Doppler velocimetry in cerebral vessels of small for gestational age infants

Impact of intrauterine growth restriction on cerebral and renal oxygenation and perfusion during the first 3 days after birth

Intrauterine growth restriction (IUGR) is associated with a higher incidence of perinatal complications as well as cardiovascular and renal diseases later on. A better insight into the disease mechanisms underlying these sequalae is important in order to identify which IUGR infants are at a higher risk and find strategies to improve their outcome. In this prospective case-control study we examined whether IUGR had any effect on renal and cerebral perfusion and oxygen saturation in term neonates. We integrated near-infrared spectroscopy (NIRS), echocardiographic, Doppler and renal function data of 105 IUGR infants and 105 age/gender-matched controls. Cerebral and renal regional oxygen saturation values were measured by NIRS during the first 12 h after birth. Echocardiography alongside Doppler assessment of renal and anterior cerebral arteries were performed at 6, 24, 48 and 72 h of age. Glomerular and tubular functions were also assessed. We found a left ventricular dysfunction together with a higher cerebral oxygen saturation and perfusion values in the IUGR group. IUGR term infants showed a higher renal oxygen saturation and a reduced oxygen extraction together with a subclinical renal damage, as indicated by higher values of urinary neutrophil gelatinase-associated lipocalin and microalbumin. These data suggest that some of the haemodynamic changes present in growth-restricted foetuses may persist postnatally. The increased cerebral oxygenation may suggest an impaired transition to normal autoregulation as a consequence of intra-uterine chronic hypoxia. The higher renal oxygenation may reflect a reduced renal oxygen consumption due to a subclinical kidney damage.

Regional splanchnic oxygen saturation for preterm infants in the first week after birth: reference values

BACKGROUND

Near-infrared spectroscopy is used in the assessment of regional splanchnic oxygen saturation (r_sSO₂), but solid reference values are scarce. We aimed to establish reference values of r_sSO₂ for preterm infants during the first week after birth, both crude and modeled based on predictors.

METHODS

We included infants with gestational age (GA) <32 weeks and/or birth weight <1200 g. We excluded infants who developed necrotizing enterocolitis or sepsis or who died. In the first week after birth, we determined a daily 2-h mean of r_sSO₂ to assess its associations with sex, GA, postnatal age (PNA), small-for-gestational age (SGA) status, patent ductus arteriosus, hemoglobin, nutrition, and head circumference at birth and translated those into a prediction model.

RESULTS

We included 220 infants. On day 1, the mean ± SD r_sSO₂ value was 48.2% ± 16.6. The nadir of r_sSO₂ was on day 4 (38.7% ± 16.6 smoothed line) to 5 (37.4%±17.3, actual data), after which r_sSO₂ increased to 44.2% ± 16.6 on day 7. The final model of the reference values of r_sSO₂ included the following coefficients: r_sSO₂ = 3.2 - 7.0 × PNA + 0.8 × PNA² - 4.0 × SGA + 1.8 × GA.

CONCLUSIONS

We established reference values of r_sSO₂ for preterm infants during the first week after birth. GA, PNA, and SGA affect these values and need to be taken into account.

IMPACT

Regional splanchnic oxygen saturation is lower in infants with a lower gestational age and in small-for-gestational age infants. Regional splanchnic oxygen saturation decreases with a higher postnatal age until day 4 after birth and then increases until day 7 after birth. Gestational age, postnatal age, and small-for-gestational age status affect regional splanchnic oxygen saturation and need to be taken into account when interpreting regional splanchnic oxygen saturations using NIRS. Reference values for infant regional splanchnic oxygen saturation can be computed with a formula based on these variables, as provided by this study.

Advanced MR imaging of the placenta: Exploring the in utero placenta-brain connection

The placenta is a vital organ necessary for the healthy neurodevelopment of the fetus. Despite the known associations between placental dysfunction and neurologic impairment, there is a paucity of tools available to reliably assess in vivo placental health and function. Existing clinical tools for placental assessment remain insensitive in predicting and evaluating placental well-being. Advanced MRI techniques hold significant promise for the dynamic, non-invasive, real-time assessment of placental health and identification of early placental-based disorders. In this review, we summarize the available clinical tools for placental assessment, including ultrasound, Doppler, and conventional MRI. We then explore the emerging role of advanced placental MR imaging techniques for supporting the developing fetus and appraise the strengths and limitations of quantitative MRI in identifying early markers of placental dysfunction for improved pregnancy monitoring and fetal outcomes.

