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Correspondence  |   December 2006
What Sunrise Might Reveal
Author Notes
  • Pontificia Universidad Católica de Chile, Santiago, Chile. or
Article Information
Correspondence
Correspondence   |   December 2006
What Sunrise Might Reveal
Anesthesiology 12 2006, Vol.105, 1282-1283. doi:
Anesthesiology 12 2006, Vol.105, 1282-1283. doi:
To the Editor:—
I read with great interest the article by Hanss et al.  1 in which the authors elegantly demonstrate a relation among heart rate variability, the risk of hypotension after spinal anesthesia for cesarean delivery, and the effectiveness of prophylactic measures such as prehydration and vasopressor use in terms of heart rate variability as well as clinical outcome.
However, I am puzzled by the fact that there was no control for the time of day when the experiments were performed. The authors did their baseline assessments between 18:00 and 20:00, which might be totally different from the values obtained during the experiments. Chassard and Bruguerolle2 recently reviewed the effects of time of day as a synchronizer for different processes and bodily functions such as drug metabolism, cortisol levels, and hepatic blood flow. Therefore, it should not be surprising to see different results depending on the time of day when the experiments were performed. A clinical observation is that early morning elective cesarean deliveries tend to have a higher incidence of hypotension than afternoon deliveries. This may represent a multifactorial problem, however, after the results of Hanss et al.  1,3 Heart rate variability might be a good representation of one of the main factors influencing postspinal hypotension: sympathetic relative overactivity, which might be synchronized with the time of day.
Pontificia Universidad Católica de Chile, Santiago, Chile. or
References
Hanss R, Bein B, Francksen H, Scherkl W, Bauer M, Doerges V, Steinfath M, Scholz J, Tonner PH. Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery. Anesthesiology 2006; 104:635–43Hanss, R Bein, B Francksen, H Scherkl, W Bauer, M Doerges, V Steinfath, M Scholz, J Tonner, PH
Chassard D, Bruguerolle B. Chronobiology and anesthesia. Anesthesiology 2004; 100:413–27Chassard, D Bruguerolle, B
Hanss R, Bein B, Ledowski T, Lehmkuhl M, Ohnesorge H, Scherkl W, Steinfath M, Scholz J, Tonner PH. Heart rate variability predicts severe hypotension after spinal anesthesia for elective cesarean delivery. Anesthesiology 2005; 102:1086–93Hanss, R Bein, B Ledowski, T Lehmkuhl, M Ohnesorge, H Scherkl, W Steinfath, M Scholz, J Tonner, PH