Scholarly article on topic 'Ephedrine versus Phenylephrine: Prevention of Hypotension during Spinal Block for Cesarean Section and Effects on the Fetus'

Ephedrine versus Phenylephrine: Prevention of Hypotension during Spinal Block for Cesarean Section and Effects on the Fetus Academic research paper on "Health sciences"

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Brazilian Journal of Anesthesiology
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{"ANESTHESIA / Obstetrics" / "COMPLICATIONS: hypotension" / "DRUGS: ephedrine / phenylephrine" / "SURGERY / Obstetrics: cesarean section" / "ANESTESIA / Obstétrica" / "CIRURGIA / Obstétrica: cesariana" / "COMPLICAÇÕES: hipotensão arterial" / "DROGAS: efedrina / fenilefrina"}

Abstract of research paper on Health sciences, author of scientific article — Edno Magalhães, Catia Sousa Govêia, Luís Cláudio de Araújo Ladeira, Bruno Góis Nascimento, Sérgio Murilo Cavalcante Kluthcouski

Summary Background and objectives Hypotension during spinal block for cesarean section is secondary to the sympathetic blockade and aorto-caval compression by the uterus and it can be deleterious to both the fetus and the mother. Ephedrine and phenylephrine improve venous return after sympathetic blockade during the spinal block. The objective of this study was to compare the efficacy of ephedrine and phenylephrine in the prevention and treatment of maternal hypotension during spinal block and to evaluate their side effects and fetal changes. Methods Sixty patients undergoing spinal block with bupivacaine and sufentanil for cesarean section were randomly divided in two groups to receive prophylactic ephedrine (Group E, n=30, dose=10 mg) or phenylephrine (Group P, n=30, dose=80 μg). Hypotension (blood pressure equal or lower than 80% of baseline values) was treated with bolus administration of the vasoconstrictor at 50% of the initial dose. The incidence of hypotension, reactive hypertension, bradycardia, and vomiting, and Apgar scores on the 1st and 5th minutes, and blood gases of the umbilical cord blood were evaluated. Results The mean dose of ephedrine used was 14.8±3.8 mg and of phenylephrine was 186.7±52.9 μg. Demographic parameters and the incidence of vomiting, bradycardia, and reactive hypertension were similar in both groups. Hypotension had an incidence of 70% in Group E and 93% in Group P (p<0.05). The mean arterial pH of the umbilical cord blood and the Apgar score in the 1st minute were lower in Group E (p<0.05). Differences in the Apgar score in the 5th minute were not observed. Conclusions Ephedrine was more effective than phenylephrine in the prevention of hypotension. Both drugs had similar incidence of side effects. Fetal repercussions were less frequent with phenylephrine and were transitory with the use of ephedrine.

Similar topics of scientific paper in Health sciences , author of scholarly article — Edno Magalhães, Catia Sousa Govêia, Luís Cláudio de Araújo Ladeira, Bruno Góis Nascimento, Sérgio Murilo Cavalcante Kluthcouski

Academic research paper on topic "Ephedrine versus Phenylephrine: Prevention of Hypotension during Spinal Block for Cesarean Section and Effects on the Fetus"

Rev Bras Anestesio! 2009; 59: 1: 11-20

ARTIGO CIENTÍFICO SCIENTIFIC ARTICLE

Efedrina versus Fenilefrina: Prevengao de Hipotensäo Arterial durante Anestesia Raquídea para Cesariana

e Efeitos sobre o Feto*

Ephedrine versus Phenylephrine: Prevention of Hypotension during Spinal Block for Cesarean Section and Effects on the Fetus

Edno Magalhäes, TSA1, Catia Sousa Govéia, TSA2, Luís Cláudio de Araújo Ladeira, TSA2, Bruno Góis Nascimento3,

Sérgio Murilo Cavalcante Kluthcouski3

RESUMO

Magalhaes E, Govéia CS, Ladeira LCA, Nascimento BG, Kluthcouski SMC — Efedrina versus Fenilefrina: Prevengao de Hipotensao Arterial durante Anestesia Raquídea para Cesariana e Efeitos sobre o Feto.

JUSTIFICATIVA E OBJETIVOS: A hipotensao arterial durante a anestesia raquídea para cesariana deve-se ao bloqueio simpático e com-pressao aorto-cava pelo útero e pode ocasionar efeitos deletérios para o feto e a mae. A efedrina e fenilefrina melhoram o retorno venoso após bloqueio simpático durante anestesia raquídea. O objetivo deste estudo foi comparar a eficácia da efedrina e da fenilefrina em prevenir e tratar a hipotensao arterial materna durante anestesia raquídea e avaliar seus efeitos colaterais e alteragóes fetais.

MÉTODO: Sessenta pacientes, submetidas á anestesia raquídea com bupivacaína e sufentanil para cesariana, foram divididas aleatoriamente em dois grupos para receber, profilaticamente, efedrina (Grupo E, n = 30, dose = 10 mg) ou fenilefrina (Grupo F, n = 30, dose = 80 pg). Hipotensao arterial (pressao arterial menor ou igual a 80% da medida basal) foi tratada com bolus de vasoconstritor com 50% da dose inicial. Foram avaliados: incidéncia de hipotensao arterial, hipertensao arterial reativa, bradicardia e vómitos, escore de Apgar no primeiro e quinto minutos e gasometria do cordao umbilical.

RESULTADOS: A dose média de efedrina foi 14,8 ± 3,8 mg e 186,7 ± 52,9 pg de fenilefrina. Os grupos foram semelhantes quanto aos parámetros demográficos e incidéncia de vómitos, bradicardia e hipertensáo arterial reativa. A incidéncia de hipotensáo arterial foi de 70% no Grupo E e 93% no Grupo F (p < 0,05). O pH arterial médio do cordao umbilical e o escore de Apgar no primeiro minuto foram menores no grupo E (p < 0,05). Nao houve diferenga no escore do quito minuto.

