Comparison of a Supraglottic Airway Device (v-gel®) with Blind Orotracheal Intubation in Rabbits

Computational fluid dynamics comparison of the upper airway velocity, pressure, and resistance in cats using an endotracheal tube or a supraglottic airway device

Intoduction

In veterinary medicine, airway management of cats under general anesthesia is performed with an endotracheal tube (ETT) or supraglottic airway device (SGAD). This study aims to describe the use of computational fluid dynamics (CFD) to assess the velocities, pressures, and resistances of cats with ETT or SGAD.

Methods

A geometrical reconstruction model of the device, trachea, and lobar bronchi was carried out from computed tomography (CT) scans that include the head, neck, and thorax. Twenty CT scans of cats under general anesthesia using ETT (n = 10) and SGAD (n = 10) were modeled and analyzed. An inspiratory flow of 2.4 L/min was imposed in each model and velocity (m/s), general and regional pressures (cmH2O) were computed. General resistance (cmH2O/L/min) was calculated using differential pressure differences between the device inlet and lobar bronchi. Additionally, regional resistances were calculated at the device's connection with the breathing circuit (region A), at the glottis area for the SGAD, and the area of the ETT exit (bevel) (region B) and the device itself (region C).

Results

Recirculatory flow and high velocities were found at the ETT's bevel and at the glottis level in the SGAD group. The pressure gradient (Δp) was more enhanced in the ETT cases compared with the SGAD cases, where the pressure change was drastic. In region A, the Δp was higher in the ETT group, while in regions B and C, it was higher in the SGAD group. The general resistance was not statistically significant between groups (p = 0.48). Higher resistances were found at the region A (p = <0.001) in the ETT group. In contrast, the resistance was higher in the SGAD cases at the region B (p = 0.001).

Discussion

Overall, the provided CT-based CFD analysis demonstrated regional changes in airway pressure and resistance between ETT and SGAD during anesthetic flow conditions. Correct selection of the airway device size is recommended to avoid upper airway obstruction or changes in flow parameters.

Sedation and Anesthesia in Exotic Animal Critical Care

Sedation and anesthesia of exotic animals in inherently challenging, but often facilitates the best care for patients. Critical illness or injury adds on another layer of complexity to their management for obtaining diagnostics and providing treatments. This article serves to review some of the more recent literature of sedation and anesthesia within exotics practice, bringing to light some nuances and considerations for when those patients are critically ill or injured.

Retrospective comparison of the effects of laryngeal mask and endotracheal tube on some cardio-respiratory variables in pet rabbits undergoing anaesthesia for elective gonadectomy

BACKGROUND

Endotracheal intubation in rabbits is challenging and supraglottic airway devices, such as laryngeal masks (LMA), represent an alternative as they are easy to insert, and do not stimulate the larynx requiring therefore a lighter plane of anaesthesia for their insertion and positioning than the endotracheal tubes. We investigated whether, compared to an endotracheal tube, the LMA can reduce the negative effects of general anaesthetics on some cardiovascular and respiratory parameters routinely monitored in rabbits anaesthetized for elective gonadectomy. The records of 21 adult mixed breed pet rabbits were collected retrospectively. Rabbits were divided in two groups based on the type of airway device used. A laryngeal mask secured the airway in group LMA (n = 11), and in group ETT (n = 10) an endotracheal tube was used. The amount of propofol used before successful insertion of the airway device was recorded. A pitot-based spirometer was connected and ventilatory variables were measured immediately after insertion. Pulse rate, non-invasive arterial blood pressure, haemoglobin oxygen saturation, respiratory rate, end-tidal carbon dioxide and volatile anaesthetic consumption were also monitored during the surgical procedure; extubation time was noted as well.

RESULTS

The use of LMA required significantly less propofol (0.8 to 4 mg/kg) for insertion than the ETT (1.2 to 5.6 mg/kg), and the difference was statistically significant (P < 0.01). No differences were observed in ventilatory variables measured immediately after airway positioning. Intraoperatively, there were no differences between groups for respiratory and cardiovascular variables, and amount of isoflurane administered. In all rabbits mean and diastolic blood pressure progressively decreased during surgery. Mean extubation time was shorter in group LMA (6 ± 2 min) than group ETT (8 ± 3 min, P < 0.01).

CONCLUSION

The airway device did not clinically affect the cardiovascular and respiratory variables during anaesthesia. Intraoperative hypoventilation was observed in most rabbits regardless of the device being used; therefore ventilatory support may be required. Rabbits with the laryngeal masks were extubated earlier.

