Case 7- treating allergic diseases Flashcards
Long acting histamine
Provides symptom relief for 8-12 hours
Shorter acting histamines
Last up to 4 hours but begin working faster
First generation antihistamine side effects
Drowsiness, difficulty urinating, dizziness, dry mouth, blurred vision, tinnitus and constipation
First generation antihistamines
Chlorphenamine, Diphenhydramine
Second generation antihistamine side effects
Less likely to cause side effects
Examples of second generation antihistamines
Cetirizine (Active ingredient in OTC medicine Zyrtec) and Loratadine (active ingredient in OTC medicine Claritin.
Eosinophilic esophagitis
An allergic inflammation of oesophagus which involves build up of eosinophils in its lining. There is dis-mobility of the oesophagus so it cant move much, you get difficulty swallowing. It is non-IgE mediated. You are likely to have other allergies which are IgE mediated
First thing to discuss in an allergic reaction
Ask about exposure- was there a clear temporal relationship with the trigger, the consistency of the reaction does it happen every time they are exposed to the substance. Is it a typical allergen? Timing, IgE mediated allergy is within 2 hours of ingestion. Ask about atopy and family history. History identifies allergen 50% of the time
Common IgE mediated food allergies
Cow’s milk, soybean, wheat, Egg white, peanut, tree nuts, fish and selfish. They account for 90% of reactions.
Allergy- examination
- Skin- eczema (extent and severity), urticaria.
- Eyes- conjunctivitis, swollen, watery.
- Nose- nasal speech, congestion and inspection
- Chest- shape and wheeze.
- Growth parameters- lots of disorders which cause symptoms similar to allergies cause a failure to thrive. This could be general malabsorption.
How useful is a skin prick test
It is cheap, painless with instant results. It has a 90% sensitivity and a 50% specificity. Due to the low specificity you will get more positive results then are clinically relevant. So when examining results be aware of clinical history.
How do you use a skin prick test
You put a drop of the allergen on the skin and place a small incision in the skin within the upper epidermis and that will mimic mast cell degranulation. If there is an allergy you will get a wheel and flare rash. You then put a drop of histamine on the skin as a control, everyone will react to the histamine. You measure the size of the reaction produced.
Allergy- blood test
Specific IgE measurements looks specifically at the allergen you are investigation. Blood tests are expensive and can take a week for results to get back. Blood tests measure the levels of allergy antibodies or IgE produced when your blood is mixed with a series of allergen in the lab
When do you use an allergy blood test
You do this when there is a risk of anaphylaxis in the skin test and if there is recent antihistamine use as the skin prick test wont work. If the patient has lots of eczma you do it instead of the skin prick test.
Components test- allergy
Identifies the part of the allergen that the patient is allergic to as this will effect on the severity of the reaction. The component test can be used as a diagnosis and risk assessment
Severity of allergies- peanuts
Patients who are sensitised to the peanut allergen Ara h 8 usually experience none or very mild oral symptoms. Patients who are sensitised to more stable components such as the seed storage proteins (i.e. Ara h 2) are more likely to experience systemic reactions.
Food challenge- allergies
It is open feeding/single blinded. There is the gradual feeding of the test food under supervision and see if they react. You need specific protocols and trained staff due to the risk of anaphylaxis. It can be done at home or in the hospital.
Blood test results for allergy
Normal range for blood tests is 0-100 ku/L so over 100 is an allergy.
EpiPen
Epinephrine autoinjectors (EpiPen)- used when the patient goes into an anaphylactic shock, two of them might need to be used. They should be carried around at all times
Allergy treatment- immunotherapy
It is associated with more risk but is used when there is inadequate control or the allergen is unavoidable. Can be used for pollen, house dust and certain foods like peanuts. Anti-IgE therapy is used for asthma and chronic urticaria
Insect stings- anaphylaxis
More common in adults and males. Can cause a local reaction or anaphylaxis. It is reported in 0.3-3% of stings. Ischaemic heart disease and chronic lung disease are risk factors for severe/fatal anaphylaxis. Half of the people who die did not know they had an allergy.
Causes of anaphylaxis
Food, pollen and insect bites, medication, miscellaneous (immunotherapy) and idiopathic (don’t know the cause).
Risk factors for food anaphylaxis
- Age 8-35 years, the highest rate of admissions is between 0-4 but fatal in older individuals.
- Asthma
- Peanut allergy
- Female
- Eating food outside the house
- Delayed adrenaline administration
The three criteria for anaphylaxis
• Sudden onset and rapid progression of symptoms.
• Life-threatening airway, breathing and circulation problems.
• Skin and/or mucosal changes (flushing, urticaria, angioedema).
Exposure to a known allergen or to a substance for the first time (penicillin) supports diagnosis
Respiratory symptoms of anaphylaxis
Shortness of breath, tachypnoea, wheeze or stridor, chest tightness and respiratory arrest.
Cardiovascular symptoms of anaphylaxis
Tachycardia/bradycardia, palpitations, hypotension, collapse and cardiac arrest.
GI and CNS symptoms of anaphylaxis
GI symptoms- abdominal pain, nausea, vomiting and Diarrhoea.
CNS symptoms- ‘feeling of impending doom’, altered mental state, confusion and drowsiness.
