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Variations in baseline blood pressure readings correlate with reactive hypertension following prophylactic phenylephrine infusions
Abstract Number: S-69
Abstract Type: Original Research
Obtaining accurate baseline blood pressures is paramount to the management of spinal anesthesia (SA) induced hypotension and in research of vasopressor use for cesarean delivery. While some studies obtain baseline blood pressure in the preoperative holding (POH) area or the ward, others assess baseline pressure after patient transfer to the operating room (OR). We hypothesized that baseline blood pressure readings in the OR prior to placement of the neuraxial block would be higher than readings obtained in POH in women undergoing cesarean delivery under SA. We also explored if any difference between POH and OR blood pressures would predict hypotension or reactive hypertension following SA and initiation of phenylephrine (PE) infusion.
We performed a post hoc analysis of data previously collected for an IRB approved study. Three independent blood pressure readings were obtained two minutes apart with standard non-invasive blood pressure in POH and one measurement was obtained in the OR prior to initiation of standardized SA. After block placement PE was started at 50 mcg/min and titrated to maintain systolic blood pressure (SBP) within 20% of baseline. The mean of the three preoperative SBP readings and the highest preoperative SBP were compared to the first blood pressure reading obtained in the OR. Groups were compared with 2-sample t-tests or Rank Sum tests, and changes were tested with paired t-tests or Signed Rank tests, as appropriate. Association of SBP change with hypotension and reactive hypertension was tested with logistic regression analysis accounting for baseline SBP, and testing for an interaction of baseline SBP with change in SBP.
293 cases were included. The first blood pressure obtained in the OR was significantly higher than both the mean and the highest POH blood pressures (P<0.0001). The mean (SD) increase was 15.6 mmHg (13.5), 95% CL = 14.1 – 17.2. There was a significant positive correlation between SBP change and occurrence of reactive hypertension (but not hypotension) following initiation of PE infusion (unadjusted OR= 1.36 for increased risk of reactive hypertension per 10mmHg increase in SBP (p=0.001, 95% CL = 1.14– 1.64). This effect remained significant (p=0.0035) and consistent (OR=1.33 per 10mmHg change) when preoperative SBP was added to the model with no significant interaction of SBP change and preoperative SBP.
Our data show that baseline blood pressure readings in the OR are significantly elevated compared to those obtained in POH. However since this is a secondary analysis, only one blood pressure obtained in the OR before neuraxial placement was available for the analysis. Further studies should examine if those results are reproducible with several readings obtained in the OR. This has implications for standard practice and studies involving vasopressor administration. The relationship between blood pressure change and reactive hypertension deserves further studies.