Evaluation of a novel, low-cost, 3D printed video laryngoscope with borescope in anesthetized Beagle dogs

OBJECTIVE

To develop and evaluate a low-cost three-dimensional (3D)-printed video laryngoscope (VLVET) for use with a commercial borescope.

STUDY DESIGN

Instrument development and pilot study.

ANIMALS

A total of six adult male Beagle dogs.

METHODS

The VLVET consisted of a laryngoscope handle and a Miller-type blade, and a detachable camera holder that attached to various locations along the blade. The laryngoscope and camera holder were 3D-printed using black polylactic acid filament. Dogs were premedicated with intravenous (IV) medetomidine (15 μg kg-1) and anesthesia induced with IV alfaxalone (1.5 mg kg-1). The VLVET, combined with a borescope, was used for laryngeal visualization and intubation. Performance was evaluated by comparing direct and video-assisted views in sternal recumbency. The borescope camera was sequentially positioned at 2, 4, 6, 8 and 10 cm from the blade tip (distanceLARYNX-CAM), which was placed on the epiglottis during intubation or laryngoscopy. At the 10 cm distanceLARYNX-CAM, laryngeal visualization was sequentially scored at inter-incisor gaps of 10, 8, 6, 4 and 2 cm. Laryngeal visualization scores (0-3 range, with 0 = obstructed and 3 = unobstructed views) were statistically analyzed using the Friedman's test.

RESULTS

Under direct visualization, the 2 cm distanceLARYNX-CAM had a significantly lower score compared with all other distanceLARYNX-CAM (all p = 0.014) because the view was obstructed by the camera holder and borescope camera. With both direct and camera-assisted views, visualization scores were higher at inter-incisor gaps ≥ 4 cm compared with 2 cm (all p < 0.05).

CONCLUSIONS AND CLINICAL RELEVANCE

During laryngoscopy and intubation, the VLVET and borescope facilitated both direct and video laryngoscopy at distanceLARYNX-CAM in Beagle dogs when inter-incisor gaps were ≥ 4 cm.

Endotracheal tube cuff rupture during anesthesia in 2 dogs

A 15-year-old intact male dachshund dog weighing 4.3 kg and a 5-year-old intact male mixed-breed dog weighing 13.6 kg were referred for examination because of paraparesis and facial paralysis, respectively. Magnetic resonance imaging (MRI) of the thoracolumbar region and brain was performed. The dogs were premedicated with IV butorphanol, 0.2 mg/kg body weight (BW) and midazolam, 0.2 mg/kg BW. Anesthesia was induced with IV propofol, 4 to 5 mg/kg BW and maintained with sevoflurane in oxygen. The dachshund was orotracheally intubated with a 5.0-millimeter internal diameter endotracheal (ET) tube. During positioning in the MRI room, intermittent positive pressure ventilation (IPPV) was applied. The mixed-breed dog was orotracheally intubated with a 6.0-millimeter internal diameter ET tube. After inflation of the ET tube cuff, a leaking test was done by applying positive pressure ventilation. In both dogs, a distinct "popping" sound was heard when positive pressure was applied, after which air leakage from the cuff was evident. Failure to inflate the pilot balloon led to suspicion of a ruptured cuff. Reintubation was completed, both dogs remained stable during anesthesia, and no postanesthetic complications were observed. Rupture of both cuffs, which was visually confirmed, was thought to be caused by overinflation of the cuff, repeated sterilization of the ET tubes, and positive pressure ventilation. Repeated sterilization of ET tubes with ethylene oxide can alter the physical integrity of cuffs. Care should be taken not to overinflate ET tube cuffs, especially when they have been repeatedly sterilized, as cuff rupture may result in failure to provide adequate IPPV. Key clinical message: This report describes 2 cases in which ET tube cuff rupture was noted during anesthesia for MRI.

Radiographic and computed tomographic evaluation of tracheal diameter and length in kittens

OBJECTIVE

To measure the tracheal diameter and length in kittens using radiography and CT and to evaluate the concordance between measurements obtained with these 2 modalities.

ANIMALS

15 kittens with an estimated age of 12 weeks and mean body weight of 1.49 kg.

METHODS

Radiographic and CT images were retrospectively evaluated to measure tracheal lengths and diameters. Tracheal diameters were measured at 5 different sites (A [at the level of the C2-3 intervertebral disk space], B [at the level of the C4-5 intervertebral disk space], C [at the cranial end of the manubrium sterni], D [at the level of the second rib], and E [1 cm cranial to the carina]) along the trachea. The cross-sectional area and transverse and vertical diameter ratios were calculated for each measurement site.

RESULTS

The cross-sectional area was largest at site A and decreased from site C to site E. Based on the vertical diameter ratio, the tracheal shape was most circular at sites A and E, whereas from sites B to D, it was elliptical. The vertical diameters of the trachea on radiography and CT did not differ statistically significantly. However, the tracheal length measured on radiography was approximately 6 mm longer than that measured on CT (P < .05).

CLINICAL RELEVANCE

Using the first rib as an anatomical reference, the placement of a cuffed endotracheal tube is recommended in kittens. In emergency situations, regression equations based on body weight may be helpful in predicting tracheal diameters.

Evaluation of a rapid sequence induction technique in dogs with or without rocuronium

OBJECTIVE

To determine, using a rapid sequence induction (RSI) technique, whether rocuronium improves the quality and speed of endotracheal intubation in healthy dogs.

STUDY DESIGN

Randomized, crossover, experimental study.

ANIMALS

Six adult intact male Beagles (12.3 ± 0.4 kg).

METHODS

Dogs were premedicated with intravenous acepromazine (0.03 mg kg-1) and hydromorphone (0.1 mg kg-1). Ten minutes later, anesthesia was induced with intravenous propofol (2 mg kg-1 over 5 seconds), followed by saline (0.06 mL kg-1, CT group) or rocuronium (0.6 mg kg-1, RT group), with orotracheal intubation attempted after 45 seconds. Intubation time (IT) and conditions (IC) were assessed. PaO2, PaCO2, arterial blood pH and serum cortisol were obtained before and after RSI. After endotracheal intubation, saline (0.04 mL kg-1) or sugammadex (4 mg kg-1) were administered intravenously in CT or RT groups, respectively. Spontaneous ventilation restoration was noted.

RESULTS

The IT was 54.3 ± 6.9 (mean ± SD) and 57.8 ± 5.2 seconds for CT and RT, respectively (p = 0.385). All laryngoscopies indicated good IC in both treatment groups. Heart rate was lower in CT group than in RT group (66 ± 16 versus 103 ± 39 beats minute-1, p = 0.016). PaCO2, pH, PaO2 and cortisol did not differ between treatments. Compared with baseline, PaCO2 increased from 47.7 ± 6.2 to 58.8 ± 5.8 (p < 0.001) and pH decreased from 7.35 ± 0.04 to 7.28 ± 0.04 (p = 0.003), independent of treatment. Dogs in both treatment groups returned to spontaneous ventilation within 30 seconds of RSI.

CONCLUSIONS AND CLINICAL RELEVANCE

RSI resulted in respiratory acidosis without hypoxemia or increased cortisol. Rocuronium did not improve IT or IC. Spontaneous ventilation was observed immediately after administering saline or sugammadex. The co-administration of rocuronium showed no clinical benefits over propofol alone in RSI in healthy dogs.

