Effects of surfactant distribution and ventilation strategies on efficacy of exogenous surfactant

Less invasive surfactant administration versus endotracheal surfactant instillation followed by limited peak pressure ventilation in preterm infants with respiratory distress syndrome in China: study protocol for a randomized controlled trial

Background

Less invasive surfactant administration (LISA) is a way of giving surfactant without endotracheal intubation and has shown to be promising in reducing the incidence of bronchopulmonary dysplasia (BPD) in preterm infants. However, the mechanism underlying its beneficial effect and variations in the technique of administration may prevent its widespread use. This trial aims to evaluate the effects of two methods of surfactant administration, LISA or endotracheal surfactant administration followed by low peak pressure (LPPSA) ventilation, in preterm infants with respiratory distress syndrome (RDS).

Methods

The LISA Or Low Peak Pressure trial is to be conducted in 14 tertiary neonatal intensive care units in China. A total of 600 preterm infants born with gestational age between 25^0/7 and 31^6/7 weeks and with a primary diagnosis of RDS will be involved in the study. Infants will be randomized to the LISA or LPPSA group when surfactant therapy is indicated. Primary outcomes include mortality, severity of bronchopulmonary dysplasia at 36 weeks of postmenstrual age (PMA), and mechanical ventilation (MV) in the first 72 h of life. Secondary outcomes include the days of MV, duration of all sorts of non-invasive respiratory support, fraction of inspired oxygen, oxygen saturation before and after surfactant administration, and time required to perform the procedure for surfactant administration. The incidence of comorbidities, including retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC), intraventricular hemorrhage (IVH), hemodynamically significant patent ductus arteriosus (hsPDA), pneumothorax, and massive pulmonary hemorrhage within 48 h of surfactant administration, and the failure rates of each technique will be determined.

Discussion

Data from recent systematic review and meta-analysis have suggested a possible improvement in outcomes of preterm infants with RDS by the LISA technique. However, robust evidence is lacking. Why LISA plays a potential role in reducing respiratory morbidity, mainly BPD in preterm infants, remains unclear. The possible explanations are the active and uninterrupted delivery of continuous positive airway pressure during the LISA procedure and the avoidance of complications caused by intubation and relatively high pressure/volume ventilation following surfactant administration. We hypothesized that LISA’s effectiveness lies mainly in avoiding relatively high-pressure positive ventilation immediately following surfactant administration. Thus, this multicenter randomized controlled trial will focus on issues of endotracheal intubation and the pressure/volume used during conventional surfactant administration. The effectiveness, safety and comorbidities of preterm infants following LISA or LPPSA will be evaluated.

Trial registration

Chinese Clinical Trial Registry: ChiCTR1900020970. Registered on 23 January 2019.

The effect of a peptide-containing synthetic lung surfactant on gas exchange and lung mechanics in a rabbit model of surfactant depletion

Background

Currently, a new generation of synthetic pulmonary surfactants is being developed that may eventually replace animal-derived surfactants used in the treatment of respiratory distress syndrome. Enlightened by this, we prepared a synthetic peptide-containing surfactant (Synsurf) consisting of phospholipids and poly-l-lysine electrostatically bonded to poly-l-glutamic acid. Our objective in this study was to investigate if bronchoalveolar lavage (BAL)-induced acute lung injury and surfactant deficiency with accompanying hypoxemia and increased alveolar and physiological dead space is restored to its prelavage condition by surfactant replacement with Synsurf, a generic prepared Exosurf, and a generic Exosurf containing Ca²⁺.

Methods

Twelve adult New Zealand white rabbits receiving conventional mechanical ventilation underwent repeated BAL to create acute lung injury and surfactant-deficient lung disease. Synthetic surfactants were then administered and their effects assessed at specified time points over 5 hours. The variables assessed before and after lavage and surfactant treatment included alveolar and physiological dead space, dead space/tidal volume ratio, arterial end-tidal carbon dioxide tension (PCO₂) difference (mainstream capnography), arterial blood gas analysis, calculated shunt, and oxygen ratios.

