Anesthesia for cesarean section on a pregnant woman with hypoplasia of the distal aorta: case report

Abstracts

JUSTIFICATIVA E OBJETIVOS: Anomalias vasculares maternas, potencialmente graves para o feto, podem colocar em risco a perfusão uterina, suscitando cuidados ainda maiores por parte da equipe anestésica. O objetivo deste relato foi mostrar a conduta anestésica para operação cesariana em uma gestante com hipoplasia de aorta distal, logo abaixo da emergência das artérias renais, com estenose da artéria renal e ausência de artérias ilíacas. RELATO DO CASO: Paciente de 30 anos, 54 kg, na segunda gestação com uma cesariana anterior sem intercorrências. Durante a realização de ecografia gestacional na 12ª semana observou-se interrupção da aorta logo abaixo da saída das artérias renais. A paciente foi encaminhada para a realização de cineangiocoronariografia que mostrou hipoplasia da aorta distal abaixo das artérias renais, com ausência das artérias ilíacas. Durante a investigação clínica a paciente mostrou-se assintomática, com exceção de hipertensão arterial e claudicação aos grandes esforços. A paciente foi submetida à anestesia peridural contínua, com titulação da dose anestésica necessária à realização da cesariana. Inicialmente foram injetados 50 mg de bupivacaína a 0,5% sem vasoconstritor e 10 µg de sufentanil. Quinze minutos após, a anestesia foi complementada com mais 25 mg de bupivacaína a 0,5%, o que foi suficiente para atingir adequado nível de bloqueio. A cesariana transcorreu sem intercorrências e a criança nasceu em boas condições clínicas. CONCLUSÕES: O uso de anestesia peridural contínua com doses fracionadas demonstrou ser uma técnica anestésica segura para a realização desse procedimento por reduzir os riscos de hipotensão arterial materna inerente ao bloqueio espinal e também por minimizar a transferência placentária de fármacos, que ocorrem quando do emprego da anestesia geral. A titulação de fármacos através do cateter peridural possibilitou atingir nível anestésico adequado à realização do ato cirúrgico.

ANALGÉSICOS, Opióide; ANESTÉSICOS, Local; CIRURGIA, Obstétrica; DOENÇA, Vascular; TÉCNICAS ANESTÉSICAS, Regional

CLINICAL REPORT

Anesthesia for cesarean section on a pregnant woman with hypoplasia of the distal aorta. Case report^*

Anestesia para cesárea en embarazada con hipoplasia de aorta distal. Relato de caso

Leonardo de Andrade Reis^I; Guilherme Frederico Ferreira dos Reis, TSA^II; Rodrigo Dias Colombano^III

^IInstrutor Convidado do CET Casa de Saúde Campinas

^IIResponsável pelo CET Casa de Saúde Campinas

^IIIEx-Residente do CET Casa de Saúde Campinas

^{Correspondence to}

SUMMARY

BACKGROUND AND OBJECTIVES: Maternal vascular anomalies, potentially severe for the fetus, can jeopardize uterine perfusion, which demands more caution by the anesthesiology team. The objective of this report was to demonstrate the anesthetic conduct for a cesarean section on a pregnant woman with hipoplasia of the distal aorta, just below the renal arteries, with stenosis of the renal artery and absence of the iliac arteries.

CASE REPORT: This is a 30-year old patient, weighing 54 kg, on her second pregnancy, with a history of an uncomplicated cesarean section. During the gestational echocardiography on the 12^th week, it was observed an interruption of the distal aorta, just below the renal arteries. The patient was referred for coronary angiography, which demonstrated hypoplasia of the distal aorta, just below the renal arteries, and absence of the iliac arteries. During the clinical investigation, the patient remained asymptomatic, except for hypertension and claudication during great efforts. She underwent continuous epidural anesthesia and the dose of the anesthetic was titrated as needed for the cesarean section. Initially, 50 mg of 0.5% bupivacaine without vasoconstrictor and 10 µg of sufentanil were administered. After 15 minutes, anesthesia was complemented with 25 mg of 0.5% bupivacaine, which was enough to achieve an adequate level of blockade. The cesarean section was performed without intercurrences, and the fetus was born in good clinical conditions.

CONCLUSION: The use of continuous epidural block in fractionated doses demonstrated to be a safe anesthetic technique for this procedure because it reduces the risks of maternal hypotension, inherent to the spinal block, and also minimized the placentary transference of drugs, which is the case with general anesthesia. Titration of drugs through the epidural catheter allowed reaching an adequate anesthetic level for this type of surgery.

Key Words: ANALGESICS, Opioids: sufentanil; ANESTHETICS, Local: bupivacaine; ANESTHETIC TECHNIQUES, Regional: continuous epidural; DISEASE, Vascular: hipoplasia of the distal aorta; SURGERY, Obstetric: cesarean section.

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: Anomalías vasculares maternas, potencialmente graves para el feto, pueden colocar en riesgo la perfusión uterina, suscitando cuidados mucho más puntuales por parte del equipo anestésico. El objetivo de este relato fue mostrar la conducta anestésica para operación en cesárea en una embarazada con hipoplasia de aorta distal, bien debajo de la emergencia de las arterias renales, con estenosis de la arteria renal y falta de arterias ilíacas.

