Diabetes and anaesthesia


This is one of two blogs on diabetes and will explain how we prepare patients who are diabetic for operations and manage them during their hospital stay. There is a second blog which explains how we can prevent and manage diabetes


Diabetic patients have a higher surgical morbidity and mortality. They suffer from more infections and stay in hospital for longer. These issues can be reduced by good preoperative assessment and optimisation together with precise management of the blood sugar during the operation.


We have two methods of measuring blood sugar control: the actual blood sugar, which is measured either with a blood sample in the laboratory or a finger prick test, provides the blood sugar at that moment and is used by diabetics to adjust their medication. The HbA1c is a blood test that measures the average blood sugar over the last 60 days and is the test we use to monitor long-term control. The current recommendations are that elective surgery should only occur if this is under 69. Otherwise surgery should be delayed until the diabetes is under better control


The amount of preoperative preparation will depend on the type of diabetes, how well it is controlled and the size of the operation so it is very important that diabetics are booked for operations well in advance and that we have plenty of time for preassessment. Investigations will include the HbA1c to give an idea of the control achieved, blood tests for the urea and electrolytes to identify any damage to the kidneys and an ECG. A high blood sugar affects the small blood vessels which leads to damage to the heart, kidneys and eyes as well as the peripheral circulation which can result in leg ulcers. A comprehensive history will identify any of these complications. We also want to know what drugs are being taken, the highest and lowest blood sugar readings, and the presence of hypos.


Armed with this information the anaesthetist can plan how best to manage diabetes during the operation. We tend to operate on diabetic patients first thing in the morning so that only one meal is missed. It is very important not to starve for longer than is absolutely essential which is six hours for food and two hours for fluids. Patients who are on insulin may need modification: long-acting insulins are often only reduced by a small amount whereas short-acting insulins may be omitted. Metformin, the commonest oral drug, cannot produce a low blood sugar and we normally continue this until the time of anaesthesia but other tablets may need to be stopped in advance. Each patient is different which is why close cooperation with your anaesthetist is absolutely essential.


Patients who are only on tablets can often be managed without further intervention and can go home the same day. Patients who are taking insulin will normally need to stay overnight if their drug program has been modified. For larger operations we tend to replace the subcutaneous injections with a continuous intravenous infusion of insulin. Most anaesthetics include an intravenous infusion of one drug for another so this is very normal for anaesthetists and allows us to closely control the blood sugar by adjusting the rate of the pump. Although insulin infusions have historically been shown to produce complications, this is usually associated with long-term infusions over several days and the difficulties of discontinuing them. We are fortunate in the private sector to be able to maintain ongoing personal care of our patients which also helps to prevent problems may arise when instructions passed from one person to another.