“How do I manage a patient with diabetes who is going for surgery? Should I start a variable rate intravenous insulin infusion? When should I resume their metformin?” For the answer to all these questions and more, check out our latest FOAMdation podcast and blog.
Dr David Ewins is a Consultant Physician specialising in Endocrinology and Diabetes at the Countess of Chester Hospital. In the episode we discuss the management of adult patients with type 1 and type 2 diabetes who are undergoing surgery.
Surgery can cause fluctuations in blood glucose with either high or low glucose levels. Particular attention is required to the care of patients with diabetes to optimise their glucose control during the perioperative period (1,2).
The physiological stress of undergoing a surgical procedure reduces insulin release and increases counter-regulatory hormones including glucagon and adrenaline. The combined effects of these factors will increase blood glucose levels and the reduction in insulin release can lead to the breakdown of fatty acids, producing a ketosis.
In addition, periods when patients are fasting before surgery increases the risk of hypoglycaemia developing if the patient is on insulin therapy or an oral hypoglycaemic agent due to the lack of carbohydrate intake.
The Joint British Diabetes Society (JBDS) updated its guidelines on the management of patients with diabetes undergoing surgery and elective procedures in March 2016. These are an excellent resource to guide the management of these patients (3).
The target peri-operative blood glucose level should be between 6 to 10mmol/l. Ideally, the glycaemic control of patients with diabetes should be optimised before an operative procedure. Although this is not be possible in the setting of an emergency operation.
Wherever possible pre-operatively, we should aim to optimise the glycaemic control of a patient with diabetes to achieve a HbA1c of 69mmol/mol or less (8.5% or less in the previous method of measuring HbA1c) with capillary blood glucose readings of in outpatient setting of 4 to 12mmol/l if this is safe to do so. It is a compromise to try to optimise their glycaemic control safely to these levels whilst avoiding the risks of hypoglycaemia (3).
The main principles in the peri-operative management of patients with diabetes depends on two key factors:
1) How long is the anticipated starvation period
- Is this going to be short (i.e. one missed meal or less)
- Is this going to be long (missing more than one meal)?
2) How good is the patient’s pre-operative diabetic control?
Is their control relatively effective with a HbA1c at the target level for surgery (of less than 69mmol/mol) or is their control less effective than this (equal to or above the target of 69mmol/mol)?
For a patient undergoing an operation with a short starvation period (one missed meal or less) and optimised pre-operative diabetic control (HbA1c less than 69mmol/mol), their existing treatment can be modified for the operative period.
If patients are undergoing an operation with a short starvation period (one missed meal or less) but have poor pre-operative control of their diabetes (HbA1c of 69mmol/mol or more) then a Variable Rate Intravenous Insulin Infusion (VRIII) will be required during the perioperative period as per your local hospital policy.
In patients who are undergoing an operation with a long starvation period (defined as missing more than one meal), then irrespective of their control, they will require a VRIII in the perioperative period according to your local hospital policy.
Modification for short starvation period and HbA1c less than 69mmol/mol
In patients with type 2 diabetes on diet alone, there are no specific changes required to their treatment.
For patients with type 2 diabetes who are receiving oral hypoglycaemic agents:
- Those treated with a sulphonylurea (e.g. gliclazide), will need this to be omitted on the morning of their operation when the patient is nil by mouth (due to the risk of hypoglycaemia) and then resumed post operatively when they are eating again.
- Patients treated with metformin or a DPP-IV inhibitor (eg sitagliptin, saxagliptin or linagliptin) can carry on taking this medication as normal including the morning of their operation.
For patients treated with insulin:
For patients with diabetes who are treated with a long acting insulin analogue (e.g. Lantus (insulin glargine) or Levemir (insulin detemir)), the dose should be reduced by 20% on the day before surgery. If the patient usually has their long acting insulin in the morning and is having a morning procedure, their long acting insulin dose should be reduced by 20% on the day of surgery also (3).
Patients treated with short acting insulin (e.g. Humulin S) or rapid acting insulin treatment (e.g. Novorapid, or Humalog) with meals should the dose of insulin omitted for the meal that they are not eating (when nil by mouth). The short/rapid acting insuling is then resumed from the next meal when they are eating and drinking once more (3,4,5).
Patients treated with twice daily pre-mixed insulin (e.g. Novomix 30, or Humulin M3) should should have doses reduced by approximately 50% on the day of surgery and then increased back to their usual doses the day after this if they are eating and drinking with no problems.