Differential diagnosis of anaphylaxis
- MI/ cardiac arrhythmia.
- Acute severe asthma.
- Pulmonary embolus
- Airway obstruction, (Chocking)- foreign body aspiration.
- Spontaneous pneumothorax.
Differential diagnosis of anaphylaxis- panic attack
Difficult to differentiate, panic may co-exist with anaphylaxis. Usually no hypotension, pallor, wheeze or urticaria.
Differential diagnosis of anaphylaxis- Vasovagal episode
Vasovagal episode- when you feel faint as your body over-reacts to certain triggers like seeing blood. There is no rash and a shallow pulse in vasovagal compared to a rapid pulse in anaphylaxis
Identifying anaphylaxis- airway
Laryngeal oedema can obstruct airway. Look for tongue/airway swelling, listen for stridor. If the airways are compromised perform basic airway manoeuvres and get anaesthetic help immediately.
How to treat airway obstruction in anaphylaxis
Perform airway manoeuvre- head tilt and chin lift if there is no spinal injury. Use airway adjuncts to keep the airways open i.e. nasopharyngeal or oropharyngeal airways. Call anaesthetics
Identifying anaphylaxis- breathing
Respiratory rate/effort for example wheezing. Cyanosis is a late sign showing their oxygen is depleted. Press and ausculate the chest. Feel for expansion and central tachycardia. Assess oxygen saturation. Use a blood gap test to check blood pH (CO2 conc)
How to improve breathing in anaphylaxis
Administer high flow oxygen (15L) in a non-rebreathe mask
Normal respiratory rate
12-20bpm
Normal oxygen saturation
> 96% or 88-92% in COPD
Identifying anaphylaxis- circulation
Check for signs of shock (pale, clammy, long capillary refill time <2sec). They might have tachycardia or bradycardia. They will have hypotension. Assess JVP and radial pulse. Check for Angiodema. Check heart rate and blood pressure. Do a liver function test and a kidney function test. Do a FBC and look at white blood cell count for inflammation. Measure urine output (>0.5ml/kg/hr).
Normal heart rate
60-90bpm
Blood pressure in anaphylaxis
Under 110, over 220
What to do with a bad anaphylaxis circulation
Put in 2 cannulas and take blood for analysis. Give the patient IV fluid 500-1000ml 0.9% saline, make sure to not overload them
Normal urine output
Measure urine output (>0.5ml/kg/hr).
Identifying anaphylaxis disability
Where on the APVU scale are they ‘Alert, Voice, Pain, Unresponsive.’ This checks how conscious they are. If the patient is drowsy or tiring get help. Ask for temperature measurements and check their pupils, take blood glucose measurements. If the GCS (level of consciousness scale) is under 8 call the anaesthetic team as the patient cant protect their airway. Consider pain relief
Identifying anaphylaxis exposure
Look for skin and mucosal changes such as rashes and bruises. See if calves are red or swollen for DVT. Look for tenderness over abdomen, assess around bed.
Adrenaline
Given first when anaphylaxis is recognised. The prescription is 0.5ml of 1 in 1000 (0.5 mg). Given IM (intramuscular). Repeat if needed. Only anaesthetics can give it IV
What does adrenaline do
Adrenaline will prevent and relieve airway obstruction from mucosal oedema. It promotes cardiac output and increases total peripheral resistance to increase blood pressure. Adrenaline is the only life saving medication in anaphylaxis everything else is secondary.
Additional anaphylaxis measures after adrenaline
- IV fluid challenge= 500-1000ml (20ml/kg in a child).
- Steroids= Hydrocortisone 100-200mg IV
- Antihistamines= Chlorphenamine 10mg IV
Test for identifying anaphylaxis
Mast cell Typtase- a major protein component of mast cell granules. Released in genuine anaphylaxis, useful in retrospective diagnostic clarification.
Types of injectable adrenaline
- 15-30Kg: self injectable device (0.15mg)
- > 30Kg: self-injectable device (0.3mg)
- Repeat the IM adrenaline dose after 5-15 minutes if there is no improvement in the patients condition.
- Dial 999 if anaphylaxis is suspected or an adrenaline auto-injector is used.
- Bronchodilators can be used after.
Types of inhalers
Aerosol inhalers
Dry powder inhalers- given to older kids as its harder to use
Anti- inflammatory / steroid inhaler- used in emergencies
How adrenaline affects the alpha 1 receptor
It causes smooth muscle contraction in the peripheries increasing blood pressure
How adrenaline affects the alpha 2 receptor
It inhibits transmitter release and causes smooth muscle contraction
How adrenaline affects the beta receptor
Causes heart muscle contraction and smooth muscle relaxation (bronchodilation)
Delivering oxygen in practise- Nasal cannulae
Nasal cannulae- give to stable patients who are mildly hypoxic. 2-4L. Gives 24-30% oxygen
Delivering oxygen in practise- Venturi masks
Venturi masks- used in COPD so you don’t get over oxygenation. Different colours give different amounts of oxygen.
Delivering oxygen in practise- Non-rebreathe masks
Non-rebreathe masks- for acutely unwell patients, 15L flow rate with 85-90% oxygen. You inflate the bag before administration. Patient breathes in from the bag and out though the one way valve minimising air from surroundings.
