Anthea Raisis

Objectives
To record the terms, definitions, and abbreviations used in the literature, investigate the rationale for employing dynamic compliance (Cdyn) in studies of anaesthetised dogs with mechanically ventilated lungs, and identify the methods used to calculate Cdyn.

Databases used
A comprehensive search across Medline, PubMed, Scopus, and CAB Abstracts databases identified studies using keywords related to canine species, anaesthesia, Cdyn, and the respiratory system. Reference lists from recent publications (2010–2024) focusing on respiratory mechanics in dogs were also reviewed. Following duplicate removal, a two-step screening process was employed. This involved reviewing titles and abstracts, followed by full-text retrieval based on predefined eligibility criteria, concentrating on studies involving anaesthetised dogs with closed chests where Cdyn was measured. Data extraction included terms, definitions, measurement equipment, and study applications.

Conclusions
Of 362 initial documents, 186 duplicates were removed, leaving 176 for abstract screening. Of these, 122 full texts were retrieved, with 54 meeting inclusion criteria. Most studies were published between 1970 and 2002, with only five published after 2010. In 49/54 studies, dogs were used as animal models for translational research. Whole-body plethysmographs and pneumotachographs were commonly used to evaluate tidal volume for the calculation of Cdyn; the sampling site of airway pressure varied. In 43/54 papers, oesophageal or pleural pressure was measured to determine transpulmonary pressure, suggesting that Cdyn of the lung was monitored, although this was not always explicitly stated. The three most recent studies involved clinical patients, using Cdyn of the respiratory system displayed by respiratory modules integrated into ventilators or multiparametric physiologic monitors. Future research should establish clear protocols for measuring Cdyn to enhance understanding and characterisation for both research and clinical purposes.

Objective:
To explore changes in urinary biomarkers of acute kidney injury (AKI) in healthy dogs experiencing intra-operative hypotension and explore the relationship between blood pressure and urinary biomarkers.

Study Design:
Observational cohort study.

Animals:
A group of 50 client owned dogs.

Methods:
Urine and blood samples were collected prior to anaesthesia (T0), within 24 hours after anaesthesia (T1) and 10 days post-surgery (T10). During anaesthesia, the lowest mean arterial pressure (MAP) in each dog. Impact of duration was explored by categorising according to arbitrary thresholds of MAP < 50, < 60, < 70 and < 80 mmHg and calculating duration (minutes) within each category Serum creatinine (Cr) and validated biomarkers of AKI including urinary gamma-glutamyl transferase (uGGT), urinary neutrophil gelatinase-associated lipocalin (uNGAL), and urinary cystatin C (uCystatin C) were measured. Biomarker measurements were standardised to urinary Cr. The frequency of dogs with proportional increases between T1 and T0 and between T10 and T0 was recorded. Multiple regression analysis was performed to determine the simplest subset of independent variables (lowest MAP, duration with each MAP category) to best explain the variance in the proportional change of each biomarker.

Results:
Hypotension, defined as MAP < 60 mmHg was observed in 38/50 (76 %) of the dogs. Between T1 and T0, increases in uGGT/Cr, uCystatin C/Cr, and uNGAL/Cr were observed in 37 (82%), 17 (41 %) and 19 (35%) of 50 dogs, respectively. Of the variance observed in uGGT/Cr at T1/T0, 62% could be explained by the lowest MAP recorded when combined with duration MAP < 50mmHg (adjusted R2 0.62).

Conclusion and clinical relevance:
In this clinical model of intra-operative hypotension uGGT/Cr demonstrated potential for diagnosis of early AKI in healthy dogs. Increases in validated biomarkers uCystatin C/Cr, and uNGAL/Cr support their use in future studies investigating different causes or severity of AKI.

Objective: Data from two-plane electrical impedance tomography (EIT) can be reconstructed into various slices of functional lung images, allowing for more complete visualisation and assessment of lung physiology in health and disease. The aim of this study was to confirm the ability of 3d EIT to visualise normal lung anatomy and physiology at rest and during increased ventilation (represented by rebreathing).

