Laboratory Animals (1992) 26, 25-28
An improved method the guineapig
25
for direct laryngeal intubation
in
M. A. TURNER, P. THOMAS & D. J. SHERIDAN Academic Cardiology Unit, St Mary's Hospital Medical School, QEQM Wing, South Wharf Road, London W21NY, UK
Summary A novel method of direct laryngeal intubation in the guineapig, using a modified laryngoscope blade, is described. The method has been used in over 400 animals and has proved suitable for recovery procedures and repeated intubation. Keywords: Anaesthesia; Guineapigs; Intubation; Laryngoscope
Direct laryngeal intubation of small laboratory animals, for example the rabbit, has been well described (Freeman et al., 1972; Lindquist, 1972; Davis & Malinin, 1974; Schuyt & Leene, 1977; Brown, 1983; Fick & Schalm, 1987), whilst few methods for oral intubation in the guineapig have been recorded. The anatomy of the buccal cavity and pharynx of the guineapig makes this procedure difficult, and therefore alternative procedures such as tracheostomy have tended to be used. In our laboratory we have developed a method of supravalvular aortic constriction in guineapigs to produce a model of chronic heart failure over 150-200 days (Sheridan et al., 1988; Thomas et al., 1988) employing a modification of a method described by Ling & deBold (1976). Initially, intubation was undertaken by tracheostomy but ingress of blood and tissue fluids into the trachea, despite placing absorbent swabs around the tracheostome, resulted in an unacceptably high morbidity and mortality from respiratory complications. This was further compounded by trauma due to the dissection of the neck. Received 25 June 1990; accepted 3 June 1991
It has been previously suggested that tracheostomy should not be the procedure of choice when recovery is intended; oral intubation being preferable (Galla, 1976). Brown (1983) found that although tracheostomy was satisfactory for acute experimental procedures, it resulted in complications from infection and tracheal obstruction when the animals were allowed to recover. A method described for use in rabbits by Bertolet & Hughes (1990), using a guide wire passed into the trachea through a percutaneous needle, which then acts as a guide for passage of an endotracheal tube, was not considered suitable in the guineapig. In order to reduce these complications we sought a method of direct laryngeal intubation. Preliminary attempts using a straight-bladed Miller laryngoscope as described for intubating rabbits (Lindquist, 1972; Davis & Malinin, 1974; Schuyt & Leene, 1977) were unsuccessful. The long and narrow buccal cavity which contains a relativelylarge tongue was unable to accommodate the large blade and bulky 'pea-type' bulb without causing tissue injury or compromising visibility. These difficulties were overcome by using a modified laryngoscope blade fitted with fibre optic illumination, thus reducing the area taken up by the b~lb inside the mouth, and by shaping the tip and lateral edges of the blade. Greater manoeuvrability was achieved, enabling retraction of the epiglottis whilst illuminating the proximal trachea. We have no experience of using other methods of endotracheal intubation in the guineapig, yet we feel this technique has advantages over others described (for example, Blouin & Cormier, 1987;
Downloaded from lan.sagepub.com at UNIV OF NORTH DAKOTA on June 7, 2015
26
Turner, Thomas & Sheridan
Kujime & Natelson, 1981), as it employs a commercially available laryngoscope which can be easily modified. Extensive workshop equipment, expertise, extra ancillary equipment or assistants are not needed and the intubation skill is easily acquired. Materials and methods Male Dunkin-Hartley strain, barrier-maintained guineapigs (Harlan-Porcellus Ltd, Sussex, UK) weighing between 550-900 g were used for the study. These animals were housed for 1-2 weeks prior to surgery in solid floored pens (Modular Systems & Development Company Ltd, London, UK) 52 x 85 x 25 cm and housed in single cages (North Kent Plastics Ltd, Kent, UK) 54 x 37 x 25 cm postoperatively with autoclaved meadow hay and sawdust bedding. Animals had unrestricted movement within the cages at all times. The room temperature was maintained at 20 ± 2°, relative humidity held at 50 ± 5OJo and the room subjected to a light/dark cycle of 13 h light, 11 h dark. All animals received RGP diet (Biosure Ltd, Cambridgeshire, UK) and fresh water ad libitum, neither were restricted pre- or postoperatively. Normal body temperature was maintained in all animals undergoing surgery by means of heating lamps positioned near the animals; operations were performed using an aseptic technique. Anaesthesia was induced using a 1 : 1 mixture of 02/N20 at a flow rate of 11/ min, in addition to 4OJo halothane, via a conical face mask placed over the animal's head and continued until response to hindlimb pinch stimuli had diminished. A standard anaesthetic apparatus (model 3000, Gardner Medical Engineering Ltd, Oxfords hire, UK) was used for gas delivery, Halothane ('Fluothane', ICI Ltd, Cheshire, UK) was introduced into the system via a calibrated vaporiser (Fluotec-Cyprane Ltd, West Yorkshire, UK). The animals were then placed on the operating table in the prone position at eye level facing the operator. The mouth of the guinea pig was opened using the left hand and the laryngoscope was introduced using the right hand. The laryngoscope used was a straight Miller size 0