A pilot study of skin stretching and blood circulation effects of dermal suctioning in dogs

Dermal suctioning has been reported to yield effects similar to those of cupping therapy in humans and horses, including pain reduction, increased blood circulation, improved flexibility, and healing. However, there is a dearth of reported outcomes concerning cupping or dermal suctioning in dogs. In this study, we examined the physiological effects of dermal suctioning in dogs. Employing the Medicell MINI pro8 device, dermal suctioning was applied to the dorsal surfaces of eight healthy beagle dogs for 20 min. Metrics such as body surface temperature, rectal temperature, pulse rate, respiratory rate, and skin pinch test results were gauged. Seven healthy beagle dogs were used as controls, and the same measurements were performed without dermal suctioning. The results showed a significant increase in the body surface temperature and skin pinch test results after dermal suctioning. We believe that the elimination of torsion in the blood vessels and nerves in the shallow fascia positively affected the thermoregulatory mechanism, resulting in an increase in body surface temperature, and also improving skin flexibility. Thus, dermal suctioning promotes subcutaneous blood circulation and improves skin flexibility in dogs. Further research is needed to identify the mechanisms underlying the effects of dermal suctioning and evaluate the stress in dogs caused by the implementation of the process.

Retrospective computed tomography analysis of endotracheal tube constriction and mispositioning in cats and dogs

OBJECTIVE

To discover the prevalence of endotracheal tube (ETT) constriction and rostral and caudal mispositioning in anaesthetized cats and dogs, and to identify associated risk factors.

STUDY DESIGN

Retrospective analysis.

ANIMALS

A total of 146 cats and 670 dogs.

METHODS

Computed tomography images of the head/neck/thorax from orotracheally intubated cats and dogs were visually assessed for constriction or mispositioning of the ETT. If constriction was present, measurements of the cross-sectional area (CSA) of the ETT lumen at constricted and un-constricted locations were compared. Location and cause of constriction were noted and the expected increase in resistance to gas flow was calculated. Animal information was collected from clinical records. Normality of continuous variables was assessed via the Shapiro-Wilk test. Chi-square tests examined associations between variables. Kendall's tau-b test was performed between measured ETT size and degree of constriction.

RESULTS

The ETT extended rostrally beyond incisors in 52% of cases; the connector was within the oral cavity in 19% of cases. The ETT extended beyond the first rib in 25.5% of cases. The prevalence of ETT constriction was 22.7%. Median reduction in CSA was 7.68% (0.14-64.19%). Median increase in resistance assuming laminar and turbulent flow was 16.5% (0.3-680%) and 21% (0.3-1200%), respectively. The most common cause of constriction was the presence of a radiotherapy mouth gag. Significant associations existed between presence of constriction and rostral mispositioning, and caudal mispositioning and extreme brachycephaly. Increased severity of constriction was more likely in smaller ETT.

CONCLUSIONS AND CLINICAL RELEVANCE

Constriction and mispositioning of ETT occurred very commonly in this population. Checking the ETT within the oral cavity for constriction and mispositioning is recommended. Radiotherapy mouth gags increase the risk of ETT compression. Smaller ETT are at greater risk of severe constriction. Brachycephalic dogs are at particular risk of caudal mispositioning.

DIAGNOSTIC IMAGING AND OROTRACHEAL INTUBATION IN CLINICALLY HEALTHY WILD SUNDA PANGOLINS (MANIS JAVANICA) IN SINGAPORE

Pangolins are amongst the most overexploited species in the world and all eight species of pangolins are threatened with extinction. These animals are rare in zoological collections and often suffer high mortality rates in captivity. Maintaining healthy populations in captivity has become more important with the declining populations in the wild, but knowledge of veterinary care of these animals is limited. Interpreting radiography and ultrasonography images in a patient can be challenging without knowledge of normal findings. The Wildlife Healthcare and Research Center (WHRC) at Mandai Wildlife Reserve (MWR) admits an average of 25 Sunda pangolins (Manis javanica) annually, which is a Critically Endangered species native to Singapore. All the pangolins are triaged on admission and anesthetized for a health assessment before release into the wild. Endotracheal intubation using an otoscope and stylet is a novel technique in the species that has been developed and is commonly performed with these pangolins. A retrospective study was done on 20 clinically healthy wild pangolins to determine normal ultrasonography and radiography findings in the species. Notable findings include the presence of radio-opaque particles in the stomachs of all pangolins, the presence of free fluid cranial to the left kidney (13/20), a spleen with multifocal hypoechoic regions (6/20), and open epiphyseal plates of long bones even in large individuals weighing as heavy as 6.8 kg. Ultrasonographic images and measurements of kidney, spleen, and adrenal gland sizes as well as intestinal, gallbladder, and urinary bladder wall thickness were also described. These diagnostic imaging findings can advance the veterinary care of captive and wild pangolins.

[Inhalation anesthesia in the cat: Development of cuff pressure when using nitrous oxide]

OBJECTIVE

During inhalation anesthesia with nitrous oxide in oxygen the pressure in the cuff of the endotracheal tube may increase due to diffusion of nitrous oxide into the cuff. The aim of the study was to investigate the development of cuff pressure during nitrous oxide anesthesia under clinical conditions in feline patients and to identify possible influencing factors such as tube size and gas flow rate.

MATERIAL AND METHODS

The prospective study included cats scheduled for inhalation anesthesia with nitrous oxide for a minimum duration of 60 minutes at the Department for Small Animals of the University of Leipzig. Cuff pressure was adjusted with a cuff manometer and its development was recorded.

RESULTS

In total, the cuff pressure values of 24 cats were recorded. Animals were allocated into groups by tube size (ID 4.0 mm and ID 4.5 mm) and by fresh gas flow rate: low flow rate (0.6 l/min) and high flow rate (3 l/min). During anesthesia, cuff pressure increased over time, with statistical significance occurring from 45 minutes onwards in comparison to the initial cuff pressure (p=0.005). After 60 minutes, there was a mean cuff pressure increase of 3 cmH2O. Despite this moderate mean increase, highly variable pressure values up to 48 cmH2O in individual animals were recorded. No cat reached the termination criterion of 60 cmH2O cuff pressure. Effects of tube size (p=0.63) and flow rate (p=0.334) on the cuff pressure were not evident.

CONCLUSION

After a period of 45 minutes of nitrous oxide administration, a significant increase in cuff pressure occurs in the cat. However, tube size and total gas flow rate do not seem to influence the cuff pressure development.

CLINICAL RELEVANCE

When using nitrous oxide during inhalation anesthesia, regular cuff pressure evaluation and correction are necessary and hence recommended in feline patients. As individual pressure changes may be highly variable, no fixed recommendations for optimal management are possible.

A case of epiglottic entrapment in a cat

OBJECTIVE

The objective of this study was to describe a case of epiglottic entrapment in a cat.

CASE SUMMARY

A 5-month-old male neutered Russian Blue cat was evaluated for progressive stertorous upper airway sounds, acute onset vestibulopathy and abnormal laryngeal anatomy. Endotracheal intubation was only able to be achieved using videoscopic guidance and identified concern for severe nasopharyngeal stenosis. A computerized tomography scan revealed otitis interna, narrowed nasopharynx and no definitive cause for the stertorous breathing. The cat recovered very slowly from anaesthesia due to concern for airway obstruction following extubation. It was discharged the following day and then passed away at home 2 weeks later. Necropsy revealed that the epiglottis was obscured by 2 cm of redundant mucosal tissue extending from the base of the tongue to the larynx resulting in epiglottic entrapment. Also noted was chronic, severe otitis interna and externa. Upper airway obstruction is suspected to be the cause of sudden death.

