The sequence method of determining baroreflex sensitivity (BRS_SEQ) has been reported to correlate poorly with the phenylephrine method of determining BRS in individuals with attenuated BRS. Inhalation anesthetics are also known to decrease BRS. We therefore assessed the effect of varying the systolic blood pressure (SBP) and R-R interval (RRI) thresholds on BRS_SEQ values and compared these results with the BRS obtained by the modified Oxford technique (BRS_MODOX).

The average number of valid sequences and BRS_SEQ values were derived by varying the SBP threshold from 0.5 to 2.5 mmHg and the RRI threshold from 1 to 6 ms, and the relation of BRS_SEQ values to BRS_MODOX values using sequential administration of nitroprusside and phenylephrine was assessed in 40 healthy individuals during sevoflurane anesthesia.

Increasing either the SBP thresholds or RRI thresholds resulted in a decrease in the number of valid sequences. As the SBP thresholds were decreased and the RRI thresholds were increased, BRS_SEQ values increased. When the SBP threshold exceeded 1 mmHg, no significant correlations were observed between BRS_SEQ and BRS_MODOX values. Significant correlations between the two methods were observed for an SBP threshold of 0.5 mmHg and RRI thresholds of 1, 2, 3 and 4 ms. Biases between the two methods were 2.1, 2.1, 0.4, and 0.4 ms/mmHg for 0.5 mmHg and 1, 2, 3 and 4 ms.

These findings suggest that adjusting the SBP threshold to 0.5 mmHg and the RRI threshold to 3 or 4 ms may improve BRS_SEQ validity during sevoflurane anesthesia, when compared to BRS_MODOX.