Comparison of Effects of an Endotracheal Tube or Facemask on Breathing Pattern and Distribution of Ventilation in Anesthetized Horses

Abstract

Equine respiratory physiology might be influenced by the presence of an endotracheal tube (ETT). This experimental, randomized cross-over study aimed to compare breathing pattern (BrP) and ventilation distribution in anesthetized horses spontaneously breathing room air via ETT or facemask (MASK). Six healthy adult horses were anesthetized with total intravenous anesthesia (TIVA; xylazine, ketamine, guaiphenesin), breathing spontaneously in right lateral recumbency, and randomly assigned to ETT or MASK for 30 min, followed by the other treatment for an additional 30 min. During a second anesthesia 1 month later, the treatment order was inversed. Electrical impedance tomography (EIT) using a thoracic electrode belt, spirometry, volumetric capnography, esophageal pressure difference (ΔPoes), venous admixture, and laryngoscopy data were recorded over 2 min every 15 min. Breaths were classified as normal or alternate (sigh or crown-like) according to the EIT impedance curve. A mixed linear model was used to test the effect of treatment on continuous outcomes. Cochran-Mantel-Haenszel analysis was used to test for associations between global BrP and treatment. Global BrP was associated with treatment (p = 0.012) with more alternate breaths during ETT. The center of ventilation right-to-left (CoVRL) showed more ventilation in the non-dependent lung during ETT (p = 0.025). The I:E ratio (p = 0.017) and ΔPoes (p < 0.001) were smaller, and peak expiratory flow (p = 0.009) and physiologic dead space (p = 0.034) were larger with ETT. The presence of an ETT alters BrP and shifts ventilation toward the non-dependent lung in spontaneously breathing horses anesthetized with TIVA.

Comparison of electrical impedance tomography and spirometry-based measures of airflow in healthy adult horses

“…We gave xylazine hydrochloride, an alpha-2 receptor agonist, as a CRI sedative to facilitate rebreathing which likely explains the presence of Cheyne-Stokes respiration. We also observed altered breath morphology on the EIT impedance curve reported as crown-like breaths in anaesthetized horses ( Kowalczyk et al, 2014 ; Moreno-Martinez et al, 2022 ). These breaths had an influence on the distribution of ventilation and shifted gas towards dependent parts of the lungs ( Moreno-Martinez et al, 2022 ).…”

“…We also observed altered breath morphology on the EIT impedance curve reported as crown-like breaths in anaesthetized horses ( Kowalczyk et al, 2014 ; Moreno-Martinez et al, 2022 ). These breaths had an influence on the distribution of ventilation and shifted gas towards dependent parts of the lungs ( Moreno-Martinez et al, 2022 ). Our study is the first to observe this phenomenon in conscious horses.…”

“…Seven out of 10 horses exhibited intermittent single or multiple breaths with incomplete expiration in between each breath which were identified as crown-like breaths ( Moreno-Martinez et al, 2022 ). One of the ten horses had crown-like breaths at T BL , five horses at T 1000 , two horses at T 2000 , T 3500 and T REC , and two different individual horses at T 6000 and T 8500 .…”

“…Our study however shows that sedation can have a significant effect on breathing pattern and breath morphology and therefore does not support the use of sedatives for PFT. Furthermore, crown-like breaths have been observed in anaesthetized horses under triple drip anaesthesia and spirometry software was unable to evaluate > 20% of data sets with crown-like breaths which might bias the spirometry data during PFTs ( Moreno-Martinez et al, 2022 ). At T 8500 , the inspired carbon dioxide concentration was unexpectedly low (mean 2.8 mmHg).…”

Electrical impedance tomography in anaesthetised chickens (Gallus domesticus)

“…The use of EIT allowed objective quantification of the changes in respiratory pattern. In this study, the method of categorising BrP using the morphology of the expiratory impedance curve was based on that reported in rhinoceros and horse EIT studies ( 40 , 47 ). It was interesting to note that in both right and left lateral recumbencies, the majority of the chickens demonstrated early expiratory breath holding (BrP3).…”