Insulin

Types

• Rapid acting
  • • Novorapid, Humulog, Fiasp, Lyumjev / lispro-aabs, Trurapi
    • Onset in 15 minutes, peaks in 1 hour, lasts 4 hours
    • If given IV – half life is 7 minutes (DKA rebounds fast when unattached to a drip!)
    • Only should be given with meals / carbohydrates
• Short acting
  • • Actrapid, Humulin S, Humulin R
    • Onset of action 45 minutes and lasts 8 hours
• Intermediate acting
  • • Humulin I, Insulinatard, Insuman Basal
    • Onset 1.5 hours, peaks in 7 hours, lasts 15 hours
• Long-acting / basal
  • • Levemir (can be given BD in type 1 DM), Lantus (glargine), Tresiba (degludec, lasts 42 hours), Toujeo (high strength), Basaglar (cheap), Inadec (newish, given weekly)
    • No peak, lasts 24-42 hours
• Long-acting insulin plus liraglutide (combo) eg Xultophy
• Biphasic/mixed (Mix of rapid acting and intermediate acting)
  • • Humulin M3 (30% rapid acting, 70% intermediate)
    • Novomix 30, Humulog mix 25 or 50 (number denotes proportion of rapid acting insulin eg. 30%, 25% or 50%)
    • Use BD, with meals and never at bedtime
    • Usually used in type 2 DM
• Insulin can come in different concentrations (units/ml). Foreigners visiting the UK may have different insulins – always check the concentration

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Insulin regimes

• Consider choice of regime depending on a patients’ job and lifestyle, their ability to manage multiple injections, if they travel, when they eat
• Some common regimens
  • • Basal only
    • Basal bolus (long acting once daily, and short acting with meals)
      • • Allows maximum flexibility
        • Good if varied meal times or intake variable
        • Multiple injections a day can be difficult for some
        • Might avoid in old age and psychiatric patients
        • If district nurse needs to administer insulin – usually best to avoid (as requires 3 visits daily)
    • Pre-mixed
      • • Usually given twice daily, occasionally TDS
        • May be a good choice if a patient has a fixed meal and activity regime (eg a nurse)
        • If admitted – might not be ideal to continue as appetite variable and hypos more likely

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Calculating doses and starting insulin

• Need to know: patient weight, eGFR, if they’re eating
• Estimate a patient’s total insulin requirement
  • • 3 units/kg if old, CKD, CLD, new T1DM, or very low BMI
    • 5 units/kg for all others
• For a basal bolus regime – 50% of total insulin will be long acting, 50% short acting, and short acting dose should be divided into three.
• If going onto pre-mixed insulin – 0.5 x weight = 24-hour requirement. Then split into 2/3 morning, 1/3 with dinner
• You can also estimate a patient’s daily insulin requirement from the last 6 hours of a sliding scale – divide the total insulin required by 6 to get hourly requirement, then multiple by 20 to get daily requirement (not 24, as a precaution against hypos)
• If not eating – avoid all short acting and mixed insulins
• For how to adjust insulin doses – see hyperglycaemia

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Issues with insulin

• Can cause weight gain, issues with occupation/driving, alteration in vision, oedema, neuritis, injection site issues, hypoglycaemia
• Factors which affect insulin absorption
  • • Large doses (so often split doses if using 50 units or more)
    • Accidental IM injection
    • Exercise
    • Body part injected into (abdomen – fast absorption, buttocks – slow)
    • Age (younger people absorb faster as less fat)
    • Fat mass (the more fat, the slower the absorption)
    • Insulin cold (straight from fridge) leads to slower absorption – ensure its out for 30 minutes before injecting
    • Lipohypertrophy

• How to manage injection problems
  • • Pain – rub ice on area first, use room temp insulin (not cold), use a new needle every injection, shorter needles
    • Bleeding / bruising – pressure, better technique, shorter needle
    • Redness / swelling / itching – consider switch to insulin analogue, or one with different preservatives in it
    • Lipohypertrophy – rotate sites
    • Cutaneous amyloid – rotate sites

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Sliding scales (variable rate infusion, VRIII)

• Indications include
  • • Uncontrolled hyperglycaemia
    • Acutely unwell and no diabetes team to advise
    • Certain conditions which require tighter control – ACS, stroke, sepsis
    • NBM (eg pre-operatively) or vomiting, TPN fed
    • Most patients on ICU
    • Post DKA and not eating and drinking well
• Can be difficult to manage if patient is eating (use with caution in this circumstance)
• Always commence a sliding scale before disconnecting an insulin pump
• Most patients will have their usual diabetes medication completely withheld whilst they are on a VRIII including oral and injectable hypoglycaemic drugs as well as most forms of insulin. The exception is long acting analogue or isophane basal insulin, which should be continued
• The prescription – 50 units of Human Actrapid insulin and add to 49.5 ml of 0.9% sodium chloride in a 50 ml luer lock syringe (1 unit / 1ml). Use a pump.
• Concurrent fluid replacement – 5% dextrose with 40mmol K+ at 125ml/hour
• Can run additional IV fluids alongside glucose infusion if dehydrated.
• Check for signs of fluid overload and use 10% glucose with a sliding scale if you want to reduce fluid burden
• If on a sliding scale for more than 24 hours – likely will need normal saline to keep Na up. Ensure K+ levels not too low
• Do hourly CBGs – commonly not achieved in A&E, and so sliding scales are a frequent cause of iatrogenic harm (therefore not really a safety net, only use if you need to)
• Standard rate of infusion is
  • • 1ml/hr (ie 1u/hr) if CBG 4-8
    • 2ml/hr if CBG 8-12
    • 4ml/hr if CBG 12-16
• However there are different scales with different rates as some patients are insulin sensitive and others insulin resistant
• If CBGs persistently > 12, or if there’s a hypo, consider changing to a different scale
• If hypoglycaemic on a sliding scale
  • • Stop infusion
    • Give 100ml 20% or 200ml 10% glucose
    • Ensure sufficient monitoring was being performed
    • Step down rate and restart after 10 mins and before 20 mins
• Stopping a sliding scale – once eating or clinically better.
  • • If a patient needs/uses insulin, a background insulin (either within a mixed insulin or as part of a basal bolus regime) MUST be given prior to stopping the VRIII.
    • VRIII should only be discontinued 30 minutes after subcutaneous insulin has been given. Can give rapid‐acting insulin with the meal and then stop the VRIII 30 minutes later.
• CSII (insulin pump) treated patients
  • • Involve the diabetes team
    • Reconnect the CSII, start the normal basal regimen, give a bolus dose of insulin with the meal and then stop the VRIII 30 minutes later
• Non-insulin treated patients
  • • Restart usual treatment when stopping the sliding scale
    • Give the medications prior to stopping the sliding scale
    • Ensure that no contra‐indications to the previous hypoglycaemic therapy have arisen
• If TPN stopped – can often stop the sliding scale
• After stopping – check CBG one hour after discontinuing the VRIII and 4 hourly for the next 24 hours to ensure there is no rebound hyperglycaemia
• If the blood glucose rises after the VRIII is discontinued, usually do not restart the infusion unless the patient is clinically unwell (but can get advice from diabetes specialist nurse if required)