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Baseline blood pressure at elective caesarean section: which reading?

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Baseline blood pressure at elective caesarean section: which reading?
DGP Luther, N Wharton, SM Kinsella
Department of Anaesthesia, St Michael's Hospital, Bristol, UK

Introduction: Recent recommendations on vasopressor management during caesarean section under spinal anaesthesia suggest maintaining systolic arterial pressure (SAP) ≥90% of baseline.1 In clinical practice, the baseline is often taken as a single reading after the woman positions herself on the operating table. This might not represent a true baseline.

Aims: To compare SAP readings taken:

•at the last antenatal clinic visit (ANC)
•preoperatively on the morning of surgery (AM)
•on arrival in the operating room (OR).

Methods: We performed a retrospective case note review of 100 non-hypertensive women having elective caesarean section. This research study did not require ethics committee approval according to the HRA decision tool.

Results: The median (IQR [range]) for SAP (mmHg) at the three time periods were:

ANC: 110 (100-120 [90-150])

AM:  116 (108-120 [90-158])

OR: 130 (120-140 [95-165])

These are illustrated in the box plot. Three-way comparisons of differences between the time points were all significant at p < 0.001 (Wilcoxon signed-rank; BioStatsHandbook).

Discussion: The SAP taken in the OR is unlikely to be an accurate baseline; for patients undergoing general anaesthesia, pre-induction blood pressure is known to be significantly elevated compared with that taken during preoperative evaluation.2 Using the OR reading as the baseline will lead to unnecessary intraoperative vasopressor use, which may lead to hypertension and potentially patient morbidity.

Until we have further data that clarifies whether the AM reading is falsely elevated or results from the normal physiological increase during late pregnancy, we suggest using the AM reading as the baseline.

References

1  Kinsella SM, Carvalho B, Dyer RA, et al. International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia. Anaesthesia 2018;73:71-92

2  van Klei WA, van Waes JAR, Pasma W et al. Relationship between preoperative evaluation blood pressure and preinduction blood pressure: a cohort study in patients undergoing general anesthesia. Anesth Analg 2017;124:431–7

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