The Spritztube: A New Device for the Extraglottic Intubation of Rabbits

The Spritztube (ST) is an extraglottic airway device developed for humans. The aim of the study was to design an ST for rabbits and to evaluate its feasibility. The study was divided into two phases. Phase I: anatomical study on 12 rabbit cadavers to design 2 STs (8 and 10 Ch, external diameter) for rabbits. Phase II: fourteen privately owned rabbits were anaesthetised, and intubation was attempted using a ST. Tube size, the method for confirming the correct positioning, the number of attempts, the time needed for the correct positioning of the ST and complications were recorded. The ST placement was feasible in all rabbits. The positioning of the ST was completed in 2.1 ± 1 attempts in 43 ± 21.4 s. A correct placement was confirmed by the visualisation of the proximal cuff at visual inspection of the oral cavity (14/14), by the detection of the airflow (9/14 rabbits) and by the visualisation of a capnographic wave (14/14 rabbits). Only one rabbit developed respiratory distress after the ST placement. The results of the present study allowed designing a ST specific for rabbits which was used a supraglottic airway device for the maintenance of isoflurane anaesthesia in spontaneously breathing rabbits.

Rabbit Sedation and Anesthesia

With the increasing frequency of rabbits as veterinary patients, the expectation for high-quality, intensive veterinary care, and resultantly an understanding of anesthesia has been increasing. Sedation and general anesthesia are commonly required for many routine and emergency procedures in rabbits, and this results in the need for a strong awareness of anesthetic principles, knowledge of limitations of anesthesia, and maintenance of high standards of anesthesia.

V-Gel® Guided Endotracheal Intubation in Rabbits

Background: General anesthesia in rabbits is associated with higher morbidity and mortality relative to other mammalian species commonly anesthetized. Unique challenges related to endotracheal intubation (ETI) in rabbits contribute to this risk. Objective: To improve the safety of ETI in rabbits, we developed two new ETI methods using a supraglottic airway device (v-gel^®) to facilitate ETI and compared them to traditional "blind" technique. We hypothesized that relative to blind ETI, v-gel^® guided ETI provides more successful placement of the endotracheal tube (ETT) in a shorter time. Outcomes included number of intubation attempts, time for achievement of ETI, endoscopic findings, and serial arterial blood gas (ABG) analysis. Study Design: Prospective, randomized, and crossover study. Methods: Ten female, New Zealand White rabbits aged 1-2 years old, weighing 4.3 ± 0.4 kg, were anesthetized four times. Each time, ETI was performed with one of the following techniques: Method 1: v-gel^® guided, polypropylene catheter facilitated, intubation using a cuffed ETT; Method 2: v-gel^® guided intubation using an uncuffed ETT directly inserted through the device airway channel; Method 3 and 4: Blind intubation with uncuffed or cuffed ETT. Upper airway endoscopy was performed before intubation attempts and after extubation. Serial ABG analysis was performed during the peri-intubation process. Results: V-gel^® guided techniques allowed successful ETI on the initial attempt for 9/10 subjects using Method 1 and 10/10 using Method 2. Relative to the v-gel^® guided techniques, the blind techniques required more intubation attempts. A median of 2 attempts (range 1-4, p < 0.007) were required for the uncuffed ETT, and a median of 4 (range 1-4, p < 0.001) attempts were performed for the cuffed ETT. The time to perform successful ETI was positively correlated with the number of attempts (ρ = 0.82), while successful ETI was negatively correlated with number of attempts (ρ = -0.82). Endoscopic findings showed mild to moderate laryngeal trauma. In the absence of oxygen supplementation, ABG analysis demonstrated low PaO₂, while PaCO₂ remained consistent. Conclusions: Facilitated ETI using the v-gel^® guided techniques allows for the rapid establishment of a secure airway to provide ventilatory support for rabbits undergoing general anesthesia.

