David B. Church, BVSc, PhD, MACVSc, MRCVs, ILTM
Department of Veterinary Clinical Sciences, The Royal Veterinary College North Mymms, Hatfield, Hertfordshire, UK
While many diabetic patients may have some level of ketosis the term "diabetic ketoacidotic" refers to animals that are not only ketotic but also clinically unwell because of the degree of their diabetic ketoacidosis. Usually a diabetic patient that is unwell, either because of intercurrent disease or due to the endogenous toxaemia that results from marked ketosis, will be inappetent making standard subcutaneous insulin therapy difficult. In these cases parenteral fluids and insulin either as a continuous intravenous infusion or repeated intramuscular injections can be a very effective means of short-term management. In the author's opinion, as long as there is a volumetric pump available a continuous intravenous insulin infusion is the simplest and least labour intensive means for treatment of these patients.
Managing the "Ketoacidotic Diabetic"
Parenteral Fluid Therapy
Inappetent diabetics usually require total parenteral hydration and, by virtue of their poorly controlled diabetes, have relatively high fluid maintenance requirements. Consequently flowing intravenous fluids at around 150 ml/kg/24 hr generally will provide some replacement and adequate maintenance. The optimum fluid composition is 0.45% NaCl with 30-40 mmol/l of KCl or a mixture of approximately 20 mmol/L of KCl and 20 mmol/L of KPO4 added. While one aim is to rehydrate the patient the other must be to provide some measure of diabetic control, or at least inhibit ongoing peripheral lipolysis and hence to start to reduce the potential for ketoacidosis.
When insulin therapy is being considered to treat clinically significant ketoacidosis the choice is continuous intravenous insulin therapy or repetitive intramuscular insulin injections. In both situations the insulin should be in a soluble and hence relatively rapidly acting form. Although an intravenous insulin infusion sounds daunting it is certainly the simplest and least labour intensive means of treating diabetic patients with GIT signs sufficiently severe to warrant a "nil per os" recommendation. In this situation we are trying to maintain adequate glucose homeostasis in a patient where parenteral drug and nutrient delivery is the only available route for administration.
One easy method for setting up the intravenous insulin fluid line is to add 25 units of soluble insulin to a 500 ml bag of fluids, producing an insulin concentration of 50 mU/ml. Since the standard insulin infusion rate is 40-60 mU/kg/hr, a convenient compromise is to flow 1 ml/kg/hr of this solution. Obviously a flow rate of approximately 1 ml/kg/hr is inadequate for maintenance. Consequently intravenous insulin has to be administered through a second infusion line, usually attached to the "Y" piece of the maintenance fluid line.
The insulin is infused at a rate of 1 ml/kg/hr until plasma glucose concentrations fall to 10-12 mmol/l. At this time the flow rate should be halved (0.5 ml/kg/hr) and a concurrent dextrose infusion introduced through the maintenance fluid line. One simple and effective means of achieving a balance between the insulin and glucose infused is too change the maintenance fluids from 0.45% NaCl and 30 mmol/l KCl to 0.45% NaCl AND 2.5% dextrose with 30 mmol/l KCl while continuing to run this combination at 150 ml /kg/hr. This will introduce a glucose infusion rate of around 150 mg/kg/hr which should balance the insulin being infused at 0.5 ml/kg/hr.
During this time the patient's blood glucose and plasma potassium are checked regularly. Over a period of 48-72 hours the blood glucose should remain relatively steady, ketonaemia, when present, should disappear and generally the patients return to a normal water and nutrient intake. Once this level of normality is established it is likely that, at least in the short term, the patient will be able to be stabilised on a regular feeding regime and a regular insulin dose regime.
For a variety of reasons it will not always be possible to administer an intravenous insulin infusion to an anorectic diabetic patient who requires relatively urgent insulin therapy. On some occasions the clinician may try and use lower doses of a subcutaneously administered Lente preparation twice daily. Although this practise may be effective and relatively safe if the dose is kept at around 0.25 IU/kg/12hr there is always the possibility of giving a little too much. Any overdose in this situation is likely to last at least 12 hours.
Consequently, in the absence of a reliable infusion pump, a more attractive alternative to a continuous intravenous insulin infusion is repeated intramuscular injections of soluble insulin.
Dogs and cats should receive soluble insulin at a loading dose of 0.2 IU/kg followed by 0.1 IU/kg hourly thereafter. All injections should be administered intramuscularly. Blood glucose levels are monitored regularly (every 2-3 hours) until they have fallen to 12-15 mmol/l. At this point it is usually satisfactory to change to subcutaneous soluble insulin every 6 hours (0.2-0.4 IU/kg). Because of the likely persistence of ketonaemia and hence inappetence, it is important to maintain adequate blood glucose concentrations by introducing dextrose into the intravenous fluids. Generally a 2.5% dextrose solution run at twice normal maintenance rates is satisfactory, although blood glucose levels should be checked every four to six hours.
Once the patient has been satisfactorily controlled more traditional methods of management can be employed.