Minimum effective dose of oxytocin bolus during the caesarean section for patients at high vs low risk of uterine atony: A non-randomized, dual-arm, dose-finding prospective trial

BACKGROUND AND AIMS: There are scanty data for oxytocin dose in patients at high risk of uterine atony. We aimed to compare the effective dose (ED) 90 of oxytocin for adequate uterine tone during the caesarean section in patients at high-risk vs low-risk uterine atony. METHODS: This dose-finding study was undertaken after ethical approval in non-labouring women aged >18 years with pre-defined risk factors for uterine atony (high-risk group) vs those without such factors (low-risk group) (n = 39 each). Starting dose of oxytocin in the first patient of low-risk and high-risk groups was 1 and 3 IU, respectively. Achieving adequate uterine tone at 3 min of oxytocin bolus was designated ‘success’, while inadequate tone constituted ‘failure’. If the response was ‘failure’, the dose of oxytocin was increased for the next patient by 0.5 or 0.2 IU (high- and low-risk groups, respectively). In case of a successful response, the dose for the next patient was decreased with a probability of 1/9 using the same dosing intervals or otherwise kept unchanged. RESULTS: The ED90 (95% CI) of oxytocin bolus was 4.7 (3.3–6.0) IU for the high-risk group and 2.2 (1.3–3.2) IU for the low-risk group (P = 0.044). Oxytocin-associated tachycardia (P = 0.247) and hypotension (P = 0.675) were clinically greater for the high-risk vs low-risk group but statistically similar. CONCLUSION: Non-labouring patients with high-risk factors for uterine atony require a greater dose of initial oxytocin bolus to achieve adequate uterine tone during the caesarean section compared to those without risk factors.