The effects of surfactant on haemodynamics in hyaline membrane disease

Hemodynamically significant patent ductus arteriosus profile in preterm neonates (26-34 weeks' gestation) undergoing surfactant replacement therapy in India: a prospective observational study

Surfactant administration significantly improves respiratory outcomes in preterm infants with respiratory distress syndrome (RDS). However, surfactant administration may lead to hemodynamic alterations, particularly in the heart, affecting the patent ductus arteriosus (PDA), the consequences of which are not fully understood. This prospective observational study took place in an Indian neonatal care unit from July 2019 to November 2020, enrolling preterm neonates (26-34 weeks' gestation) with RDS needing non-invasive positive pressure ventilation. They were divided into two groups: those who received surfactant while on respiratory support and those who did not. All newborns in the study had an initial echocardiogram within 24 h to detect PDA flow. Subsequent echocardiograms were conducted between 48 and 72 h or earlier based on symptoms. Of 220 infants requiring respiratory support, 84 were enrolled, with 42 in each group. While demographic variables were similar, the surfactant group had a lower median gestational age (29.0 vs. 31.0 weeks). In the surfactant group, a significantly higher percentage of neonates had hemodynamically significant PDA (hsPDA) compared to the non-surfactant group (54.76% vs. 26.19%, P-value = .008). Multiple logistic regression found no significant association between gestation, birth weight, or shock and hsPDA occurrence. Pulmonary hemorrhage occurred more often in the surfactant group. Bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH) > grade 2, and necrotizing enterocolitis (NEC) ≥ grade 2 did not differ significantly between the groups. Surfactant therapy via the less invasive surfactant administration technique was associated with a higher incidence of hsPDA. While surfactant is crucial for neonatal respiratory care, its potential hemodynamic effects, including hsPDA, should be considered.

Persurf, a new method to improve surfactant delivery: a study in surfactant depleted rats

PURPOSE

Exogenous surfactant is not very effective in adults with ARDS, since surfactant does not reach atelectatic alveoli. Perfluorocarbons (PFC) can recruit atelectatic areas but do not replace impaired endogenous surfactant. A surfactant-PFC-mixture could combine benefits of both therapies. The aim of the proof-of-principal-study was to produce a PFC-in-surfactant emulsion (Persurf) and to test in surfactant depleted Wistar rats whether Persurf achieves I.) a more homogenous pulmonary distribution and II.) a more homogenous recruitment of alveoli when compared with surfactant or PFC alone.

METHODS

Three different PFC were mixed with surfactant and phospholipid concentration in the emulsion was measured. After surfactant depletion, animals either received 30 ml/kg of PF5080, 100 mg/kg of stained (green dye) Curosurf™ or 30 ml/kg of Persurf. Lungs were fixated after 1 hour of ventilation and alveolar aeration and surfactant distribution was estimated by a stereological approach.

RESULTS

Persurf contained 3 mg/ml phospholipids and was stable for more than 48 hours. Persurf-administration improved oxygenation. Histological evaluation revealed a more homogenous surfactant distribution and alveolar inflation when compared with surfactant treated animals.

CONCLUSIONS

In surfactant depleted rats administration of PFC-in-surfactant emulsion leads to a more homogenous distribution and aeration of the lung than surfactant alone.

Does retrograde diastolic flow in the descending aorta signify impaired systemic perfusion in preterm infants?

High-volume systemic-to-pulmonary ductal shunting occurs frequently in preterm infants and is indicated by diastolic flow reversal in the descending aorta (DAo). We studied the relationship between ductal diameter, diastolic DAo reversal, and left ventricular output (LVO); and superior vena caval (SVC) flow (upper body perfusion) and DAo flow (lower body perfusion) in preterm (<31 wk) infants. Echocardiographic assessments were performed at 5, 12, 24, and 48 h postnatal age (80 infants, median gestation 28 wk, 1060 g). Incidence of ductal patency fell from 100% at 5 h to 72% at 48 h; incidence of pure systemic-to-pulmonary shunting increased from 66% to 95% of infants with patent ducts. In infants with duct diameter greater than the median, 35-48% of infants had DAo flow reversal. In infants with duct diameter greater than median, DAo reversal was associated with 23-29% increases in LVO at 5-48 h, and 35% decreases in DAo flow volume at 24-48 h, but no differences in SVC flow. In conclusion, a large duct with left-to-right shunting is common in preterm infants. Retrograde DAo flow is a marker of high-volume shunt, evidenced by increased LVO. Preterm infants with high-volume ductal shunt may have preserved upper body perfusion but reduced lower body perfusion.

