Anaphylaxis Flashcards
(16 cards)
What is the pathophysiology of anaphylaxis?
Anaphylaxis occurs through allergen-bound IgE (immunogobulin E) antibodies where the antigen activates mast cells and basophils (monocytes, neutrophils) that release in a massive histamine response. This histamine response and the release of other chemical mediators (prostaglandins) causes vasodilation. These mediators bind to receptors which increases vascular permeability (capillary leakage into the interstitial space) that causes swelling. The vasodilation reduces systemic vascular resistance (SVR) due to the dilation of the arteries (distributive shock) and venous return which lowers the blood pressure (BP) (BP = CO X SVR). The chemical mediators also cause bronchoconstriction, increase mucus production and mucosal oedema, which all leads to acute bronchospasm. The release of histamine causes the itching and rash associated with the reaction.
What are the different types of anaphylaxis?
refractory and biphasic
Provide the definition of refractory anaphylaxis
It refers to a persistent anaphylactic reaction that does not improve or resolve despite receiving two appropriate doses of IM adrenaline.
Provide the definition of biphasic anaphylaxis
Refers to a second wave of symptoms occurring after an initial anaphylactic reaction has subsided, even without further exposure to the allergen which can happen within 6 and 12 hours after the first reaction.
Give a rationale as to why patients are unable to breathe during an anaphylaxis episode?
The swelling around the upper airway and bronchoconstriction occurs due to a histamine response that causes bronchospasm and increases capillary permeability, leading to fluid leakage and swelling.
Give rationale as to why the body reacts with hives and rashes during anaphylaxis
The release of histamine causes the blood vessels to dilate, increasing blood flow which leads to redness, itching and swelling.
What is the first line drug treatment for anaphylaxis? include route and dosage
Adrenaline given through intramuscular injection with the dosage of 0.5mg, 500mcg in 1:1000mg/ml
What is the pharmacodynamics of adrenaline?
Adrenaline is a potent antihistamine which helps reduce the swelling of the airways, bronchoconstriction and increase blood pressure by causing vasoconstriction of smooth muscle through the activation of alpha-1 adrenergic receptors. This process increases systemic vascular resistance (SVR) (BP = CO x SVR). Moreover, it stimulates beta-1 receptors which elevates heart rate and stroke volume. This results in an increase in cardiac output which also raises blood pressure and assists in preventing distributive shock, hypoxia, and cardiac arrest.
What is the rationale of not using antihistamine as a treatment for anaphylaxis?
Adrenaline as the first line drug treatment. Antihistamines takes 1-2 hours to peak which takes too long. It also only treats rash and itching due to the very large histamine response but it can be considered once the patient is stable.
Why is oxygen not the 1st line of treatment for anaphylaxis?
It is not recommended as 1st line of treatment due to the swelling which obstructs the airways and reduced perfusion. This means that oxygen cannot reach cells which causes multi-organ failure and respiratory/cardiac arrest.
How do you administer oxygen during anaphylaxis?
High flow of oxygen (15L) given through non-rebreathe mask with saturation levels aiming at 94%-98%.
What crystalloid is recommended to use for anaphylaxis?
Non-glucose containing crystalloid (hartmann’s)
Why is non-glucose containing crystalloid (hartmann’s) is given during anaphylaxis?
For anaphylaxis, a non-glucose containing crystalloid is given (eg Hartmann’s) as the fluid concentration is the same in the inside and outside of the cells. This is called an isotonic solution which means that it has the similar composition of human plasma. It works to treat hypovolemia due to anaphylaxis by restoring fluid volume and restoring electrolyte balance.
Why is hartmann’s preferred over NA saline?
Hartmann’s is preferred as the crystalloid to use rather than 0.9% sodium chloride saline to reduce the risk of hyperchloraemia (elevated chloride ions/ electrolyte imbalance).
How many mLs is recommended to be given during IV fluids challenge?
500-1000 mL in adults
What is the pharmacokinetics of adrenaline? use ADME
Absorption - Adrenaline is administered through IM to allow for rapid absorption due to vascular nature of the tissue.
Distribution - the drug is delivered directly into the bloodstream, avoiding first pass metabolism.
Metabolism - Adrenaline will then be quickly metabolised in the liver with a very short half-life of 3-5 minutes.
Excretion - Adrenaline will then be excreted in the urine.
