Perioperative Anaphylaxis in an Egyptian Population.

Perioperative anaphylaxis is associated with significant morbidity and mortality. Most textbooks describe it as a rare event of the order of 1 in 10 to 1 in 20,000 general anaesthetic cases. However, a recent study in the United Kingdom suggested that 1 in 350 cases have features suspicious of perioperative anaphylaxis. This study suggests that perioperative anaphylaxis may be under recognised and under reported.

When perioperative anaphylaxis is recognised, it would be ideal to carry out investigations firstly to confirm the diagnosis of anaphylaxis and secondly to identify the causative agent. The latter can be difficult in the context of anaesthesia where the patient is exposed to several drugs and other reagents in a short space of time.

One of the interesting aspects of perioperative anaphylaxis is that there is variability in its epidemiology between different countries, for example between the United Kingdom, France, Scandinavia and Australia and New Zealand. There are currently no data from Egypt to include in such comparisons and to inform clinical practice.

As well as being at risk if a drug allergen is not identified, patients can also be at risk from an incorrect allergy label. The most common example of this is penicillin allergy where fewer than 10% of patients with a history of penicillin allergy are found to be allergic. Incorrect penicillin allergy labels are potentially harmful for patients attending for surgery because the label independently increases the risk of developing infection to resistant organisms, longer hospital stays and mortality.

Aim of the work:

This project proposes the following studies:

1. The incidence of suspected perioperative anaphylaxis in an Egyptian population.

2. Defining normal mast cell tryptase concentrations in perioperative patients in Egypt.

3. Defining non-irritant concentrations of neuromuscular blocking drugs.

4. Acute penicillin allergy de-labelling.

Patient and Methods:

1. In order to define the incidence of possible anaphylaxis, data will be collected on 1000 consecutive general anaesthetic procedures in Assiut University Hospitals. After each elective operating list the anaesthetist will be asked to complete a form in which they will document the number of patients receiving general anaesthesia on the list and the number of those patients who developed any of the following features: unexpected, unexplained hypotension; unexpected bronchospasm resistant to treatment; angioedema; urticaria; severe itching; widespread erythema.

2. Tryptase is a relatively stable protein released from mast cells alongside histamine during allergic anaphylaxis. Mast cell tryptase is recognised as a useful biomarker for perioperative anaphylaxis but there is debate concerning what degree of change in mast cell tryptase produces the greatest combination of sensitivity and specificity for perioperative anaphylaxis. Variable results from different countries suggest that population specific normal responses may need to be defined.

This study will be conducted in Assiut University Hospitals. A blood cell sample for mast cell tryptase will be taken immediately prior to surgery and 1 hour following induction of anaesthesia in the following groups of patients (n = 30 in each case):

1. Children undergoing elective surgery between the ages of 3 and 10 years

2. Adults between the ages of 16 and 30 years undergoing orthopaedic trauma surgery

3. Adults more than 60 years of age undergoing orthopaedic surgery

4. Women of any age undergoing gynaecological surgery

5. Adults of any age undergoing emergency general surgery

6. Adults undergoing cardiac surgery involving cardiopulmonary bypass (samples will be taken immediately preoperatively, prior to cardiopulmonary bypass and 1 hour after cardiopulmonary bypass)

7. Women undergoing caesarean section under general or regional anaesthesia

3. Skin prick testing and intradermal testing with potential drug allergens are a useful part of investigation of perioperative anaphylaxis. Epidemiological data suggest differences between populations in the incidence of anaphylaxis with NMBDs and also differences between the different NMBDs implicated. There is controversy about the appropriate concentration of drugs used in skin testing and different regimens may explain some of the variability.

Skin prick and intradermal testing will be done using available neuromuscular blocking drugs. For each drug serial dilutions will be used for the tests to determine the highest concentration that does not produce a positive response.

The study will be done on 2 groups of individuals with no history of anaesthetic problems. The first group will be patients, who as far as can be determined, have not received any NMDBs during their lifetime and the second group will be patients who it is known have received an NMDB without complication.

4. Patients presenting at Assiut University Hospital for elective surgery with a self-reported penicillin allergy will be questioned. Patients suitable for this study will be those who are deemed to be low risk for true penicillin allergy. The criteria for identifying a patient at low risk are as follows:

1. History of allergic reaction occurring more than 15 years ago

2. Symptoms are either unknown, a non-specific rash (erythema and non-raised rash that was not itchy), nausea or diarrhoea

3. No symptoms suggestive of a true allergic reaction (swelling, urticaria rash, itch, anaphylaxis) Low risk patients will be entered in an abbreviated acute penicillin allergy challenge test. This will be done in a monitored environment such as an anaesthetic room or post anaesthesia care unit where they can be monitored continually and with availability of an anaesthetist.

An intravenous cannula will be inserted and non-invasive monitoring established. For the challenge the prophylactic penicillin that is to be used for the surgery will be given at the standard dose divided at 20 minute intervals. At time zero 10% of the total dose will be given. Providing that no symptoms of allergy develop within 20 minutes a further 40% of the total dose will be given and after a further 20 minutes, assuming no symptoms of allergy, the remaining 50% of the total dose will be administered. The patient will be monitored for at least another 20 minutes before administration of anaesthesia.