BACK TO BASICS: FOUNDATIONAL CLINICAL SKILLS FOR EQUINE PRACTICE


patient to various therapies. A minimum database on a blood sample from the acute abdomen case should include a manual packed cell volume and total solids, as well as an L-lactate concentration. The value in these parameters is to assess the patient’soverall hydration status (packed cell volume/total solids) and the patient’s ability to perfuse their tissues (L-lactate), as well as to assist in themedical versus surgical deci- sion-making process (discussed later). Additional lab work that may be useful in assessing the colicking horse include blood gas analysis (either venous or arte- rial—typically venous in an emergency triage situa- tion),measurement of serum/plasma electrolytes (most preferably to include ionized calcium), a serum bio- chemical profile (or components thereof—renal param- eters, liver enzymes, muscle enzymes, and protein differential), complete blood count, and peritoneal fluid analysis (discussed later).


Blood Gas Analysis


Most blood gas analyzers will includemeasurement of serum electrolytes, including ionized calcium. Some etiologies of colic can produce acid-base changes (e.g., hypochloremic metabolic alkalosis due to large vol- ume gastric reflux, metabolic acidosis due to colitis), which can be prognostic in nature or simply diagnostic of a change; correction of metabolic perturbations can reduce case fatality rate and/or make the patient a better anesthetic and surgical candidate. However, a complete review of acid-base interpretation and cor- rection of abnormalities is beyond the scope of this review.Measurement of ionized calciumcan be excep- tionally useful for the management of the colicking horse. Since calcium is required as part of the mecha- nism for smooth muscle contraction and ionized cal- cium is considered the biologically available or active fraction of total calcium, correction of hypocalcemia should be aggressive; a rule of thumb for calciumsup- plementation is 25 to 50mL of 23% calcium gluconate or calcium borogluconate per liter of isotonic crystal- loids since oversupplementation of calciumis unlikely due to efficient renal excretion of excessive calcium in an equine patient with otherwise appropriately func- tioning parathyroid and thyroid glands. Additionally, portable blood gas analyzers are widely available and can be used in the clinic, stall-side, and in an ambula- tory setting.


Biochemical Profile


The author reserves the biochemical profile (or the components therein as aforementioned) for when azo- temia may be suspected, helping to elucidate a medi- cal versus surgical lesion (discussed later) and helping to rule in or out forms of colic or other etiologies that may mimic gastrointestinal disease. As will be dis- cussed in the treatment section of these proceedings, NSAIDs are one of themainstays of analgesia for colic cases; however, it is widely recognized that NSAIDs are potentially nephrotoxic, especially in the face of dehydration. Therefore, if the practitioner feels as though it is clinically indicated, assessment of renal


192 2022 / Vol. 68 / AAEP PROCEEDINGS


values is recommended. Muscle enzyme assessment can help determine if the patient is experiencing rhab- domyolysis, whichmay be the primary problemor sec- ondary to the colic episode. The reader will recall that elevations in muscle enzymes can occur simply sec- ondarily to some of the signs that horses exhibit as a result of abdominal pain, such as rolling; however, the presence of firm musculature upon musculoskeletal palpation in conjunction with a stiff gait and elevated muscle enzymes in the absence of additional classic colic signs may be indicative of rhabdomyolysis as the primary medical issue. That said, the author rec- ommends (especially for liability purposes) for the workup and management to be exhaustive, particu- larly if the presenting complaint is colic. Muscle enzymes can also be helpful to elucidate a medical versus surgical lesion,whichwill be discussedmore in later sections. Evaluation of liver enzymes can also be useful for horses experiencing signs of colic. Horses with primary liver disease (e.g., hepatobiliary disease, cholelithiasis)may present as a colic; however, certain types of gastrointestinal lesionsmay also cause eleva- tions in liver enzymes, such as proximal enteritis2 and large colon displacements, especially right dorsal displacements.3


Complete Blood Count


Indications for a complete blood count would primar- ily include elevated rectal temperature (i.e., fever or hyperthermia) on presentation, the presence of diar- rhea, and/or the visualization of thickened or edema- tous intestinal walls on transabdominal ultrasound. In addition to rendering a proper diagnosis, the assessment of the patient’s leukogram is important for biosecurity, regardless of whether the patient is being assessed in the field or the hospital. Changes in the patient’s white blood cell count when evaluated in conjunction with these clinical signs can be indicative of a potentially infectious and/or contagious pathogen. Primary differentials for the aforementioned abnor- malities would be enteritis, colitis, and enterocolitis, in which case the leukogram will most likely reveal leukopenia characterized by a neutropenia and/or a lymphopenia with or without immature neutrophils, depending on the underlying etiology and the stage at which the patient presents, and may be an indication for isolation.


Abdominocentesis


The final clinicopathological data set thatmay be use- ful is peritoneal fluid analysis. Abdominocentesis can be performed inboththe hospital and field settings. Indications for abdominocentesis in horses with colic include a high degree of pain, ultrasonographic visual- ization of colonic vasculature in the right hemiabdo- men consistent with a right dorsal colon displacement or large colon volvulus, the presence of dilated loops of small intestine on transabdominal ultra- sound, thickened or edematous intestinal walls on transabdominal ultrasound, an increased quantity or abnormal echogenicity of peritoneal fluid on


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