Oxytocin – A high-alert medication, even in low doses

Dear Editor, Oxytocin, the uterotonic of choice during caesarean section (CS), is now recommended in low doses of 1–3 units.1 However, it is a ‘high-alert medication’ and even low doses may not be completely safe and must be administered cautiously.2 A 22-year-old pregnant woman weighing 60kg and about 150cm tall, presented for emergency CS with the diagnosis of G2P1L1 (gravida 2, para 1, living 1) with 36-week gestation and in labour with a history of previous CS done 3 years back under spinal anaesthesia. She was conscious and oriented and had stable vital parameters with no significant medical history or positive findings on examination. She had been adequately fasting and had a pre-operative haemoglobin level of 10 g/dL. On the operating table, her heart rate (HR) was 82/min and regular, the blood pressure (BP) was 124/84 mmHg, the peripheral oxygen saturation (SpO2) was 99% on room air, and electrocardiogram (ECG) showed normal sinus rhythm. After infusing Ringer’s lactate 500 mL, spinal anaesthesia was given with 10 mg hyperbaric bupivacaine and 10 µg fentanyl and a level of block till T6 dermatome was achieved. After delivery, 3 international units (IU) of oxytocin were administered over 30 seconds as a slow intravenous (IV) bolus dose followed by an IV infusion at 7.5 IU/h. After about 2 min, the patient developed hypotension with the systolic BP falling to 70 mmHg. The ECG was normal with no ventricular premature beats. The oxytocin infusion was stopped, IV fluids were rapidly infused, and mephentermine 3 mg followed by 6 mg was administered, but no clinical improvement was seen. IV phenylephrine 100 µg was injected about 2 minutes after the last dose of mephentermine, but this also failed to improve the BP. All this while, the patient was conscious, oriented, and responding to commands. Suddenly, the patient developed monomorphic ventricular tachycardia (VT) with a rate of 160–180/min, which responded to lignocaine 60 mg IV. Her ECG reverted back to normal sinus rhythm with HR 110/min and BP 100/60 mmHg. By this time, her saturation dropped, consciousness started deteriorating, and bilateral crepts developed on auscultation. Her trachea was intubated after giving IV propofol 40 mg, midazolam 1 mg, and succinylcholine 100 mg. Post intubation, her vitals included: BP 110/68 mmHg, HR 108/min, and SpO2 55%. IV vecuronium 6 mg, morphine 4.5 mg and furosemide 10 mg were administered. Mechanical ventilation was continued with 100% oxygen and a positive end-expiratory pressure (PEEP) of 12 cm H2O. The patient’s SpO2 gradually increased to 94%, and the crepts decreased. After surgery, she was managed on mechanical ventilation with PEEP, morphine, furosemide, and head-up position in the intensive care unit (ICU). The levels of cardiac enzymes were normal, and there were no further episodes of arrhythmias. Her condition gradually improved over the next 8 hours, and her trachea was extubated. Due to unavoidable reasons, a radiogram of her chest could be obtained only in the evening when her chest condition had improved and therefore, it did not reveal any signs of pulmonary oedema. Echocardiography done on the next day was normal. After overnight observation in the ICU, the patient was shifted to the ward. The International Consensus Statement on the use of uterotonics during CS recommends the administration of 3 IU oxytocin intravenously over at least 30 seconds followed by an IV infusion at 7.5–15 IU/h during intrapartum CS.1 Hypotension following high-dose oxytocin administration is a common occurrence.3 However, refractory hypotension following 3 IU oxytocin is rare. Our patient developed refractory hypotension followed by VT and pulmonary oedema. Oxytocin has been reported to predispose the patient to develop arrhythmias, especially patients with a prolonged QT interval.4 In addition, oxytocin in high doses can induce QTc prolongation or alter the autonomic nervous system tone, which can contribute to its arrhythmogenic potential.4,5 The treatment of choice for unstable VT is cardioversion. When our patient developed VT, the assistant was instructed to prepare the defibrillator for cardioversion. In the meantime, lignocaine was injected, which reverted the ECG to normal sinus rhythm. This was followed by the development of pulmonary oedema. Some common causes of sudden-onset pulmonary oedema during CS include preeclampsia, severe anaemia, underlying cardiac disease, and fluid overload. Oxytocin has been reported to cause pulmonary oedema due to its antidiuretic effect and also cardiovascular effects of vasodilation along with negative chronotropic and ionotropic effects.6 Our patient’s echocardiography performed on the next day did not reveal any cardiac disease. She had received only 2 L fluid over a period of about an hour, and thus, fluid overload was an unlikely cause. She did not have preeclampsia or severe anaemia. Thus, the most probable cause of pulmonary oedema in this case was oxytocin administration. Although oxytocin-induced VT and pulmonary oedema have been reported separately, an extensive search of literature did not reveal any case reporting both these complications in the same patient. Thus, this is probably the first case being reported in which the patient developed refractory hypotension with VT and pulmonary oedema, that too following low-dose oxytocin administration as per the recommendations of the consensus statement. In conclusion, although an oxytocin dose of 3 IU administered over 30 seconds has been recommended during intrapartum CS, even this low dose can cause serious complications and hence demands extreme caution during administration. Study data availability All data related to the case are included as part of the article. Disclosure of use of artificial intelligence (AI)-assistive or generative tools No artificial intelligence (AI)-assistive or generative tools were used. Declaration of Patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient consented to the clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.