‘Diabetes and Anaesthesia'
Professor George Hall, St. George's Hospital, London
The meeting was opened by the President, Professor Jennifer Hunter, who went onto introduce the speaker, Professor George Hall from St George’s Hospital, London.
Professor Hall started his talk with a classification of diabetes mellitus into type I and II. He spoke about the diagnosis of diabetes mellitus and how it had changed in recent years. Normal plasma glucose levels after 8 hours of fasting should be less than 5.6 mmols/L. However, a fasting blood sugar of 7mmols/L or more, on more than two occasions made the diagnosis. He described the prevalence of diabetes in the UK with 1.8 million people or 3% of the population known to have the disease. It is estimated by Diabetes UK, that a further million people will have undiagnosed type II diabetes. 80% of type II diabetics are obese or overweight. There is clearly a genetic predisposition to the disease as the prevalence in Afro-Caribbean or Asian people is 5 times greater. Professor Hall then described the reasons for the increase in diabetes with an ageing population and the rise in average BMI of the population. He commented that the risk of type II diabetes is increased tenfold in people with a BMI of greater than 30 and that the UK has the fastest increase in the rate of obesity in the developed world. Type I diabetes reduced life expectancy by 20 years while type II reduced it on average by 10 years. This high mortality rate is mainly attributable to the greater incidence of cardio-vascular disease. The treatment and consequences of diabetes accounts for more than 10% of resources spent on health in the UK.
Professor Hall then addressed the principles of managing the diabetic in the peri-operative period. These were the avoidance of hypo-glycaemia, excessive hyper-glycaemia and electrolyte loss, as well as to prevent lipolysis and proteolysis. He said that the target blood glucose concentration should ideally always be less than 10 mmols/L. He then looked at the deleterious effects of hyperglycaemia including impaired healing of wounds and surgical anastomoses, the increased risk of, in particular, pulmonary infection, the exacerbation of ischaemic damage to the brain and myocardium and dehydration and electrolyte loss as a consequent of the osmotic diuresis. These were summed up in an editorial in Anesthesia and Analgesia (2007; 104: 4-6).
Professor Hall then looked at the consequences of tight control (4.5 to 6.1 mmols/L) of blood glucose, and asked whether the benefits of tight control outweighed the risks. He looked at the paper by Van de Berghe (NEJM 2001; 345: 1359-67) which showed a reduction in the mortality from 8.0 to 4.6% in ITU patients associated with a significant reduction in multi-organ failure, blood stream infection, acute renal failure and polyneuropathy. There have been consistent data to show that the early mortality is increased by about 50% in diabetic patients undergoing CABGs. He then looked at a paper by Gandhi et al (Ann Intern Med 2007; 146: 233-43) which looked at intensive insulin therapy compared to usual intra-operative care in patients undergoing CABG. It found that intensive insulin therapy did not reduce peri-operative deaths or morbidity. In fact, there was an increased incidence of death and stroke in the intensive treatment group which raised concerns about this method of treatment. He concluded that there was very little evidence that tight control of glucose had a significant effect on outcome in diabetic patients undergoing routine surgery.
Professor Hall then looked at the problem of metabolic care in the peri-operative period. In particular he talked about starvation and the hormonal and metabolic response to surgery. He commented that all volatile anaesthetic agents reduce insulin secretion. He thought that a full pre-operative evaluation of patients was essential with investigations including urinalysis for the presence of ketones and albumin which is often neglected. He looked at the metabolic management of diabetic patients. He said that type I diabetics should almost always have a glucose insulin potassium (GIK) regimen. However, in type II diabetics, the GIK regimen may only be necessary for major or moderate surgery, and for minor surgery, it may cause more metabolic upset than having no treatment at all. He looked at the two methods of administering IV insulin. Firstly the Alberti regimen lacked flexibility but was essentially safe. A separate insulin infusion on a sliding scale may improve glucose control but hypoglycaemia can occur if patients are not monitored closely. Professor Hall thought that the maximum interval between blood glucose estimations with a sliding scale in particular, should be two hours. Plasma potassium should also be monitored regularly and ideally arterial blood gas and urine testing should be performed to detect the presence of keto-acidosis. He commented that estimations of blood hydroxybutyrate would soon be available which would give a better warning of ketoacidosis. Professor Hall touched on the misconceptions about type II diabetics being easy to treat with tight metabolic control being unnecessary.