*Recebido do (Received from) CET/SBA do Centro de Anestesiología do Hospital Universitario de Brasilia, Universidade de Brasilia (UnB), Brasilia, DF

1. Chefe dos Centros de Anestesiologia e de Clínicas Cirúrgicas do Hospital Universitario de Brasilia; Responsável pelo CET/SBA do Centro de Anestesiologia da UnB

2. Médico Assistente do Hospital Universitario de Brasilia; Co-Responsável pelo CET/SBA do Centro de Anestesiologia da UnB

3. ME3 do CET/SBA Centro de Anestesiologia da UnB

Apresentado (Submitted) em 13 de margo de 2008

Aceito (Accepted) para publicagao em 27 de outubro de 2008

Enderego para correspondencia (Correspondence to):

Dr. Edno Magalhaes

SQS 113, bloco C/406

70736-030 Brasilia, DF

E-mail: ednomag@gmail.com

© Sociedade Brasileira de Anestesiologia, 2009

CONCLUSÓES: A efedrina foi mais eficiente que fenilefrina na pre-vengao de hipotensao arterial. Ambos os fármacos apresentaram incidéncia semelhante de efeitos colaterais. As repercussóes fetais foram menos freqüentes com o uso da fenilefrina e apenas transi-tórias com a utilizagao da efedrina.

Unitermos: ANESTESIA, Obstétrica; CIRURGIA, Obstétrica: cesariana; COMPLICAQÓES: hipotensao arterial; DROGAS: efedrina, fenilefrina.

SUMMARY

Magalhaes E, Goveia CS, Ladeira LCA, Nascimento BG, Kluthcouski SMC — Ephedrine versus Phenylephrine: Prevention of Hypotension During Spinal Block for Cesarean Section and Effects on the Fetus.

BACKGROUND AND OBJECTIVES: Hypotension during spinal block for cesarean section is secondary to the sympathetic blockade and aorto-caval compression by the uterus and it can be deleterious to both the fetus and the mother. Ephedrine and phenylephrine improve venous return after sympathetic blockade during the spinal block. The objective of this study was to compare the efficacy of ephedrine and phenylephrine in the prevention and treatment of maternal hypotension during spinal block and to evaluate their side effects and fetal changes.

METHODS: Sixty patients undergoing spinal block with bupi-vacaine and sufentanil for cesarean section were randomly divided in two groups to receive prophylactic ephedrine (Group E, n = 30, dose = 10 mg) or phenylephrine (Group P, n = 30, dose = 80 pg). Hypotension (blood pressure equal or lower than 80% of baseline values) was treated with bolus administration of the vasoconstrictor at 50% of the initial dose. The incidence of hypotension, reactive hypertension, bradycardia, and vomiting, and Apgar scores on the 1st and 5h minutes, and blood gases of the umbilical cord blood were evaluated.

RESULTS: The mean dose of ephedrine used was 14.8 ± 3.8 mg and of phenylephrine was 186.7 ± 52.9 pg. Demographic parameters and the incidence of vomiting, bradycardia, and reactive hypertension were similar in both groups. Hypotension had an incidence of 70% in Group E and 93% in Group P (p < 0.05). The mean arterial pH of the umbilical cord blood and the Apgar score in the 1st minute were lower in Group E (p < 0.05). Differences in the Apgar score in the 5th minute were not observed.

CONCLUSIONS: Ephedrine was more effective than phenylephrine in the prevention of hypotension. Both drugs had similar incidence of side effects. Fetal repercussions were less frequent with phenylephrine and were transitory with the use of ephedrine.

Key Words: ANESTHESIA, Obstetrics; COMPLICATIONS: hypotension; DRUGS: ephedrine, phenylephrine; SURGERY, Obstetrics: cesarean section.

INTRODUQAO

Hipotensáo arterial durante anestesia raquídea para cesa-nana deve-se ao bloqueio simpático e pode ocasionar efei-tos deletérios para o feto e a máe. Entre eles, diminuigáo do fluxo sanguíneo uteroplacentário, comprometimiento da oxi-genagáo fetal, acidose fetal e sintomas de diminuigáo do débito cardíaco materno, como náuseas, vómitos e altera-gáo de consciéncia 1.

A incidéncia de hipotensáo arterial após anestesia raquídea para cesariana pode chegar a 80% 2-4 se náo forem utilizadas medidas profiláticas, tais como hidratagáo prévia, desvio uterino para a esquerda e uso de vasopressores 56. A efedrina é um agente simpaticomimético náo-catecola-mina que estimula os receptores alfa- e beta-adrenérgicos por agáo direta e predominantemente indireta, produzindo seus efeitos por causar a liberagáo de norepinefrina das terminales nervosas do sistema nervoso autónomo. Tradici-onalmente, é utilizada como vasopressor de escolha em anestesia obstétrica, apesar de sua superioridade em rela-gáo aos outros vasopressores náo ter sido confirmada 78. As intercorréncias com o uso de efedrina podem incluir taquicardia supraventricular materna, taquifilaxia e acidose fetal. Estudos anteriores relataram que o aumento da pres-sáo arterial com efedrina associa-se a preservagáo do fluxo sanguíneo uteroplacentário, sobretudo em decorréncia do seu efeito beta-adrenérgico 910. Entretanto, outros autores sugeriram que a efedrina pode diminuir o pH do sangue umbilical fetal, embora sem prejuízo em relagáo ao escore de Apgar 411.

A fenilefrina é considerada um fármaco agonista a1-adre-nérgico puro. Promove constrigáo venosa mais que arterial de maneira dose-dependente, melhorando o retorno venoso após o bloqueio simpático durante anestesia raquídea. Estudos demonstraram que a fenilefrina mantém o fluxo sanguíneo uteroplacentário e valores de pH do sangue umbilical maiores em relagáo a efedrina e apresenta, portan-to, eficácia semelhante em controlar a hipotensáo arterial, mas com menor risco de acidose fetal 51213. A hipótese deste estudo é a de que a fenilefrina apresente perfil farmacológico superior ao da efedrina para o tratamiento da hipotensáo arterial durante cesariana sob anestesia raquídea, em relagáo a vitalidade do recém-nascido. Os objetivos do trabalho foram comparar a eficácia da fenilefrina e efedrina em prevenir e tratar a hipotensáo arterial materna no período intra-operatório, avaliar os efeitos colaterais dessa terapia vasopressora e estudar as alteragoes fetais por meio do escore de Apgar e gasometrias arterial e venosa do sangue do cordáo umbilical.

