Prenatal tobacco exposure influences cerebral oxygenation in preterm infants

Aim

Our aim was to determine the influence of prenatal tobacco exposure on regional cerebral tissue oxygen saturation (r_cSO₂) and fractional tissue oxygen extraction (FTOE) in preterm infants. We hypothesized that as a result of vasoconstriction caused by prenatal tobacco exposure r_cSO₂ would be lower and FTOE would be higher during the first days after birth in infants exposed to tobacco during pregnancy.

Methods

Sixty preterms were included in this prospective, observational cohort study (median gestational age 29.9 weeks, range 26.0-31.8, median birth weight 1248 g, range 615-2250). Fourteen infants had been exposed to tobacco during pregnancy. All mothers smoked more than five cigarettes a day till delivery. We measured r_cSO₂ and transcutaneous arterial oxygen saturation (tcSaO₂) in all infants on days 1-5, 8, and 15. FTOE was calculated: FTOE = (tcSaO₂ − r_cSO₂) / tcSaO₂.

Results

In preterm infants exposed to tobacco during pregnancy, r_cSO₂ was lower during days 1, 2, and 8 after birth, median 73% versus 81%, 73% versus 80% and 71% versus 78% respectively. FTOE was higher during days 1 and 8 after birth, median 0.24 versus 0.15 and 0.26 versus 0.19 respectively. On the second day, FTOE tended to be higher, 0.18 versus 0.14.

Conclusions

During the first two days and day 8 after birth cerebral oxygen saturation is lower and oxygen extraction higher in preterm infants following prenatal tobacco exposure. Our data suggest that prenatal tobacco exposure may have an effect on cerebral oxygenation of the infant.     

Cerebral hemodynamics during arousals in preterm infants

The aim of the study was to evaluate potential changes of cerebral blood volume (CBV) related to arousals in preterm infants. As arousals are known to change different physiological parameters, it was postulated that this could also hold true for CBV. Polygraphic recordings were performed in 38 preterm infants (18 female, 20 male). The infants' gestational age at birth was 32.0+/-2.3 weeks, postconceptional age was 35.1+/-1.2 weeks and postnatal age at study entry was 24.3+/-2.9 days, birth weight was 1793+/-527 g and actual weight at study entry was 2011+/-324 g [mean (+/- standard deviation)]. CBV was measured using near infrared spectroscopy. Arousals were scored due to the guidelines of the "International Paediatric Work Group on Arousals" and categorized as either cortical (CA) or subcortical arousals (SCA). Altogether, 122 arousals (66 CA, 56 SCA) were scored. According to sleep stage, 77 arousals were analyzed in active sleep, 23 in quiet sleep and 22 in intermediate sleep. Mean duration of arousals was 8.8+/-0.3 s. CBV, cerebral vascular oxygenation and the balance between oxygen delivery and oxygen consumption remained constant during arousals in preterm infants. This was demonstrated for both CA and SCA and was independent of sleep stage, suggesting that the impact of arousals in stable preterm infants is too small to alter cerebral vascular autoregulation.     

Heart rate variability during extracorporeal membrane oxygenation and recovery in severe neonatal disease

BACKGROUND: Heart rate variability (HRV) reveals information on the functional state of the autonomic nervous system (ANS) in neonates. During severe illness, heart rate variability is impaired. AIM: This study was initiated to measure the changes in HRV in neonates during extracorporeal membrane oxygenation (ECMO) and recovery from severe respiratory and circulatory failure. Moreover, we compared our data with HRV data of healthy newborns and we investigated the differences in HRV parameters between ECMO-survivors and non-survivors. STUDY DESIGN: This study is of an observational character. We performed short-term recordings of heart rate variability in 14 neonates during ECMO and recovery. We computed time- and frequency-domain HRV parameters. RESULTS: ECMO significantly affects time-domain HRV parameters. Severe neonatal illness causes a significant reduction of all calculated HRV parameters; clinical recovery is accompanied by an increase of HRV. In comparison with normative data of healthy newborns, however, HRV remains impaired. The ECMO-development ratio separated the non-survivors from the survivors during ECMO therapy. CONCLUSIONS: During severe neonatal illness, HRV is impaired. It remains to be clarified whether the impairment of HRV during severe illness can predict the neurological outcome. The ability of the E/D ratio as an HRV parameter to serve as a predictive tool has to be corroborated in larger group of patients.     