Professor Hall then looked at future drug innovations for the treatment of diabetes. Firstly he showed a graph of the Incretin effect. Incretins are a type of gastro-intestinal hormone which cause an increase in the amount of insulin release from beta cells after eating, even before blood glucose levels become elevated. They also slow the rate of absorption of nutrients into the blood stream by reducing gastric emptying and directly reduce food intake. Exenatide is an Incretin mimetic that acts physiologically in a similar way to glucogon-like peptide-1 (GLP-1) which lowers blood glucose by stimulating insulin secretion, inhibiting glucagon release and slowing gastric emptying. He anticipated that a long-acting version of this drug would become available which required twice weekly injection. In combination with oral hypoglycaemic agents, this new drug could greatly improve the control of type II diabetes. The next drug he looked at was Sitagliptin, which was a dipeptidyl peptidase for (DPP-4) inhibitor which prevents the degradation of Incretins. A Sitagliptin/Metformin combination is currently available in the US.
Professor Hall then looked at anaesthesia for diabetic patients. He said that there was no current evidence that anaesthetic technique affects mortality and morbidity. He looked at regional anaesthesia in diabetic patients. He thought the advantages of an awake patient was the detection of hypoglycaemia, the obtunding of the surgical stress response and as with non-diabetic patients, there was decreased blood loss and risk of thrombo-embolism. However, neuro-axial blockade did reduce cardiovascular stability, particularly for major surgery such as abdominal aortic aneurysm repair. There was also an increased risk of infection when catheters are inserted, particularly if diabetic control is poor. A paper by Williams et al (Anesthesiology 2008) looked at subclinical neuropathy and diabetics. The recent editorial in Anesthesiology by Williams et al, (Anesthesiology 2008; 109: 361-2) looked at the possibility of local anaesthetics being more toxic and nerve stimulators being less effective in diabetics.
Professor Hall looked at intravenous fluids in diabetic patients. In particular, he said that Hartmann’s solution was safe to use in diabetics and postoperative hyponatraemia is very common if only glucose solutions are infused. The common misconception that Hartmann’s solution significantly impairs diabetic control, he thought to be untrue. This is because a litre contained 27 mMs of lactate which would yield 14.5 mM of glucose, but only if gluconeogenesis was perfect. The distribution of this glucose in the ECF volume of about 14 litres would mean the maximum increase in blood glucose with 1 litre of Hartmann’s solution would be no more than 1 mMl/l.
In the final section of his talk, Professor Hall looked at the postoperative care of diabetic patients. He said that IV insulin should be maintained for at least 2 hours after the first meal. There should be careful fluid balance with nausea and vomiting being prevented and treated vigorously if it occurred because of the consequent difficulties re-establishing oral intake. He said that NSAIDs should be used with caution although good pain relief will always decrease the catabolic hormone release. He finally looked at special situations such as day surgery, obstetrics, paediatrics and emergency surgery in patients with DKA. He said there was no evidence to guide treatment in these special situations so could give no specific insight.
Professor Hunter thanked Professor Hall for his talk and asked for any questions from the floor. Among other questions Keith Stevens asked how real the problem of hypoglycaemia actually was. Professor Hall commented that he didn’t believe hypoglycaemia was as dangerous as is made out, and the actual definition of hypoglycaemia was still uncertain, depending on which papers were read. He did say that diabetics were often more used to having higher blood glucoses so they be more sensitive to hypoglycaemia than normal patients. He commented that diabetic physicians were often too busy for the routine care of peri-operative diabetics. In answer to a further question about on the day admission for surgery, he thought that the advice that diabetics should be first on the list probably is now unrealistic as they often come ill prepared, having literally just been admitted to the hospital. Better advice may be to have them second on the list once their diabetic plan of control had been instituted on the ward.
Professor Ron Jones gave the vote of thanks and commented that he must be the first Professor to have a hospital named after him. The meeting finished at 20.30.