Fig. 1. Photograph of laryngoscope blade as viewed from above.
Neonatal blade, with a fibre optic illumination conduit (Welch Allyn Inc., Skaneateles Falls, NY, USA). An 8 mm X 2 mm section had been removed from each side of the blade as shown in Figs 1 and 2. The blade was inserted over the dorsum of the tongue and advanced to the epiglottis. At this stage the upper incisors rested on the cross bar of the blade retracting the jaws open, thus freeing the left hand for further manipulations. On retraction of the epiglottis downward with the tip of the blade the proximal trachea was revealed. Mucus and ingesta were removed from the pharynx using a sterile 10 FG suction catheter (Portex Ltd, Kent, UK) attached to a vacuum pump (Aerosol Products Ltd, London, UK). The pharynx was sprayed with lignocaine ('Xylocaine spray', Astra Ltd, Kings Langley, UK) and 30-60 s later the excess fluid was removed by suction. Using the left hand, the endotracheal tube, attached to an intermediate adaptor, was
L--J
1 em
Fig. 2. Diagram of blade, dotted line indicating shape prior to shaping.
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Intubation of the guinea pig
27
1cm
-
A
B
c
Fig. 3. Endotracheal tubes used in intubation of guineapigs. (A) A 2·0 Fa Neonatal endotracheal tube used for animals > 800 g. (B) 12 a i. v. Cannula sheath used for animals 600-800 g. (C) 14 a Lv. Cannula sheath used for animals 500-600 g. Connector for tubes to ventilator shown on right.
positioned between the abducted chords and advanced into the trachea. The endotracheal tube comprised of a plastic sheath taken from a 14 G intravenous cannula (' Argyle Medicut', Sherwood Inc., Tullamore, Ireland). The adaptor comprised of a 2 cm length of silastic tubing attached to a luer lock connector. Each tube was bevelled to a 45° angle at the tip and was slightly curved along its length, as shown in Fig. 3. If resistance was felt, the tube was rotated slightly, giving a smooth atraumatic passage down the trachea. Correct placement of the tube into the trachea was ascertained by the detection of air passing through the tube during the animal's respirations. Failure to detect respirations via the tube indicated incorrect intubation, the tube was then removed and the procedure repeated. The animals were then placed into the supine position and connected to a pressure-controlled small animal ventilator (model 50-1916, Harvard Apparatus Ltd, Kent, UK). The ventilator delivered oxygen to the animal at
set at a flow rate of 0·4l/min. Halothane was introduced as necessary to maintain adequate anaesthesia. Following the surgical procedure, animals were continued on intermittent positive pressure ventilation until spontaneous breathing occurred. Animals were then disconnected from the ventilator, placed into the prone position and oxygen at 1-1 . 5l/min was administered via the face mask. Mucus and ingesta were removed from the pharynx by suction. Animals were then extubated and further suction applied as considered necessary. To preclude postoperative hypothermia animals were placed into an opentopped rodent cage, where body temperature was maintained using an overhead heating lamp. A single dose of buprenorphine ('Temgesic' , Reckitt & Coleman, Hull, UK) was given by subcutaneous injection (0' 05 mg/kg) and each animal was observed for an hour before it was introduced into a single cage to resume postoperative recovery. Results and discussion We have intubated over 400 animals using this method, which has provided effective ventilation during thoracotomy. Reintubation has been carried out at intervals following the surgical procedure for monitoring purposes using the same technique. In larger animals (> 800 g) we have used a 12 G cannula sheath with success. We have employed a 2·0 FG endotracheal tube ('Blue Line', Portex Ltd, Kent, UK), cut at 5 ,75 cm from the tip and cemented onto a plastic luer hub fitting for use in animals weighing over I kg, with no complications encountered (see Fig. 3). Once the procedure had been perfected, . all of the animals could be intubated on the first attempt, intubation took no longer than 60 s to perform, considerably faster than performing a tracheostomy.
