7.16: Anaphylaxis
- Page ID
- 59719
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Anaphylaxis is a severe life threatening allergic reaction. It is initiated by antigen binding to immunoglobulin E (IgE) antibodies. (Anaphylactoid reactions are clinically similar but are not initiated by IgE).
Common drugs that can cause anaphylaxis include some antibiotics, protamine, some neuromuscular blocking agents and blood products. The anaphylaxis usually occurs immediately but may be delayed for 2 to 15 minutes.
Assessment
The anesthetized patient is often covered with drapes and unconscious so some of the signs and symptoms of anaphylaxis may not occur.Approximately:
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75% Hypotension (due to peripheral vasodilation and increased capillary permeability), tachycardia, hypotensive shock. (Hypotension may be the only sign of anaphylaxis in the anesthestized patient).
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70% Urticaria, flushing, rash
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50% Bronchospasm, stridor, dyspnoea, airway oedema, respiratory arrest
Prevention
The anesthetist must ask the patient about allergies during the preoperative visit.Drugs known to cause anaphylaxis (e.g. antibiotics) should be given as a “test dose”first when appropriate. The drug should be diluted to 20 ml and then 2 ml given as a test. The anesthetist should wait several minutes and then if there is no signs of anaphylaxis give the remainder of the drug.As anaphylaxis and a relative overdose of induction agents will both cause hypotension, it is wise not to give drugs that can cause anaphylaxis (e.g. antibiotics) at the same time as induction agents.
Management
Stop giving the drug that may have caused the anaphylaxis. Call for help, inform the surgeon. Ensure the patient is oxygenated and ventilating. Give 100% oxygen. Intubate the patient if necessary. Remember that anaphylaxis will cause airway oedema, and that the patient’s breathing and intubation may become much more difficult with time. If concerned about the patient’s airway, intubate early.
Treat the hypovolaemia with intravenous fluids. The patient may need many liters of intravenous fluids.
Mild anaphylaxis may only need 0.5 to 1.0 mg of intramuscular adrenaline (epinephrine). Severe anaphylaxis will need repeated intravenous doses of 100 ug of adrenaline to treat the hypotensive shock. Once the blood pressure is treated the patient may need an adrenaline infusion for 24 to 48 hours.
Severe anaphylaxis will cause cardiorespiratory arrest. Be prepared to start cardiopulmonary resuscitation if the patient arrests.
Histamine-1 blockers (diphenhydramine intravenously 50 mg) and corticosteroids (dexamethasone intravenously 20 mg, methylprednisolone intravenously 100 mg) may be useful.
Ideally, blood testing for tryptase should be done at the time of the anaphylaxis and the patient should return in 6 weeks time for skin testing for allergy.