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DIFFERENCES
AND ACCURACY OF VOLUME-TARGETED VENTILATORS |
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Sharma
A, Milner AD, Greenough A. Performance of neonatal
ventilators in volume targeted ventilation mode.
Acta Paediatrica. 2007; 96: 176-180.
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may apply for full text articles.) |
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Jaecklin
T, Morel DR, Rimensberger PC. Volume-targeted
modes of modern neonatal ventilators: how stable is
the delivered tidal volume? Intens Care
Med. 2007, 33: 326-335.
(For non-journal subscribers, an additional fee
may apply for full text articles.) |
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Sharma’s
recent bench study evaluated 4 types of volume-targeted ventilators:
SLE 5000 (SLE systems, UK), Dräger Babylog 8000 (Dräger
Medical, Germany), Stephanie pediatric (F Stephan Biomedical,
Germany) and V.I.P. Bird® Gold (Viasys Healthcare, USA).
The researchers developed a 500 ml glass bottle lung model
with two inlets: one for a 3.0 mm endotracheal tube, the other
with a syringe attached to simulate respiratory effort. Compliance
was 0.4 ml/cm H2O
and resistance was 70 cm H2O/L/sec,
similar to babies with RDS. Ventilators were tested at 2 inspiratory
times (IT) (0.35 and 0.5 seconds), and 2 tidal volumes (5
ml and 10 ml).
For mean airway pressure, the Stephanie delivered significantly
higher Paw than the Dräger (p = 0.001), SLE (p = 0.007),
and V.I.P. Bird (p < 0.0001). The Dräger delivered
significantly higher peak pressures at both IT (p = 0.012
and p = 0.029) than the Stephanie and SLE, while the SLE was
significantly higher than the Stephanie (p = 0.001) and V.I.P.
Bird (p < 0.0001). IT were significantly lower for the
SLE than the Dräger (p < 0.0001) and Stephanie (p
< 0.0001), while IT for the V.I.P. Bird were significantly
lower than the Stephanie (p < 0.0001) and the Dräger
(p < 0.0001).
There were no significant differences at 5 ml for the ventilators,
while the V.I.P. Bird delivered significantly higher volumes
at 10 ml for both IT than the Stephanie (p = 0.012 and p =
0.016). Overall, the mean coefficient of variation for volume
delivery was 3.7%, with the V.I.P. Bird being significantly
lower than the Dräger (p = 0.003), Stephanie (p = 0.017),
and SLE (p < 0.0001).
Similarly, Jaecklin’s group performed a bench study of 6 volume-targeted
ventilators defined by their volume-targeted mode: volume
guarantee (Babylog 8000, Dräger Medical, Lübeck,
Germany), autoflow (Evita XL, Dräger Medical), adaptive
pressure ventilation (Galileo Gold, Hamilton Medical, Rhäzüns,
Switzerland), pressure-regulated volume control (Servo-i,
Maquet, Solna, Sweden), targeted Vt (SLE 5000, SLE, South
Croydon, UK), and volume-assured pressure support (V.I.P.
Gold, Bird, Palm Springs, USA). Ventilators were compared
for their ability to maintain set Vt when rapid changes in
compliance, airway leak, and resistance were introduced. Tidal
volumnes were set at 2 levels: pre-term levels (8-10 ml) or
term levels (25-28 ml).
Both increases and decreases in leak were handled well by
all ventilators, with little change in Vt. With decreases
in compliance in term settings, the Dräger 8000, Evita
XL, and Galileo Gold all maintained volume, while only the
Evita XL maintained Vt in preterm settings. With compliance
increases, the only ventilator with acceptable Vt in term
settings was the Evita XL, with no ventilators responding
with acceptable Vt to increases in compliance in preterm settings.
With increases in resistance, the Babylog 8000 and Galileo
Gold both maintained acceptable Vt in term settings, while
the Babylog 8000, Evita XL and Servo I did so in preterm settings.
When resistance suddenly decreased, only the Babylog 8000
responded with appropriate Vt in term settings, while the
Babylog 8000, Evita XL and Galileo Gold all responded appropriately
in preterm settings.
The Sharma study indicates that different ventilators all
respond differently with pressure, volume, and flow despite
similar set parameters, and even under ideal conditions (ie,
stable resistance and compliance) deliver variable tidal volumes.
The Jaecklin study identifies how different ventilators respond
to typical neonatal clinical conditions (fluctuation compliance
and resistance) with tidal volume overshoot or undershoot.
These bench studies are a start, but further studies and refinement
of volume-target ventilation parameters are needed. |
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