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The effect of epidural anesthesia on oxytocin-induced labor
The effect of epidural anesthesia on oxytocin-induced J.
S.
HENRY,
M.
B.
KINGSTON,
G.
B.
MAUGHAN,
Montreal,
Quebec
JR.,
labor M.D. M.D.
M.D.
Eighteen cases of induced labor at or near term were monitored with continuous amniotic pressure recordings, and the intensity, frequency, and uterine activity of contractions were measured. Epidural anesthesia was given at varying points in the first stage and maintained untiE delivery, and the progress of labor in terms of timedilatation and time-uterine work was measured in each case. No significant changes were noted in contractility or progress of labor in the series. Theoretical considerations suggest that in this series none of the known factors which change contractility were operative.
E P I D u R A L anesthesia has in recent years played an increasingly important role in the management of labor and dehvery. In spite of its common use there is still controversy over the effect it has on contractility and on the progress of labor. A few recent studies have compared the length of labor in cases with epidural and those without. Heinrichs, Kornmesser, and Tullochl reported shorter labors for both primiparas and multiparas, although they stated that Pitocin was given to many patients to counteract the secondary inertia which may follow epidural anesthesia. Nielsen and associates2 observed that a transient slowing and weakening of contractions might occur, although contractions usually remained strong and effective. Cowles3 found an ac-
celeration in primiparous labor but no change in multiparas, compared with a control group. Several recent studies have reported objective measurements of contractility. Vasicka and Kretchmer4 measured amniotic pressure in 9 patients given epidural anesthesia during oxytocin induced labor. They found no over-all inhibitory or stimulating effect on contractility, although they noted an almost consistent temporary fall in the intensity of contractions. Vasicka and co-workers’ further reported on 18 cases and noted again no important changes providing the maternal arterial pressure was maintained within normal limits. Acute postepidural hypotension resulted in decreased uterine contractility. This study is presented to add further objective evidence of the effect of epidural anesthesia on contractility and to attempt to correlate the contractility with the progress of labor.
From the Department of Obstetrics and Gynaecology, Royal Victoria Hospital and McGill University. The work presented in this paper was aided by the Medical Research Council of Canada Grant No. 298-88 and by a grant from the Banting Research Foundation.
Material Eighteen patients who were selected for induction of labor at or near term were chosen for this study. Table I outlines the significant details.
Presented at the Twenty-second Annual Meeting of the Society of Obstetricians and Gynaecologists of Canada, Jasper, Alberta, June 17-19, 1966. 350
Epidural
Table I. Ciinical
__-
I
Case No. 64
(
7
details
39
1
in oxytocin-induced
labor
351
of the 18 cases
I Age
anesthesia
I Parity G4,
( PO
Weeks
Dilatation at epidural (cm.)
Maternal blood pressure
Drug and concentration
42
10
Xylocaine
1%
Normotension
Normotension
64 22
22
Gl
37
5
Xylocaine
1%
65 4
35
Gl
40
7
Xylocaine
1%
65
10
21
Gl
39
6
Xylocaine
1%
Normotension
65
14
25
Gl
40
5
Xylocaine
1%
Normotension
65 20
22
Gl
41
6
Xylocaine
2%
Normotension
66 3
22
Gl
38
4
Xylocaine
1%
Normotension
66 5
21
Gl
40
6
Xylocaine
1%
Normotension
66 6
18
Gl
42
6
Xylocaine
1%
Normotension
64
17
24
G3,
P2
42
8
Xylocaine
1%
Normotension
64 20
28
G2.