NEW OR UNIQUE INFORMATION

To the authors' knowledge, this is the first report of these oropharyngeal anatomic abnormalities in a cat.

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.

Implementation of a Low-Cost 3D-Printed Feline Larynx Model for Veterinary Students

Endotracheal intubation (EI) in domestic cats is an important skill that veterinary students learn in order to perform anesthesia safely in this species. Implementing a 3D-printed larynx model (LaryngoCUBE) during the instruction process may improve student's learning of EI in felines. Twenty-two third-year students performed EI in cats with standard training (ST), and 16 students trained with the model (MT) the day before the laboratory. It was evaluated whether training with the model decreases the time and number of EI attempts, students' perceived difficulty performing EI using a visual analog score (VAS; 0 cm = very easy, 10 cm = extremely difficult; median [minimum-maximum]), and the incidence of failure to perform EI. The EI time on ST (58 [18-160] seconds) was longer, but not statistically different from MT (29 [13-120] seconds; p = .101). The number of EI attempts on ST (2 [1-3]) was higher than MT (1 [1-3]; p = .005). The VAS on the ST and MT were 4.5 (0.0-10.0) cm and 3.0 (0.2-10.0) cm, respectively (p = .029). The failure rate was 27% on the ST and 25% on the MT (p = 1.000). Students who practiced with a larynx model took fewer attempts to perform EI, tended to be faster, and found that EI was easier. However, the EI success rate in MT was not improved.

Endotracheal Intubation Using a Flexible Intubation Endoscope As a Standardized Model for Safe Airway Management in Swine

Endotracheal intubation is often a basic requirement for translational research in porcine models for various interventions that require a secured airway or high ventilation pressures. Endotracheal intubation is a challenging skill, requiring a minimum number of successful endotracheal intubations to achieve a high success rate under optimal conditions, which is often unachievable for non-anaesthesiology researchers. Due to the specific porcine airway anatomy, a difficult airway can usually be assumed. The impossibility of establishing a secure airway can result in injury, adverse events, or death of the laboratory animal. Using a prospective, randomized, controlled evaluation approach, it has been shown that fiberoptic-assisted endotracheal intubation takes longer but has a higher first-pass success rate than conventional intubation without causing clinically relevant drops in oxygen saturation. This model presents a standardized regimen for endoscopically guided endotracheal intubation, providing a secured airway, especially for researchers who are inexperienced in the technique of endotracheal intubation via direct laryngoscopy. This procedure is expected to minimize animal suffering and unnecessary animal losses.

Optimising endotracheal length in adult cats: a retrospective CT study

OBJECTIVES

The aim of this study was to determine the maximal endotracheal insertion length by measuring the larynx to carina (L-C) distance by means of CT. An additional objective was to establish certain anatomical landmarks to optimise the process of endotracheal intubation (ETI).

METHODS

Head, neck and thoracic CT images from adult cats at a single referral hospital between 2013 and 2020 were retrospectively evaluated. After standardising and identifying key markers (larynx, carina and first rib) the L-C, larynx to first rib (L-1R) and first rib to carina (1R-C) distances were measured.

RESULTS

Forty-five adult cats were enrolled in the study, from which a total of nine different breeds were identified. The L-C distance was 14.3 ± 1.1 cm. This was longer in male (14.7 ± 1.1 cm) than in female cats (13.5 ± 0.7 cm). The first rib (1R) was 8.8 ± 0.7 cm from the larynx and the mean 1R-C distance was 5.4 ± 0.7 cm. The carina was found within the fifth intercostal space in 93.3% (n = 42) of the cats.

CONCLUSIONS AND RELEVANCE

The process of ETI in adult cats may be guided by using the L-C and L-1R distance for a maximal and optimal endotracheal tube introduction, respectively. In addition, the maximal insertion length may be guided by estimating the position of the carina parallel to the fifth intercostal space.

Tracheal stenosis following endotracheal intubation in a dog

A 2-month-old intact female Rottweiler was presented for investigation of coughing and respiratory distress 9 d after an exploratory laparotomy for intestinal foreign body removal. Tracheal stenosis was suspected by radiography and confirmed with computed tomography (CT) and tracheoscopy. After 1 wk of medical management, clinical signs had resolved and the severity of the tracheal narrowing was markedly improved, as confirmed by radiography and tracheoscopy. Tracheal stenosis is a considerable complication of endotracheal intubation in veterinary medicine and may be medically managed, depending on the severity of the tracheal injury. Key clinical message: To our knowledge, this is the first clinical case report of tracheal stenosis resulting from endotracheal intubation in a dog and its resolution after medical management.

Assessment of intramuscular administration of three doses of alfaxalone combined with hydromorphone and dexmedetomidine for endoscopic-guided orotracheal intubation in domestic rabbits (Oryctolagus cuniculus)

OBJECTIVE

To determine the dose of alfaxalone for IM administration combined with dexmedetomidine and hydromorphone that would allow endoscopic-guided orotracheal intubation in rabbits without causing a decrease in respiratory rate or apnea.

ANIMALS

15 sexually intact (9 females and 6 males) healthy Miniature Lop rabbits weighing a mean ± SD of 2.3 ± 0.3 kg and ranging in age from 4 to 9 months.

PROCEDURES

In a randomized, controlled clinical trial, rabbits received 0.1 mg of hydro-morphone/kg and 0.005 mg of dexmedetomidine/kg, plus alfaxalone at either 2 mg/kg (5 rabbits), 5 mg/kg (5 rabbits), or 7 mg/kg (5 rabbits). Drugs were mixed in a single syringe and administered IM. Semiquantitative rating scales were used to evaluate quality of anesthesia and intubation. Orotracheal intubation was attempted with endoscopy and confirmed by capnography.

RESULTS

The number of successful intubations was 0, 3, and 4 in rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. Median (range) anesthesia quality scores (scale, 0 to 12; 12 = deepest anesthesia) were 3 (2 to 5), 6 (5 to 6), and 6 (4 to 9) for rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. The median (range) intubation quality scores (scale, 0 to 3 [ie, intubation not possible to easiest intubation]) were 0 (0 to 0), 2 (0 to 3), and 2 (0 to 3) for rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. None of the rabbits experienced a decrease in respiratory rate or apnea.

CONCLUSIONS AND CLINICAL RELEVANCE

Increasing doses of alfaxalone combined with hydromorphone and dexmedetomidine increased the success rate of endoscopic-guided orotracheal intubation. Increasing the dose of alfaxalone had no effect on respiratory rate.

Diagnosis of a tracheal tear by use of an oxygen analyzer in a dog with cervical trauma

CASE DESCRIPTION

A 7.75-year-old sexually intact male Welsh Terrier was examined because of cervical soft tissue wounds and an inability to maintain hemoglobin oxygen saturation without oxygen supplementation following a dog attack.

CLINICAL FINDINGS

A 2-cm-long penetrating wound that extended into a large open pocket was identified on the left ventral aspect of the dog's neck. The dog was anesthetized and underwent advanced imaging, the findings of which suggested that the trachea was intact. However, when the cuff of the endotracheal tube was deflated during the dog's recovery from anesthesia, sudden oxygen desaturation occurred. Given no radiographic signs of deteriorating lung injury, a tracheal tear was suspected. For rapid confirmation of a tracheal tear, without the need for additional advanced imaging, the oxygen concentration at the skin wound was investigated by use of an oxygen analyzer. When the dog was breathing 100% oxygen, the analyzer identified a higher oxygen concentration at the edge of the penetrating wound, compared with the concentration of oxygen in room air; the leakage of oxygen-rich gases from the airway through the wound confirmed the presence of a tracheal tear, immediately indicating the need for surgical exploration and repair.

