Patients admitted to a surgical department are often fasted for long periods and for multiple days while on the acute theatre lists. Insulin dependent patients (both type 1 and 2 diabetics) require monitoring to ensure (something close to) euglycaemia.
Fasting patients with a basal insulin requirement
The general rule is to continue basal insulin in the fasted patient. Consider that the insulin dependent patient is taking the insulin because their endogenous supply is absent or insufficient…
Long acting insulins (Lantus, Protophane, Isophane NPH)
These should be continued, usually at 80% of the usual dose. Fasting is not a reason to withhold basal insulin unless there is significant risk of hypoglycaemia, in which case one should start thinking about glucose-insulin infusion.
Short acting insulins (Actrapid, Apidra, Novorapid, Humalog)
These should be withheld unless required to prevent or treat hyperglycaemia.
Glucose-insulin infusions…
Are probably the best way to manage blood sugar in the insulin dependent inpatient. They can be charted in many ways and most hospitals will have a protocol so you should consult that…
Generally a variable rate intravenous insulin infusion (VRIII) is worth consider in patients with:
- Type 1 diabetes who are unable tolerate oral intake;
- Type 1 diabetes with recurrent vomiting;
- Type 1 or 2 diabetes who is or will be fasted for prolonged periods; or
- Type 1 or 2 diabetes with uncontrolled hyperglycaemia.
The infusion is some kind of dextrose containing saline solution (commonly 5% dextrose + 20mmol KCl in half normal saline) together with a rapid acting insulin. These are continuous infusion with fast-on/fast-off profiles, if they are stopped it should not be for long.
If you are lost...
- 5% dextrose + 20mmol potassium chloride in 0.45% sodium chloride at 80-125mL/hour;
- 50 IU neutral insulin (Acrapid) in 50mL (1IU/mL) per sliding scale;
- Continue long acting insulins during continuous infusions.
- Probably continue oral diabetic medications (but don’t forget the clinical judgement you learnt in medical school).
Standard insulin sliding scale for continuous infusions
| Capillary glucose (mmol/L) | Rate (mL/hour=IU/hour) |
|---|---|
| <4.0 | STOP |
| 4.1 - 8.0 | 1 |
| 8.1 - 12.0 | 2 |
| 12.1 - 16.0 | 4 |
| 16.1 - 20.0 | 5 |
| 20.1 - 24.0 | 6 |
| >24.1 | 8 |
Warning
If the insulin drops below 4.0: STOP the infusion, treat the hypoglycaemia, and RESTART the infusion within 20 minutes.
If the the capilliary glucose is consistently borderline (~4.0-6.0mmol) the insulin dosing should be reduced to maintain something closer to euglycaemia. Particularly in patients with CVA or ACS.
Other antihyperglycaemic agents
There are no general rules for the oral hypoglycaemic agents because some (SGLT2 inhibitors) may precipitate life threatening pathologies (EKA) while others are unlikely to cause much trouble. If in doubt, withholding is probably the best course of action.
Suhur and Iftar
The below table is the author’s own, its evidence base comes largely from advice for diabetics who fast during Ramadan, but also a brief review of recent anaesthetic guidelines.
| Agent | Prolonged fasting (on the acute board) |
|---|---|
| Metformin | Continue But consider administering when the patient is fed in the afternoon |
| Sulphonylureas (Glipizide, gliclazide) | Withhold Probably safe to give if the patient is fed in the afternoon |
| DPP4 inhibitors (Vildagliptin) | Probably safe to continue |
| GLP1 agonists (‘glutides) | Continue unless other reasons to withhold (dehydration, vomiting) |
| SGLT2 inhibitors (‘gliflozins) | WITHHOLD |
All oral agents can be restarted at their regular doses and frequencies once the patient is eating and drinking normally post-op.
There seems to be some evidence the SGLT2 inhibitors are safe for use during fasting in Ramadan1. It stands to reason, therefore, that continuation during the intermittent fasting in patients awaiting acute theatre may well be possible; the author is not that brave.
Further reading
- Your local VRIII guideline/protocol
Footnotes
-
Ibrahim M, Davies MJ, Ahmad E, Annabi FA, Eckel RH, Ba-Essa EM, et al. Recommendations for management of diabetes during Ramadan: update 2020, applying the principles of the ADA/EASD consensus. BMJ Open Diab Res Care. 2020 May;8(1):e001248. ↩