100 cycles/min, giving an intermittent positive
It should be noted that animals are placed in
pressure of 5 and 20 cm of water. The pressure preset control knob on the ventilator was set at the minimum position allowing the inflation pressure to be controlled using oxygen from the anaesthetic apparatus to the ventilator, and was
the prone position as opposed to the usual accepted supine position, whilst intubating. The procedure can be achieved quicker and easier in the prone position, it places less strain on the lower jaw of the animal and allows the trachea
Downloaded from lan.sagepub.com at UNIV OF NORTH DAKOTA on June 7, 2015
Turner, Thomas & Sheridan
28
to be kept in straight alignment along its length, in contrast to being deflected upwards whilst in supine position. Additionally, the risk of over-extension of the neck, in order to view the trachea is precluded. Trauma to the pharynx and glottis was minimal when observed directly following extubation and repeated intubation caused no complications. Postmortem dissection of the upper airways has rarely shown any macroscopic trauma. It is widely acknowledged that the guineapig poses problems for the anaesthetist, the reaction to a given anaesthetic is extremely variable between individuals, the choice of injectable or inhalation anaesthetics can be contradictory with regard to route, dosage and efficacy, a knowledge of its physiological effect on the animal should be sought before use. Halothane, along with other halogenated volatile inhalational agents, carry the risk of provoking cardiorespiratory depression, their use should always be accompanied with adequate ventilation and monitoring of heart rate. The anaesthetic or combination of anaesthetic best suited to the surgical procedure should be used in all cases. This method of inhalation anaesthesia should be combined with a pre-anaesthetic sedative if
it is thought the procedure would stress the animals unduly, as may occur whilst learning the technique. Animals are less likely to wake up during the intubation procedure if given preanaesthetic sedation, such as those described and recommended by Green (1981). A pre-anaesthetic dose of Atropine (0'05 mg/ kg) given by intramuscular injection 30 min prior to intubation did not prevent mucus secretion and in concurrence with Green, atropine was found to exacerbate tracheal and bronchal occlusion by producing a more viscid mucus which proved difficult to aspirate. The modified laryngoscope blade described enables atraumatic, efficient intubation of the guineapig. Administration of an inhalation anaesthetic, to give a controllable, reversible level of anaesthesia can be achieved, thereby reducing the problems associated with using less predictable injectable anaesthetic agents. The use of inhalational anaesthetic agents, irrespective of the concentration and length of exposure should only be used in areas with adequate ventilation served with an efficient anaesthetic scavenging system to minimalize the risk to the operator.
