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OBSTETRIC ANESTHESIA

The Cesarean Delivery of a Twin Gestation Under 2 Minimum Alveolar Anesthetic Concentration Isoflurane: One Normal and One with a Large Neck Mass

Robert R. Gaiser, MD^*, Charles Dean Kurth, MD^*, David Cohen, MD^*, and Timothy Crombleholme, MD

Departments of *Anesthesiology and Surgery, Hospital of the University of Pennsylvania and the Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania

Address correspondence and reprint requests to Robert R. Gaiser, MD, Department of Anesthesiology, Hospital of the University of Pennsylvania, Children’s Hospital, 3400 Spruce St., Philadelphia, PA 19104.

	Introduction

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We recently published a case series describing the anesthetic management of a parturient whose fetus has a large neck mass that required intrapartum treatment (1). A straightforward cesarean section in these cases presents two problems for the pediatric surgeon: the limited time to secure the airway before neonatal hypoxemia and the lack of anesthesia in the neonate. The procedure used by our pediatric and obstetric surgeons for infants with large neck masses involves delivering the fetal head and performing laryngoscopy, bronchoscopy, and possibly surgery, while the uteroplacental unit continues to provide gas exchange before delivery of the fetus. The described anesthetic technique was nearly 2 minimum alveolar anesthetic concentration (MAC) isoflurane in 100% oxygen. Using this anesthetic approach, the goals of adequate maternal and fetal anesthesia, as well as uterine relaxation, were achieved. In this article, we describe the added complexity of applying this technique in a twin gestation in which one was normal and the other had a giant neck mass. The normal fetus, exposed to the high concentrations of isoflurane before delivery, provided an opportunity to observe the effects of this approach on a fetus not requiring surgery.

	Case Report

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A 30-yr-old parturient, gravida 2, para 1, with a twin gestation at 36 wk required cesarean section with intrapartum management of one fetus with a giant neck mass. At 24 wk gestation, the male twin was diagnosed with a neck mass and was observed by serial ultrasound examinations. At 28 wk gestation, the patient developed premature labor and was successfully tocolyzed with terbutaline and nifedipine. At 36 wk gestation, an amniocentesis was performed and documented fetal lung maturity. Because laryngoscopy, rigid bronchoscopy, and intubation to secure the fetal airway were planned before umbilical cord clamping, general anesthesia with isoflurane was selected because it provides fetal and maternal anesthesia and uterine relaxation. Maternal premedication consisted of 30 mL of sodium bicitrate orally and metoclopramide 10 mg and cimetidine 300 mg IV. Maternal monitoring consisted of pulse oximetry, automated blood pressure, electrocardiography, and end-tidal carbon dioxide. The concentration of the inspired and exhaled inhalation drug was monitored by intermittent mass spectrometry. Rapid-sequence induction with cricoid pressure was performed using thiopental 300 mg and succinylcholine 100 mg. For maintenance of anesthesia, vecuronium 6 mg in divided doses and end-tidal concentrations of isoflurane ranging from 2.0% to 2.68% in a balance of oxygen were used. The end-tidal concentration was titrated to uterine tone as palpated by the surgeons. Ephedrine 50 mg in divided doses was required to maintain systolic blood pressure >100 mm Hg. Ultrasonography was used to locate the position of the fetuses and the placenta before uterine incision, which occurred 38 min after induction. During this period, the fetal heart rates were monitored by using two-dimensional echocardiography and demonstrated good heart rate and stroke volume.

Twenty minutes after uterine incision, the head of the fetus without the neck mass was delivered. The trachea was intubated with a 3.0 cuffless endotracheal tube, and the infant was delivered. Umbilical arterial blood gas obtained from a doubly clamped segment of umbilical cord was pH 7.07, PCO₂ 86 mm Hg, and PO₂ 19 mm Hg. The Apgar scores at 1 and 5 min were 1 and 6, respectively. The maternal end-tidal concentration of isoflurane at delivery of this fetus was 2.35%. The neonate was rapidly transferred to an adjacent operating room (OR) with a heart rate of 160 bpm, no movement, and no respiratory effort. Initial heart rate was 168 bpm and mean blood pressure was 50 mm Hg. The first end-tidal concentration of isoflurane was 0.2%, which decreased to 0.08% within 8 min of the initial recording. The neonate was manually ventilated with 100% oxygen. Seventeen minutes after delivery, he was tracheally extubated without difficulty. He was vigorous, his airway reflexes were intact, and he had good muscle tone.