Amplitude-integrated electroencephalographic activity and middle cerebral artery Doppler flow measurements in preterm small for gestational age infants

Amplitude-integrated encephalography (EEG) is frequently used in neonatal intensive care units to monitor brain functions. Its bedside application and easy interpretation are the most important features. Brain development of small for gestational age infants can be affected by intrauterine chronic hypoxia. The current study aimed to evaluate cerebral functions of small for gestational age infants by means of amplitude-integrated EEG. Thirty- to 34-week-old 22 small for gestational age and 27 appropriate for gestational age preterm infants were included in the study. The mode of delivery, gender, birth weight, and Apgar scores of the patients were recorded. Following middle cerebral artery mean velocity measurement with cranial Doppler at the 24th hour of birth, an amplitude-integrated EEG recording was performed on all infants, for a period of 4 to 24 hours. Small for gestational age infants had significantly higher middle cerebral artery mean velocity than appropriate for gestational age infants (21.09 ± 4.25 vs 17.8 ± 4.07; P = .029). The amplitude-integrated EEG recordings showed lower "lower border of quiet sleep" and total Burdjalov score in small for gestational age infants when compared with appropriate for gestational age infants (2.5 [1-3.25] µV vs 3 [2.75-4] µV; P = .04, 8 [6-10], 9 [9-11]; P = .04, respectively). Increased middle cerebral artery blood flow observed in small for gestational age infants might be a marker of chronic intrauterine hypoxia to which these infants were exposed. These infants demonstrated a more immature pattern of amplitude-integrated EEG.

Brain-Sparing in Intrauterine Growth Restriction: Considerations for the Neonatologist

Intrauterine growth restriction (IUGR) is most commonly caused by placental insufficiency, in response to which the fetus adapts its circulation to preserve oxygen and nutrient supply to the brain ('brain-sparing'). Currently, little is known about the postnatal course and consequences of this antenatal adaptation of the cerebral circulation. The altered cerebral haemodynamics may persist after birth, which would imply a different approach with regard to cerebral monitoring and clinical management of IUGR preterm neonates than their appropriately grown peers. Few studies are available with regard to this topic, and the small body of evidence shows controversy. This review discusses the cerebral circulatory adaptations of IUGR fetuses and appraises the available literature on their postnatal cerebral circulation with potential clinical consequences.

Fetal liver blood flow distribution: role in human developmental strategy to prioritize fat deposition versus brain development

Among primates, human neonates have the largest brains but also the highest proportion of body fat. If placental nutrient supply is limited, the fetus faces a dilemma: should resources be allocated to brain growth, or to fat deposition for use as a potential postnatal energy reserve? We hypothesised that resolving this dilemma operates at the level of umbilical blood distribution entering the fetal liver. In 381 uncomplicated pregnancies in third trimester, we measured blood flow perfusing the fetal liver, or bypassing it via the ductus venosus to supply the brain and heart using ultrasound techniques. Across the range of fetal growth and independent of the mother's adiposity and parity, greater liver blood flow was associated with greater offspring fat mass measured by dual-energy X-ray absorptiometry, both in the infant at birth (r = 0.43, P<0.001) and at age 4 years (r = 0.16, P = 0.02). In contrast, smaller placentas less able to meet fetal demand for essential nutrients were associated with a brain-sparing flow pattern (r = 0.17, p = 0.02). This flow pattern was also associated with a higher degree of shunting through ductus venosus (P = 0.04). We propose that humans evolved a developmental strategy to prioritize nutrient allocation for prenatal fat deposition when the supply of conditionally essential nutrients requiring hepatic inter-conversion is limited, switching resource allocation to favour the brain if the supply of essential nutrients is limited. Facilitated placental transfer mechanisms for glucose and other nutrients evolved in environments less affluent than those now prevalent in developed populations, and we propose that in circumstances of maternal adiposity and nutrient excess these mechanisms now also lead to prenatal fat deposition. Prenatal developmental influences play important roles in the human propensity to deposit fat.

My approach to performing a perinatal or neonatal autopsy

An opportunity to determine the cause of death, factors that may have a role in it, and the extent and cause of malformations is provided by perinatal autopsy. The family may be assisted in finding closure after the death of their infant by the information obtained. Insight into classifying infants appearing normal into one of three groups, small, appropriate and large for gestational age, has been provided, as each group tends to have specific causes of death. In infants with congenital anomalies, patterns of malformation may lead us to the diagnosis. An accurate diagnosis is required to provide counselling for a subsequent pregnancy.

