Pierre Tourneux

Pulmonary Circulatory Effects of Norepinephrine in Newborn Infants with Persistent Pulmonary Hypertension

OBJECTIVE To evaluate the respiratory and the pulmonary circulatory effects of norepinephrine in newborn infants with persistent pulmonary hypertension (PPHN)-induced cardiac dysfunction. STUDY DESIGN Inclusion criteria were: 1) Newborn infants >35 weeks gestational age; 2) PPHN treated with inhaled nitric oxide; and 3) symptoms of circulatory failure despite adequate fluid resuscitation. Lung function and pulmonary hemodynamic variables assessed with Doppler echocardiography were recorded prospectively before and after starting norepinephrine. RESULTS Eighteen newborns were included (gestational age: 37 +/- 3 weeks; birth weight: 2800 +/- 700 g). After starting norepinephrine, systemic pressure and left ventricular output increased respectively from 33 +/- 4 mm Hg to 49 +/- 4 mm Hg and from 172 +/- 79 mL/kg/min to 209+/-90 mL/kg/min (P < .05). Although the mechanical ventilatory variables have not been changed, the post-ductal transcutaneous arterial oxygen saturation increased from 89% +/- 1% to 95% +/- 4%, whereas the oxygen need decreased from 51% +/- 24% to 41% +/- 20% (P < .05). The pulmonary/systemic pressure ratio decreased from 0.98 +/- 0.1 to 0.87 +/- 0.1 (P < .05). Mean left pulmonary artery blood flow velocity increased by 20% (P < .05). CONCLUSION Norepinephrine may improve lung function in newborn infants with PPHN through a decrease in pulmonary/systemic artery pressure ratio and improved cardiac performance.

Hypotension in Preterm Infants with Significant Patent Ductus Arteriosus: Effects of Dopamine

OBJECTIVE To study the effects of dopamine on systemic arterial pressure (SAP) and systemic blood flow (SBF) (estimated with the superior vena cava [SVC] flow) in preterm infants with hypotension and patent ductus arteriosus (PDA). STUDY DESIGN Clinical and echocardiographic variables were measured before and 2 hours after starting dopamine in premature infants <32 weeks gestational age with PDA and systemic hypotension. RESULTS Seventeen premature infants were included (gestational age, 28+/-2 weeks; birth weight, 1030 +/- 400 g). A mean rate of 8 +/- 2 microg/kg/min of dopamine raised SAP from 30 +/- 3 to 41 +/- 5 mm Hg (P < .05), and the pulmonary artery pressures from 25 +/- 5 to 32 +/- 8 mm Hg (P < .05). The SVC flow increased by 30% (from 130 +/- 40 to 170 +/- 44 mL/kg/min; P < .05). The left ventricular output and the end-diastolic and mean left pulmonary artery blood flow velocities did not change despite the increase in pulmonary artery pressure. CONCLUSION In preterm infants with hypotension and PDA, dopamine (<10 microg/kg/min) increases the systemic blood pressure and the systemic blood flow. Our results suggest that dopamine decreases left-to-right shunting across ductus arteriosus, caused by a rise in pulmonary vascular resistances.

Échanges thermiques et thermorégulation chez le nouveau-né

The newborns energy expenditure is used in order of priority for: (i) basic metabolism; (ii) body temperature regulation and (iii) body growth. Thermal regulation is an important part of energy expenditure, especially for low birth-weight infants or preterm newborns. The heat exchanges with the environment are greater in the infant than in the adult, explaining the increased risk of body hypo- or hyperthermia. The newborn infant is a homeotherm, but over a long period of time, he cannot maintain the thermal processes. Further developments are expected to improve the infants thermal environment, with assessment of the various heat exchange mechanisms by conduction, convection, radiation and evaporation. The quantification of the respective parts of these exchanges would improve nursing care through clinical procedures or equipment used to ensure the control of the optimal thermohygrometric conditions in incubators, especially when the likelihood of excessive body cooling is high. The present review focuses on the various body heat exchange mechanisms, the thermoregulation processes of the newborn, and their implications in clinical usage and limitations in the neonatal intensive care unit.

Noradrenaline for management of septic shock refractory to fluid loading and dopamine or dobutamine in full-term newborn infants.

Aim: To determine the effects of noradrenaline in full‐term newborns with refractory septic shock.

Ventilatory response to a hyperoxic test is related to the frequency of short apneic episodes in late preterm neonates.