TREATMENT AND OUTCOME

Surgical repair of the tracheal tear with a left sternothyroideus muscle flap was successfully performed.

CLINICAL RELEVANCE

For this dog, an oxygen analyzer was used to confirm the presence of a tracheal tear, suggesting that application of an oxygen analyzer may be useful in the emergency management of neck trauma cases.

The time required to achieve endotracheal intubation in dogs: a comparison of veterinary students and qualified veterinary surgeons

OBJECTIVE

To determine whether final year veterinary students take longer to perform endotracheal intubation than qualified veterinary surgeons.

STUDY DESIGN

Observational cohort study.

ANIMALS

A total of 38 healthy mesocephalic dogs undergoing general anaesthesia for a clinical purpose unrelated to this study.

METHODS

Time to successful endotracheal intubation, measured from termination of intravenous induction drug administration to confirmation of endotracheal intubation, was recorded for two groups: final year veterinary students (group S) and qualified veterinary surgeons (group V). Animal age, breed and anaesthetic induction agent were also recorded. Following normality testing the groups were compared for each variable using the Student's t test or Mann-Whitney U test where appropriate. The level of significance was defined as p < 0.05. Timed data are presented as median and interquartile range.

RESULTS

Time to successful intubation was 54.2 (31.3) seconds in group S and 11.7 (8.5) seconds in group V, the difference being significant (p < 0.001). There was also a significant difference between groups for animal age (p = 0.036) but not for breed (p = 0.573) or induction agent (p = 0.239).

CONCLUSIONS

and clinical relevance Veterinary students take longer to achieve successful endotracheal intubation of anaesthetized healthy dogs compared with qualified veterinary surgeons. To mitigate any additional risk of dogs developing hypoxaemia, it is recommended that a 55 second time limit is set after which the supervisor intervenes and takes over the intubation procedure. Preoxygenation may be used as an additional mitigation strategy.

Effects of airway management and tidal volume feedback ventilation during pediatric resuscitation in piglets with asphyxial cardiac arrest

To compare the effect on the recovery of spontaneous circulation (ROSC) of early endotracheal intubation (ETI) versus bag-mask ventilation (BMV), and expiratory real-time tidal volume (VTe) feedback (TVF) ventilation versus without feedback or standard ventilation (SV) in a pediatric animal model of asphyxial cardiac arrest. Piglets were randomized into five groups: 1: ETI and TVF ventilation (10 ml/kg); 2: ETI and TVF (7 ml/kg); 3: ETI and SV; 4: BMV and TVF (10 ml/kg) and 5: BMV and SV. Thirty breaths-per-minute guided by metronome were given. ROSC, pCO2, pO2, EtCO2 and VTe were compared among groups. Seventy-nine piglets (11.3 ± 1.2 kg) were included. Twenty-six (32.9%) achieved ROSC. Survival was non-significantly higher in ETI (40.4%) than BMV groups (21.9%), p = 0.08. No differences in ROSC were found between TVF and SV groups (30.0% versus 34.7%, p = 0.67). ETI groups presented lower pCO2, and higher pO2, EtCO2 and VTe than BMV groups (p < 0.05). VTe was lower in TVF than in SV groups and in BMV than in ETI groups (p < 0.05). Groups 1 and 3 showed higher pO2 and lower pCO2 over time, although with hyperventilation values (pCO2 < 35 mmHg). ETI groups had non significantly higher survival rate than BMV groups. Compared to BMV groups, ETI groups achieved better oxygenation and ventilation parameters. VTe was lower in both TVF and BMV groups. Hyperventilation was observed in intubated animals with SV and with 10 ml/kg VTF.

Effect of Instructional Format on Veterinary Students' Task Performance and Emotional State during a Simulation-Based Canine Endotracheal Intubation Laboratory: Handout versus Video

Video- versus handout-based instructions may influence student outcomes during simulation training and competency-based assessments. Forty-five third-year veterinary students voluntarily participated in a simulation module on canine endotracheal intubation. A prospective, randomized, double-blinded study investigated the impact of video (n = 23) versus handout (n = 22) instructions on student confidence, anxiety, and task performance. Students self-scored their confidence and anxiety before and after the simulation. During the simulation laboratory, three raters independently evaluated student performance using a 20-item formal assessment tool with a 5-point global rating scale. No significant between- or within-group differences (p > .05) were found for both confidence and anxiety scores. Video-based instructions were associated with significantly higher (p < .05) total formal assessment scores compared with handout-based instructions. The video group had significantly higher scores than the handout group on 3 of the 20 individual skills (items) assessed: placement of tie to the adaptor-endotracheal tube complex (p < .05), using the anesthetic machine (p < .01), and pop-off valve management (p < .001). Inter-rater reliability as assessed by Cronbach's α (.92), and Kendall's W (.89) was excellent and almost perfect, respectively. A two-faceted crossed-design generalizability analysis yielded G coefficients for both the handout (E_p² = .68) and the video (E_p² = .72) groups. Video instructions may be associated with higher performance scores than handout instructions during endotracheal intubation simulation training. Further research into skill retention and learning styles is warranted.

Effects of ketamine or midazolam continuous rate infusions on alfaxalone total intravenous anaesthesia requirements and recovery quality in healthy dogs: a randomized clinical trial

OBJECTIVE

To determine the alfaxalone dose reduction during total intravenous anaesthesia (TIVA) when combined with ketamine or midazolam constant rate infusions and to assess recovery quality in healthy dogs.

STUDY DESIGN

Prospective, blinded clinical study.

ANIMALS

A group of 33 healthy, client-owned dogs subjected to dental procedures.

METHODS

After premedication with intramuscular acepromazine 0.05 mg kg^-1 and methadone 0.3 mg kg^-1, anaesthetic induction started with intravenous alfaxalone 0.5 mg kg^-1 followed by either lactated Ringer's solution (0.04 mL kg^-1, group A), ketamine (2 mg kg^-1, group AK) or midazolam (0.2 mg kg^-1, group AM) and completed with alfaxalone until endotracheal intubation was achieved. Anaesthesia was maintained with alfaxalone (6 mg kg^-1 hour^-1), adjusted (±20%) every 5 minutes to maintain a suitable level of anaesthesia. Ketamine (0.6 mg kg^-1 hour^-1) or midazolam (0.4 mg kg^-1 hour^-1) were employed for anaesthetic maintenance in groups AK and AM, respectively. Physiological variables were monitored during anaesthesia. Times from alfaxalone discontinuation to extubation, sternal recumbency and standing position were calculated. Recovery quality and incidence of adverse events were recorded. Groups were compared using parametric analysis of variance and nonparametric (Kruskal-Wallis, Chi-square, Fisher's exact) tests as appropriate, p < 0.05.

RESULTS

Midazolam significantly reduced alfaxalone induction and maintenance doses (46%; p = 0.034 and 32%, p = 0.012, respectively), whereas ketamine only reduced the alfaxalone induction dose (30%; p = 0.010). Recovery quality was unacceptable in nine dogs in group A, three dogs in group AK and three dogs in group AM.