RELATO DEL CASO: Paciente de 30 años, 54 kg, en el 2° embarazo con una cesárea anterior sin intercurrencias. Durante la realización de ecografía de gestación en la 12ª semana se observó una interrupción de la aorta bien debajo de la salida de las arterias renales. A la paciente se le realizó cineangiocoronariografía que mostró hipoplasia de la aorta distal por debajo de las arterias renales, con ausencia de las arterias ilíacas. Durante la investigación clínica la paciente se mostró asintomática, con excepción de hipertensión arterial y claudicación a los grandes esfuerzos. La paciente fue sometida a la anestesia peridural continua, con titulación de la dosis anestésica necesaria para la realización de la cesárea. Inicialmente se inyectaron 50 mg de bupivacaína a 0,5% sin vasoconstrictor y 10 µg de sufentanil. Quince minutos después, la anestesia fue complementada con 25 mg más de bupivacaína a 0,5%, lo que fue suficiente para alcanzar un adecuado nivel de bloqueo. La cesárea transcurrió sin intercurrencias y el niño nació en buenas condiciones clínicas.

CONCLUSIONES: El uso de anestesia peridural continua con dosis fraccionadas demostró ser una técnica anestésica segura para la realización de este procedimiento por reducir los riesgos de hipotensión arterial materna inherente al bloqueo espinal y también por minimizar la transferencia placentaria de fármacos que ocurren cuando se usa la anestesia general. La titulación de fármacos a través del catéter peridural posibilitó alcanzar un nivel anestésico adecuado para la realización de la operación.

INTRODUCTION

Obstetric anesthesia demands special attention by the anesthesiologist responsible for the safety and well-being of two lives. Anesthetic techniques used should first consider safety and for this reason conductive anesthesia is preferred instead of general anesthesia due to the reduced placental transference of drugs ¹ and lower maternal risk of aspiration of gastric contents². However, neuroaxis blocks are associated with maternal hypotension and consequent fetal distress.

A few measures are recommended to prevent or minimize the development of hypotension, such as: moving the uterus to the left, prior hydration and, in some cases, titration of the local anesthetic in the epidural space ².

Those measures are all based on some factors and, among them, there is the anatomical relationship of abdominal blood vessels to the gravid uterus. However, vascular abnormalities can render useless some maneuvers, such as moving the uterus.

In the case presented here, due to the maternal circulatory abnormality associated with the unpredictable placentary circulation and possibility of marked compromise of uterine blood flow, measures to prevent uterine hypoperfusion were fundamental.

The objective of this report was to demonstrate the anesthetic conduct for a cesarean section in a pregnant woman with hipoplasia of the distal aorta just below the renal arteries associated with stenosis of the renal artery and absence of iliac arteries.

CASE REPORT

A 30-year old patient, weighing 54 kg, 1.60 m, on her second pregnancy, presented for pre-anesthetic evaluation on the 28^th week of gestation. She had a history of cesarean section under spinal block without complications. Clinically, the patient had hypertension (probable of renovascular etiology) controlled with alphamethyldopa, blood pressure 150 ´ 80 mmHg, heart rate 90 beats per minute (bpm), claudication on moderate exertion, marked aortic systolic murmur, absence of dorsal pedis pulse and reduced perfusion of the lower limbs. Laboratory exams showed hemoglobin 12.3 g.dL^-1, hematocrit 35.7%, blood glucose 65 mg.dL^-1 and urinalysis was normal. The echocardiogram showed concentric hypertrophy of the left ventricle and an ejection fraction of 0.8.

Routine obstetric ultrasound during the present pregnancy showed an anomaly of the aorta, and coronary angiography demonstrated hipoplasia of the distal aorta below the renal arteries with stenosis of the left renal artery and absence of the iliac arteries (Figure 1).

Continuous epidural block, with fractionated administration of the local anesthetic through the catheter until an adequate anesthetic level was achieved, was the anesthesia chosen for the scheduled elective surgery. The development of hypotension should have been avoided, but if necessary, ephedrine would be used.

On the day of the surgery, the patient was on the 40^th week of gestation, blood pressure 180 ´ 90 mmHg, and heart rate 100 bpm. After proper monitoring, an intravenous access was established and 500 mL of Ringer's lactate was administered before and during the lumbar puncture. With the patient in the sitting position, a lumbar puncture was performed on the L₃-L₄ space; 50 mg of 0.5% bupivacaine without vasopressor and 10 µg of sufentanil were administered. An epidural catheter was introduced afterwards and the patient was placed on left lateral decubitus. Fetal heart rate was monitored continuously by the obstetrician with a portable Doppler. Fifteen minutes after the administration of the anesthetic solution, the anesthetic level was below T₈, blood pressure 180 ´ 89 mmHg, and heart rate 105 bpm. Anesthesia was complemented with 25 mg of 0.5% bupivacaine. Subsequently, the sensitive level was on T₆, blood pressure 150 x 80 mmHg; the patient was placed on dorsal decubitus and the uterus was moved to the left. The cesarean section evolved without intercurrences and the fetus was delivered in good conditions with an Apgar score of 9 and 10 on the first and fifth minutes respectively. After removal of the fetus, the surgery evolved as usual with blood loss compatible with the type of surgery, without the need to supplement the anesthesia. A total of 1.000 mL of crystalloid solution was administered and the administration of vasopressors was not necessary. Oxytocin (10 IU) was administered to aid uterine contraction and a significant reduction in blood pressure was not observed.

