title: Accuracy of inhaled agent usage displays of automated target control anesthesia machines.
abstract: Automated low flow anesthesia machines report how much inhaled anesthetic agent has been used for each anesthetic. We compared these reported values with the amount of agent that had disappeared by weighing the vaporizer/injectors before and after each anesthetic. The vaporizers/injectors of the Aisys, Zeus and FLOW-i were weighed with a high precision weighing scale before and after anesthesia with either desflurane in O2/air or sevoflurane in O2/N2O. These values were compared with the values reported by the cumulative agent use display tools of the respective anesthesia machines using a linear curve fit. Twenty-five measurements were performed in each group, except for the sevoflurane data with the Aisys that were available from another study (87 pairs). We also determined the amount lost by inserting and removing the vaporizers/injectors or by performing a machine checkout, corrected the measured amounts for these artifacts and repeated the linear fits. The average amount of sevoflurane and desflurane wasted by inserting and removing the cassette for the Aisys, Zeus, and FLOW-i were 0.21, 0.12, and 0.04 mL and 0.12, 0.61, and 1.13 mL liquid agent, respectively. The average amount of sevoflurane and desflurane wasted by the machine checkout with the Aisys, Zeus, and FLOW-i were 1.78, 0.21, and 1.67 mL and 2.39, 0.67, and 4.19 mL, respectively. Performance error of the displayed amount of agent use remained within 10 % of the weighed amount, expect for amounts less than 3 mL sevofurane with the FLOW-i and less than 20 mL desflurane with the Aisys and FLOW-i. Cumulative agent usage displayed by the Aisys, Zeus, and FLOW-i is within 10 % of the measured consumption, except for low consumption cases (<3 mL sevoflurane, <20 mL desflurane). The differences may be due to either measurement error or cumulative agent display error. The current results can help the researchers decide whether the displayed amounts are accurate enough for their study purposes. The extent to which these discrepancies differ between different units of the same machine remains unstudied.
authors.affiliation: Department of Anesthesiology, Intensive Care and Pain Therapy, OLV Hospital, Moorselbaan 164, 9300, Aalst, Belgium.
authors.forename: Alexander
authors.initials: A
authors.lastname: Dehouwer
authors.affiliation: Department of Anesthesiology, Intensive Care and Pain Therapy, OLV Hospital, Moorselbaan 164, 9300, Aalst, Belgium.
authors.forename: Rik
authors.initials: R
authors.lastname: Carette
authors.affiliation: Department of Anesthesiology, Intensive Care and Pain Therapy, OLV Hospital, Moorselbaan 164, 9300, Aalst, Belgium.
authors.forename: Simon
authors.initials: S
authors.lastname: De Ridder
authors.affiliation: Department of Anesthesiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
authors.forename: Andre M
authors.initials: AM
authors.lastname: De Wolf
authors.affiliation: Department of Anesthesiology, Intensive Care and Pain Therapy, OLV Hospital, Moorselbaan 164, 9300, Aalst, Belgium. jcnwahendrickx@yahoo.com.
authors.forename: Jan F A
authors.initials: JF
authors.lastname: Hendrickx
mesh_terms: D000764:Anesthesia, Closed-Circuit / Q000379:methods*; D000776:Anesthesiology / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D016477:Artifacts; D000077335:Desflurane; D016503:Drug Delivery Systems; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage / Q000031:analogs & derivatives; D016014:Linear Models; D008738:Methyl Ethers / Q000008:administration & dosage; D009330:Nebulizers and Vaporizers; D015203:Reproducibility of Results; D000077149:Sevoflurane; D012815:Signal Processing, Computer-Assisted
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane
keywords: Anesthesia machine; Automated low flow; Closed loop; Equipment; Target control