Written By: Ali Rengers, Angus Hazelton, Steve Whitfield
Introduction
Anaphylaxis is a rapid, systemic and potentially fatal allergic reaction to an allergen (1-4). According to multiple sources including the Australian Society of Clinical Immunology and Allergy, anaphylactic presentation includes urticaria, erythema and/or angioedema with respiratory, cardiovascular and/or severe gastrointestinal symptoms. The definition also extends to the onset of acute bronchospasm, upper airway obstruction or hypotension where anaphylaxis is considered a possibility, without skin feature presentation (1-4).
Anaphylaxis in the paramedic setting can be defined as either the involvement of two or more organ systems following a possible exposure to an allergen or hypotension following exposure to a known allergen. Anaphylactic response is caused by the allergen reaction with antigen specific antibodies borne by effector cells (i.e., basophils and neutrophils) (1-4). These effector cells suddenly systemically release mediators, most notably histamine and cysteinyl leukotrienes, resulting in bronchoconstriction, vasodilation, increased vascular permeability, tachycardia and hypotension. (1-4).
Anaphylaxis treatment guidelines direct the treating paramedic to place the patient in a supine position and remove the allergen (if present) (5). The paramedic is to consider the administration of intramuscular adrenaline to produce bronchodilation and vasoconstriction, oxygen to increase oxygenation and/or sodium chloride 0.9% bolus to enhance inadequate tissue perfusion (1,2,5). A Canadian Emergency Department Evaluation conducted across five Canadian provinces demonstrated the efficacy of administering second-generation antihistamines in conjunction with adrenaline in reducing the possibility of negative outcomes (6).
The Case
During a late night shift, a paramedic crew were dispatched to a 29-year-old female patient suffering an allergic reaction in a residential apartment. Due to some unclear information filtering to dispatch from the scene a second solo paramedic was also dispatched to back up the original crew.
When the first crew arrived, they found the patient in obvious respiratory distress. The patient was anxious and unable to speak in full sentences, with an obvious red rash over her chest, arms and neck with some associated facial swelling. During the initial verbal exchange, it was ascertained that the patient had several known severe allergies to eggs, dairy, and iodine, however a trigger was not identified. The initial vital signs taken from the patient are recorded below in table one.
The solo paramedic arrived eight minutes after the arrival of the first crew and found that the crew on scene had been hesitant to administer adrenaline due to the patients higher than usual blood pressure. The crew were advised to immediately administer adrenaline for noticeable anaphylaxis.
The patient was immediately administered 500 micrograms of intramuscular adrenaline, placed on high flow oxygen via a non-rebreather mask at 15 litres per minute and then the crew prepared 5 milligrams of nebulised salbutamol (5mg /2.5ml) mixed with 500 micrograms of nebulised Atrovent. Whilst on scene, subsequent doses of intramuscular adrenaline and nebulised salbutamol were administered. Nebulised adrenaline was not administered. Following marginal improvement to the patient’s respiratory status, she was extricated using a stair chair to an awaiting stretcher and transported to hospital for further care.
Discussion
In the present case it appears that some confusion existed between the initial crew regarding the definition of anaphylaxis resulting in the delayed treatment of the patient. Definitions of anaphylaxis have been subject of continual debate but generally emphasise an acute and life-threatening allergic or hypersensitivity reaction with involvement of one or more organ systems (1-3). The variations in definitions can be confusing and misleading with the requirement of particular or multiple organ systems as well as the severity of the presentation which can lead to inappropriate treatment (1-3). In the present case it is evident that the absence of typical cardiovascular presentation of hypotension or shock resulted in delayed adrenaline administration. It must be understood that diagnosis of anaphylaxis does not require cardiovascular involvement. The World Allergy Organisation proposes a revised definition which acknowledges the absence of hypotension and typical skin features:
“Anaphylaxis is a serious systemic hypersensitivity reaction that is usually rapid in onset and may cause death. Severe anaphylaxis is characterised by potentially life-threatening compromise in breathing and/or the circulation, and may occur without typical skin features or circulatory shock being present.” (4)
A small group of Anaphylaxis patients may present with bi-phasic or late phase reactions where hypotension or shock is initially absent (6,7). A 10-year retrospective study of 741 adult patients presenting to an emergency department with anaphylaxis found 340 patients to be hemodynamically stable (SBP ≥90mmHg) on arrival (7). Of this patient group 11.8% later developed hypotension during their hospital stay. One retrospective study of 324 patients undergoing procedures for diagnosis and treatment found 62 patients to develop anaphylaxis, vital signs for the patients were recorded and 12.9% (8) of patients were found to be hypertensive (8).
This presentation may be due to compensatory mechanisms and sympathetic stimulation following the insult of anaphylaxis. When an individual is exposed to an allergen, immunoglobulin-E (IgE) antibodies typically present on effector cells (mast cells and basophils) and form a complex with a specific allergen leading to activation and release of mediators and manifestation of symptoms (1-3). While anaphylaxis mediator release can cause vasodilation, distress, or anxiety, it may stimulate the sympathetic nervous system triggering release of catecholamines as well as activation of the angiotensin system. This may potentially cause the initial presentation of hypertension as seen in this case. Pre-existing hypertension may also be a consideration, however, this may be less likely considering the age of the patient. Therefore, the presence of normotension or hypertension with anaphylaxis is possible for many reasons.
Paramedics in this study initially withheld adrenaline after identifying a high blood pressure, most likely on the basis that adrenaline can further increase blood pressure. While this is an important consideration in adrenaline administration, it does not address the indication for adrenaline in anaphylaxis and excludes the non-cardiovascular benefits of this drug. Adrenaline is accepted as the first-line treatment for anaphylaxis (1,2,5). it is a sympathomimetic medication that acts as an agonist at adrenergic receptors throughout the body causing peripheral vasoconstriction, reduced oedema, increased cardiac contractility and conduction, bronchodilation, and inhibition of mast cell degranulation (7,8).
Evidence demonstrates adrenaline to be safe in anaphylaxis with adverse events being rare in adults. Its safety is particularly evident via the intramuscular route. Serious adverse cardiovascular events are more commonly seen with intravenous administration. As there is limited risk associated to adrenaline administration in anaphylaxis, the greatest risk to safety of patients with anaphylaxis exists in delayed or withheld adrenaline administration. This has been found to be associated with increased risk of death and in normotensive presentations may be associated with later development of cardiovascular symptoms (6-9).
Conclusion
Considering the safety of adrenaline and its benefits in anaphylaxis, it is clear that whilst being cautions, a lower threshold for its administration is warranted. Paramedics must understand the pharmacological action of the drug relevant to the pathophysiology of Anaphylaxis. In addition to this, paramedics must also understand the potential risks and complications to inform their decision to administer adrenaline in anaphylaxis cases presenting with hypertension.
References
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