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.

Traumatic endotracheal intubation in the cat

BACKGROUND

Orotracheal intubation is a commonly performed procedure in the cat, but it is not without complications. Tracheal rupture has been reported in cats, but trauma to the arytenoids from intubation has not been documented.

OBSERVATIONS

An otherwise healthy, 5-year-old male domestic shorthair cat presented for total ear canal ablation to resolve intractable otitis media and externa. The cat was premedicated with glycopyrrolate, hydromorphone, and acepromazine. Anesthesia was induced with diazepam and ketamine, and maintained with isoflurane in oxygen. During orotracheal intubation, the larynx was poorly visualized and excessive force was used to perform intubation. Subsequently, blood was observed in the larynx and laryngoscopy revealed a tear lateral to the patient's right arytenoid which had been created during intubation. The larynx was re-intubated normally and the cat suffered no obvious ill effects from the trauma to the larynx.

CONCLUSIONS

Direct observation and proper technique must be employed during orotracheal intubation in cats in an attempt to avoid laryngeal trauma.

Airway management with the laryngeal tube in rabbits

The rabbit's oropharyngeal anatomy complicates the use of endotracheal intubation for airway management during surgical procedures. To determine if the laryngeal tube is useful for airway management in rabbits, the authors applied the device and evaluated its efficacy to ventilate the lungs. The laryngeal tube was inserted blindly and without difficulty in six healthy male New Zealand White rabbits; all of the rabbits were ventilated adequately with and without neuromuscular blockade. The authors conclude that the laryngeal tube can be used as an alternative means of airway management in rabbits.

Teaching a new method of rabbit intubation

Veterinary technology students were asked to participate in a study comparing 2 methods of teaching endotracheal intubation of rabbits. The first group of students was taught to intubate rabbits by the classic 'sblind' method. This method entailed holding a sternally recumbent rabbit by its head while the intubator listened to breath sounds through a partially passed endotracheal tube inserted through the rabbit's oral cavity. When the rabbit inhaled, the intubator introduced the endotracheal tube to the lower respiratory tract, timing the movement of the endotracheal tube with the opening of the laryngeal inlet. A second technique, based on the blind method of intubation of horses, was taught to a second set of students. In this method, the operator visualizes the condensation of exhalation from the respiratory tract in the transparent silicon endotracheal tube positioned at the rostral larynx. The operator uses this information to advance the endotracheal tube into the airway. All students were successful with both techniques. Although students intubated the rabbits more quickly with the classic blind technique, they expressed unanimous preference for the lateral recumbency method.

An investigation of the bacterial contamination of small animal breathing systems during routine use

OBJECTIVE

To investigate the need for sterilization of anaesthetic breathing systems to prevent cross-infection between animals due to the re-use of anaesthetic circuit tubing.

STUDY DESIGN

Prospective microbiological study.

METHODS

Bacteriology samples were taken from 37 sterile breathing systems, each used for 1 day, at two sampling sites (one proximal and one distal to the animal). The number of patient connections, cumulative anaesthesia time, culture results, number of colony-forming units and the number of different species were recorded. Secondly, four sterile breathing systems were used for 2 months under routine conditions and sampled every 2 weeks and the same parameters recorded. Finally, the inner surfaces of four sterile breathing systems were inoculated with a known load of canine oropharyngeal bacteria. Bacteriology samples were taken at 1 minute, 1 hour and 1 day post-deposition. The number of colonies identified was compared with the initial load.

RESULTS

Only a very small number of micro-organisms were isolated and these were generally organisms of low pathogenic potential. The proximal site was found to be significantly more colonized than the distal site (p < 0.001). Neither longer daily connection time (p = 0.54), nor a higher number of connections (p = 0.81) increased the incidence of proximal site colonization. Over the 2-month study period, the bacterial population did not increase. There was no correlation between cultures isolated from successive samples taken from the same tubing. There was rapid loss of viability of the micro-organisms deliberately inoculated onto the tubing surface: the number of colonies isolated from the breathing system after 1 minute was significantly lower than in the inoculum (p = 0.042).

