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.

Spontaneous resolution of iatrogenic chylothorax in a cat

Chylothorax is an uncommon condition of dogs and cats defined by the accumulation of chylous effusion within the pleural space. Chylothorax has been experimentally created in dogs and cats by ligation of the cranial vena cava and has been reported to occur spontaneously in dogs with naturally occurring obstruction of the cranial vena cava. In the cat of this report, iatrogenic chylothorax was caused by surgical ligation and transection of the left brachiocephalic vein during a tracheal resection and anastomosis procedure. The chylous effusion resolved with medical management 9 weeks after surgery.

A novel method for endotracheal intubation of mice and rats used in imaging studies

A safe and efficient method for endotracheal intubation was needed to mechanically ventilate mice and rats for various research projects. We developed an easy, reliable, and expeditious method for intubating these rodents. Inexpensive disposable Teflon intravenous catheters are used as endotracheal tubes. Both mice and rats are anesthetized using a combination of injectable and inhalational anesthetics before intubation. A relatively inexpensive custom-designed fiber-optic light guide and battery-powered light source allows visualization of the oropharynx for quick and easy intubation. The fiber-optic light guide has two functions: 1) the light guide transports light from the illuminator to the tip of the fiber for direct visualization of the larynx, and 2) the fiber is used as a stylet to stiffen the Teflon catheter. Direct illumination of the larynx allows its clear visualization and makes the procedure easier and more efficient and, as a result, less traumatic to the animals. This method has been easy to learn, and it allows repeated intubations, even in debilitated or dyspneic animals, for respiratory-gated, noninvasive imaging procedures. With it, we can acquire higher-quality images with fewer motion artifacts than we could before.

Noninvasive mechanical ventilation of mice by using a balloon-tipped cannula

Cardiovascular research in mouse models can lead to respiratory insufficiency with the need for temporary mechanical ventilation to reduce mortality. We developed a noninvasive method for brief ventilation in which a balloon-tipped cannula is inserted into the oral cavity of the mouse. The rubber balloon is constructed in such a way that it becomes inflated when the pressure in the tube rises. We tested the cannula in ten C57BL/6J mice which underwent mechanical ventilation by a membrane-pump-driven ventilator. Results of blood gas analyses in the ten cannulated animals were in the normal range after 1 h of mechanical ventilation and did not differ significantly from those of anesthetized and spontaneously breathing mice (n = 5) and mice mechanically ventilated via tracheal intubation (n = 5). Noninvasive mechanical ventilation by using the balloon-tipped cannula is a useful method which is quick and easy to manipulate.

Severe hypoxaemia in field-anaesthetised white rhinoceros (Ceratotherium simum) and effects of using tracheal insufflation of oxygen

White rhinoceros anaesthetised with etorphine and azaperone combination develop adverse physiological changes including hypoxia, hypercapnia, acidosis, tachycardia and hypertension. These changes are more marked in field-anaesthetised rhinoceros. This study was designed to develop a technique to improve safety for field-anaesthetised white rhinoceros by tracheal intubation and oxygen insufflation. Twenty-five free-ranging white rhinoceros were anaesthetised with an etorphine and azaperone combination for translocation or placing microchips in their horns. Once anaesthetised the rhinoceros were monitored prior to crating for transportation or during microchip placement. Physiological measurements included heart and respiratory rate, blood pressure and arterial blood gas samples. Eighteen rhinoceros were intubated using an equine nasogastric tube passed nasally into the trachea and monitored before and after tracheal insufflation with oxygen. Seven rhinoceros were not intubated or insufflated with oxygen and served as controls. All anaesthetised rhinoceros were initially hypoxaemic (percentage arterial haemoglobin oxygen saturation (%O2Sa) = 49% +/- 16 (mean +/- SD) and PaO2 = 4.666 +/- 1.200 kPa (35 +/- 9 mm Hg)), hypercapnic (PaCO2 = 8.265 +/- 1.600 kPa (62 +/- 12 mm Hg)) and acidaemic (pHa = 7.171 +/- 0.073 ). Base excess was -6.7 +/- 3.9 mmol/l, indicating a mild to moderate metabolic acidosis. The rhinoceros were also hypertensive (systolic blood pressure = 21.861 +/- 5.465 kPa (164 +/- 41 mm Hg)) and tachycardic (HR = 107 +/- 31/min). Following nasal tracheal intubation and insufflation, the %O2Sa and PaO2 increased while blood pHa and PaCO2 remained unchanged. Tracheal intubation via the nose is not difficult, and when oxygen is insufflated, the PaO2 and the %O2Sa increases, markedly improving the safety of anaesthesia, but this technique does not correct the hypercapnoea or acidosis. After regaining their feet following reversal of the anaesthesia, the animals' blood gas values return towards normality.

