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TIDAL VOLUME DELIVERY DECREASES
WITH INCREASING FiO2 DURING VOLUME AND PRESSURE VENTILATION IN THREE
OF FOUR PEDIATRIC VENTILATORS.
John W. Berkenbosch1,
Ryan Grueber2, Osauma Dabbagh3, Andrew McKibben3.
Departments of Child Health1, Respiratory Care2, and Internal
Medicine3, The University of Missouri-Columbia, Columbia, MO, USA
INTRODUCTION: It is well
recognized that alterations in gas density can impact ventilator and pneumotach
function. While it has been assumed that the small difference in density between
room air and 100% oxygen would have negligible effect on these functions, we
have been unable to find published data to confirm this.
Methods: We investigated
the effect of FiO2 (0.2, 0.4, 0.6, 0.8, 1.0) on delivered tidal volume
(VT) during volume and pressure ventilation in 4 pediatric ventilators,
the BIRD VIP and VIP Gold and the Siemans Servo 900C and Servo 300. During volume
ventilation, set tidal volumes (VT) ranged from 20-250 mL. During
pressure ventilation, inspiratory pressures were chosen to deliver tidal volumes
in the same range. Inspiratory VT?s displayed on the ventilator (displayed
VT) were recorded and compared with the inspiratory VT displayed during ventilation with room air (expected VT Dis). Actual
delivered VT?s were measured with a Neonatal Bicore connected to
the side port of a ?bag-in-box? spirometer, making volume measurements independent
of inspired gas properties. This volume (delivered VT) was compared
to the VT delivered by the ventilator during ventilation with room
air (expected VT Del). For each ventilator, ratios of displayed VT and delivered VT/expected VT (Dis or Del) were calculated
and compared at each FiO2 with a Kruskal-Wallis analysis of variance.
A p value <0.05 was considered significant.
Results: During volume ventilation,
there was a small decrease (2.2%) in displayed VT with increasing
FiO2 with the VIP Gold. Displayed VT was unaffected by
FiO2 with the VIP, Servo 900, and Servo 300 ventilators. There was
a progressive decrease in delivered VT with increasing FiO2 with the VIP (6.5%), VIP Gold (5.4%), and Servo 900C (13%) (p<0.001). This
decrease was present over the range of tidal volumes measured, and is similar
to the difference in density between room air and 100% O2 (10.8%).
Delivered VT was unaffected by changes in FiO2 with the
Servo 300 ventilator.
During pressure ventilation, there
was a small but significant increase in displayed VT with increasing
FiO2 with the VIP (3.0%), VIP Gold (4.5%) and Servo 900C (6.3%) ventilators
(p<0.005). In contrast, displayed VT decreased 3.2% with increasing
FiO2 with the Servo 300 ventilator (p<0.001). As with during volume
ventilation, delivered VT decreased with increasing FiO2 with the VIP (4.3%), VIP Gold (2.4%) and Servo 900C (2.3%) ventilators (p<0.01).
However, the magnitude of this decrease was less than during volume ventilation.
There was no significant effect of FiO2 on actual delivered VT with the Servo 300 ventilator.
DISCUSSION: This is the first
study to demonstrate a decrease in tidal volume delivery with increasing FiO2 in 3 of 4 ventilators commonly used in pediatric patients. This decrease was
both ventilator and ventilation-mode specific. Changes were most pronounced
during volume ventilation but the effects did not appear to be sensed by the
ventilator. The absence of an effect with the Servo 300 is most likely a result
of its gas module design. While the clinical significance of this effect is
likely minimal in most scenarios, the practitioner should consider this when
making large changes in FiO2.
OF-02-063
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