CONCLUSIONS AND CLINICAL RELEVANCE

Sterile anaesthesia breathing systems were colonized by environmental micro-organisms of low pathogenicity. Although long-term survival of recognized pathogens in a dry environment is still possible, the use of a bacterial filter or a sterilized breathing system for routine veterinary anaesthesia cannot be supported by current evidence.

A novel and simple method for endotracheal intubation of mice

Endotracheal intubation in mice is necessary for experiments involving intratracheal instillation of various substances, repeated pulmonary function assessments and mechanical ventilation. Previously described methods for endotracheal intubation in mice require the use of injection anaesthesia to immobilize the animal during the intubation procedure or the use of a volatile anaesthetic prior to intubation for immobilization. With these methods, the control of anaesthetic depth during the intubation procedure is absent. We describe a method for simple and rapid intratracheal intubation in mice for mechanical ventilation, using a self-built plastic support to facilitate the intubation procedure. General anaesthesia is maintained by means of inhalation through a non-rebreathing circuit connected to the plastic support. This set-up gives the operator control of anaesthetic depth and sufficient time to perform the intubation procedure. A purpose-made laryngoscopic blade is used to facilitate the intubation tube entering the trachea. The blade of the purpose-made laryngoscope is constructed as a retraction guide and is curved for easy handling. Under direct vision, the epiglottis is gently lifted by the laryngoscopic blade while the intubation tube is pushed into the trachea. Following this novel intubation technique, we were able to mechanically ventilate mice for at least 2 h without severely disturbing blood gases. Histological evaluation of the lungs and microscopic evaluation of the trachea and larynx showed no signs of trauma related to the intubation technique or mechanical ventilation.

Tracheal necrosis following tracheal intubation in a dog

Tracheal rupture and stenosis are well-reported problems in human beings and cats following endotracheal intubation. However, this problem has been rarely reported in dogs. This case report describes a case of tracheal necrosis 5 days following endotracheal intubation in a dog associated with overinflation of the endotracheal tube cuff and multiple changes in position.

Management of airway difficulties during induction of general anesthesia in an American miniature horse with dwarfism

This report describes previously unreported upper airway abnormalities encountered in a 5-month-old American miniature horse colt presented for elective surgery. Caution should be exercised when administering general anesthesia or heavy sedation to individuals of this breed that present with multiple congenital abnormalities.

Endotracheal intubation in the dog

In dogs, endotracheal intubation is often necessary for surgery, dental prophylaxis, or other procedures that require gas anesthesia or ventilation. Following a few simple guidelines can help ensure that the procedure is done safely and effectively.

Effect of Intrathecal Amikacin Administration and Repeated Centesis on Digital Flexor Tendon Sheath Synovial Fluid in Horses

OBJECTIVE

To determine the effect of intrathecal amikacin administration and repeated tenovaginocentesis on the total nucleated cell count (TNCC), total protein (TP) concentration and cytologic characteristics of synovial fluid of the equine digital flexor tendon sheath (DFTS).

STUDY DESIGN

Randomized, cross-over experimental design.

ANIMALS

Adult horses (n=8).

METHODS

Synovial fluid was aseptically collected from the DFTS and either 1 mL amikacin sulfate (250 mg/mL) or lactated Ringer's solution (LRS) was injected into the DFTS. Serial synovial fluid samples were obtained at 0, 12, 24, 48, and 72 hours. The opposite treatment was administered to the contralateral DFTS after a washout period of 2 weeks.

RESULTS

Treatment increased TP concentration, TNCC, percentage of neutrophils, and neutrophil counts from baseline levels. There was no difference between treatment of the DFTS with amikacin or LRS. Values peaked at 12-24 hours after the initial centesis and then declined toward baseline levels.