Approach: Two-plane EIT data, using two electrode planes 20cm apart, were collected in 20 standing sedate horses at baseline (resting) conditions, and during rebreathing. EIT data were reconstructed into 3d EIT whereby tidal impedance variation (TIV), ventilated area, and right-left and ventral-dorsal centres of ventilation (CoVRL and CoVVD, respectively) were calculated in cranial, middle and caudal slices of lung, from data collected using the two planes of electrodes.

Main results: There was a significant interaction of time and slice for TIV (p < 0.0001) with TIV increasing during rebreathing in both caudal and middle slices. The ratio of right to left ventilated area was higher in the cranial slice, in comparison to the caudal slice (p = 0.0002). There were significant effects of time and slice on CoVVD whereby the cranial slice was more ventrally distributed than the caudal slice (p < 0.0009 for the interaction).

Significance: The distribution of ventilation in the three slices corresponds with topographical anatomy of the equine lung. This study confirms that 3d EIT can accurately represent lung anatomy and changes in ventilation distribution during rebreathing in standing sedate horses.

Screw fixation failures remain clinically challenging especially hip fracture fixation in osteoporotic bone. Prior studies have shown that expandable orthopaedic screw devices can improve biomechanical fixation in bone, but concerns over their removability remains. A novel expandable screw implant has been developed that optimizes both implant fixation and removability. The present study investigated the implant removability in an animal model.

A specially manufactured expandable screw implant was surgically implanted in 5 sheep for 4 months. The distal femur were extracted with the implants in-situ after euthanasia. The bone samples were scanned using micro-CT and the retraction torque of the expandable screw wings were measured to assess ease of removability.

Analysis of the micro-CT images verified that bone had not grown inside the expandable screw mechanism and all expandable screw samples were removed without complication. The mean peak torque to fully retract the screws ready for removal was 0.86 Nm (0.59-1.30 Nm) and the mean peak removal torque for the retracted screws was 7.98 Nm (1.70-15.40 Nm).

This large animal study result shows the feasibility of an expandable screw concept with a novel gapless design, to improve screw fixation strength mechanically, without compromising on the implant removability.

Objective
To explore the influence of acepromazine on the cardiovascular effects of dobutamine in isoflurane-anaesthetised horses premedicated with romifidine.

Study design
Prospective randomised clinical trial.

Animals
A total of 18 horses undergoing elective arthroscopy were enrolled, of which 12 horses requiring dobutamine were included.

Methods
orses were randomised to receive acepromazine 0.02 mg kg-1 (Group A+) intravenously (IV) or none (Group A-), 35 minutes before anaesthesia. Horses received xylazine 0.2 mg kg-1 concurrently to facilitate IV access. Horses were premedicated with romifidine 0.08 mg kg-1, induced with ketamine 2.2 mg kg-1 and diazepam 0.08 mg kg-1 IV, and maintained with isoflurane in oxygen. Dobutamine infusion was commenced when mean arterial pressure (MAP) was < 60 mmHg. Cardiovascular data were collected prior to dobutamine, and at a target MAP of ≥ 70 mmHg. Dobutamine start time from induction, duration and dose to reach target MAP were compared using Mann-Whitney U test. Cardiovascular variables were compared using repeated measures ANOVA and post-hoc Fisher’s least significant difference test.

Results
Cardiac index (CI) and its percentage change was significantly higher at target MAP in group A+ [42.8 (17.0–68.7) %] than in A- [-4.05 (-21.2–13.0) %] (p = 0.003). Group A+ required significantly earlier dobutamine [20 (18–25) minutes] than group A- [36 (27–60) minutes] (p = 0.02). Group A+ required significantly higher dobutamine dose [1.5 (1–2.5) μg kg-1 minute-1] to reach target MAP than group A- [0.5 (0.5–1) μg kg-1 minute-1] (p = 0.009). No significant difference in infusion duration to reach target MAP was found between groups.