MÉTODO

Após aprovagáo do protocolo pelo Comité de Ética em Pesquisa (CEP) em seres humanos da Universidade de Brasília e assinatura de consentimento livre e esclarecido, 60 mu-

Iheres foram selecionadas para o estudo prospectivo, duplamente encoberto e aleatorio.

Os critérios de inclusao foram: estado físico ASA I ou II, ges-tagao a termo de feto único e indicagao de cesariana. Critérios de exclusao foram: recusa em participar do estudo, idade inferior a 18 anos, hipertensao arterial sistémica preexistente ou induzida pela gravidez, doengas cardiovasculares ou cerebrovasculares, anormalidades fetais, historia de reagoes de hipersensibilidade aos fármacos utilizados no estudo, contra-indicagoes á anestesia raquídea. As pacientes foram monitorizadas com eletrocardiograma contínuo, pressao arterial nao-invasiva e oxímetro de pulso. Foram colocadas em posigao de decúbito dorsal durante alguns minutos e a pressao arterial e freqüéncia cardíaca registradas a cada trés minutos, por trés vezes, para a média aritmética dos valores basais. Com a paciente em decúbito lateral esquerdo, foi realizada anestesia raquídea com agulha 25 x 3,5 do tipo Quincke entre L2-L3 ou L3-L4 e solugao contendo 10 mg de bupivacaína a 0,5% hiperbárica e 3 |jg de sufentanil. A seguir, com a paciente em decúbito dorsal, foi colocada cunha de Crawford sob o flanco direito com o objetivo de deslocar o útero para a esquerda. Logo após a injegao subaracnóidea, foi iniciada infusao de 2 litros de solugao de Ringer com lactato antes da incisao uterina e, depois, mantida infusao lenta. As pacientes foram distribuídas de forma aleatoria em dois grupos, por meio de envelopes seqüenciais lacrados conten-do números aleatorios gerados previamente por computador. O resultado da alocagao foi mantido em sigilo, nao sendo conhecido pelas pacientes e pelos médicos responsáveis pela coleta e análise dos dados do estudo. A definigao do tamanho da amostra baseou-se em estudos prévios 12,13. Os grupos foram constituídos por 30 pacientes cada, denominados Grupo E (efedrina) e Grupo F (fenilefrina). As pacientes do Grupo E receberam profilaticamente bolus de 10 mg de efedrina por via venosa logo após o bloqueio subarac-nóideo e as pacientes do Grupo F, bolus profilático de 80 jg de fenilefrina por via venosa. As seringas com as substán-cias em estudo foram preparadas por médico nao envolvido na coleta de dados e análise dos resultados. Hipotensao arterial materna foi definida como pressao menor ou igual a 80% da medida basal e tratada com bolus de 50% da dose inicial do vasopressor em estudo. Hipertensao arterial reativa foi caracterizada como pressao arterial 20% maior que o valor inicial, após uso do vasopressor. Frequén-cia cardíaca inferior a 50 batimentos por minuto caracterizou bradicardia, se acompanhada de hipotensao arterial, e foi tratada com 0,75 mg de atropina.

O nível de bloqueio sensitivo foi avaliado a cada minuto após a pungao, por meio de estímulo doloroso com agulha, até o fim do procedimento. Somente foi autorizado o início da operagao com bloqueio no nível de T5. Foram registrados os tempos decorridos do bloqueio até a incisao da pele, inci-sao uterina e retirada do feto.

Também foram analisadas a incidência de hipotensâo arterial materna, hipertensâo arterial reativa, bradicardia, náuseas e vómitos e a dose total de vasopressor utilizada. Todos os recém-nascidos foram avaliados pelo escore de Apgar após um e cinco minutos do nascimento e foi considerado Apgar baixo valor inferior a 8. Sangue do cordâo umbilical fetal venoso e arterial foi coletado logo após o nascimento para medida de gasometria e foi considerado como acidose fetal pH umbilical menor que 7,2. Os resultados obtidos foram submetidos à análise esta-tística com os testes t de Student para os dados continuos, Mann-Whitney para os dados ordinais e Qui-quadrado para os dados nominais. Foi considerado como significativo p < 0,05.

RESULTADOS

A idade média dos pacientes no Grupo E foi 27,2 anos e 26,5 no Grupo F. O índice de massa corpórea (IMC) médio foi se-melhante entre os grupos, bem como o peso. A idade gesta-cional média foi de 39 semanas nos dois grupos. Nâo houve diferença estatística significativa quanto às outras características demográficas e quanto ao estado físico (Ta-bela I).

O tempo médio do bloqueio espinal á incisáo da pele foi 7,4 minutos no Grupo E e 6,9 no Grupo F. O tempo médio até a incisáo uterina foi 12,7 e 12,8 minutos nos grupos E e F, respectivamente, e o tempo até a retirada do feto foi 13,8 e 14,2 minutos. Náo houve diferenga estatística entre os grupos analisados em relagáo a tais parámetros. A dose média de vasopressor no Grupo E foi de 14 mg e no Grupo F, 186 |jg. Quanto ao nível de bloqueio sensitivo, a maioria dos pacientes apresentou bloqueio até T4 (Tabela II). Em relagáo á incidéncia de efeitos colaterais, no Grupo E houve sete episódios de náuseas e quatro de vómitos, en-quanto no Grupo F ocorreram dez episódios de náuseas e seis de vómitos. A incidéncia de hipertensáo arterial reativa foi semelhante entre os grupos: cinco episódios no Grupo E e quatro no Grupo F. Apenas uma paciente no Grupo F apresentou bradicardia, adequadamente tratada com atropina. Náo houve diferenga estatística significativa entre os grupos em relagáo á incidéncia desses efeitos colaterais. No Grupo F, 28 pacientes (93%) apresentaram hipo-tensáo arterial e no Grupo E, 21 (70%), uma diferenga estatística significativa (p < 0,05). O número de episódios de hipotensáo arterial foi muito maior no Grupo F (80 episó-dios) em relagáo ao Grupo E (29 episódios), com p < 0,05 (Tabela III).

