Correspondence  |   April 2018
In Reply
Author Notes
  • Columbia University, New York, New York.
  • (Accepted for publication December 21, 2017.)
    (Accepted for publication December 21, 2017.)×
Article Information
Correspondence   |   April 2018
In Reply
Anesthesiology 4 2018, Vol.128, 861-862. doi:10.1097/ALN.0000000000002096
Anesthesiology 4 2018, Vol.128, 861-862. doi:10.1097/ALN.0000000000002096
We are gratified, but not surprised, by the interest in our recent article,1  given that we examined one of the oldest recommendations regarding maternal position for cesarean delivery. In their letters, Riley et al.2  and Shayegan et al.3  correctly note that cardiac output was slightly lower among women kept supine, and that more phenylephrine was required (probably related). The goal of anesthetic management, however, is not to maintain specific hemodynamic parameters, but rather to maintain adequate or optimal conditions for mother and fetus. There is no evidence that the lower cardiac output or increased phenylephrine requirements caused any injury, nor any plausible mechanism by which these levels of cardiac output should be harmful. It is probable, as suggested by Dyer et al.4  in their work on the effects of phenylephrine as the vasopressor for management of spinal hypotension, that the maternal cardiac output may be significantly higher than it needs to be, especially once spinal anesthesia is established. In fact, Dyer et al. proposed that phenylephrine is the optimal vasopressor to use during spinal anesthesia because it decreases cardiac output, offsetting the increase in cardiac output that results from the decreased systemic vascular resistance.4  Because the purpose of maternal cardiac output is to maintain maternal and fetal homeostasis, any increase above this level may be “unnecessary.” Looking at specific numbers, in our study, using the NICOM cardiac output monitor (Cheetah Medical Inc., USA), maternal cardiac output before spinal anesthesia was 8.1 l/min in the supine position and 8.4 l/min in the tilted position; this increased to over 9 l/min in both groups after spinal anesthesia.1  Therefore, the measured “decrease” in cardiac output with higher phenylephrine dosing, both in our study1  and in Dyer et al.’s4  (where boluses were given) may be mostly a return to prespinal baseline due to restoration of systemic vascular resistance.
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