ANESTHESIA AND ANALGESIA. . . Current Researches VOL.54, NO 6, Nov.-DEc., 1975

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The Effect of Lumbar Epidural Anesthesia on Fetal Heart Rate Baseline Variability FRANK H. BOEHM, M.D., FACOG* LEON F. WOODRUFF, JR., M.D.? JAMES H. GROWDON, JR., M.D.$ Nashville, Tennessees

Baseline fetal heart r a t e (FHR) variability has become a n important parameter in the diagnosis of fetal distress when electronically monitoring the fetus, Loss of this baseline variability has been noted to be associated with fetal distress, and in association with late deceleration or severe variable deceleration patterns h a s been shown to be ominous. Baseline F H R variability, however, has been modified not only by fetal distress but also by prematurity and t h e administration of certain drugs to the mother. Because F H R is often monitored during labor in parturients given lumbar anesthesia, the question of the effect of this procedure on FHR variability arose. Fifteen such patients with no antepartum or intrapartum complications were

studied in active labor. All were monitored by electrocardiography on a continuous basis, F H R being studied before and after epidural anesthesia with lidocaine, with and without epinephrine. Of the 15 patients, tracings in 8 (53 percent) revealed a minimal or moderate change in baseline variability within several minutes of drug injection. This change i n variability was recorded from 4 to 18 minutes, after which time the pre-epidural F H R variability was reestablished. Although the mechanism for this result was not definitively determined, such variability in F H R does not i n itself seem significant of fetal distress but suggests supportive measures for the patient.

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effect of this procedure on FHR variability arose. Hehre and coworkers10 noticed a transient stabilization of FHR variability at an epidural drug dose range of 129 2 5.8 mg/hr of lidocaine, disappearing within 3 to 4 minutes as the fetus redistributed the drug. This variability, or beat-to-beat interval, was displayed by a positive or negative deflection with regard to both the FHR baseline and the previous impulse.

ASELINE fetal

heart rate (FHR) variability has become an important parameter in the diagnosis of fetal distress when electronically monitoring the fetus.1-3 Loss of this baseline variability has been noted to be associated with fetal distress, and in association with late deceleration or severe variable deceleration patterns has been shown to be ominous."^' Such variability has been noted to be modified not only by fetal distress but also by prematurity and the administration of certain drugs to the mother.8.9 Because many of our patients are given lumbar epidural anesthesia while being electronically monitored, the question of the

The present study was undertaken to ascertain the effect of epidural anesthesia on baseline variability, read out on a fetal monitor11 as routinely used in our hospital.

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IICorometrics, Wallingford, Connecticut.

:kAssociate Professor. ?Resident, Obstetrics and Gynecology. XAssistant Professor. %Departmentof Obstetrics and Gynecology, Vanderbilt University Hospital, Nashville, Tennessee 37232. Paper received: 2/27/75 Accepted for publication: 3/31/75

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ANESTHESIA AND ANALGESIA . . . Current Researches VOL.54,NO.6,Nov.-DEc.,1975 ~~

CKARACTERISTIC EXAMPLE OF EACH CLASSIFICATIM OF BASELIWI: VARIABILITY

LQW FREQJEW.3

HIGH F R E Q U W

13-5 cycie/minutc)

(180 cycls/ainutef

-HARKED-

- MODERATE - MINIMAL

*

- ABSENT -

FIG1. Classification of fetal heart rate variability. (From Boehm FH, Growdon JH Jr: The effect of scopolamine on fetal heart baseline variability. Amer J Obstet Gynec 120:1099-1104,1974.)

PATIENTS AND PROCEDURES Fifteen uncomplicated patients in active labor at term were studied. All were electronically monitored. The beat-to-beat FHR was computed with the interval between fetal electrocardiographic peak (R-wave) by a peak-detecting digital tachometer gaining input via a spiral fetal scalp electrode. The FHR was examined for changes in high frequency (180 cpm*) and low frequency ( 3 to 5 cpm) variability, as described by Yeh and associates.8 Before and after the lumbar epidural procedure, each FHR pattern was classified as showing marked, moderate, minimal, or absent high and low frequency variability (fig 1).A baseline FHR pattern was established for a minimum of 15 minutes before epidural injection. Variability was then interpreted for the next 60 minutes and classified. Brachial blood pressure recordings were obtained each 3 minutes for the first 15 minutes and thereafter each 10 minutes. Patients with a significant drop in sys-

*cpm = cycles per minute.

tolic blood pressure (less than 100 torr) were eliminated from the study. All patients sustained an anesthetic level of T-11 or higher and were then tilted to the left side. Epidural analgesia and anesthesia was achieved by 1, 1.5, or 2 percent lidocaine, 90 to 200 mg (mean 142 mg) ,with epinephrine 1:200,000 in 11cases and 1 to 1.5 percent lidocaine, 100 to 180 mg (mean 145 mg), without epinephrine, in 4 patients, 5 minutes after a 1 or 2 ml test dose of lidocaine. No pathologic FHR patterns were recorded during the study.

RESULTS Of the 15 patients, the FHR tracings of 8 (53 percent) revealed slight or minimal reduction in baseline variability within 5 minutes after drug injection (figs 2-5). This change in variability, which usually was no more than a one-grade change (fig 1) persisted from 4 to 18 minutes (mean 9.2 min) , after which time the pre-epidural variability was re-established. Of the 8 patients whose variability was noted to change, 7 had been given lidocaine with epinephrine while one

Fetal Heart Rate Baseline

,

. . Roehm, et a1

78 1

FIG2. Fetal heart rate variability prior to epidural analgesia. Case 1.

