OBSTETRIC ANESTHESIA Section Editor Mieczyslaw Finster
Vasopressor Therapy for Hypotension During Epidural Anesthesia for Cesarean Section: Effects on Maternal and Fetal Flow Velocity Ratios Peter M. C.Wright, MB, FFARCS, Mohammed Iftikhar, MB, MRCOG, Keran T.Fitzpatrick, MB, FFARCS, James Moore, MD, FCANAES, and William Thompson, m, FRCOG Department of Anesthetics, The Queen's University of Belfast; Department of Obstetrics and Gynaecology, Institute of Clinical Sciences; and Jubilee Maternity Hospital, Belfast, Northern Ireland
The purpose of this study was to identify the influence of hypotension as a result of epidural anesthesia and of its treatment with either ephedrine or methoxamine on uteroplacental and umbilical flow velocity ratios and fetal acid-base status. Fifty healthy women with an uncomplicated full-term pregnancy were studied during elective cesarean section under epidural anesthesia. A method of continuously recording flow velocity waveforms was used that allowed the identification of simultaneous values of maternal and fetal Doppler indices related to events during the induction of anesthesia. In 15 patients in whom arterial blood pressure did not decrease, the uteroplacental pulsatility index (UtPI) did not change, but the umbilical pulsatility index (UmPI) decreased from a mean (95% confidence interval) of 0.98 (0.861.09)to 0.91 (0.82-0.99)(P < 0.05).In 32 patients who experienced hypotension of at least
L
umbar epidural anesthesia is extensively used for delivery by cesarean section and is widely accepted as offering advantages over general anesthesia (1). Hypotension may occur during the induction of epidural anesthesia and if severe or prolonged, will compromise fetal well-being (2). In treating episodes of hypotension, vasopressor therapy is frequently required to obtain an immediate response. Ephedrine, a mixed a- and Padrenergic agonist, is widely used, and drugs with pure aadrenergic agonist activity are avoided because animal studies indicate that they reduce uteroplacental blood flow (3). However, the use of pure a-agonists Accepted for publication February 20, 1992. Address correspondence to Dr. Wright, Department of Clinical Anaesthesia, Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BA, Northern Ireland. Reprints are not available.
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Anesth Analg 1992;755643
15%, the UtPI increased from 0.82 (0.76-0.89)to 1.04 (0.92-1.17)(P < 0.01).Treatment with ephedrine had no influence on either the UtPI or UmPI, but treatment with methoxamine resulted in brief increases in the UP1 of 0.47 (0.244.69)during the first 5 min after its administration; the increases were brief and resolved within 2 min. The choice of vasopressor drug had no influence on the UtPI recorded just before surgery commenced (final UtPI), but those patients who experienced hypotension had significantly larger final UtPIs (1.02(0.91-1.10))than those who never became hypotensive (0.86(0.72-0.99)),and this was associated with significantly increased placental hydrogen ion gradients. The choice of vasopressor drug appears to be of minor importance compared with the avoidance of hypotension. (Anesth Analg 1 9 9 2 ; 7 5 W )
to treat hypotension from epidural anesthesia for cesarean section in humans did not result in fetal acidosis, and their lack of chronotropic activity may make them desirable for use in pregnant women with preexisting cardiac disease (4). In another publication (5), their use is suggested in spinal anesthesia because hypotension occurs more rapidly and can be more severe than with epidural blockade. Difficulties in the repeated measurement of human uteroplacental absolute blood flow have prevented the evaluation of vasopressor therapy in this respect. However, Doppler velocimetry does enable the repeated semiquantitative evaluation of both uteroplacental and fetoplacental flow resistance. The purpose of this study was to evaluate the effects of both acute hypotension and its treatment with either ephedrine or methoxamine (a pure q-adrenergic agonist) on uteroplacental and fetoplacental flow resistance and fetal outcome by using a method that allowed 01992 by the International Anesthesia Research society 0003-2999/92/$5.00
ANESTH ANALG 1992;75:%43
simultaneous recording of maternal cardiovascular changes and those occurring in the uteroplacental circulation.
OBSTETRIC ANESTHESIA WRIGHT ET AL. VASOPRESSOR THERAPY FOR HYPOTENSION
57
was supplemented if necessary and surgery was allowed to proceed.