Pl
40
5
Xylocaine
2 “7
Normotension
64 21
25
G4,
P2
40
7
Propitocaine
2%
Normotension
64 23
21
40
5
Propitocaine
2%
Normotension
65 3
26
P2
40
8
Carbocaine
2%
Normotension
65
7
22
P2, Al
40
6
Carbocaine
2%
Normotension
65 9
42
G6,
P4
38
6
Xylocaine
2%
Normotension
65
16
33
G3,
P2
41
Xylocaine
2%
Normotension
65
18
35
G3,
I’2
41
Xylocaine
2%
Hypotension -80
G3,
G3,
G4,
Pl,
Al
Remarks Low forceps, 2.860 grams, Apgar 10 Diabetes, hydramnios, low forceps, cord around neck, 4,060 grams Apgar 5 Difficult midforceps, 3,621 grams, Apgar 10 Low forceps, 3,200 grams, Apgar 9 Low forceps, 3.175 grams, Apgar 10 Mid forceps, 3.510 grams, Apgar 10 Spontaneous, 3010 grams, Apgar 10 Low forceps, 3,360 grams, Apgar 9 Spontaneous, 3,180 grams, Apgar 9 Low forceps, 3.600 grams, Apgar 9 Low forceps, 4,000 grams, Apgar 10 Spontaneous, 2.960 grams, Apgar 10 Spontaneous, 3,680 grams, Apgar 10 Spontaneous, 3,180 grams, Apgar 10 Spontaneous, 3,960 grams, Apgar 10 Rh negative with antibodies. spontaneous, 3,760 grams, Apgar 10 Low forceps, 3,190 grams. Apgar 10 Spontaneous, 3,360 grams, .4pgar 10
352
Henry, Kingston,
All our patients graphic examination and fetal maturity. centas had already study.
February 1, 1967 Am. J. Obst. & Gynec.
and Maughan
are submitted to radiofor placental position Those with anterior plabeen excluded from the
Methods
Before instrumentation for recording, each patient received a continuous infusion of Demerol and chlorpromazine at the initial rate of 0.1 mg. of Demerol and 0.05 mg. of chlorpromazine per minute and this continued until the epidural anesthetic was given. Analgesia in this amount does not significantly influence normal contractility.6* 7 Contractions were recorded by means of a fluid-filled polyvinyl catheter passed transabdominally into the amniotic cavity. The fetal heart rate was recorded with a cardiotachometer fed from the fetal ECG complex obtained by direct electrode contact with the fetus. Amniotic pressure and fetal heart rate were recorded on a Sanborn polygraph (Fig. 1). The fetal heart rate served in these cases
Fig.
1. Sample
tracing
of amniotic
fluid
pressure
as a monitor of fetal well-being. Its relation to contractility with epidural anesthesia was the subject of a previous study.* Labor was induced with a constant rate infusion of oxytocin beginning at 1 or 2 milliunits per minute and increasing to rates of 4 or 8 milliunits as needed. Cervical dilatation was assessed by sterile vaginal examination, and at a suitable point in the labor the membranes were ruptured artificially. At a suitable level of contractility the infusion rate of oxytocin was maintained constant and the patient’s position was not changed,9 in an effort to reduce to a minimum the variables which might affect contractility. Lumbar epidural anesthesia was performed by staff anesthetists and continued until after delivery. under their supervision. Maternal blood pressure and level of anesthesia were determined by the usual clinical methods. Anesthesia was begun when the patient became uncomfortable (rather than at a uniform dilatation) in order to simulate the
and fetal
heart
rate.
Volume Number
97 3
Epidural
clinical situation. The level of anesthesia was from T,, or T,, to L, or L, in all patients. Blood pressure was maintained at the preanesthetic level in all but one patient, who exhibited a fall to 80/O mm. Hg. This was rest.ored to normal with Methedrine. Results Contractility. First fifteen contractions during anesthsia. The fifteen contractions INTENSITY
BEFORE
I
WRING
,
PhttMO Multipam Awage
50
[BEFORE
~ DURING
t ‘\
‘\.
----Y--1 1 ‘\
---. I
, CABEB SNWtNG
mmH9
70
1
epidural before
IO
I
I
I
CASES SHOWHG
MXEABE
DECREASE
Fig. 2. Intensity of 15 contractions before compared with 15 contractions during epidural anesthesia.
