Design: randomised, double-blind, non-inferiority trial with a margin of two physician interventions
Population: 80 healthy women with term uncomplicated singleton pregnancies for elective caesarean under spinal anaesthesia
Primary outcome: number of physician interventions needed to hold systolic blood pressure in the target range
Effect: median 3 (IQR 2–4) with boluses vs 6 (5–8) with infusion; difference of medians −3 (95% CI −4 to −2); total phenylephrine 300 µg vs 630 µg; no difference in maternal or neonatal outcomes

Prophylactic phenylephrine by variable-rate infusion is preferred at elective caesarean under spinal anaesthesia on the grounds of workload rather than efficacy: boluses were understood to control pressure just as well but to demand more of the anaesthetist's attention. A randomised, double-blind non-inferiority trial in 80 healthy women with term uncomplicated singleton pregnancies tested a modified bolus regimen against that assumption, with a non-inferiority margin of two interventions.

The bolus group received 100 µg immediately after the spinal and a further 100 µg whenever systolic pressure fell below 90% of baseline; the infusion group started at 50 µg/min titrated to hold systolic pressure at 90–99% of baseline. The median number of physician interventions was 3 (interquartile range 2–4) with boluses against 6 (5–8) with the infusion, a difference of medians of −3 (95% confidence interval −4 to −2). Total phenylephrine was 300 µg against 630 µg. Overall accuracy of blood pressure control did not differ, and neither did rates of hypotension, hypertension or bradycardia, umbilical cord gases, Apgar scores or maternal complications.

The implication is a straightforward one for any theatre without a syringe pump on every spinal, which is most theatres in most of India. The workload argument for the infusion was the argument, and it did not survive the comparison — the bolus regimen used less drug and less of the anaesthetist's time. It has been tested only in healthy women having elective surgery, so it should not be carried into pre-eclampsia or emergency caesarean without thought, but for the elective list it is a defensible default.

Record the baseline systolic pressure before the spinal; the regimen is defined entirely against it.
Give the first 100 µg bolus immediately after the block rather than waiting for a fall.
Repeat at every systolic value below 90% of baseline, not at an absolute threshold.
Keep the monitoring interval unchanged — fewer interventions is not less observation.
Do not extend this regimen to pre-eclampsia or emergency caesarean; it was tested only in healthy elective cases.

Why it matters

The only argument for the infusion was that it saves the anaesthetist's attention, and it did the opposite.

The statistics, in plain English

The trial set out to show non-inferiority within two interventions and found the bolus arm better: the confidence interval for the difference (−4 to −2) sits entirely on the bolus side, so this is superiority on the primary endpoint rather than a close call. The neonatal and complication findings are the weak part. With 40 women per group the trial could only have detected a large difference in cord gases, Apgar scores or maternal complications, so 'no difference' there means the study could not see one, not that none exists.