Discussion
bradycardia, hypertension, hypotensive, hypotension
ADVERSE EVENTS, HYPERTENSION, HYPOTENSIVE, COLD
In this randomized controlled study, we compared the performance of ADIVA versus DIVA in managing hypotension during spinal anesthesia for cesarean delivery. The use of ADIVA did not significantly change the incidence of hypotension, hypertension, bradycardia, ephedrine consumption, and other relevant clinical outcomes compared to DIVA. However, ADIVA was associated with a greater proportion of hypotensive SBP readings, reduced phenylephrine consumption, and increased umbilical arterial pH than DIVA. Lastly, ADIVA exhibited greater MDAPE and wobble than DIVA, although MDPE and divergence were comparable between the two systems.Three modifications were incorporated into ADIVA that we postulated will improve hemodynamic stability. First, ADIVA delivered low vasopressor doses at SBP was between 90 to 110% of baseline, in contrast to DIVA which administered the same vasopressor dose when SBP fell between 90 to 100% of baseline. We hypothesized that pre-emptive use of small vasopressor doses may prevent SBP from dropping below baseline levels and reduce the incidence of hypotension, albeit at the theoretical cost of increased hypertension risk. However, we did not detect a significant difference in the incidence of hypotension and hypertension between ADIVA and DIVA, which may suggest that the vasopressor dose (25 μg phenylephrine or 2 mg ephedrine) was insufficient to forestall the development of hypotension. Future studies should investigate if a higher pre-emptive vasopressor dose delivered between 90 to 110% of baseline reduces the incidence of hypotension, without concomitant increase in the risk of hypertension.Second, hypotensive parturients with SBP readings below 80% of baseline received larger vasopressor doses (75 μg phenylephrine or 6 mg ephedrine) from ADIVA, in contrast to the 50 μg phenylephrine or 4 mg ephedrine administered by DIVA. We postulated that larger vasopressor doses will rapidly return SBP above 80% of baseline and minimize the duration of hypotension, but paradoxically, our results showed that ADIVA had greater proportion of hypotensive SBP readings compared to DIVA. Given that SBP was monitored continuously in a beat-to-beat fashion, it is possible that short periods of hypotension occurring during vasopressor administration or the subsequent 10 s lockout period were not treated, hence preventing higher vasopressor doses from reducing the proportion of hypotensive readings.Third, ADIVA calculated the SBP trend and administered vasopressors rapidly if SBP trended downward in the ten-second interval preceding vasopressor delivery, while the same vasopressor dose would be delivered over 30 s if SBP trended upward. In comparison, DIVA delivered all vasopressors over 30 s, regardless of SBP trend. We hypothesized that delivering vasopressors rapidly may halt the decline in SBP and hence forestall the onset of hypotension, while slow infusion of vasopressors with rising SBP may reduce the incidence of hypertension. However, our results showed that this was not the case, as no significant difference in the incidence of hypotension was found between ADIVA and DIVA groups.When evaluated with performance measures used to evaluate similar closed-loop systems, ADIVA exhibited significantly higher MDAPE of 13.1% compared to DIVA (9.5%), indicating that ADIVA resulted in greater deviation of SBP values above and below the baseline. Also, ADIVA was associated with a MDPE of 5.4%, showing that SBP values were maintained at a median of 5.4% above baseline, compared to 3.2% with DIVA. Similarly, wobble was higher in ADIVA (8.3%) than DIVA (6.3%), indicating that the former was associated with greater fluctuation of SBP values around MDPE. The combination of these findings suggests that ADIVA tended to maintain SBP values higher above baseline with greater SBP fluctuation than DIVA. This may be due to the addition of pre-emptive vasopressor delivery starting at 110% of baseline, as well as the rapid administration of vasopressors that may introduce greater fluctuation in SBP readings.It should be noted that the incidence of hypotension in this study was markedly greater than in our previous randomized controlled study comparing DIVA with manual vasopressor boluses [The use of a closed-loop feedback system for vasopressor delivery was firstly described by Ngan Kee et al. by maintaining the maternal blood pressure in Cesarean patients with a simple on–off algorithm to activate phenylephrine infusion of 100 μg/min [We acknowledge several limitations in this study. Our study may have been inadequately powered to detect small differences in the incidence of hypotension between parturients receiving ADIVA compared to those receiving DIVA, although the clinical significance of such differences is debatable. In this study, we chose to use a validated non-invasive blood pressure monitoring, Nexfin, rather than intra-arterial measurement which is invasive with accompanying risk of adverse events. The accuracy and precision of Nexfin for continuous SBP measurement may be affected by movement or cold temperature leading to peripheral vasoconstriction, nonetheless, the accuracy of Nexfin has been validated against intra-arterial measurements [