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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.54 no.6 Campinas Nov./Dec. 2004
Preload during spinal anesthesia for cesarean section. Comparison between crystalloid and colloid solutions*
Expansión volemica en raquianestesia para cesárea. Comparación entre cristaloide y coloide
Mônica Maria Siaulys Capel Cardoso, TSA, M.D.I; Sandra Bliacheriene, M.D.II; Cláudia R C Freitas, M.D.III; Daniel S César, M.D.III; Marcelo Luís Abramides Torres, TSA, M.D.IV
em Anestesiologia pela FMUSP. Médica Supervisora da Anestesia Obstétrica
do HCFMUSP. Anestesiologista do Hospital e Maternidade Santa Joana
IIME3 da Disciplina de Anestesiologia da FMUSP
IIIME2 da Disciplina de Anestesiologia da FMUSP
IVDoutor em Anestesiologia pela FMUSP. Anestesiologista da Maternidade Pro-Matre Paulista
OBJECTIVES: Maternal hypotension is the most common complication following
spinal anesthesia for cesarean section. This study aimed at comparing the incidence
of hypotension and the need for vasopressors in patients submitted to cesarean
section under spinal anesthesia following preload with either crystalloid or
colloid (modified fluid gelatin).
METHODS: Participated in this prospective study 50 term pregnant patients, physical status ASA I, submitted to cesarean section under spinal anesthesia. Patients were randomly allocated into two groups receiving preload as follows: Crystalloid group, 10 mL.kg-1 lactated Ringer; Colloid group, 10 mL.kg-1 colloid (modified fluid gelatin). Control blood pressure was defined as the mean of three successive systolic blood pressure (SBP) values. SBP was measured at 1-minute intervals and 0.2 mg intravenous bolus of metaraminol was administered for SBP decrease above 10% of control blood pressure, and 0.4 mg bolus of the same drug for SBP decrease above 20% of control. Apgar score was evaluated after delivery and umbilical artery blood was sent for analysis. Modified Student's t test was used for statistical analysis and p < 0.05 was considered statistically significant.
RESULTS: Hypotension 10% (100% and 100% of patients); hypotension 20% (72% and 72% of patients), nausea (4% and 8% of patients); vasopressor consumption (1.67± 0.89 mg and 1.88 ± 0.74 mg) and umbilical artery pH (7.25 ± 0.04 and 7.26 ± 0.04), in Crystalloid and Colloid groups, respectively, were similar.
CONCLUSIONS: In the conditions of this study, colloid (modified fluid gelatin) was equivalent to crystalloid (lactate Ringer) in preventing or decreasing the incidence of hypotension in patients submitted to cesarean section under spinal anesthesia
Key Words: COMPLICATIONS: arterial hypotension; SURGERY, Obstetric: cesarean section; VOLEMY: colloid, crystalloid expansion
Y OBJETIVOS: La hipotensión arterial materna es la complicación
más común después de raquianestesia para cesárea.
El objetivo de este estudio fue comparar el bien estar materno y fetal de pacientes
sometidas a cesárea bajo raquianestesia, después de expansión
volemica con cristalóide o coloide (gelatina fluida modificada).
MÉTODO: Fueron estudiadas prospectivamente 50 gestantes de término, estado físico ASA I, sometidas a cesárea bajo raquianestesia. Las pacientes fueron aleatoriamente divididas en dos grupos que recibieron expansión volemica a seguir: Grupo Cristaloide 10 ml.kg-1 de Ringer con lactato y Grupo Coloide, 10 ml.kg-1 de solución coloidal (gelatina fluida modificada). Se definió como presión arterial de control la media de tres valores sucesivos de presión arterial sistólica (PAS). La PS fue medida a cada minuto y se administró bolus de 0,2 mg de metaraminol, por vía venosa, para disminución de PS mayor que 10% y bolus de 0,4 mg para disminución de PS mayor que 20%. Al nacimiento se evaluó el índice de Apgar y se realizó gasometria de la arteria umbilical. El análisis estadístico fue hecho con los tests t de Student modificado y para igualdad de las variables (p < 0,05).
RESULTADOS: La hipotensión arterial 10% (100% y 100% de las pacientes); hipotensión arterial 20% (72% y 72% de las pacientes), náusea (4% y 8% de las pacientes); consumo de vasopresor (1,67 ± 0,89 mg y 1,88 ± 0,74 mg) y pH de la arteria umbilical (7,25 ± 0,04 y 7,26 ± 0,04), en los grupos Cristaloide y Coloide, fueron semejantes respectivamente.
CONCLUSIONES: En las condiciones estudiadas, el coloide (gelatina fluida modificada) se mostró equivalente al cristaloide (Ringer con lactato) en el sentido de garantizar el bien estar materno y fetal.
