Diabetic ketoacidosis

  • Diabetic ketoacidosis may be defined to occur in patients with positive serum ketones and an arterial blood pH of less than or equal to 7.30 and/or a serum bicarbonate less than or equal to 15 mmol/l.
  • Hallmark of Type 1 diabetes
  • It is usually seen in the following circumstances;
  • Previously undiagnosed diabetes
  • Interruption of insulin therapy
  • Stress of intercurrent illness

Pathophysiology

  • Due to uncontrolled catabolism associated with insulin deficiency and increased levels of glucagon
  • Deficient insulin causes an increase in breakdown of adipose stores which generates free fatty acids
  • Oxidation of fatty acids by the liver produces ketone bodies via acetyl CoA
  • If ketone bodies are formed at a rate greater than they are used, this results in ketoaemia and ketouria
  • If urinary excretion is compromised by dehydration this results in increased H+ ion concentration and an acidaemia

Biochemical features

  • Hyperglycaemia
  • Blood/urine ketones
  • Sodium levels are usually lowered
  • Potassium levels are often raised but total body potassium can be normal
  • Urea, can be raised if there is poor renal function or dehydration
  • Arterial pH, generally less than 7.3 may be accompanied by hypoxia

Clinical features;

  • Signs of dehydration – intracellular and extracellular water depletion
  • Increased depth and rate of breathing
  • Ketosis
  • Additional symptoms are abdominal pain, anorexia or vomiting, with or without diarrhoea
  • On examination, the patient may show signs of weight loss, rapid pulse of low volume with a low systolic pressure. There may also be postural hypotension
  • There may be signs of a precipitating condition such as an infection (bronchopneumonia, foot ulcer). Infection may not also present with a fever in such patients, indeed the patient may by hypothermic

Differential diagnosis of coma in diabetics

  • Hypoglycaemic coma
  • Severe diabetic ketoacidosis
  • Hyperglycaemic hyperosmolar non-ketotic coma
  • Lactic acidosis
  • Non-metabolic comas

Treatment

 

Fluid replacement

  • Normal saline to replace both fluid and sodium loss
  • Once insulin has been administered, plasma sodium concentration will rise as water moves intracellularly along with potassium and glucose
  • Most patients with ketoacidosis have a low plasma sodium concentration as an osmolar compensation for hyperglycaemia

Insulin

  • Required to inhibit inappropriate gluconeogenesis and excessive adipose tissue lipolysis
  • Aim for the maximum uptake of glucose by peripheral tissues which is 3-5mmol/l/hr

Potassium

  • Patients with ketoacidosis are hypokalaemic
  • A major action of insulin is to increase tissue potassium uptake
  • A contraindication of potassium administration is a grossly inadequate circulation preventing insulin and potassium reaching the same tissues
  • Potassium should be given once insulin administration has commenced
  • Patients particularly at risk of hypokalaemia are newly diagnosed diabetics (as opposed to those who are already on insulin) and this taking thiazide or similar diuretics
  • ECG can be used as a guide to potassium status, inversion of the T waves implies low plasma potassium

Bicarbonate

  • If acidaemia is severe (pH<7) tissue function can be impaired with a negative ionotropic effect on the heart, peripheral vasodilation and depressed CNS
  • Bicarbonate infusion can reduce metabolic acidosis but has the problem in that it can cause hypokaemia, with cardiac dysrythmia and a shift in the oxygen dissociation curve of haemoglobin to the left resulting in less oxygen reaching the tissues
  • When the patient is admitted with ketoacidosis the oxygen dissociation curve is normal, any right sided shift that might be expected is compensated for by decreased levels of red cell 2,3-diposhoglycerate. Rapid correction therefore shifts it to the left
  • Bicarbonate should therefore not be given without a reasonable circulation as it will stop oxygen getting to the tissues. However it can be given (along with potassium) once sufficient saline has been given to restore blood pressure

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