CONCLUSIONS

Injection and repeat centesis of the normal DFTS with 250 mg amikacin or an equivalent volume of LRS resulted in mild increases in synovial fluid analytes from baseline. Synovial inflammation in this study was not accompanied by lameness at the walk and measured analytes returned toward baseline levels within 12-24 hours of first injection.

CLINICAL RELEVANCE

The effect of tenovaginocentesis and intrathecal administration of amikacin or LRS on DFTS synovial fluid values are modest in most horses; however, some horses can develop marked increases in synovial fluid values that may be interpreted as sepsis.

Tracheal injury after endotracheal intubation and anesthesia in rabbits

This case report describes sublaryngeal tracheal injury and ulceration in 15 rabbits from 3 institutions as sequelae to routine intubation and general anesthesia with isoflurane in oxygen. The rabbits were intubated for general anesthesia and mechanically ventilated for experimentally diverse procedures, with periods of anesthesia lasting 1.5 to 5 h. Of the 15 animals, 6 developed minimal to moderate postanesthesia clinical signs of moist rales or cyanosis or both; 2 of these 6 rabbits later died unexpectedly, their deaths attributed to respiratory obstruction by necrotic tracheal debris. The pathogenesis of this lesion is reviewed. Our findings suggest that rabbits may be predisposed to developing serious tracheal injury and clinically significant sequelae in association with routine intubation.

Influence of lidocaine and diazepam on peri-induction intraocular pressures in dogs anesthetized with propofol-atracurium

The purpose of this study was to evaluate the effects on the intraocular pressure (IOP) of lidocaine or diazepam administered intravenously (IV) before induction of anesthesia with propofol-atracurium and orotracheal intubation in normal dogs, as well as the effects on the IOP of lidocaine applied topically to the larynx after induction with propofol-atracurium. We randomly assigned 32 random-source dogs, obtained from municipal pounds, to receive the following: lidocaine, 2 mg/kg IV, with saline, 0.1 mL/kg topically applied to the larynx (LIDOsal); saline, 0.1 mL/kg IV, with lidocaine, 2 mg/kg topically applied to the larynx (SALlido); diazepam (Valium), 0.25 mg/kg IV, with saline, 0.1 mL/kg topically applied to the larynx (VALsal); or saline, 0.1 mL/kg IV, with saline, 0.1 mL/kg topically applied to the larynx (SALsal). We measured arterial pressure directly, by means of an indwelling catheter placed in a peripheral artery. Anesthesia was induced with propofol, 8 mg/kg IV, until loss of jaw tone, followed by atracurium, 0.3 mg/kg IV. We measured the IOP in triplicate in each eye before premedication, before induction, before intubation, and after intubation. After induction, the IOP was significantly increased except in the VALsal group, in which the IOP was significantly lower than in the negative-control group before intubation. After intubation, the IOP was significantly elevated in all the groups compared with the values before induction. Cardiovascular parameters were essentially similar in all the groups, except for a significant increase in blood pressure after intubation in the SALlido group. Thus, propofol-atracurium anesthesia causes an increase in IOP that is blunted by diazepam. However, diazepam does not blunt the increase in IOP observed with intubation.

Oropharyngeal aspiration of a silica suspension produces a superior model of silicosis in the mouse when compared to intratracheal instillation

Instillation of crystalline silica into the lungs of mice is a common experimental model of pulmonary fibrosis. Typically, a suspension of silica in saline is injected into the trachea via intubation or surgical tracheostomy. These techniques require a high degree of technical skill, have a lengthy training period, and can suffer from a high failure rate. In oropharyngeal aspiration, a droplet of liquid is placed in the animal's mouth while simultaneously holding its tongue (to block the swallow reflex) and pinching its nose shut, forcing it to breathe through its mouth, aspirating the liquid. To determine whether oropharyngeal aspiration (OA) could replace intratracheal instillation (IT) in a model of silica-induced fibrosis, a comparison was performed. Crystalline silica was introduced into the lungs of male C57BL/6 mice by the IT or OA procedure, and the resulting inflammation and fibrosis was assessed after 3 weeks. IT and OA instillation of silica both resulted in neutrophilic inflammation and fibrotic changes, including interstitial fibrosis and dense fibrotic foci. Mice treated via IT demonstrated a few large lesions proximal to conducting airways with little involvement of the distal parenchyma and large interanimal variability. In contrast, OA resulted in a diffuse pathology with numerous fibrotic foci distributed throughout the lung parenchyma, which is more representative of human fibrotic lung disease. OA- but not IT-treated mice exhibited significantly increased lung collagen content. Furthermore, the interanimal variability within the OA group was significantly less than in the IT group. Oropharyngeal aspiration should be considered as an alternative to intratracheal instillation of silica and other particulates in studies of respiratory toxicity and lung disease.

