In vitro validation of a Pitot-based flow meter for the measurement of respiratory volume and flow in large animal anaesthesia.
OBJECTIVE
To remodel and validate commercially available monitors and their Pitot tube-based flow sensors for use in large animals, using in vitro techniques.


METHODS
Prospective, in vitro experiment.


METHODS
Both the original and the remodelled sensor were studied with a reference flow generator. Measurements were taken of the static flow-pressure relationship and linearity of the flow signal. Sensor airway resistance was calculated. Following recalibration of the host monitor, volumes ranging from 1 to 7 L were generated by a calibration syringe, and bias and precision of spirometric volume was determined. Where manual recalibration was not available, a conversion factor for volume measurement was determined. The influence of gas composition mixture and peak flow on the conversion factor was studied.


RESULTS
Both the original and the remodelled sensor showed similar static flow-pressure relationships and linearity of the flow signal. Mean bias (%) of displayed values compared with the reference volume of 3, 5 and 7 L varied between -0.4% and +2.4%, and this was significantly smaller than that for 1 L (4.8% to +5.0%). Conversion factors for 3, 5 and 7 L were very similar (mean 6.00 +/- 0.2, range 5.91-6.06) and were not significantly influenced by the gas mixture used. Increasing peak flow caused a small decrease in the conversion factor. Volume measurement error and conversion factors for inspiration and expiration were close to identity.


CONCLUSIONS
The combination of the host monitor with the remodelled flow sensor allowed accurate in vitro measurement of flows and volumes in a range expected during large animal anaesthesia.


CONCLUSIONS
This combination has potential as a reliable spirometric monitor for use during large animal anaesthesia.
Moens
Yves P S
YP
Clinic of Anaesthesiology and Perioperative Intensive Care, University of Veterinary Medicine, Vienna, Austria. yves.moens@vu-wien.ac.at
Gootjes
Peter
P
Ionita
Jean-Claude
JC
Heinonen
Erkki
E
Schatzmann
Urs
U
D000769:Anesthesia, Inhalation / Q000295:instrumentation / Q000662:veterinary*; D000818:Animals; D008176:Lung Volume Measurements / Q000295:instrumentation / Q000662:veterinary*; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000662:veterinary*; D012121:Respiration, Artificial / Q000295:instrumentation / Q000662:veterinary*