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Endocrinology

Created: 15/6/2006
Updated: 10/1/2007
 

Diabetes


Classification


Type I

  • Autoimmune disease, 40-50% concordance, β-cell destruction, ? viral or environmental trigger, insulin deficiency
  • Prone to diabetic ketoacidosis (DKA)
  • Presents at an early age
  • Requires insulin replacement

Type II

  • 100% genetic concordance, increased in obese, insulin resistance
  • Not prone to DKA, but may develop hyperglycaemic hyperosmolar coma
  • Presents in middle aged or elderly (except MODY)
  • Initial therapy often with diet, exercise, oral agents, later insulin

Insulin

Synthesized in endocrine pancreas (islets of Langerhans) by β cells:

  • α Cells secrete glucagon, δ cells secrete somatostatin, F cells secrete pancreatic polypeptide
  • Normal secretion 1 U/kg/day, peaks after meals, t1/2 5 min

Release stimulated by:

  • Plasma glucose and fructose, amino acids, glucagon, gastrin, secretin, CPK, ACh, catechols via β-receptors
  • GH increases insulin responsiveness

Release inhibited by:

  • Somatostatin, catechols via α-receptors

Perioperative management

Evidence

  • Diabetics are at increased risk of complications
    • Due to secondary effects of diabetes (IHD, renal disease…) not due to
      hyperglycaemia
  • Tight control of blood sugar
    • Reduces chronic complications of diabetes
    • Benefits foetus in pregnancy
      • Less macrosomia
    • Beneficial during cardiopulmonary bypass
      • More responsive to inotropes
      • Stress response produces hyperglycaemia
      • Hypothermia diminishes insulin sensitivity
    • Beneficial during cerebral ischaemia
      • Lower risk of neurological damage
    • Otherwise little evidence for advantages in tight perioperative control

Major risks in the diabetic patient:

  • Cardiovascular: IHD, PVD, microvascular disease 
  • Renal impairment 
  • Neuropathies 
  • Impaired cellular immunity 
  • Joint collagen abnormality (jaw stiffness, poor deep wound healing)

Resuscitation of the DKA patient for emergency surgery:

  • Usually time for fluid replacement, electrolyte correction 
  • Fluid deficit 3-10 L (Saline 5-10 ml/kg plus 1-4 L/h) 
  • Potassium deficit 3-10 mmol/kg (KCl 10-20 mmol/L fluid)
  • Insulin deficit
    • Correct K+ <3 mmol/L first
    • 10 U bolus plus 5-10 U/h titrated against blood sugar
    • Add 5% dextrose to fluids when glucose <15 mmol/L
  • Hourly ABG and glucose 
  • Aim for glucose 10-14 mmol/L, pH >7.35, Na+ < 155 mmol/L, K+ 3-5 mmol/L 
  • Also phosphate, magnesium deficient

Classic “non-tight control” regimen:

  • Fast from midnight for morning surgery 
  • 5% dextrose 125 ml/h IV from 6 am 
  • Half normal morning dose of insulin 
  • Check BSL 1-4 hourly 
  • Sliding scale insulin from recovery until return to normal diet


“Tight” regimen

  • Check fasting glucose day before surgery 
  • 5% dextrose 50 ml/h IV
  • Initial insulin IV rate (U/h) = BSL/8.3 (mmol/L) (or BSL/5.5 if on steroids)
  • Titrate insulin rate to BSL 5.5-11.1 mmol/L
  • Check BSL at start of surgery and every 1-2 h for 24 h

Other perioperative concerns

  • Autonomic neuropathy
    • Increase in gastric emptying time, risk of aspiration
    • Painless myocardial ischaemia
    • Signs include hypertension, lack of sweating, lack of R-R variability, postural hypotension, peripheral neuropathy
  • Microvascular disease
    • ? Increased risk of neuropraxia with regional

Perioperative corticosteroid supplementation


Evidence

  • Few patients with adrenocortical suppression have problems even without steroid cover: documented cases are rare
  • Acute adrenal insufficiency is life-threatening
  • Perioperative steroid cover carries minimal risks
  • Primate study found no difference between physiologic and supraphysiological doses


 

Physiology

  • Maximum adrenal cortisol output 200-500 mg/d
  • Normal 25 mg/d

Risks of supplementation

  • Possible
    • Minor impairment of wound healing (antagonized by vitamin A)
    • Impaired immune function
    • Hypertension, fluid retention, stress ulcers, psychosis
    • Aseptic necrosis of head of femur


Recommended regimen

  • Indicated for all patients receiving steroids within past year
  • Not less than usual preoperative dose equivalent
  • Hydrocortisone 200 mg/d for 70 kg adult (100 mg for minor procedures)
  • Reducing 25% per day until oral steroids resumed


Kindly provided by Dr James Mitchell from his pharmacodynamics series


ArticleDate:20060615
SiteSection: Article
 
   
    
                                            
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