BEFORE
Primipom Multipam Abropr
in oxytocin-induced
labor
353
and the first fifteen contractions during the epidural anesthesia were compared for changes in intensity, frequency, and uterine activity (Figs. 2, 3, and 4). In 5 cases the intensity rose and in 13 it fell. In 11 cases the frequency increased and in 7 it decreased. Uterine activity, the product of intensity and frequency, increased in 7 cases and in 11 there was a decrease. There was no significant difference between the primiparas and the multiparas. The degree of change in each parameter of contractility was analyzed and expressed as per cent of change from the pre-epidural values (Fig. 5). Intensity varied from an increase of 31 per cent to a decrease of 57 per cent. The average value was a decrease of 13.5 per cent. Frequency varied from an increase of 83 per cent to a decrease of 16 per cent with an average value of 9 per cent increase. Uterine activity varied between a 64 per cent increase and a 41 per cent decrease. The average value was a decrease of 4.3 per cent. There was no relationship between the degree of change in any parameter and the cervical dilatation at the initiation of the epidural anesthesia. An analysis of the relationship between the
IO FREQUENCY
anesthesia
UTERINE ACTIVITY
contrllmin.
t WRINi
Primpnra _----
- - -
CASES SHOWING
MMipam
INCREASE
CASES
SHOWING DECREASE
Fig., 3. Frequency
of 15 contractions
pared
contractions
with
anesthesia.
15
during
before comepidurai
Fig. 4. Uterine activity of 15 contractions before compared with 15 contractions during epidural anesthesia.
354
Henry,
Kingston,
and
February 1, 1967 Am. J. Obst. & Gynec.
Maughan
changes in the various parameters shows that the small over-all decrease in uterine activity is primarily the result of the depression of the intensity (Fig. 6). Effect of epidural anesthesia beyond the first fifteen contractions. The analysis of
uterine activity was carried out where possible to include the thirty contractions following the onset of the epidural anesthesia (Fig. 7). There was an average decrease of 32 Montevideo units, or 20 per cent in the primiparas, an average increase of 6 Monte-
60
60
60
INTENSITY
40
(%)
20 0 -20 -40
FREPUENCY
UTERINE ACTIVITY
40
.
l ’
20
.:;t
.
l e
‘g:‘.
l * .
0
’
-20
l .
-40
I 4 6 . INDIVIDUAL CASES 0 AVERAGE VALUES
6
4
IO
FIGURE 5:
Fig. with
5. Per cent 15 contractions
change in preceding
-60
CERVICAL
values for it. (Cervical
6
6
-60 4
IO
between
6
IO
15 contractions after epidural anesthesia dilatation is expressed in centimeters.)
-40
variation
6
DILATATION
-20
0 VARIATION
Fig. 6. Relationship anesthesia.
60
.
in
intensity
and
20 IN INTENSITY
uterine
40
compared
.
W
activity
caused
by
epidural
Volume
97
Number
3
Epidural
in oxytocin-induced
I --I
PRIMIPARAS
250
I50 i
20
15
IO
5
5
BEFORE
and during
IO
15 WRING
CONTRACTIONS
Fig. 7. Uterine activity before
labor
355
Cervical dilatation and uterine work. Cervical dilatation was then plotted against “uterine work.” This is the effort exhibited by the uterus during a given interval and is measured in millimeters of mercury by adding the intensities of all the contractions during that period.‘O When uterine work is plotted against dilatation, the slope of the line serves as an index of the efficiency of the uterus. Time-dilatation curves can only record the result without taking into account the contractility required to produce it. In Figs. 10 and 11, the cervical dilatation-uterine work curves of these groups are displayed. For the primiparous group the curves show greater efficiency in 6 cases, no change in one, and a period of reduced efficiency in the one who exhibited stationary dilatation. The remaining patient had epidural anesthesia in the second stage. In the multiparous group, 6 cases showed greater efficiency, one showed a period of decreased efficiency although progress was maintained, and 2 showed a period of more markedly decreased efficiency.