Results

BAL led to acute lung injury characterized by an increasing arterial PCO₂ and a simultaneous increase of alveolar and physiological dead space/tidal volume ratio with no intergroup differences. Arterial end-tidal PCO₂ and dead space/tidal volume ratio correlated in the Synsurf, generic Exosurf and generic Exosurf containing Ca²⁺ groups. A significant and sustained improvement in systemic oxygenation occurred from time point 180 minutes onward in animals treated with Synsurf compared to the other two groups (P < 0.001). A statistically significant decrease in pulmonary shunt (P < 0.001) was found for the Synsurf-treated group of animals, as well as radiographic improvement in three out of four animals in that group.

Conclusion

In general, surfactant-replacement therapy in the animals did not fully restore the lung to its prelavage condition. However, our data show that the formulated surfactant Synsurf improves oxygenation by lowering pulmonary shunt.

[Value of surfactant replacement therapy in the treatment of acute respiratory distress syndrome]

Acute respiratory distress syndrome (ARDS) is a common, devastating clinical problem arising from a number of conditions, such as pneumonia, trauma or sepsis. Because of its significant mortality and morbidity, ARDS has been in the focus of extensive experimental and clinical research. Since there is little doubt that alterations of the surfactant system contribute to lung dysfunction and the onset of ARDS, several clinical studies examined the therapeutic safety and efficacy of a surfactant replacement therapy. Clinical experience with exogenous surfactant has proven inconsistent as a therapeutic modality for adult patients with ARDS. This is mainly due to a number of confounding factors, e.g. severity of injury at the time of treatment, dosing regimes and delivery methods used in different trials. However, current data suggest that patients with direct ARDS (e.g. pneumonia, aspiration) could benefit from surfactant replacement therapy rather than patients with indirect ARDS (e.g. sepsis, trauma). Although surfactant replacement therapy has been shown to significantly reduce mortality in neonates with ARDS, there has been no large randomised clinical trial showing that exogenous surfactant improves outcome in adults with respiratory failure. Therefore, surfactant therapy cannot be recommended for routine clinical use in adult patients and has to be considered as a last resort treatment.

Treatment with aerosols in mechanically ventilated patients: is it worthwhile?

Aerosol medications are commonly used in mechanically ventilated patients. Several classes of drugs with different properties and indications may be given by inhalation. In all cases, compared with the systemic route, the inhaled therapy has the main advantage that for a given therapeutic response, the drug dose is several-fold lower, while the systemic absorption is negligible, thus the side effects are greatly minimized. In addition, for some medications the systemic route either causes non-acceptable side effects or results in considerably inferior therapeutic response, rendering the inhaled route the method of choice of drug administration. Bronchodilators, corticosteroids, vasoactive drugs, surfactants, antibiotics, helium and perfluorocarbons are the medications that can be given by inhalation during mechanical ventilation. Some of those represent part of the standard treatment for various groups of mechanically ventilated patients, while the role of others has not been well established yet.

Serotonin Transporter Abnormality in the Dorsal Motor Nucleus of the Vagus in Rett Syndrome: Potential Implications for Clinical Autonomic Dysfunction