Neonatal color Doppler US study: normal values of cerebral blood flow velocities in preterm infants in the first month of life

The aim of this study is to generate normal reference values of cerebral blood flow velocities (CBFV) and Doppler indices (DI) in the anterior (ACA) and the middle (MCA) cerebral arteries during the first month of life in "healthy" preterm infants. CBFV were obtained with color Doppler technique in seventy selected preterm infants divided in four groups of gestational age (GA) (25 to 28; 29 to 30; 31 to 32; 33 to 35 wk). Our data demonstrate that CBFV increase with rising GA, birth weight (BW) and postnatal age. Additionally, we can provide the median values, tenth and ninetieth percentiles of CBFV and DI, in the ACA and MCA in each GA group as reference normal values of CBFV and DI in preterm newborn.

Ecografia transfontanelar com fluxo a cores em recém-nascidos prematuros

Com o objetivo de determinarmos, evolutivamente, a medida da velocidade do fluxo sangüíneo nas artérias intracranianas, em recém-nascidos prematuros (RNP) normais e com hemorragia intracerebral, avaliamos - no período de junho de 1994 a março de 1999 - 73 recém-nascidos prematuros. A idade gestacional variou de 28 a 36 semanas e o peso ao nascimento variou de 720g a 2530g. O diagnóstico da hemorragia intracerebral foi realizado utilizando-se a ecografia transfontanelar (EGT). Para avaliação seqüencial da medida da velocidade do fluxo sangüíneo nas artérias intracranianas os 73 foram submetidos a EGT, com Doppler pulsátil, no 3º, 7º, 30º e 90º dias de vida. Após obtermos os valores numéricos destas velocidades determinamos o indice de resistência (IR). Ao analisarmos os valores do IR, comparando-se os 2 grupos de RNP, concluimos que os valores do IR são sempre mais elevados nos RNP normais (RNP-N) que nos RNP com hemorragia intracerebral (RNP-HIC); que tanto no grupo de RNP normais quanto no grupo de RNP com hemorragia intracerebral os valores do IR decrescem significativamente com o acréscimo da idade dos neonatos. Analisando-se ainda, comparativamente, os valores do IR nos RNP com hemorragia intracerebral, em seus diversos graus, observamos não haver, evolutivamente, diferença estatisticamente significante. Analisando-se também , comparativamente, os valores do IR nos RNP com hemorragia intracerebral localizada no hemisfério cerebral direito ou esquerdo concluimos não haver diferença estatisticamente significante entre os valores do IR obtidos das artérias localizadas no hemisfério cerebral acometido comparados aos valores do IR obtidos do hemisfério cerebral não afetado.

[Neonatal Doppler velocimetry in full term small-for-gestational age newborns]

This study aimed to evaluate the cerebral blood flow of full term small-for-gestational age newborns, using cranial ultrasound Doppler at birth. This study was performed at CAISM/UNICAMP (Tertiary Health Center for Women). Sixty term newborns were selected and divided in two groups: appropriate-for-gestational age (AGA) (36 neonates) and small-for-gestational age (SGA) (24 neonates). Cranial ultrasound Doppler evaluation was performed on both groups, between 24 and 48 hours after birth. Cerebral blood flow velocity (CBFV) was lower in the small-for-gestational age group, in the anterior cerebral artery (ACA). Doppler measurements were different statistically between the groups only for values related to peak systolic flow velocity (PSFV) and mean flow velocity (MFV) in the ACA. There was no significant difference for any evaluated parameters of flow velocity in the middle cerebral artery (MCA). It was concluded that SGA newborns showed PSFV and MFV significantly reduced only in the ACA. Weight/gestational age, neonatal polycythemia and mean arterial blood pressure values were statistically related to MFV in the ACA. In presence of fetal suffering, mean arterial blood pressure values and smoking in the pregnancy were statistically related to MFV in the MCA.

Mode of delivery and perinatal cerebral blood flow

OBJECTIVE

To ascertain whether the perinatal cerebral blood flow velocity differed between vaginally delivered appropriate for gestational age (vag. AGA) term babies, AGA babies delivered by Caesarean section (C.s. AGA), and small for gestational age (C.s. SGA) babies also delivered by Caesarean section.

STUDY DESIGN

Forty-five babies were examined by Doppler ultrasound of the middle cerebral artery prior to and immediately after delivery, and at 1 h and 24 h after birth. The pulsatility index (PI) and time-averaged maximum velocity (TAMXV) were calculated.

RESULTS

No differences in TAMXV were found between the vag. AGA and C.s. AGA groups at any of the four recordings. A significantly higher PI value was found in the C.s. AGA group 1 h after birth. The C.s. SGA group had lower PI values before and just after birth, but did not differ significantly from the C.s. AGA group at 1 h or 24 h after birth.