Evaluation of laryngeal mask as an alternative to endotracheal intubation in cats anesthetized under spontaneous or controlled ventilation

OBJECTIVE

To compare the cardiorespiratory effects and incidence of gastroesophageal reflux with the use of a laryngeal mask airway (LMA) or endotracheal tube (ET) in anesthetized cats during spontaneous (SV) or controlled ventilation (CV).

STUDY DESIGN

Prospective randomized experimental trial.

ANIMALS

Thirty-two adult crossbred cats, weighing 2.7 +/- 0.4 kg.

METHODS

The cats were sedated with intramuscular (IM) methotrimeprazine (0.5 mg kg(-1)) and buprenorphine (0.005 mg kg(-1)), followed 30 minutes later by induction of anesthesia with intravenous (IV) thiopental (12.5-20 mg kg(-1)). An ET was used in 16 cats and an LMA in the remaining 16 animals. Anesthesia was maintained with 0.5 minimum alveolar concentration (0.6%) of halothane in oxygen using a Mapleson D breathing system. Cats in both groups were further divided into two equal groups (n = 8), undergoing either SV or CV. Neuromuscular blockade with pancuronium (0.06 mg kg(-1)) was used to facilitate CV. Heart and respiratory rates, direct arterial blood pressure, capnometry (PE'CO2) and arterial blood gases were measured. Gastric reflux and possible aspiration was investigated by intragastric administration of 5 mL of radiographic contrast immediately after induction of anesthesia. Cervical and thoracic radiographs were taken at the end of anesthesia. Data were analyzed using anova followed by Student-Newman-Keuls, Kruskal-Wallis or Friedman test where appropriate.

RESULTS

Values for PaCO2 and PE'CO2 were higher in spontaneously breathing cats with the LMA when compared with other groups. Values of PaO2 and hemoglobin oxygen saturation did not differ between groups. Gastroesophageal reflux occurred in four of eight and two of eight cats undergoing CV with ET or LMA, respectively. There was no tracheal or pulmonary aspiration in any cases.

CONCLUSIONS AND CLINICAL RELEVANCE

The use of an LMA may be used as an alternative to endotracheal intubation in anesthetized cats. Although aspiration was not observed, gastric reflux may occur in mechanically ventilated animals.

Unstable endobronchial intubation in a cat undergoing tracheal laceration repair

A peri-carinal tracheal laceration was produced in a 11-year-old cat during tracheal intubation. Before reconstructive surgery began, the leak was bypassed with an endobronchial tube positioned using endoscopy and direct vision. However, single-lung ventilation could not be sustained because the tube became dislodged and could not be repositioned. Consequently, surgery was completed with periods of intermittent apnoea interspersed with manually controlled hyperventilation. Cardiovascular variables were stable during anaesthesia and no signs of hypoxia were detected. The difficulties in maintaining endobronchial tube position resulted from the animal's small size relative to the dimensions of the endotracheal tube.

