Viridia 24C, Nellcor N-395, and Novametrix MARS, in a similar population of seven infants for a total of 28 hours. We added to the test criteria the ability of the various pulse oximeters to track acute changes in HR.RESULTS: Compared with Nellcor, Masimo SET had 86% fewer false alarms, which also were shorter in duration, resulting in 92% less total alarm time. Masimo SET also identified nearly all bradycardias versus 14% for the Nellcor. Compared with the new-generation pulse oximeters, false desaturations, data drop-outs, and false bradycardias were lowest for Masimo SET, as was the capture of true desaturations and bradycardias. Notably, the new-generation devices differed greatly in their ability to detect changes in HR (i.e., the frequency of frozen PR during times of ECG HR change was 0, 6, 11, and 46 for Masimo, Nellcor, Philips, and Novametrix, respectively).CONCLUSIONS: Masimo SET pulse oximetry recorded markedly fewer false SpO2 and PR alarms and identified more true hypoxic and bradycardic events than either conventional or other new-generation pulse oximeters. Masimo SET also most closely reflected the ECG rate irrespective of accelerations or decelerations in HR.SPECULATION: Routine use of Masimo SET pulse oximetry in the NICU could improve clinician confidence in the parameter leading to more judicious titration of oxygen with possible reductions in hypoxic (e.g., pulmonary hypertension) and hyperoxic (e.g., retinopathy of prematurity) pathology. Additionally, a more trustworthy technology should equate with fewer confirmatory arterial blood gas analyses (less blood loss), and faster weaning from the mechanical ventilation (less chronic lung disease).

Investigating the causes of low birth weight in contrasting ovine paradigms

Intrauterine growth restriction (IUGR) still accounts for a large incidence of infant mortality and morbity worldwide. Many of the circulatory and transport properties of the sheep placenta are similar to those of the human placenta and as such, the pregnant sheep offers an excellent model in which to study the development of IUGR. Two natural models of ovine IUGR are those of hyperthermic exposure during pregnancy, and adolescent overfeeding, also during pregnancy. Both models yield significantly reduced placental weights and an asymmetrically growth‐restricted fetus, and display altered maternal hormone concentrations, indicative of an impaired trophoblast capacity. Additionally, impaired placental angiogenesis and uteroplacental blood flow appears to be an early defect in both the hyperthermic and adolescent paradigms. The effects of these alterations in placental functional development appear to be irreversible. IUGR fetuses are both hypoxic and hypoglycaemic, and have reduced insulin and insulin‐like growth factor‐1 (IGF‐1), and elevated concentrations of lactate. However, fetal utilization of oxygen and glucose, on a weight basis, remain constant compared with control pregnancies. Maintained utilization of these substrates, in a substrate‐deficient environment, suggests increased sensitivities to metabolic signals, which may play a role in the development of metabolic diseases in later adult life.

Early aggressive nutrition in preterm infants

Increasingly, neonatologists are realizing that current feeding practices for preterm infants are insufficient to produce reasonable rates of growth, and earlier and larger quantities of both parenteral and enteral feeding should be provided to these infants. Unfortunately, there is very little outcome data to recommend any particular nutritional strategy to achieve better growth. Instead, the rationale for feeding regimens in many nurseries has been quite variably extrapolated from animal data and human studies conducted in gestationally more mature and/or stable neonates. Additionally, there are no well-controlled, prospective studies that validate any nutritional regimen for the very preterm and or sick, unstable neonate. The goal of this review is to present available data to help define the risks and benefits of early parenteral and enteral nutrition, particularly in very preterm neonates, concluding with a more aggressive approach to feeding these infants than has been customary practice.

Adaptation of ovine fetal pancreatic insulin secretion to chronic hypoglycaemia and euglycaemic correction

Fetal pancreatic adaptations to relative hypoglycaemia, a characteristic of intra‐uterine growth restriction, may limit pancreatic β‐cell capacity to produce and/or secrete insulin. The objective of this study was to measure β‐cell responsiveness in hypoglycaemic (H) fetal sheep and ascertain whether a 5 day euglycaemic recovery period would restore insulin secretion capacity. Glucose‐stimulated insulin secretion (GSIS) was measured in euglycaemic (E) control fetuses, fetuses made hypoglycaemic for 14 days, and in a subset of 14‐day hypoglycaemic fetuses returned to euglycaemia for 5 days (R fetuses). Hypoglycaemia significantly decreased plasma insulin concentrations in H (0.13 ± 0.01 ng ml−1) and R fetuses (0.11 ± 0.01 ng ml−1); insulin concentrations returned to euglycaemic control values (0.30 ± 0.01 ng ml−1) in R fetuses (0.29 ± 0.04 ng ml−1) during their euglycaemic recovery period. Mean steady‐state plasma insulin concentration during the GSIS study was reduced in H fetuses (0.40 ± 0.07 vs. 0.92 ± 0.10 ng ml−1 in E), but increased (P < 0.05) in R fetuses (0.73 ± 0.10 ng ml−1) to concentrations not different from those in the E group. Nonlinear modelling of GSIS showed that response time was greater (P < 0.01) in both H (15.6 ± 2.8 min) and R (15.4 ± 1.5 min) than in E fetuses (6.3 ± 1.1 min). In addition, insulin secretion responsiveness to arginine was reduced by hypoglycaemia (0.98 ± 0.11 ng ml−1 in H vs. 1.82 ± 0.17 ng ml−1 in E, P < 0.05) and did not recover (1.21 ± 0.15 ng ml−1 in R, P < 0.05vs. E). Thus, a 5 day euglycaemic recovery period from chronic hypoglycaemia reestablished GSIS to normal levels, but there was a persistent reduction of β‐cell responsiveness to glucose and arginine. We conclude that programming of pancreatic insulin secretion responsiveness can occur in response to fetal glucose deprivation, indicating a possible mechanism for establishing, in fetal life, a predisposition to type 2 diabetes.