After delivery of the fetus without the neck mass, blood loss exceeded 1 L. The mother received 1 U of packed red blood cells to maintain oxygen delivery to the fetus undergoing surgery. Despite of an end-tidal concentration of isoflurane of 2.68%, the surgeons noted that the uterus was contracting. Four doses of nitroglycerin 50 µg was required to provide uterine relaxation. There was a transient decrease in blood pressure to 80/50 mm Hg, which was treated with 10 mg of ephedrine. After the fetal head was delivered, the fetus with the neck mass received laryngoscopy, rigid bronchoscopy, and intubation with a 3.0 cuffless endotracheal tube. The umbilical artery and vein were cannulated to assist with the resuscitation after delivery. During these procedures, there was no fetal movement. The fetal heart rate ranged between 140 and 150 bpm, and the oxygen saturation was 60%–67%. The fetus was delivered 35 min after uterine incision and had an umbilical arterial blood gas from a doubly clamped segment of umbilical cord, of pH 7.10, PCO₂ 87 mm Hg, and PO₂ 14 mm Hg. Apgar scores at 1 and 5 min were 1 and 5, respectively. Oxytocin 30 U was added to the IV solution, and the isoflurane was discontinued. There was good contraction of the uterus. Nitrous oxide was added to the oxygen at a flow ratio of 2:1, and morphine was administered. After reversal of the neuromuscular blockade, the mother was tracheally extubated awake and without complications. The estimated blood loss was 1700 mL, with a urinary output of 700 mL. Total IV fluids administered were 3000 mL of saline and 250 mL of packed red blood cells. Her pre- and postoperative hemoglobin were 11.7 g/dL and 8.7 g/dL, respectively.

The fetus with the neck mass underwent postnatal evaluation by magnetic resonance imaging and the lymphangioma was partially resected 1 wk after delivery. A tracheostomy was performed due to involvement of the epiglottis by the lymphangioma. The infant was discharged from the hospital 2 mo later and is awaiting excision of the extensive neck mass.

	Discussion

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Although similar to the previous case series of intrapartum management of a fetus with a large neck mass (1), this case report differs in two important respects. In the previous series, the infants were ventilated and sedated after delivery. In this twin gestation, only one infant was to be ventilated for a significant period postoperatively. The other normal infant was anesthetized in utero with isoflurane and required emergence after delivery. There is no literature discussing the effect of high concentrations of isoflurane in utero on the infant in regard to his or her respiratory depressant and hemodynamic effects. In addition, this case illustrates that adequate uterine relaxation may not be achieved despite high concentrations of isoflurane. In this case, the administration of IV nitroglycerin was required.

The use of isoflurane for cesarean section has been studied extensively. Tunstall and Sheikh (2) administered 1.25% isoflurane in 100% oxygen to 56 parturients undergoing elective cesarean section. There were no cases of maternal awareness or of depression of the newborn. Piggott et al. (3) increased the concentration of isoflurane to 1.8% for 5 min, then decreased it to 1.2%. Again, there was no neonatal depression. In our previous case series, in which the concentrations of isoflurane administered to the mother ranged from 1.8% to 2.5%, there was no fetal movement during the procedure, which was desired, as the surgeons were performing laryngoscopy and bronchoscopy on the fetus. In the current case, this was desired for one of the fetuses only; thus, we were confronted with recovering the normal neonate who had been exposed to high concentrations of isoflurane in utero for 58 min.

Biehl et al. (4) investigated the uptake of isoflurane by the fetal lamb in utero by anesthetizing eight pregnant ewes with 2.0% isoflurane in oxygen. Isoflurane crossed the placenta rapidly, appearing in the fetal circulation 2 min after initial exposure. However, the arterial levels of isoflurane increased more slowly in the fetus and remained approximately two thirds of maternal levels by 90 min. Dwyer et al. (5) examined the uptake of isoflurane by the human fetus in mothers undergoing cesarean section. Twelve parturients received 0.8% isoflurane in a 50% nitrous oxide in oxygen mixture. The umbilical venous partial pressure of isoflurane as a fraction of maternal arterial partial pressure was 0.71. The ratio of the maternal arterial partial pressure to inspired pressure was 0.44. Hence, isoflurane crossed the placenta, but fetal levels were lower than maternal levels. However, despite this rapid placental transfer reported in the literature, we did not observe a significant end-tidal concentration in the neonate. In fact, the first end-tidal concentration of isoflurane was 0.2%—much lower than expected.

Gibbs et al. (6) demonstrated that isoflurane is more soluble in maternal than in fetal blood. The blood-gas partition coefficient for maternal and fetal blood is 1.51 and 1.35, respectively. While transferring the neonate to the other OR, the neonate was ventilated. The lower solubility resulted in rapid elimination of isoflurane from the neonate. With positive pressure ventilation, the neonate was moving by 5 min and could be tracheally extubated 15 min after delivery. The fact that isoflurane is so rapidly eliminated by the neonate when used to provide anesthesia for cesarean section is reassuring.