Tabela I - Dados Demográficos

Características Gerais Grupo E (n = 30) Grupo F (n = 30)

Idade (anos) 27,2 ± 4,5 26,5 ± 5,1

Peso (kg) 83,5 ± 6,9 79,2 ± 9,7

Altura (cm) 159,6 ± 5,3 158,5 ± 5,8

IMC (kg.m-2) 32,8 ± 2,5 31,1 ± 3,5

Idade gestacional (semanas) 39,5 ± 1,1 39,6 ± 1,3

Estado Físico (ASA I/II) 20/10 20/10

Peso neonato (g) 3.641 ± 499,1 3.538 ± 535,4

Valores expressos em Média ± DP *p < 0,05.

Tabela II - Parámetros Anestésico-Cirúrgicos

Parámetros anestésico-cirúrgicos Grupo E (n = 30) Grupo F (n = 30)

Tempo do bloqueio á incisao da pele (min) 7,4 ± 2,2 6,9 ± 2,4

Tempo do bloqueio á incisao uterina (min) 12,7 ± 2,2 12,8 ± 3,7

Tempo do bloqueio á retirada do feto (min) 13,8 ± 2,3 14,2 ± 3,5

Dose de vasopressor 14 mg 186 |jg

Nível sensitivo em T4 (%) 22 (73,3%) 22 (73,3%)

Nível sensitivo em T5 (%) 8 (26,7%) 8 (26,7%)

Valores expressos em Média ± DP. *p < 0,05.

MAGALHÄES, GOVÉIA, LADEIRA E COL.

Tabela III - Efeitos Colaterais, Número de Episodios e Proporgäo

Efeitos colaterais Grupo E (n = 30) Grupo F (n = 30)

Náuseas (episodios) 7 10

Vómitos (episodios) 4 6

Hipotensäo arterial (episodios)* 29 80

Hipotensäo arterial (pacientes)* 21 (70%) 28 (93,3%)

Hipertensäo reativa (episodios) 5 4

Bradicardia (episodios) 0 1

*p < 0,05.

O escore de Apgar no primeiro minuto demonstrou propor-gäo maior de recém-nascidos com valores abaixo de 8 no Grupo E (27%) em relagäo ao Grupo F (10%), sendo essa diferenga estatística significativa (p < 0,05). No Grupo E, no primeiro minuto, oito recém-nascidos (27%) apresentaram Apgar igual a 7, 17 (56%) apresentaram Apgar 8 e cinco recém-nascidos (17%), Apgar 9. No Grupo F, trés recém-nascidos (10%) apresentaram Apgar igual a 7 no primeiro minuto, quinze (50%) apresentaram Apgar 8, onze (37%) apresentaram Apgar 9 e, finalmente, um (3%), Apgar 10. Os valores de Apgar no quinto minuto näo mostraram dife-rengas entre os grupos. No Grupo E, dois recém-nascidos (6%) apresentaram Apgar igual a 8, 20 (67%) apresentaram Apgar 9, e oito (27%), Apgar 10. No Grupo F, metade dos re-cém-nascidos apresentou Apgar igual a 9 no quinto minuto, enquanto a outra metade, Apgar 10. Em relagäo ä gasometria arterial e venosa do sangue do cordäo umbilical, houve diferenga estatística significativa apenas no valor médio do pH arterial: 7,22 no Grupo E e 7,27 no Grupo F (p < 0,05). Os valores médios de gasometria es-täo representados na Tabela IV.

Tabela IV - Gasometria em Artéria e Veia do Cordäo Umbilical

Gasometria Grupo E (n=30) Grupo F (n=30)

pH artéria* 7,22 ± 0,03 7,27 ± 0,06

BE artéria -10,5 ± 2,6 -9,2 ± 4,2

pCO2 artéria 40,0 ± 3,8 38,9 ± 8,9

pO2 artéria 19,5 ± 3,6 18,0 ± 4,8

HCO-3 artéria 16,2 ± 2,4 16,5 ± 4,0

pH veia 7,27 ± 0,04 7,28 ± 0,06

BE veia -7,2 ± 3,5 -7,9 ± 4,4

pCO2 veia 34,7 ± 6,7 35,2 ± 11,1

pO2 veia 25,6 ± 6,3 24,3 ± 7,1

HCO-3 veia 18,4 ± 2,9 18,7 ± 3,5

Valores expressos em Média ± DP. *p < 0,05.

DISCUSSAO

A indicagao de anestesia regional em obstetrícia consagrou-se em relagao á anestesia geral, devido á redugao da morbi-mortalidade materna e fetal 14. No entanto, alguns estudos associaram maior incidéncia de acidose fetal após anestesia raquídea, possivelmente em decorréncia da hipotensao arterial materna ou de fatores que alterem o fluxo uteropla-centário 1516.

Deslocamento uterino para esquerda e administragao de fluido por via venosa tém sido utilizados para reduzir a gravidade da hipotensao arterial, mas com eficácia limitada. A administragao de fármacos vasopressores, muitas vezes, também se faz necessária 17.

A utilizagao da efedrina como vasopressor de escolha em obstetrícia já é uma tradigao, apesar de sua superioridade ainda nao comprovada 1,7,9 Acreditava-se que a efedrina aumentava a pressao arterial materna com preservagao do fluxo uteroplacentário por causa do seu efeito beta-adrenér-gico, enquanto o uso de vasopressores alfa-agonistas puros associava-se á redugao no fluxo uteroplacentário 810. Entretanto, estudos subseqüentes demonstraram que no tratamento de hipotensao arterial após anestesia raquídea para cesarianas a efedrina apresenta igual eficácia, mas pode, por vezes, promover acidose fetal 18- 20. No presente trabalho, foram controladas as variáveis asso-ciadas á hipotensao arterial pós-anestesia raquídea com o objetivo de avaliar qual entre os fármacos, efedrina ou fe-nilefrina, seria mais eficaz na prevengao de hipotensao arterial e com menores efeitos deletérios para o feto. Estudos anteriores apresentaram diferentes metodologias e resultados incertos quanto ao tipo ideal de vasopressor, dose, regime de administragao, bem como a utilizagao de outras técnicas para o controle da pressao arterial materna, com mínimos efeitos sobre o feto 12 1920.

