Steeplechase...? Flashcards
You have received a call to see a violently painful colic. Unfortunately your boss was so appalled at the state of your car he has arranged to have it valeted. Another car is available but has none of your kit inside. Fortunately there are spare items of equipment in the store room and pharmacy.
List the items you would need to take with you to ensure that you could cope with all situations in the treatment of a colic.
Medication
- Ensure that you have included an anti-spasmodic, a suitable NSAID, medications for sedation.
- You should ensure that you have means of euthanasing the horse.
Equipment
- Assortment of stomach tubes
- Bucket
- Funnel
- Graduated jug
- (Stirrup pump if available)
- Rectal gloves
- Obstetric lubricant
- Stethoscope
- Thermometer
- Teat cannula or needles of an appropriate size and gauge for performing an abdominocentesis (such as?)
- Sterile gloves
- Clippers (ideally cordless)
- Hibiscrub and cotton wool/swabs
- Plain and EDTA tubes
- Twitch
- Tail bandage
Ptosis is a common feature of horses suffering from grass sickness (equine dysautonomia). Hahn et al. proposed a simple diagnostic test for grass sickness involving the application of phenylephrine into one eye. If the ptosis is reversed (i.e. the angle of the eyelash becomes more horizontal with reference to the untreated eye) then this supports the diagnosis (see figure).
The method describes involves the application of 0.5ml of 5mg.ml-1 solution into one eye. It is very important the horse has not been sedated prior to this test. You have a 1ml syringe, a bag of saline solution and a bottle of phenylephrine eye drops (5%).
How would you make a solution of the appropriate concentration?
For what purpose is phenylephrine used as an ophthalmic preparation?
Why might it be effective at reversing ptosis?
What type of drug is phenylephrine? Which receptors does it act upon?)
A 5% solution is 50mg.ml-1
In 0.5ml of your eye drop solution you require 2.5mg, or 5mg in 1ml.
Therefore by drawing 0.1ml of phenylephrine solution into the syringe and diluting this with 0.9ml of saline you will have made the appropriate concentration to be administered to the horse’s eye.
Alpha 1 Adrenergic agonist
This picture shows an idiopathic focal eosinophilic enteritis lesion.
Describe the appearance of the intestine in this picture. Which region of gut is illustrated in this picture and how can you tell? Which section of intestine is oral and which is aboral.
Describe how the clinical signs exhibited by the horse will deteriorate over time if the horse if left untreated. What changes will occur in the gut without surgical treatment?
This is a section of jejunum. Of the three regions of small intestine in the horse only the ileum and jejunum may be exteriorised (the duodenum is fixed to the body wall with an attachment to the jejunum at the duodenocolic ligament). This region can be identified as the jejunum through the lack of an antimesenteric band (and continuation of the ileocaecal fold which can be traced from the dorsal band of the caecum). In addition the ileum has a single arterial and venous supply (the ileocaecal artery). This picture shows two arcuate vessels extending back to a single major jejuna vessel (top right). The arcuate vessels form a loop with vasa recta (meaning “straight vessel”) running to the mesenteric border of the jejunum.
The oral segment, which has become impacted with ingesta is to the right of the image. To the left is the empty aboral segment. This is how normal small intestine should appear (derived from the Latin jejunus meaning “empty” or “fasting”; the jejunum normally appears empty).
You are working in a practice which operates on a small number of colic cases. You are called to see a Thoroughbred cross weighing approximately 500kg which acutely showed violent signs of pain which began approximately one hour ago. The horse has a heart rate of 72 beats per minute with slightly congested, tacky mucous membranes. You are able to give the horse 200mg of xylazine which allows you to safely perform further examination. On rectal examination you can feel very tympanitic large colon extending back into the pelvic canal, and you are concerned that these may be consistent with a colon torsion. There is no response to the administration of 2g of phenylbutazone; however, the horse remains dull but does not continue to roll following the administration of 50mg of butorphanol.
The owner has transport available, and you call the partner who agrees to meet you at the practice. There is no-one else available apart from the nurse on call, and therefore it is up to you to anaesthetise the horse.
Explain how you would cope with the situation once the horse arrives at the practice. Suggest a suitable anaesthetic protocol for anaesthetising this animal.
The first priority once the horse arrives is to gain a suitable site of venous access. Once this has been achieved then you will be easily able to administer further analgesia or fluids if required. In addition, if the horse remains violently uncomfortable then anaesthesia can be induced.