Spontaneous cries can alter the physiological well-being and cerebral oxygenation of very preterm infants

Introduction

Infant crying is a major expression of distress and can occur without any exogenous stimulation. Little is known, however, about the effects of crying on physiological homeostasis in very preterm infants (VPIs).

Methods

Environmental, behavioral (video and audio recording) and physiologic (heart rate [HR], respiratory rate [RR], and systemic [SaO₂] and regional cerebral oxygenation [rSO₂]) parameters were prospectively evaluated over 10 h in 18 VPIs (median gestational age, 28 [27–31] weeks). Only episodes of “spontaneous” and isolated cries were analyzed. Changes in parameters were compared over 5-second periods between baselines and 40 s following the onset of crying. Two periods were distinguished: 0–20 s (a) and 20–40 s (b). Minimal and/or maximal values in these periods were also compared to the baseline.

Results

Of the 18 VPIs initially studied, 13 (72%) presented crying episodes (CE). They experienced 210 “spontaneous” and isolated CE, with a median of 9 [range, 1–63] CEs per child. Physiological values varied significantly from the baseline with mainly a mean decrease in HR of − 4.8 ± 5.3 beats/min (b) after an initial mean increase of + 2.6 ± 2.0 beats/min (a); a mean decrease in RR of − 3.8 ± 4.8 cycles/min (a), followed by a mean increase of + 5.6 ± 7.3 cycles/min (b) and mean unidirectional decreases in SaO₂ and rSO₂ (minimal values) of − 1.8 ± 2.3% and − 2.5 ± 3.0%, respectively.

Conclusion

Spontaneous cries can alter the homeostasis of VPIs. Their possible adverse consequences and high occurrence emphasize the need for better prevention and response to them.     

Relationship of the ventilatory response to hypoxia with neonatal apnea in preterm infants

OBJECTIVE: Correlate the ventilatory response of preterm infants to hypoxic exposure with incidence of neonatal apnea.Study design Seventeen stable convalescing premature infants underwent bedside cardiorespiratory monitoring of respiration using respiratory inductance plethysmography, heart rate, and oxygen saturation (SaO(2)) for a 12-hour period. These studies were scored for number of apneas > or =15 and > or =20 seconds. Infants then underwent a 3-minute hypoxic exposure. Minute ventilation (V(E)) was calculated for 30-second epochs from the time inspired oxygen reached 15%. Linear regression analysis was used to correlate the change in V(E) normalized for decrease in SaO(2) (DeltaV(E)/DeltaSaO(2)) during the first and third minutes of hypoxic exposure with the number of apneic episodes during the 12-hour study. RESULTS: The majority of infants exhibited an anticipated biphasic ventilatory response to hypoxia. There was a significant positive correlation between DeltaV(E)/DeltaSaO(2) during the first and third minutes of hypoxic exposure and number of apneic episodes > or =15 and > or =20 seconds during the preceding 12 hours. CONCLUSIONS: Preterm infants with a greater number of apneic episodes exhibit an increased ventilatory response to hypoxic exposure, suggesting that apnea of prematurity may be associated with enhanced peripheral chemoreceptor activity.     