Current surfactant use in premature infants

Exogenous surfactant therapy has been a significant advance in the management of preterm infants with RDS. It has become established as a standard part of the management of such infants. Both natural and synthetic surfactants lead to clinical improvement and decreased mortality, with natural surfactants having additional advantages over currently available synthetic surfactants. The use of prophylactic surfactant administered after initial stabilization at birth to infants at risk for RDS has benefits compared with rescue surfactant given to treat infants with established RDS. In infants who do not receive prophylaxis, earlier treatment (before 2 hours) has benefits over later treatment. The use of multiple doses of surfactant is a superior strategy to the use of a single dose, whereas the use of a higher threshold for retreatment seems to be as effective as a low threshold. Adverse effects of surfactant therapy are infrequent and usually not serious. Long-term follow-up of infants treated with surfactant in the neonatal period is reassuring. In the future we are likely to see the development of new types of surfactants. Further research is required to determine the optimal use of surfactant in conjunction with other respiratory interventions.

Haemodynamic effects of altering arterial oxygen saturation in preterm infants with respiratory failure

AIMS

To examine the haemodynamic effects of brief alteration in arterial oxygenation in preterm infants with respiratory failure.

METHODS

Eighteen preterm infants with respiratory failure, aged 9-76 hours, underwent detailed Doppler echocardiographic assessment at 86%, 96%, and 100% SaO2, achieved by altering the FIO2. Sixteen were receiving intermittent positive pressure ventilation, median FIO2 0.45 (0.20-0.65), median mean airway pressure 12 cm H2O (0-20). SaO2 was stable for 15 minutes at each stage. Four parameters of pulmonary arterial pressure were measured: peak velocity of tricuspid regurgitation and peak velocity of left to right ductal flow, TPV:RVET ratio and PEP:RVET ratio, measured at the pulmonary valve, along with flow velocity integrals at the aortic and pulmonary valves, and systemic arterial pressure. Ductal size was graded into closed, small, moderate, large with imaging, pulsed and continuous wave Doppler.

RESULTS

Between 86% and 96% SaO2, there were no consistent changes, but in three of the 12 with a patent ductus arteriosus (PDA) there was ductal constriction, with complete closure in one. Between 96% and 100% SaO2, peak ductal flow velocity rose significantly in four of eight with a PDA. Ductal constriction occurred in four infants; in three this was associated with a significant fall in aortic flow integral and a rise in aortic pressure (4-6 mm Hg). Overall, 11 infants went from 86% to 100% SaO2 and pulmonary arterial pressure fell significantly in seven.

CONCLUSION

A brief rise in SaO2 within the range maintained by most neonatal units can cause significant ductal constriction. The fall in pulmonary arterial pressure with 100% SaO2 seen in most infants was associated with a fall in pulmonary blood flow (or no change), rather than a rise, indicating that the dominant haemodynamic effect was ductal constriction rather than pulmonary vasodilation.

A comparison of the hemodynamic and respiratory effects of surfactant instillation during interrupted ventilation versus noninterrupted ventilation in rabbits with severe respiratory failure

The purpose of this study was to evaluate whether avoiding interruption of ventilation during surfactant instillation improves the effects on lung function and surfactant distribution and whether it prevents the adverse effects on blood pressure and cerebral blood flow. The study was performed using rabbits with severe respiratory failure induced by lung lavages. These rabbits were randomized to 99mTc-Nanocoll labeled surfactant instillation through a side lumen of the endotracheal tube without interrupting ventilation or instillation during a short interruption of ventilation. After surfactant instillation with interruption of ventilation, PaO2 rose from 8.7+/-1.3 to 24.9+/-6.4 kPa (mean+/-SEM). Without interruption, PaO2 rose from 8.4+/-0.8 to 32.4+/-4.3 kPa. PaCO2 decreased with interruption from 4.69+/-0.51 to 3.61+/-0.26 kPa and without interruption from 5.06+/-0.41 to 4.13+/-0.23 kPa. Dynamic and static compliance indices were not statistically different after both procedures. Surfactant distribution tended to be less nonuniform after instillation without interrupting ventilation. In contrast, avoidance of interruption of ventilation resulted in less uniform lobar distribution and less peripheral deposition of surfactant. By instillation with interruption, blood pressure increased quickly (28+/-6.6%), followed by a 22+/-5.3% decrease. Blood pressure increased quickly (16+/-4.2%), followed by a 40+/-10% decrease by surfactant instillation without interruption. Cerebral blood flow, measured by an ultrasonic transit time flow probe on the carotid artery, increased quickly (45+/-14%), followed by a 64+/-11% decrease with interruption, whereas it increased 15+/-4.9% (p = 0.06 versus with interruption) and decreased 61+/-13% without interruption of ventilation. Therefore, avoiding interruption of ventilation during surfactant instillation tends to prevent the potential adverse effects of a rapid rise in cerebral blood flow, and furthermore, tends to improve uniformity of surfactant distribution, whereas having no detrimental effect on respiratory function.

