Insulin infusion (VRII)

A routine VRII (variable rate insulin infusion) prescription includes simultaneous infusions of:

• short-acting insulin (prepared in a 50ml syringe and diluted to 1 unit/ml)

• substrate intravenous fluid

Both infusions should be run through a single cannula. In NHS Lothian, the recommended substrate fluid for most patients is 1000mls glucose 4% and sodium chloride 0.18% with potassium chloride 40mmol. Usually this is prescribed at a rate of 100ml/hr. The standard Edinburgh Diabetes peri-operative VRII protocol is available here.

Patients with advanced chronic kidney disease are at risk of fluid overload, hyperkalaemia and hypoglycaemia using standard VRII regimes.  Therefore, the insulin and substrate fluid should be tailored to the individual patient / circumstance.

In patients receiving dialysis it is important to find out how much urine the patient makes as this will guide the choice and volume of fluid. Anuric patients are at the greatest risk of volume overload. The most helpful questions to ask are: “do you pass any urine at all?”, “what is your usual fluid restriction?” and “how much fluid do you usually remove on each dialysis session?”.

For patients with advanced kidney disease (eGFR <30 mL/min): we advise beginning the VRII using the insulin sensitive scale (see table) for insulin infusion rate, and a lower volume mixed bag e.g. 25-50ml/hr glucose 4% and sodium chloride 0.18%. The insulin scale used can be adjusted to the standard scale if necessary to achieve a target CBG of 6 – 12 mmol/L.

Capillary blood glucose (mmol/L)	Sensitive scale Infusion rate (units/hr)	Standard scale Infusion rate (units/hr)
<4.0	Nil (treat hypo)	Nil (treat hypo)
4.0 – 8.0	0.5	1
8.1 – 12.0	1	2
12.1 – 16.0	2	4
16.1 – 20.0	3	5
20.1 – 24.0	4	6
>24.0	6	8

Where patients are at particularly high risk of volume overload (e.g. those on dialysis): we suggest omitting substrate fluid until blood glucose is ≤12, then beginning 10% dextrose at 50ml/hr. This requires very close monitoring to avoid hypoglycaemia, particularly in general wards where nursing staff may be less familiar with this. If insulin is being infused at ≥3 units/hr and no substrate fluid is running, we would suggest initial CBG monitoring every 30 minutes due to the risk of hypoglycaemia; the frequency can be reduced if the CBG is stable. The dextrose concentration and infusion volume may be adjusted if tighter volume control is required (e.g. 20% dextrose at 25ml/hr) or to maintain blood glucose levels.

We suggest daily U&Es to monitor potassium. Patients with stage 4 or 5 CKD must never have potassium chloride added to substrate fluid unless specifically instructed by the renal team.

As with all diabetic patients on insulin, background long-acting insulin must always be given alongside a VRII.

Managing diabetes in advanced CKD can be challenging.  Have a very low threshold to consult with the renal and diabetes teams.

If you are interested in learning more about how insulin therapy differs in dialysis patients (specifically in the context of DKA) then you can read more here.

This page was written by Dr. Fiona Chapman, Renal SpR (December 2024).  It was reviewed by Dr. Robert Hunter (Renal Consultant), Dr. Nicola Zammitt (Diabetes and Endocrinology Consultant) and Dr. Kathryn Linton (Diabetes and Endocrinology Consultant).