Effect of Oxytocin Bolus Versus Slow Infusion on Haemodynamic Stability During Caesarean Section Under Spinal Anaesthesia

Postpartum haemorrhage remains a leading cause of maternal mortality worldwide. Oxytocin is the first-line uterotonic agent used after delivery of the baby during caesarean section. When given as a rapid intravenous bolus, oxytocin can cause significant hypotension, tachycardia and other haemodynamic changes, especially in women under spinal anaesthesia.

This prospective, randomised, controlled trial will compare the haemodynamic effects of oxytocin 5 IU administered as a rapid intravenous bolus versus the same dose given as a slow intravenous infusion over 15 minutes in women undergoing elective caesarean section under spinal anaesthesia.

Sixty women aged 18-40 years with singleton pregnancy at 37-42 weeks, ASA physical status I or II, will be randomly allocated to one of two groups:

Group A (Bolus): Oxytocin 5 IU given as an intravenous bolus over 15 seconds immediately after umbilical cord clamping.

Group B (Infusion): Oxytocin 5 IU diluted and infused over 15 minutes via syringe pump immediately after umbilical cord clamping.

The primary outcome is the change in systolic blood pressure from baseline at 2, 5 and 10 minutes after oxytocin administration. Secondary outcomes include changes in diastolic blood pressure and heart rate, incidence of hypotension and tachycardia, vasopressor requirements, uterine tone assessed by a 5-point scale, estimated blood loss, and side effects such as nausea, vomiting, flushing and chest discomfort.

The study will be conducted at Hayatabad Medical Complex, Peshawar. All participants will receive standard spinal anaesthesia and routine care. The results are expected to provide local evidence to support safer oxytocin administration practices during caesarean section under spinal anaesthesia.

• Oxytocin (Drug), also known as Syntocinon: Oxytocin 5 IU administered either as a rapid intravenous bolus over 15 seconds or as a slow intravenous infusion over 15 minutes immediately after umbilical cord clamping during elective caesarean section under spinal anaesthesia.

Primary outcomes

• Change in Systolic Blood Pressure (SBP) from Baseline [Baseline; 2 minutes, 5 minutes, and 10 minutes after oxytocin administration]: Change in systolic blood pressure from baseline (mean of three pre-anaesthesia readings) measured at 2, 5, and 10 minutes after oxytocin administration.

Secondary outcomes

• Change in Diastolic Blood Pressure and Heart Rate from Baseline [1, 2, 3, 5, 10, 15, and 20 minutes after oxytocin administration]: Change in diastolic blood pressure and heart rate from baseline at defined time points after oxytocin administration.
• Incidence of Clinically Significant Hypotension [Within 20 minutes after oxytocin administration]: Proportion of participants who develop systolic blood pressure < 90 mmHg or a fall of > 20% from baseline after oxytocin administration.
• Uterine Contraction Scale Score [5 minutes after placental delivery]: Uterine tone assessed by the operating obstetrician using a 5-point scale (Grade 1 = atonic to Grade 5 = very well contracted) at 5 minutes after placental delivery. Grade 1 or 2 is classified as uterine atony.

Sex: Female, ages: 18 Years to 40 Years

Inclusion Criteria:

* Adult female patients aged 18 to 40 years
* American Society of Anesthesiologists (ASA) physical status class I or II
* Singleton pregnancy at 37 to 42 weeks gestational age
* Scheduled for elective caesarean section under spinal anaesthesia
* Written informed consent obtained

Exclusion Criteria:

* Patients with anticipated hemodynamic instability including severe preeclampsia/eclampsia, placenta previa with active bleeding, placental abruption, or hemorrhagic shock
* Pre-existing cardiovascular disease including ischemic heart disease, valvular heart disease, cardiomyopathy, or arrhythmias
* Baseline systolic blood pressure < 100 mmHg or heart rate > 100 bpm before spinal block
* Known hypersensitivity to oxytocin
* Failed spinal anaesthesia requiring conversion to general anaesthesia
* Patients receiving medications that may alter the hemodynamic response to oxytocin (beta-blockers, calcium channel blockers, ACE inhibitors, or angiotensin receptor blockers)
* Pre-existing anaemia (Hb < 8 g/dL)