References Bertolet RD & Hughes HC (1980) Endotracheal intubation: an easy way to establish a patent airway in rabbits. Laboratory Animal Science 30, 227-230 Blouin A & Cormier Y (1987) Endotracheal Intubation in Guinea Pigs by Direct Laryngoscopy. Laboratory Animal Science 37, 244-245 Brown PM (1983) A laryngoscope for use in rabbits. Laboratory Animals 17, 208-209 Costa DL, Lehmann JR, Harold WM & Drew RT (1986) Transoral tracheal intubation of rodents using a fibreoptic laryngoscope. Laboratory Animal Science 36, 256-261 Davis NL & Malinin TI (1974)Rabbit intubation and halothane anesthesia. Laboratory Animal Science 24, 617-621 Flick TE & Schalm SW (1987) A simple technique for endotracheal intubation in rabbits. Laboratory Animals 21, 265-266 Freeman MJ, Bailey SP & Hodesson S (1972) Premedication, tracheal intubation and methoxyflurane anesthesia in the rabbit. Laboratory Animal Science 22, 576-580 Galla SJ (1969) Techniques of anaesthesia. Federation Proceedings 28, 1404-1409
Green CJ (1981) Animal Anaesthesia. Theydon Bois, Essex: Laboratory Animals Ltd Kujime K, Natelson BH (1981)A method for endotracheal intubation of guinea pigs. Laboratory Animal Science31,78-79 Lindquist PA (1972) Induction of methoxyflurane anesthesia in the rabbit after ketamine hydrochloride and endotracheal intubation. Laboratory Animal Science 22, 898-899 Ling ET & deBold AJ (1976) An improved method for the production of experimental heart failure in the guinea pig. Laboratory Animals 10, 285-289 Schuyt HC, Leene W (1977) An improved method of tracheal intubation in the rabbit. Laboratory Animal Science 27, 690-693 Sheridan DJ, Thomas P & Turner MA (1988)Characterisation of haemodynamic, electrocardiographic and respiratory changes in a model of chronic congestive heart failure in the anaesthetised guinea pig. Journal of Physiology 403, 83 Thomas P, Turner MA & Sheridan DJ (1988) Temporal changes in haemodynamic and respiratory characteristics of a model of chronic heart failure. Medical Research Society 75, 30
Downloaded from lan.sagepub.com at UNIV OF NORTH DAKOTA on June 7, 2015
An improved method the guineapig
25
for direct laryngeal intubation
in
M. A. TURNER, P. THOMAS & D. J. SHERIDAN Academic Cardiology Unit, St Mary's Hospital Medical School, QEQM Wing, South Wharf Road, London W21NY, UK
Summary A novel method of direct laryngeal intubation in the guineapig, using a modified laryngoscope blade, is described. The method has been used in over 400 animals and has proved suitable for recovery procedures and repeated intubation. Keywords: Anaesthesia; Guineapigs; Intubation; Laryngoscope
Direct laryngeal intubation of small laboratory animals, for example the rabbit, has been well described (Freeman et al., 1972; Lindquist, 1972; Davis & Malinin, 1974; Schuyt & Leene, 1977; Brown, 1983; Fick & Schalm, 1987), whilst few methods for oral intubation in the guineapig have been recorded. The anatomy of the buccal cavity and pharynx of the guineapig makes this procedure difficult, and therefore alternative procedures such as tracheostomy have tended to be used. In our laboratory we have developed a method of supravalvular aortic constriction in guineapigs to produce a model of chronic heart failure over 150-200 days (Sheridan et al., 1988; Thomas et al., 1988) employing a modification of a method described by Ling & deBold (1976). Initially, intubation was undertaken by tracheostomy but ingress of blood and tissue fluids into the trachea, despite placing absorbent swabs around the tracheostome, resulted in an unacceptably high morbidity and mortality from respiratory complications. This was further compounded by trauma due to the dissection of the neck. Received 25 June 1990; accepted 3 June 1991