Com o intuito de limitar distorgóes nos resultados, todas as pacientes receberam hidratagao com 2.000 mL de solugao de Ringer com lactato, iniciada apenas após o bloqueio espinal, uma vez que estudos recentes comprovaram a inefi-cácia da hidratagao prévia devido á rápida redistribuigao 21. Foi ainda desviado o útero para a esquerda com o objetivo de

diminuir a compressáo aorto-cava e o bloqueio foi mantido no mesmo nível em todas as pacientes. Apesar dos cuidados relacionados com o método emprega-do, alguns fatores podem limitar a interpretagáo do estudo. O número de pacientes envolvidas, embora maior que alguns estudos publicados, pode ser um fator de viés, uma vez que o tamanho da amostra náo foi calculado. Outra limi-tagáo foi a diferenga de tempo entre a coleta de sangue do cordáo umbilical e a análise dos gases sanguíneos. Essa diferenga pode ter alterado os valores dos gases sanguíneos e, possivelmente, interferido nos resultados. Estudos prévios sugeriram que 30 mg de efedrina por via venosa em bolus seria a dose mais efetiva para prevengáo de hipotensáo arterial, mas á custa de incidéncia aumentada de hipertensáo arterial reativa 22. Em contraste, um estudo prospectivo observacional demonstrou que dose por via venosa, de 15 ou 20 mg de efedrina diminuiu a incidéncia de hipotensáo arterial materna sem aumentar a ocorréncia de hipertensáo arterial reativa 20. Em metanálise em 2004 19, concluiu-se que doses maiores que 14 mg de efedrina náo diminuíram a incidéncia de hipotensáo arterial materna, mas causaram hipertensáo arterial reativa e pequena redugáo no pH umbilical. No presente estudo, a dose considerada como eficaz e, ao mesmo tempo, com mínimos efeitos co-laterais, foi de 10 mg de efedrina.

Em relagáo á fenilefrina, recente estudo demonstrou que mesmo com altas doses (acima de 2.000 jg) utilizadas para o controle da pressáo arterial, náo houve efeitos deletérios para o feto, medidos pelo escore de Apgar e gasometria do sangue do cordáo umbilical 23. No atual estudo, escolheu-se a dose de 80 jg de fenilefrina profilática, com base em estudo prévio, que mostrou ser essa uma dose eficaz quando administrada em bolus por via intravenosa, sem efeitos co-laterais graves 12.

Para a avaliagáo do controle da hipotensáo arterial, estudos demonstraram igual eficácia entre efedrina e fenilefrina na prevengáo e no tratamento dessa complicagáo, tanto em bolus quanto em infusáo contínua 23,24. No presente traba-lho, por praticidade, optou-se por utilizar administragáo das substáncias em bolus. A fenilefrina teve menor eficácia na prevengáo de hipotensáo arterial em relagáo á efedrina, como demonstrado pelo número de pacientes que apresen-taram hipotensáo arterial e número de episódios em cada grupo. Tal fato deve-se provavelmente á duragáo de agáo mais fugaz desse vasopressor e a forma de administragáo empregada. Uma vez que foi administrada em bolus e de forma profilática, apenas repetindo-se a dose quando a pres-sáo arterial fosse menor ou igual a 80% da medida basal, flutuagoes da concentragáo plasmática da substáncia tam-bém podem ter contribuído. Apesar de a fenilefrina apresen-tar controle menos eficaz da pressáo arterial, náo houve diferenga na incidéncia de efeitos colaterais maternos, tais como náuseas, vómitos e alteragáo do nível de consciéncia, possivelmente porque a diminuigáo da pressáo arterial náo foi muito intensa.

Em revisáo sistemática sobre os fatores associados a pH e excesso de bases após anestesia raquídea para cesariana, concluiu-se que o tempo entre a incisáo uterina e a retirada do feto associou-se a valores baixos de pH e de excesso de bases 24. Contudo, no presente estudo, náo houve diferenga entre os grupos em relagáo ao tempo cirúrgico decorrido entre a instalagáo do bloqueio e a retirada do recém-nasci-do. Náo se acredita que idade gestacional ou peso do re-cém-nascido tenham causado algum grau de interferéncia na avaliagáo, uma vez que ambos os grupos apresentaram características semelhantes em relagáo a tais parámetros. Estudos prévios relataram alteragoes na gasometria do cordáo umbilical associadas ao uso de efedrina, mas sem re-percussoes deletérias para o feto, quando avaliadas pelo escore de Apgar no primeiro e no quinto minuto 18,19. Alguns autores citaram possível interferéncia do fenómeno de taqui-filaxia e alteragáo no metabolismo fetal por causa do efeito beta-adrenérgico da efedrina 18,19,24. A fenilefrina, por ser uma substáncia alfa-agonista pura, náo causaria tal alteragáo. No presente estudo, apesar da auséncia de caracterizagáo numérica de acidose fetal propriamente dita, a efedrina as-sociou-se a pH arterial mais baixo que a fenilefrina. Tal fato pode sugerir interferéncia no metabolismo fetal, uma vez que o pH da veia náo apresentou diferenga significativa entre os grupos. Outra possível etiologia para alteragáo gasomé-trica poderia ser representada por alteragáo do fluxo ute-roplacentário. Entretanto, os recém-nascidos no grupo E apresentaram valores de Apgar considerados baixos predominantemente no primeiro minuto, com melhoras no quinto minuto, indicando alteragoes de caráter transitório nos re-cém-nascidos, sem repercussáo a médio e longo prazos. Os resultados dáo suporte apenas parcial á hipótese aventada, o que poderia ser justificado por deficiéncias técnicas no método e pelo tamanho da amostra. Contudo, as reper-cussoes deletérias para o feto, analisadas pelo escore de Apgar e pela gasometria, foram menos freqüentes com o uso da fenilefrina e apenas transitórias com o uso da efedrina.

Ephedrine versus Phenylephrine: Prevention of Hypotension during Spinal Block for Cesarean Section and Effects on the Fetus

Edno Magalhäes, TSA, M.D.; Catia Sousa Govéia, TSA, M.D.; Luís Cláudio de Araújo Ladeira, TSA, M.D.; Bruno Góis Nas-cimento, M.D.; Sérgio Murilo Cavalcante Kluthcouski, M.D.