The patient was discharged form the recovery room one hour after the end of the procedure with a BP 140 ´ 80 mmHg, heart rate 90 bpm, awake and oriented, and with total reversion of the anesthetic block.

DISCUSSION

The uterine artery is a branch of the anterior ramification of the internal iliac artery. In this patient, due to the hipoplasia of the aorta just below the renal arteries, the iliac arteries were absent. Thus, the probable source of the uterine circulation was the ovarian arteries that ramifies directly from the aorta, just below the renal arteries, which normally have extensive anastomosis with the uterine arteries ³.

Due to the history of one pregnancy carried to term without intercurrences and the present pregnancy apparently without fetal distress, one can infer that the basal circulatory demand was achieved, despite the 20% a 30% increase in oxygen ⁴ consumption that occurs during pregnancy to meet maternal and fetal needs. However, what would happen in the uterine blood flow in case of maternal hypotension?

Since the patient was on her second pregnancy and the circulatory abnormality was only discovered in the obstetric ultrasound, the capacity of investigation of this case was limited.

Maintenance of maternal homeostasis is related to better fetal conditions and higher pH in the umbilical artery ⁵. Clinical evidence demonstrated that ephedrine is associated with a higher incidence of fetal acidosis ⁶ than phenylephrine with a higher incidence of fetal tachycardia and reduction in the variability of fetal heart rate ⁷. Due to the maternal desensitization to sympathomimetics and reduced responsivity of uterine arteries to vasoconstrictors in animal models, phenylephrine tends to cause constriction of peripheral arteries, previously dilated due to the sympathetic block, therefore preserving the uterine circulation⁸. This allows the use of high doses of phenylephrine, enough to maintain maternal blood pressure without fetal side effects ^6,9. However, since the uterine circulation of this patient derived from collateral arteries with smaller diameters, the effects of vasoconstrictors would be unpredictable and could reduce blood flow through those arteries. Therefore, supported by the large clinical experience with its use and its limited alpha-adrenergic activity, ephedrine was chosen as the vasoconstrictor. In fact, ephedrine corrects hypotension secondary to spinal block mainly by increasing the heart rate through its action on b1-adrenergic receptors and not by acting on peripheral vessels ^10,11. The use of high doses of ephedrine is related with fetal side effects, such as an increase in fetal metabolism and heart rate, and a reduction in umbilical artery pH ^5-7,10. Although metaraminol has advantages over ephedrine, similar to phenylephrine ¹², it can also cause vasoconstriction of the collateral circulation supplying the uterus.

The option of continuous epidural anesthesia considered the possibility of titrating the dose of the local anesthetic as well as the slow installation of the anesthetic block, therefore avoiding the development of hypotension and the need of vasopressors. Despite being associated with negligible placental transfer of drugs, spinal block is associated with a higher incidence of maternal hypotension and greater need to use vasopressors to treat this complication. Besides, in spinal block it is not possible to make a slow titration of the anesthetic.

The fact that the patient had already been exposed to a spinal block in the previous pregnancy without intercurrences and the fetus was born in good conditions was also taken in consideration.

In the present case, continuous epidural block with fractionated doses of the local anesthetic demonstrated to be a safe technique since it reduced the risks of maternal hypotension inherent to the spinal block, minimizing placental transference of drugs and decreasing the risk of maternal aspiration of gastric contents, complications associated with general anesthesia. The titrating of the local anesthetic dose through the epidural catheter allowed achieving an adequate anesthetic level with hemodynamic stability and preserved the uterine blood flow.

A review of the literature did not find any reports of aortic abnormality. Among the cases reported more frequently in the literature, the one that resembles the most this patient was a case of coarctation of the aorta, but in this situation there is an important reduction in blood flow in the proximal aorta, with a significant increase in ventricular preload ¹³. However, in the case presented here, the abnormality was located in the distal aorta and, despite the magnitude of the lesion, one can infer that blood flow below the lesion was adequate, since the patients had a history of claudication on moderate exertion and had a favorable obstetric history. Therefore, it was possible to conclude that the collateral circulation developed along her life time provided adequate blood flow to the lower extremities and pelvis. It was also possible that the physiological increase in blood volume and cardiac output by 30% to 50% ⁴ and maternal hemodilution also contributed, favoring the flow in the microcirculation.

REFERENCES

Submitted em 1 de fevereiro de 2007

Accepted para publicação em 29 de outubro de 2007

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*

Received from CET Casa de Saúde Campinas, SP

Publication Dates

• Publication in this collection
  17 Jan 2008
• Date of issue
  Feb 2008

History

• Received
  02 Jan 2007
• Accepted
  29 Oct 2007