Endotracheal tubes versus laryngeal mask airways in rabbit inhalation anesthesia: ease of use and waste gas emissions

In this study, we compared two endotracheal tubes (cuffed [Murphy Eye type] and uncuffed [Cole type]) and a pediatric laryngeal mask airway (LMA) with respect to their ease of use in rabbits and their capacities to limit waste isoflurane emissions. Animals (New Zealand White, 3.3 to 5.0 kg, n = 8) were sedated with intramuscular ketamine (50 mg/kg) and xylazine (10 mg/kg). After 5 min, the larynx was numbed with cetocaine, an intubation device was positioned, and anesthesia was maintained with isoflurane (2%) in oxygen (1 liter/min). Real-time atmospheric isoflurane emissions were assessed at the rabbit's oral commissure and in the operator's breathing zone (45 cm from the rabbit's nose) by using a portable infrared spectrophotometer. The LMA was placed more easily than was either endotracheal tube, especially by novices. The cuffed tube was positioned more readily than was the uncuffed variant. All three devices emitted isoflurane. The concentrations measured at the oral commissure for the LMA (mean +/- standard error, 8.4 +/- 0.6 ppm) were modestly higher than those acquired for the cuffed (6.7 +/- 0.5 ppm) and uncuffed (6.3 +/- 0.4 ppm) endotracheal tubes; the difference between the LMA and uncuffed tube was significant (P = 0.012). Isoflurane was not detected in the operator's breathing zone. These data show that the uncuffed endotracheal tube (usually used to anesthetize birds and reptiles) and the pediatric LMA can be used in rabbits as readily as a cuffed tube. In addition, our findings indicate that tradeoffs will be required in selecting a delivery system for this species, as the easiest apparatus (the LMA) also emits the most isoflurane waste.

Midazolam/ketamine induction and isoflurane maintenance of anaesthesia in a 2-month-old, hand-raised African buffalo (Syncerus caffer)

The use of a midazolam/ketamine combination for induction of anaesthesia in a 2-month-old, hand-raised buffalo calf (Syncerus caffer) is described to allow endotracheal intubation for the maintenance of anaesthesia with isoflurane and oxygen. Intraoperative complications were hypotension and hypothermia. For postoperative analgesia meloxicam and butorphanol was administered intramuscularly.

Mouse cardiac surgery: comprehensive techniques for the generation of mouse models of human diseases and their application for genomic studies

Mouse models mimicking human diseases are important tools in trying to understand the underlying mechanisms of many disease states. Several surgical models have been described that mimic human myocardial infarction (MI) and pressure-overload-induced cardiac hypertrophy. However, there are very few detailed descriptions for performing these surgical techniques in mice. Consequently, the number of laboratories that are proficient in performing cardiac surgical procedures in mice has been limited. Microarray technologies measure the expression of thousands of genes simultaneously, allowing for the identification of genes and pathways that may potentially be involved in the disease process. The statistical analysis of microarray experiments is highly influenced by the amount of variability in the experiment. To keep the number of required independent biological replicates and the associated costs of the study to a minimum, it is critical to minimize experimental variability by optimizing the surgical procedures. The aim of this publication was to provide a detailed description of techniques required to perform mouse cardiac surgery, such that these models can be utilized for genomic studies. A description of three major surgical procedures has been provided: 1) aortic constriction, 2) pulmonary artery banding, 3) MI (including ischemia-reperfusion). Emphasis has been placed on technical procedures with the inclusion of thorough descriptions of all equipment and devices employed in surgery, as well as the application of such techniques for expression profiling studies. The cardiac surgical techniques described have been, and will continue to be, important for elucidating the molecular mechanisms of cardiac hypertrophy and failure with high-throughput technology.

