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Preamble
Fetal heart rate (FHR) monitoring is the most frequently employed screening technique for intrapartum fetal well-being.1 FHR changes seen after induction of regional analgesia for labor often profoundly affect the obstetric management of labor. Fetal bradycardia may occur following initiation of analgesia using either epidural local anesthetics or subarachnoid opioids.2 This slowing is usually benign and short-lived but can cause much anxiety amongst both patients and medical personnel alike. It typically results in intense increased surveillance and preparations for a possible urgent trip to the O.R. Is intervention necessary?
The definition of fetal bradycardia varies. However, a decrease in baseline by 50 beats per minute for 3 minutes or a decrease to below 100 beats per minute for 1 minute is widely accepted as significant. 3,4 Bradycardia resulting from regional analgesia tends to occur within 30 minutes of completion of the block, lasts 5-8 minutes, then resolves spontaneously. This phenomenon is distinct from other causes of fetal bradycardia such as aortocaval compression, maternal hypotension, systemic opioid effect, cord compression, or other obstetric entities.
The purpose of these guidelines are twofold. First, to increase awareness by educating the Birth Unit team (nurses, midwives, family practitioners, anesthesiologists and obstetricians) as to the existence of this phenomenon. Second, to make suggestions for its prudent management so as to jointly ensure optimum neonatal and maternal outcomes while avoiding unnecessary emergent operative deliveries.
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Risk Factors
The understanding of this entity is in a state of flux. Incidence in the literature varies widely from 12-17%5,6 using combined spinal-epidural techniques to 6-8% using epidural-only methods. Studies by Clarke7 and Mercier8 suggest that higher doses of subarachnoid narcotic are the cause. However these results are not supported by Nielson9 and Eberle.5 Concomitant use of oxytocin, 10 lack of intravenous preload and pre-existing uteroplacental bloodflow (UBF) pathology are also all speculated as being risk factors.
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Mechanism
The mechanism remains unclear. Adverse effects on UBF, rapid fetal descent, as well as direct effects on the fetus have all been suggested as the primary cause of pathology. 9,4,11,13
Increased uterine tone almost certainly plays a role. UBF can be compromised post-block as a result of uterine hypertonus from redistribution of maternal and fetal cardiac output or by an acute drop in catecholamine levels. It has been proposed that rapid decreases in maternal catecholamines seen with the onset of pain relief result in a reduction of circulating beta agonists and a predominance of alpha activity.11 This favors uterine hypertonus. Indeed, ephedrine (a beta agonist) given in the absence of maternal hypotension may decrease uterine activity and thus be of some benefit in the treatment of prolonged fetal bradycardia. Nitroglycerin8, 12 and beta 2 agonists (ritodrine, terbutaline) have also proved useful, presumably from their acute tocolytic properties.
Prophylaxis
Preventive measures of course should always be utilized. These include adequate pre-block intravenous preloading and use of patient positioning to avoid aortocaval compression.
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Management
In most cases the condition resolves spontaneously. A suggested course of action may include:
1. Ensure maternal left uterine displacement. Consider other positions, such as full lateral and knee-chest.
2. Administer supplemental maternal oxygen
3. Rule out or treat maternal hypotension and hypovolemia
4. Check progression of labor (dilation, position); while doing so, rule out other obstetrical emergencies such as presence of prolapsed cord.
5. Check for uterine hypertonus; if present, discontinue oxytocin and consider treatment with one or more of the following:
IV nitroglycerin 50-200 ugs
nitroglycerin spray 2-4 puffs
ventolin puffer, 2-4 puffs
IV ephedrine 10-15 mgs
IV ritodrine 100-350 ug/minute
SC terbutaline 0.1-0.25 ugs
6. Continue FHR monitoring and consider emergent delivery if fetal bradycardia persists
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References
1. Parer JT, Livingston EG. What is fetal distress? Am J Obstet Gynecol 192;741-7.
2. Albright GE, Forster RM. Does combined spinal-epidural analgesia with subarachnoid
sufentanil increase incidence of emergency cesarean delivery? Reg Anesth 1997;22(5):400-5.
3. Stavrou C, Hofmeyr G, Boezaart AP. Prolonged fetal bradycardia during epidural analgesia.SAMJ 1990;77:66-8.
4. Cohen SE, Cherry CM, Molbrook H, El-Sayed YY, Gibson RN, Joffe RA. Intrathecal sufentanil for labor analgesia ? sensory changes, side-effects, and fetal heart rate changes. Anesth Analg 1997;77:1155-60.
5. Eberle RC, Norris MC, Eberle AM, Naulty JS, Arkoosh VA. The effect of maternal position on fetal heart rate during epidural or intrathecal analgesia. Am J Obstet Gynecol 1998;179(1):150-5.
6. Palmer CM, Maciulla JE, Cork RC, Nogani WM, Gossler K, Alves D. The incidence of fetal heart rate changes after intrathecal fentanyl labor analgesia. Anesth Analg 1999;88:577-81.
7. Clark VT, Smiley RM, Finster M. Uterine hyperactivity after intrathecal injection of fentanyl for analgesia during labor: A cause of fetal bradycardia? Anesthesiology 1994;81(4):1083
8. Mercier J, Dounas M, Bouaziz H. Thuissier C, Behhanou D. Intravenous nitroglycerin to relieve intrapartum fetal distress related to uterine hyperactivity: a prospective observational study. Anesth Analg 1997;84:1117-20.
9. Nielsen P, Erickson JR, Abouleish EI, Perriott S, Sheppard C. Fetal heart rate changes after intrathecal sufentanil or epidural bupivacaine for labor analgesia: Incidence and clinical significance. Anesth Analg 1996;83:742-6.
10. Friedlander JD, For HE, Cain CF, Dominiguy CL, Smiley RM. Fetal bradycardia and uterine hyperactivity following subarachnoid administration of fentanyl during labor. Reg Anesth 1997;22(4):378-81.
11. Beilin Y, Leibowitz A, Bernstein H, Abramoritz S. Controversies of labor epidural analgesia. Anesth Analg 1998;89(4):969-8.
12. Segal S, Csavoy AN, Datta S. The tocolytic effect of catecholamine in the gravid rat uterus. Anesth Analg 1998;87:864-9.
13. Gambling DR, Sharma SK, Ramis SM, Lucas MJ, Leveno KJ. A randomized study of combined spinal-epidural analgesia versus intravenous meperidine during labor. Anesthesiology 1998;89(6):1336-44.
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