Maternal hypotension is the most common complication after cesarean section under spinal anesthesia. Most frequent preventive and therapeutic measures to decrease its incidence and severity include uterine shift to the left, preload and vasopressors 1.
Preload may be achieved in several ways: with different fluid volumes and infusion rates; before, during or after regional anesthesia; or even with different solutions. These differences determine different clinical responses in terms of preventing hypotension.
In non obstetric patients, Ewaldsson et al. 2 have shown that fast preload, performed immediately after the end of spinal anesthetic injection, was more effective in decreasing hypotension incidence and severity as compared to slow preload performed immediately before spinal anesthesia. However, this has not been observed by Cardoso et al. 3, who have shown that in obstetric patients submitted to spinal anesthesia the incidence of hypotension and the consumption of vasopressors was similar in groups receiving fast or slow preload, before or after anesthesia.
It has been also shown that colloid solutions would be more beneficial as compared to crystalloids to prevent hypotension after spinal anesthesia for cesarean section. Colloids would be more effective due to their higher colloidosmotic effect and for remaining for a longer time in the intravascular space 4.
There are several colloid solutions available in the market. Although classified within the same pharmacological group, they have different physical-chemical, hence pharmacodynamic profiles.
This study aimed at comparing variables related to maternal (incidence of hypotension and nausea, vasopressor consumption) and fetal (pH, pCO2, umbilical artery EB and Apgar score) wellbeing in patients submitted to cesarean section under spinal anesthesia after preload with crystalloid or colloid (modified fluid gelatin) solutions).
After the Ethics and Research Project Analysis Committees approval, participated in this prospective study 50 healthy pregnant patients with single term fetus, to be submitted to cesarean section under spinal anesthesia. Exclusion criteria were patients with chronic hypertension or gestation-induced hypertension, with cardiovascular or brain vascular diseases, with known fetal abnormalities and those with total or partial spinal anesthesia failure.
Patients were randomly distributed in two groups of 25 patients receiving immediately after spinal anesthetic injection:
Crystalloid group: preload with 10 mL.kg-1 lactated Ringer at maximum infusion rate allowed by cephalic vein catheterization with 18G catheter using as standard infusion solution height the maximum extension of the device (1.43 m);
Colloid group: preload with 10 mL.kg-1 colloid solution (Gelafundin®), at maximum infusion rate allowed by cephalic vein catheterization with 18G catheter using as standard infusion solution height the maximum extension of the device (1.43 m).
Study was double blind and randomized (drawing of closed envelopes).
Spinal anesthesia was induced with 0.5% hyperbaric bupivacaine associated to 40 mg morphine injected in 60 seconds in L2-L3/L3-L4 with patients in the sitting position.
Control blood pressure was defined as the mean of three successive systolic blood pressure (SBP) values obtained immediately before spinal anesthesia. Blood pressure was controlled at 1-minute intervals and decreases above 10% of control SBP were corrected with 0.2 mg bolus metaraminol and decreases above 20% with 0.4 mg bolus metaraminol. Uterine shift was performed with modified Crawford wedge and maintained until fetal extraction.
Oxytocin was administered after delivery (10 U in 500 mL lactated Ringer at the rate of 30 drops per minute). Umbilical cord blood was collected immediately after delivery.
Maternal variables studied were: incidence of hypotension, nausea and/or vomiting, and metaraminol consumption. Fetal variables evaluated were: pH, pCO2, umbilical artery EB and Apgar scores at 1 and 5 minutes. Neonate weight and minutes elapsed between induction-delivery and uterine incision-delivery were recorded.
Analysis of variance for repeated measures was used to compare blood pressure, heart rate and metaraminol consumption means along time between groups. Student's t and Fisher Exact tests were used to compare remaining variables, as appropriate, considering statistically significant p < 0.05.
Demographics data were similar for both crystalloid and colloid groups (Table I). Similarly, there were no differences in the incidence of hypotension 10% and 20% above control values, nausea and metaraminol consumption before delivery. Data are summarized in table II. No patient in both groups presented vomiting. Groups were also similar in fetal variables (Table III).
Our study has shown that preload with colloid (modified fluid gelatin) was similar to crystalloid (lactated Ringer) in preventing or decreasing maternal hypotension severity after spinal anesthesia for cesarean section. These data are in disagreement with Ueyama et al. 5 and Riley et al. 6 who have shown higher incidence of hypotension in patients submitted to preload with crystalloids as compared to the group receiving colloids. Differences in results could be attributed to several factors:
1) Our study has used Modified Fluid Gelatin and those studies have used 6% hetastarch. Although colloids are in general classified within the same pharmacological group, they have different physico-chemical and pharmacokinetic profiles, which could explain the higher efficiency of one as compared to the other. Vercauteren et al. 7, in comparing the efficacy of two different colloid solutions (hetastarch versus modified fluid gelatin) for preload during spinal anesthesia for cesarean section, have observed higher efficacy of hetastarch. So, it is possible that in our study, the equivalence between colloid and crystalloid to prevent hypotension during spinal anesthesia for cesarean section has been a consequence of the use of modified fluid gelatin and the same concept should not be generalized to other colloids such as hetastarch.
