Factors affecting the neonatal response to artificial surfactant

Do Different Amounts of Exogenous Surfactant Differently Influence Cerebrovascular Instability in a Consecutive Group of Preterm Babies? Preliminary Results from a Single-Center Experience

BACKGROUND

Thirty years ago, the first attempt by Saliba and colleagues was made to reduce the negative effects (hypercarbia) of exogenous surfactant (ES) by slowing its administration. Sixteen years later, we observed the first less invasive surfactant administration (LISA) attempt by Kribs and colleagues. Many studies, since that time, have tried to minimize the invasiveness of ES and subsequent cerebral blood flow perturbations through studies using near-infrared spectroscopy (NIRS). We sought to address this medical challenge by identifying a less problematic modality of ES administration by delivering multiple aliquots of ES instead of a single one, as typically performed. The aim of this study was to test the hypothesis that a different way of administering ES using more aliquots could be a safe alternative that should be assessed in further studies.

METHODS

Patients between 26 + 0 and 35 + 6 weeks of gestational age (GA) requiring ES administration were enrolled (April 2023-February 2024). Differently fractioned doses were delivered according to an arbitrary standard dosage (0.3 mL per aliquot in babies < 29 weeks; 0.6 mL in babies ≥ 29 weeks), while NIRS and transcutaneous CO2 (tCO2) monitoring were always performed. ES's effectiveness was assessed based on the reduction in the Oxygen Saturation Index (OSI) after administration. Persistent desaturation, bradycardia, and airway obstruction were defined as adverse effects and used to evaluate safety during ES administration, as well as variability in NIRS-rSO2 values and tCO2.

RESULTS

Twenty-four patients were enrolled with a median GA of 29 weeks (IQR 4.5) and BW of 1223 ± 560 g. In addition, 50% of the cohort received fewer than three aliquots, whereas the other 50% received more than three. Monitoring was started before the procedure and continued 30' after the last ES aliquot administration. The variability in NIRS-SpO2 values was significantly higher in the group (p = 0.007) with a lower number of aliquots administered. Similarly, increased NIRS-rSO2 values (p = 0.003) and increased tCO2 levels (p = 0.005) were observed in infants who underwent an ES split after the administration of a low number of aliquots.

CONCLUSIONS

Our data obtained from the group with > 3 fractionated doses of ES seem to justify the preparation of a more robust study, as the combination of reduced NIRS variability and reduced tCO2 maximum levels is consistent with more stable cerebral blood flow during the challenging time of ES administration.

Acute Neonatal Respiratory Failure

Acute respiratory failure requiring assisted ventilation is one of the most common reasons for admission to the neonatal intensive care unit. Respiratory failure is the inability to maintain either normal delivery of oxygen to the tissues or normal removal of carbon dioxide from the tissues. It occurs when there is an imbalance between the respiratory workload and ventilatory strength and endurance. Definitions are somewhat arbitrary but suggested laboratory criteria for respiratory failure include two or more of the following: PaCO₂ > 60 mmHg, PaO₂ < 50 mmHg or O₂ saturation <80 % with an FiO₂ of 1.0 and pH < 7.25 (Wen et al. 2004).

Pathophysiology of Neonatal Respiratory Distress Syndrome

Neonatal respiratory distress syndrome (RDS) remains one of the major causes of neonatal mortality and morbidity despite advances in perinatal care. The initial management of infants with RDS has almost become 'too routine' with little thought about the pathophysiological processes that lead to the disease and how the clinician can use the existing therapeutic interventions to optimize care. The transition from fetus to infant involves many complex adaptations at birth; the most important is the function of the lungs as a gas exchange organ. Preterm surfactant-deficient infants are less well equipped to deal with this transition. Optimum gas exchange is achieved through matching of ventilation and perfusion. In RDS, ventilation may be affected by homogeneity of the airways with atelectasis and over distension, as hyaline membranes block small airways. In turn this contributes to the inflammation that becomes bronchopulmonary dysplasia. Exogenous surfactant given early, particularly with positive end-expiratory pressure and, where necessary, gentle ventilation, would seem to be the optimum way to prevent atelectasis. How this can be achieved in neonates after surfactant therapy is explored through a review of the normal physiology of the newborn lung and how this is affected by RDS. The therapeutic interventions of resuscitation, exogenous surfactant, ventilation and inhaled nitric oxide are discussed in relation to their effects and what are currently the optimum ways to use these. It is hoped that with a better understanding of the normal physiology in the newborn lung, and the effects of both disease and interventions on that physiology, the practising clinician will have a greater appreciation of management of preterm infants with, or at risk of, RDS.

Soluble intercellular cell adhesion molecule-1 and L-selectin plasma concentrations and response to surfactant in preterm infants

OBJECTIVE

To investigate whether plasma concentrations of soluble intercellular cell adhesion molecule (ICAM)-1 and L-selectin at 24 hrs of life are related to good or poor response to exogenous surfactant in preterm infants.

DESIGN

Prospective study of markers of inflammation in circulating blood at 24 hrs of life.

SETTING

Level III neonatal intensive care unit.

PATIENTS

Twenty-nine preterm newborns suffering from severe respiratory distress syndrome (Fio(2) > 0.4) without signs of infection or fetal acidosis, and 17 healthy preterm newborns of similar gestational age serving as controls.

INTERVENTIONS

Infants with respiratory distress were treated with natural surfactant at 0.3-5 hrs of life. A response to surfactant, defined as a decrease of Fio(2) >50% within 6 hrs after surfactant, was seen in 21 infants.

MEASUREMENTS AND MAIN RESULTS

Soluble ICAM-1 and L-selectin concentrations were determined in plasma samples taken at 24 hrs of age. ICAM-1 was elevated (p <.001) in infants who responded poorly to surfactant (median, 392 ng/mL; range, 58.26-4884.24 ng/mL) compared with good responders (20.52 ng/mL, 2.32-138.58 ng/mL) or controls (21.91 ng/mL, 2.61-65.73 ng/mL), without differences between controls and good responders. L-selectin was lower (p =.004) in surfactant-treated infants (4.45 nmol/L, 2.0-10.4 ng/mL) than in controls (6.0/2.35-10.25 nmol/L) without differences between surfactant good and poor responders. However, infants requiring supplemental oxygen at 36 wks of gestational age had reduced L-selectin at 24 hrs of age (3.2/2.0-3.45 vs. 5.0/2.35-10.4 nmol/L, p =.004), whereas there was no difference in ICAM-1.

CONCLUSIONS

In preterm infants with respiratory distress, a poor response to surfactant within 6 hrs of administration is associated with elevated circulating ICAM-1 concentrations at 24 hrs of age. Low plasma L-selectin at 24 hrs of age predicts prolonged requirement for supplemental oxygen.