Arytenoid mucosal injury in young Thoroughbred horses — investigation of a proposed aetiology and clinical significance

AIM

To determine whether trauma to the larynx caused by nasotracheal intubation induced mucosal ulceration of the arytenoid cartilages of adult horses, and to determine the incidence of such ulceration in yearling Thoroughbred horses and its effect on athletic performance.

METHODS

Laryngeal trauma was induced in a group of 21 adult horses by introduction of a nasogastric tube into the trachea three times within 5 min. Injury to the arytenoid cartilages or vocal cords was subjectively assessed immediately after intubation, and thereafter at weekly intervals for 10 weeks. The outcome and athletic performance of 33 Thoroughbred yearling horses with idiopathic disease of the arytenoid cartilages, diagnosed at the yearling sales, were evaluated and compared to those of control horses of the same gender and age, from the same sale.

RESULTS

Mucosal injury was noted immediately after intubation in every horse. Evidence of injury to the vocal or corniculate processes of the arytenoid cartilages or vocal cords was still apparent in 10/21 (48%) horses 1 week after intubation, five of which developed persistent lesions that remained present and unchanged from 28 days following intubation until the end of the 10-week observation period. All persistent lesions were nodules or focal swellings of the vocal cords or arytenoid cartilages, and there was no evidence of mucosal ulceration, infection or discharge. Mucosal ulceration of the vocal processes was the most common abnormality detected in the yearlings, affecting 16/33 (48%) that were diagnosed with idiopathic arytenoid disease at the yearling sales. Five of the 33 (15%) horses were diagnosed with arytenoid chondritis at the time of sale and were excluded from the performance outcome analysis. Of the 28 horses diagnosed with arytenoid abnormalities excluding chondritis, 19 (68%) raced with no history of respiratory-related problems, two (7%) were subsequently diagnosed with laryngeal hemiplegia, and seven (25%) were lost to follow-up. The case animals were 2.7 times more likely to race than control horses, but there was no difference between cases and controls in the likelihood of starting more than three times.

CONCLUSIONS

This study showed that nasotracheal intubation in adult horses could result in immediate mucosal trauma, persistent swelling, and focal scarring of the arytenoid cartilages, but this did not mimic mucosal ulceration or chondritis of the arytenoid cartilages observed in yearling Thoroughbred horses. The population studied, however, may not accurately represent the population in which idiopathic disease occurs. In this study, arytenoid mucosal ulceration detected at sale did not commonly progress to arytenoid chondritis. However, a study of a larger population of horses with untreated, naturally occurring disease is required to confirm these findings.

CLINICAL RELEVANCE

It is unlikely that trauma from nasogastric intubation caused arytenoid mucosal ulceration, therefore this procedure should not necessarily be discouraged. This study did not find evidence that horses diagnosed with arytenoid mucosal ulceration at yearling sales had a reduced performance history, therefore it is reasonable to continue to pass horses with uncomplicated arytenoid mucosal ulceration during post-sale endoscopic examination. However, monitoring of the lesions and treatment, if required, may be indicated in the post-sale period.