2) The second factor refers to the volume of colloid used. Ueyama et al. 5 have only found significant decrease in maternal hypotension during spinal anesthesia for cesarean section in the group using 1000 mL of 6% hetastarch. In our study, the volume of colloid was limited to 10 mL.kg-1 (mean 727.5 mL colloid administration), because the objective was to compare with our routine practice of never administering crystalloids in volumes above 10 mL.kg-1. This standardization is based on the observation that a high number of patients have developed anemia after higher fluid amounts 8. In addition to anemia, other disadvantages of large colloid volumes are the risk for cardiovascular system overload, especially in the immediate postoperative period, and the potential risk for coagulation disorders 9.
3) The third variable is related to preload timing. Traditionally, and as performed by Ueyama et al. 5, preload has always been performed immediately before regional anesthesia. In our study, we decided to perform it simultaneously with spinal anesthesia, since in theory it seems to be more effective. Preload would be more effective when performed after sympathetic block because the constant of body fluid excretion is decreased after regional anesthetic induction 2. This is translated into a higher trend of the body to preserve administered fluid in the central compartment. This phenomenon would not be so important for colloids because they naturally tend to remain in the intravascular compartment.
However for crystalloids, which are promptly redistributed from the central to the peripheral compartment (30 minutes later only 28% of administered volume remains in the central compartment), their administration after anesthetic induction could determine better results in preventing hypotension because their loss from the central to the peripheral compartment would be minimized. So, it is possible that the equivalence of colloids and crystalloids in preventing hypotension after regional anesthesia in our study could be exclusively explained by better yield of crystalloid. Its administration at a theoretically more adequate moment, would have contributed to less crystalloid volume loss to the intravascular compartment. This would make it similar to colloid, which initially remains in the extravascular compartment and would decrease possible differences in solutions redistribution.
Metaraminol was the vasopressor of choice to treat post-regional anesthesia hypotension because a-agonists have been shown to be superior to ephedrine both for fetal and maternal wellbeing 10. In pregnant patients submitted to elective cesarean section under spinal anesthesia, it has been shown that low metaraminol doses were associated to lower incidence of nausea and tachycardia as compared to ephedrine 11.
The incidence of maternal hypotension was similar for Crystalloid and Colloid groups, both in control blood pressure decrease above 10% (100% and 100%) and above 20% (72% and 72%). It is interesting to note that, although almost all therapeutic measures have been taken (preload, uterine shift to the left and vasopressors), the incidence of maternal hypotension in both groups was significantly high.
This is probably a reflex of the way in which hypotension was defined and of changes related to the frequency in which blood pressure is measured. Traditionally, maternal hypotension was defined as control systolic blood pressure decrease equal to or above 20%, or systolic blood pressure decrease below 100 mmHg, being blood pressure measured every 3 minutes. Currently hypotension is defined as pressure decrease equal to or above 10% and blood pressure is measured every minute until delivery12. More frequent blood pressure measurements and earlier blood pressure decrease correction would explain its higher incidence.
However, in spite of the high incidence of hypotension, significantly low incidence of nausea (4% to 8%) and absence of vomiting have been observed. This in theory shows the advantage of early treating blood pressure changes in obstetric patients under regional anesthesia for cesarean section. Although numerically there has been a higher incidence of hypotension with this technique, we were able to assure major maternal comfort.
Crystalloid and colloid groups were also similar in fetal variables. This once more suggests that the wellbeing of fetuses of obstetric patients under regional anesthesia is more dependent on the prevention of prolonged hypotension periods than on the type of solution used for preload or even on the choice of the vasopressor to be used to prevent and treat such complication.
In conclusion, preload with crystalloid or colloid, provided it is achieved immediately after regional anesthesia induction and with volumes not higher than 10 mL.kg-1, was similar to prevent maternal hypotension during spinal anesthesia for cesarean section. In this sense, preload with crystalloid would be advantageous for being a lower cost solution with less potential risk for complications in terms of cardiovascular overload, allergic reactions and coagulation disorders.
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Submitted for publication
March 3, 2003
Accepted for publication May 7, 2004
* Received from Disciplina de Anestesiologia do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HCFMUSP), Departamento de Anestesiologia do Hospital e Maternidade Santa Joana/Pro-Matre, São Paulo, SP