Continuous Spinal Analgesia with Sufentanil for Labor and Delivery in a Parturient with Severe Pulmonary Stenosis

Abstract

Pulmonary valvular stenosis constitutes roughly 10%-15% of all congenital heart disease [1]. The valvular lesion is usually unchanged until late in adult life [2], but in severe cases, secondary infundibular hypertrophy can arise during childhood or early adolescence. This subvalvular lesion can be progressive, resulting in a dynamic right ventricular outflow obstruction. If progression has occurred in the pregnant patient, right ventricular failure can result secondary to an inability to compensate for the increases in heart rate, right ventricular preload, and oxygen consumption associated with pregnancy. This can increase the risk of further maternal morbidity, most commonly manifested as congestive failure, by 50% over patients with nonprogressive stenosis [3]. The incidence of spontaneous abortion and fetal death is significantly increased as well [3]. Spinal and epidural anesthetic techniques so well suited to the obstetric population are often avoided in this condition because of the potential for cardiovascular side effects. As a result, these mothers frequently receive less than adequate analgesia for their labor and delivery. The use of continuous spinal anesthesia with sufentanil for the management of labor and delivery in a patient with severe combined pulmonic and infundibular stenosis is described in this report. Case Report A 26-yr-old female primigravida presented for cardiology evaluation because of severe pulmonary valve stenosis in the setting of her recently identified pregnancy. Her valvular disease was first diagnosed at age 1 yr while she was living in Vietnam, but she was asymptomatic until age 10 when she experienced an episode of syncope. She had further episodes of syncope during her teen years when she also began experiencing dyspnea, palpitations, and fatigue with only mild exercise. She also reported intermittent episodes of acrocyanosis and lower-extremity edema. After relocating to the United States, she was seen by a local cardiologist in her home state but was subsequently referred to our facility for definitive therapy in light of her recently diagnosed pregnancy. The patient presented to our cardiology division with mild dependent edema, easy fatigability, and dyspnea with minimal exertion. Heart rate was 68 bpm and arterial blood pressure 110/70 mm Hg. Cardiac evaluation showed a Grade IV/VI systolic ejection murmur over the entire precordium with a systolic ejection click at the left upper sternal border, heard best on expiration. Jugular veins were flat. Her electrocardiogram (ECG) showed normal sinus rhythm with right ventricular strain pattern and biatrial enlargement. Chest radiograph revealed right ventricular enlargement with prominence of the main pulmonary artery. Echocardiographic evaluation by M-mode, 2-D, and color flow showed severe pulmonary valvular stenosis with a peak gradient of 151 mm Hg and a mean of 85 mm Hg. She also had severe right ventricular hypertrophy with severe subpulmonary stenosis and mild tricuspid regurgitation. Her estimated right ventricular systolic pressure was 235 mm Hg. Because the patient's pregnancy was only recently diagnosed, an obstetric evaluation was deemed necessary before she could undergo an interventional procedure to improve her cardiovascular status. An intrauterine pregnancy of 9 6/7 weeks' gestation was confirmed by ultrasound. Of important clinical significance was her hematocrit of 47.6%, because this polycythemia and also the hypercoagulable state associated with her pregnancy placed her at increased risk for thromboembolic or thrombotic complications after procedures. Despite this increased risk, the severity of her stenosis necessitated intervention. It was felt the patient would best benefit from balloon valvuloplasty of her pulmonic value, and, furthermore, this should be undertaken without delay. At catheterization the patient had a right atrial pressure of 13/8 mm Hg, a right ventricular pressure of 177/6 mm Hg, a main pulmonary artery pressure of 18/7 mm Hg, and an ejection fraction of 39%. She was also found to have a small secundum atrial septal defect (ASD) with a right-to-left shunt fraction of 27%. A femoral arterial blood gas immediately before the procedure showed a PaO2 of 49 mm Hg, PaCO2 of 27 mm Hg, pH of 7.37, and a room air oxygen saturation of 87%. Four dilatations were performed with a single balloon catheter, and right ventricular pressure at the conclusion of the procedure was 120/4 mm Hg with improvement in her ejection fraction to 53%. She tolerated the procedure well, with improvement in her room air oxygen saturation to 97%, but severe residual infundibular stenosis was found to be present. The patient was started on aspirin therapy as well as atenolol for beta blockade, and this was continued for the duration of her pregnancy. The patient was receiving her prenatal care from her primary physician in her home state but returned to our facility for a follow-up evaluation 5 mo postvalvuloplasty. Heart rate was 70 bpm and arterial blood pressure 110/70 mm Hg. Her hematocrit was 37.3%. Echocardiogram showed a significant decline in the pulmonary gradient and right