Chemoreception is frequently involved in the processes underlying apnea in premature infants. Apnea could result from a decrease in carotid body effectiveness. However, increased carotid body activity could also initiate apnea through hypocapnia following hyperventilation when the receptors are stimulated. The aim of this study was to analyze the relationship between carotid body effectiveness and short apneic episodes in older preterm neonates. Carotid body effectiveness was assessed at thermoneutrality in 36 premature neonates (2.07 ± 0.26 kg) by performing a 30-s hyperoxic test during sleep, the oxygen inhalation involving a ventilation decrease. Blood O2 saturation (Spo2) and ventilatory parameters were monitored before and during the hyperoxic test. Short episodes of apnea (frequency and mean duration) were recorded during the mornings 3-h interfeeding interval. Pretest Spo2 was not related to any of the measured respiratory parameters. A higher frequency of short apneic episodes was linked to a greater ventilation decrease in response to the hyperoxic test (ρ = −0.32; p = 0.01). Increased carotid body response is correlated with greater apneic episodes frequency, even in the absence of concomitant oxygen desaturation. Fetal or early postnatal hypoxemia could have increased peripheral chemoreceptor activity, which could initiate a “overshoot/undershoot” situation, which in turn could induce a critical Po2/Pco2 combination and apnea.

Patient-ventilator asynchrony during noninvasive pressure support ventilation and neurally adjusted ventilatory assist in infants and children.

Objectives: To document the prevalence of asynchrony events during noninvasive ventilation in pressure support in infants and in children and to compare the results with neurally adjusted ventilatory assist. Design: Prospective randomized cross-over study in children undergoing noninvasive ventilation. Setting: The study was performed in a PICU. Patients: From 4 weeks to 5 years. Interventions: Two consecutive ventilation periods (pressure support and neurally adjusted ventilatory assist) were applied in random order. During pressure support (PS), three levels of expiratory trigger (ETS) setting were compared: initial ETS (PSinit), and ETS value decreased and increased by 15%. Of the three sessions, the period allowing for the lowest number of asynchrony events was defined as PSbest. Neurally adjusted ventilator assist level was adjusted to match the maximum airway pressure during PSinit. Positive end-expiratory pressure was the same during pressure support and neurally adjusted ventilator assist. Asynchrony events, trigger delay, and cycling-off delay were quantified for each period. Results: Six infants and children were studied. Trigger delay was lower with neurally adjusted ventilator assist versus PSinit and PSbest (61 ms [56–79] vs 149 ms [134–180] and 146 ms [101–162]; p = 0.001 and 0.02, respectively). Inspiratory time in excess showed a trend to be shorter during pressure support versus neurally adjusted ventilator assist. Main asynchrony events during PSinit were autotriggering (4.8/min [1.7–12]), ineffective efforts (9.9/min [1.7–18]), and premature cycling (6.3/min [3.2–18.7]). Premature cycling (3.4/min [1.1–7.7]) was less frequent during PSbest versus PSinit (p = 0.059). The asynchrony index was significantly lower during PSbest versus PSinit (40% [28–65] vs 65.5% [42–76], p < 0.001). With neurally adjusted ventilator assist, all types of asynchronies except double triggering were reduced. The asynchrony index was lower with neurally adjusted ventilator assist (2.3% [0.7–5] vs PSinit and PSbest, p < 0.05 for both comparisons). Conclusion: Asynchrony events are frequent during noninvasive ventilation with pressure support in infants and in children despite adjusting the cycling-off criterion. Compared with pressure support, neurally adjusted ventilator assist allows improving patient–ventilator synchrony by reducing trigger delay and the number of asynchrony events. Further studies should determine the clinical impact of these findings.

Optimizing patient-ventilator synchrony during invasive ventilator assist in children and infants remains a difficult task

Objectives: To document and compare the prevalence of asynchrony events during invasive-assisted mechanical ventilation in pressure support mode and in neurally adjusted ventilatory assist in children. Design: Prospective, randomized, and crossover study. Setting: Pediatric and Neonatal Intensive Care Unit, University Hospital of Geneva, Switzerland. Patients: Intubated and mechanically ventilated children, between 4 weeks and 5 years old. Interventions: Two consecutive ventilation periods (pressure support and neurally adjusted ventilatory assist) were applied in random order. During pressure support, three levels of expiratory trigger setting were compared: expiratory trigger setting as set by the clinician in charge (PSinit), followed by a 10% (in absolute values) increase and decrease of the clinician’s expiratory trigger setting. The pressure support session with the least number of asynchrony events was defined as PSbest. Therefore, three periods were compared: PSinit, PSbest, and neurally adjusted ventilatory assist. Asynchrony events, trigger delay, and inspiratory time in excess were quantified for each of them. Measurements and Main Results: Data from 19 children were analyzed. Main asynchrony events during PSinit were autotriggering (3.6 events/min [0.7–8.2]), ineffective efforts (1.2/min [0.6–5]), and premature cycling (3.5/min [1.3–4.9]). Their number was significantly reduced with PSbest: autotriggering 1.6/min (0.2–4.9), ineffective efforts 0.7/min (0–2.6), and premature cycling 2/min (0.1–3.1), p < 0.005 for each comparison. The median asynchrony index (total number of asynchronies/triggered and not triggered breaths ×100) was significantly different between PSinit and PSbest: 37.3% [19–47%] and 29% [24–43%], respectively, p < 0.005). With neurally adjusted ventilatory assist, all types of asynchrony events except double-triggering and inspiratory time in excess were significantly reduced resulting in an asynchrony index of 3.8% (2.4–15%) (p < 0.005 compared to PSbest). Conclusions: Asynchrony events are frequent during pressure support in children despite adjusting the cycling off criteria. Neurally adjusted ventilatory assist allowed for an almost ten-fold reduction in asynchrony events. Further studies should determine the clinical impact of these findings.