It has been previously suggested that tracheostomy should not be the procedure of choice when recovery is intended; oral intubation being preferable (Galla, 1976). Brown (1983) found that although tracheostomy was satisfactory for acute experimental procedures, it resulted in complications from infection and tracheal obstruction when the animals were allowed to recover. A method described for use in rabbits by Bertolet & Hughes (1990), using a guide wire passed into the trachea through a percutaneous needle, which then acts as a guide for passage of an endotracheal tube, was not considered suitable in the guineapig. In order to reduce these complications we sought a method of direct laryngeal intubation. Preliminary attempts using a straight-bladed Miller laryngoscope as described for intubating rabbits (Lindquist, 1972; Davis & Malinin, 1974; Schuyt & Leene, 1977) were unsuccessful. The long and narrow buccal cavity which contains a relativelylarge tongue was unable to accommodate the large blade and bulky 'pea-type' bulb without causing tissue injury or compromising visibility. These difficulties were overcome by using a modified laryngoscope blade fitted with fibre optic illumination, thus reducing the area taken up by the b~lb inside the mouth, and by shaping the tip and lateral edges of the blade. Greater manoeuvrability was achieved, enabling retraction of the epiglottis whilst illuminating the proximal trachea. We have no experience of using other methods of endotracheal intubation in the guineapig, yet we feel this technique has advantages over others described (for example, Blouin & Cormier, 1987;
Downloaded from lan.sagepub.com at UNIV OF NORTH DAKOTA on June 7, 2015
26
Turner, Thomas & Sheridan
Kujime & Natelson, 1981), as it employs a commercially available laryngoscope which can be easily modified. Extensive workshop equipment, expertise, extra ancillary equipment or assistants are not needed and the intubation skill is easily acquired. Materials and methods Male Dunkin-Hartley strain, barrier-maintained guineapigs (Harlan-Porcellus Ltd, Sussex, UK) weighing between 550-900 g were used for the study. These animals were housed for 1-2 weeks prior to surgery in solid floored pens (Modular Systems & Development Company Ltd, London, UK) 52 x 85 x 25 cm and housed in single cages (North Kent Plastics Ltd, Kent, UK) 54 x 37 x 25 cm postoperatively with autoclaved meadow hay and sawdust bedding. Animals had unrestricted movement within the cages at all times. The room temperature was maintained at 20 ± 2°, relative humidity held at 50 ± 5OJo and the room subjected to a light/dark cycle of 13 h light, 11 h dark. All animals received RGP diet (Biosure Ltd, Cambridgeshire, UK) and fresh water ad libitum, neither were restricted pre- or postoperatively. Normal body temperature was maintained in all animals undergoing surgery by means of heating lamps positioned near the animals; operations were performed using an aseptic technique. Anaesthesia was induced using a 1 : 1 mixture of 02/N20 at a flow rate of 11/ min, in addition to 4OJo halothane, via a conical face mask placed over the animal's head and continued until response to hindlimb pinch stimuli had diminished. A standard anaesthetic apparatus (model 3000, Gardner Medical Engineering Ltd, Oxfords hire, UK) was used for gas delivery, Halothane ('Fluothane', ICI Ltd, Cheshire, UK) was introduced into the system via a calibrated vaporiser (Fluotec-Cyprane Ltd, West Yorkshire, UK). The animals were then placed on the operating table in the prone position at eye level facing the operator. The mouth of the guinea pig was opened using the left hand and the laryngoscope was introduced using the right hand. The laryngoscope used was a straight Miller size 0
Fig. 1. Photograph of laryngoscope blade as viewed from above.
Neonatal blade, with a fibre optic illumination conduit (Welch Allyn Inc., Skaneateles Falls, NY, USA). An 8 mm X 2 mm section had been removed from each side of the blade as shown in Figs 1 and 2. The blade was inserted over the dorsum of the tongue and advanced to the epiglottis. At this stage the upper incisors rested on the cross bar of the blade retracting the jaws open, thus freeing the left hand for further manipulations. On retraction of the epiglottis downward with the tip of the blade the proximal trachea was revealed. Mucus and ingesta were removed from the pharynx using a sterile 10 FG suction catheter (Portex Ltd, Kent, UK) attached to a vacuum pump (Aerosol Products Ltd, London, UK). The pharynx was sprayed with lignocaine ('Xylocaine spray', Astra Ltd, Kings Langley, UK) and 30-60 s later the excess fluid was removed by suction. Using the left hand, the endotracheal tube, attached to an intermediate adaptor, was
L--J
1 em
Fig. 2. Diagram of blade, dotted line indicating shape prior to shaping.