Conclusion and clinical relevance
Dobutamine significantly increased MAP and CI following pre-anaesthetic acepromazine sedation, in isoflurane-anaesthetised horses premedicated with romifidine. Without acepromazine, dobutamine increased MAP but not CI. Interactions between acepromazine, romifidine and dobutamine on the cardiovascular system should be considered.

Introduction: In clinical practice, evaluating dynamic compliance of the respiratory system (Cdyn) could provide valuable insights into respiratory mechanics. Reference values of Cdyn based on body weight have been reported, but various factors may affect them and the evidence is scanty. This study aimed to establish a reference interval for Cdyn and identify associated variables.

Methods: Data were collected from 515 client-owned dogs requiring anesthesia, excluding those with lower airway disease. The dogs were anesthetized, the tracheas intubated, and lungs ventilated at clinicians' discretion across 11 centers in six countries, with no restrictions on anesthesia protocols or ventilation settings, except avoiding inspiratory pauses. Three Cdyn measurements from three consecutive breaths per dog were recorded using a standardized form, which also documented factors affecting Cdyn identified through literature and an online survey. Various spirometry technologies were used. The substantial variance in Cdyn measurements led to a comprehensive analysis using a multiple linear regression model. Multicollinearity (variables highly correlated with each other) was addressed by investigating, transforming, or excluding factors. Initial simple linear regression assessed each variable's individual effect on Cdyn, followed by a multiple linear regression model constructed via stepwise forward selection and backward elimination.

Results: The best-fitting model identified a linear relationship between Cdyn and body mass when the following conditions were met: high BCS (Body Condition Score), orotracheal tubes <7% smaller than predicted, the use of a D-lite flow sensor, and the absence of a high FIO2 (>80%) exposure for more than 10 minutes before Cdyn measurement. In cases where these conditions were not met, additional factors needed to be incorporated into the model. Low (1/9, 2/9, 3/9) and medium (4/9, 5/9) BCS, an orotracheal tube of the predicted size or larger and longer inspiratory times were associated with increased Cdyn. The use of alternative spirometry sensors, including Ped-lite, or prolonged exposure to high FIO2 levels resulted in decreased Cdyn.

Conclusion and clinical relevance: Establishing a reference interval for Cdyn proved challenging. A single reference interval may be misleading or unhelpful in clinical practice. Nevertheless, this study offers valuable insights into the factors affecting Cdyn in healthy anesthetized dogs, which should be considered in clinical assessments.

Introduction: Spirometry devices, which are components of many anaesthesia machines, are commonly used to assess lung mechanics during anaesthesia. Spirometry calibration usually adheres to manufacturer recommendations without established guidelines. Although more accurate and less variable than inbuilt spirometry in certain General Electric anaesthesia ventilators, near-patient spirometry lacks adequate evaluation.

Methods: We assessed near-patient spirometers’ performance using Pedi-lite and D-lite flow sensors. Certified 1 L calibration syringes were used on 67 monitors located in 14 veterinary hospitals. Three consecutive inspired and expired volume values displayed by the monitors for each volume of the calibration syringe were recorded. Volumes studied were 50, 100, 150, 250, 300 mL for Pedi-lite and 150, 300, 450, 500, 750 mL for D-lite. Measured and targeted volumes were averaged, agreement error calculated. Accuracy was assessed plotting agreement errors against calibration volumes. A linear mixed-effects model was used to obtain linear regression between the error and the calibration volume. Mean, differential and proportional bias, limits of agreement, claimed accuracy and 10% clinical tolerance were calculated and displayed. Differences among monitors were evaluated using the Friedman rank sum test, differences between inspired and expired volumes using the Wilcoxon signed-rank.

Results: Inter-monitor variability for inspired and expired volume readings using both sensors was high; intra-monitor variability was low. The error magnitude was independent of volumes evaluated. Using Pedi-lite, only a minority of measurements met manufacturer’s specification or a 10% clinical tolerance; both inspired and expired volumes were significantly underestimated. Using D-lite, superior performance was demonstrated for volumes between 300 and 750 mL (mean biases close to zero and the majority of measurements meeting manufacturer’s specifications and clinical tolerance). The difference between measured inspired and expired volumes with both sensors was significant.