INTRODUCTION

Hypotension during spinal block for cesarean section is secondary to the sympathetic blockade and it can be harmful to both the fetus and mother. Among the deleterious effects

one can mention a reduction in uterine and placental blood flow, disruption of fetal oxygenation and fetal acidosis, and maternal symptoms of reduced cardiac output, such as nausea, vomiting, and altered level of consciousness 1. The incidence of hypotension after spinal block for cesarean section can be as high as 80% 2-4 if prophylactic measures, such as prior hydration, moving the uterus to the left side, and vasopressors, are not instituted 56.

Ephedrine is a non-catecholamine sympathomimetic agent that stimulates alpha and beta adrenergic receptors direct and predominantly indirectly, producing its effects by releasing norepinephrine from nerve endings in the autonomous nervous system. Traditionally it is the vasopressor of choice in obstetric anesthesia despite the lack of confirmation of its superiority over other vasopressors 78. The intercur-rences of epinephrine include maternal supraventricular tachycardia, tachyphylaxis, and fetal acidosis. Prior studies reported that the increase in blood pressure caused by ephedrine is related to preservation of uterine and placental blood flow, especially due to its beta-adrenergic action 910. However, other authors have suggested that ephedrine can reduce umbilical cord pH without affecting Apgar scores 411. Phenylephrine is considered a pure ^-adrenergic agonist. It promotes dose-dependent vasoconstriction, which is more pronounced in the venous than in the arterial bed, improving venous return after the sympathetic blockade during spinal block. Studies have shown that phenylephrine maintain uterine and placental blood flow and higher umbilical cord blood pH than ephedrine, having similar efficacy in controlling hypotension but with a lower risk of fetal acidosis 51213. The present study hypothesized that the pharmacologic profile of phenylephrine regarding the vitality of the newborn is superior to that of ephedrine in the treatment of hypotension during cesarean section under spinal block. The objective of this study was to compare the efficacy of phenylephrine and ephedrine in the prevention and treatment of intraoperative maternal hypotension, evaluate the side effects of this therapy, and to study fetal changes using Apgar scores and arterial and venous umbilical cord blood gases.

METHODS

After approval by the Ethics on Research Committee (CEP, from the Portuguese) in humans of the University of Brasilia and signing of the informed consent, 60 women were selected for this randomized, double blind, prospective study. Inclusion criteria were as follows: physical status ASA I or II, term pregnancy of a single fetus, and indication for cesarean section. Exclusion criteria were refusal to participate in the study, patients younger than 18 years, preexisting or pregnancy-induced systemic hypertension, and presence of cardiovascular or cerebrovascular diseases, fetal abnormalities, history of allergy to the drugs used in the study, and contraindications to spinal block.

Monitoring included continuous electrocardiogram, noninvasive blood pressure, and pulse oximetry. Patients were placed in dorsal decubitus for a few minutes and blood pressure and heart rate were recorded every three minutes for three times to obtain mean baseline levels. With the patient in left lateral decubitus, spinal puncture was done with a 25 x 3.5 Quincke needle between L2-L3 or L3-L4 and a solution containing 10 mg of 0.5% hyperbaric bupivacaine and 3 |jg of sufentanil was administered. Afterwards, with the patient in dorsal decubitus, a Crawford wedge was placed under her right hip to obtain left uterine displacement. Immediately after the subarachnoid injection and before the incision of the uterus, an infusion of two liters of Ringer's lactate was initiated, followed by a slow infusion.

Patients were randomly divided into two groups using sequential, sealed envelopes with random numbers generated previously by a computer. The result of the allocation was ignored by both the patients and the physicians responsible for collecting and analyzing the study parameters. The determination of sample size was based on prior studies 12,13. Groups were composed of 30 patients each and denominated Group E (ephedrine) and Group P (phenylephrine). Patients in Group E received a prophylactic intravenous bolus of 10 mg of ephedrine immediately after the subarachnoid block and patients in Group P received a prophylactic intravenous bolus of 80 |g of phenylephrine. The syringes with the study drugs were prepared by a physician who was not involved in the collection of the data and analysis of the results.

Maternal hypotension was defined as a blood pressure equal or lower than 80% of baseline values and it was treated with a bolus of 50% of the initial dose of the vasopressor. Reactive hypertension was characterized as blood pressure 20% higher than baseline levels after the use of the vasopressor. Heart rate below 50 bpm characterized bradycardia, when accompanied by hypotension, and it was treated with 0.75 mg of atropine.

The level of sensitive blockade was evaluated every minute after the puncture, by painful stimuli with a needle, until the end of the procedure. Authorization for the surgical procedure was given only when the level of the blockade reached T5. The time from the blockade to the incision of the skin, incision of the uterus, and removal of the fetus were recorded. The incidence of maternal hypotension, reactive hypertension, bradycardia, nausea and vomiting, and the total dose of vasopressor were also analyzed.

Apgar scores on the first and fifth minutes of all newborns were determined and a score below eight was considered low. Venous and arterial blood were drawn from the umbilical cord immediately after delivery for blood gases determination, and a pH below 7.2 was considered fetal acidosis. The Student t test for continuous data, Mann-Whitney test for ordinal data, and Chi-square test for nominal data were used to analyze the results. A p < 0.05 was considered significant.

RESULTS

The mean age of patients in Group E was 27.2 years, and 26.5 years in Group P. The mean body mass index (BMI) was similar in both groups, as well as the weight. Patients had a mean gestational age of 39 weeks. Other demographic parameters and physical status did not show statistically significant differences (Table I).

The mean time from the spinal puncture to skin incision in Group E was 7.4 minutes and 6.9 minutes in Group P. The mean time to uterine incision was 12.7 and 12.8 in Groups E and P, respectively, and the mean time for delivery of the fetus was 13.8 and 14.2 minutes. Those parameters did not show statistically significant differences. In Group E the mean dose of vasopressor used was 14 mg and in Group P 186 |jg. As for the sensitive blockade in most patients it reached T4 (Table II).