The horse has already received a dose of non-steroidal analgesics, as well as a high dose of opioid. Further analgesia is therefore best achieved with α2-agonists such as xylazine.
List the common non-lethal congenital abnormalities which might cause colic in new born foals.
Common congenital abnormalities
Hernias - umbilical
scrotal/inguinal
diaphragmatic
Atresia coli, ani or recti
Describe how you might diagnose a case of atresia coli.
Atresia coli is suspected when there is no evidence of faecal staining around the anus, or palpable meconium within the rectum. The diagnosis can be achieved using positive contrast radiograpy.
Discuss what drugs you might use to sedate the foal.
In a new born foal it is best to avoid α2 agonists as animals of this age do not have a fully developed hepatic clearance system, or indeed neurological system. It is better to use benzodiazepines e.g. diazepam or midazolam.
You gently perform a digital exploration of the anus and discover a large amount of meconium impacted beyond your finger. Describe how you might attempt to manage this foal.
Critical when handlings any foals is to wear gloves and clean protective clothing at all times. Neonates are very susceptible to bacteraemia leading to septicaemia. The immunity passed on from the mother will be targeted at pathogens in the immediate environment, not those brought in on a large fomite such as yourself! Any venipuncture must be performed with significantly more care than on an adult horse which has an innate and functional immune system, and the site of jugular administration should be thoroughly aseptically prepared.
Management of meconium impactions is by the administration of an enema. Ideally the foal should be positioned in lateral recumbency with its hind quarters raised on a towel. A lubricated foley catheter is inserted into the anus and the enema solution is allowed to pass in using gravity only. A 50ml catheter tipped syringe is an ideal receiving vessel. The foal will often strain further as the rectum becomes further distended with fluid.
Several proprietary solutions are available which in general are phosphate buffered. Using acetylcysteine is perhaps the most useful enema compound, and may be mixed with sodium bicarbonate causing it to effervesce. This increases the mixing of the solution within the rectum. Acetylcysteine acts by breaking down disulphide bonds and thus has a mucolytic action (it is also used in the treatment of paracetamol poisoning by augmenting glutathione reserves in the body which are required to conjugate the toxic metabolite NAPQI).
What diagnostic tests might you choose to employ in a colicing foal. Are there any investigations that you should perform even if you are able to quickly resolve the signs of colic?
Further diagnostic tests might include radiography and ultrasonography. Generally once the impaction is cleared the foal becomes more comfortable.
It is very important that the levels of IgG are checked in the foal to ensure full passive transfer of immunity. This was traditionally performed by a zinc sulphate turbidity test; however, point of care ELISA tests (SNAP foal IgG test, IDEXX) are available which give an accurate assessment within 7 minutes.
How and when might cause colic Parascaris equorum. What age group of animal is typically affected?
These typically cause colic by means of an impaction due to rapid killing of all worms present within the SI following anthelmintic treatment. Typically this type of impaction has been associated with a poor prognosism even though they cause a simple obstruction with no ischaemic compromise of the intestine. It is possible that the dead worms release toxins which may adversely affect the young horse’s chance of survival, or that by the time surgery is performed there is significant hypovolaemic shock doe to sequestration of fluid. Ascarids may grow up to 50cm in length!
What other species of intestinal parasites are implicated in causing colic in horses (other than P.Equorum? What anthelmintics are effective against each type?
Small roundworms (cyathosomins), of which there are over 50 different species, are the most common equine parasite. The third larval stage in infective and following ingestion migrate to the intestinal wall. If large numbers of dormant larvae erupt at the same time, or are killed by anthelmintics then extensive damage may result. Small roundworms are implicated in spasmodic colics, intussusceptions and diarrhoea.
Large roundworms (S. vulgaris, S. edentatus) cause disease by larval migration into the arteries of the intestinal tract. With the advent of modern wormers, and strict regimens this is not commonly seen today.
Tapeworms (Anoplocephala perfoliata) is relatively short (up to 8cm) compared to tapeworms found in dogs, cats and humans (which can be in excess of 10m). They are generally found at the ileocaecal junction. Previously thought of as relatively harmless, they have since been shown to be important in the aetiology of several types of colic including ileal impaction and various forms of intussusception involving the ileum and caecum. The level of tapeworm burden can now be detected by means of an antibody ELISA.
Bots (Gastrophilus intestinalis) are parasites which attach to the mucosa of the non-glandular portion of the stomach. They are now significantly less common as a result of the advent of avermectin anthelmintics. May cause mild damage to the mouth, gums and gastric mucosa.