ventricular systolic pressure, but significant infundibular obstruction remained, as did the right-to-left shunt through the ASD. She reported an overall improvement in her symptoms but still felt somewhat dyspneic when supine, and at night slept on three pillows. Her pregnancy was progressing without complications. The patient was instructed to continue atenolol and aspirin and to return for induction of labor at the appropriate time. At 39 wk gestational age, the patient was admitted for elective induction of labor. Monitors included ECG, pulse oximetry, and arterial line and central venous pressure (CVP) line in addition to the tocodynamometer and fetal heart tones monitor. Initial hemodynamic variables were: arterial blood pressure 174/98 mm Hg, heart rate 74 bpm, and CVP 11 mm Hg, and her oxygen saturation by pulse oximetry was 91% with a fractional inspired oxygen concentration of 0.4. The patient had no apparent history of hypertension, and the increase in blood pressure was attributed to stress secondary to line placement for invasive monitoring and incorrect initial placement of the arterial pressure transducer. Upon completion of invasive line placement and adjustment of the pressure transducer, arterial blood pressure was 130-144/70-88 mm Hg throughout her labor. The patient was to receive oxytocin augmentation of labor after monitor placement, but spontaneous uterine contractions began shortly after monitoring was established. Active labor was established over the next 90 min, so a 24-gauge indwelling spinal catheter was placed. After confirmation of freely flowing cerebral spinal fluid (CSF), a loading dose of 10 micro gram of sufentanyl was administered. Excellent analgesia was noted immediately after narcotic administration, and a continuous intrathecal infusion of sufentanyl 5 micro gram/h was initiated for maintenance of analgesia using an Abbott Registered Trademark Pain Management Provider Trademark infusion pump. Hemodynamic measurements after initiation of the infusion showed no significant changes in arterial blood pressure, CVP, or heart rate. Oxygen saturation was maintained in the 91%-95% range with supplemental oxygen via 40% venturi mask. The patient remained comfortable with the sufentanyl infusion alone throughout 5 h of labor. Her hemodynamic variables remained stable during this time as well with arterial blood pressure in the 130- to 150/70- to 90-mm Hg range, CVP in the 10- to 12-mm Hg range, and heart rate in the 70- to 90-bpm range. One hour before delivery, the patient began experiencing increased pressure in the lower abdomen and perineum. Fifteen mg of 1% lidocaine plain was given cautiously in divided doses via the spinal catheter with near complete resolution of the patient's pain and no hemodynamic changes. After 5.5 h of labor, the cervix was found to be completely dilated, and a vacuum extractor was used to help bring the baby's head down over a left mediolateral episiotomy. A 2375-g male infant was delivered with Apgar scores of 8 and 9 at 1 and 5 min, respectively. Forty-five minutes postdelivery, arterial blood pressure decreased over 15 min from 128/72 to 100/42 mm Hg. CVP fell from 12 to 3 mm Hg over the same time period, necessitating two 250 mL fluid boluses of Lactated Ringer's solution. After fluid administration, CVP returned to 7 to 8 mm Hg. The remainder of her postdelivery course was uneventful, and she was subsequently discharged after 3 days with plans to return in the future to undergo repair of her ASD. Discussion Pulmonary valvular stenosis is one of the more common congenital cardiac anomalies seen in adolescents and adults [4]. Normal development of the infundibulum and pulmonary valve occurs during the 4th and 6th wk of gestation, respectively, from proliferation of the bulbus cordis and a resorptive and hollowing process [5]. Errors in this process result in malformation leading to subsequent valvular or infundibular stenosis. The right outflow tract obstruction can impose a pressure overload on the right ventricle, causing clinical manifestations such as those noted in our patient. In most cases, the stenosis is well tolerated into adult life. This has been confirmed by Levine and Blumenthal [6], who found that when pulmonary stenosis is diagnosed in a young child, right ventricular systolic pressure rarely increases as the child ages. When it does, they found progression to be due to hypertrophy of the infundibular muscle rather than worsening of the valvular stenosis. Consequently, with treatment of the valvular stenosis using balloon valvuloplasty or surgical intervention, the subvalvular hypertrophy often regresses. Percutaneous balloon valvuloplasty has been shown to decrease the degree of valvular obstruction effectively and with few complications [7]. At many institutions it is the procedure of choice for the treatment of isolated pulmonic stenosis [8], and has been used effectively in pregnant patients with pulmonic as well as mitral stenosis [9-10]. The procedure is performed via the femoral vein by placing a balloon catheter or catheters with total diameters 20%-30% larger than the valve annulus across the stenotic valve and inflating these several times. The mechanism by which balloon valvuloplasty achieves its result involves