Autonomic dysfunction is prevalent in girls with Rett syndrome, an X-chromosome-linked disorder of mental retardation resulting from mutations in the gene encoding methyl-CpG-binding protein 2 (MeCP2). This gene plays a role in regulating neuronal activity-dependent gene expression, including brain-derived neurotrophic factor (BDNF), which is a potent serotonergic (5-HT) neuronal growth factor. We analyzed selected parameters of the 5-HT system of the medulla in autopsied patients with Rett syndrome because of the role of BDNF in 5-HT cell development and because 5-HT plays a key role in modulating autonomic control. 5-HT neurons were identified by immunostaining for tryptophan hydroxylase, the biosynthetic enzyme for 5-HT. We quantitated the number of 5-HT cells in the medulla at 2 standardized levels in 11 Rett and 7 control cases. There was no significant difference in 5-HT cell number between the groups. We analyzed binding to the serotonin transporter (SERT) using the radioligand [(125)I]-RTI-55 with tissue autoradiography in 7 Rett and 5 controls in 9 cardiorespiratory-related nuclei. In the dorsal motor nucleus of the vagus (DMX) (preganglionic parasympathetic outflow), SERT binding for the control cases decreased significantly over time (p = 0.049) but did not change in the Rett cases (p = 0.513). Adjusting for age, binding between the Rett and control cases differed significantly in this nucleus (p = 0.022). There was a marginally significant age versus diagnosis interaction (p = 0.06). Thus, altered 5-HT innervation and/or uptake in the DMX may contribute to abnormal 5-HT modulation of this major autonomic nucleus in patients with Rett syndrome. These data suggest hypotheses concerning 5-HT modulation of vagal function for testing in MeCP2 knockout mice to understand mechanisms underlying autonomic dysfunction in patients with Rett syndrome.

Differential development of 5-HT receptor and the serotonin transporter binding in the human infant medulla

Tissue receptor autoradiography with 3H-lysergic acid diethylamide (3H-LSD), 3H-8-hydroxy-2-[di-N-propylamine] tetralin (3H-8-OH-DPAT), and 125I-RTI-55 was used to map the distribution and developmental profile of 5-HT(1A-1D) and 5-HT2 receptors, 5-HT1A receptors, and the serotonin (5-HT) transporter (SERT), respectively, to nuclei with cardiorespiratory function in the human medulla from midgestation to maturity. The distribution pattern of the 5-HT markers was heterogeneous, with variable densities of binding of each observed both in nuclei with and without 5-HT cell bodies. The highest density of binding for each marker was observed in the raphé nuclei, the site of the highest density of 5-HT cell bodies. A significant reduction in 5-HT receptor binding measured with 3H-LSD was observed between midgestation and infancy, and between infancy and maturity in multiple nuclei, but no changes were observed across infancy. A significant increase in 5-HT1A receptor binding density was observed across infancy in the hypoglossal nucleus (regression slope coefficient = 0.008 +/- 0.002, P = 0.02), and a marginally significant increase was observed in the raphé obscurus (regression slope coefficient = 0.061 +/- 0.026 [mean +/- SEM], P = 0.05). No significant age-related changes in SERT binding were observed at any time. With the exception of the hypoglossal nucleus, where 5-HT1A receptor binding increases while SERT binding remains stable, the medullary 5-HT markers analyzed in the study are essentially "in place" at birth. This study provides important baseline data that serve as a foundation for future work in pediatric 5-HT brainstem disorders, including sudden infant death syndrome.

High-frequency oscillation and exogenous surfactant administration in lung-injured adult sheep

OBJECTIVE

To evaluate the effects of high-frequency oscillation on the response to exogenous surfactant in lung-injured adult sheep.

DESIGN

A prospective, controlled, in vivo, animal laboratory study.

SETTING

Animal research facility of a health sciences university.

SUBJECTS

Twenty-eight adult sheep.

INTERVENTIONS

Animals were anesthetized and instrumented with a tracheostomy and vascular catheters. Following whole lung saline lavage, animals were randomized to one of four groups: Group S-CMV received surfactant and was ventilated for 4 hrs using a conventional mechanical ventilation strategy, group S-HFOV/CMV received surfactant and was ventilated with a high-frequency oscillation technique for 2 hrs and a conventional mechanical strategy for 2 hrs, group HFOV/CMV underwent the latter ventilatory strategies without receiving surfactant, and group HFOV was ventilated with high-frequency oscillation only for 4 hrs. At the end of the ventilatory period, the distributions of ventilation and surfactant were evaluated in animals that received surfactant.