Pinworms (Oxyuris equi) are not thought to be harmful but may cause irritation are the anus and perineum. Found in the large and small colon and have a simple life cycle. Eggs produced by the female are coated with a sticky substance which causes irritation.
Benzimidazoles e.g. fenbendazole, mebendazole. Effective against adult small cyathostomins (5 day course of fenbendazole required to kill larval stages). Some resistance. No effect against tapeworms.
Avermectins – highly effective against roundworms, ivermectin has limited effect on inhibited mucosal stages. No efficacy against tapeworms.
Pyrantel – good against cyathostomins, not effective against encysted larval stages. Double dose (38mg/kg) is effective against tapeworms.
Praziquantel – effective treatment against tapeworms, no effect on roundworms.
All classes are effective against large Strongyles, Parascaris or Oxyuris unless stated.
You are in charge of the post-operative care of a horse which has recovered from gastrointestinal surgery. The horse is a 24 year Thoroughbred cross, weighing 450kg. A pedunculated lipoma was found to have incarcerate a short section of jejunum. In total 3m of small intestine were resected and a hand-sewn jejuno-jejunal anastomosis was performed.
Post operative parameters 4 hours after surgery are:
T 36.9°
P 72 beats per minute
R 24 breaths per minute
PCV 51%
TP 67g.L-1
You have been told that the horse should be kept on 1.5x maintenance fluids. What concerns might you have in this animal once normal circulating volume has been restored? With the drip set you are using, each drop is 0.1ml. What fluid rate should you set?
Calculate the fluid rate which you have been asked to keep this horse on
If the horse is estimated to have a 10% fluid deficit, what volume of fluids are required to replace this? How long would it take to replace this volume of fluid at 1.5x maintenance?
Estimates for maintenance fluid rates vary, but are typically around 60ml/kg/day for an adult or up to double this rate for a foal.
This equates to 2.5ml/kg/hour for maintenance rate, or 3.75ml/kg/h @ 1.5x maintenance
Therefore this horse requires 1687 ml per hour
or 28.1ml per minute
or 0.47 ml per second ≈ 0.5ml per second
Therefore this horse requires a drip rate of 5 drops per second
An estimate of 10% dehydration indicates that the overall fluid deficit of this horse in 45 litres (0.1x450). Assuming that there were no ongoing losses you would replace the fluid deficit at a rate of 1.25 ml/kg/h or 562ml/h. It will therefore take 80 hours to replace the horse’s fluid deficit.
Which region of the intestine is illustrated in this picture. How do you know?
What forms of colic are associated with this section of the intestine?
This is a section of small colon which can be determined by the prominent anti-mesenteric band. There is a second taenial band within the mesocolon. Anatomically this is the descending colon of the horse.
Common forms of colic associated with the small colon in the UK are:
- Strangulating lipoms
- Small colon impaction
- Volvulus, herniation and intussusceptions (as for the small intestine)
- Neoplasia
- Mesocolic rupture (seen typically in mares)
- Meconium impaction (foals)
- Atresia coli (foals)
- Faecolihts or other accumulations of organic and inorganic material
- Infarction
What is the course of ingesta from oesophagus through to the rectum in a horse? Describe each and every section of intestine that ingesta will pass through, and name each important junction, flexure or sphincter
- Oesophagus
- Cardiac sphincter
- Stomach
- Pyloric sphincter
- Duodenum
- Jejunum
- Ileum
- Ileocaecal junction
- Caecum
- Caecocolic junction
- Right ventral colon
- Sternal flexure
- Left ventral colon
- Pelvic flexure
- Left dorsal colon
- Diaphragmatic flexure
- Right dorsal colon
- Transverse colon
- Small colon (descending colon)
- Rectum
How many taenia does each section of the large intestine have? What is their role?
Caecum – four taenial bands
Ventral colon – four taenial bands (two free ventral bands, two dorsal bands associated with the mesentery, the media l dorsal band is associated with the colonic vasculature)
Pelvic flexure – one band, palpable on rectal examination
Left dorsal colon – one band
Right dorsal colon – three bands
Small colon – two bands
They provide mechanical support and maintain orientation of the colon. They are composed of smooth muscle and collagen in varying degrees. In the ventral colon, the main site of bacterial fermentation they have a higher proportion of elastin. In the right dorsal colon there is an increased proportion of smooth muscle to help regulate the passage on ingesta into the transverse colon.
What is this?
P. Equorum