EVALUATION OF A LARYNGEAL MASK AIRWAY AS AN ALTERNATIVE TO OROTRACHEAL INTUBATION FOR MAINTAINING AIRWAY PATENCY DURING INHALANT ANESTHESIA UNDER SPONTANEOUS VENTILATION IN CAPYBARAS (HYDROCHOERUS HYDROCHAERIS)

Orotracheal intubation carries greater difficulty in rodents than in most domestic species. The human laryngeal mask airway (LMA) was compared with an endotracheal tube (ET_tube) for maintaining airway patency in anesthetized capybaras (Hydrochoerus hydrochaeris). Six capybaras (24-52 kg) were remotely darted with intramuscular ketamine, midazolam, and acepromazine on two occasions (≥7-day intervals). After isoflurane mask induction for random placement of an ET_tube or a LMA during each episode, anesthesia was maintained with isoflurane in oxygen under spontaneous ventilation for 90-120 min. Computed tomography of the pharynx and larynx was performed in two of six animals and three of six animals with the ET_tube and LMA, respectively. End-tidal isoflurane [median (range)] was not significantly different between ET_tube [0.6% (0.5-1.5%)] and LMA [0.6% (0.4-0.9%)]. Heart rate [67 ± 11 beats/min (ET_tube) and 67 ± 18 beats/min (LMA)], mean arterial pressure [74 ± 13 mm Hg (ET_tube) and 74 ± 14 mm Hg (LMA)], arterial CO2 tension [41 ± 2 mm Hg (ET_tube) and 43 ± 4 mm Hg (LMA)], and arterial O2 tension [360 ± 59 mm Hg (ET_tube) and 360 ± 63 mm Hg (LMA)] were not significantly different between treatment groups. Computed tomography showed gas in the esophagus with the LMA (three of three animals); the fit of the LMA to the larynx was adequate in two of three animals and fair in one of three animals. Recovery from anesthesia was uneventful. The LMA is a feasible alternative to the ET_tube for maintaining airway patency during inhalant anesthesia in spontaneously breathing capybaras. However, the LMA may be dislodged during movement of the animal.

Surgical ventricular restoration for rabbit dilated cardiomyopathy model: Preliminary study

Dilated cardiomyopathy (DCM) is a common cardiovascular disease in dogs. It is primarily treated with beta-blockers. The aim of this preliminary study was to evaluate the efficacy of surgical ventricular restoration on daunorubicin-induced DCM in rabbits. The DCM model was generated in six rabbits by intravenous administration of daunorubicin (4 mg/kg/week) for 6 weeks. Echocardiography was performed before and after left ventricular (LV) reconstruction surgery to evaluate the LV function. The surgery was performed using non-absorbent prosthetic sheets and 5-0 polypropylene sutures, between the left anterior descending branch and the circumflex branch of the left coronary artery. We measured LV function 3 weeks postoperatively and collected the hearts for histopathological examination. We observed significant improvements in the LV internal dimension volume at both end-diastole and end-systole compared to the preoperative values. Fraction shortening showed a substantial improvement from 23.8 ± 1.4% to 30.9 ± 1.3%. In addition, the ejection fraction increased from 35.3% to 51.9%. On histological examination, the left ventricular wall was markedly thin. Furthermore, we observed fibrosis between the myocardial cells around the sutured site. The LV volume and LV functions significantly improved postoperatively. However, further investigation is required to determine the long-term effects of surgical ventricular restoration.

Evaluation of supraglottic airway device use during inhalation anesthesia in healthy African pygmy hedgehogs (Atelerix albiventris)

OBJECTIVE

To evaluate a supraglottic airway device (SGAD) designed for rabbits in African pygmy hedgehogs (Atelerix albiventris) during inhalation anesthesia.

STUDY DESIGN

Prospective, randomized, blinded experimental study.

ANIMALS

A total of 12 adult African pygmy hedgehogs (seven male, five female).

METHODS

Hedgehogs were placed in a chamber and anesthesia was induced using isoflurane in oxygen. Oropharyngeal endoscopy was performed and video recorded. The SGAD (v-gel R1) was inserted and connected to a Mapleson D circuit. Capnography, pulse oximetry and physiologic variables were measured during anesthesia, and lung inflation was tested at 10 and 20 cmH₂O. With the SGAD temporarily disconnected, anesthetized hedgehogs were randomly positioned into right and left lateral, dorsal and sternal recumbency to evaluate the effect of a change in body position on SGAD placement. Oropharyngeal endoscopy was repeated at the end of anesthesia, and recovery time was recorded. Pre- and post-SGAD placement endoscopy videos were retrospectively reviewed and scored for gross trauma.