Downloaded from lan.sagepub.com at UNIV OF NORTH DAKOTA on June 7, 2015
Intubation of the guinea pig
27
1cm
-
A
B
c
Fig. 3. Endotracheal tubes used in intubation of guineapigs. (A) A 2·0 Fa Neonatal endotracheal tube used for animals > 800 g. (B) 12 a i. v. Cannula sheath used for animals 600-800 g. (C) 14 a Lv. Cannula sheath used for animals 500-600 g. Connector for tubes to ventilator shown on right.
positioned between the abducted chords and advanced into the trachea. The endotracheal tube comprised of a plastic sheath taken from a 14 G intravenous cannula (' Argyle Medicut', Sherwood Inc., Tullamore, Ireland). The adaptor comprised of a 2 cm length of silastic tubing attached to a luer lock connector. Each tube was bevelled to a 45° angle at the tip and was slightly curved along its length, as shown in Fig. 3. If resistance was felt, the tube was rotated slightly, giving a smooth atraumatic passage down the trachea. Correct placement of the tube into the trachea was ascertained by the detection of air passing through the tube during the animal's respirations. Failure to detect respirations via the tube indicated incorrect intubation, the tube was then removed and the procedure repeated. The animals were then placed into the supine position and connected to a pressure-controlled small animal ventilator (model 50-1916, Harvard Apparatus Ltd, Kent, UK). The ventilator delivered oxygen to the animal at
set at a flow rate of 0·4l/min. Halothane was introduced as necessary to maintain adequate anaesthesia. Following the surgical procedure, animals were continued on intermittent positive pressure ventilation until spontaneous breathing occurred. Animals were then disconnected from the ventilator, placed into the prone position and oxygen at 1-1 . 5l/min was administered via the face mask. Mucus and ingesta were removed from the pharynx by suction. Animals were then extubated and further suction applied as considered necessary. To preclude postoperative hypothermia animals were placed into an opentopped rodent cage, where body temperature was maintained using an overhead heating lamp. A single dose of buprenorphine ('Temgesic' , Reckitt & Coleman, Hull, UK) was given by subcutaneous injection (0' 05 mg/kg) and each animal was observed for an hour before it was introduced into a single cage to resume postoperative recovery. Results and discussion We have intubated over 400 animals using this method, which has provided effective ventilation during thoracotomy. Reintubation has been carried out at intervals following the surgical procedure for monitoring purposes using the same technique. In larger animals (> 800 g) we have used a 12 G cannula sheath with success. We have employed a 2·0 FG endotracheal tube ('Blue Line', Portex Ltd, Kent, UK), cut at 5 ,75 cm from the tip and cemented onto a plastic luer hub fitting for use in animals weighing over I kg, with no complications encountered (see Fig. 3). Once the procedure had been perfected, . all of the animals could be intubated on the first attempt, intubation took no longer than 60 s to perform, considerably faster than performing a tracheostomy.
