Idiopathic hypertrophic subaortic stenosis (IHSS), also known as hypertrophic obstructive cardiomyopathy, is characterized by dynamic obstruction of the left ventricular outflow tract secondary to asymmetric hypertrophy of the ventricular septum. Pregnancy is usually well tolerated, but acute peripartum pulmonary edema and a fatal ventricular arrhythmia have been reported. [1,2] Epidural anesthesia for vaginal delivery and general anesthesia for cesarean section have been described previously. [3,4] We report the use of combined spinal and epidural anesthesia using intrathecal fentanyl followed by epidural infusion of a diluted bupivacaine-fentanyl infusion for pain relief during labor and delivery in a parturient with IHSS.
A 19-yr-old primigravida who had been diagnosed as having IHSS 5 yr previously was referred for anesthetic preassessment at 31 weeks gestation. Before pregnancy, her symptoms were controlled with propranolol, although exercise tolerance was limited to walking for 15 min on level ground. During the pregnancy she had been well and had stopped the propranolol by her own choice in the first trimester. Echocardiography showed asymmetric interventricular septal thickening, systolic anterior motion of the mitral valve, and mild mitral regurgitation with a left ventricular outflow tract gradient of 15 mmHg at rest. The obstetric plan was for vaginal delivery.
The patient was admitted in early labor at 37 weeks gestation. Examination showed that she weighed 54 kg, was 157 cm tall, and had an arterial pressure of 130/80 mmHg, heart rate of 90 beats/min, and a grade 2/6 holosystolic murmur at the lower left sternal border. Her airway was assessed as Mallampati class 1. There was no jugular venous distention, and the chest was clear to auscultation. Obstetric examination showed cephalic presentation, cervical dilatation of 1 cm, and regular painful contractions. Monitoring with continuous cardiotocography, electrocardiography, and pulse oximetry was established. A radial artery catheter was inserted for continuous arterial pressure measurement, and a central venous pressure catheter was placed via the right cubital fossa, with the position checked with a chest radiograph. The central venous pressure, measured supine, was 3 cm H2O initially and increased to 5 cm H2O after intravenous preload of 250 ml lactated Ringer's solution.
Combined spinal and epidural anesthesia was performed with the patient in the left lateral position using a needle-through-needle technique at the L3-L4 lumbar interspace. The epidural space was located with a 16-gauge Tuohy needle using a loss-of-resistance technique. Fentanyl (25 micro gram) was given intrathecally via a 25-gauge Whitacre spinal needle, followed by insertion of an epidural catheter. The patient was turned to a wedged supine position. There were minimal hemodynamic changes and the patient was pain free after 5–10 min. Epidural infusion of 0.1% bupivacaine and 2 micro gram/ml fentanyl was commenced at 8 ml/h and increased to 9 ml/h after 8 h because of a slight increase in discomfort. With this infusion rate, the patient was comfortable with no detectable leg weakness throughout labor, and no epidural boluses of local anesthetic were required. The maximum cephalad level of sensory block, tested with ice, was T10 and the patient remained hemodynamically stable, with heart rate < 105 beats/min and central venous pressure kept within 3–4 cm H2O of baseline with intravenous infusion of lactated Ringer's solution at 80 ml/h. Two doses of 50 mg ranitidine were given intravenously 6 h apart.
After 13 h, vaginal delivery of a male infant weighing 2,900 g was performed using low forceps. No additional analgesia was required for delivery. Apgar scores were 10 at 1 min and 10 at 5 min. Estimated blood loss was 300 ml. Intravenous polygeline solution (500 ml; Haemaccel; Behring, Marburg, Germany) was given in two boluses and an infusion of 40 IU oxytocin was given over 8 h. The postpartum course was uncomplicated and there was no postdural puncture headache during 5 days of follow-up.
The use of regional anesthesia in IHSS is controversial. Previously researchers recommended that these techniques be avoided because of the potential detrimental effects of vasodilation.  However, Minnich et al.  reported the use of epidural anesthesia with intermittent injection of 10 ml 0.125% bupivacaine with 5 micro gram/ml fentanyl during the first stage, and 10 ml 0.25% bupivacaine during the second stage of labor in a parturient with IHSS. Invasive monitoring was used and the patient was hemodynamically stable. The use of CSE followed by epidural infusion in our patient had several advantages over the technique described by Minnich et al. The initial intrathecal injection of fentanyl provided rapid onset of analgesia without sympathetic block. [5,6] This enabled gradual establishment and maintenance of epidural analgesia using an infusion of diluted bupivacaine and fentanyl without the need for boluses of local anesthetic. The use of continuous epidural infusions for analgesia in labor has been shown previously to be associated with a lower incidence of hypotension compared with an intermittent top-up regimen.  Our patient received adequate analgesia throughout labor with the epidural infusion alone, and a bolus dose of local anesthetic was not required for forceps delivery. Dural puncture with small-gauge spinal needles before epidural injection of local anesthetic was shown previously to improve caudal spread and sacral analgesia,  although whether this effect contributed to analgesia 13 h later in our patient is uncertain.
We did not administer a test dose before commencing the epidural infusion, but we closely observed the patient for signs of local anesthetic toxicity. Injection of an epinephrine-containing test dose may have caused tachycardia, which could have exacerbated left ventricular outflow obstruction.
Combined spinal and epidural anesthesia with intrathecal fentanyl followed by an epidural infusion of a diluted bupivacaine-fentanyl solution provided satisfactory analgesia for labor and instrumental delivery with stable hemodynamics in a patient with IHSS.