Thursday, October 4, 2012

Surfactant Therapy

So what about surfactant therapy?  Since a primary role of surfactant is to decrease surface tension within the lung and keep the alveoli open, it makes sense that water entering the alveoli, which results in both direct cellular damage and surfactant washout, could lead to alveolar collapse and, therefor, decreased gas exchange.  

The Handbook on Drowning, published in 2006 (most recent edition released this year), provided a review of the literature up until then, which was primarily animal models and case studies, all of which provided some evidence to consider surfactant early in the treatment course of acute lung injury due to drowning.  This entry will first cover a review article from 2008 which covers the use of surfactant in pediatric acute lung injury, and will then present 2 more case studies which have been published since that edition of The Handbook on Drowning.

This article reviews the literature on the use of surfactant for acute lung injury in the pediatric population from the last 3 decades.  Some heavy ready, but definitely provides a solid overview of what data is out there.  Here are a few of the important points based on their review:
  • Available evidence best supports the use of surfactant in ALI/ARDS secondary to direct lung injury, as opposed to indirect causes (sepsis, hypovolemic shock, non-thoracic trauma).
  • Most evidence so far from case studies.  Best clinical evidence from studies involving meconium aspiration in neonates
  • Most positive effect seen in younger populations. No long term negative effects from studies of adults or peds.  Most prevalent positive effect is rapid improvement of hypoxia.
  • Direct delivery (Endotracheal tube or bronch) more effective than aerosolized
Conclusion statement: “Exogenous surfactant therapy now is standard in the prevention and treatment of RDS in premature infants, and basic science and clinical evidence support its use in at least some patients who have lung injury associated respiratory failure as described in this article.”

Few randomized controlled trials have been done to determine the effectiveness of surfactant therapy in humans.  In addition, large population studies are scarce.  For this reason, most of the human-based evidence for its use in the drowning patient comes from case studies, two of the more recent ones are reviewed here:

This case study describes the treatment course of a 2.5 year female after prolonged submersion and pulselessness and with fairly dismal prognostic factors.  After hypoxia refractory to multiple ventilation modalities (high PEEP which resulted in pneumothorax, Nitric Oxide, and High Frequency Oscillatory Ventilation), the decision was made to administer surfactant.  The authors report a fairly quick (10 minutes) improvement in pt condition, based both on radiologic and ventilatory findings, leading to an eventual extubation and full neurological recovery.

This letter to the Editor reports on the treatment course of two pediatric patients treated in the ICU from the same submersion event.  A timecourse displaying arterial blood gas levels for both patients shows a rapid improvement shortly after surfactant administration.  In the end, one patient was extubated and had no neurologic dysfunction and one patient died of cerebral injury.

Setting the obvious weaknesses of case reports aside (primarily the lack of control of confounding factors and the small sample sizes), case reports like this do provide some evidence for considering surfactant use, especially in the pediatric population and especially when hypoxia remains despite other standard treatments.  Although the initial review article does advocate for its use early in the treatment process, there is still a large lack of high quality evidence to universally support this, nevertheless something to keep in mind.