Clinical application of a new glucose analyzer in the neonatal intensive care unit: Comparison with other methods†

We evaluated the operation of the Yellow Springs Instrument Co. (YSI) glucose analyzer (model 23A) by clinical nurses for the measurement of blood glucose in the intensive care nursery. In vitro performance was determined with the use of aqueous standards; with a 2-point calibration of 0.0 and 200 mg/dl, a precision of better than 1.0% of each standard (25, 50, 100, 200 mg/dl) was achieved, and the linearity was excellent (Y = 0.99X - 0.49, r = 0.99). The YSI correlated well with a manual spectrophotometric glucose oxidase method (r = 0.99) and the Kodak Ektachem analyzer (r = 0.98) using human umbilical cord blood samples. Five trained clinical nurses performed all YSI and glucose reagent strip analyses, including all in vitro and patient samples. Four reagent strip methods were compared with the YSI from 104 neonatal heel-stick blood samples: Glucometer II with memory (r = 0.73), Glucostix (r = 0.74), Dextrostix (r = 0.70), and Chemstrip bG (r = 0.83). We conclude that clinical nurses can and do learn to use the YSI with excellent precision and that the YSI represents an improved method for measuring glucose concentrations in the newborn intensive care nursery.

Development of primary culture of ovine fetal hepatocytes for studies of amino acid metabolism and insulinlike growth factors

SummaryWe report the development and characterization of a system of primary culture of ovine fetal hepatocytes to aid in the understanding of the cellular regulation of fetal growth and metabolism with emphasis on amino acid metabolism and insulinlike growth factor gene expression and to allow comparison to in vivo studies. Hepatocytes were isolated from late gestation fetal lambs by in situ perfusion and collagenase digestion utilizing occlusion of the ductus venosus to limit intrahepatic shunting. Hepatocytes were cultured in media modified to mimic fetal concentrations of glucose, lactate, and amino acids. Ovine fetal hepatocytes in primary culture maintain the pattern of fetal amino acid production and utilization seen across the fetal liver in vivo. Specifically, there is a net production of serine and a net utilization of glycine. Cultured ovine fetal hepatocytes specifically increase tritiated thymidine incorporation in response to insulin and insulinlike growth factor II (IGF-II). IGF-II mRNA abundance is high and IGF-I mRNA is low in cultured ovine fetal hepatocytes as in the fetal sheep liver in vivo. These data demonstrate the successful isolation of ovine fetal hepatocytes that retain some of the characteristics of the ovine fetal liver while maintained in short-term culture.

Coordinated changes in hepatic amino acid metabolism and endocrine signals support hepatic glucose production during fetal hypoglycemia

Reduced fetal glucose supply, induced experimentally or as a result of placental insufficiency, produces an early activation of fetal glucose production. The mechanisms and substrates used to fuel this increased glucose production rate remain unknown. We hypothesized that in response to hypoglycemia, induced experimentally with maternal insulin infusion, the fetal liver would increase uptake of lactate and amino acids (AA), which would combine with hormonal signals to support hepatic glucose production. To test this hypothesis, metabolic studies were done in six late gestation fetal sheep to measure hepatic glucose and substrate flux before (basal) and after [days (d)1 and 4] the start of hypoglycemia. Maternal and fetal glucose concentrations decreased by 50% on d1 and d4 (P < 0.05). The liver transitioned from net glucose uptake (basal, 5.1 ± 1.5 μmol/min) to output by d4 (2.8 ± 1.4 μmol/min; P < 0.05 vs. basal). The [U-¹³C]glucose tracer molar percent excess ratio across the liver decreased over the same period (basal: 0.98 ± 0.01, vs. d4: 0.89 ± 0.01, P < 0.05). Total hepatic AA uptake, but not lactate or pyruvate uptake, increased by threefold on d1 (P < 0.05) and remained elevated throughout the study. This AA uptake was driven largely by decreased glutamate output and increased glycine uptake. Fetal plasma concentrations of insulin were 50% lower, while cortisol and glucagon concentrations increased 56 and 86% during hypoglycemia (P < 0.05 for basal vs. d4). Thus increased hepatic AA uptake, rather than pyruvate or lactate uptake, and decreased fetal plasma insulin and increased cortisol and glucagon concentrations occur simultaneously with increased fetal hepatic glucose output in response to fetal hypoglycemia.