FIG3. Loss of fetal heart rate variability within 5 minutes after injecting the epidural catheter. Case 1.

FIG4. Fetal heart rate variability prior to epidural analgesia. Case 2.

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FIQ5. Loss of fetal heart rate variability within 5 minutes after injecting the epidural catheter. Case 2.

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ANESTHESIA AND ANALGESIA. . . Current Researches VOL.54, NO.6, Nov.-DEc.,1975

was given lidocaine alone. No correlation between dosage of lidocaine and change in FHR variability could be established. At delivery, all 5-minute Apgar scores were 8, 9, or 10, and all neonates appeared to be healthy. COMMENT Local anesthetic agents, such as lidocaine, with amide linkage which prevents the enzymatic degradation by the placenta, cross the placental barrierll.'~and are considered myocardial depressants.l" Anesthetic agents injected into the epidural space have been shown to accumulate in the fetus, the amount dependent on dosage and the presence or absence of epinephrine, which can decrease the maternal drug uptake by as much as 20 percent.14*15 While the noted change in FHR variability in these 8 patients could be secondary to fetal myocardial depression resulting in fetal hypotension caused by lidocaine, as proposed by Hehre and coworkers,](' it is also possible, despite the fact that brachial blood pressures were within normal limits, that uterine perfusion decreased following epidural injection, leading to mild acidosis, with early but transient signs of fetal distress.l"l7 Another possible explanation of these results is the electrocardiographic lengthening of the PR interval and widening of the QRS complex, suggesting a decreased rate of intracardiac electrical conduction, seen after administration of local anesthetics.l* Whatever the mechanism responsible, only subtle changes in FHR variability were noted, beginning within several minutes after the start of lumbar anesthesia and lasting no more than 18 minutes, as read on the fetal monitor printout. While this change does not seem significant of fetal distress, the onset of late deceleration, with or without further loss of FHR variability, indicates the need to treat the patient with 0 2 , a change in position from supine to lateral decubitus, an increase in fluid intake, and possibly the use of vasoactive drugs. REFERENCES 1. Davidsen PCB: Continuous monitoring of the foetal heart rate and uterine contractions during labor. Acta Obstet Gynec Scand 50:51-60, 1971

2. Schifrin BS: Fetal heart rate monitoring during labor. JAMA 222: 196-202, 1972 3. Gabert HA, Stenchever MA: Continuous electric monitoring of fetal heart rate during labor. Amer J Obstet Gynec 115:919-923, 1973

4. Schifrin BS, Dame L: Fetal heart rate patterns. Prediction of Apgar score. JAMA 219: 13221325, 1972 5. Paul RH, Hon EH: Views and reviews. Clinical fetal monitoring. A survey of current usage. Obstet Gynec 37:779-784, 1971 6. Paul RH: Clinical fetal monitoring. Experience on a large clinical service. Amer J Obstet Gynec 113:573-577, 1972

7. Shenker 1,: Clinical experience with fetal heart rate monitoring on one thousand patients in labor. Amer J Obstet Gynec 115:1111-1115, 1973 8. Yeh S, Forsythe A, Hon EH: Quantification of fetal heart beat-to-beat interval differences. Obstet Gynec 41:355-363, 1973

9. Boehm FH, Growdon J H Jr: The effect of scopolamine on fetal heart rate baseline variability. Amer J Obstet Gynec 120:1099-1104, 1974 10. Hehre FW, Hook R, Hon EH: Continuous lumbar peridural anesthesia in obstetrics VI: The fetal effects of transplacental passage of local anesthetic agents. Anesth & Analg 48:909-913, 1969 11. Morishima HO, Daniel SS, Finster M, et al: Transmission of mepivacaine hydrochloride (Carbocaine) across the human placenta. Anesthesiology 27:147-154. 1966

12. Fox GS, Houle GL, Desjardins PD, et al: Intrauterine fetal lidocaine concentrations during continuous epidural anesthesia. Amer J Obstet Gynec 110:896-899, 1971 13. Austen WG, Moran JM: Cardiac and peripheral vascular effects of lidocaine and procaineamide. Amer J Cardiol 10:701-707, 1965 14. Rromage PR, Robson JG: Concentrations of lignocaine in the blood after intravenous, intramuscular, epidural and endotracheal administration. Anaesthesia 16:461-478, 1961

15. Braid DP, Scott DB: Dosage of lignocaine in epidural block in relation to toxicity. Brit J Anaesth 38:596-602, 1966 16. Wingate MB, Wingate L, Iffy L, et al: The effect of epidural analgesia upon fetal and neonatal status. Amer J Obstet Gynec 119:llOl-1106, 1974 17. Zilianti M, Salazer JR, Aller J, et al: Fetal heart rate and pH of fetal capillary blood during epidural analgesia in labor. Obstet Gynec 36:881886, 1970 18. McDonald JS, Bjorkman LL, Reed EC: Epidural analgesia for obstetrics. Amer J Obstet Gynec 120:1055-1065, 1974

The effect of lumbar epidural anesthesia on fetal heart rate baseline variability.

Baseline fetal heart rate (FHR) variability has become an important parameter in the diagnosis of fetal distress when electronically monitoring the fe...
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