CONCLUSIONS

The results suggest mode of delivery to have a transitory effect on cerebral vascular resistance in healthy term AGA babies. The C.s. SGA group differed in the initial recording just after birth, but later manifested similar blood flow velocities in middle cerebral artery as the C.s. AGA group.

Accuracy of the middle-cerebral-to-umbilical-artery resistance index ratio in the prediction of neonatal outcome in patients at high risk for fetal and neonatal complications

OBJECTIVE

The purpose of this study was to determine the accuracy of the middle-cerebral-to-umbilical-artery resistance index ratio in the prediction of fetal outcome in pregnancies at high risk for fetal and neonatal morbidity and mortality.

STUDY DESIGN

A prospective controlled nonrandomized study was conducted in the high-risk pregnancy unit of a teaching hospital. The control group was formed by 20 healthy women with uncomplicated singleton pregnancies and healthy children delivered at term. The study group consisted of 115 women referred to the high-risk pregnancy unit because of a variety of pregnancy complications. Longitudinal evaluation of the control group and cross-sectional evaluation of the study group were carried out at different gestational ages by means of duplex Doppler ultrasonography. The main outcome measures were fetal growth retardation, preterm birth, and neonatal morbidity.

RESULTS

The middle-cerebral-to-umbilical-artery ratio remains relatively constant (mean +/- SD 1.33 +/- 0.19) between 27 and 37 weeks. A cutoff value of 1.0 (sensitivity 57.9%, specificity 75.6%, false-positive rate 24.4%) was selected from the receiver-operator characteristic curve analysis. This cutoff value successfully identified a population at significant risk of fetal growth retardation (relative risk 3.07, 95% confidence interval 1.73 to 5.45, exact two-tailed p = 0.0009) and severe neonatal morbidity (Mann-Whitney U = 463.5, two-tailed p = 0.03). The middle-cerebral-to-umbilical-artery ratio was not useful in the prediction of preterm birth.

CONCLUSIONS

A middle-cerebral-to-umbilical-artery ratio of < or = 1.0 identifies a subgroup of patients at high risk for fetal growth retardation and severe neonatal morbidity.

Cardiac output and cerebral blood flow velocity in small for gestational age infants during the first 5 days after birth

Small for gestational age (SGA) infants are at an increased risk of neurologic handicap. Cardiac output and cerebral blood flow velocity (CBFV) were measured by pulsed Doppler sonography in 15 SGA infants and in 15 appropriate for gestational age (AGA) infants on days 1 and 5 after birth. The gestational age of both groups ranged from 32 to 40 weeks and averaged 37 weeks. Cardiac output was higher in the SGA infants than in the AGA infants on day 1 (314 +/- 62 vs. 275 +/- 36 ml/min/kg; P < 0.05), but similar in the SGA and AGA infants on day 5 (319 +/- 66 vs. 318 +/- 53 ml/min/kg). On day 1, both haematocrit (0.53 +/- 0.04 vs. 0.49 +/- 0.04 l/l; P < 0.05) and systemic red blood cell transport (169 +/- 35 vs. 136 +/- 24 ml/kg/min; P < 0.01) were higher in the SGA infants than in the AGA infants. Systemic red cell flow increased in the AGA infants from day 1 to day 5 (157 +/- 27 ml/min/kg; P < 0.05), but not in the SGA infants (166 +/- 39 ml/kg/min). Mean cerebral blood flow velocity (CBFV) was higher in the AGA infants than in the SGA infants on both days (P < 0.05). However, cerebral red blood cell transport (CBFV x haematocrit) was similar in both groups. We conclude that on day 1, systemic red blood cell transport is higher in SGA infants than in AGA infants due to increased cardiac output and haematocrit.(ABSTRACT TRUNCATED AT 250 WORDS)

Early postnatal cerebral Doppler changes in relation to birth weight

Serial Doppler studies of the anterior cerebral artery were performed on 50 healthy term infants in the first 5 days of life. This study aims to establish a normative database for cerebral Doppler measurements in infants born appropriate for gestational age (AGA) and to compare them with those born small for gestational age (SGA). The difference between SGA and AGA infants was documented. In AGA infants, the Pourcelot's resistance index (PI) decreased over the first 5 days, while both the peak systolic flow velocity and end diastolic flow velocity increased. In SGA infants, the PI was significantly lower in the first 24 h of life. This was accounted for by an increase in the end diastolic flow velocity which may be a continuation of the intrauterine situation. The significance of the difference is discussed.