plv has piqued the fascination of critical care practitioners since it 		   was described in 1991 . it was proposed to enhance gas 		   exchange in the setting of the acute respiratory distress syndrome , and 		   laboratory studies quickly demonstrated that alveolar recruitment and 		   redistribution of pulmonary blood flow , presumably due to the presence of the 		   high - density perfluorocarbons in the dependent regions of the lungs , 		   contributed to the observed improvement in gas exchange . it was also 		   noted , both in the laboratory and the clinical settings , that perfluorocarbons 		   accumulated predominately in the dependent regions of the lungs . this observation led to the concern 		   that areas of relative hypoxia might exist if ventilation with oxygen was 		   insufficient to oxygenate the perfluorocarbon - filled alveoli in these regions . it is worthwhile to note that oxygenation of the perfluorocarbon - filled 		   alveolus is likely dependent on convection , rather than diffusion , because the 		   diffusion of oxygen in a liquid is several orders of magnitude less than that 		   in a gas . whether this dependent hypoxic phenomenon occurs tutuncu et al   demonstrated a 		   reduction in oxygenation in normal rabbits in which pulmonary perfluorocarbon 		   was administered . that ventilation - perfusion matching may be compromised in 		   these normal animals suggests that oxygenation of the liquid - filled alveolus 		   may be incomplete . in this issue of critical care , max et al 		   examine the time course of changes in arterial oxygenation after administration 		   of 7.5 ml / kg of the perfluorocarbon fc 3280 into the lungs of saline lavage 		   lung - injured pigs . specifically , the authors measured pao2 and other 		   physiologic parameters at 5 and 30 min after perfluorocarbon instillation , with 		   the hypothesis that a time - dependent decrease in pao2 would suggest 		   failure of ongoing ventilation - oxygenation to support the initial increase in 		   pao2 attributed to the oxygen dissolved in the administered 		   perfluorocarbon . indeed , the authors observed two important findings : first , a 		   dose - dependent increase in pao2 was observed ; and second , 		   pao2 at 30 min was significantly less than that observed at 5 min 		   after administration of 22.5 and 30 ml / kg fc 3280 . the latter is an intriguing 		   observation that suggests that oxygenation of the perfluorocarbon may be 		   insufficient after initial administration . there are , however , a number of 		   issues that need to be considered in the interpretation of these findings . one 		   premise of the derived conclusions is that the administered perfluorocarbon was 		   sufficiently oxygenated so as to have a substantial impact on pao2 . we have no information on the oxygenation status of the perfluorocarbon at the 		   time of administration , however . even so , the theoretic amount of oxygen 		   contributed by fully saturated fc 3280 would be fairly small ( approximately 3 ml 		   o2/kg ) . one enhancement to the study by max et al   might be to assess the effect of hyperoxygenated , room air , 		   and deoxygenated perfluorocarbon on pulmonary gas transport at 5 min and 30 min 		   after dosing . these data would provide more convincing evidence that an 		   increase in oxygenation at 5 min and the subsequent decrease at 30 min were due 		   to changes in perfluorocarbon oxygen content . other confounding variables that 		   may affect the difference in pao2 between 5 and 30 min include 		   evaporation of fc 3280 and changes in other physiologic variables , such as 		   cardiac output , which might independently affect pao2 . for instance , 		   oxygen delivery , probably the most important parameter of oxygen dynamics , is 		   not significantly different between the 5-min and 30-min time periods in the 		   study . studies such as that by max et al 		   contribute toward refining the plv technique ; these data might suggest that 		   application of higher levels of peak inspiratory pressure or positive 		   end - expiratory pressure could enhance gas distribution and minimize the effects 		   observed . the technique of perfluorocarbon administration and the amount dosed 		   may need to be altered . it would be intriguing to consider whether similar 		   findings would be observed in newborn animals in which the relatively small 		   height of the chest is less likely to provide regional differences in 		   perfluorocarbon and gas distribution . a randomized , controlled , multicentered study evaluating plv in adults 		   with the acute respiratory distress syndrome is underway . however , the pilot 		   study preceding that trial   failed to demonstrate an 		   enhancement in parameters of oxygenation in the plv group when compared with 		   the conventional mechanical ventilation group . we have much to learn about plv 		   and , even though it is currently undergoing clinical trials , we are still 		   defining the optimal application of this technique .
perfluorocarbons accumulate in the dependent regions of the lungs , 			  which may result in regional hypoxia if ventilation with oxygen is insufficient 			  to oxygenate the dependent perfluorocarbon - filled alveoli . in this issue of 			  critical care , 
 max et al present data that demonstrate a 			  decrease in arterial oxygen tension ( pao2 ) at 30 min compared to that 			  observed at 5min after administration of fc 3280 . 
 these data suggest failure of 			  on - going attributed to the oxygen ventilation / oxygenation to support the 			  initial increase in pao2dissolved in the administered 			  perfluorocarbon . 
 studies such as this one demonstrate that development of the 			  optimal partial liquid ventilation ( plv ) technique is ongoing .