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Anaesthesia and Surgery - Small Mammals (view source)
Revision as of 07:28, 18 August 2011
, 07:28, 18 August 2011no edit summary
==Introduction==
==Introduction==
Because small mammals are prey species, they do not take to intensive conditions of surgery and hospitalisation very readily. Those that are handled very frequently by their owners are more bonded with humans and better surgical subjects as a result.
Because small mammals are prey species, they do not take to intensive conditions of surgery and hospitalisation very readily. Those that are '''handled very frequently''' by their owners are more bonded with humans and better surgical subjects as a result.
Rodents and rabbits are particularly susceptible to the surgical complications of dehydration (blood and fluid loss), core temperature depression, hypovolaemic shock, ileus and renal and respiratory depression.
Rodents and rabbits are particularly susceptible to the '''surgical complications''' of dehydration (blood and fluid loss), core temperature depression, hypovolaemic shock, ileus and renal and respiratory depression.
==Surgical Principles==
==Surgical Principles==
===Pre-operative preparation===
===Pre-operative preparation===
A thorough pre-operative examination is required, and may bring to light problems which means surgery has to be delayed.
A thorough '''pre-operative examination''' is required, and may bring to light problems which means surgery has to be delayed.
Pre-operative haematology, biochemistry and clotting times may be indicated if organ failure is suspected.
Pre-operative '''haematology, biochemistry''' and clotting times may be indicated if organ failure is suspected.
Pre-operative antibiosis can be considered in debilitated animals. Many small mammals have subclinical respiratory infections which can lead to problems during surgery and post-operatively.
'''Pre-operative antibiosis''' can be considered in debilitated animals. Many small mammals have subclinical respiratory infections which can lead to problems during surgery and post-operatively.
Hydration and nutritional shortfalls should be addressed, especially in cases which have had a prolonged history of anorexia due to dental disease for example.
'''Hydration and nutritional shortfalls''' should be addressed, especially in cases which have had a prolonged history of anorexia due to dental disease for example.
'''Starving''' is not usually necessary in small mammals due to their high metabolic rate. Rabbits cannot vomit and so food does not need to be withheld. There is often food in the oropharynx of these animals, and the mouth can be flushed out before anaesthetic induction to ensure a patent airway.
Preparation for surgery:
<u>Preparation for surgery</u>:
Small mammal fur (especially rabbits, chinchillas and ferrets) is usually quite difficult to clip, and can clog clippers, so special clippers should be used. The skin is very delicate and prone to tearing or developing clipper rash. The amount of fur clipped should be kept to a minimum.
'''Small mammal fur''' (especially rabbits, chinchillas and ferrets) is usually quite difficult to clip, and can clog clippers, so special clippers should be used. The skin is very delicate and prone to tearing or developing clipper rash. The amount of fur clipped should be kept to a minimum.
Clear self-adhesive plastic drapes are useful as they are lightweight and enable monitoring of the patient.
'''Clear self-adhesive plastic drapes''' are useful as they are lightweight and enable monitoring of the patient.
Antiseptic fluids used for aseptic preparation should be warmed before use, and alcohol-based antiseptics should be avoided as they lead to excess heat loss.
'''Antiseptic fluids''' used for aseptic preparation should be '''warmed''' before use, and alcohol-based antiseptics should be avoided as they lead to excess heat loss.
Care must be taken to avoid hyperthermia as well. Electric heat pads are prone to overheating, and surgeons tend to prefer hot water bottles or incandescent lights. Operating in a warm room with additional heat from the operating light is usually enough.
Care must be taken to avoid '''hyperthermia''' as well. Electric heat pads are prone to overheating, and surgeons tend to prefer hot water bottles or incandescent lights. Operating in a warm room with additional heat from the operating light is usually enough.
Rabbits are prone to developing respiratory distress at ambient temperatures above 25°c.
Rabbits are prone to developing '''respiratory distress''' at ambient temperatures above 25°c.
===Surgical technique===
===Surgical technique===
Haemostasis is very important in small mammals, as the loss of small volumes of blood is much more significant for them than in cats and dogs.
'''Haemostasis''' is very important in small mammals, as the loss of small volumes of blood is much more significant for them than in cats and dogs.
Haemostasis can be achieved by ligation, or using vascular clips. Diathermy units are also popular.
Haemostasis can be achieved by ligation, or using vascular clips. Diathermy units are also popular.
Choice of suture material and method of closure:
'''Choice of suture material and method of closure:'''
Rabbits readily develop caseous suppurative responses to foreign bodies and suture material like catgut. Polyglycolic acid sutures cause the least reaction. The size of the suture material is also important, and fine instruments and material should be used.
Rabbits readily develop '''caseous suppurative responses''' to foreign bodies and suture material like catgut. Polyglycolic acid sutures cause the least reaction. The '''size''' of the suture material is also important, and fine instruments and material should be used.
Rabbits and rodents are very likely to groom skin sutures out if left above the surface of the skin. Subcuticular suture patterns and a buried knot, such as the Aberdeen knot, are recommended.
Rabbits and rodents are very likely to '''groom skin sutures''' out if left above the surface of the skin. Subcuticular suture patterns and a buried knot, such as the '''Aberdeen knot''', are recommended.
Tissue glue can be used in some cases, such as rodent castration.
'''Tissue glue''' can be used in some cases, such as rodent castration.
==Anaesthesia Principles==
==Anaesthesia Principles==
===Analgesia===
This is essential for any anaesthetic procedure, as small mammals do not show signs of pain very well and it may go unnoticed.