Discussion: These results support caution when interpreting clinical measurements of lung volumes and mechanics in anaesthetised patients when using these sensors. This is particularly important in smaller patients where lung volumes are below 300 mL. Trends should be reliable.

Respiratory disease in cattle is a significant global concern, yet current diagnostic methods are limited, and there is a lack of crush-side tests for detecting active disease. To address this gap, we propose utilizing electrical impedance tomography (EIT), a non-invasive imaging technique that provides real-time visualization of lung ventilation dynamics. The study included adult cattle from farms in Western Australia. The cattle were restrained in a crush. A standardized respiratory scoring system, which combined visual, auscultation, and clinical scores, was conducted by two non-conferring clinicians for each animal. The scores were blinded and averaged. During assessment, an EIT electrode belt was placed around the thorax. EIT recordings of ten suitable breaths were taken for analysis before the cattle were released back to the herd. Based on the combined examination scoring, the cattle were categorized as having healthy or diseased lungs. To allow visual interpretation of each breath and enable the creation of the quartile ventilation ratio (VQR), Flow/Tidal Impedance Variation curves (F/TIV) were generated for each breath. The analysis focused on two EIT variables: The novel VQR over time during inhalation and exhalation and global expiratory impedance (TIVEXP) adjusted by breath length. A mixed effects model was used to compare these variables between healthy and diseased cattle. Ten adult cattle of mixed ages were used in the current analysis. Five cattle were scored as healthy and five as diseased. There was a significant difference in the examination scores between the healthy and diseased group (P = 0.03). A significant difference in VQR during inhalation (P = 0.03) was observed between the healthy and diseased groups. No difference was seen in VQR over time during exhalation (P = 0.3). The TIVEXP was not different between groups (P = 0.36). In this study, EIT was able to detect differences in inhalation mechanics when comparing healthy and diseased cattle as defined via clinical examination, highlighting the clinical utility of EIT.

Background: The bedside diagnosis of acute pulmonary edema is challenging. This study evaluated the breath-by-breath information from electrical impedance tomography (EIT), respiratory mechanics and volumetric capnography (VCap) to assess acute pulmonary edema induced by xylazine administration in anesthetized sheep.

Objective: To determine the ability and efficiency of each monitoring modality in detecting changes in lung function associated with onset of pulmonary edema.

Methods: Twenty healthy ewes were anesthetized, positioned in sternal (prone) recumbency and instrumented. Synchronized recordings of EIT, spirometry and VCap were performed for 60 s prior to start of injection, during xylazine injection over 60 s (0–60 s) and continuously for 1 min (60–120 s) after the end of injection. After visual assessment of the recorded mean variables, statistical analysis was performed using a mixed effect model for repeated measures with Bonferroni’s correction for multiple comparisons, to determine at which breath after start of injection the variable was significantly different from baseline. A significant change over time was defined as an adjusted p < 0.05. All statistics were performed using GraphPad Prism 0.1.0.

Results: Electrical impedance tomography showed significant changes from baseline in all but two variables. These changes were observed simultaneously during xylazine injection at 48 s and were consistent with development of edema in dependent lung (decreased end-expiratory lung impedance, ventilation in centro-ventral and ventral lung region) and shift of ventilation into non-dependent lung (decreased non-dependent silent spaces and increased center of ventilation ventral to dorsal and increased ventilation in centro-dorsal and dorsal lung region). All changes in lung mechanics also occurred during injection, including decreased dynamic respiratory system compliance and increased peak expiratory flow, peak inspiratory pressure and airway resistance at 48, 54 and 60 s, respectively. Changes in VCap variables were delayed with all occurring after completion of the injection.

Conclusion: In this model of pulmonary edema, EIT detected significant and rapid change in all assessed variables of lung function with changes in regional ventilation indicative of pulmonary edema. Volumetric capnography complemented the EIT findings, while respiratory mechanics were not specific to lung edema. Thus, EIT offers the most comprehensive method for pulmonary edema evaluation, including the assessment of ventilation distribution, thereby enhancing diagnostic capabilities.