Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Management of type 1 diabetes and perioperative fasting

  • Comment

The standards document of The National Service Framework for Diabetes has recognised that inpatient management of diabetic patients is often inadequate (Department of Health, 2001). Suggestions to improve care included enhanced communication with patients, improved liaison with hospital diabetes teams (particularly the inpatient diabetes specialist nurse) and implementation of locally agreed evidence-based guidelines. Management of diabetic patients around the time of surgery lends itself to each of these improvements. Unfortunately, the evidence base in this area is not strong and most of the recommendations in this article are based on best practice or consensus of opinion (Gill, 2003). Protocols and procedures vary between trusts and an improved evidence base could strengthen uniformity and treatment.

Abstract

VOL: 99, ISSUE: 15, PAGE NO: 56

Simon E.M. Eaton, BMedSci, BMBS, MRCP, is specialist registrar in diabetes and endocrinology, Royal Hallamshire Hospital, Sheffield

The standards document of The National Service Framework for Diabetes has recognised that inpatient management of diabetic patients is often inadequate (Department of Health, 2001). Suggestions to improve care included enhanced communication with patients, improved liaison with hospital diabetes teams (particularly the inpatient diabetes specialist nurse) and implementation of locally agreed evidence-based guidelines. Management of diabetic patients around the time of surgery lends itself to each of these improvements. Unfortunately, the evidence base in this area is not strong and most of the recommendations in this article are based on best practice or consensus of opinion (Gill, 2003). Protocols and procedures vary between trusts and an improved evidence base could strengthen uniformity and treatment.

The effects of fasting and surgery In response to stress, for example during surgery, people who do not have diabetes release hormones such as adrenaline and cortisol, and their insulin levels increase to balance this. Therefore, insulin levels may be higher than normal, even though the patient is fasting. This process is controlled in non-diabetic patients so that glucose levels remain normal.
Patients with type 1 diabetes are unable to produce insulin and therefore cannot balance the effects of these hormonal changes. If insulin is not given, the body’s ability to use glucose as a fuel is affected and proteins and fat are broken down instead. Along with an increase in blood glucose levels, this can also lead to a rise in ketone bodies and ketosis (an abnormal accumulation of ketones in the body). If this situation is allowed to continue unchecked it could develop into diabetic ketoacidosis, which causes severe acidosis, dehydration and metabolic disturbances, and is potentially fatal.

Giving too much insulin may cause hypoglycaemia. This is particularly dangerous for a sedated or anaesthetised patient as it makes it difficult to identify warning signs such as drowsiness and if left undetected could lead to brain damage or even death.

Principles of management Treatment needs to be carefully balanced to avoid giving too much or too little insulin. The aim is to keep the capillary blood glucose (CBG) level between 7 and 11 mmol/l. This can only reliably be achieved by adequately preparing the patient, using the correct treatment regime, regularly monitoring CBG and responding with appropriate actions.
Preparation for surgery It is not unusual for a patient, who may have waited many months on a waiting list, to have their operation cancelled on the day of surgery because of poor diabetic control. In most instances this could have been anticipated by the referring team and efforts made to improve control through liaison with the specialist diabetes team while the patient awaits surgery.

Patients should be provided with clear written instructions regarding the management of their diabetes on the days before surgery (Table 1). They should be advised to check their CBG levels before meals and before they go to sleep for at least two days before surgery to allow any patterns in CBG levels to be detected. The risks of hypoglycaemia and the appropriate treatment needed to avoid these risks should be fully explained to the patient.

Treatment regimes The choice of regime can be broadly divided into whether or not the patient is given intravenous insulin.
IV insulin should be given if the patient is to undergo moderate or major surgery or if the period of postoperative fasting is likely to be prolonged. There are two different regimes commonly used. The choice between the two regimes will depend on the procedure and the patient, as well as the individual preferences of the anaesthetist and/or diabetes team. Glucose levels can usually be well controlled on either regime and both require hourly monitoring of CBG. Both regimes should be started at least four hours before the procedure to allow glucose levels to stabilise.

Intravenous sliding scale - An intravenous sliding scale (IVSS) is used when insulin and glucose are infused separately. Soluble insulin is delivered via a syringe pump at a rate according to a prescribed sliding scale. Glucose is infused separately at a constant rate.

The main disadvantage of this regime is the potential for either infusion to inadvertently stop while the other continues, for instance if one line is disconnected or blocked. This may also be a problem if normal saline is inadvertently prescribed rather than dextrose. For this reason, it is often useful to consider the insulin, potassium chloride and 10 per cent dextrose infusions as a package to control blood sugar and for other fluids that are given for volume or electrolyte replacement to be prescribed and given separately.

Glucose potassium insulin (GKI) infusion - This is an alternative regime where 500ml of 10 per cent dextrose, 10mmol potassium chloride and 10 units of insulin are all given in the same infusion at a rate of 100ml/hour. CBG levels should be measured hourly to ensure the glucose remains within the target of 7-11mmol/l. If the CBG remains out of this range for two consecutive hours a different dose of insulin is required. For example, if CBG is less than 7mmol/l the insulin dose could be reduced to five units in 500ml of 10 per cent dextrose. If CBG is greater than 11mmol/l it could be increased to 20 units.

Fast and check - IV insulin may not be required for patients who are likely to eat - and therefore have their insulin - shortly after their procedure. The usual insulin is omitted before surgery and CBG levels are monitored hourly. The patient must be placed on the operating list early in the day. Once they have recovered from the procedure they can have their usual insulin with a meal. If the CBG rises above 17mmol/l during the fasting period, a prescribed dose of soluble insulin should be given. If it continues to rise, or the procedure is further delayed, IVSS should be considered.

Monitoring Inadequate monitoring of CBG levels or an inappropriate response are the usual causes of any problems. The CBG should be measured hourly with a reliable, calibrated meter and the results documented clearly whichever regime is being used. Abnormal readings should be acted upon immediately. The development and use of clear protocols or guidelines to assist this process are invaluable.
Returning to subcutaneous insulin Insulin requirements will frequently be higher in the postoperative period and patients should be aware that their normal insulin doses may need to be increased in the first few days after surgery.

Precautions need to be taken when transferring a patient from an IV regime to subcutaneous insulin. IV insulin is used very quickly whereas subcutaneous insulin does not work immediately. Therefore, it is suggested that the subcutaneous insulin should be given 30 minutes before a meal and the IV insulin should be stopped 60 minutes after the dose of subcutaneous insulin.

Key learning points - Problems specific to type 1 diabetes and fasting can be largely avoided with careful monitoring and treatment;
- Insulin requirements are often higher than normal, even when fasting;

- Missing insulin doses can have very serious consequences, including diabetic ketoacidosis;

- Hypoglycaemia is a particular risk as it may be difficult to recognise in a sedated or anaesthetised patient.

  • Comment

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Links may be included in your comments but HTML is not permitted.