Maternal heart rate responses in the supine position and their relationship with hypotension and phenylephrine...

Hypotension is the main side effect of spinal anaesthesia (SA) for elective caesarean delivery (CD). An increased in heart rate in response to inferior vena cava (IVC) compression has been reported to be predictive of hypotension and vasopressor requirements in this setting. The objective of the study was to evaluate the prevalence of an increase in heart rate in response to IVC compression and its potential effect on hypotension and phenylephrine requirements.

Healthy parturients scheduled for elective CD under SA were preoperatively investigated for a positive supine stress test (SST). It was defined as an increase in heart rate (HR) > 10 beats/min after 5 min of supine position. A crystalloid coload and prophylactic phenylephrine infusion were systematically used to maintain systolic arterial pressure (SAP) between 90-100% of baseline. Hypotension was defined as SAP < 80% of baseline.

Among 100 women, 26% had a positive SST. There was no significant difference in the incidence of hypotension: 38% versus 24.3% (p = 0.17) in women with positive SST or without, respectively. The cumulative dose of phenylephrine (450 µg [325-625] versus 350 µg [250-500], p = 0.09) was not significantly different between the two groups. Incidences of reactive hypertension, bradycardia, nausea or vomiting and neonatal outcomes were comparable.

A positive SST to IVC compression was found in a quarter of term women scheduled for elective CD under SA. This condition has no significant impact on hypotension and phenylephrine requirements when using a crystalloid coload and a phenylephrine infusion targeted at maintaining SAP close to baseline.