NEGATIVE-PRESSURE PULMONARY EDEMA COMPLICATED BY ACUTE RESPIRATORY DISTRESS SYNDROME IN AN ORANGUTAN (PONGO PYGMAEUS ABELII)

A 22-yr-old, 86-kg, morbidly obese female orangutan (Pongo pygmaeus abelii) was immobilized and transported to the Denver Zoological Gardens hospital for a routine physical examination. Immediately after arriving at the hospital, cyanosis and apparent inadequate ventilatory efforts were noted. Clinically significant hypoxia occurred despite attempts to ventilate the orangutan through face mask, and attempts to place an endotracheal tube began. A large volume of pink-tinged frothy fluid flowed from the trachea when the laryngoscope was inserted into the oropharynx. Severe pulmonary edema due to negative-pressure pulmonary edema, precipitating life-threatening hypoxia was suspected. The orangutan was maintained on a mechanical ventilator using the neuromuscular blocking agent cisatracurium besylate and sedation with periodic doses of isoflurane and midazolam for 48 hr. Positive end-expiratory pressure was used while the orangutan was ventilated mechanically to improve respiratory function. The edema and hypoxia improved, but respiratory arrest ensued 30 min after extubation, when the orangutan was removed from mechanical ventilation. Necropsy and histopathology demonstrated that serious lung injury had led to acute respiratory distress syndrome.

Minimum alveolar concentration of sevoflurane in spontaneously breathing llamas and alpacas

OBJECTIVE

To determine the minimum alveolar concentration (MAC) of sevoflurane in spontaneously breathing llamas and alpacas.

DESIGN

Prospective study.

ANIMALS

6 healthy adult llamas and 6 healthy adult alpacas.

PROCEDURE

Anesthesia was induced with sevoflurane delivered with oxygen through a mask. An endotracheal tube was inserted, and a port for continuous measurement of end-tidal and inspired sevoflurane concentrations was placed between the endotracheal tube and the breathing circuit. After equilibration at an end-tidal-to-inspired sevoflurane concentration ratio > 0.90 for 15 minutes, a 50-Hz, 80-mA electrical stimulus was applied to the antebrachium until a response was obtained (ie, gross purposeful movement) or for up to 1 minute. The vaporizer setting was increased or decreased to effect a 10 to 20% change in end-tidal sevoflurane concentration, and equilibration and stimulus were repeated. The MAC was defined as the mean of the lowest end-tidal sevoflurane concentration that prevented a positive response and the highest concentration that allowed a positive response.

RESULTS

Mean +/- SD MAC of sevoflurane was 2.29 +/- 0.14% in llamas and 2.33 +/- 0.09% in alpacas.

CONCLUSIONS AND CLINICAL RELEVANCE

The MAC of sevoflurane in llamas and alpacas was similar to that reported for other species.

Video-assisted orotracheal intubation in mice

Orotracheal intubation in mice is a complicated technique because of the peculiar oropharyngeal anatomy and the difficulty in visualizing the laryngis aditus. Here we report a new and simple method for rapid endotracheal intubation by using a small bore, straight fibre-optic arthroscope. Under endoscope-assisted visualization of the laryngis aditus, a polyethylene cannula, inserted on a guide-wire in order to facilitate the introduction of the tip across the vocal cords, was advanced in the trachea. The success rate of intubation was 100%. We were also able to re-intubate the mice 4 and 8 weeks later without any major complications. We conclude that this method can be easily and safely used for studies where controlled pulmonary ventilation is necessary.

Provision of anaesthesia for porcine cardiac transplantation at the veterinary school in Trinidad and Tobago

