Biphasic Anaphylaxis
Here is a timely retrospective study (albeit in adults) given the frequent, on-going, lengthy discussion on the list-serv about anaphylaxis:
This study out of Canada called patients shortly after an ED visit for anaphylaxis to evaluate whether or not they had recurrence of symptoms. They were said to have a biphasic anaphylactic reaction if they had recurrence of symptoms involving 2 organ systems, and a non-anaphylactic biphasic reaction if it involved only 1 organ system. They enrolled 148 patients, mean age of 30, majority of whom had a history of anaphylaxis.
They found a 2nd reaction in 29 patients, 22 (16%) involved 2 systems. The mean time to recurrence was 19 hours and only 1/3 of biphasic reactions occurred within 8 hours. Secondary symptoms were noted to be much more mild, with only 4 patients requiring repeat doses of epinephrine.
Bottom line: Biphasic anaphylactic reactions do occur with some frequency (prior literature says anywhere from 1-20%). This study demonstrates that they generally happen later and are more mild than the original reaction. A shorter observation (such as the 2 hours stated on the list-serv) is likely fine, but it is imperative to tell parents about the potential for recurrent symptoms and give very good return precautions!
This study out of Canada called patients shortly after an ED visit for anaphylaxis to evaluate whether or not they had recurrence of symptoms. They were said to have a biphasic anaphylactic reaction if they had recurrence of symptoms involving 2 organ systems, and a non-anaphylactic biphasic reaction if it involved only 1 organ system. They enrolled 148 patients, mean age of 30, majority of whom had a history of anaphylaxis.
They found a 2nd reaction in 29 patients, 22 (16%) involved 2 systems. The mean time to recurrence was 19 hours and only 1/3 of biphasic reactions occurred within 8 hours. Secondary symptoms were noted to be much more mild, with only 4 patients requiring repeat doses of epinephrine.
Bottom line: Biphasic anaphylactic reactions do occur with some frequency (prior literature says anywhere from 1-20%). This study demonstrates that they generally happen later and are more mild than the original reaction. A shorter observation (such as the 2 hours stated on the list-serv) is likely fine, but it is imperative to tell parents about the potential for recurrent symptoms and give very good return precautions!