RESULTS

The median [interquartile range (IQR)] time to successful SGAD placement was 38 (16-68) seconds. The time to SGAD placement decreased as the study progressed. SGAD required repositioning in six hedgehogs, median 2.5 (IQR, 1-3.5) adjustments each, to successfully perform lung inflation or maintain capnography readings. Lung inflation at 10 cmH₂O was successfully performed without leakage in nine animals, and in the other three animals after adjusting the SGAD at 1-2 time points. Inflation at 20 cmH₂O was rarely achieved without an air leak. Changes in heart and respiratory rates during anesthesia were not clinically relevant. Median endoscopic scores were 0 (no lesions) for both pre-and postplacement.

CONCLUSIONS AND CLINICAL RELEVANCE

The SGAD was relatively quickly and easily placed, permitted lung inflation and caused no significant oropharyngeal damage. The SGAD is a practical option for airway management in African pygmy hedgehogs.

Benefit of Physiologically Variable Over Pressure-Controlled Ventilation in a Model of Chronic Obstructive Pulmonary Disease: A Randomized Study

Introduction

The advantages of physiologically variable ventilation (PVV) based on a spontaneous breathing pattern have been demonstrated in several respiratory conditions. However, its potential benefits in chronic obstructive pulmonary disease (COPD) have not yet been characterized. We used an experimental model of COPD to compare respiratory function outcomes after 6 h of PVV versus conventional pressure-controlled ventilation (PCV).

Materials and Methods

Rabbits received nebulized elastase and lipopolysaccharide throughout 4 weeks. After 30 days, animals were anesthetized, tracheotomized, and randomized to receive 6 h of physiologically variable (n = 8) or conventional PCV (n = 7). Blood gases, respiratory mechanics, and chest fluoroscopy were assessed hourly.

Results

After 6 h of ventilation, animals receiving variable ventilation demonstrated significantly higher oxygenation index (PaO₂/FiO₂ 441 ± 37 (mean ± standard deviation) versus 354 ± 61 mmHg, p < 0.001) and lower respiratory elastance (359 ± 36 versus 463 ± 81 cmH₂O/L, p < 0.01) than animals receiving PCV. Animals ventilated with the variable mode also presented less lung derecruitment (decrease in lung aerated area, –3.4 ± 9.9 versus –17.9 ± 6.7%, p < 0.01) and intrapulmonary shunt fraction (9.6 ± 4.1 versus 17.0 ± 5.8%, p < 0.01).

Conclusion

PVV applied to a model of COPD improved oxygenation, respiratory mechanics, lung aeration, and intrapulmonary shunt fraction compared to conventional ventilation. A reduction in alveolar derecruitment and lung tissue stress leading to better aeration and gas exchange may explain the benefits of PVV.

A modified rabbit model of tracheal stenosis and a household endoscope. More simplicity and accessibility

Purpose:

To develop a simpler animal model for benign tracheal stenosis and introduce a low-cost household endoscope for postmodeling endotracheal evaluation.

Methods:

Twenty rabbits were randomly divided into a model group (15 rabbits, subjected to transoral nylon brush scraping of the trachea) and a mock group (5 rabbits, merely exempted from scraping), a household endoscope was then introduced for weekly endoscopic examination. Meanwhile, other 15 rabbits (modeling like the model group) underwent batch tracheal resection at different postintervention times for pathological analysis.

Results:

The model group presented a low mortality and few complications. The endoscope could obtain adequate images for stenosis assessment, which showed that the models presented homogeneous injury after scraping and developed a mature scar stricture at 28 days postoperatively with a mean stenosis degree of 65.9%, and 71.4% (10/14) above Myer–Cotton’s grade II. The pathological findings were consistent with the clinicopathological process of human. No stenosis was found in mock group.

Conclusion:

The modified model is simpler, minimally invasive and reliable, while the household endoscope is competent for model’s follow-up, providing easily accessible and useful tools for facilitating more extensive studies of benign tracheal stenosis.

