Are IV fluids useful for the treatment of large colon impactions?

Abstract

Large colon impactions, defined as an accumulation of dehydrated ingesta (Plummer 2009), are a common cause of colic in the horse. The aetiology of colon impactions is not fully understood, although a dysfunction of intestinal motility has been suggested as have other management changes that lead to fluid shifts out of the large colon (Dabareiner and White 1995). Treatment of affected horses involves rehydration of ingesta whilst withholding feed and providing analgesia. Rehydration of ingesta is typically performed by administering fluids via nasogastric tube or intravenously; suggested to create a state of systemic overhydration and promote colonic secretion. Intravenous fluids are more expensive than oral fluids, require intravenous catheterisation and adequate facilities for fluid delivery, therefore it is important to critically evaluate the evidence pertaining to their use. Do intravenous fluids reduce treatment time when managing large colon impactions in the horse? Large colon impaction AND horse AND fluids Colonic hydration AND horse AND fluids Search one yielded 5 results of which 2 (Dabareiner and White 1995; Hallowell 2008) were relevant. Due to the relative paucity of clinical evidence, a further search was undertaken to include experimental studies of normal colon physiology, yielding 3 additional references (Lopes et al. 2002, 2004; Lester et al. 2013). Both Dabareiner and White (1995) and Hallowell (2008) are retrospective studies of hospital admissions, as such treatments were not randomly allocated and results are subject to selection bias and unblinded evaluation. Despite this Hallowell demonstrated no difference in admission data between treatment groups suggesting groups may be comparable. Treatment protocols were standardised in Hallowell's work with patients receiving one of 4 treatment protocols (IVFT or 3 different rates of nasogastric fluids), whereas treatments were not standardised by Dabareiner and White. See Table 1. Both Dabareiner and White (1995) and Hallowell (2008) included horses with naturally occurring large colon impactions, although cases were possibly more severe than encountered in first opinion practice given the referral population. In both studies fluids rates administered were comparable to those achievable in practice. Unfortunately the lack of an untreated control group means that it is not possible to determine if the use of intravenous fluids was beneficial. Three prospective cross-over studies investigating the effect of intravenous fluid therapy on hydration of colonic ingesta and faeces in clinically normal horses were identified (Lopes et al. 2002, 2004; Lester et al. 2013). In these studies each horse acted as its own control, treatment were standardised and order administered randomised, therefore the quality of evidence is higher. Although no untreated control group is present in 2 of these studies (Lopes et al. 2002; Lester et al. 2013) baseline levels of faecal hydration prior to interventions being performed are used to determine outcome. See Table 2. 1. IVFT + 1 g/kg bwt MgSO4 2. Oral fluids and MgSO4 10 l/h (16.8–22.8) ml/kg bwt/h for 6 h 1. IVFT 2. MgSO4 per os 3. NaSO4 per os 4. Water per os 5. Balanced electrolytes per os 6. No treatment The 2 studies by Lopes and co-workers were performed in clinically normal horses with right dorsal colon fistulation, without impactions of the large colon. How the results relate to the clinical case with a large colon impaction and disturbed gastrointestinal physiology is difficult to extrapolate. Lester et al. (2013) attempted to address this by withholding water for 24 h prior to comparing treatment effects, this resulted in an approximate 5–8% reduction in faecal water content. All 3 studies monitored change in faecal water content as their major outcome; however, the magnitude of change in faecal water content required to significantly contribute to the resolution of an impaction is unknown. The administration of 10 l/h (17–23 ml/kg bwt/h) of IVFT resulted in increases in faecal water content in healthy normovolaemic horses after 6 h, whilst this was not achieved at a lower dose of 5 l/h (9–11 ml/kg bwt/h) after 12 h. Increases in the faecal water content were observed in dehydrated horses treated with lower doses of IVFT (2, 4 and 6 ml/kg bwt/h). Intravenous fluids are beneficial in rehydrating the ingesta of the normal and dehydrated large colon, whether this translates to a clinical benefit in the treatment of the horse with a large colon impaction has not been established. A randomised prospective clinical trial to evaluate the use of different doses of i.v. fluids is required and study design would ideally include an untreated control group, although this may be ethically challenging to include. No conflicts of interests have been declared.