[Anaphylactoid reactions to muscle relaxants]

Anaphylactoid (i. e. anaphylactic-like) reactions have been estimated to occur in between one in 600 and one in 1,000 general anaesthesias. Two thirds of these reactions are caused by neuromuscular blocking drugs used during anaesthesia. An anaphylactoid potential is inherent in all muscle relaxants, albeit to a varied extent, reflecting an obligatory feature of their molecular structure (quaternary ammonium groups) and common physicochemical characteristics. Hence, also newer relaxants are not void of anaphylactoid risk. In Britain, the recent availability of drug-specific radioallergosorbent tests (RAST) has initiated much controversy on preanaesthetic antibody screening and possible medicolegal consequences. Since every anaesthetist must expect to be faced with such an unforeseen and occasionally life-threatening reaction, the characteristic clinical manifestations, basic therapeutic strategies and current opinion on underlying pathophysiological mechanisms are summarized in this review article. Based on the recommendations of the British National Adverse Anaesthetic Reaction Advisory Service (NAARAS), essential diagnostic procedures during and after anaphylactoid events are discussed. Finally, prophylactic precautions including the preoperative administration of H1- and H2-antihistamines are recommended.