video units, or 4 per cent, in the multiparas. The over-all change for the series was a fall of 13 Montevideo units or 8.5 per cent. Progress of labor. Each case was then examined for the effect epidural anesthesia might have on the progress of labor. Cervical dilatation and time. Cervical dilatation was plotted against time to delivery. In Figs. 8 and 9, the “curves” have been separated along the ordinate of dilatation to exhibit each one individually. The time scale on the abscissa is maintained. In the primiparous group, 6 patients exhibited an accleration of dilatation during epidural anesthesia. In one the rate of dilata.tion remained steady. In one there was a period of one hour and 7 minutes of stationary dilatation; the ninth received her epidural anesthesia in the second stage. In the multiparous group the rate of dilatation accelerated in 5 cases; in one there was a slight decrease, but progress was maintained. In one there was a period of 40 minutes of stationary dilatation following the and in 2 cases the epiepidural anesthesia, dural anesthesia was given too close to full dilatation to assess the effect on progress. 350
anesthesia
epidural
anesthesia.
20
25
30
356
Henry,
Kingston,
and
I 6
b I
Maughan
February 1,1967 Am. J. Obst. & Gynec.
I 5
I 4 Noms
I 3
I 2
, I
t 0
T O CEWERV
Fig. 8.
TIME-DILATATION
h
I
CURVES FOR MULTIWRAS
41
3I IaJRS
Fig. 9.
To
#LIVERY
2.
I I
8
Volulne 97 Number 3
Epidural
UTERINE
WORK -DlLAlAlIoW
anesthesia
in oxytocin-induced
labor
357
CURVES FOR PRIMIPARAS
CERYICAL D)LAIATIoW
UTERINE
WRK
T O DELIVERY
Fig. 10. UTERINE
WORK--MLATATION
CURVES
FOR MULTIPARAS
CERWCU DILATA7lDK
c mmNg 6ow
I xl00
I 6nDD
UTERINE
Fig. 11.
I do
I sew rrmK
T O DELIVERY
I x00
I
2ooo
I m
t 0
358
Henry, Kingston,
and Maughan
Postepidural hypotension. The one patient who exhibited postepidural hypotension showed a decrease of 25.5 per cent in the intensity of her contractions, an increase of 19 per cent in their frequency, and a resultant fall of 5.8 per cent in uterine activity. Her labor exhibited a slight decreasein the rate of dilatation after the epidural anesthesia and the efficiency fell slightly as well. Comment
In this small seriesof induced labors there were minimal to marked individual variations in the parameters of contractility mentioned. There was not, however, a trend in either the primiparas or the multiparas suggesting a significant change in contractility with epidural anesthesia. The progress of labor, whether measured against time or against uterine work, did not appear to be materially affected by the epidural anesthesia. If any generalization may be drawn it should be to say that the labors tended to exhibit a slight acceleration of progressand greater efficiency. These are the conclusions to be drawn from the measurementsmade. On theoretical grounds how should we expect epidural anesthesia to affect induced labor? There is evidence that uterine contractility may be influenced in a number of ways: 1. Ferguson reflex. Although there has been no convincing proof to date of the existence in women of the reflex which Fergusonll observed in rabbits, it is probable that it plays a part in the augmentation of uterine activity which accompaniesdilatation in spontaneous labor. Certainly the total uterine activity observed as induced labor progressesis commonly greater than that expected of the infused oxytocin alone. The epidural anesthesiasin our casesdid not descendbelow L, or L, until the perineal dose was given during the second stage. It is unlikely then that an active Ferguson reflex, if present, would have been interfered with. 2. Effect of epinephrine and norepinephrine. The work of Garrett’2 and of Alvarez
February 1, 1967 Am. J. Obst. & Gym.
