Discussion
Syntocinon is a widely used synthetic oxytocin that stimulates contractions of uterine smooth muscle. It is used for induction and augmentation of labour, and prevention of PPH.1Syntocinon rarely causes anaphylaxis, but reported side effects include nausea, vomiting, reflex tachycardia, hypotension, headache, and uterine rupture.2 There are very few documented reports of anaphylactic reactions to Syntocinon, and these were hypothesized to precipitate from concurrent latex exposure,9-21 and chlorobutanol exposure,3, 4 a formulated ingredient in Syntocinon.5 This case involved a rare non-immune mediated anaphylactic response to Syntocinon that was recognised early and responded well to appropriate treatment. The only drug that was administered prior to the onset of anaphylaxis was Syntocinon and the rapid abatement of symptoms following its withdrawal suggested that the patient had suffered an allergic reaction to the drug.
Non-immune mediated anaphylaxis, also known as an anaphylactoid reaction is a non-IgE mediated immune response.6,7 In this case, immunological blood testing of serial tryptase, IgE and Complement assays (C3 and C4) levels were all within normal range suggesting the diagnosis.8 Inflammatory mediators such as bradykinin and prostaglandin modulate mast cell and basophil degranulation resulting in vasodilation and bronchoconstriction, resulting in anaphylaxis.9 These reactions are rare, with an incidence of less than 1 in 20,000 in anaesthesia, however, their life-threatening outcomes present concern for anaesthesiologists.10-12 While in pregnancy IgE does not cross the placenta, maternal haemodynamic instability can jeopardize placental perfusion.13 Laboratory tests may be used to support the diagnosis, but it is important to note that anaphylaxis is a clinical diagnosis,8 and results of tests are not specific and may not be quick enough to impact acute management. Further, it has been shown that serum tryptase levels are more likely to be elevated in those with hypotension and shock, than in those with anaphylaxis who are normotensive.14
Another hypothesized cause of anaphylaxis during delivery is an allergic sensitivity to latex.15 In obstetrics and gynaecological surgical procedures, a high incidence of latex anaphylaxis (1 in 310) has been observed.16Interestingly, previous case reports have suggested that allergic sensitization to latex may be an important predisposing factor for anaphylaxis or systemic reactions to Syntocinon.17However, our patient had frequent exposure to latex in her workplace and prenatal check-ups with no documented reactions. Other differential diagnoses at the time were pulmonary thromboembolism and air embolism, however, the absence of typical risk factors, suspicious ECG changes, and normal central venous pressure and right ventricular function on Echocardiogram did not support the diagnosis. The most common symptoms of pulmonary embolism are dyspnoea (73%), pleuritic pain (66%), and cough (37%), however, haemodynamic collapse is only present in less than 10% of cases.18,19 Another possible diagnosis was amniotic fluid embolism, but with an incidence of 1 in 40,000 delivery, it is a difficult diagnosis to make.20,21The Society for Maternal-Foetal Medicine (SMFM) states the diagnosis for amniotic fluid embolism must have all of the four following: sudden cardiorespiratory arrest, documentation of overt dissemination (platelet counts <50,000/mL, fibrinogen <200 mg/L), clinical onset during labour, and absence of fever during labour.22 In this case, amniotic fluid embolism was unlikely, given the SMFM criteria and normal findings on blood panel, Echocardiogram, ECG, and chest x-ray. Other differential diagnoses of acute respiratory distress during pregnancy included aspiration of gastric contents and acute heart failure, both of which were ruled out clinically.
Non-immune mediated anaphylaxis to Syntocinon is extremely rare and only a few case reports exist. Here, we presented a case of non-immune mediated anaphylaxis to Syntocinon in the setting of vacuum-assisted birth, shoulder dystocia and PPH in a healthy 26-year-old primigravid woman. The patient developed novel symptoms including patchy erythema, bronchospasm, angioedema, and laryngeal oedema. Although the symptoms resolved on withdrawal of Syntocinon, the mechanism(s) which precipitated this response warrants further investigation.
Acknowledgments: The authors would like to thank the patient who encouraged us to write this case report and clinical team members for their excellent case.
Conflict of Interest: None declared.
Authors Contribution: Shyam Prakaash Bhagavata Srinivasan, Ishith Seth, Gabriella Bulloch, Alexander Mills, and Nita Dhupar drafted the original manuscript. All authors were involved in reading, critically reviewing, and approving the manuscript.
Ethics statement: Appropriate written informed consent (available upon request) was obtained for publication of this case report and accompanying images.