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Diabetes - General Comments

• Diabetes terminology - The preferred terminology is Type 1 and Type 2 diabetes instead of insulin-dependent and non-insulin-dependent diabetes. Some patients may have other forms of diabetes such as Maturity Onset Diabetes of the Young (MODY).
• Unstable blood glucose - Patients with diabetes, who are admitted to hospital for reasons other than diabetic control, often experience unstable blood glucose results. Any sustained increase in blood glucose will lead to a delay in wound healing and slow the resolution of infection.
• Does a hospitalized patient with high glucose values have diabetes? Inpatients with no previous history of diabetes may have a temporary elevation in glucose in response to stress and medications (e.g., corticosteroids). However many of these patients will have undiagnosed diabetes. A glycated haemoglobin assay (see below) may help distinguish transient impairment of glucose tolerance from undiagnosed diabetes. If in doubt, arrange GP follow-up after discharge.
  • The preferred screening test for well patients is HbA1c. An HbA1c ≥50 mmol/mol is diagnostic of diabetes mellitus if confirmed on a second sample. A diagnosis of diabetes can also be made on two fasting results ≥7 mmol/L, or random glucose ≥11.1 mmol/L.
  • HbA1c levels above 41 mmol/mol are suspicious of diabetes and dictate further testing or monitoring.
• Glycated haemoglobin (HbA1c):
  • This is a useful test to measure average glycaemic control over the preceding 3 months. It can be misleading in those with abnormal red cell turnover (bleeding, transfusions, recent pregnancy, etc.) or haemoglobin variants (e.g., thalassaemia). Typical target is 53 mmol/mol (7%), but this needs to be individualized.
  • If recent glycaemic control is uncertain, consider ordering an HbA1c, especially if inpatient review by a member of the diabetes team has been requested.

Changes in inpatient insulin requirements

• Some patients who were previously well controlled on diet and tablets, may require insulin on a temporary basis during their hospital stay.
• Most patients on insulin will require a temporary adjustment to their insulin dose if they are in hospital more than 48 hours.
• If insulin is needed an 'average' starting regimen would be Humalog Mix25™, 60% in the morning and 40% at the evening meal, at a total dose of 0.3 units/kg per 24 hours. For example a 100 kg patient might be prescribed Humalog Mix25™, 18 units before breakfast and 12 units before the evening meal time. This starting dose is likely to be insufficient for most patients and will need daily adjustment. (A small percentage of patients will experience hypoglycaemia - this mandates immediate adjustment of the regimen.)
• Supplemental subcut fast acting insulin such as lispro (Humalog™), glulisine (Apidra™) or aspart (NovoRapid™) insulin can be given in addition to the twice daily Humalog Mix25™. Subcut fast acting insulin should be prescribed before or with meals, e.g., 6 units if blood glucose is ≥15 mmol/L.
• Subcutaneous fast acting insulin injections with aspart (NovoRapid™) or lispro (Humalog™) are preferred to subcut neutral insulin injections using Actrapid™ or Humulin R™.
• As a rule of thumb, in an insulin-sensitive person, 1 unit of aspart (NovoRapid™), 1 unit of glulisine (Apidra™), or 1 unit of lispro (Humalog™) will lower blood glucose by 3 mmol/L.
• Patients using 3 mL insulin cartridges can obtain pen injectors (e.g., Novopen™, Humapen™) from the Christchurch Hospital Pharmacy or from the Diabetes Centre during normal working hours.
• Patients using subcutaneous insulin pump therapy:
  • Patients who routinely use a continuous subcutaneous insulin pump may be admitted to the ward. If the admission is for hyperglycaemia, the insulin in the pump, the tubing and the cannula should be changed. A consult to the Diabetes Centre should be made to check the pump if there are any concerns about the pump or the infusion rates.
  • In the event of DKA, they can be managed as per the standard protocol with or without the subcutaneous pump continuing in the background.

Description of Insulins currently available in New Zealand

Patient autonomy

• Most patients on insulin are competent at diabetes self-care, including self-adjustment of insulin. Maintenance of this autonomy should be encouraged during hospitalization.

  Changes in insulin dose should therefore be made in consultation with the patient.

Ward capillary blood glucose testing

• Many patients require frequent testing when admitted acutely or during the perioperative period.
• Once the patient's condition has stabilized, four times a day testing is usually adequate (pre-meals and at bedtime).
• Patients on premixed insulins should be tested before main meals and at bedtime.
• Patients on fast acting insulins (aspart (NovoRapid™) or lispro (Humalog™)) may need to do additional tests 2 hours after mealtime injections.

Hyperglycaemia induced hyponatraemia

• Mild hyponatraemia is common in well hydrated patients with hyperglycaemia. Hyperglycaemia is associated with a shift in water from intracellular to extracellular fluid and this causes a dilutional hyponatraemia. Osmolarity (tonicity) is however usually elevated.
• Corrected sodium can be calculated by adding 2.4 mmol/L for each 5.6 mmol/L rise in glucose above a level of 5.6 mmol/L. Thus for each 10 mmol/L rise in serum glucose, an approximately 4 mmol/L fall in serum sodium is expected.
• It follows that a fall in glucose is usually associated with a rise in sodium, i.e., correction of both elevated glucose and associated dehydration will usually result in normalization of the serum sodium.
• The most relevant measure of osmolarity in this setting is effective osmolarity (2xNa + glucose). See below for further explanation.

Osmolarity and osmolality

Osmolarity is the number of particles of a substance in a volume of fluid (e.g., mmol/L), and osmolality is the number of particles dissolved in a mass of fluid (e.g., mmol/kg). In clinical practice, these values are virtually the same. Strictly speaking, osmolality is the term used in the reports issued from the laboratory, and osmolarity is what is calculated from mmol/L of the venous solutes. "Effective" osmolarity is a calculation that excludes urea since this moves freely between extracellular and intracellular compartments.

Metformin - induced lactic acidosis

• Lactic acidosis is a rare but potentially fatal complication of metformin treatment.
• Metformin should be avoided or used in a reduced dose in patients who are at increased risk of lactic acidosis. This includes patients with renal impairment (serum creatinine >160 micromol/L or eGFR <30 mL/min), overt cardiac failure, acute myocardial infarction, severe hepatic impairment, hypoxia, severe dehydration and sepsis.
• Patients with a severe intercurrent illness will require temporary cessation of metformin.

Pre-discharge planning

This should be undertaken at least 48 hours before patients on insulin leave hospital. Questions you should consider include:

• Does the patient need to go back onto their usual insulin dose at discharge, particularly if they are resuming their usual eating and activity patterns?
• Have you discussed a plan of action with the patient and caregivers, if blood glucose results do not stabilize, after discharge?
• Have you prescribed the right sort of insulin? Most patients use 3 mL cartridges - some patients use 10 mL vials or disposable pens.
• Have you prescribed pen injector needles of the correct length or insulin syringes, if required?
• Have you prescribed the right sort of glucose test strips for the patient's blood glucose meter?

Contact the Diabetes Centre if you require further advice about diabetes inpatient management, including pre-discharge planning, from either the Diabetes Registrar or Diabetes Nurse Specialist. Some general practitioners are very confident with insulin initiation and dose adjustment. Consider using Primary Care in suitable patients.

Topic Code: 1366