and Caldeyro-BarciaZ3 indicates that infusions of pure epinephrine are capable of depressing uterine contractility while norepinephrine increases the frequency of contractions and introduces incoordination. Infusions of extracts of the adrenal medulla which contain 80 per cent epinephrine and 20 per cent norepinephrine reduce the intensity and increase the frequency and tonus of contractions, and they become incoordinated. Caldeyro-Barcia6 suggests that “pain, anxiety and other conditions which increase the secretion of the adrenal medulla may disturb uterine contractility in a similar manner.” Since our patients did not experience even the average amount of pain, fear, anxiety, etc., as a result of the constant presence of attendants, the analgesic infusion, and the epidural anesthesia, it is unlikely that this factor was present in any significant sense. It is our belief, however, that in patients who are experiencing fear and pain in labor, the introduction of epidural anesthesiamay be responsible for an observed improvement in the progress of labor for the reasons mentioned above. 3. Position of the mother. Caldeyro-Barcia and ’ co-worker? have described a reciprocal change in the intensity and frequency of contractions which occurs when some patients change from dorsal to lateral position. We have noted these changes in some of our monitored labors and maintained the patient’s position as much as possiblein this seriesto eliminate this source of error in our observations. 4. Oxytocin. The amount of contractility induced by a constant rate infusion of oxytotin increasesfor a period of time and then remains stabIe as long as that rate of infusion is maintained14. This principle was observed in the series; no observations were begun until the period of stable induced contractility was reached. On these grounds it might have been reasonable to predict that epidural anesthesia would not produce any marked changes in the contractility or the progress of these labors.
Volume Number
97 3
Epidural
anesthesia
in oxytocin-induced
labor
359
REFERENCES
1. Heinrichs, W. L., Kornmesser, J. G., and Tulloch, J. A.: Harper Hosp. Bull. 20: 6, 1962. 2. Nielsen, J. S., Spoerel, W. E., Keenleyside, H. B., Slater, P. E., and Clancy, P. R.: Canad. Anesth. Sot. J. 9: 143, 1962. 3. Cowles, G. T.: Obst. & Gynec. 26: 734, 1965. 4. Vasicka, A., and AM. J. Kretchmer, H.: OBST. & GYNEC. 82: 600, 1961. 5. Vasicka, A., Hutchison, H. T., Eng, M., and Allen, C. R.: AM. J. OBST. & GYNEC. 90: 800, 1964. 6. Caldeyro-Barcia, R.: Proc. Second Internat. Congr. Gynec. & Obst. vol. 1: 65, 1958. 7. Caldeyro-Barcia, R., Poseiro, J. J., Alvarez, H., and Test, P.: AM. J. OBST. & GYNEC. 75: 1088, 1958. 8. Henry, J. S., Jr., Hierz, O., Maughan, G. B., and Melanson, G. A.: Proc. Symposium on the Effect of Labor on the Fetus and
9.
10.
11. 12. 13. 14.
Newborn, Montevideo, Uruguay, October, 1964. In press. Caldeyro-Barcia, R., Noriega-Guerra, L., Cibils, L. A., Alvarez, H., Poseiro, J. J., Pose, S. V., Sica-Blanco, Y., Menda-Bauer, C., and Gonzalez-Pan&a, V. H.: Anr. J. OBST. & GYNEC. 80: 284, 1960. Alvarez, H., Cibils, L. A., and GonzalesPan&a, V. H.: In Caldeyro-Barcia, R., and Heller, H., editors: Oxytocin, New York, 1961, Pergamon Press, Inc., p. 203. Surg., Gynec. & Obst. Ferguson, J. K. W.: 73: 379, 1941. Garrett, W.: J. Obst. & Gynaec Brit. Emp. 61: 586, 1954. Alvarez, H., and Caldeyro-Barcia, R.: Maternidade e Infancia 13: 11, 1954. Sica-Blanco, Y., and Sala, N. L.: In Caldeyro-Barcia, R., and Heller, H., editors: Oxytocin, New York, 1961, Pergamon Press, Inc., p. 127.
