Evidencia de manejo de la hipotensión materna en anestesia neuroaxial para cesárea

Diversas estrategias han sido propuestas para el manejo de la hipotensión luego de anestesia neuroaxial en las pacientes sanas que se someten a una cesárea, éstas incluyen: prehidratación, cambios de posición, y administración de fenilefrina o efedrina.
Puntos divergentes encontramos en esta revisión, aunque es importante recalcar los esfuerzos que se hacen para encontrar mecanismos profilácticos a esta hipotensión.
Para su consideración presento los siguientes resúmenes de estudios para el manejo de la hipotensión materna durante la anestesia neuroaxial, principalmente espinal, en la cesárea.

Heart Rate Variability–guided Prophylactic Treatment of Severe Hypotension after Subarachnoid Block for Elective Cesarean Delivery
Hanss, Robert M.D.*; Bein, Berthold M.D.†; Francksen, Helga M.D.†; Scherkl, Wiebke M.S.‡; Bauer, Martin M.D., M.P.H.†; Doerges, Volker M.D.§; Steinfath, Markus M.D.§; Scholz, Jens M.D.∥; Tonner, Peter H. M.D.#
Anesthesiology:
April 2006 - Volume 104 - Issue 4 - pp 635-643
Abstract

Background: Baseline low-to-high frequency ratio (LF/HF) of heart rate variability predicted hypotension after subarachnoid block (SAB). LF/HF-guided treatment of hypotension with vasopressors or colloids was investigated.
Methods: In 80 women scheduled to undergo cesarean delivery during SAB, LF/HF and systolic blood pressure (SBP) were analyzed. Patients were randomly assigned to a control group (n = 40) or a treatment group (n = 40). Control patients were assigned by their baseline LF/HF to one of two subgroups: LF/HF less than 2.5 or LF/HF greater than 2.5. Treatment patients with baseline LF/HF greater than 2.5 were treated with vasopressor infusion right after SAB (n = 20) or colloid prehydration until LF/HF decreased below 2.5 (n = 20). The incidences of hypotension (SBP < 80 mmHg) and hypertension (SBP > 140 mmHg) were investigated. LF/HF is presented as median and range, and SBP is presented as mean ± SD.
Results: Three of 17 control patients with low baseline LF/HF (1.7 [1.3/1.8]) demonstrated hypotension, and mean SBP remained stable (lowest SBP = 105 ± 14 mmHg). In contrast, 20 of 23 control patients with high baseline LF/HF (3.8 [3.3/4.8]; P < 0.0001 vs. low baseline LF/HF) demonstrated hypotension after SAB: lowest SBP = 78 ± 15 mmHg (P < 0.0001 vs. lowest SBP of control group with low baseline LF/HF). LF/HF-guided vasopressor therapy prevented hypotension in 19 of 20 patients: baseline SBP = 123 ± 15 mmHg, lowest SBP = 116 ± 17 mmHg. Mean prophylactic colloid infusion of 1,275 ± 250 ml reduced elevated baseline LF/HF from 5.4 (4.1/7.5) to 1.3 (0.8/1.59) (P < 0.0001). Hypotension was prevented in 17 of 20 patients: baseline SBP = 115 ± 13 mmHg, lowest SBP = 104 ± 19 mmHg. No hypertensive episode was recognized.
Conclusions: LF/HF may be a tool to guide prophylactic therapy of patients at high risk for hypotension after SAB. Vasopressor therapy tended to be more effective compared with colloid prehydration.

Prevention of Hypotension during Spinal Anesthesia for Cesarean Delivery: An Effective Technique Using Combination Phenylephrine Infusion and Crystalloid Cohydration
Kee, Warwick D. Ngan M.B.Ch.B., M.D., F.A.N.Z.C.A., F.H.K.A.M.*; Khaw, Kim S. M.B.B.S., F.R.C.A., F.H.K.A.M.†; Ng, Floria F. R.N., B.A.Sc.‡
Anesthesiology:
October 2005 - Volume 103 - Issue 4 - pp 744-750
Abstract
Background: Many methods for preventing hypotension during spinal anesthesia for cesarean delivery have been investigated, but no single technique has proven to be effective and reliable. This randomized study studied the efficacy of combining simultaneous rapid crystalloid infusion (cohydration) with a high-dose phenylephrine infusion.
Methods: Nonlaboring patients scheduled to undergo elective cesarean delivery received an intravenous infusion of 100 μg/min phenylephrine that was started immediately after spinal injection and titrated to maintain systolic blood pressure near baseline values until uterine incision. In addition, patients received infusion of lactated Ringer's solution that was given either rapidly (group 1, n = 57) or at a minimal maintenance rate (group 0, n = 55). Maternal hemodynamic changes and neonatal condition were compared.
Results: Six patients were excluded from analysis. Only 1 of 53 patients (1.9% [95% confidence interval, 0.3–9.9%]) in group 1 experienced hypotension versus 15 of 53 patients (28.3% [95% confidence interval, 18.0–41.6%]) in group 0 (P = 0.0001). Compared with group 0, patients in group 1 had greater values for the following: serial measurements of systolic blood pressure (P = 0.02), minimum recorded systolic blood pressure (P = 0.0002), and minimum recorded heart rate (P = 0.013). Total phenylephrine consumption was smaller in group 1 compared with group 0 (P = 0.008). Neonatal outcome and maternal side effects were similar between groups.
Conclusions: Combination of a high-dose phenylephrine infusion and rapid crystalloid cohydration is the first technique to be described that is effective for preventing hypotension during spinal anesthesia for cesarean delivery.


