Regional ventilation distribution and dead space in anaesthetized horses treated with and without continuous positive airway pressure: novel insights by electrical impedance tomography and volumetric capnography. (January 2018)

• Record Type: Journal Article
• Authors: Mosing, Martina; Auer, Ulrike; MacFarlane, Paul; Bardell, David; Schramel, Johannes P.; Böhm, Stephan H.; Bettschart-Wolfensberger, Regula; Waldmann, Andreas D.
• Is Part Of: Veterinary anaesthesia and analgesia. Volume 45:Number 1(2018)
• Page Start: 31
• Page End: 40
• Publication Date: 2018-01
• Subjects: centre of ventilation -- electrical impedance tomography -- equine -- silent space -- spontaneous ventilation; Veterinary anesthesia -- Periodicals; 636.089
• DOI: 10.1016/j.vaa.2017.06.004
• Languages: English
• ISSNs: 1467-2987

Abstract

Abstract: Objective: The aim of this study was to evaluate the effect of continuous positive airway pressure (CPAP) on regional distribution of ventilation and dead space in anaesthetized horses. Study design: Randomized, experimental, crossover study. Animals: A total of eight healthy adult horses. Methods: Horses were anaesthetized twice with isoflurane in 50% oxygen and medetomidine as continuous infusion in dorsal recumbency, and administered in random order either CPAP (8 cmH2 O) or NO CPAP for 3 hours. Electrical impedance tomography (and volumetric capnography (VCap) measurements were performed every 30 minutes. Lung regions with little ventilation [dependent silent spaces (DSSs) and nondependent silent spaces (NSSs)], centre of ventilation (CoV) and dead space variables, as well as venous admixture were calculated. Statistical analysis was performed using multivariate analysis of variance and Pearson correlation. Results: Data from six horses were statistically analysed. In CPAP, the CoV shifted to dependent parts of the lungs ( p < 0.001) and DSSs were significantly smaller ( p < 0.001), while no difference was seen in NSSs. Venous admixture was significantly correlated with DSS with the treatment time taken as covariate ( p < 0.0001; r = 0.65). No differences were found for any VCap parameters. Conclusions and clinical relevance: In dorsally recumbent anaesthetized horses, CPAP of 8 cmH2 O results in redistribution of ventilation towards the dependent lung regions, thereby improving ventilation-perfusion matching. This improvement was not associated with an increase in dead space indicative for a lack in distension of the airways or impairment of alveolar perfusion.