100 cycles/min, giving an intermittent positive
It should be noted that animals are placed in
pressure of 5 and 20 cm of water. The pressure preset control knob on the ventilator was set at the minimum position allowing the inflation pressure to be controlled using oxygen from the anaesthetic apparatus to the ventilator, and was
the prone position as opposed to the usual accepted supine position, whilst intubating. The procedure can be achieved quicker and easier in the prone position, it places less strain on the lower jaw of the animal and allows the trachea
Downloaded from lan.sagepub.com at UNIV OF NORTH DAKOTA on June 7, 2015
Turner, Thomas & Sheridan
28
to be kept in straight alignment along its length, in contrast to being deflected upwards whilst in supine position. Additionally, the risk of over-extension of the neck, in order to view the trachea is precluded. Trauma to the pharynx and glottis was minimal when observed directly following extubation and repeated intubation caused no complications. Postmortem dissection of the upper airways has rarely shown any macroscopic trauma. It is widely acknowledged that the guineapig poses problems for the anaesthetist, the reaction to a given anaesthetic is extremely variable between individuals, the choice of injectable or inhalation anaesthetics can be contradictory with regard to route, dosage and efficacy, a knowledge of its physiological effect on the animal should be sought before use. Halothane, along with other halogenated volatile inhalational agents, carry the risk of provoking cardiorespiratory depression, their use should always be accompanied with adequate ventilation and monitoring of heart rate. The anaesthetic or combination of anaesthetic best suited to the surgical procedure should be used in all cases. This method of inhalation anaesthesia should be combined with a pre-anaesthetic sedative if
it is thought the procedure would stress the animals unduly, as may occur whilst learning the technique. Animals are less likely to wake up during the intubation procedure if given preanaesthetic sedation, such as those described and recommended by Green (1981). A pre-anaesthetic dose of Atropine (0'05 mg/ kg) given by intramuscular injection 30 min prior to intubation did not prevent mucus secretion and in concurrence with Green, atropine was found to exacerbate tracheal and bronchal occlusion by producing a more viscid mucus which proved difficult to aspirate. The modified laryngoscope blade described enables atraumatic, efficient intubation of the guineapig. Administration of an inhalation anaesthetic, to give a controllable, reversible level of anaesthesia can be achieved, thereby reducing the problems associated with using less predictable injectable anaesthetic agents. The use of inhalational anaesthetic agents, irrespective of the concentration and length of exposure should only be used in areas with adequate ventilation served with an efficient anaesthetic scavenging system to minimalize the risk to the operator.
References Bertolet RD & Hughes HC (1980) Endotracheal intubation: an easy way to establish a patent airway in rabbits. Laboratory Animal Science 30, 227-230 Blouin A & Cormier Y (1987) Endotracheal Intubation in Guinea Pigs by Direct Laryngoscopy. Laboratory Animal Science 37, 244-245 Brown PM (1983) A laryngoscope for use in rabbits. Laboratory Animals 17, 208-209 Costa DL, Lehmann JR, Harold WM & Drew RT (1986) Transoral tracheal intubation of rodents using a fibreoptic laryngoscope. Laboratory Animal Science 36, 256-261 Davis NL & Malinin TI (1974)Rabbit intubation and halothane anesthesia. Laboratory Animal Science 24, 617-621 Flick TE & Schalm SW (1987) A simple technique for endotracheal intubation in rabbits. Laboratory Animals 21, 265-266 Freeman MJ, Bailey SP & Hodesson S (1972) Premedication, tracheal intubation and methoxyflurane anesthesia in the rabbit. Laboratory Animal Science 22, 576-580 Galla SJ (1969) Techniques of anaesthesia. Federation Proceedings 28, 1404-1409
Green CJ (1981) Animal Anaesthesia. Theydon Bois, Essex: Laboratory Animals Ltd Kujime K, Natelson BH (1981)A method for endotracheal intubation of guinea pigs. Laboratory Animal Science31,78-79 Lindquist PA (1972) Induction of methoxyflurane anesthesia in the rabbit after ketamine hydrochloride and endotracheal intubation. Laboratory Animal Science 22, 898-899 Ling ET & deBold AJ (1976) An improved method for the production of experimental heart failure in the guinea pig. Laboratory Animals 10, 285-289 Schuyt HC, Leene W (1977) An improved method of tracheal intubation in the rabbit. Laboratory Animal Science 27, 690-693 Sheridan DJ, Thomas P & Turner MA (1988)Characterisation of haemodynamic, electrocardiographic and respiratory changes in a model of chronic congestive heart failure in the anaesthetised guinea pig. Journal of Physiology 403, 83 Thomas P, Turner MA & Sheridan DJ (1988) Temporal changes in haemodynamic and respiratory characteristics of a model of chronic heart failure. Medical Research Society 75, 30
Downloaded from lan.sagepub.com at UNIV OF NORTH DAKOTA on June 7, 2015
