Position changing with blood distribution to different portions of lung
   can produce V/Q mismatch, and finally extend to oxygenation disruption.
   Thus, if position changing  is done’ neglecting the patients’ pulmonary
   problem types, not only does it fail to cause oxygenation improvement, but
   it also induces gas exchange impairment, and with provocation of
    hypoxemia and respiratory acidosis, serious problems  result. The goals of this
   research are to determine the semi-fowler’s position and its duration effect
   on the arterial blood gases(ABGs)results in patients under mechanical
   ventilation hospitalized in general ICU.

          In this study , 30 ICU patients(22 males and 8 females) under mechanical
   ventilation were chosen. Then using questionnaires , the patients’
   demographic data were collected . A sample of arterial blood from these
   patients lying in supine position, was taken . Again the patients immediately  
   were placed in semi-fowler’s position and after 15,30,45,and 60minutes lying
   in this position, samples of arterial blood were taken and sent to laboratory.

          The findings showed that semi-fowler’s position did not have any positive
   effects on oxygenation and gas exchange. Also, the findings indicated that
   the effect of lying duration(15,30,45,60 minutes) in semi-fowler’s position on
   oxygenation and gas exchange wasn’t significant.

          It was concluded that without considering the lung pathology, semi
   fowler’s position should not be used , because not only is this position unable
   to induce oxygenation-improvement, but actually it may causes gas
   exchange impairment.