High Oxygen Concentrations Adversely Affect the Performance of Pulmonary Surfactant Craig D Smallwood RRT, Parnian Boloori-Zadeh PhD, Maricris R Silva PhD, and Andrew Gouldstone PhD BACKGROUND: Although effective in the neonatal population, exogenous pulmonary surfactant has not demonstrated a benefit in pediatric and adult subjects with hypoxic lung injury despite a sound physiologic rationale. Importantly, neonatal surfactant replacement therapy is administered in conjunction with low fractional F while pediatric/adult therapy is administered with high F . IO2 IO2 We suspected a connection between F and surfactant performance. Therefore, we sought to IO2 assess a possible mechanism by which the activity of pulmonary surfactant is adversely affected by direct oxygen exposure in in vitro experiments. METHODS: The mechanical performance of pul- monary surfactant was evaluated using 2 methods. First, Langmuir-Wilhelmy balance was utilized to study the reduction in surface area (␦A) of surfactant to achieve a low bound value of surface tension after repeated compression and expansion cycles. Second, dynamic light scattering was utilized to measure the size of pulmonary surfactant particles in aqueous suspension. For both experiments, comparisons were made between surfactant exposed to 21% and 100% oxygen. RESULTS: The ␦A of surfactant was 21.1 ؎ 2.0% and 35.8 ؎ 2.0% during exposure to 21% and Furthermore, dynamic light-scattering experiments revealed .(02. ؍ oxygen, respectively (P 100% a micelle diameter of 336.0 ؎ 12.5 ␮m and 280.2 ؎ 11.0 ␮m in 21% and 100% oxygen, respectively (P < .001), corresponding to a ϳ16% decrease in micelle diameter following exposure to 100% oxygen. CONCLUSIONS: The characteristics of pulmonary surfactant were adversely affected by short-term exposure to oxygen. Specifically, surface tension studies revealed that short-term expo- sure of surfactant film to high concentrations of oxygen expedited the frangibility of pulmonary surfactant, as shown with the ␦A. This suggests that reductions in pulmonary compliance and associated adverse effects could begin to take effect in a very short period of time. If these findings can be demonstrated in vivo, a role for reduced F during exogenous surfactant delivery may have IO2 a clinical benefit. Key words: pulmonary surfactant; oxygen toxicity; infasurf; langmuir-wilhelmy; dynamic light scattering. [Respir Care 2017;62(8):1085–1090. © 2017 Daedalus Enterprises] Introduction carbon dioxide. In healthy subjects, ambient concentrations of oxygen (21%) are sufficient to sustain metabolism. How- Human metabolism relies primarily on an aerobic process ever, a number of pathophysiologic processes can impede for the combustion of nutrients and extraction of energy at the exchange of oxygen from the lungs into the blood, and there- cellular level. The process consumes oxygen and generates fore administration of high concentrations of oxygen is re- quired to maintain adequate arterial oxygen levels and tissue oxygenation. Although sometimes clinically indicated, high Mr Smallwood and Drs Boloori-Zaden, Silva and Gouldstone are affil- iated with the College of Engineering, Northeastern University; and Mr Smallwood also is affiliated with the Division of Critical Care Medicine, Department of Anesthesia, Perioperative and Pain Medicine, Boston Chil- dren’s Hospital, and Harvard Medical School, Boston, Massachusetts. Correspondence: Andrew Gouldstone PhD, College of Engineering, De- partment of Mechanical and Industrial Engineering, Northeastern Uni- The authors have disclosed no conflicts of interest. versity, Boston, MA 02115. E-mail: [email protected]. Mr Smallwood and Dr Boloori-Zadeh contributed equally to this work. DOI: 10.4187/respcare.05388 RESPIRATORY CARE • AUGUST 2017 VOL 62 NO 8 1085 HIGH F AND PULMONARY SURFACTANT PERFORMANCE IO2 oxygen concentrations may lead to oxygen toxicity. In vivo research suggests this toxicity may manifest as changes in QUICK LOOK airways responsiveness, inflammation, increased lung vol- Current knowledge umes, and depletion of type II pneumocyte proliferation.1-3 Pulmonary surfactant has been the subject of extensive Exogenous surfactant administration is effective in the not research since its successful administration in newborn in- neonatal population with surfactant deficiency, but is fants with respiratory distress syndrome was described by effective for pediatric and adult patients with ARDS de- spite data showing that surfactant function is allayed. We Fujiwara et al4 in the early 1980s. Since that time, its role in the care of premature infants as well as chemical constituents suspected a connection between oxygen concentration and surfactant performance. and specific function have been well described.5 