3D Printed Biomimetic Rabbit Airway Simulation Model for Nasotracheal Intubation Training

Rabbit inhalation anesthesia by endotracheal intubation involves a higher risk among small animals owing to several anatomical and physiological features, which is pathognomonic to this species of lagomorphs. Rabbit-specific airway devices have been designed to prevent misguided intubation attempts. However, it is believed that expert anesthetic training could be a boon in limiting the aftermaths of this procedure. Our research is aimed to develop a novel biomimetic 3D printed rabbit airway model with representative biomechanical material behavior and radiodensity. Imaging data were collected for two sacrificed rabbit heads using micro-computed tomography (μCT) and micro-magnetic resonance imaging for the first head and cone beam computed tomography (CBCT) for the second head. Imaging-based life-size musculoskeletal airway models were printed using polyjet technology with a combination of hard and soft materials in replicates of three. The models were evaluated quantitatively for dimensional accuracy and radiodensity and qualitatively using digital microscopy and endoscopy for technical, tactic, and visual realism. The results displayed that simulation models printed with polyjet technology have an overall surface representation of 93% for μCT-based images and 97% for CBCT-based images within a range of 0.0-2.5 mm, with μCT showing a more detailed reproduction of the nasotracheal anatomy. Dimensional discrepancies can be caused due to inadequate support material removal and due to the limited reconstruction of microstructures from the imaging on the 3D printed model. The model showed a significant difference in radiodensities in hard and soft tissue regions. Endoscopic evaluation provided good visual and tactile feedback, comparable to the real animal. Overall, the model, being a practical low-cost simulator, comprehensively accelerates the learning curve of veterinary nasotracheal intubation and paves the way for 3D simulation-based image-guided interventional procedures.

Comparison of blind intubation and a smartphone-based endoscope-assisted intubation in rabbits

OBJECTIVE

To compare between blind and smartphone-based endoscope-assisted techniques for endotracheal intubation in rabbits.

STUDY DESIGN

Prospective clinical study.

ANIMALS

A total of 34 rabbits.

METHODS

Rabbits were assigned to four groups: intubation by a veterinary anesthesiologist (VA) or an exotic pet medicine specialist (EPS) using blind or endoscope-assisted techniques. Propofol dose, number of attempts until successful intubation, total time for intubation, duration of the successful attempt and occurrence of lingual cyanosis/laryngeal lesions were recorded. Data were analyzed by t test, Wilcoxon-Mann-Whitney U test or chi-square test. Pearson correlation for body weight was performed.

RESULTS

The success rate of blind intubation was 88.9% and 77.8% for VA and EPS, respectively. Propofol dose, total and median number of attempts, total time for intubation and duration of the successful attempt were 3.1 (0-6.2) mg kg^-1, 19, 2 (1-5), 79 ± 65 and 30 ± 20 seconds for VA and 1.5 (0-4.5) mg kg^-1, 24, 3 (1-5), 136 ± 92 and 38 ± 16 seconds for EPS. The success rate of endoscope-assisted intubation was 87.5% for both operators. Propofol dose, total and median number of attempts, total time for intubation and duration of the successful attempt were 2.5 (1.3-7.4) mg kg^-1, 22, 3 (1-5), 170 (65-368) and 46 (22-150) seconds for VA and 3.2 (0-6) mg kg^-1, 11, 1 (1-4), 56 (27-432) and 55 (26-79) seconds for EPS. VA performed blind intubation more quickly, propofol dose was lower and cyanosis was less frequent than in the endoscope-assisted group.

CONCLUSIONS AND CLINICAL RELEVANCE

Both techniques were reliable for rabbit endotracheal intubation. Best results were achieved when the operator was experienced in the technique. The smartphone-based endoscope is a useful aid for rabbit intubation.

Comparison of endoscopic endotracheal intubation and the v-gel supraglottic airway device for spontaneously ventilating New Zealand white rabbits undergoing ovariohysterectomy

BACKGROUND

Due to the technical difficulties with endotracheal intubation of rabbits, a prospective, randomised, controlled study was performed to compare a rabbit-specific supraglottic airway device (SGAD), the v-gel, with endoscopic endotracheal intubation (EEI) in spontaneously breathing rabbits undergoing ovariohysterectomy.

METHODS

Fourteen adult female New Zealand white rabbits were randomly allocated to one of two groups based on the method of airway establishment: EEI or v-gel SGAD. Anaesthesia was induced with ketamine and xylazine and maintained using isoflurane in 100 per cent oxygen. Comparisons were made between groups based on placement time of endotracheal tube/SGAD, number of attempts and adjustments, the necessity to increase isoflurane concentrations to maintain a surgical plane of anaesthesia, arterial blood gas values, gross laryngeal evaluation, and laryngotracheal histopathology.

RESULTS

Both techniques resulted in elevated arterial pCO₂ levels, but the v-gel was associated with more elevated pCO₂ in comparison with EEI (P=0.045). Airway trauma was histologically present but clinically negligible in both groups, with no statistically significant differences observed between techniques (P>0.05). Placement time of the v-gel was significantly faster (P=0.003) and required less technical skill than EEI, but was more easily displaced when changing the animal's position (P=0.004).