Nasal continuous positive airway pressure and early surfactant therapy for respiratory distress syndrome in newborns of less than 30 weeks' gestation

OBJECTIVE

To determine whether early versus late treatment with porcine surfactant (Curosurf) reduces the requirement of mechanical ventilation in very preterm infants primarily supported by nasal continuous positive airway pressure (nasal CPAP).

DESIGN

Multicenter randomized, controlled trial.

PATIENTS

The study population comprised 60 infants <30 weeks' gestation with respiratory distress syndrome (RDS) who had an arterial to alveolar oxygen tension ratio (a/APO2) of 0.35 to 0.22. The cohort from which the study population was generated comprised 397 infants.

RESULTS

The need for mechanical ventilation or death within 7 days of age was reduced from 63% in the late-treated infants to 21% in early-treated infants. Increasing numbers of antenatal steroid doses also improved the outcome, especially in the early-treated infants. Six hours after randomization mean a/APO2 rose to 0.48 in the early-treated infants compared with 0.36 in the late-treated. The need of mechanical ventilation before discharge was reduced from 68% in the late-treated to 25% in the early-treated infants.

CONCLUSIONS

Nasal CPAP in combination with early treatment with Curosurf significantly improves oxygenation and reduces the subsequent need for mechanical ventilation in infants <30 weeks' gestational age with RDS.

Current perspectives on the drug treatment of neonatal respiratory distress syndrome

Respiratory distress syndrome (RDS) in preterm neonates is caused by a lack of alveolar surfactant, which leads to decreased pulmonary compliance and increased work of breathing. Effective therapy for RDS has reduced mortality at the expense of increasing the number of preterm survivors with chronic lung disease. Drugs such as corticosteroids, proterelin (thyrotropin-releasing hormone) and ambroxol have all been administered to mothers to promote fetal lung maturation, but of these only corticosteroids have been proven to be of benefit. The management of RDS includes assisted ventilation and surfactant replacement therapy. There are several surfactant preparations, some synthetic and others derived from animal lungs, and recent research has been directed at finding which, if any, is superior. The timing of the first dose has also been studied. Prophylactic surfactant administration within the first 15 minutes of life appears to be more efficacious than later treatment for very preterm babies, but could lead to some neonates being treated unnecessarily and perhaps being exposed to adverse effects. Newer treatments for neonates with RDS are aimed at reducing the pulmonary inflammation that occurs as a result of ventilatory barotrauma and oxygen toxicity. Superoxide dismutase, along with other antioxidants, may be beneficial as a free radical scavenger to reduce oxygen toxicity. Inhaled nitric oxide may reduce oxygen requirements by reducing ventilation-perfusion mismatching, and early treatment with corticosteroids may reduce pulmonary inflammation. All of these treatments are currently undergoing clinical trials.

Surfactant nebulization versus instillation during high frequency ventilation in surfactant-deficient rabbits

Surfactant nebulization improves lung function at low alveolar doses of surfactant. However, efficiency of nebulization is low, and lung deposition seems to depend on lung aeration. High frequency ventilation (HFV) has been shown to improve lung aeration. We hypothesize that the combination of HFV and surfactant nebulization may benefit lung deposition of surfactant and consequently, lung function. The aim of this study was to compare the effect of surfactant nebulization versus instillation during HFV on lung function, surfactant distribution, and cerebral blood flow. Therefore, severe respiratory failure was induced by lung lavages in 18 rabbits. HFV was applied: frequency = 8 Hz, mean airway pressure = 12 cm H2O, amplitude = 100%, fraction of inspired O2 = 1.0. Technetium-99m-labeled surfactant (Alveofact, 100 mg/kg of BW) was nebulized or instilled (n = 6 each). Six other rabbits did not receive surfactant (control, HFV only). We found that after instillation partial arterial O2 tension increased from 7.0 kPa (95% confidence interval, 6.3-8.0 kPa) to 34 kPa (16-51 kPa), and during nebulization from 7.0 kPa (6.0-9.0 kPa) to 46 kPa (27-58 kPa). Partial arterial CO2 tension decreased after instillation from 6.1 kPa (5.3-7.1 kPa) to 4.8 kPa (3.9-5.6 kPa), and during nebulization, after an initial rise, it decreased from 6.3 kPa (5.3-7.4 kPa) to 4.9 kPa (4.4-5.6 kPa). Both treatments resulted in nonuniform distribution. Surfactant deposition after nebulization was 9.8%. Instillation resulted in a drop of mean arterial blood pressure of 17% (8-31%), and an even more pronounced drop in cerebral blood flow of 39% (18-57%). Nebulization did not affect blood pressure. Cerebral blood flow decreased with a maximum of 27% (10-37%). We conclude that surfactant nebulization during HFV improves lung function in rabbits with severe respiratory failure, without improving distribution, but with less effects on blood pressure and cerebral blood flow, when compared with surfactant instillation.