Glucostasis in equine patients

be regarded as one of the most stressful events in a horse’s life and the condition is rapidly fatal without intervention. Knowles and Mair (2009) present clinical data on an unusual case of total volvulus of the ascending colon associated with multiple mesenteric abnormalities in a yearling Friesian colt. Meckel’s diverticulum is the most common congenital anomaly of the human gastrointestinal tract, affecting 1–2% of the general population. Although a diverticulum of the small intestine was noted in 1598 by Fabricius Hildanus, the diverticulum is named after Johann Friedrich Meckel, who described its anatomy and embryology in 1809 (Geier et al. 2007). In comparison, it has been stated that mesodiverticular bands, which are remnants of the vitelline duct, are the most common congenital abnormalities of the intestine encountered during exploratory laparotomy in horses with colic (Edwards 2004) although Meckel’s diverticulum has also been reported in horses (Grant and Tennant 1973; Hooper 1989; Edwards 2004). However, the reported incidence of congenital abnormalities of the gastrointestinal tract of horses is very low (Edwards 2004). To differentiate between enteritis and strangulation as the cause of colic remains a challenge especially in nonadult horses. Although the clinical examination in the case reported failed to identify a definitive cause of the colic, surgery was fully justified on the basis of the continuous pain unresponsive to analgesic drugs. Remarkably, the possibility of an inflammatory component in the current case is not well appreciated in the discussion given the granulocytosis upon admission, the signs of acute inflammation on the serosal surface of the colon detected at post mortem examination and last but not least mucosal inflammation in the caecum found on histology. It underscores assessment of the rectal temperature as a cardinal parameter during clinical examination. The (secondary) involvement of bacterial pathogens such Salmonella and Clostridium spp. can not be excluded in the reported case. Transabdominal ultrasonography revealed small volumes of peritoneal fluid. Although abdominocentesis was not performed as it was considered unlikely to have altered the decision of whether to proceed with an exploratory laparotomy, there were certainly indications for it in order to evaluate possible inflammatory involvement (leucocyte count, leucocyte differentiation, protein content, the presence of bacteria with the option of culturing) and associated prognosis. On the other hand, abdominocentesis is also of interest regarding the prognosis in intestinal strangulation such as volvulus of the ascending colon. For example, colours of the peritoneal fluid other than yellow are associated with a poorer prognosis. In addition, peritoneal fluid lactate concentration may aid in early detection of intestinal ischaemia secondary to a strangulating obstruction. Horses with large colon ischaemia secondary to a strangulating obstruction had a higher peritoneal lactate concentration than those with nonstrangulating obstruction (8.09 ± 5.20 [n = 8] vs. 2.07 ± 2.37 [n = 60] mmol/l). Plasma lactate concentrations exceeded peritoneal fluid lactate (i.e. peritoneal:plasma lactate ratio <1.0) less frequently as peritoneal fluid lactate values increased (Latson et al. 2005). Stress activates the hypothalamo-pituitary-adrenal (HPA) axis, generating a cascade of hormonal messages from the hypothalamus to the pituitary which culminates in an increase in plasma cortisol concentration (Alexander et al. 1996). As preceded by the elevated plasma cortisol concentration, the plasma glucose concentration increases following acute stress either due to increased gluconeogenesis and/or decreased insulin sensitivity. Indeed, 21% of horses presenting with acute abdominal disease had ‘extreme hyperglycaemia’, defined as blood glucose concentrations above 10 mmol/l at admission with horses that did not survive to hospital discharge having a higher mean blood glucose concentration at admission (Hollis et al. 2007). This finding raises the question of who is afraid of hyperglycaemia in horses? First of all within the stress concept ‘extreme hyperglycaemia’ in horses suffering from colic reflects the severity of the disorder and indicates the urgency to eliminate its cause usually by surgical intervention. In addition, the excess of glucose will be eliminated via the urine associated with (transient) diuresis. On the other hand, many studies have shown an association between (short-term) hyperglycaemia and adverse outcome of a critical illness, both in adult and EQUINE VETERINARY EDUCATION Equine vet. Educ. (2009) 21 (8) 401-403 doi: 10.2746/095777309X443048 401