As for side effects, Group E had seven episodes of nausea and four of vomiting, while Group P had 10 episodes of nausea and six of vomiting. The incidence of reactive hypertension was similar: five episodes in Group E and four in Group P. Only one patient in Group P developed bradycardia, which was treated with atropine. Those differences were not statistically significant. In Group P, 28 patients (93%) de-

veloped hypotension and in Group E 21 (70%) patients developed this complication, and this difference was statistically significant (p < 0.05). The number of episodes of hypotension was significantly higher in Group P (80 episodes) than in Group E (29 episodes), p < 0.05 (Table III). Group E had a higher proportion of newborns with Apgar scores in the first minute that were lower than 8 (27%) than group P (10%), and this difference was statistically significant (p < 0.05).

In Group E, eight newborns (27%) had Apgar scores in the first minute of seven, 17 (56%) had scores of eight, and five (17%) of nine. In Group P, three newborns (10%) had Apgar scores in the first minute of seven, fifteen (50%) of eight, eleven (37%) of nine, and one (3%) of 10. Apgar scores in the fifth minute did not show differences between both groups. In Group E, two newborns (6%) had Apgar scores of eight, twenty (67%) had scores of nine, and eight (27%) of ten. In Group P, half of the newborns had Apgar scores in the fifth minute of nine and ten in the other half.

As for arterial and venous umbilical cord blood gases, mean pH showed statistically significant differences between both groups: 7.22 in Group E and 7.27 in Group P (p < 0.05). Table IV shows the mean blood gases levels.

Table I - Demographic Data

General Characteristics Group E (n = 30) Group P (n = 30)

Age (years) 27.2 ± 4.5 26.5 ± 5.1

Weight (kg) 83.5 ± 6.9 79.2 ± 9.7

Height (cm) 159,6 ± 5.3 158.5 ± 5.8

BMI (kg.m-2) 32.8 ± 2.5 31.1 ± 3,.5

Gestational age (weeks) 39.5 ± 1.1 39.6 ± 1.3

Physical Status (ASA I / II) 20 / 10 20 / 10

Weight of the newborn (g) 3,641 ± 499.1 3,538 ± 535.4

Values expressed as Mean ± SD. * p < 0.05.

Table II - Anesthetic-Surgical Parameters

Anesthetic-surgical parameters Group E (n = 30) Group P (n = 30)

Time from the blockade to skin incision (min) 7.4 ± 2.2 6.9 ± 2.4

Time from the blockade to uterine incision (min) 12.7 ± 2.2 12.8 ± 3.7

Time from the blockade to delivery (min) 13.8 ± 2.3 14.2 ± 3.5

Vasopressor dose 1 4 mg 186 |jg

Sensitive level at T4 (%) 22 (73.3%) 22 (73.3%)

Sensitive level at T5 (%) 8 (26.7%) 8 (26.7%)

Values expressed as Mean ± SD. * p < 0.05.

Table III - Side Effects, Number of Episodes, and Proportion

Side effects Group E (n = 30) Group P (n = 30)

Nausea (episodes) 7 10

Vomiting (episodes) 4 6

Hypotension (episodes)* 29 80

Hypotension (patients)* 21 (70%) 28 (93.3%)

Reactive hypertension (episodes) 5 4

Bradycardia (episodes) 0 1

* p < 0.05.

Table IV - Arterial and Venous Umbilical Cord Blood Gases

Blood gases Group E (n=30) Group P (n=30)

Arterial pH* 7.22 ± 0.03 7.27 ± 0.06

Arterial BE -10.5 ± 2.6 -9.2 ± 4.2

Arterial pCO2 40.0 ± 3.8 38.9 ± 8.9

Arterial pO2 19.5 ± 3.6 18.0 ± 4.8

Arterial HCO-3 16.2 ± 2.4 16.5 ± 4.0

Venous pH 7.27 ± 0.04 7.28 ± 0.06

Venous BE -7.2 ± 3.5 -7. 9 ± 4.4

Venous pCO2 34.7 ± 6.7 35.2 ± 11.1

Venous pO2 25.6 ± 6.3 24.3 ± 7.1

Venous HCO-3 18.4 ± 2.9 18.7 ± 3.5

Values expressed as Mean ± SD. * p < 0.05.

DISCUSSION

The indication of regional block in obstetrics has gained acceptance due to the reduction in maternal and fetal morbidity and mortality 14. However, some studies have associated a greater incidence of fetal acidosis after spinal block, probably secondary to maternal hypotension or factors that modify uterine and placental blood flow 1516. Moving the uterus to the left and administering intravenous fluids have been used to reduce the severity of hypotension, but with limited efficacy. The administration of vasopressors is frequently necessary 17.

Historically, ephedrine has been the vasopressor of choice in obstetrics despite the uncertainty about its superiority 179. It was believed that ephedrine increases maternal blood pressure, therefore preserving uterine and placental blood flow due to its beta-adrenergic action, while pure alpha-agonist vasopressors were associated with a reduction in this blood flow 810. However, subsequent studies demonstrated that in the treatment of post-spinal block hypotension in

cesarean sections ephedrine has similar efficacy, but it can occasionally promote fetal acidosis 18"20. In the present study, parameters associated with post-spinal block hypotension were controlled to evaluate which drug would be more effective in the prevention of hypotension with fewer deleterious consequences to the fetus. Prior studies have presented different methodologies and questionable results regarding the ideal vasopressor, dose, and administration regimen, as well as the use of other techniques to control maternal blood pressure with minimal deleterious effects on the fetus 12,19,20

To limit distortions, all patients were hydrated with 2,000 mL of Ringer's lactate, which was instituted after the spinal block since recent studies have demonstrated the inefficacious of prior hydration due to the fast redistribution 21. The uterus was moved to the left to reduce aortocaval compression, and the blockade was maintained on the same level in all patients. Despite the care with the method employed, some factors can limit the interpretation of the study. The number of patients involved although greater than in some studies reported can be a bias since sample size was not calculated. The difference of time between the time the umbilical cord blood was drawn and the analysis of blood gases is another limitation. This difference might have altered the results of blood gases and possibly interfered with the results. Prior studies have suggested that a bolus of 30 mg of intravenous ephedrine would be more effective in the prevention of hypotension, but with an increased incidence of reactive hypertension 22. In contrast, a prospective, observational study demonstrated that the intravenous administration of 15 to 20 mg of ephedrine reduced the incidence of maternal hypotension without increasing the incidence of reactive hypertension 20. A 2004 metaanalysis 19 concluded that doses above 14 mg of ephedrine did not reduce the incidence of maternal hypotension, but they caused reactive hypertension in the mother and a small reduction in umbilical cord blood pH. In the present study, a dose of 10 mg of ephedrine was considered to be effective and, at the same time, had little side effects.