MEASUREMENTS AND MAIN RESULTS

Animals in the S-CMV group had a significantly greater mean PaO2 value at the end of the experimental period than animals in the S-HFOV/CMV or HFOV/CMV groups. Evaluation of the distribution of ventilation relative to surfactant demonstrated that animals ventilated with high-frequency oscillation followed by conventional mechanical ventilation had a significantly greater disproportionate distribution of ventilation relative to surfactant compared with the CMV-only group.

CONCLUSIONS

A period of high-frequency oscillation, as used in this study, immediately following exogenous surfactant administration mitigates the host's response to surfactant when subsequently switched to conventional mechanical ventilation.

The role of exogenous surfactant in the treatment of acute lung injury

A number of conditions, such as pneumonia, trauma, or systemic sepsis arising from the gut, may result in the acute respiratory distress syndrome (ARDS). Because of its significant morbidity and mortality, ARDS has been the focus of extensive research. One specific area of interest has been the investigation of the role of the surfactant system in the pathophysiology of this disease. Several studies have demonstrated that alterations of surfactant contribute to the lung dysfunction associated with ARDS, which has led to investigations into the use of exogenous surfactant as a therapy for this syndrome. Clinical experience with surfactant therapy has been variable owing to a number of factors including the nature of the injury at the time of treatment, the specific surfactant preparation utilized, the dose and delivery method chosen, the timing of surfactant administration over the course of the disease, and the mode of ventilation used during and after surfactant administration.

Polyethylene glycol (PEG) attenuates exogenous surfactant in lung-injured adult rabbits

Exogenous surfactant administration in patients with the acute respiratory distress syndrome is currently being evaluated, although resource limitations and the potential expense are existing concerns. Previous in vitro and in vivo studies have shown that substances such as polyethylene glycol (PEG) added to exogenous surfactant improved the function of the surfactant. Based on these data, we hypothesized that PEG would augment surfactant function in an adult rabbit model of lung injury induced by lung lavage and mechanical ventilation, and that this would be accomplished by altering surfactant metabolism. Contrary to our hypothesis, however, mean Pa(O(2)), Pa(CO(2)), and peak inspiratory pressures values 3 h after treatment were significantly worse in the surfactant + PEG treatment groups compared with the surfactant alone groups. These effects were observed for two different doses of surfactant tested. Lavage analyses after sacrifice showed that animals given PEG with their surfactant had significantly lower total and large aggregate surfactant pool sizes compared with animals given surfactant alone. We conclude that in this lung injury model, PEG attenuated surfactant responses, suggesting that further preclinical studies are required before testing this approach in humans.

Effects of high-frequency oscillation on endogenous surfactant in an acute lung injury model

This study evaluated the effects of high-frequency oscillation (HFO) and conventional mechanical ventilation (CMV) on gas exchange and the pulmonary surfactant system in an acute lung injury model. Following induction of lung injury with N-nitroso-n-methylurethane, adult rabbits were anesthetized and randomized to one of the following ventilatory strategies: HFO for 120 min, CMV for 120 min, HFO for 60 min, followed by CMV for 60 min, CMV for 60 min followed by HFO for 60 min or CMV for 60 min. Separate animals were ventilated using CMV with a lower tidal volume and a positive end-expiratory pressure level that was increased throughout the experimental period. Oxygenation was significantly greater in animals ventilated with HFO compared with animals ventilated with CMV. The proportion of surfactant in large aggregate forms was significantly greater following ventilatory support with HFO compared with CMV. Surfactant aggregate conversion was also significantly lower during HFO compared with CMV. We conclude that in our model of acute lung injury, HFO was a superior mode of ventilation and reduced the conversion of alveolar surfactant large aggregates into small aggregate forms, resulting in a greater percentage of large aggregate forms in the alveolar space.