title: What is the optimal duration of ventilation in the prone position in acute lung injury and acute respiratory distress syndrome?
abstract: OBJECTIVE
  To evaluate the effects of prone ventilation on respiratory parameters and extravascular lung water (EVLW) in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) in order to characterise the optimal duration of ventilation in the prone position.
  
  
  METHODS
  Prospective, observational study.
  
  
  METHODS
  Nine-bed general intensive care unit.
  
  
  METHODS
  Eleven patients with refractory hypoxaemia due to ALI/ARDS were prospectively investigated during 12 consecutive episodes of prone ventilation.
  
  
  METHODS
  Ventilation in the prone position for 18 h.
  
  
  RESULTS
  Measurements were obtained supine and after 1, 2, 6, 12 and 18 h in the prone position and 1 h after returning supine. There was a progressive improvement in PaO(2)/fraction of inspired oxygen (FIO(2)) ratio which reached significance after 12 h [121 (81-151) to 258 (187-329) torr; p<0.05]. EVLW index increased transiently at 1 h [14.2 (7.6-20.8) to 15.1 (9.0-20.2); p=0.05] and thereafter declined progressively and was significantly decreased at 18 h [12.1 (7.2-17.0); p=0.043]. The shunt fraction showed an early fall [0.41 (0.40-0.42) to 0.31 (0.30-0.32) at 1 h; p<0.001] preceding a subsequent progressive fall [0.22 (0.21-0.23) at 18 h; p<0.001].
  
  
  CONCLUSIONS
  Over the 18 h period studied there was progressive improvement in gas exchange, pulmonary shunt and EVLW. Although it is not possible to exclude that improvement over this period was unrelated to prone positioning, these findings suggests that ventilation in the prone position for more prolonged periods may be required for optimal improvement and warrants further study.
authors.affiliation: Intensive Care Unit, Birmingham Heartlands Teaching Hospital, Bordesley Green East, Birmingham B9 5SS, UK. dan.mcauley@dtn.ntl.com
authors.forename: D F
authors.initials: DF
authors.lastname: McAuley
authors.forename: S
authors.initials: S
authors.lastname: Giles
authors.forename: H
authors.initials: H
authors.lastname: Fichter
authors.forename: G D
authors.initials: GD
authors.lastname: Perkins
authors.forename: F
authors.initials: F
authors.lastname: Gao
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015633:Extravascular Lung Water; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D016684:Prone Position; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial / Q000009:adverse effects / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000628:therapy*; D015656:Respiratory Mechanics; D013997:Time Factors; D016896:Treatment Outcome