i.e give adrenaline and if it doesn’t work, you just keep giving more.
Adrenaline dosing: 10mcg/kg up to 0.5mg IM in the anterolateral thigh
If repeated dosing IM adrenaline is unable to produce lasting resolution of symptoms start an adrenaline IV infusion. Various dosing schedules exist – check local guidelines. One published dosing schedule is: 1mg in 100ml N/S- commence at 0.5-1ml/kg per hour and titrate to effect.
Steroids have long been presumed to have benefit in anaphylaxis and prevent the delayed phase reaction. However there is a lack of data to answer this question although steroids have been effective in other allergic diseases. As relatively unstudied whether to use steroids or not and the choice of agent and duration is debatable. Generally newer guidelines tend to leave steroids out of 1st line management. Certainly if there is wheeze it makes sense to add steroids and perhaps also consider in the severe cases or those not responding well or persistently to initial adrenaline.
If using steroids IV hydrocortsione 4mg/kg up to 200mg is most frequently recommended and is often followed by 1-3 days of oral prednisolone 1mg/kg up to 50mg. Alternatively a single dose of IV dexamethasone 0.15mg/kg up to 8mg may work just as well … again simply unstudied.
While IM adrenaline remains the mainstay of treatment the following adjunctive treatments may be useful depending on the symptoms:
A: if airway swelling/compromise is unresponsive, consider nebulised adrenaline (5mg in 5mls in adults i.e 5 x 1:1000 adrenaline ampules)
B: if wheeze present give inhaled salbutamol eg MDI via spacer or nebs.
C: if hypotension present lie flat and give IV fluids – 20ml/kg boluses up to 50ml/kg. If hypotension is resistant to adrenaline and fluids, consider selective vasopressors such as metaraminol, vasopressin or noradrenailne.
Antihistamines have no direct role in acute anaphylaxis management and IV promethazine should not be used as it can worsen hypotension. However antihistamines can be used second line for symptom control of cutaneous manifestations. If using antihistamines a non-drowsy oral agent is likely to be an optimal choice.
Observation: Most patients can be discharged after 4-6 hours post symptom resolution and their last dose of adrenaline.
Most anaphylaxis patients responds quickly and substantially to adrenaline and are easy to manage in the Emergency Department but a minority of cases can be severe and unresponsive to therapy. In such patients, engage senior clinician help early including senior airway skills where appropriate – rapid severe airway compromise is a real risk and intubation of the severe anaphylactic patient is notoriously difficult, which may end up requiring alternatives to standard RSI intubation (eg awake fibreoptic intubation or cricothryotomy).
Tips for recognition of tricky cases
Presentation: The skin manifestations of anaphylaxis can be absent or minimal especially in the presence of hypotension. Anaphylaxis should therefore still be considered as the possible diagnosis, with or without skin manifestations, where there is:
– sudden onset of symptoms affecting 2 organ systems
– hypotension on its own
– or acute onset SOB/bronchospasm. This may present in an intubated patient as suddenly becoming more difficult to ventilate/increasing airway pressures.
Causes: While medicines, insect stings and foods account for the vast majority of anaphylaxis cases and deaths, consideration should be given to less commonly suspected aetiologies such as summation anaphylaxis where a co-factor is required for anaphylaxis to occur eg food-dependant exercise induced anaphylaxis. Drugs such as aspirin/NSAIDS and high ambient temperatures can also be co-factors in summation anaphylaxis.
Mast Cell Tryptase: Where the diagnosis is uncertain, a serum mast cell tryptase can be useful for making a retrospective diagnosis to aid outpatient referral, investigation and management. While single measurements have low sensitivity, taking serial measurements on arrival, after 1hr and in convalescence can improve sensitivity by up to 75%.