Laser doppler flowmetry in anaesthetic allergy skin testing

Laser Doppler flowmetry (LDF) is an inexpensive, non-invasive method of measuring the blood flow in the small vessels of the skin. In allergic patients, following skin testing the small blood vessels in the skin open and blood flow increases. This can be detected by LDF in a manner that is more objective. The laser used in LDF is a Moor FLPI-2. It is classified as a “class 1” laser. The product information states it is “safe to use without eye protection”. The Monash University OHS website states that class 1 lasers “…are safe under most circumstances and are incapable of damaging the eyes or skin because of either engineered design or inherently low power output”. The study will involve testing concurrently, at the same site, conventional skin testing and LDF testing. Conventional skin testing will be undertaken to the drugs that the patient was exposed to perioperatively that could have been potential causal agents for allergy. Therefore the drugs tested will be specific to each individual case and we cannot predict what drugs will be skin tested as that depends on what drugs were administered during the anaesthetic. Our testing involves intradermal administration of all the drugs that were given. Intradermal testing involves giving 0.02ml of dilute drug into the dermis of the skin. The dilutions vary depending on the drug from 1:100 to 1:100 000. That equates to about one millionth of the dose of the drug that was administered in the anaesthetic. We also do a positive control - that is a skin prick test (much <0.02mL) of 8mg/ml histamine. Here is a list of drugs that may be required to be tested: Drug Dilution Original concentration Alfentanil 100 0.5 mg/mL Amoxicillin 100 100 mg/mL Atracurium 10,000 10 mg/mL Atropine 1,000 600 mcg/mL Bupivacaine 100 2.5 mg/mL (0.25%) Cephazolin 100 100 mg/mL Chlorhexidine 1,000 0.20% Cisatracurium 1,000 2 mg/mL Clindamycin 100 150mg/mL Codeine 1,000 50 mg/mL Dexamethasone 100 4mg/mL Diazepam 100 5 mg/mL Diclofenac 1,000 75 mg/mL Droperidol 1,000 5 mg/mL Erythromycin 1,000 50mg/mL Fentanyl 100 50 mcg/mL Gelofusine 100 Gentamicin 100 40 mg/mL Glycopyrolate 100 200 mcg/mL Granisetron 1000 1 mg/mL Iodine 100 5% (Half) Ketamine 100 20 mg/mL Lignocaine 100 10 mg/mL (1%) Metoclopromide 1,000 5 mg/mL Midazolam 20 1 mg/mL Mivacurium 1,000 2 mg/mL Morphine 100,000 10 mg/mL Neostigmine 1,000 2.5 mg/mL Ondansetron 1000 2 mg/mL Pancuronium 1,000 2 mg/mL Paracetamol 100 10 mg/mL Parecoxib 1,000 10 mg/mL Patent blue 100 Half strength Pethidine 100,000 50 mg/mL Prilocaine 100 10 mg/mL (1%) Propofol 100 10 mg/mL Protamine 1,000 50 mg/mL Remifentanil 1,000 0.5 mg/mL Rocuronium 1,000 10 mg/mL Ropivacaine 100 2 mg/mL (0.2%) Suxamethonium1,000 50 mg/mL Thiopentone 100 25 mg/mL Tropisetron 100 1 mg/mL Vancomycin 10,000 50 mg/mL Vecuronium 1,000 4 mg/mL One clinician will inject all the drugs to be tested into the skin at the same time as per conventional skin testing protocols. At 20 minutes after skin injection, a second clinician will assess the patient’s test site, again, using conventional skin testing protocols. The LDF testing will be recorded by the first clinician and stored on a password protected, specifically assigned computer. At another time (to allow blinding) the second clinician will assess the LDF results. The conclusions made using both assessment methods will be compared.