tearing of the valve cusp, or commissural splitting. Often the valvuloplasty will unmask the presence of infundibular obstruction, as was the case in our patient, necessitating further treatment of the stenosis--usually with fluid management and beta blockade [8]. Despite the improvement in hemodynamics resulting from this procedure, close monitoring of these patients should continue throughout pregnancy. Improved hemodynamics resulting from interventions such as balloon valvuloplasty do not eliminate the need for analgesics during labor since significant hemodynamic alterations in response to pain can still occur, and these responses may be detrimental to both mother and fetus. Mangano [11] recommends intravenous narcotics and inhalational agents along with pudendal and/or paracervical blocks to manage pain in pregnant patients with pulmonic stenosis who are exhibiting classic symptoms of dyspnea, fatigue, edema, and syncope. However, pain control is often inadequate with systemic analgesics, and repeat doses may cause maternal hypercarbia and acidosis. Fetal risk is also increased because of potential cardiorespiratory depression secondary to systemic analgesics which may reach the fetus through placental transfer. Epidural narcotic/local anesthetic combinations are routinely used for pain relief during labor and delivery, but the risk of hypotension and subsequent reduction in preload may not be tolerated in the setting of severe pulmonic stenosis. The single-shot spinal technique using narcotic has previously been used successfully in laboring patients who are at risk for cardiovascular compromise from local anesthetic administration [12]. However, as Minnich et al. [13] point out, the duration of action is often shorter than the course of labor, particularly in the primigravid patient, necessitating repeat lumbar punctures with an associated increased risk of postdural puncture headache in these situations. Another consideration regarding a regional technique is the potential for hemorrhage or hematoma formation. In the absence of a preexisting hematologic condition, such as hemophilia A or von Willebrand's disease; however, recent aspirin ingestion is not a contraindication to a regional technique in the pregnant patient [14]. Our choice of continuous spinal anesthesia with narcotic for this patient offered the advantage of cardiovascular stability combined with essentially unlimited duration of analgesia. Sufentanil has a more favorable side effect profile than some other narcotics administered intrathecally in that it may be associated with less nausea, vomiting, and pruritus [15]. It is effective alone for providing analgesia during the first stage of labor, but during the second stage we have often found it necessary to supplement the spinal narcotic with local anesthetic, as was done in this case. The dosage of local anesthetic used in conjunction with sufentanil during the second stage of labor is minimal and significantly less than that required when local anesthetic is used alone. This allows for more hemodynamic stability without other undesirable local anesthetic effects such as motor blockade [16]. Meperidine has been used via indwelling spinal catheters for labor and delivery, and may offer advantages over sufentanil, given its partial anesthetic activity. However, Johnson, et al. [17] reported early tachyphylaxis with meperidine. When the dosage was increased to offset this effect, their patients developed undesirable leg heaviness and numbness. Additionally, other authors have reported more nausea with meperidine than with sufentanil [15]. Fentanyl has also been administered intrathecally for labor analgesia, but in our hands has not been as effective as sufentanil [18], possibly because of differences in lipid solubility or potency. The use of the indwelling catheter allows for continuous infusion of sufentanil and, therefore, continuous analgesia. The major disadvantage of this technique, particularly in the obstetric population, is the potential for postdural puncture headache. The reported incidence varies between 1.7% and 80% (20%-25% in our patient population) [14]. Studies were underway to evaluate the headache profile of the micro catheters (28-32 gauge) when the Food and Drug Administration ordered the removal of all catheters smaller than 24-gauge from the market. The reports leading to this action have all been associated with the use of "anesthetic strength" local anesthetic administered via intrathecal catheters. No incidents have been reported with the use of intrathecal catheters to deliver narcotics and dilute local anesthetic solutions. The 24-gauge catheter requires a 20- or 22-gauge needle for placement, which is associated with an increased risk of postdural puncture headache in the obstetric population. Our patient experienced no such headache postdelivery. Regardless, given her cardiac dysfunction, the increased risk of postdural puncture headache was felt to be outweighed by the significant benefit this technique offered in terms of hemodynamic control in conjunction with excellent analgesia. We conclude that continuous spinal analgesia with sufentanil provides a suitable alternative for labor analgesia in patients in whom hemodynamic stability is essential.