EQUINE | Proceedings
EQUINE | Proceedings
easily and it is frequently in excess of 5cm .
On the right side , the caecum is unexciting . Almost everyone who has heard about ultrasonography of the abdomen knows of its use for identifying intussusceptions – the “ target lesion ”. This is a very minor use of abdominal ultrasonography . Further cranially , between T 10 and 14 , there is an important window . Ventral to the lung field , the liver is easily visualised , and deep to this the right dorsal colon lies against the liver as an echogenic bright line . In right dorsal colitis the wall of the colon is obviously thicker in this site [ 2 ]. Between the colon and the liver , the duodenum can be seen . It is not always visible , hidden under the lung field at times . However , distension of the duodenum is usually clearly visible and is a cardinal sign of gastric distension and reflux .
Post operative ultrasonography has been one of the developments of recent years . Monitoring distension of the duodenum is very valuable in the management of ileus . We used to religiously follow the dogma of stomach tubing a horse every four hours , which is stressful for the horse and staff . We now scan the duodenum and only stomach tube if there is duodenal distension , or signs of abdominal pain , or an increasing heart rate . Intestinal motility can be assessed subjectively , simply by watching a patch of small intestine patiently . This can affect the decision to re-operate , or to advise a client about the economic impact of continued management .
Acid Base Status
You will all be familiar with the three rules of blood gas interpretation , p02 is proportional to shunting in the lungs , pC02 is proportional to alveolar ventilation , and the the Henderson Hasselbach equation concerning acid base balance . Notwithstanding that there are many “ apps ” now which will do the interpretation for you , acid base balance is still a minefield for the surgeon , with respiratory conditions superimposed on metabolic conditions . There is an easier way . As equine surgeons we are not usually that bothered by chronic lung disease , and our interest is metabolic acidosis ( or alkalosis ). Thus , rather than measuring the C02 levels , at considerable expense , we could just measure the metabolic acid .
Lactate is the product of anaerobic metabolism . Measurement of it has two principle uses – as a measure of tissue perfusion , and as a measure of aerobic fitness at intense exercise . Due to its latter use there is a large market for portable lactate analysers in human sports medicine , and they are relatively cheap and available . We use the EDGE analyser , which cost £ 300 , and the individual strips cost about £ 1 . The analyser is handheld , requires a drop of blood and gives a “ horse side ” result in a few seconds . Lactate can also be measured in peritoneal fluid using the same meter .
The meters actually measure plasma lactate and a correction factor is applied to account for the lower intracellular levels of lactate . Therefore calibration of the meters with each new batch of strips is recommended though is seldom practiced . Rapid ( horse side ) testing is necessary or the blood sample must be stored in a metabolic inhibitor ( fluoride oxalate or grey top ). More relevantly , the correction factor for plasma / intracellular lactate levels means that the reading is inaccurate with a PCV of greater than 53 %.
This can be relevant with severe colic cases and is important if the meter is used for exercise physiology or for monitoring more chronic cases , typically severe diarrhoea . The meters also underestimate lactate concentrations > 10mmol / l , but this degree of lactic acidosis is sufficient that the precise measurement is unnecessary . The use of lactate as a marker of severe disease , a prognostic indicator , and a trigger point for therapy has stood the test of time in human critical care [ 3 ].
Normal equine levels are between 0.6 and 1.5 mmol / l [ 4 ]. The traditional ( American ) units are mg / dl , and many
28 • Equine Health Update •