Aerosolized surfactant therapy for endotoxin-induced experimental acute respiratory distress syndrome in rats

Current Issues and Challenges in the Use of Aerosolized Surfactant for Respiratory Distress Syndrome in the Newborns

BACKGROUND: Surfactant replacement therapy is a recognized treatment for respiratory distress syndrome (RDS) in the newborns. Over the past 30 years, human and animal trials have been performed regarding administration of aerosolized surfactant to the injured lung, however the result has been unsatisfactory when compared with instilled surfactant delivery via endotracheal tube (ETT). This review aims to investigate the current issues, challenges and future recommendation of aerosolized surfactant therapy.CONTENT: Five randomized clinical trials in humans and 13 animal trials met the inclusion criteria and were reviewed. Most animal trials agree that this method of treatment is feasible. However, human trials presented conflicting results, and generally showed it to be ineffective. When compared with surfactant delivery via ETT, aerosolized surfactant is less effective in improving respiratory function.SUMMARY: The current data from human trials does not support the implementation of aerosolized surfactant therapy to treat newborns with RDS. Further research is necessary to improve nebulization, delivery, distribution and deposition in the lung, to investigate aerosolized surfactant delivery via ETT and to determine the appropriate dose.KEYWORDS: surfactant, aerosol, prematurity, respiratory distress syndrome

Aerosolised surfactant generated by a novel noninvasive apparatus reduced acute lung injury in rats

Introduction

Exogenous surfactant has been explored as a potential therapy for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). In the present study, a nebuliser driven by oxygen lines found in the hospital was developed to deliver aerosolised porcine pulmonary surfactant (PPS). We hypothesised that aerosolised surfactant inhaled through spontaneous breathing may effectively reduce severe lung injury.

Methods

Rats were intravenously injected with oleic acid (OA) to induce ALI and 30 minutes later they were divided into five groups: model (injury only), PPS aerosol (PPS-aer), saline aerosol (saline-aer), PPS instillation (PPS-inst), and saline instillation (Saline-Inst). Blood gases, lung histology, and protein and TNF-α concentrations in the bronchoalveolar lavage fluid (BALF) were examined.

Results

The PPS aerosol particles were less than 2.0 μm in size as determined by a laser aerosol particle counter. Treatment of animals with a PPS aerosol significantly increased the phospholipid content in the BALF, improved lung function, reduced pulmonary oedema, decreased total protein and TNF-α concentrations in BALF, ameliorated lung injury and improved animal survival. These therapeutic effects are similar to those seen in the PPS-inst group.

Conclusions

This new method of PPS aerosolisation combines the therapeutic effects of a surfactant with partial oxygen inhalation under spontaneous breathing. It is an effective, simple and safe method of administering an exogenous surfactant.

Aerosolized surfactant and dextran for experimental acute respiratory distress syndrome caused by acidified milk in rats

BACKGROUND

Inhibition of pulmonary surfactant by plasma-derived proteins is an important pathogenetic factor of acute respiratory distress syndrome (ARDS). Inhalation of aerosolized surfactant may be suitable for early treatment of ARDS. However, requirement of a high dose is a drawback. Because dextran reverses surfactant inhibition, we examined whether dextran improves the therapeutic effects of aerosolized surfactant in rats with experimental ARDS.

METHODS

Acidified milk (pH 1.8, 1.5 ml kg(-1)) was injected into the trachea of the rats ventilated with pure oxygen using 2.45 kPa peak inspiratory pressure and 0.74 kPa positive end-expiratory pressure. When PaO2 decreased to <13 kPa, the rats were assigned to four groups: control group (n = 8), receiving no material; D-only group (n = 6), receiving aerosolized dextran for 45 min; S-only group (n = 8), receiving aerosolized modified natural surfactant (MNS) for 30 min; and S-plus-D group (n = 9), receiving aerosolized MNS for 30 min followed by aerosolized dextran for 15 min.

RESULTS

In the control group and D-only groups, the mean PaO2 remained at <10 kPa for 180 min. In the S-only and S-plus-D groups, the PaO2 increased to 50 kPa (P < 0.01 vs. untreated). The PaO2 of the surfactant-only group gradually decreased to <17 kPa at 180 min, whereas the PaO2 of the S-plus-D group was maintained at >38 kPa for 180 min (P < 0.01 vs. S-only group).

CONCLUSION

Inhalation of aerosolized dextran potentiates the effects of aerosolized surfactant by prolonging the therapeutic response.