Transport and Absorption of Anesthetic Vapors in a Mouth-Lung Model Extending to G9 Bronchioles - Pages 6-19

Jinxiang Xi1, JongWon Kim1 and Xiuhua A. Si2

1Department of Mechanical and Biomedical Engineering, Central Michigan University, Mount Pleasant, MI, USA; 2Department of Engineering, Calvin College, Grand Rapids, MI, USA

DOI: http://dx.doi.org/10.14205/2310-9394.2013.01.01.2

Abstract:

Background: The inhalation of anesthetic vapors into the lungs is a function of both the respiration and inhalant property. Factors which influence the alveolar concentration of anesthetics include breathing activities, airway morphology, anesthetic diffusivity, and wall absorption rate. Administered anesthetic levels could be significantly different from the alveolar level due to wall absorption loss and gas mixing in the airway.

Objective: To assess the transport and absorption of inhaled anesthetics in an anatomically accurate respiratory airway geometry. Specifically aims include understanding the transport of inhaled vapors, quantifying the pulmonary dosage of administered anesthetics, and identifying factors that influence airway absorption losses.

Methods: The geometry consisted of a CT-based mouth-throat (MT) model and a tracheobronchial (TB) model which extends to G9 bronchioles and consists of 115 outlets. Vapor transport and absorption were simulated using the Chemical Species model coupled with a user-defined vapor-absorption module.

Results: Unlike previously assumed developed flows after G6, features of developing flows are still apparent in the G9 bronchioles in this study. Large variations of bronchiolar vapor concentrations were observed among the five lobes. Under quiet breathing conditions, vapor concentrations at the G9 outlets are 15 – 30% of the inhaled concentration level due to gas mixing and wall absorption. The delivered dose to the pulmonary region varies from 48% to 96%, depending on the vapor diffusivity and solubility. Vapor depletion due to wall absorption is significant (52%) for highly soluble anesthetics and is inconsequential for low solubility ones.

Conclusion: A computer model was developed that implemented a wall absorption module in a realistic mouth-lung model extending to G9. This model provides the basis for future quantitative studies of the relationship between administered anesthetics and induced anesthetic level.

Keywords: Vapor transport, wall absorption, inhalation anesthetics, ultrafine aerosols, lung model.