Extras

• Anaemia:

  • Low haemoglobin due to decreased red cell mass
  • Normal range 11-18g/dl for females (13-18g/dl for males)
  • Full blood count = haemoglobin, white cells and platelets
• Main types of anaemia:

  • Microcytic hypochromic - iron deficiency
  • Normocytic - anaemia of chronic disease (rheumatoid arthritis, chronic kidney disease)
  • Macrocytic - B12, folate deficiency
• Normal white cell count = 4,000-11,000 per microlitre
• Normal platelet count = 150,000-400,000 per microlitre
• Neutrophils - bacterial:

  • Increase in neutrophils - bacterial infection, surgery, trauma
  • Decrease in neutrophils - viral infections, some drugs
• Lymphocytes:

  • Increase - viral infections, CLL (chronic lymphocytic leukaemia)
  • Decrease - steroid treatment, SLE (systemic lupous erythema)
• An increase in eosinophils is seen in some allergic disorders.
• Pernicious anaemia:

  • Malabsorption of vitamin B12 due to decreased intrinsic factor
  • Everyone with pernicious anaemia has a vitamin B12 deficiency, but not everyone with a vitamin B12 deficiency has pernicious anaemia
  • Associations: thyroid, vitiligo, Addison's
  • Haemoglobin decreased
• Sickle cell anaemia:

  • Homozygote = disease
  • Heterozygote = trait
  • Cells sickle on exposure to decreased oxygen tension leading to infarction etc
• Thalassaemias:

  • Group of disorders
  • Decreased production of one or more globin chains
  • Alpha and beta types refer to decreased alpha and beta chain production respectively
• Relevance of sickling/thalassaemia = care with decreased oxygen tension - in particular sedation/GA
• Platelet abnormalities:

  • Numbers (thrombocytopenia) <50 is an issue
  • Von Willebrand's disease
• Liver problems:

  • Decreased vitamin K leading to decreased clotting factors II, VII, IX, X
• Disorders of blood:

  • Leukaemias, acute, chronic - many now treatable
  • Lymphoma - Hodgkin's, Non-Hodgkin's - many present as a neck lump
  • Effects of chemotherapy
• Bone marrow failure:

  • Leads to pancytopenia
  • Myeloma - plasma cell neoplasm leading to marrow infiltration and osteolytic deposits
• Erythrocyte Sedimentation Rate (ESR):

  • A non-specific indicator of the presence of disease
  • Age-dependent
  • Men = age divide by 2, women = age + 10 divide by 2
• A 2.2ml cartridge of 2% lidocaine 1:80,000 adrenaline contains 44 mg of lidocaine. In 1/10th of a cartridge there is 4.4 mg of lidocaine. This allows circulation of the maximum dose of lidocaine based on the patient's body weight. Eg a 70kg fit and healthy pt could have 7 2.2ml cartridges of 2% lidocaine with 1:80,000 adrenaline, whereas a 25kg child could have 2.5 cartridges of the same solution.
• The maximum dose of 2% lidocaine with 1:80,000 is 500 mg, which is equivalent to approximately 11 cartridges. In order to avoid local anaesthetic toxicity you should always calculate the appropriate dose for your pt, aspirate, and inject slowly.
• Lidocaine is metabolised in the liver.
• Articaine is metabolised in the serum by plasma cholinesterase and liver.
• Prilocaine is metabolised in the liver and lungs.
• Local anaesthetic agents can be classified as ester or amide. Within the chemical structure the intermediate chain defines which group the local anaesthetic belongs to. Allergies are more common with the ester group, this is often due to the metabolite of this group being paraminobenzoic acid. If a patient reports an allergy to local anaesthetic agents they should be referred to immunology for allergy/patch testing.
• Amides are the local anaesthetic agents that produce active metabolites.
• Two theories of local anaesthetic action are: membrane expansion and specific receptor.
• Local anaesthetic agents are vasodilators, except for cocaine, which is a powerful vasoconstrictor.
• Ionisation governs LA onset. Partition co-efficient governs onset (higher the coefficient, the faster the onset). Protein-binding governs duration of action.
• Local anaesthetics containing a vasoconstrictor will contain a reducing agent - it acts as a preservative because vasoconstrictors are unstable in solution and prevent oxidation & breakdown.
• The 5 stages of metabolism of amide local anaesthetics are:

  • Dealkylation
  • Hydrolysis
  • Hydroxylation
  • Further dealkylation
  • Conjugation
• The treatment of a local anaesthetic overdose involves:

  1. Stop procedure
  2. Get help (remember ABCDE)
  3. Lie pt flat
  4. Maintain airway
  5. Administer oxygen
  6. IV anticonvulsants, lipid emulsion & fluids
  7. Basic life support