Oxygen saturation in healthy infants immediately after birth

OBJECTIVE: Because the optimal concentration of oxygen (FiO2) required for stabilization of the newly born infant has not been established, the FiO2 is commonly adjusted according to the infant's oxygen saturation (SpO2). We aimed to determine the range of pre-ductal SpO2 in the first minutes of life in healthy newborn infants. STUDY DESIGN: We applied an oximetry sensor to the infant's right palm or wrist of term and preterm deliveries immediately after birth. Infants who received any resuscitation or supplemental oxygen were excluded. SpO2 was recorded at 60 second intervals for at least 5 minutes and until the SpO2 was >90%. RESULTS: A total of 205 deliveries were monitored; 30 infants were excluded from the study. SpO2 readings were obtained within 60 seconds of age from 92 of 175 infants (53%). The median (interquartile range) SpO2 at 1 minute was 63% (53%-68%). There was a gradual rise in SpO2 with time, with a median SpO2 at 5 minutes of 90% (79%-91%). CONCLUSION: Many newborns have an SpO2 <90% during the first 5 minutes of life. This should be considered when choosing SpO2 targets for infants treated with supplemental oxygen in the delivery room.     

Early versus late cord clamping: effects on peripheral blood flow and cardiac function in term infants

BACKGROUND: In the debate on the best cord clamping time in newborn infants, we hypothesized that late cord clamping enables an increased volemia due to blood transfer to the newborn from the placenta. AIM: To assess whether clamping time can affect limb perfusion and heart hemodynamics in a group of 22 healthy term newborn infants. STUDY DESIGN: A case-control study. SUBJECTS: Eleven early-clamped (at 30 s) vaginally-delivered newborn infants were compared with eleven late-clamped (at 4 min) newborns. OUTCOME MEASURES: The two groups were studied using near-infrared spectroscopy and M-mode echocardiography. RESULTS: Late cord clamping coincided with a higher hematocrit (median 62% versus 54%) and hemoglobin concentration (median 17.2 versus 15 g/dL), whilst there were no changes in bilirubin level. Echocardiography showed a larger end-diastolic left ventricle diameter (1.7 cm median value versus 1.5) coupled with unvaried shortening and ejection fraction values. There were no changes in calf blood flow, oxygen delivery, oxygen consumption or fractional oxygen extraction calculated from the NIRS measurements, or in foot perfusion index. CONCLUSIONS: Our results demonstrated that late cord clamping coincides with an increased placental transfusion, expressed by higher hematocrit and hemoglobin values, and larger left ventricle diameter at the end of the diastole, with no changes in peripheral perfusion or oxygen metabolism.     

Elimination of ventilator dead space during synchronized ventilation in premature infants

BACKGROUND: Mainstream airflow sensors used in neonatal ventilators to synchronize mechanical breaths with spontaneous inspiration and measure ventilation increase dead space and may impair carbon dioxide (CO(2)) elimination. OBJECTIVE: To evaluate a technique consisting of a continuous gas leakage at the endotracheal tube (ETT) adapter to wash out the airflow sensor for synchronization and ventilation monitoring without CO(2) rebreathing in preterm infants. DESIGN: Minute ventilation (V'(E)) by respiratory inductance plethysmography, end-inspiratory and end-expiratory CO(2) by side-stream microcapnography, and transcutaneous CO(2) tension (TcPCO(2)) were measured in 10 infants (body weight, 835+/-244 g; gestational age, 26+/-2 weeks; age, 19+/-9 days; weight, 856+/-206 g; ventilator rate, 21+/-6 beats/min; PIP, 16+/-1 centimeters of water (cmH(2)O); PEEP, 4.2+/-0.4 cmH(2)O; fraction of inspired oxygen (FIo(2)), 0.26+/-0.6). The measurements were made during four 30-minute periods in random order: IMV (without airflow sensor), IMV+Sensor, SIMV (with airflow sensor), and SIMV+Leak (ETT adapter continuous leakage). RESULTS: Airflow sensor presence during SIMV and IMV+Sensor periods resulted in higher end-inspiratory and end-expiratory CO(2), Tcpco(2), and spontaneous V'(E) compared with IMV. These effects were not observed during SIMV+Leak. CONCLUSIONS: The significant physiologic effects of airflow sensor dead space during synchronized ventilation in preterm infants can be effectively prevented by the ETT adapter continuous leakage technique.