Impact of four different recumbencies on the distribution of ventilation in conscious or anaesthetized spontaneously breathing beagle dogs: An electrical impedance tomography study

Abstract

The aim was to examine the effects of recumbency and anaesthesia on distribution of ventilation in beagle dogs using Electrical Impedance Tomography (EIT). Nine healthy beagle dogs, aging 3.7±1.7 (mean±SD) years and weighing 16.3±1.6 kg, received a series of treatments in a fixed order on a single occasion. Conscious dogs were positioned in right lateral recumbency (RLR) and equipped with 32 EIT electrodes around the thorax. Following five minutes of equilibration, two minutes of EIT recordings were made in each recumbency in the following order: RLR, dorsal (DR), left (LLR) and sternal (SR). The dogs were then positioned in RLR, premedicated (medetomidine 0.01, midazolam 0.1, butorphanol 0.1 mg kg-1 iv) and pre-oxygenated. Fifteen minutes later anaesthesia was induced with 1 mg kg-1 propofol iv and maintained with propofol infusion (0.1–0.2 mg kg-1 minute-1 iv). After induction, the animals were intubated and allowed to breathe spontaneously (FIO2 = 1). Recordings of EIT were performed again in four recumbencies similarly to conscious state. Centre of ventilation (COV) and global inhomogeneity (GI) index were calculated from the functional EIT images. Repeated-measures ANOVA and Bonferroni tests were used for statistical analysis (p < 0.05). None of the variables changed in the conscious state. During anaesthesia left-to-right COV increased from 46.8±2.8% in DR to 49.8±2.9% in SR indicating a right shift, and ventral-to-dorsal COV increased from 49.8±1.7% in DR to 51.8±1.1% in LLR indicating a dorsal shift in distribution of ventilation. Recumbency affected distribution of ventilation in anaesthetized but not in conscious dogs. This can be related to loss of respiratory muscle tone (e.g. diaphragm) and changes in thoracic shape. Changing position of thoraco-abdominal organs under the EIT belt should be considered as alternative explanation of these findings.

Thoracic Electrical Impedance Tomography—The 2022 Veterinary Consensus Statement

“…Further work has focused on internal validation, centred on the repeatability of EIT measurements, and the robustness of these measurements in the face of changing conditions (position, ventilation, induced bronchoconstriction, age, species etc.) (10,34,42,43). This demonstrates the value of EIT as a non-invasive monitoring tool of changing physiology.…”

“…Overall, the Graz consensus Reconstruction algorithm for EIT (GREIT) is the most commonly method used for image reconstruction in the existing veterinary literature. Gaussian spatial and lowpass temporal filters have also been used to reconstruct images (22,42).…”

Advances in the Diagnosis of Equine Respiratory Diseases: A Review of Novel Imaging and Functional Techniques

“…The EIT is well situated for adults, neonates, and pediatric patients [89]. In the veterinary field, EIT is at an early stage of clinical development, however, in equine medicine the global and regional peak respiratory flows have recently been investigated [73,[90][91][92][93].…”

Assessment of Regional Ventilation During Recruitment Maneuver by Electrical Impedance Tomography in Dogs

“…Electrical impedance tomography (EIT) can infer atelectasis and lung overdistention during mechanical ventilation in both men and dogs during anesthesia and in the ICU ( 1 ). Experimental studies in dogs verify that EIT can identify pulmonary edema, changes in lung air and liquid volumes, lung hyperinflation, and effects of anesthesia and body positioning on EIT.…”

“…Experimental studies in dogs verify that EIT can identify pulmonary edema, changes in lung air and liquid volumes, lung hyperinflation, and effects of anesthesia and body positioning on EIT. Also a correlation of EIT and CT images was demonstrated in anesthetized dogs ventilated at different PEEP levels ( 1 ). Only one clinical study evaluated EIT during the recruitment maneuver (RM) in dogs undergoing sterilization surgery ( 2 ).…”