Monitoring of tidal ventilation by electrical impedance tomography in anaesthetised horses. (18th August 2018)

• Record Type: Journal Article
• Authors: Mosing, M.; Waldmann, A. D.; Raisis, A.; Böhm, S. H.; Drynan, E.; Wilson, K.
• Is Part Of: Equine veterinary journal. Volume 51:Number 2(2019)
• Page Start: 222
• Page End: 226
• Publication Date: 2018-08-18
• Subjects: horse -- mechanical ventilation -- spirometry -- tidal impedance variation -- tidal volume; Horses -- Diseases -- Periodicals; 636.108905
• DOI: 10.1111/evj.12998
• Languages: English
• ISSNs: 0425-1644

Abstract

Summary: Background: Electrical impedance tomography (EIT) is a method to measure regional impedance changes within the thorax. The total tidal impedance variation has been used to measure changes in tidal volumes in pigs, dogs and men. Objectives: To assess the ability of EIT to quantify changes in tidal volume in anaesthetised mechanically ventilated horses. Study design: In vivo experimental study. Methods: Six horses (mean ± s.d.: age 11.5 ± 7.5 years and body weight 491 ± 40 kg) were anaesthetised using isoflurane in oxygen. The lungs were mechanically ventilated using a volume‐controlled mode. With an end‐tidal carbon dioxide tension in the physiological range, and a set tidal volume (VTvent ) of 11–16 mL/kg (baseline volume), EIT data and VT measured by conventional spirometry were collected over 1 min. Thereafter, VTvent was changed in 1 L steps until reaching 10 L. After, VTvent was reduced to 1 L below the baseline volume and then further reduced in 1 L steps until 4 L. On each VT step data were recorded for 1 min after allowing 1 min of stabilisation. Impedance changes within the predefined two lung regions of interest (EITROI ) and the whole image (EITthorax ) were calculated. Linear regression analysis was used to assess the relationship between spirometry data and EITROI and EITthorax for individual horses and pooled data. Results: Both EITROI and EITthorax significantly predicted spirometry data for individual horses with R 2 ranging from 0.937 to 0.999 and from 0.954 to 0.997 respectively. This was similar for pooled data from all six horses with EITROI (R 2 = 0.799; P<0.001) and EITthorax (R 2 = 0.841; P<0.001). Main limitations: The method was only tested in healthy mechanically ventilated horses. Conclusions: The EIT can be used to quantify changes in tidal volume.