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.