More re- cently, the role of exogenous surfactant in the care of adult What this paper contributes to our knowledge and pediatric subjects with ARDS has been investigated.6-9 Pathogenesis of ARDS has been partly attributed to altera- The characteristics of pulmonary surfactant were ad- tions in endogenous surfactant.10 The physiologic rationale versely affected by short-term exposure to oxygen. Spe- for the administration of surfactant in this population is to cifically, surface tension studies revealed that short- restore surfactant function, thereby improving pulmonary sys- term exposure of surfactant film to high concentrations tem compliance and oxygenation. Despite promising data in of oxygen expedited the frangibility of pulmonary sur- pilot trials, large controlled investigations have not demon- factant, as shown with the surface area change. These strated a clear benefit of exogenous surfactant in subjects data suggest that reductions in pulmonary compliance with ARDS as it had little or no effect on oxygenation or and associated adverse effects could begin to take effect long-term outcomes.7,11 However, since the majority of ex- in a very short period of time. ogenous surfactant protocols in pediatric and adult patients call for high concentrations of inspired oxygen during ther- apy (which is not the case in the neonatal population), we suspected that there may be a connection between oxygen cal behavior. That is to say, lungs inflated with 100% concentration and surfactant performance. oxygen have significantly greater stiffness and hysteresis Furthermore, most research has focused on the cellular than those exposed to air. This effect was most apparent at ϳ mechanisms of oxygen toxicity, but the effects of direct low lung pressures ( 4cmH2O) and smaller at much ϳ 24 high-concentration oxygen on surfactant mechanical prop- higher pressures ( 20 cm H2O). Mechanical responses erties have not been adequately described in a controlled at low pressures are known to be dominated by surfactant laboratory investigation. Oxygen toxicity, which results behavior, and we hypothesized that the gas composition from the delivery of increased concentrations of oxygen, was directly affecting this substance. has been associated with absorption atelectasis, pulmonary It should be noted that experiments by Wildebeer-Ven- edema and lung fibrosis.12-15 Oxygen toxicity is com- ema25 showed that exposure to different gases had little to pounded by increased F as well as duration of exposure. no effect on the static minimum surface tension of surfac- IO2 Typically, F Յ 0.50 has been recommended as a ther- tant. However, that study did not explore dynamic surface IO2 apeutic target to reduce the likelihood of oxygen toxicity tension and re-spreading of surfactant, which is very im- in human subjects.16 portant in vivo because the surface area expands and con- A biochemical mechanism, as the basis for oxygen tox- tracts inside the alveoli with breathing. Therefore, we sought icity, has been proposed; it results from the cellular pro- to describe the performance of isolated pulmonary surfac- duction of partly reduced oxygen metabolites.17,18 Indeed, tant at high oxygen concentration (100%) and low oxygen lung injury may be exacerbated by an oxygen free radical concentration (air, 21%) through the careful implementa- process that results in cellular damage and impeded gas tion of 2 distinct experiments: 1) on the performance (di- exchange.19-22 In vivo translational research has demon- rectly related to ability of surfactant to redistribute), and 2) strated that administration of an oxygen free radical-fight- on the suspension structure of surfactant. ing molecule, superoxide dismutase, prevents many dele- terious effects of breathing high-concentration oxygen in Methods an animal model.23 However, survival rates, morphologic changes, and histologic findings were not completely pre- Surfactant Preparation served, suggesting mechanisms other than those mediated by oxygen free radicals may contribute to lung injury. The surfactant preparation utilized for the experiments The present research group has previously demonstrated was Infasurf (ONY, Amherst, New York), a bovine, non- that in excised lungs, exposure to different oxygen con- pyrogenic pulmonary surfactant. It is a natural calf lung centrations can have near-immediate effects on mechani- surfactant extract that includes phospholipids, mainly di- 1086 RESPIRATORY CARE • AUGUST 2017 VOL 62 NO 8 HIGH F AND PULMONARY SURFACTANT PERFORMANCE IO2 palmitoylphosphatidylcholine, neutral lipids, and hydro- turer’s specifications. Preparation of the instrument in- phobic surfactant-associated proteins B and C, and is cluded deposition of a 50 ␮L of pure water onto the bal- cleared