Now, to highlight the care of a patient with diabetes who is undergoing surgery in more detail, let’s look at a typical case example:
• 57-year-old lady
• Type 2 diabetes, insulin treated with Novomix 30, 20 units BD
• Admitted with sepsis and biliary tract obstruction
• Planned for an urgent inpatient cholecystectomy
Following the main principles in the perioperative management of patients with diabetes above, the first factor to establish is how long is the anticipated nil by mouth period likely to be?
With the above scenario, due to being unwell and the nature of the procedure, the patient will likely be missing more than one meal and therefore regardless of their diabetic control will require a VRIII during the peri-operative period.
If instead, the patient was well and undergoing a day case cholecystectomy for stable biliary colic, expected to miss only one meal, with optimised glycaemic control for surgery (HbA1c less than 69mmol/mol), then their usual treatment could be adjusted. The Novomix 30 would be reduced to 10 units BD on the day of surgery and increased back to 20 units BD once eating and drinking without issue.
However, if the patient was scheduled for a day case procedure but had relatively poor control (HbA1c 69mmol/mol or more), then they would require admission for a VRIII (3).
Variable Rate Intravenous Insulin Infusion (VRIII)
A Variable Rate Intravenous Insulin Infusion (VRIII) is an infusion of insulin, made up in a syringe typically with 50 units of short acting insulin e.g. actrapid in 50ml of 0.9% sodium chloride solution. The VRIII rate of insulin infused from this syringe is altered on the syringe driver pump according to hourly capillary blood glucose measurements.
When using a VRIII, substrate containing fluids shuold run in parallel usually through a Y connector. A typical example is: 5% dextrose with 0.45% sodium chloride with 10 to 20mmol of potassium chloride as recommended by the Joint British Diabetes Society. Your hospital or trust will probably have a policy for you to follow and use to prescribe accordingly. The fluid typically runs at 100ml/hr with the rate adjusted according to the fluid balance requirements of the individual patient and clinical judgement (6).
A VRIII prescription chart will typically have a tabular column on the chart for altering the insulin infusion rate depending upon the hourly capillary blood glucose reading. In patients who are known to be insulin sensitive and prone to episodes of hypoglycaemia, often those with a total daily insulin dose of less than 24 units, a reduced insulin infusion rate on the VRIIII may be used. Depending on your local policy and the individual patient, this may be shown on the chart as an ‘insulin sensitive or decreased’ column to be used in these cases.
By comparison, in overweight patients with insulin resistance, and typically a daily insulin dose of more than 100 units, when a VRIII is used these patients may require higher doses of insulin. Depending on your local policy this can be seen on some VRIII charts as an ‘insulin resistant or increased’ column to be used in these patients.
Occasionally the VRIII adjustment table can be manually altered by the inpatient diabetes team to suit the insulin requirements of an individual patient (6).
It’s important to note that in patients who usually take long acting subcutaneous insulin e.g. (e.g. Lantus (insulin glargine) or Levemir (insulin detemir)) this should be continued whilst they are on the VRIII to provide some background insulin. This avoids hyperglycaemia when the VRIII is stopped and the patient is transferred back to their usual subcutaneous insulin regime post operatively (6).
Advantages of VRIII
The advantage of a VRIII here is that it allows rapid and effective control of the patient’s blood glucose levels in the perioperative period.
Frequency of blood glucose level monitoring
The capillary blood glucose (CBG) level should be checked hourly on a VRIII.
Transitioning from VRIII to usual insulin regime
The VRIII should be continued until satisfied that the patient is eating and drinking as normal. The ideal timing for this is early in the day when it is easier to detect and manage subsequent issues. The patient should be given their usual regime subcutaneous insulin dose before their next meal (e.g. breakfast or lunch) and 30-60 minutes later, the VRIII should be stopped and disconnected (3,6). The same applies for patients taking metformin or a sulphonylurea (e.g. gliclazide), these are given 30-60 minutes before the VRIII is taken down when they are eating and drinking normally.
Pitfalls in managing diabetic patients undergoing surgery
The main pitfalls are hyperglycaemia and hypoglycaemia.
