title: Effect of body position on gas exchange in patients with idiopathic pulmonary alveolar proteinosis: no benefit of prone positioning.
abstract: BACKGROUND
  Prone positioning may improve oxygenation in patients with acute lung injury/ARDS. However, the beneficial effect of prone positioning on gas exchange has never been investigated in patients with diffuse pulmonary infiltrates who breathe spontaneously.
  
  
  OBJECTIVE
  To evaluate the effect of body position on gas exchange in patients with idiopathic pulmonary alveolar proteinosis (PAP) with special reference to the benefit of prone positioning.
  
  
  METHODS
  A prospective study.
  
  
  METHODS
  Tertiary medical center.
  
  
  METHODS
  Eight patients with PAP were studied on 25 occasions using spirometry, body plethysmography, and single-breath diffusing capacity of the lung for carbon monoxide (Dlco). Arterial blood gas levels were measured in the sitting position and in four lying positions randomly while patients breathed room air. To serve as control subjects, 16 age-matched healthy hospital personnel were studied. To evaluate the impact of oxygen therapy on positional effect in gas exchange, arterial blood gas levels were measured in the supine and prone positions in some PAP patients while breathing 40% oxygen.
  
  
  RESULTS
  Normal to varying degrees of restrictive ventilatory defect and gas exchange impairment, as evidenced by Dlco, Pao(2), and alveolar-arterial oxygen pressure difference (P[A-a]O(2)), were found in PAP patients. The ventilatory function parameters correlated positively with Pao(2) and negatively with P(A-a)O(2). The values of Pao(2) and P(A-a)O(2) measured in four lying positions showed no significant difference in both PAP patients and healthy control subjects. Furthermore, the differences in Pao(2) and P(A-a)O(2) between measurements made in the supine and prone positions and the ratio of Pao(2) measured in the prone position/Pao(2) measured in the supine position were comparable between PAP patients and healthy control subjects. Arterial blood gas levels showed no significant difference between measurements made in PAP patients in the supine and prone positions while breathing 40% oxygen.
  
  
  CONCLUSIONS
  Positional change did not significantly affect gas exchange, and no benefit of prone positioning was found in both PAP patients and healthy control subjects. Further studies are needed to verify the benefit of prone ventilation in patients with diffuse pulmonary disorders who breathe spontaneously.
authors.affiliation: Institute of Clinical Medicine, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: Fang-Chi
authors.initials: FC
authors.lastname: Lin
authors.forename: Yi-Chu
authors.initials: YC
authors.lastname: Chen
authors.forename: Huei-Ing
authors.initials: HI
authors.lastname: Chang
authors.forename: Shi-Chuan
authors.initials: SC
authors.lastname: Chang
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D016684:Prone Position; D011649:Pulmonary Alveolar Proteinosis / Q000503:physiopathology / Q000628:therapy*; D011653:Pulmonary Diffusing Capacity; D011659:Pulmonary Gas Exchange; D012129:Respiratory Function Tests