Breath-hold device for laboratory rodents undergoing imaging procedures

The increased use in noninvasive imaging of laboratory rodents has prompted innovative techniques in animal handling. Lung imaging of rodents can be a difficult task because of tissue motion caused by breathing, which affects image quality. The use of a prototype flat-panel computed tomography unit allows the acquisition of images in as little as 2, 4, or 8 s. This short acquisition time has allowed us to improve the image quality of this instrument by performing a breath-hold during image acquisition. We designed an inexpensive and safe method for performing a constant-pressure breath-hold in intubated rodents. Initially a prototypic manual 3-way valve system, consisting of a 3-way valve, an air pressure regulator, and a manometer, was used to manually toggle between the ventilator and the constant-pressure breath-hold equipment. The success of the manual 3-way valve system prompted the design of an electronically actuated valve system. In the electronic system, the manual 3-way valve was replaced with a custom designed 3-way valve operated by an electrical solenoid. The electrical solenoid is triggered by using a hand-held push button or a foot pedal that is several feet away from the gantry of the scanner. This system has provided improved image quality and is safe for the animals, easy to use, and reliable.

Laryngeal mask airway insertion requires less propofol than endotracheal intubation in dogs

OBJECTIVE

To compare the doses of propofol required for insertion of the laryngeal mask airway (LMA) with those for endotracheal intubation in sedated dogs.

STUDY DESIGN

Randomized prospective clinical study. Animals Sixty healthy dogs aged 0.33-8.5 (3.0 +/- 2.3, mean +/- SD) years, weighing 2.2-59.0 (23.4 +/- 13.6, mean +/- SD) kg, presented for elective surgery requiring inhalation anaesthesia.

METHODS

Animals were randomly assigned to receive either a LMA or an endotracheal tube. Pre-anaesthetic medication was intravenous (IV) glycopyrrolate (0.01 mg kg(-1)) medetomidine (10 microg kg(-1)) and butorphanol (0.2 mg kg(-1)). Repeated IV propofol injections (1 mg kg(-1) in 30 seconds) were given until LMA insertion or endotracheal intubation was achieved, when the presence or absence of laryngospasm, the respiratory rate (fr) and the total dose of propofol used were recorded.

RESULTS

The total propofol dose (mean +/- SD) required for LMA insertion (0.53 +/- 0.51 mg kg(-1)) was significantly lower than for endotracheal intubation (1.43 +/- 0.57 mg kg(-1)). The LMA could be inserted without propofol in 47% of dogs; the remainder needed a single 1 mg kg(-1) bolus (n = 30). Endotracheal intubation was possible without propofol in 3.3% of the dogs, 47% needed one bolus and 50% required two injections (n = 30). The f(r) (mean +/- SD) was 18 +/- 6 and 15 +/- 7 minute(-1) after LMA insertion and intubation, respectively.

CONCLUSION AND CLINICAL RELEVANCE

Laryngeal mask airway insertion requires less propofol than endotracheal intubation in sedated dogs therefore propofol-induced cardiorespiratory depression is likely to be less severe. The LMA is well tolerated and offers a less invasive means of securing the upper airway.

Rat Intubation and Ventilation for Surgical Research

Effective outcomes in cardiothoracic surgical research using rodents are dependent upon adequate techniques for intubation and mechanical ventilation. Multiple methods are available for intubation of the rat; however, not all techniques are appropriate for survival studies. This article presents a refinement of intubation techniques and a simplified mechanical ventilation setup necessary for intrathoracic surgical procedures using volatile anesthetics. The procedure is defined and complications of the procedure are elucidated that provide a justification for animal numbers needed for initiating new studies. Lewis rats weighing 178-400 g (287 +/- 44) were anesthetized using Enflurane and intubated with a 16-G angiocatheter using transillumination. Mechanical ventilation (85 bpm, 2.5 mL TV, enflurane 1.5-2%) maintained adequate sedation for completion of an intrathoracic procedure. Complications of the intubation and ventilation included mortality from anesthetic overdose, intubation difficulty, pneumothorax, traumatic extubation, and ventilation disconnection. Anesthetic agents and their related effects on the rat heart and reflexes are compared. This article also underscores the importance of refinement, reduction, and replacement in the context of cardiothoracic surgery using rodent models.