As for phenylephrine, a recent study demonstrated that even high doses (above 2,000 |jg) were not associated with deRevista Brasileira de Anestesiologia Vol. 59, No 1, Janeiro-Fevereiro, 2009

leterious effects on the fetus, as determined by the Apgar scores and umbilical cord blood gases 23. In the present study, the dose of 80 jg of phenylephrine was chosen based on a prior study that demonstrated that this was the effective dose when administered as an intravenous bolus, without severe side effects 12.

On evaluating the control of hypotension, several studies have demonstrated similar efficacy of ephedrine and phenylephrine on the prevention and treatment of this complication, both when used in bolus or continuous infusion 23,24. In the present study, for practical purposes, it was decided to administer the medication as a bolus. Phenylephrine showed lower efficacy on the prevention of hypotension than ephedrine, demonstrated by the number of patients who developed hypotension and the number of episodes in each group. This probably was secondary to the shorter duration of action of this vasopressor and the way it was administered, since it was administered as a bolus and prophylac-tically, only repeating the dose when the blood pressure was equal or lower than 80% of baseline levels, and fluctuations in its plasma concentrations could also have contributed. Although phenylephrine is less effective in controlling blood pressure, differences in the incidence of maternal side effects, such as nausea, vomiting, and changes in the level of consciousness, were not detected probably because the reduction in blood pressure was not severe. A systematic revision of the factors associated with pH and base excess after spinal block for cesarean section concluded that the time between uterine incision and removal of the fetus was associated with low pH and base excess 24. However, in the present study, differences in the time between the installation of the blockade and removal of the fetus were not detected. We do not believe that gestational age and the weight of the newborn caused any interference with the evaluation, since those parameters were similar in both groups.

Prior studies reported changes in umbilical cord blood gases associated with the use of ephedrine, but without deleterious repercussions on the fetus, as demonstrated by the Apgar scores in the first and fifth minutes 18,19. Some authors have mentioned possible interferences of tachyphylaxis and changes in fetal metabolism due to the beta-adrenergic actions of ephedrine 18,19,24. Since it is a pure alpha-agonist, phenyle-phrine would not have the same effects. In the present study, despite the absence of numerical characterization of fetal acidosis, ephedrine was associated with a lower arterial pH than phenylephrine. This could suggest an influence in fetal metabolism, since venous pH did not show significant differences between both groups. Other possible etiology for this change in blood gases could be related to the change in uterine and placental blood flow. However, newborns in group E had low Apgar scores predominantly in the first minute, with a substantial improvement in the fifth minute, indicating transitory changes on the newborns, without medium- and long-term repercussions.

The results of the present study only give partial support to the hypothesis guiding this study, what could be justified by technical deficiencies of the method and the size of the study population. However, deleterious repercussions on the fetus, analyzed by the Apgar scores and blood gases, were less frequent with phenylephrine and only transitory with ephedrine.

REFERÊNCIAS - REFERENCES

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34. Hawkins JL, Koonin LM, Palmer SK et al. — Anesthesia-related deaths during obstetric delivery in the United States, 1979-1990. Anesthesiology, 1997;86:277-284. 45. Roberts SW, Leveno KJ, Sidawi JE et al. — Fetal acidemia associated with regional anesthesia for elective cesarean delivery. Obstet Gynecol, 1995;85:79-83. 56. Mueller MD, Brühwiler H, Schüpfer GK et al. — Higher rate of fetal acidemia after regional anesthesia for elective cesarean delivery. Obstet Gynecol, 1997;90:131-134.

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RESUMEN

Magalháes E, Govéia CS, Ladeira LCA, Nascimento BG, Kluthcouski SMC — Efedrina versus Fenilefrina: Prevención de Hipotensión Arterial durante Anestesia Raquidea para Cesárea y Efectos sobre el Feto.

JUSTIFICATIVA Y OBJETIVOS: La hipotensión arterial durante la anestesia raquídea para cesárea se debe al bloqueo simpático y a la compresión aortocava por el útero y puede ocasionar efectos malignos para el feto y su madre. La efedrina y fenilefrina mejoran el retorno venoso después del bloqueo simpático durante la anestesia raquídea. El objetivo de este estudio fue comparar la eficacia de la efedrina y de la fenilefrina en prevenir y tratar la hipotensión arterial materna durante la anestesia raquídea y evaluar así sus efectos colaterales y las alteraciones fetales.

MÉTODO: Sesenta pacientes, sometidas a la anestesia raquídea con bupivacaína y sufentanil para cesárea, se dividieron aleatoriamente en dos grupos para recibir, profilácticamente, efedrina (Grupo E, n = 30, dosis = 10mg) o fenilefrina (Grupo F, n = 30, dosis = 80 jg). Hipotensión arterial (presión arterial menor o igual a un 80% de la medida basal) fue tratada con bolo de vasoconstrictor con un 50% de la dosis inicial. Se evaluaron: incidencia de hipotensión arterial, hipertensión arterial reactiva, bradicardia y vómitos, puntuación de Apgar en el 1° y 5° minutos y gasometría del cordón umbilical.

RESULTADOS: La dosis promedio de efedrina fue 14,8 mg (± 3,8) y 186,7 jg (± 52,9) de fenilefrina. Los grupos fueron similares en cuanto a los parámetros demográficos y a la incidencia de vómitos, bradicardia e hipertensión arterial reactiva. La incidencia de hipotensión arterial fue de un 70% en el Grupo E y un 93% en el Grupo F (p < 0,05). El pH arterial promedio del cordón umbilical y el puntaje de Apgar en el 1° minuto fueron menores en el grupo E (p < 0,05). No se registró diferencia en el puntaje del 5° minuto.

CONCLUSIONES: La efedrina fue más efectiva que la fenilefrina en la prevención de la hipotensión arterial. Los dos fármacos presentaron una incidencia similar de efectos colaterales. Las repercusiones fetales fueron menos frecuentes con el uso de la fenilefrina y apenas transitorias con el uso de la efedrina.