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam, but not ketamine, reduced the alfaxalone infusion rate, and both co-adjuvant drugs reduced the alfaxalone induction dose. Alfaxalone TIVA allowed anaesthetic maintenance for dental procedures in dogs, but the quality of anaesthetic recovery remained unacceptable irrespective of its combination with ketamine or midazolam.

Investigating novel anatomical predictors for endotracheal tube selection in dogs

The selection of an appropriate endotracheal tube (ET) for orotracheal intubation in dogs is based largely on experience, with no well-established guidelines available. This study examined relationships between several novel and published methods for selecting endotracheal tubes in a heterogenous population of 79 adult dogs. The following measurements were included: left and right nare width, nasal septum width, sum of left and right nares width plus the nasal septum width, total nose width and height, tracheal width, metacarpal and digital footpad width and height, and body mass. Using the Bland and Altman ratio method, the calculation of Cube Root Mass provided the greatest accuracy and precision, predicting actual ET size use within 3 to 4 tube sizes. A simpler to calculate, but less precise method was Width of Nose/3. The majority of published methods for estimating ET size performed poorly, including nasal septum and tracheal width.

Intravenous rocuronium 0.3 mg/kg improves the conditions for tracheal intubation in cats: a randomized, placebo-controlled trial

OBJECTIVES

We evaluated the use of rocuronium 0.3 mg/kg intravenously (IV) to facilitate tracheal intubation in cats anesthetized for elective ovariohysterectomy.

METHODS

Thirty female cats were randomly allocated to receive rocuronium 0.3 mg/kg IV or an equal volume of normal saline, following induction of anesthesia with ketamine and midazolam. Thirty seconds after induction, a single investigator, unaware of treatment allocation, attempted tracheal intubation. The number of attempts and the time to complete intubation were measured. Intubating conditions were assessed as acceptable or unacceptable based on a composite score consisting of five different components. Duration of apnea after induction was measured and cases of hemoglobin desaturation (SpO2 <90%) were identified.

RESULTS

Intubation was completed faster (rocuronium 12 s [range 8-75 s]; saline 60 s [range 9-120 s]) and with fewer attempts (rocuronium 1 [range 1-2]; saline 2 [range 1-3], both P = 0.006) in cats receiving rocuronium. Unacceptable intubating conditions on the first attempt occurred in 3/15 cats with rocuronium and in 10/15 with saline ( P = 0.01). Apnea lasted 4 ± 1.6 mins with rocuronium and 2.3 ± 0.5 mins with saline ( P = 0.0007). No cases of desaturation were observed.

CONCLUSIONS AND RELEVANCE

Rocuronium 0.3 mg/kg IV improves intubating conditions compared with saline, and reduces the time and number of attempts to intubate with only a short period of apnea in cats.

Impact of Stroke Therapy Academic Industry Roundtable (STAIR) Guidelines on Peri-Anesthesia Care for Rat Models of Stroke: A Meta-Analysis Comparing the Years 2005 and 2015

Numerous studies using rats in stroke models have failed to translate into successful clinical trials in humans. The Stroke Therapy Academic Industry Roundtable (STAIR) has produced guidelines on the rodent stroke model for preclinical trials in order to promote the successful translation of animal to human studies. These guidelines also underline the importance of anaesthetic and monitoring techniques. The aim of this literature review is to document whether anaesthesia protocols (i.e., choice of agents, mode of ventilation, physiological support and monitoring) have been amended since the publication of the STAIR guidelines in 2009. A number of articles describing the use of a stroke model in adult rats from the years 2005 and 2015 were randomly selected from the PubMed database and analysed for the following parameters: country where the study was performed, strain of rats used, technique of stroke induction, anaesthetic agent for induction and maintenance, mode of intubation and ventilation, monitoring techniques, control of body temperature, vascular accesses, and administration of intravenous fluids and analgesics. For each parameter (stroke, induction, maintenance, monitoring), exact chi-square tests were used to determine whether or not proportions were significantly different across year and p values were corrected for multiple comparisons. An exact p-test was used for each parameter to compare the frequency distribution of each value followed by a Bonferroni test. The level of significant set at < 0.05. Results show that there were very few differences in the anaesthetic and monitoring techniques used between 2005 and 2015. In 2015, significantly more studies were performed in China and significantly fewer studies used isoflurane and nitrous oxide. The most striking finding is that the vast majority of all the studies from both 2005 and 2015 did not report the use of ventilation; measurement of blood gases, end-tidal carbon dioxide concentration, or blood pressure; or administration of intravenous fluids or analgesics. The review of articles published in 2015 showed that the STAIR guidelines appear to have had no effect on the anaesthetic and monitoring techniques in rats undergoing experimental stroke induction, despite the publication of said guidelines in 2009.

Videoendoscopic endotracheal intubation of the rat

Mechanical ventilation is essential to the proper maintenance of anaesthesia in research animals undergoing laparoscopic research investigations with prolonged pneumoperitoneum. Ventilatory assistance is greatly aided by endotracheal intubation, which in rats can be a challenging procedure with a substantial risk of complication. The difficulty of the procedure arises primarily from the limited exposure and access to the laryngeal opening. We describe a simple and safe technique for endotracheal intubation in the rat that permits the introduction of a large-bore tube under direct visualization using equipment commonly found in the endosurgical research setting.

Postanaesthetic tracheal strictures in three rabbits

Within an 11-day period, three rabbits were anaesthetized for neutering. All were endotracheally intubated with 12 cm long, 2.5 mm (inner diameter [ID]) polyvinylchloride (PVC) tubes. All rabbits developed clinical signs of dyspnoea and upper respiratory tract obstruction, 17–21 days later. One rabbit was found dead; the other two were treated, but one was euthanized and one died. At necropsy examination, focal chronic inflammation and significant localized narrowing of the tracheal lumen was found in all cases. The affected sites corresponded to the position of the bevel of the endotracheal tube (ETT) during anaesthesia. Histopathology could not differentiate between a traumatic or chemical cause for the narrowing. Possible causes include trauma by the bevel of the ETT when turning the rabbit or preparing the surgical site or a chemical burn from incorrect disinfection or inadequate rinsing of the tubes. Iatrogenic tracheitis should be considered as a cause of dyspnoea, when clinical signs arise 2–3 weeks after anaesthesia.

Efficacy of endotracheal tube disinfection strategies for elimination of Streptococcus zooepidemicus and Bordetella bronchiseptica

OBJECTIVE

To evaluate the efficacy of various endotracheal tube disinfection strategies for elimination of Streptococcus zooepidemicus and Bordetella bronchiseptica.

DESIGN

Experimental in vitro study.

SAMPLE

12 sterile endotracheal tubes.

PROCEDURES

Endotracheal tubes were inoculated with S zooepidemicus or B bronchiseptica and subjected to 1 of 5 treatments (spraying with accelerated hydrogen peroxide solution [AHP] or soaking in one of the following: AHP, 0.5% chlorhexidine gluconate solution [CHG], 0.3% triclosan-containing soap solution, or tap water) or left untreated (controls). After 5 minutes, tubes were rinsed with water and swabbed for direct and enrichment culture. Culture results were scored semiquantitatively. Each isolate was tested separately (10 endotracheal tubes/isolate/treatment).

RESULTS

No growth was identified by direct culture of any samples collected from CHG-treated endotracheal tubes, whereas S zooepidemicus and B bronchiseptica were each identified from 1 of 10 tubes sprayed or soaked with AHP and from all tubes (10/10 each) treated by other methods or used as controls. The CHG and AHP treatments resulted in significantly lower median growth scores after direct culture than did other treatments. After enrichment culture, samples from CHG-treated tubes had significantly lower growth scores than samples from AHP-treated tubes, which had significantly lower scores than samples from other treatment groups.