A simple, inexpensive, and effective light- carrying laryngoscopic blade for orotracheal intubation of rats

The research paradigm of using large laboratory animals, in which oroendotracheal intubations are relatively easy, is shifting toward the use of small animals, such as rodents, in which oropharyngeal access is limited, the arytenoid cartilage cycles are faster, and the glottis is much smaller. The considerable growth recently seen in preclinical imaging studies is accompanied by an increased number of rats and mice requiring in vivo intubation for airway management. Tracheal access is important for ventilation, administration of inhaled anesthetics, instillation of drugs or imaging agents, and maintenance of airway patency to reduce mortality during and after operations. I fashioned a light-carrying laryngoscopic blade (laryngoscope) from readily available acrylic-polymethyl methacrylate tubing and used it to perform rapid, effective tracheal intubation in rats. The laryngoscope design and intubation techniques are presented.

Total intravenous anaesthesia in horses using medetomidine and propofol

OBJECTIVE

To examine the clinical suitability of medetomidine-propofol infusions for total intravenous anaesthesia in horses.

ANIMALS

Fifty client-owned horses of mixed breed, age [mean +/- SD (range)] 6.6 +/- 4.4 (0.04-18) years, mass 478 +/- 168.3 (80-700) kg presented for a range of operations requiring general anaesthesia.

MATERIALS AND METHODS

Pre-anaesthetic medication was intravenous (IV) medetomidine 7 mug kg(-1). Anaesthesia was induced with IV ketamine (2 mg kg(-1)) and diazepam (0.02 mg kg(-1)). After endotracheal intubation, O2 was delivered (FiO2 > 0.85). Positive pressure ventilation was initiated if breath-holding in excess of 1 minute occurred. Anaesthesia was maintained with a constant rate medetomidine infusion (3.5 microg kg(-1) hour(-1)) and propofol infused IV to effect (initial dose 0.1 mg kg(-1) minute(-1)). Heart (HR) respiratory (fr) and propofol administration rates, and systemic arterial blood pressures were recorded at 5-minute intervals. Arterial blood gas (O2 and CO2) tensions and pH values were recorded every 15 minutes. Ten minutes after ending medetomidine-propofol infusion, medetomidine (2 microg kg(-1); IV) was given. Cardiopulmonary data were analysed using descriptive statistical techniques.

RESULTS

Thirty-three orthopaedic, seven integumentary and 10 elective abdominal operations were performed. Cardiopulmonary data, presented as range of mean individual (and absolute individual minimum and maximum values) were: HR: 28.0-39.2 (16-88) beats minute(-1); mean arterial blood pressure: 74.0-132.5 (42-189) mmHg; PaO2: 22.1-42.9 (4.9-67.8) kPa; [166-322 (37-508) mmHg], PaCO2: 6.7-8.1 (4.2-11.8) kPa [50-61 (32-88) mmHg] and pH 7.35-7.39 (7.15-7.48). Positive pressure ventilation was required in 23 horses. In three horses, HR values below 20 beats minute(-1) were treated with 20 microg kg(-1) atropine (IV). Mean propofol infusion rates were 98-108 microg kg(-1) minute(-1). During anaesthesia, movement occurring in 14 horses was controlled with thiopental. Duration of anaesthesia was 111.6 +/- 41.4 (46-225) minutes. Recovery in all horses was uneventful and completed within 42.2 +/- 19.8 (12-98) minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Medetomidine-propofol infusion produces adequate conditions for a range of surgical procedures. Cardiovascular function was adequate, as no pressor agents were required. Positive pressure ventilation was required in 23 horses.

A simple device for intubation of rats

Endotracheal intubation of rats is often necessary for lengthy survival surgeries, but the animal's small size and the lack of suitable equipment may complicate the procedure. The authors describe the construction and use of a simple device for the easy intubation of rats, requiring no expensive, specialized equipment.