Experimental evaluation of four airway devices in anaesthetized New Zealand White rabbits

Cadaveric Study on Comparison of Neck Extension Angles for Endotracheal Intubation in Rabbits Using a Rigid and Flexible Endoscope

Endotracheal intubation in rabbits is always challenging due to the unique anatomical conformation. To improve endotracheal intubation success, this study determined the relationship between head placement angles guided by endoscope-assisted visualization techniques and the endotracheal intubation success rate. Thirty-two rabbit cadavers were used in the study. Six veterinary practitioners who had no experience with rabbit endotracheal intubation were randomly assigned to intubate rabbit cadavers using the guidance of either a rigid endoscope (RE) or flexible endoscope (FE), with the head placement angles with an ascending neck at 90, 100, 110, 120 and 130 degrees. The endotracheal intubation completed in 90 s was determined to be a success. The success rates using RE and FE were 97.2% and 95.9%, respectively. The means and standard error of means (SEM) of endotracheal intubation times guided by RE and FE were 53.7 ± 4.68 and 55.2 ± 4.24 s, respectively. Results from survival time analysis show that the five veterinarians successfully intubated the rabbit within 90 s, regardless of the different types of endoscopes. Angle was the only significant factor that affected the endotracheal intubation success. The head placement angle at 110 and 120 degrees had the highest success rate of endotracheal intubation compared to 90 degrees (p ≤ 0.05). In conclusion, for inexperienced veterinarians, the success of endotracheal intubation in rabbits, guided by endoscope-assisted visualized techniques regardless of rigid endoscope or flexible endoscope guidance, is improved when the head extension is 110 and 120 degrees.

Development and evaluation of an anatomically designed and 3D printed device to enhance orotracheal intubation success in rabbits by inexperienced veterinarians

OBJECTIVE

To assess whether the use of a three-dimensional (3D) printed device enhances the success rate of orotracheal intubation in rabbits.

STUDY DESIGN

Prospective, crossover randomized controlled trial.

ANIMALS

A total of six mixed-breed rabbits.

METHODS

A device to guide the endotracheal tube was designed based on computed tomography images and then manufactured using 3D printing. Rabbits were randomly assigned for intubation by two inexperienced veterinarians using the blind (BLI), borescope- (BOR) or device- (DEV) guided techniques. Success rate, number of attempts, time to success, injury scores and propofol dose were recorded and compared. Significance was considered when p < 0.05.

RESULTS

Success rate was higher in DEV (58.3%) than in BLI (8.3%) (p < 0.023), but not different from that in BOR (41.6%). Total time until successful intubation was lower in DEV (45 ± 23 seconds) and BOR (85 ± 62 seconds) than in BLI (290 seconds; p < 0.006). Time for the successful attempt was lower for DEV (35 ± 10 seconds) and BOR (74 ± 43 seconds) than in BLI (290 seconds; p < 0.0001). The propofol dose required was lower for DEV (2.3 ± 1.2 mg kg-1) than for BLI (3.4 ± 1.6 mg kg-1) (p < 0.031), but not different from BOR (2.4 ± 0.9 mg kg-1). Number of attempts and oxygen desaturation events were not different among techniques (p < 0.051 and p < 0.326, respectively). Injury scores [median (range)] before and after attempts were different in BLI [0 versus 1 (0-3), p < 0.005] and BOR [0 (0-1) versus 1 (0-3), p < 0.002] but not in DEV [0 (0-2) versus 0 (0-3), p < 0.109].

CONCLUSIONS AND CLINICAL RELEVANCE

The device facilitated orotracheal intubation with a time similar to the borescope-guided technique but faster than the traditional blind technique.

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.

Endotracheal intubation in rabbits using a video laryngoscope with a modified blade

Rabbits are being increasingly used as companion animals, and in research; thus, the need for proper veterinary care for rabbits has increased. Surgical access is more challenging in rabbits under inhalation anesthesia compared to other animals, such as dogs and cats. Rabbits have a very narrow and deep oral cavity, large incisors, and a large tongue. Moreover, their temporomandibular joint has limited mobility, making it more difficult to approach the larynx. Various methods have been proposed to overcome this difficulty. The video laryngoscope was introduced in 1999 and is useful when airway intubation is unsuccessful using a conventional laryngoscope. We postulated that a video laryngoscope with a modified size 1 Macintosh blade (McGrath MAC Video Laryngoscope, Medtronic, USA) would facilitate the intubation of New Zealand White rabbits. Sixteen specific-pathogen-free male New Zealand White rabbits weighing 3.45–4.70 kg were studied. All rabbits were intubated using the video laryngoscope. Typically, a 3.0 mm endotracheal tube was used for rabbits weighing < 4 kg, while a 3.5 mm tube was used in those weighing > 4 kg. During surgery, anesthesia was well maintained, and there were no major abnormalities in the animals’ conditions. No rabbit developed breathing difficulties or anorexia after recovering from anesthesia. We established an intubation method using a video laryngoscope with a modified blade and stylet in the supine (ventrodorsal) position and successfully applied it in 16 rabbits. It is useful for training novices and for treating rabbits in veterinary hospitals with few staff members and animal research facilities where there are insufficient human resources.

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.

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.

The Use of Animal Models to Assess Engineered Corneal Tissue

Tissue-engineered corneal constructs offer the potential of readily available corneal substitutes for transplantation. As with all medical devices and implants, these constructs require rigorous safety assessments, combined with well-described analyses of the implant's physical and biological characteristics. Although the constructs are developed in vitro, such studies are currently unable to fully emulate the complex biomechanical and biochemical conditions within living tissue, as well as the interplay between this environment and immunological factors. For these reasons, animal models remain essential to characterize such interactions. They form a stage where corneal implants can be tested for utility and survival in a living location to assess their ability to provide vision and avoid adverse event. Here, we examine the surgical considerations of animal models and we describe how the rabbit can be used for this purpose. This animal has been the routine model for ophthalmological studies and we set out methods to implant corneal constructs with this species.

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.

Technological Advances in Exotic Pet Anesthesia and Analgesia

Even when performed by skilled operators, locating the nerves can be challenging in small exotic pets; in such cases, the use of an electrical nerve stimulator may be useful to confirm the correct identification of the target nerve. Exotic animal anesthesia and analgesia have dramatically progressed over the past decade and continue to do so as more research and technologies develop. Technological advancements such as airway devices, endoscopic intubation techniques, positive intermittent pressure ventilators, and invasive and noninvasive blood pressure monitors have played a significant role in improving patient safety and the anesthetic outcomes of exotic animals.

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.