Placental Transfer and Fetal Metabolic Effects of Phenylephrine and Ephedrine during Spinal Anesthesia for Cesarean DeliveryNgan Kee, Warwick D. M.B.Ch.B., M.D., F.A.N.Z.C.A., F.H.K.A.M.*; Khaw, Kim S. M.B.B.S., F.R.C.A., F.H.K.A.M.†; Tan, Perpetua E. B.Sc., M.Phil.‡; Ng, Floria F. R.N., B.A.Sc.§; Karmakar, Manoj K. M.B.B.S., F.R.C.A., F.H.K.A.M.†
Abstract
Background: Use of ephedrine in obstetric patients is associated with depression of fetal acid-base status. The authors hypothesized that the mechanism underlying this is transfer of ephedrine across the placenta and stimulation of metabolism in the fetus.
Methods: A total of 104 women having elective Cesarean delivery under spinal anesthesia randomly received infusion of phenylephrine (100 μg/ml) or ephedrine (8 mg/ml) titrated to maintain systolic blood pressure near baseline. At delivery, maternal arterial, umbilical arterial, and umbilical venous blood samples were taken for measurement of blood gases and plasma concentrations of phenylephrine, ephedrine, lactate, glucose, epinephrine, and norepinephrine.
Results: In the ephedrine group, umbilical arterial and umbilical venous pH and base excess were lower, whereas umbilical arterial and umbilical venous plasma concentrations of lactate, glucose, epinephrine, and norepinephrine were greater. Umbilical arterial Pco2 and umbilical venous Po2 were greater in the ephedrine group. Placental transfer was greater for ephedrine (median umbilical venous/maternal arterial plasma concentration ratio 1.13 vs. 0.17). The umbilical arterial/umbilical venous plasma concentration ratio was greater for ephedrine (median 0.83 vs. 0.71).
Conclusions: Ephedrine crosses the placenta to a greater extent and undergoes less early metabolism and/or redistribution in the fetus compared with phenylephrine. The associated increased fetal concentrations of lactate, glucose, and catecholamines support the hypothesis that depression of fetal pH and base excess with ephedrine is related to metabolic effects secondary to stimulation of fetal β-adrenergic receptors. Despite historical evidence suggesting uteroplacental blood flow may be better maintained with ephedrine, the overall effect of the vasopressors on fetal oxygen supply and demand balance may favor phenylephrine.

Ephedrine and Phenylephrine Use during Cesarean Delivery
Gambling, David R. M.B., B.S., F.R.C.P.C.*; McLaughin, Kimberly Robbins M.D
Anesthesiology:
May 2010 - Volume 112 - Issue 5 - pp 1287-1288
We read with interest the articles by Ngan Kee et al.1 and Dyer et al.,2 as well as the editorial by Smiley,3 all of which concern comparisons of phenylephrine and ephedrine for the treatment of hypotension associated with spinal anesthesia for cesarean delivery (CD). It is reassuring to know that phenylephrine can be used safely in this setting, something that I (D.R.G.) have advocated to residents and colleagues for more than 10 yr. However, it is important to remember that ephedrine too has been used safely for decades to treat hypotension after induction of spinal anesthesia for CD. Therefore, it is crucial that the results of these recent studies are put into perspective and do not lead to an imposed or voluntary discontinuation of ephedrine use during CD. The reasons for this are as follows:
1. Phenylephrine is not always effective, and some patients seem to be phenylephrine nonresponders who only get effective response to vasopressor treatment when ephedrine is administered.
2. Phenylephrine can cause bradydysrhythmias that require treatment with atropine. This seems to be more of a problem when an infusion is used.
3. The observed differences in neonatal acid–base status demonstrated in many of the studies by Ngan Kee et al. are of unknown clinical significance, but the neonatologists in our center believe that the reported differences are not clinically important. The published normal values for umbilical artery pH after uncomplicated labor and vaginal birth at term are mean pH = 7.28 ± 0.05 (range, 7.15–7.43).4 Compare those with the values reported in the two studies recently published in Anesthesiology
4. One study suggests that Apgar scores are a better measure of neonatal outcome than umbilical cord blood gases.5 No study that we reviewed on the subject of phenylephrine versus ephedrine for spinal hypotension during CD has been able to show a significant difference in Apgar scores or in neonatal clinical outcome between groups, despite reported differences in umbilical arterial and venous pH.6–13
We would not want to see ephedrine discarded based on the evidence reported to date. Instead, we advocate a common sense approach to the treatment of spinal hypotension during CD. For example, phenylephrine could be used as a first-line treatment, with ephedrine being used either as a second-line treatment or in combination with phenylephrine. Maternal heart rate can be used as a guide to therapy. In addition, it may be prudent to use phenylephrine as the first-line agent in nonelective CD because small differences in fetal pH may have greater effect on clinical neonatal outcome in cases of intrauterine fetal stress. To date, however, studies have failed to show a significant difference in pH or clinical neonatal outcome in this setting, regardless of the vasopressor used.10
Ultimately, more research is necessary to look beyond initial umbilical cord blood gas measurements in the delivery room and instead at more long-term neonatal outcomes. This is especially true for cases of CD in which there is suspected fetal compromise. Until such data are available, do not “throw away” the ephedrine syringe, but rather use a common sense approach based on sound clinical judgment when treating maternal hypotension in this setting.
David R. Gambling, M.B., B.S., F.R.C.P.C.,*
Kimberly Robbins McLaughin, M.D.