Analgesia can be given '''pre-operatively''' to pre-emp the painful surgery.
Drug available include:
'''Opiates''': pethidine, buprenorphine
'''NSAIDs''': meloxicam, carprofen
'''Local anaesthetics''': lidocaine, bupivicaine (low safety margin), EMLA cream for venepuncture.
===Intubation===
===Intubation===
This can be difficult in small mammals, but it provides access to the airways and is preferable in all cases.
This can be '''difficult''' in small mammals, but it provides access to the airways and is preferable in all cases.
In rabbits, intubation is difficult due to: large tongue and cheek teeth, small airway, large epiglottis, acute angle between mouth and larynx, prone to laryngospasm.
In '''rabbits''', intubation is difficult due to: large tongue and cheek teeth, small airway, large epiglottis, acute angle between mouth and larynx, prone to laryngospasm.
It can be done blind, which requires practice, or visually using an otoscope.
It can be done '''blind''', which requires practice, or '''visually''' using an otoscope.
Most smaller rodents are not intubated, but techniques have been described.
Most smaller rodents are not intubated, but techniques have been described.
Ferret intubation is usually straightforward, after spraying the epiglottis with lignocaine.
'''Ferret intubation''' is usually straightforward after spraying the epiglottis with lignocaine.
===Considerations during surgery===
===Considerations during surgery===
Position is important, as most small mammals have a significant weight in their abdominal viscera which may press against the diaphragm and cause breathing difficulties. They should be positioned with the thorax slightly above the abdomen to avoid this problem.
'''Position''' is important, as most small mammals have a significant weight in their abdominal viscera which may press against the diaphragm and cause breathing difficulties. They should be positioned with the '''thorax slightly above the abdomen''' to avoid this problem.
Eye lubricants should be used to protect the eyes as they are often bulging.
'''Eye lubricants''' should be used to protect the eyes as they are often bulging.
===Monitoring===
===Monitoring===
The best monitoring equipment is a '''nurse's close observation'''. '''Written records''' allow trends to be seen and provide a reference if problems occur.
'''Eye reflexes''' are difficult to monitor as the pupillary response is lost when ketamine is used.
The '''depth and pattern of breathing''' gives information on: the depth of anaesthesia, the level of analgesia, respiratory problems.
But it can be hard to monitor due to a high respiratory rate in small mammals.
The '''pedal withdrawal''' response is lost at medium and deep planes of anaesthesia.
'''Cardiac monitoring''' is important, and a sudden tachycardia may indicate an inadequate plane of anaesthesia.
'''Temperature monitoring''' is essential: all anaesthetics depress thermoregulation, and some cause peripheral vasodilation. Opening body cavities and removing fur removes insulation, and water loss from lungs and viscera removes heat.
'''Other monitoring''' equipment that can be used includes: oesophageal stethoscope, capnography, doppler.
===Anaesthetic protocols===
===Anaesthetic protocols===
In all cases the animal should be weighed to gain an accurate figure and to avoid over or under-dosing.
In all cases the animal should be '''weighed''' to gain an accurate figure and to avoid over or under-dosing.
====Rabbits====
====<u>Rabbits</u>====
Rabbits breath-hold if a face mask or an induction chamber is used, and so these methods are not preferred.
Rabbits breath-hold if a '''face mask or an induction chamber''' is used, and so these methods are not preferred.
'''Pre-medicants''' such as diazepam or acepromazine can be used in particularly nervous or fractious animals.
'''Medetomidine and ketamine''' provide good surgical anaesthesia and will enable intubation.
The '''triple combination''' of: medetomidine, ketamine and butorphanol is useful for short procedures and prior to anaesthetic maintenance.
'''Fentanyl and fluanisone''' ('Hypnorm') can be combined with diazepam.
'''Inhalation agents''' include isoflurane and sevoflurane. Sevoflurane is the agent of choice if chamber induction is essential, as it is less likely to irritate the airways.
====<u>Guinea-pigs</u>====
Xylazine can be combined with ketamine and given i/m or s/c, but this can lead to a prolonged recovery.
Guinea pigs can also be anaesthetised in an induction chamber with isoflurane, after several minutes of pre-oxygenation.
====<u>Chinchillas</u>====
'''Ketamine and acepromazine''' i/m or s/c works well but can also lead to a prolonged recovery.
Inducing with '''isoflurane''' in an induction chamber is also possible.
====<u>Other Rodents</u>====
'''Isoflurane induction''' and maintenance is the method of choice.
Various injectable combinations can be injected intraperitoneally, but the response is variable and there is little control over the depth of anaesthesia.
====<u>Ferrets</u>====
'''Medetomidine and ketamine''' can be given s/c. A small amount of isoflurane may be necessary to allow intubation.
Maintenance is with '''isoflurane''', and antipamezole can be given to reverse the medetomidine, given at the same volume of medetomidine that was injected.
Alternatively, '''acepromazine''' can be given as a premedicant, and the ferret can be masked down with isoflurane.
'''Propofol''' can be used if an intra-venous line is available.
{{Learning
|flashcards = [[Small Mammals Q&A 14]]
}}
====Guinea-pigs====
==References==
Malley, D. (2010) '''Anaesthesia and analgesia of rabbits''' ''RVC student notes''
Sayers, I. (2010) '''Rabbit Surgery''' ''RVC Elective student notes''
Lewis, W. (2010) '''Small Mammals''' ''RVC Elective student notes''
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