Equine Health Update EHU Vol 19 Issue 3 - Page 29

EQUINE | Proceedings lactate meters will display the result in this format – the conversion is mg/dl x 0.111 = mmol/l, close enough to be very worrying if you are presented with a horse with a lactate of 10… - 5 mmol/l likely to need surgery with a reasonable out- come, 5 - 8 mmol/l likely to be expensive, > 8mmol/l, deep trouble. There have been numerous studies linking lactate levels with prognosis. A simple summary is that lactate lev- els rise in ischaemic disease (but not exclusively). The higher levels are usually associated with more marked disease and a worse chance of survival. [5] reported that no horses with a level >8mmol/l survived. The odds of non survival increase by 29% for each mmol/l increase in lactate concentration at admission [6]. Sequential lactate levels are invaluable in monitoring progress, and give clients valuable information to balance economics against success during critical care. For each mmol/l in- crement, at 12 hours the risk or mortality increased 3.84 x, at 24 hours 5.62 x and at 72 hours 49.9 x [6]. Another parameter easily measured with a point of care meter is glucose. Hyperglycaemia is much more com- mon than hypo, and is a mark of critical disease. Hy- perglycemia in the first 48 hours of hospitalisation is as- sociated with a worse prognosis for survival to hospital discharge, and 1-mM (18 mg/dL) increase in glucose concentration at admission decreased the odds of sur- viving to hospital discharge by 24% It is reported that the peritoneal (and pleural) fluid level of lactate is usually less than that of blood and a ratio of blood lactate : peritoneal lactate >1 is a strong indicator of the need for intensive and expensive medical therapy at least, if not surgical intervention. This has not been our experience. We have found peri- toneal lactate frequently elevated above plasma lactate in cases of colic admitted to Donnington Grove Veteri- nary Surgery. We have found the use of lactate on peri- toneal fluid to be relatively sensitive for strangulating intestinal disease, thus horses requiring surgery for in- testinal ischaemia usually have peritoneal lactate levels of >3mmol/l. Lactate is not only useful in a hospital setting. Many of our ambulatory and referring vets carry lactate meters in the car. When presented with a horse with colic, par- ticularly one which has been colicking overnight, they use lactate levels to advise owners of the likely outcome, using this simple formula - <2mmol/l, maybe normal, 2 Glucose [7]. Data from human cases suggests that control of hy- perglycaemia does improve the prognosis, though this is quite involved and requires an insulin drip Fluids The commonest cause of increased lactate is decreased tissue perfusion. Thus, increasing the circulatory vol- ume can be a very effective way of reducing lactate. This is easily done by pouring lactated Ringers solution intravenously into the horse - the kidneys will remove ay excess. Well, not quite. Excessive fluids have been shown to have a few teeny weeny issues, such as, mortality, slower intestinal heal- ing, delayed wound healing, ileus and pulmonary dys- function [8]. Another important point is that purchased crystalloid fluids are expensive. Most colics in the UK die because of lack of money, rather than incurable dis- ease. Thus, avoiding wasting money on expensive and detrimental treatments is important. As a general rule, resuscitation with 10l of fluids is indicated, followed by fluids at 0.5 - 2l per hour. The best way to monitor fluid therapy is not PCV, but urine specific gravity. Urine SG should be 10.10 - 10.20. Excessive chloride is also bad, and thus the chosen fluids should be lactated Ringers or Normosol-R, and not 0.9% sodium chloride [8]. • Volume 19 no 3 • September 2017 • 29