CONCLUSION

The v-gel is a practical alternative to EEI for securing the airway of healthy spontaneously ventilating rabbits, provided a capnograph is utilised to ensure continuous placement. Both airway techniques appear safe and effective with few complications, as long as intermittent positive pressure ventilation can be employed to correct hypercapnia.

Hypoventilation following oxygen administration associated with alfaxalone-dexmedetomidine-midazolam anesthesia in New Zealand White rabbits

OBJECTIVE

To investigate the relationship between oxygen administration and ventilation in rabbits administered intramuscular alfaxalone-dexmedetomidine-midazolam.

STUDY DESIGN

Prospective, randomized, blinded study.

ANIMALS

A total of 25 New Zealand White rabbits, weighing 3.1-5.9 kg and aged 1 year.

METHODS

Rabbits were anesthetized with intramuscular alfaxalone (4 mg kg^-1), dexmedetomidine (0.1 mg kg^-1) and midazolam (0.2 mg kg^-1) and randomized to wait 5 (n = 8) or 10 (n = 8) minutes between drug injection and oxygen (100%) administration (facemask, 1 L minute^-1). A control group (n = 9) was administered medical air 10 minutes after drug injection. Immediately before (PRE_oxy/air5/10) and 2 minutes after oxygen or medical air (POST_oxy/air5/10), respiratory rate (f_R), pH, PaCO₂, PaO₂, bicarbonate and base excess were recorded by an investigator blinded to treatment allocation. Data [median (range)] were analyzed with Wilcoxon, Mann-Whitney U and Kruskal-Wallis tests and p < 0.05 considered significant.

RESULTS

Hypoxemia (PaO₂ < 88 mmHg, 11.7 kPa) was observed at all PRE times: PRE_oxy5 [71 (61-81) mmHg, 9.5 (8.1-10.8) kPa], PRE_oxy10 [58 (36-80) mmHg, 7.7 (4.8-10.7) kPa] and PRE_air10 [48 (32-64) mmHg, 6.4 (4.3-8.5) kPa]. Hypoxemia persisted when breathing air: POST_air10 [49 (33-66) mmHg, 6.5 (4.4-8.8) kPa]. Oxygen administration corrected hypoxemia but was associated with decreased f_R (>70%; p = 0.016, both groups) and hypercapnia (p = 0.016, both groups). Two rabbits (one per oxygen treatment group) were apneic (no thoracic movements for 2.0-2.5 minutes) following oxygen administration. f_R was unchanged when breathing air (p = 0.5). PaCO₂ was higher when breathing oxygen than air (p < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

Early oxygen administration resolved anesthesia-induced hypoxemia; however, f_R decreased and PaCO₂ increased indicating that hypoxemic respiratory drive is an important contributor to ventilation using the studied drug combination.

Anaesthetic and Perioperative Management of 14 Male New Zealand White Rabbits for Calvarial Bone Surgery

Simple Summary

Bone substitutes are commonly used when bone grafts are necessary in human craniofacial surgery. To study the properties and biologic behaviour of those substitutes, they can be implanted in experimental animals. A frequently used model involves the creation of critical-sized defects (defects that are too large to heal by themselves) in the rabbits calvaria (the top part of the skull). The procedure was initially described in 1989 and the authors considered and reported that post-operative analgesia was not necessary. In our experience, this procedure is invasive and can result in severe postoperative pain. The anaesthetic management of rabbits undergoing this procedure is challenging. Most of the recent publications using this model fail to provide sufficient information on perioperative animal management. With this report we have aimed to document a possible practical and simple anaesthetic and postoperative management of rabbits undergoing this procedure. Particular emphasis has been placed on postoperative pain assessment, duration and treatment.

