Dead Space Ventilation in Volume Controlled versus
Pressure Controlled Mode of Mechanical Ventilation
APASSORN WATHANASORMSIRI, M.D.*, AROONWAN PREUTTHIPAN, M.D.*,
TEERACHAI CHANTA ROJANASIRI, M.D.*, SUBHAREE SUWA NJUTHA, M.D.*
Affiliation : *Department of Pediatrics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand.
AbstractDead space ventilation (Vo) is one of the important measurements that indicates the ventilatory efficiency of a patient who requires mechanical ventilation. However, Vo is not constant
and can change according to the pathology in the lungs, ventilatory patterns, perfusion and ventilation-perfusion matching. The objective of this study was to measure and compare the dead space in
pediatric patients who were using pressure controlled and volume controlled modes of mechanical
ventilatory by measuring the difference between arterial PC02 and end-tidal PC02 [P(a-ET)COJ. From
November 1996 to March 1997, 12 patients who were admitted to the pediatric intensive care unit
and needed ventilator support for various reasons, were enrolled in the study. Their ages ranged from
2 to 15 years. The mechanical ventilator (Benett 7200 or Servo 900C) setting during Vo measurement
i.e. tidal volume, inspiratory time and positive end expiratory pressure were kept constant between
changing from pressure controlled to volume controlled mode or vice versa for twenty minutes in order
to allow adequate time for equilibration.
The P(a-ET)C02 between volume controlled and pressure controlled mode were 3.1 and 2.6
torr (p=0.5) and peak inspiratory pressure were 20.0 and 17.3 torr (p=0.01), respectively; whereas
mean airway pressure, Pa02, 0 2 saturation and heart rate revealed no significant difference between
these two modes.
The authors concluded that Vo in pressure controlled mode from the present study was not
significantly different from Vo when using volume controlled mode of mechanical ventilation in the
same patient. However, Vo will change according to the pathophysiologic change in respiratory
system and can be used for monitoring of ventilatory pattern of patients in the pediatric intensive care
unit.
Keywords : Dead Space, Mechanical Ventilation, Respiratory Failure
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