To prevent hypoglycaemia, it is essential for those patients receiving a VRIII to have an intravenous fluid carbohydrate substrate running parrallel, as described previously. This is usually 5% dextrose with 0.45% sodium chloride with 10 to 20mmol of potassium chloride (guided by your local hospital protocol). This should be run through a Y connector into the same intravenous (IV) cannula as the VRIII. If the cannula tissues or becomes displaced, the patient will not receive insulin alone and develop hypoglycaemia as both the insulin and carbohydrate substrate will cease to be infused until a new cannula is inserted.
Should hypoglycaemia develop then it should be treated according to your local policy. A guide would be 50-100ml of 10% Gucose IV as a bolus and recheck the blood sugar 15 minutes later, repeated as needed.
Hyperglycaemia can be prevented through the patient being managed effectively according to the above guidance, including using a VRIII if they are fasting for more than one meal. A patient who is hyperglycaemic and unwell or vomiting, especially is the blood sugar is above 12mmol/L, you should consider the patient may be in a state of Diabetic Ketoacidosis (DKA). You may need to check a venous glucose, venous blood gas, U&Es, bicarbonate and ketones. If they are in a state of DKA, this should be managed accordingly (see here).
Once you are satisfied you are not facing DKA, you can give a single dose of subcutaneous insulin such as Novorapid. Type 1 diabetic patient will often know how much they need so ask them! Otherwise, 1 unit should reduce the blood glucose by approximately 3mmol/L. In the non-insulin treated patient with a high blood sugar, consider giving 0.1 units/kg as these patients are often insulin resistent. If the blood sugar is not falling then contact the diabetes team.
When does Metformin need stopping?
In patients who are having a short starvation period (only one missed meal) and who have a low risk of acute kidney injury (normal renal function prior to surgery), metformin should be continued peri-operatively.
If a patient is undergoing a procedure with a longer starvation period (more than one missed meal) and/or is at risk of an acute kidney injury (AKI) then metformin should be stopped at the time of the pre-operative fasting period. Metformin should only be resumed post-operatively when the patient is eating and drinking and their renal function (urea and electrolytes) is stable post-operatively.
Patients at risk of an AKI include (1,2,7):
- Over the age of 65 years
- eGFR < 60 ml/min
- Hypotensive or hypovolaemic
- Patients receiving potentially nephrotoxic medications
- Administered iodinated contrast media (due to the risk of contrast nephropathy)
Realistically, the only people who should adjust these are the diabetes team and the patient. If the patient is unable to do this, they should be placed on a VRIII. If the operation is short or the patient is awake throughout (eg labour or C-section), they may be able to adjust their insulin themselves. If you are in any doubt, the safest approach is to stop the pump and take control with a VRIII.
Enhanced Recovery Protocols
Often these protocols mandate complex carbohydrate drinks in the pre-operative period. Obviously, these cause potential problems for diabetic patients. A well controlled patient with adjustment of their base regime may not be suitable for complex carbohydrate drinks. A patient treated with VRIII can receive these drinks because the VRIII can be adjusted accordingly.
Complications can be easily avoided by paying due diligence to the management of diabetic patients in the peri-operative period.
A reference which is really useful for further reading is the Joint British Diabetes Societies inpatient guidelines for the management of adults with diabetes undergoing surgery and elective procedures (3). You need to be familiar with your local policy.
I’d like to thanks Dr David Ewins for his time and effort in recording this podcast and the medical education department at Chester for their continued support.
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- Kasper, Fauci et al. Harrison’s Principles of Internal Medicine 19th edition. McGrawhill 2016
- Kumar, Clark et al. Kumar and Clark’s Clinical Medicine 9th edition. Elsevier 2016
- Management of adults with diabetes undergoing surgery and elective procedures: Improving standards. Revised March 2016. Joint British Diabetes Societies Inpatient Care Group. http://www.diabetologists-abcd.org.uk/JBDS/Surgical_guidelines_2015_full_FINAL_amended_Mar_2016.pdf
- NICE Guideline [NG17], Type 1 Diabetes in adults: diagnosis and management. Published: August 2015. Last updated: July 2016.
- NICE Guideline [NG28], Type 2 Diabetes in adults: management. Published: December 2015. Last updated: May 2017
- Joint British Diabetes Societies for inpatient care. The use of variable rate intravenous insulin infusion (VRIII) for medical inpatients. October 2014.
- NICE Clinical Guideline [CG169], Acute kidney injury: prevention, detection and management. Published: August 2013