Measurements
Methods This study was approved by the local medical ethical research committee, and each patient provided informed consent. Fifty healthy women in the age range 1840 yr undergoing elective cesarean section for cephalopelvicdisproportion, breech presentation, or repeat cesarean section were studied. All the women recruited had a full-term uncomplicated singleton gestation. The patients were given ranitidine 150 mg by mouth on the evening before and the morning of surgery. In the operating room the patients were placed in a 15" left lateral tilt position, and intravenous access was established with a 14-gauge cannula in a large arm vein. With the patient in the left lateral position, an 18-gauge epidural catheter was introduced through a 16-gauge Tuohy needle at the L3-4 interspace, leaving 3 cm of the cannula lying in the epidural space. A 3-mL test dose of 2% lidocaine with epinephrine (5 @mL) was administered. The patient was returned to the 15" tilt position, and a rapid intravenous infusion of Hartmann's solution (10 mL/kg) followed. After 5 min, an additional 17mL of 2% lidocaine with epinephrine was given over a period of 2 min. Patients in whom hypotension (defined as a reduction in systolic blood pressure of 15% or any reduction to
Vasopressor Therapy for Hypotension During Epidural Anesthesia for Cesarean Section: Effects on Maternal and Fetal Flow Velocity Ratios Peter M. C.Wright, MB, FFARCS, Mohammed Iftikhar, MB, MRCOG, Keran T.Fitzpatrick, MB, FFARCS, James Moore, MD, FCANAES, and William Thompson, m, FRCOG Department of Anesthetics, The Queen's University of Belfast; Department of Obstetrics and Gynaecology, Institute of Clinical Sciences; and Jubilee Maternity Hospital, Belfast, Northern Ireland
The purpose of this study was to identify the influence of hypotension as a result of epidural anesthesia and of its treatment with either ephedrine or methoxamine on uteroplacental and umbilical flow velocity ratios and fetal acid-base status. Fifty healthy women with an uncomplicated full-term pregnancy were studied during elective cesarean section under epidural anesthesia. A method of continuously recording flow velocity waveforms was used that allowed the identification of simultaneous values of maternal and fetal Doppler indices related to events during the induction of anesthesia. In 15 patients in whom arterial blood pressure did not decrease, the uteroplacental pulsatility index (UtPI) did not change, but the umbilical pulsatility index (UmPI) decreased from a mean (95% confidence interval) of 0.98 (0.861.09)to 0.91 (0.82-0.99)(P < 0.05).In 32 patients who experienced hypotension of at least
L
umbar epidural anesthesia is extensively used for delivery by cesarean section and is widely accepted as offering advantages over general anesthesia (1). Hypotension may occur during the induction of epidural anesthesia and if severe or prolonged, will compromise fetal well-being (2). In treating episodes of hypotension, vasopressor therapy is frequently required to obtain an immediate response. Ephedrine, a mixed a- and Padrenergic agonist, is widely used, and drugs with pure aadrenergic agonist activity are avoided because animal studies indicate that they reduce uteroplacental blood flow (3). However, the use of pure a-agonists Accepted for publication February 20, 1992. Address correspondence to Dr. Wright, Department of Clinical Anaesthesia, Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BA, Northern Ireland. Reprints are not available.
56
Anesth Analg 1992;755643
15%, the UtPI increased from 0.82 (0.76-0.89)to 1.04 (0.92-1.17)(P < 0.01).Treatment with ephedrine had no influence on either the UtPI or UmPI, but treatment with methoxamine resulted in brief increases in the UP1 of 0.47 (0.244.69)during the first 5 min after its administration; the increases were brief and resolved within 2 min. The choice of vasopressor drug had no influence on the UtPI recorded just before surgery commenced (final UtPI), but those patients who experienced hypotension had significantly larger final UtPIs (1.02(0.91-1.10))than those who never became hypotensive (0.86(0.72-0.99)),and this was associated with significantly increased placental hydrogen ion gradients. The choice of vasopressor drug appears to be of minor importance compared with the avoidance of hypotension. (Anesth Analg 1 9 9 2 ; 7 5 W )
to treat hypotension from epidural anesthesia for cesarean section in humans did not result in fetal acidosis, and their lack of chronotropic activity may make them desirable for use in pregnant women with preexisting cardiac disease (4). In another publication (5), their use is suggested in spinal anesthesia because hypotension occurs more rapidly and can be more severe than with epidural blockade. Difficulties in the repeated measurement of human uteroplacental absolute blood flow have prevented the evaluation of vasopressor therapy in this respect. However, Doppler velocimetry does enable the repeated semiquantitative evaluation of both uteroplacental and fetoplacental flow resistance. The purpose of this study was to evaluate the effects of both acute hypotension and its treatment with either ephedrine or methoxamine (a pure q-adrenergic agonist) on uteroplacental and fetoplacental flow resistance and fetal outcome by using a method that allowed 01992 by the International Anesthesia Research society 0003-2999/92/$5.00
ANESTH ANALG 1992;75:%43
simultaneous recording of maternal cardiovascular changes and those occurring in the uteroplacental circulation.
OBSTETRIC ANESTHESIA WRIGHT ET AL. VASOPRESSOR THERAPY FOR HYPOTENSION
57
was supplemented if necessary and surgery was allowed to proceed.
Measurements
Methods This study was approved by the local medical ethical research committee, and each patient provided informed consent. Fifty healthy women in the age range 1840 yr undergoing elective cesarean section for cephalopelvicdisproportion, breech presentation, or repeat cesarean section were studied. All the women recruited had a full-term uncomplicated singleton gestation. The patients were given ranitidine 150 mg by mouth on the evening before and the morning of surgery. In the operating room the patients were placed in a 15" left lateral tilt position, and intravenous access was established with a 14-gauge cannula in a large arm vein. With the patient in the left lateral position, an 18-gauge epidural catheter was introduced through a 16-gauge Tuohy needle at the L3-4 interspace, leaving 3 cm of the cannula lying in the epidural space. A 3-mL test dose of 2% lidocaine with epinephrine (5 @mL) was administered. The patient was returned to the 15" tilt position, and a rapid intravenous infusion of Hartmann's solution (10 mL/kg) followed. After 5 min, an additional 17mL of 2% lidocaine with epinephrine was given over a period of 2 min. Patients in whom hypotension (defined as a reduction in systolic blood pressure of 15% or any reduction to
