Diagnostic tests


Use of diagnostic tests at the primary assessment of horses presenting with colic will depend on individual case circumstances, including case presentation, facilities available, financial considerations and any safety concerns


The three most commonly performed diagnostic tests at the primary assessment are:


Blood samples for haematology and biochemistry, abdominal paracentesis and ultrasonography are used less frequently on the primary assessment.


Conducting further diagnostic tests in ambulatory practice can be a challenge for veterinary practitioners with added safety concerns, financial considerations and limited facility availability. Two studies of how diagnostic tests are used in the primary assessment had very similar findings. One study was an online survey of veterinary practitioners' opinions, and the second was a prospective survey of the primary assessment of horses with colic ( Curtis et al. 2015, Trewin et al. 2015, Curtis and Freeman 2015).


Both studies identified that the most commonly used tests were response to analgesia/treatment, rectal examination, and nasogastric intubation. Blood samples for haematology and biochemistry, abdominal paracentesis and ultrasonography are used less frequently in the primary assessment.


Diagnostic tests 1 - printable


Regarding each of the above tests, recommendations from the consensus study are listed below:


Response to analgesia

Class Drug Dose Comments

NSAIDS


NSAIDs may be associated with gastrointestinal and renal toxicity. Injection with other anti-inflammatory drugs, such as other NSAIDs and corticosteroids, should be avoided.

Phenylbutazone 2.2-4.4mg/kg IV q12h  
Flunixin

0.55-1.1mg/kg IV q12-24h OR

0.5mg/kg IV q6h

Potent visceral analgesic and anti-inflammatory. Use high doses with care: may mask evidence of severe pain and delay onset of deteriorating clinical signs.
Ketoprofen 2.2mg/kg IV or IM q12-24h May be less analgesic than flunixin
Meloxicam 0.6-0.8mg/kg IV or IM q12h Very rapidly eliminated from the plasma in donkeys, and therefore may be impractical to administer in this species

Alpha-2 agonists


Alpha-2 agonists can cause cardiovascular depression and should be used with care in compromised patients. Administration of alpha-2 agonists causes reduced motility so should be used with care, and multiple doses in normal horses may lead to impactions.

Xylazine

0.2-0.8mg/kg IV (sedation)

0.5-2.2mg/kg IM (sedation)

 
Detomidine

0.004-0.02mg/kg IV (sedation)

0.02-0.05mg/kg IM

(sedation)

 
Romifidine

0.04-0.08mg/kg IV (sedation)

0.1-0.2mg/kg IM

(sedation)

 
Opioids Butorphanol 0.01-0.1mg/kg IV 0.04-0.2mg/kg IM Minimal analgesia at low doses. Potentiates sedative effect of alpha-2 agonists.
Pethidine 0.4-2.0mg/kg IM  

Drug doses: Corley and Stephen, Equine Hospital Manual, Blackwell Publishing


Response to analgesia table - printable


Rectal examination

Rectal examination should be considered (except where safety of horse or personnel is compromised):

  • In all cases with the evidence of severe pain on clinical examination
  • In any cases of colic which are suspected to be surgical or critical in nature
  • In all cases with a high heart rate on clinical examination
  • In all cases with a history and/or clinical signs or colic

Rectal examination may not be appropriate:

  • Where the vet considers there is an excessive risk to the vet, horse or handler
  • Where the vet considers there is an unacceptable risk of rectal tear


  • Lubrication should be used in every case prior to rectal examination
  • Owners should be informed immediately of any complications/tears

For a video on how to perform and interpret a rectal examination, please see the BI Academy website.


Rectal examination - printable


Information for owners on rectal examination can be found here: The BHS REACT Campaign


Nasogastric intubation

Nasogastric intubation should be considered (except where safety of horse or personnel is compromised):

  • In all cases with spontaneous reflux
  • In cases with distended small intestine on rectal examination
  • In suspected critical cases of colic
  • In cases showing signs of severe pain
  • In horses that require oral fluids
  • In cases with a high heart rate on clinical examination
  • As the first procedure performed in cases with sponataneous reflux
  • In cases with a primary impaction on rectal examination

Other factors to consider:

  • Nasogastric intubation should be the first procedure performed in cases with spontaneous reflux
  • Obtaining >2L of reflux in horse/pony is indicative of a critical or surgical case
  • It may require repeated attempts to access reflux
  • Owners can find the procedure of passing a nasogastric tube unpleasant or distressing, and therefore the procedure and any potential complications should be explained before it is performed

Nasogastric intubation - printable


Information for owners on nasogastric intubation can be found here: The BHS REACT Campaign


Abdominocentesis

Abdominocentesis should be considered (except where safety of horse or personnel is compromised):

  • In cases with suspected peritonitis
  • In cases with suspected intestinal rupture
  • In cases where it has not been possible to determine whether the case is surgical
  • In cases with suspected abdominal mass

Abdominocentesis may not be appropriate:

  • Where there is excessive risk to the horse, vet or handler
  • Where sterility may be compromised
  • Where this would delay referral


Where possible investigation should include:

  • Evaluation of gross appearance
  • Measurement of total protein
  • Measurement of white blood cells
  • Evaluation of cytology
  • Measurement of lactate concetration

Abdominocentesis - printable


Ultrasonography

Ultrasonography should be considered (except where safety of horse or personnel is compromised):

  • In foals where rectal examination cannot be performed
  • In small ponies where rectal examination cannot be performed safely
  • In cases with suspected abdominal mass
  • For identifying suitable sites for abdominocentesis
  • For suspected small intestinal lesions that cannot be palpated on rectal examination
  • Where it has not been possible to determine whether the case is medical or surgical
  • In suspected cases of enteritis
  • In suspected cases of peritonitis
  • Where the owner and/or vet requires further information before deciding on referral

Ultrasonography may not be appropriate:

  • Where there is excessive risk to the horse, vet or handler
  • Where there are limited facilites or equipment

Ultrasonography - printable



Sources of evidence


Prospective study of the primary evaluation of 1016 horses with clinical signs of abdominal pain by veterinary practitioners, and the differentiation of critical and non-critical cases.


Veterinary practitioners' selection of diagnostic tests for the primary evaluation of colic in the horse.


There is no level 1 or 2 evidence on the primary assessment of colic in the horse. The recommendations are based on outcomes of multi-disciplinary workshops and surveys of owners and veterinary practitioners with experience of colic. Statements were voted on by vets with experience of colic, accepted if >75% agreement on statements.