title: Comparison of pneumotachography and anemometery for flow measurement during mechanical ventilation with volatile anesthetics.
abstract: Volatile anesthetics alter the physical properties of inhaled gases, such as density and viscosity. We hypothesized that the use of these agents during mechanical ventilation would yield systematic biases in estimates of flow ([Formula: see text]) and tidal volume (VT) for two commonly used flowmeters: the pneumotachograph (PNT), which measures a differential pressure across a calibrated resistive element, and the hot-wire anemometer (HWA), which operates based on convective heat transfer from a current-carrying wire to a flowing gas. We measured [Formula: see text] during ventilation of a spring-loaded mechanical test lung, using both the PNT and HWA placed in series at the airway opening. Delivered VTwas estimated from the numerically-integrated [Formula: see text]. Measurements were acquired under baseline conditions with room air, and during ventilation with increasing concentrations of isoflurane, sevoflurane, and desflurane. We also evaluated a simple compensation technique for HWA flow, which accounted for changes in gas mixture density. We found that discrepancies in estimated VTbetween the PNT and HWA occurred during ventilation with isoflurane (6.3 ± 3.0%), sevoflurane (10.0 ± 7.3%), and desflurane (25.8 ± 17.2%) compared to baseline conditions. The magnitude of these discrepancies increased with anesthetic concentration. A simple compensation factor based on density reduced observed differences between the flowmeters, regardless of the anesthetic or concentration. These data indicate that the choice and concentration of anesthetic agents are primary factors for differences in estimated VTbetween the PNT and HWA. Such discrepancies may be compensated by accounting for alterations in gas density.
authors.affiliation: Department of Biomedical Engineering and School of Medicine, Boston University, 44 Cummington Mall, Boston, MA, 02215, USA.
authors.forename: Jarred R
authors.initials: JR
authors.lastname: Mondoñedo
authors.affiliation: Departments of Biomedical Engineering and Anesthesia, University of Iowa, Iowa City, IA, 52242, USA.
authors.forename: Jacob
authors.initials: J
authors.lastname: Herrmann
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, PO Box 800710, Charlottesville, VA, 22908-0710, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: McNeil
authors.affiliation: Departments of Anesthesia, Biomedical Engineering, and Radiology, University of Iowa, 200 Hawkins Drive, Iowa City, IA, 52242, USA. david-kaczka@uiowa.edu.
authors.forename: David W
authors.initials: DW
authors.lastname: Kaczka
mesh_terms: D000776:Anesthesiology / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D002138:Calibration; D000077335:Desflurane; D004867:Equipment Design; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage / Q000031:analogs & derivatives*; D008168:Lung; D008738:Methyl Ethers / Q000008:administration & dosage*; D016343:Monitoring, Intraoperative / Q000379:methods; D008991:Monitoring, Physiologic / Q000379:methods; D015203:Reproducibility of Results; D012121:Respiration, Artificial / Q000379:methods*; D000077149:Sevoflurane; D013696:Temperature; D013990:Tidal Volume
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane
keywords: Anesthetics; Artificial respiration; Flowmeters