Abstract

Calvarial bone surgery on rabbits is frequently performed. This report aims to document a simple and practical anaesthetic and perioperative management for this procedure. Fourteen male New Zealand white rabbits were included in the study. Subcutaneous (SC) dexmedetomidine, ketamine and buprenorphine ± isoflurane vaporized in oxygen administered through a supraglottic airway device (V-gel^®) provided clinically suitable anaesthesia. Supplemental oxygen was administered throughout recovery. Monitoring was clinical and instrumental (pulse-oximetry, capnography, invasive blood pressure, temperature, arterial blood gas analysis). Lidocaine was infiltrated at the surgical site and meloxicam was injected subcutaneously as perioperative analgesia. After surgery, pain was assessed five times daily (composite behavioural pain scale and grimace scale). Postoperative analgesia included SC meloxicam once daily for four days and buprenorphine every 8 h for three days (unless both pain scores were at the lowest possible levels). Rescue analgesia (buprenorphine) was administered in case of the score > 3/8 in the composite pain scale, >4/10 on the grimace scale or if determined necessary by the caregivers. Airway management with a V-gel^® was possible but resulted in respiratory obstruction during the surgery in two cases. Hypoventilation was observed in all rabbits. All rabbits experienced pain after the procedure. Monitoring, pain assessments and administration of postoperative analgesia were recommended for 48 h.

Assessing the Efficacy of Ventilation of Anesthetized Neonatal Calves Using a Laryngeal Mask Airway or Mask Resuscitator

Calves that have undergone a dystocia are often hypoxic and acidemic, which can result in reduced vigor and subsequent mortality. Methods of field resuscitation of apneic newborn calves are often ineffective and therefore underutilized. This proof-of-concept study aimed to determine the efficacy of the laryngeal mask airway (LMA) as well as the current industry standard method of ventilation, the McCulloch Calf Aspirator/ Resuscitator (MMR) for positive pressure ventilation of neonatal calves. Five LMA models of various sizes were first tested in cadaver heads to assess anatomical fit. Three LMA models in two sizes each were then tested in two anesthetized calves to determine the model best suited to ventilate calves. Next, the selected LMA and the MMR were both assessed for efficacy of ventilation. Six anesthetized calves had hypoventilation induced by administering alfaxalone intravenously. Calves were ventilated for 3 min with the LMA, allowed a brief washout period, then given a second administration of alfaxalone prior to ventilation with the MMR. Serial arterial blood gas analyses were performed prior to ventilation (baseline), at 1, 2, and 3 min during ventilation, and 1 min after ventilation had ceased. Success of ventilation was assessed by monitoring partial pressure of oxygen (PaO₂), partial pressure of carbon dioxide (PaCO₂), bicarbonate (HCO3-), pH, L-lactate, and hemoglobin saturation (SaO₂) in arterial blood. A one-way ANOVA for repeated measures with Bonferroni correction was used to assess the efficacy of ventilation of each device compared to baseline. For the LMA, PaO₂, SaO₂, and pH were significantly higher than baseline throughout ventilation and PaCO₂ was significantly lower than baseline at 1 min of ventilation. For the MMR, PaO₂ and SaO₂ were significantly higher and PaCO₂ and HCO3- were significantly lower than baseline for 1 to 2 min of ventilation. This proof-of-concept study showed the LMA is an effective means of ventilating neonatal calves, as was the MMR.

Altai pika (Ochotona alpina) alarm calls: individual acoustic variation and the phenomenon of call-synchronous ear folding behavior

Non-hibernating pikas collect winter food reserves and store them in hay piles. Individualization of alarm calls might allow discrimination between colony members and conspecifics trying to steal food items from a colony pile. We investigated vocal posture, vocal tract length, and individual acoustic variation of alarm calls, emitted by wild-living Altai pikas Ochotona alpina toward a researcher. Recording started when a pika started calling and lasted as long as possible. The alarm call series of 442 individual callers from different colonies consisted of discrete short (0.073-0.157 s), high-frequency (7.31-15.46 kHz), and frequency-modulated calls separated by irregular intervals. Analysis of 442 discrete calls, the second of each series, revealed that 44.34% calls lacked nonlinear phenomena, in 7.02% nonlinear phenomena covered less than half of call duration, and in 48.64% nonlinear phenomena covered more than half of call duration. Peak frequencies varied among individuals but always fitted one of three maxima corresponding to the vocal tract resonance frequencies (formants) calculated for an estimated 45-mm oral vocal tract. Discriminant analysis using variables of 8 calls per series of 36 different callers, each from a different colony, correctly assigned over 90% of the calls to individuals. Consequently, Altai pika alarm calls are individualistic and nonlinear phenomena might further increase this acoustic individualization. Additionally, video analysis revealed a call-synchronous, very fast (0.13-0.23 s) folding, depression, and subsequent re-expansion of the pinna confirming an earlier report of this behavior that apparently contributes to protecting the hearing apparatus from damage by the self-generated high-intensity alarm calls.