Assessment of whole body and regional evaporative heat loss coefficients in very premature infants using a thermal mannequin : influence of air velocity

In human adults, experimental assessment of the evaporative heat loss coefficient (h(e)) requires a fully wetted skin surface area implying exposure to severe heat stress. For ethical reasons, this type of experimental situation is impossible to perform on neonates. The aim of the present study was to assess h(e) values in clinical situations for the body as a whole and for the different body segments, in particular, in natural and forced convection and using an anthropomorphic, sweating, thermal mannequin to represent a very small premature neonate (body mass 900 g). Skin hydration (i.e., simulated sweating) was performed by two electronic pumping systems, providing a steady adjustable flow of water to the mannequin surface. Experiments were carried out in a closed-incubator heated to air temperatures of 33 degrees C and 36 degrees C, with air velocities (Va) ranging from 0.01 to 0.7 m s(-1), and with four levels of air relative humidity (40, 50, 60, and 80%). For the body as a whole, h(e)=7 W m(-2) mb(-1) in natural convection, whereas in forced convection h(e) was 11.7, 12.4, and 14.1 W m(-2) mb(-1) for air velocities of 0.2, 0.4, and 0.7 m s(-1), respectively. As far as local h(e) is concerned, our results showed that the relative values of regional water loss in forced convection differ greatly from those observed under still air conditions. Thus, increasing air velocity enhances the heterogeneity in regional skin cooling, which may contribute to the neonates thermal discomfort.

Why wrapping premature neonates to prevent hypothermia can predispose to overheating

Wrapping low-birth-weight neonates in a plastic bag prevents body heat loss. A bonnet can also be used, since large amounts of heat can be lost from the head region, but may provide too much thermal insulation, thus increasing the risk of overheating. We assessed the time required to reach warning body temperature (t38 degrees C), heat stroke (t40 degrees C), or extreme value (t43 degrees C) in a mathematical model that involved calculating various local body heat losses. Simulated heat exchanges were based on body surface temperature distribution measured in preterm neonates exposed to 33 degrees C air temperature (relative air humidity: 35%; air velocity: <0.1 m/s) and covered (torso and limbs) or not with a transparent plastic bag. We also compared metabolic heat production with body heat losses when a bonnet (2 or 3.5 mm thick) covered 10%, 40%, or 100% of the head. Wrapping neonates in a bag (combined or not with a bonnet) does not induce a critical situation as long as metabolic heat production does not increase. When endogenous heat production rises, t38 degrees C ranged between 75 and 287, t40 degrees C between 185 and 549, and t43 degrees C between 287 and 702 min. When this increase was accompanied by a fall in skin temperature, overheating risk was accentuated (37<or=t38 degrees C<or=45; 99<or=t40 degrees C<or=117; 169<or=t43 degrees C<or=194 min). Thus plastic bag and bonnet may result in hyperthermia but only when metabolic heat production rises while skin temperature falls (impeding body heat losses), as can sometimes happen with fever.

Congenital diaphragmatic hernia: does gestational age at diagnosis matter when evaluating morbidity and mortality?

OBJECTIVE The objective of the investigation was to study the relationship between gestational age at diagnosis and mortality and morbidity in fetuses with an isolated congenital diaphragmatic hernia. STUDY DESIGN Between January 2008 and November 2013, 377 live births with isolated congenital diaphragmatic hernia diagnosed antenatally at a known gestational age were recorded in the database of the French National Center for Rare Diseases. The primary outcome studied was mortality estimated at 28 days and at 6 months. The secondary outcome was morbidity evaluated by pulmonary arterial hypertension at 48 hours, oxygen therapy dependence at 28 days, oral disorders, enteral feeding, and prosthetic patch repair. Analyses were adjusted for the main factors of congenital diaphragmatic hernia severity (side of the hernia, thoracic herniation of the liver, gestational age at birth, lung-to-head ratio, and prenatal treatment by tracheal occlusion. RESULTS Mortality rates at 28 days decreased significantly (P < .001) when gestational age at diagnosis increased: 61.1%, 39.2%, and 10.4% for a diagnosis in the first, second, and third trimester, respectively. Adjusted odds ratios were 3.12 [95% confidence interval, 1.86-5.25] and 0.35 [95% confidence interval, 0.18-0.66] for a diagnosis in the first and third trimesters, respectively, compared with a diagnosis in the second trimester. Similarly, morbidity decreased significantly when gestational age at diagnosis increased, and the trend remained significant after adjustment for the main factors of congenital diaphragmatic hernia severity (P < .001). CONCLUSION Gestational age at diagnosis is an independent predictor of postnatal prognosis for children presenting an isolated congenital diaphragmatic hernia and should be taken into account when estimating postnatal morbidity and mortality.