A successful heterotopic cardiac transplantation was performed between sibling female Yorkshire Juvenile swine. Adequate pre-medication with azaperone and a smooth induction were ensured for both pigs, which were anaesthetized simultaneously with sodium thiopentone followed by endotracheal intubation and intermittent positive pressure ventilation. Inhalation anaesthetic agents were used for maintenance, neuromuscular blockade was achieved with cisatracurium and both fentanyl and tramadol were used to provide analgesia. Invasive monitoring was used in both the donor and recipient. Central venous pressure (CVP) was maintained at > 10 cm H2O and mean arterial pressure (MAP) > 60 mmHg. Heparin was injected during the surgical dissection of the heart in the donor to prevent coronary thrombosis and prior to aortic side clamping for end-to-side anastomosis of the donor heart in the recipient abdomen. After transplantation, the cardiovascular parameters of the recipient showed a MAP of 85-105 mmHg and a CVP of 8-10 cm H2O while echocardiography of the transplanted heart confirmed an ejection fraction (EF) of 80%. A functional anaesthetic team was assembled and trained to provide anaesthesia for porcine cardiac transplantation. The transplanted heart suffered pump failure after 69 days and was excised for performance of tissue analysis.

Use of rocuronium for endotracheal intubation of North American Gulf Coast box turtles

OBJECTIVE

To determine whether rocuronium, a reversible neuromuscular blocking agent, would provide safe, short-term immobilization to facilitate endotracheal intubation in turtles.

DESIGN

Prospective study.

ANIMALS

30 healthy adult Gulf Coast box turtles.

PROCEDURE

Turtles were given rocuronium, and responses were recorded every 3 minutes. Times to onset of effects, intubation, and recovery were recorded and analyzed for associations with dose and patient characteristics to determine an optimal dose range. Neostigmine and glycopyrrolate were given to augment recovery from neuromuscular blockade.

RESULTS

Rocuronium administered at a dose of 0.25 to 0.5 mg/kg (0.11 to 0.23 mg/lb), IM, permitted intubation; lower doses were not effective. Mean +/- SD time to loss of the palpebral reflex was 6.4 +/- 4.0 minutes, and mean time to intubation was 9.2 +/- 6.4 minutes. Mean time to return of the palpebral reflex was 44 +/- 13.2 minutes, and mean time to walking was 55 +/- 16.6 minutes. Time to onset of effects was not associated with dose, but recovery times were prolonged with higher doses of rocuronium. Cardiac arrhythmias were observed in 13 (43%) turtles.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of rocuronium at a dose of 0.25 to 0.5 mg/kg is a safe and effective adjunct to general anesthesia in Gulf Coast box turtles. Because rocuronium does not provide any analgesic or sedative effects, the duration of neuromuscular blockade without anesthesia should be minimized to avoid undue distress.

Successful management of long-term general anesthesia in rabbits used as an animal model of human disease

The rabbit represents a popular animal model for basic science research, but projects requiring anesthesia and endotracheal intubation represent a technical challenge because of the difficulty in accessing the animal's airway and sensitivity to common anesthetic agents. We hypothesized that transoral intubation under direct visualization with guidewire assistance would improve airway access success and reduce perioperative mortality in the rabbit. Of the 39 New Zealand White rabbits that had passive inhalation anesthesia and were intubated using wire-guided assistance under direct laryngeal visualization, 33 were intubated using a flexible wire after the rigid guide had resulted in airway injury in three of the first six rabbits. Animals were then maintained under general anesthesia during a 4- to 5-h procedure. At the completion of the procedure, animals were recovered from anesthesia and extubated. All 39 animals were successfully intubated, mostly on the first attempt. There were two animal deaths, both in the first six animals; one death was a direct result of laryngeal injury from the rigid wire guide initially used. One additional animal in the first six had pulmonary difficulty after an airway injury but recovered and was successfully used in the experiment. Two animals developed gastric distention during anesthesia, which was alleviated with placement of an orogastric tube without adverse sequelae. No animals developed problems with oxygenation during the experiment, but over half (52.8%) had end-tidal CO2 (ETCO2) above 45 mmHg at least once during the surgery, and 13 rabbits were above this level for longer than 1 h. An average of 18 min elapsed between withdrawal of anesthesia and the time when spontaneous respirations and chewing movements returned. Animals then could be safely extubated. There was no correlation between high perioperative ETCO2 and time to recovery from anesthesia (P = 0.18, r = 0.23).