Pulse Oximetry: As Good as it Gets?

Pulse oximetry is now the standard noninvasive method of measuring blood oxygenation in neonatal patients. Pulse oxygen saturation values (SpO2) are measured on nearly every neonatal patient, and more and more frequently, are incorporated into modular “vital sign” monitors. In fact, SpO2 is now generally accepted as the fifth vital sign. It probably is considered more often and perhaps assigned an even greater clinical importance than heart rate, respiratory rate, blood pressure, or temperature. Although pulse oximetry has not completely replaced blood gas measurements, there are many neonatal patients who can be managed by pulse oximetry and less frequent measures of arterial or venous PCO2 and pH. Nearly universal acceptance of conventional pulse oximetry, however, is not without reservation. Although trials have shown that SpO2 correlates very closely with blood oxygen saturation 2 and quite accurately predicts PaO2, 3 conventional pulse oximetry instrumentation to date has had difficulty in producing accurate and reliable SpO2 values during subject motion 4 and low blood flow conditions. This problem of motion artifact is inherent to conventional pulse oximeters, because motion adds another signal to the pulse waveform signal, thereby changing the apparent amounts of light transmitted to the photoreceptor at the two wavelengths, red (R) and infrared (IR), that are used to detect the relative proportions of oxyhemoglobin and deoxyhemoglobin (R/IR transmitted light ratio). – 8 Motion adds pulsatility to nonarterial blood components (e.g., venous blood), which are mistakenly included in the R/IR ratio generated by the pulsatile arterial blood. The magnitude of error in SpO2 measurement will be influenced by the venous blood saturation, arterial signal amplitude, and magnitude of motion. The motion-added signal produces false SpO2 values to the extent that the extra signal, which does not represent the arterial pulse oxyhemoglobin/deoxyhemoglobin signal, is large relative to the arterial pulse signal. When the motion is marked, absolutely or in relation to the arterial pulse signal during low peripheral blood flow conditions, the motion-added signal tends to predominate over the pulse signal, so that the R/IR ratio transmitted to the photoreceptor produces a false SpO2 value. An additional and specific source of error in conventional pulse oximetry occurs when “noise” from a variety of signal inputs that are not part of the true arterial pulse signal is introduced equally into both the R and IR channels, driving the R/IR ratio toward unity (1.0). A R/IR ratio of 1.0, whether real or artifactual due to noise, predicts a saturation value of ;82% according to conventional pulse oximeter algorithms. Such motion and noise artifacts are disturbing. They also limit accurate assessment of oxygenation, particularly in the sickest of patients (those with low peripheral blood flow), who are most susceptible to erroneous saturation readings. Motion and noise artifacts also can lead to unintentional neglect of the patient’s oxygenation, the pulse oximetry values, or both, and to inadvertent overtreatment of the falsely low SpO2 values with excessive oxygen administration (Goldman JM, Petterson MT, Kopotic RJ, Barker SJ, submitted for publication). Recent conventional pulse oximetry methods to eliminate motion artifact include reporting only new, correct values, freezing and reporting of old values, or reporting zero. These methods only cover up or ignore the true blood oxygenation and SpO2 values, often for relatively long periods. Most medical personnel who do pay attention to the pulse oximeter carefully wait until the motion stops, the pulse waveform signal “looks good” (on those instruments that show it), and the pulse rate matches the heart rate. Such practices are costly in time, and they also emphasize that considerable periods of absent or inaccurate SpO2 values are part of conventional pulse oximetry practice. Periods of absent or inaccurate SpO2 values due to motion artifact are not insignificant. Recent reports have documented as many as 6 changes in behavioral state per hour in preterm infants, with at least 10 changes that last

A GENERALIZED MICHAELIS–MENTEN RESPONSE SURFACE

10 minutes per 4 hours. Nursing interventions and noise independently result in significant changes in both the behavioral and physiological responses of infants studied. Motion artifact during pulse oximetry recordings is dependent on behavioral state, and overall affects up to 50% of recorded traces. Such problems are worse during transport and more physically active periods such as resuscitations. These are situations in which accurate pulse oximetry values would improve understanding of the degree of abnormal oxygenation and the optimization of oxygen therapy and other necessary medical management. Is there any new approach to significantly decrease or eliminate motion artifact? Several preliminary reports now have documented that a new electronic signal processing technique and sensor design, called “signal extraction technology” (SET) by Masimo Corporation (Irvine, CA), markedly decreases false SpO2 values during patient motion –22 and improves the accuracy of SpO2 values during conditions of low peripheral blood flow when even minimal motion can Department of Pediatrics and Section of Neonatology, University of Colorado School of Medicine, Denver, CO.