CONCLUSIONS AND CLINICAL RELEVANCE

High-level disinfection (ie, elimination of all vegetative bacterial growth) was not achieved with any treatment tested. Although optimal approaches are not known, processing of endotracheal tubes with CHG or AHP appears to be the best approach when sterilization is not feasible.

Comparison of a ferret model with an inanimate simulator for training novices in techniques for intubating neonates

Simulators for neonatal intubation training have improved, prompting us to compare a state-of-the-art simulator with live ferrets for training novice family-medicine residents in this crucial skill. After a scripted didactic presentation, we used a crossover study design and randomly assigned residents to receive simulator or live ferret training, after which they repeated the procedure by using the opposite method. Participants were asked to report their level of confidence and competence before and after each training session and the usefulness of each training method. In addition, residents were videotaped performing the procedure and evaluated by using a modified global rating scale. The 2 methods did not differ in regard to self-reported confidence, competence, or usefulness of each training procedure. A majority of participants indicated that they preferred using the ferrets over the simulator, with realism cited most frequently as the reason for their choice. Videotape scores for time and motion and flow of the procedure were higher when the simulator was used, but higher for instrument handling when ferrets were intubated. Overall scores were higher for videotaped evaluations with the simulator compared with the ferrets. According to these findings, the simulator appears to provide adequate instruction for the initial training of novice learners in neonatal intubation techniques.

Two cases of intraoperative herniation of the endotracheal tube cuff

During anaesthesia for elective procedures, 2 dogs developed acute airway obstruction caused by herniation of the endotracheal cuff. This is an uncommon but potentially fatal complication especially when minimal monitoring of the patient leads to late recognition of the condition. The most typical symptoms are decreased thoracic excursions and tidal volume, absence of gas flow through the endotracheal tube, change in the capnographic waves morphology and increased airway pressures. In both cases desaturation of haemoglobin (measured by pulse oximetry) occurred in-between 6 and 8 minutes after cuff herniation. All signs normalised following partial deflation of the cuff. Careful management of cuff pressures especially when nitrous oxide is used, awareness of the condition and monitoring of the patient can prevent fatal consequences.

Use of a laryngeal mask airway in a brachycephalic dog with masticatory myositis and trismus

An 8-month old, male, neutered bulldog was presented for investigation of a 2-day history of trismus. Endotracheal intubation was impossible as the dog was only able to open his mouth approximately 2 cm. A laryngeal mask airway was blindly inserted after induction of general anesthesia to maintain the patient on inhalational anesthesia and improve respiration for computed tomography and muscle biopsy. The dog recovered from anesthesia uneventfully.

The effects of succinylcholine or low-dose rocuronium to aid endotracheal intubation of adult sows

This randomized, prospective, blinded study compared the use of succinylcholine or rocuronium to aid endotracheal intubation of 27 adult sows [mean body weight 261 ± 28 (standard deviation) kg]. Preliminary trials allowed development of the intubation technique and skills. The sows were premedicated with azaperone, atropine, and morphine, and anesthesia was induced with thiopental [6 mg/kg body weight (BW)]. Nine sows each received succinylcholine (1.0 mg/kg BW), rocuronium (0.5 mg/kg BW), or saline (15 mL) after induction. Increments of thiopental (1 mg/kg BW) were used if swallowing impaired intubation. Intubation was performed 45 s after injection of the test drug and was timed and scored. The intubation scores were analyzed with Kruskal-Wallis analysis of variance (ANOVA). Time taken for intubation, body weight, and total dose of thiopental were analyzed with ANOVA and Bonferroni's multiple-comparisons test. No significant differences (at P < 0.05) were found between the groups with regard to intubation score, time taken for intubation, or total thiopental dose. Thus, neuromuscular blocking agents did not aid endotracheal intubation of adult sows anesthetized with thiopental.

One-lung ventilation using a wire-guided endobronchial blocker for thoracoscopic pericardial fenestration in a dog

Instead of a conventional double lumen tube, an Arndt wire-guided endobronchial blocker was used to achieve one-lung ventilation in a dog undergoing thoracoscopic pericardiectomy. Overall, lung separation was easy to perform and surgical conditions for the creation of a pericardial window were adequate. Special ventilation strategies were applied.

Assessing the effectiveness of intubation as a challenge model in contagious bovine pleuropneumonia vaccine experiments

A study was carried out to assess the effectiveness of a bronchoscope in administering a pathogenic field strain of Mycoplasma mycoides subsp. mycoides (MmmSC) in cattle challenge experiments. Out of 16 animals inoculated using the bronchoscope, 10 (62.2%) showed clinical disease as evidenced by fever and 15 (93.8%) displayed typical lesions of CBPP from which MmmSC was isolated. Serum samples collected weekly were tested by Complement Fixation Test (CFT) and competitive enzyme-linked immunosorbent assay (c-ELISA). Antibodies to MmmSC were detected in 10 out of the 16 animals by the CFT and 11 out of the 16 animals by c-ELISA. The onset of clinical disease was as early as 2 days post-inoculation, and most of the animals developed clinical disease 2 to 3 weeks post-infection. These results clearly demonstrate that nasotracheal inoculation of pathogenic strain of MmmSC with the aid of a bronchoscope can lead to early onset of clinical disease; similar to previous studies but with higher numbers of animals showing clinical disease. This is in contrast with previous studies where early clinical disease was observed in as little as 15% of inoculated animals. This nasotracheal inoculation method using a bronchoscope can, therefore, be adopted for use in experimental challenge infections of cattle. This method is found to be a better replacement to the contact transmission method whose drawback includes extra cost of donor animals and unpredictable rate and timing of transmission from intubated to challenge animals.

Intravenous and intratracheal administration of trimetoquinol, a fast-acting short-lived bronchodilator in horses with ‘heaves’

REASON FOR PERFORMING STUDY

Trimetoquinol (TMQ) is a potent beta-adrenoceptor agonist bronchodilator used in human medicine but has not been evaluated for potential use as a therapeutic agent for horses with 'heaves'.

OBJECTIVES

To assess the pharmacodynamics of TMQ in horses with 'heaves' to determine potential therapeutic effects.

METHODS

Increasing doses of TMQ were administered to horses with 'heaves' by i.v. and intratracheal (i.t.) routes. Doses ranged 0.001-0.2 microg/kg bwt i.v. and 0.01-2 microg/kg bwt i.t. Cardiac and airways effects were assessed by measurement of heart rate (HR) and maximal change in pleural pressure (deltaPplmax), respectively. Side effects of sweating, agitation and muscle trembling were scored subjectively. Duration of action to i.v. (0.2 microg/kg bwt) and i.t. (2 microg/kg bwt) TMQ was evaluated over 6 h.

RESULTS

Intravenous TMQ was an exceptionally potent cardiac stimulant. Heart rate increased at 0.01 microg/kg bwt, and was still increasing after administration of highest dose, 0.2 microg/kg bwt. Airway bronchodilation, measured as a decrease in deltaPplmax, also commenced at 0.01 microg/kg bwt. By the i.t. route, TMQ was 50-100-fold less potent than by i.v. Side effects included sweating, agitation and muscle trembling. Overall, the onset of HR and bronchodilator effects was rapid, within about 3 min, but effects were over at 2 h.