However, the rapid elimination of isoflurane by the neonate cannot completely explain the initial low level, as the neonate was only ventilated 30–45 s before arriving in the adjacent OR. The most likely explanation would be a decrease in uteroplacental perfusion limiting delivery of isoflurane to the fetus. Another aspect studied by Biehl et al. (4) in the fetal lamb was the effect of 2.0% isoflurane in oxygen on the fetus and regional blood flow. Although fetal heart rate and blood pressure were unaffected during the study period, fetal pH decreased significantly at 48 min of exposure. At 60 min, cardiac index began to decrease with a decrease in blood flow to the placenta. This decrease in pH and in blood flow to the placenta does not occur with brief (<30 min) exposures to 2.0% isoflurane (7). In our case, the induction to delivery time for the normal neonate was 58 min, and for the fetus with the neck mass, it was 1 h and 12 min. The low umbilical arterial pH values, increased PCO₂, and decreased PO₂ in these infants, as well as the low level of isoflurane in the normal neonate, may represent impaired uteroplacental blood flow. We did not observe this decrease in pH in the previous case series, although exposure to high isoflurane levels were shorter. Thus, there might be a limit to the time period in which the fetus can be exposed to high concentrations of isoflurane in oxygen, as would occur with cesarean section complicated by intrapartum management of the fetal airway.

The other significant difference from the previous series was the need for IV nitroglycerin. All previous patients had adequate uterine relaxation. This case, in which one infant was delivered before the surgical procedure on the other, required the IV administration of a tocolytic as the uterus was contracting. Nitroglycerin was chosen because of its rapid onset. Skeletal muscle relaxants would not provide relaxation for the uterus as the uterus consists of smooth muscle. Numerous case reports describe the use of IV nitroglycerin to provide uterine relaxation for the removal of a retained placenta or for the extraction of a second twin (8,9). In this case, 200 µg of nitroglycerin was administered in divided doses to provide uterine relaxation. It was surprising that the uterus would contract despite an end-tidal concentration of isoflurane of 2.68%. This suggests that extensive manipulation of the uterus, such as with delivery of an infant, stimulates the uterus to contract, despite the use of high concentrations of isoflurane. One concern with the use of nitroglycerin for tocolysis is the possibility of pulmonary edema. DiFederico et al. (10) presented a unique case of increased permeability pulmonary edema when nitroglycerin was administered as a continuous infusion for tocolysis.

The high concentration of isoflurane in oxygen technique for the twin gestation may carry risks not present for the single fetus. The prolonged induction to delivery times with a twin gestation may increase fetal acidosis and also limit isoflurane exposure due to a decrease in fetal placental blood flow. The delivery of the first fetus may initiate uterine contractions not controlled by isoflurane alone. Despite these risks, in this case, the outcome for both fetuses was good. The normal fetus who had been exposed to high concentrations of isoflurane for 58 min (maternal end-tidal concentration of isoflurane of 2.35% at delivery) was able to eliminate the drug quickly and was vigorous within 15 min of delivery. The fetus with the neck mass was delivered with good oxygenation and hemodynamics after an exposure of 1 h 15 min.

	References

Top Introduction Case Report Discussion References

 

1. Gaiser RR, Cheek TG, Kurth CD. Anesthetic management of cesarean delivery complicated by ex utero intrapartum treatment of the fetus. Anesth Analg 1997;84:1150–3.[Web of Science][Medline]
2. Tunstall ME, Sheikh A. Comparison of 1.5% enflurane with 1.25% isoflurane in oxygen for caesarean section: avoidance of awareness without nitrous oxide. Br J Anaesth 1989;62:138–43.[Abstract/Free Full Text]
3. Piggott SE, Bogod DG, Rosen M, et al. Isoflurane with either 100% oxygen or 50% nitrous oxide in oxygen for caesarean section. Br J Anaesth 1990;65:325–9.[Abstract/Free Full Text]
4. Biehl DR, Yarnell R, Wade JG, Sitar D. The uptake of isoflurane by the foetal lamb in utero: effect on regional blood flow. Can Anaesth Soc J 1983;30:581–6.[Web of Science][Medline]
5. Dwyer R, Fee JPH, Moore J. Uptake of halothane and isoflurane by mother and baby during caesarean section. Br J Anaesth 1995;74:379–83.[Abstract/Free Full Text]
6. Gibbs CP, Munson ES, Tham MK. Anesthetic solubility coefficients for maternal and fetal blood. Anesthesiology 1975;43:100–3.[Web of Science][Medline]
7. Bachman CR, Biehl DR, Sitar D, et al. Isoflurane potency and cardiovascular effects during short exposures in the foetal lamb. Can Anaesth Soc J 1986;33:41–7.[Web of Science][Medline]
8. DeSimone CA, Norris MC, Leighton BL. Intravenous nitroglycerin aids manual extraction of a retained placenta. Anesthesiology 1990;73:787.
9. Wessen A, Elowsson P, Axemo P, Lindberg B. The use of intravenous nitroglycerin for emergency cervico-uterine relaxation. Acta Anaesthesiol Scand 1995;39:847–9.[Web of Science][Medline]
10. DiFederico EM, Harrison M, Matthay MA. Pulmonary edema in a woman following fetal surgery. Chest 1996;109:1114–7.[Abstract/Free Full Text]

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