9. Diabetes Flashcards
What is diabetes and how is it classified?
Diabetes mellitus (DM) is a group of metabolic diseases
characterised by hyperglycaemia
resulting from defects in
insulin secretion,.
insulin action
or both.
Patients with any form of diabetes may require insulin treatment at some stage of their disease.
It can be classified, based on aetiology, as
follows:
> Type 1 diabetes (previously insulin-dependent diabetes mellitus) Characterised by loss of insulin- producing beta cells of the islets of Langerhans in the pancreas, via an immune or idiopathic mechanism.
It usually presents in childhood
requires exogenous insulin
administration to prevent ketosis.
> Type 2 diabetes
(previously non-insulin-dependent diabetes mellitus)
Characterised by insulin resistance,
which may be combined with
relatively reduced insulin secretion.
The main risk factors include
central obesity,
increasing age
and family history.
Treatment involves
increasing physical activity,
reducing carbohydrate intake
and weight reduction,
may require oral hypoglycaemic agents
and/or non-insulin injectables.
In later stages, insulin may also be necessary.
Other specific types include:
> Gestational diabetes – any degree of glucose intolerance with onset or first recognition during pregnancy.
> Genetic defects of beta-cell function (e.g. maturity onset diabetes of the young or MODY).
> Genetic defects in insulin action (defects in insulin receptor or post-receptor signal transduction pathways).
> Diseases of the exocrine pancreas
(pancreatitis, trauma, infection,
pancreatectomy, adenocarcinoma, cystic fibrosis, haemochromatosis).
> Endocrinopathies (acromegaly, Cushing’s, glucagonoma, phaeochromocytoma, i.e. increase in hormones that antagonise insulin).
> Drug- or chemical-induced
(drugs or toxins that may precipitate diabetes in individuals with insulin resistance, e.g. β-blockers, thiazides,
glucocorticoids).
> Infections
(congenital rubella, CMV, coxsackievirus B, mumps).
> Uncommon forms of immune-mediated diabetes (anti-insulin receptor antibodies).
> Other genetic syndromes sometimes associated with diabetes (Down’s, Klinefelter’s, Turner’s).
What do you understand by the terms impaired glucose tolerance (IGT) and impaired fasting glucose
(IFG)?
Intermediate group of patients whose
glucose levels do not meet the criteria for diabetes
but are nevertheless too high to be considered normal.
They are considered as having ‘pre-diabetes’ indicating a relatively high risk of developing DM later.
Criteria are:
> IFG: fasting plasma glucose = 5.6–6.9 mmol/L
> IGT: glucose = 7.8–11.1 mmol/L (2-h post glucose load)
What are the complications of diabetes?
> Acute complications:
• Diabetic ketoacidosis (DKA);
more common in Type 1 than Type 2.
• Hyperosmolar non-ketotic state (HONK);
more common in Type 2 than Type 1.
• Hypoglycaemia, usually iatrogenic resulting from excess insulin administration.
All of the acute complications are potentially life-threatening and constitute medical emergencies.
> Chronic complications:
• Vascular – accelerated atherosclerosis, cerebrovascular disease, coronary artery disease, hypertension and peripheral vascular disease.
• Diabetic nephropathy –
early signs of renal failure are proteinuria and
elevated serum creatinine.
• Autonomic neuropathy –
postural hypotension and
impaired gastric motility.
• Peripheral neuropathy –
increased risk of tissue damage and
ulceration.
• Diabetic retinopathy.
• Infection –
increased risk of post-operative wound infection.
• Musculoskeletal –
Collagen glycosylation may lead to stiff joint
syndrome and has been associated with a higher incidence of difficult
intubation as it can affect the temporomandibular joints.
What are the anaesthetic implications of a diabetic
patient presenting for surgery?
The aims of pre-operative assessment are to:
> Determine the severity of any systemic complications.
> Assess the adequacy of blood glucose control.
> Exclude the presence of ketoacidosis.
Diabetic patients are at increased risk of peri-operative complications including silent MI, stroke, pressure sores, infections of wounds/chest/urinary tract, and ketogenesis.
What peri-operative management consideration should be made for patients with Types 1 and 2 diabetes on elective lists?
There is evidence that poor
pre-operative glycaemic control is associated
with greater post-operative mortality and morbidity after elective surgery,
including silent MI, stroke, pressure sores, infections of wounds/chest/urinary tract and ketogenesis.
Peri-operative considerations:
> The patient will undergo a period of enforced fasting – blood glucose will need to be maintained during this period.
> Patients presenting for emergency surgery may be metabolically deranged,
with major acid–base and electrolyte disturbances, which need correcting.
> Patients presenting for elective surgery should have good glycaemic control.
Measure glycosylated haemoglobin (HbA1c) levels, which correlate with blood glucose control in the preceding 2 months
(normal <7%).
> The surgical stress response will cause a rise in
blood glucose intra-operatively.
> The patient may not be allowed
oral intake of fluid or nutrition for a period post-operatively,
e.g. following abdominal laparotomy.
Peri-operative management
Guidelines were published by
NHS Diabetes and the Joint British Diabetes
Societies Inpatient Care Group in April 2011 to improve the standard of care received by diabetic patients undergoing elective surgery
(some principles can be applied to the emergency setting).
- Minimise starvation time by prioritising diabetic patients on the operating list.
- > When starvation times are limited to one meal:
• patients on oral hypoglycaemic agents should continue
only metformin and pioglitazone as normal on the day of surgery and
omit all others.
- • patients on insulin should
continue intermediate or long-acting insulin
and either halve or omit short-acting insulins
(this depends on the type of insulin regimen).
- > When starvation times are expected to exceed more:
• all patients should receive a Variable Rate Intravenous Insulin Infusion (VRIII),
formerly called insulin sliding scale. - > Measure blood glucose on admission
and then hourly intra-operatively
and in the immediate post-operative period. - > If pre-operative glucose is above 12 mmol/L,
check blood and urinary ketones. If <3+ administer subcutaneous insulin (as per guideline) and
reassess;
if >3+, then cancel surgery and treat as DKA.
- > Implement the WHO Surgical Safety Checklist bundle.
The target blood glucose should be 6–10 mmol/L (acceptable range 4–12 mmol/L).
8.
> Use multimodal analgesia and anti-emetics
to enable early resumption of usual diet and self-managed diabetes regimen.
- > Implement principles of the Enhanced Recovery Programme:
early mobilisation with resumption of normal diet and return to usual diabetes management. - > Involve diabetes specialists where indicated.
How is a variable rate intravenous insulin infusion used?
- > VRIII are indicated if starvation time is expected to be more than one meal, or if diabetes is decompensated.
2.
> Insulin should be administered via a syringe driver, and intravenous fluid via a volumetric infusion pump, both through a single cannula with oneway or antisiphon valves.
3.
> The recommended intravenous fluid for a VRIII is 0.45% sodium chloride
with 5% glucose and either
0.15% potassium chloride (KCl) or 0.3% KCl.
- > The dose requires adjusting according to hourly capillary blood glucose
(CBG).
• If CBG is <4 mmol/L reduce VRIII to 0.5 mL/h
and administer 10% dextrose
(this is to limit ketogenesis that occurs in the absence of background insulin).
Stop the infusion only if a long-acting insulin has
been continued.
• Once patient is eating and drinking revert back to their regular medication.
- Dose adjustments
(especially short-acting insulin and
sulphonylureas) may be necessary and there should be a period of overlap between VRIII and subcutaneous insulin administration. - > Insulin should be prescribed according to National Patient Safety Agency (NPSA) recommendations for safe use of insulin.