CONCLUSION

When administered i.v. and i.t., TMQ is a highly potent cardiac stimulant and a modest bronchodilator. It may not be an appropriate pharmacological agent by i.v. and i.t. routes for the alleviation of signs in horses with 'heaves'. Further studies of TMQ by oral and aerosol routes are necessary.

POTENTIAL RELEVANCE

In horses, TMQ is a fast-acting bronchodilator with a short duration of action. It could be used as a rescue agent during an episode of 'heaves'. The i.v. and i.t. administration of TMQ is associated with side effects, similar to those reported for all other beta-agonists. However, other routes, such as aerosol and oral, may prove useful and safe for the alleviation of bronchoconstriction typical of 'heaves'.

Minimizing trauma to the upper airway: a ferret model of neonatal intubation

Our objective was to determine whether an adult ferret can be intubated as many as 10 times per training session without resulting in trauma to the upper airway. In this program, 8 male ferrets rotated through intubation laboratories, limiting the use of each animal to once every 3 mo. Animals were examined by the veterinary staff after intubations to assess for trauma to upper airway tissue. Each examination was given a trauma grade of 0 for no visible signs of trauma, 1 if erythema of the larynx was present, 2 if visible excoriation of the mucus membranes was present, and 3 if bleeding (frank hemorrhage) was observed. The number of intubation attempts was restricted to 10 per animal per training session. A total of 170 intubations were completed on the ferrets during a 12-mo period. The average number of intubations per laboratory was 8.1 intubations per ferret. In addition, 1.8% of the intubations resulted in erythema (score, 1) after training, and 0.6% of the intubations resulted in excoriation (score, 2). Frank hemorrhage (score, 3) was not noted. The overall percentage of intubations resulting in any trauma during a training session was 0.02%. None of the animals have experienced any major complications to date. This ongoing training program has been used to teach neonatal intubation skills to emergency medicine residents for the past 12 mo. Ensuring the health and safety of the ferrets was paramount. Our results suggest that as many as 10 intubation attempts per session can be performed safely on each ferret without causing excessive trauma.

Induction of anaesthesia with either midazolam or propofol in rabbits premedicated with fentanyl/fluanisone

Fifty-four rabbits that were to be neutered were premedicated with 0.1 ml/kg fentanyl/fluanisone and then randomly allocated to be anaesthetised with either midazolam or propofol. Anaesthesia was then maintained with isoflurane. The ease of orotracheal intubation, the rabbits' cardiorespiratory variables, and the speed and quality of recovery from anaesthesia were assessed by the same anaesthetist who was unaware of the induction agent used. Hypotension was common in both groups. The mean (sd) respiratory rates were 30 (12) breaths per minute in the midazolam group and 43 (15) breaths per minute in the propofol group. The mean (sd) time to first head lift was 36 (21) minutes in the midazolam group and 14 (11) minutes in the propofol group, and the mean (sd) times to the return of the righting reflex were 35 (19) minutes and 15 (eight) minutes, respectively. The quality of recovery was better in the propofol group than in the midazolam group.

Comparison of endotracheal intubation techniques in llamas

This study evaluated a retrograde orotracheal intubation technique and compared it to the traditional normograde intubation technique used in llamas. Oral anatomical features, which can impair visualization of the epiglottis and laryngeal structures, and the production of excessive salivary secretions make it difficult to establish an airway under emergency conditions. Normograde intubation involves placing a stylet through the mouth into the trachea and advancing the endotracheal tube over the stylet into the trachea. For retrograde intubation, a nested trochar with cannula is placed into the cervical trachea and a stylet is advanced through the cannula and out the mouth. The endotracheal tube is advanced over the stylet back into the trachea. Our evaluation of both techniques found no statistical difference in time to place the stylet or endotracheal tube; however, fewer attempts were needed to place the tube using the retrograde technique. We found the retrograde technique to be a viable option for intubating llamas.

Effect of intravenous lidocaine on heart rate, systolic arterial blood pressure and cough responses to endotracheal intubation in propofol-anaesthetized dogs

OBJECTIVE

To evaluate the effect of intravenous lidocaine on coughing and variations in heart rate (HR) and systolic arterial pressure (SAP) at endotracheal intubation in propofol-anaesthetized dogs.

STUDY DESIGN

Prospective, randomized, blinded clinical study.

ANIMALS

Eighty dogs, ASA grades I/II.

METHODS

Dogs were randomly assigned to one of two treatments, with dogs in the lidocaine group receiving 1 mg kg(-1) lidocaine intravenously and those in the saline group receiving 0.05 mL kg(-1) saline intravenously before induction of anaesthesia with up to 6.5 mg kg(-1) propofol intravenously. An electrocardiogram was recorded continuously. Heart rate was calculated and SAP (using Doppler ultrasonic flow detection) was recorded at the following time points: pre-treatment, following lidocaine or saline administration, before and after intubation. The occurrence, number and strength of coughs were recorded. Systolic arterial pressure and HR were compared using one-sample t-tests to examine whether SAP and HR changed with test drug administration or following intubation. The number of coughs was compared between groups using t-tests. A cross tabulation and chi-square or Fisher's exact test was used to compare proportions of dogs that coughed and intensity of coughing in each group. The level of significance was set at p < 0.05.

RESULTS

Heart rate did not change in either group. Systolic arterial blood pressure increased following intubation in both the lidocaine (p = 0.003) and saline groups (p = 0.001). There was no difference in the increase in SAP or in the number or intensity of coughs at intubation between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Intravenous lidocaine had no effect on the occurrence or intensity of coughing or on changes in SAP at endotracheal intubation in dogs anaesthetized with propofol. The use of 1 mg kg(-1) lidocaine intravenously before intubation in dogs to attenuate cough and the pressor response was not supported.

Use of laryngeal mask airway compared to endotracheal tube with positive-pressure ventilation in anesthetized swine

OBJECTIVE

To compare the ease of placement and ventilatory parameters of a laryngeal mask airway (LMA) with an endotracheal tube (ETT) in anesthetized swine during positive-pressure ventilation (PPV).

STUDY DESIGN

Prospective, randomized, experimental trial.

ANIMALS

Nine young domestic swine, weighing between 40 and 49 kg (mean 45.1 kg), being used for a separate terminal surgical study.

METHODS

The pigs were immobilized with tiletamine/zolazepam, 2.7-3.6 mg kg(-1), intramuscularly, followed by isoflurane in oxygen delivered by facemask. The lungs were mechanically ventilated through an ETT or an LMA, in random order, during the anesthetic period. Positive-pressure ventilation was adjusted to maintain end-tidal CO2 (Pe'CO2) between 35 and 45 mmHg, with peak inspiratory pressure (P(insp)) of 15-23 cmH2O. Buprenorphine, 0.3 mg intramuscularly, was given to each pig after instrumentation. Isoflurane vaporizer settings were adjusted to maintain a surgical plane of anesthesia. Respiratory rate (RR), tidal volume (V(T)), minute volume (V(E)), and Pe'CO2 were measured and recorded at 5-minute intervals. After the collection of 1 hour of data, the alternate airway was placed. Swine were given at least 30 minutes to stabilize and another hour of data were recorded. At the time of airway placement, the ease of placement was assessed based on time and the number of personnel required. Data were analyzed using paired Student's t-test or Wilcoxon signed rank test where appropriate.

