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Anesthesiology:
Correspondence

Nitroglycerin to Facilitate Insertion of a Labor Epidural

Carvalho, Brendan M.B.B.Ch., F.R.C.A.

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To the Editor:—

Placement of a labor epidural or combined spinal–epidural in advanced labor is technically challenging. Regular painful contractions often make it difficult for the parturient to remain still during epidural placement, and this may increase the chance of an accidental dural tap or nerve injury. Decreasing the intensity and frequency of uterine contractions during neuraxial placement in this setting may be advantageous. Previous reports show that nitroglycerin produces rapid effective uterine relaxation.1–5 Nitroglycerin to facilitate the placement of a labor epidural has not previously been reported. This case describes the use of nitroglycerin in the setting of advanced labor to facilitate the placement of a labor epidural.
A 35-yr-old, healthy, 90-kg, gravida 3, para 2 parturient admitted to labor and delivery in advanced labor requested an epidural for pain relief. She had two previous uncomplicated normal vaginal deliveries without the use of a labor epidural. A recent cervical examination showed her cervix to be dilated 8 cm, with the fetal head at +1 station. She was moving and uncooperative during contractions, which occurred every 45–60 s. She had not responded to 100 μg intravenous fentanyl given 5 min previously. With difficulty, we managed to position her in a sitting position to administer the epidural. After a sterile preparation of her back with a 10% povidone-iodine solution and 1% lidocaine skin infiltration, we attempted to insert the epidural catheter using a 17-gauge Tuohy needle. However, she kept moving and was uncooperative during and between uterine contractions. After informing the obstetrician and the patient that we were going to administer medication to help ease the painful contractions, we administered three sprays (400 μg per spray dose) of sublingual nitroglycerin (Nitrolingual® Pumpspray; First Horizon Pharmaceutical Corporation, Alpharetta, GA). This produced a temporary decrease in her uterine contractions (reduction in peak uterine pressures and an increased between-contraction interval as measured by external tocodynamometer) and resulted in some transient pain relief. It was then possible to perform the combined spinal–epidural during the interval between contractions. The patient experienced no hypotension or cardiovascular disturbances after administration of the nitroglycerin and resumed her normal uterine contraction pattern within a few minutes. The patient was delivered of a healthy baby vaginally 2 h later, with 1- and 5-min Apgar scores of 8 and 9, respectively.
Reducing contraction pain during placement of a labor epidural is potentially beneficial. However, the risks of uterine tocolysis must be balanced with the potential benefit of safer epidural placement and labor analgesia. Although there have been no studies demonstrating increased dural puncture or neural damage after epidural placement in an uncooperative and moving parturient, most clinical anesthesiologists believe that a relation must exist. Decreasing the intensity and frequency of uterine contractions during neuraxial placement in this setting should be potentially advantageous. Remifentanil has been described in this setting to improve analgesia and facilitate the insertion of a labor epidural.6 However, potent narcotics have potential adverse effects, in particular maternal apnea, dysphoria, and emesis. Nitroglycerin is a safe, effective uterine tocolytic commonly used in labor, with a rapid onset and brief half-life.2,7 Nitroglycerin has minimal, short-lived cardiovascular effects compared with β-adrenergic tocolytics. Although the safety of nitroglycerin during obstetric emergencies seems high, with no adverse maternal or neonatal outcomes,2 maternal hypotension and hemodynamics changes are possible, especially if high doses are given.8 No more than three metered sprays are recommended within a 15-min period.9
A number of studies and case reports describe the use of nitroglycerin in achieving rapid uterine relaxation.2,3,5 Nitroglycerin has been used as a tocolytic to reduce uterine hyperactivity,10 assist reduction of an inverted uterus,11 facilitate intrapartum external cephalic version,12 and manage preterm labor contractions.13 Nitroglycerin can be administered via a number of routes (intravenous, sublingual, or ointment); however, bioavailability is highly variable between subjects because of a pronounced first-pass metabolism. After sublingual administration, bioavailability is approximately 38%.14
Nitroglycerin may be useful in a setting where advanced labor and parturient movement during uterine contractions makes the placement of an epidural difficult and potentially dangerous. It exposes the mother and fetus to minimal risk and, in selected patients, may offer potential benefits justifying its use in this setting. However, physicians should remember that this is “off-label” use of nitroglycerin.9 Both the risks and the benefits must be considered, and the patient and her obstetrician must be consulted before uterine tocolytics are administered in this setting.
Brendan Carvalho, M.B.B.Ch., F.R.C.A.
Stanford University School of Medicine, Stanford, California. bcarvalho@stanford.edu
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References

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6. Brada SA, Egan TD, Viscomi CM: The use of remifentanil infusion to facilitate epidural catheter placement in a parturient: A case report with pharmacokinetic simulations. Int J Obstet Anesth 1998; 7:124–7

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9. Nitrolingual® Pumpspray [package insert]. First Horizon Pharmaceutical Corporation, Alpharetta, Georgia, 2003

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