RESULTS

Laryngeal mask airways were significantly easier to place than ETT. Values for V(T) and V(E) were not significantly different between treatments. Peak inspiratory pressures were higher in ETT-ventilated swine.

CONCLUSIONS AND CLINICAL RELEVANCE

An LMA may be used as an alternative to an ETT in mechanically-ventilated anesthetized swine. Use of an LMA may reduce time and personnel required for placement of an airway.

Evaluation of an anaesthetic technique used in dogs undergoing craniectomy for tumour resection

OBJECTIVE

To evaluate a total intravenous anaesthetic technique in dogs undergoing craniectomy.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Ten dogs admitted for elective surgical resection of rostro-tentorial tumours.

METHODS

All dogs were premedicated with methadone, 0.2 mg kg(-1) intramuscularly 30 minutes prior to induction of anaesthesia. Anaesthesia was induced with propofol administered intravenously (IV) to effect, following administration of lidocaine 1 mg kg(-1) IV and maintained with a continuous infusion of propofol at < or =0.4 mg kg(-1) minute(-1) during instrumentation and preparation and during movement of the animals to recovery. During surgery, anaesthesia was maintained using a continuous infusion of propofol at <or =0.4 mg kg(-1) minute(-1) and alfentanil < or =1 microg kg(-1) minute(-1). Lidocaine was administered at 1 mg kg(-1) IV immediately prior to extubation. Arterial blood pressure and heart rate (HR) were recorded prior to induction and every 5 minutes throughout preparation and surgery. Central venous pressure was recorded every 5 minutes throughout surgery.

RESULTS

Administration of propofol and lidocaine prevented significant increases in mean arterial blood pressure (MAP) and HR during endotracheal intubation and extubation. Adequate MAP was maintained throughout anaesthesia. Recovery was smooth and excitement free. There was no association between duration of anaesthesia, total drugs administered, or severity of neurological disease and recovery times. Postoperatively there was no deterioration in neurological function in the immediate postoperative period with complete resolution of pre-existing neurological deficits within 7 days of surgery.

CONCLUSION

This technique provided minimal response to intubation and extubation, adequate arterial blood pressure and a smooth predictable recovery. All animals were neurologically improved by the time of discharge, suggesting that this technique had not caused significant neuronal damage.

CLINICAL RELEVANCE

Total intravenous anaesthesia with propofol and alfentanil appears to be a satisfactory anaesthetic technique for use in dogs undergoing surgery for debulking/removal of rostro-tentorial tumours.

Peri-operative body temperatures in isoflurane-anaesthetized rabbits following ketamine-midazolam or ketamine-medetomidine

OBJECTIVE

To investigate alterations in peri-operative body temperatures and oesophageal-skin temperatures in isoflurane-anaesthetized rabbits following either ketamine-midazolam or ketamine-medetomidine induction of anaesthesia.

ANIMAL POPULATION

Fifty client-owned rabbits, (25 male, 25 female) of different breeds anaesthetized for elective neutering (age range: 3-42 months; mass range: 1.15-4.3 kg).

STUDY DESIGN

Randomized, blinded clinical study.

METHODS

Pre-anaesthetic rectal temperature was measured. A 24 SWG catheter was placed in a marginal ear vein after local anaesthesia. Ketamine (15 mg kg(-1)) with medetomidine (0.25 mg kg(-1)) (group KMT) or with midazolam (3 mg kg(-1)) (group KMZ) was injected intramuscularly (IM). Following endotracheal intubation anaesthesia was maintained with isoflurane in oxygen. Carprofen (3 mg kg(-1)) and glucose saline (5 mL kg(-1) hour(-1)) were administered through the intravenous catheter. Room temperature and humidity, skin temperature (from tip of pinna) and oesophageal temperature were measured during anaesthesia. Ovariohysterectomy or castration was performed. Rectal temperature was taken when isoflurane was discontinued (time zero) and 30, 60 and 120 minutes thereafter. Atipamezole (0.5 mg kg(-1)) was administered IM to rabbits in group KMT at zero plus 30 minutes. Mass, averaged room temperature and duration of anaesthesia data were compared using a two-tailed t-test. Age, averaged room humidity, rectal temperature decrease, oesophageal temperature decrease and oesophageal-skin difference data were compared using a Kruskal-Wallis test. p < 0.05 was considered significant.

RESULTS

The averaged oesophageal-skin temperature difference was significantly greater in group KMT [median 9.85 degrees C (range 6.42-13.85 degrees C)] than in group KMZ [4.38 degrees C (2.83-10.43 degrees C)]. Rectal temperature decreased over the anaesthetic period was not significantly different between the two groups; however, oesophageal temperature decrease was significantly less in group KMT [1.1 degrees C (-0.1-+2.7 degrees C)] than in group KMZ [1.4 degrees C (0.6-3.1 degrees C)].

CONCLUSIONS

Oesophageal-skin temperature difference is larger in rabbits anaesthetized with ketamine-medetomidine combination than ketamine-midazolam.

CLINICAL RELEVANCE

The oesophageal temperature in rabbits anaesthetized with ketamine-medetomidine and isoflurane decreases significantly less than in animals anaesthetized with ketamine-midazolam and isoflurane, during anaesthesia.

Influence of the mode of ventilation on ketamine/xylazine requirements in rabbits

OBJECTIVE

To evaluate the effect of the mode of mechanical ventilation (MV) on the dose of intravenous anesthetic during 3 hours of ketamine/xylazine anesthesia.

STUDY DESIGN

Prospective laboratory study.

ANIMALS

Sixty-one adult male New Zealand White rabbits.

METHODS

Rabbits were anesthetized (ketamine/xylazine 35 + 5 mg kg(-1), IM), the trachea was intubated and randomized to four groups - (1) CMV-1 (n = 14), ventilated with traditional conventional volume-cycled MV [V(T) = 12 mL kg(-1), RR = 20, positive end-expiratory pressure (PEEP) = 0 cmH(2)O]; (2) CMV-2 (n = 13), ventilated with a modern lung-protective regimen of volume-cycled MV (V(T) = 6 mL kg(-1), RR = 40, PEEP = 5 cmH(2)O); (3) HFPV (n = 17) ventilated with high-frequency percussive ventilation [high-frequency oscillations (450 minute(-1)) superimposed on 40 minute(-1) low-frequency respiratory cycles, I:E ratio = 1:1], oscillatory continuous positive airway pressure (CPAP) of 7-10 cmH(2)O, and demand CPAP of 8-10 cmH(2)O. (4) A fourth group, spontaneously ventilating (SV, n = 17), was anesthetized, intubated, but not ventilated mechanically. FiO(2) in all groups was 0.5. Anesthesia was maintained at a surgical plane by IV administration of a ketamine/xylazine mixture (10 + 2 mg kg(-1), as necessary) for 3 hours after intubation. Total dose of xylazine/ketamine administered and the need for yohimbine to facilitate recovery were quantitated.

RESULTS

The total dose of xylazine/ketamine was significantly higher in the HFPV and SV groups compared with CMV-1 (p < 0.01). Fewer animals required yohimbine to reverse anesthesia in the HFPV than CMV-1 group (p < 0.05).

CONCLUSIONS

The HFPV mode of MV led to higher doses of ketamine/xylazine being used than the other modes of MV.

CLINICAL RELEVANCE

In rabbits, anesthetic dose for the maintenance of anesthesia varied with the mode of MV used. Investigators should be aware of the possibility that changing the mode of ventilation may lead to an alteration in the amount of drug required to maintain anesthesia.