S.
HENRY,
M.
B.
KINGSTON,
G.
B.
MAUGHAN,
Montreal,
Quebec
JR.,
labor M.D. M.D.
M.D.
Eighteen cases of induced labor at or near term were monitored with continuous amniotic pressure recordings, and the intensity, frequency, and uterine activity of contractions were measured. Epidural anesthesia was given at varying points in the first stage and maintained untiE delivery, and the progress of labor in terms of timedilatation and time-uterine work was measured in each case. No significant changes were noted in contractility or progress of labor in the series. Theoretical considerations suggest that in this series none of the known factors which change contractility were operative.
E P I D u R A L anesthesia has in recent years played an increasingly important role in the management of labor and dehvery. In spite of its common use there is still controversy over the effect it has on contractility and on the progress of labor. A few recent studies have compared the length of labor in cases with epidural and those without. Heinrichs, Kornmesser, and Tullochl reported shorter labors for both primiparas and multiparas, although they stated that Pitocin was given to many patients to counteract the secondary inertia which may follow epidural anesthesia. Nielsen and associates2 observed that a transient slowing and weakening of contractions might occur, although contractions usually remained strong and effective. Cowles3 found an ac-
celeration in primiparous labor but no change in multiparas, compared with a control group. Several recent studies have reported objective measurements of contractility. Vasicka and Kretchmer4 measured amniotic pressure in 9 patients given epidural anesthesia during oxytocin induced labor. They found no over-all inhibitory or stimulating effect on contractility, although they noted an almost consistent temporary fall in the intensity of contractions. Vasicka and co-workers’ further reported on 18 cases and noted again no important changes providing the maternal arterial pressure was maintained within normal limits. Acute postepidural hypotension resulted in decreased uterine contractility. This study is presented to add further objective evidence of the effect of epidural anesthesia on contractility and to attempt to correlate the contractility with the progress of labor.
From the Department of Obstetrics and Gynaecology, Royal Victoria Hospital and McGill University. The work presented in this paper was aided by the Medical Research Council of Canada Grant No. 298-88 and by a grant from the Banting Research Foundation.
Material Eighteen patients who were selected for induction of labor at or near term were chosen for this study. Table I outlines the significant details.
Presented at the Twenty-second Annual Meeting of the Society of Obstetricians and Gynaecologists of Canada, Jasper, Alberta, June 17-19, 1966. 350
Epidural
Table I. Ciinical
__-
I
Case No. 64
(
7
details
39
1
in oxytocin-induced
labor
351
of the 18 cases
I Age
anesthesia
I Parity G4,
( PO
Weeks
Dilatation at epidural (cm.)
Maternal blood pressure
Drug and concentration
42
10
Xylocaine
1%
Normotension
Normotension
64 22
22
Gl
37
5
Xylocaine
1%
65 4
35
Gl
40
7
Xylocaine
1%
65
10
21
Gl
39
6
Xylocaine
1%
Normotension
65
14
25
Gl
40
5
Xylocaine
1%
Normotension
65 20
22
Gl
41
6
Xylocaine
2%
Normotension
66 3
22
Gl
38
4
Xylocaine
1%
Normotension
66 5
21
Gl
40
6
Xylocaine
1%
Normotension
66 6
18
Gl
42
6
Xylocaine
1%
Normotension
64
17
24
G3,
P2
42
8
Xylocaine
1%
Normotension
64 20
28
G2.
Pl
40
5
Xylocaine
2 “7
Normotension
64 21
25
G4,
P2
40
7
Propitocaine
2%
Normotension
64 23
21
40
5
Propitocaine
2%
Normotension
65 3
26
P2
40
8
Carbocaine
2%
Normotension
65
7
22
P2, Al
40
6
Carbocaine
2%
Normotension
65 9
42
G6,
P4
38
6
Xylocaine
2%
Normotension
65
16
33
G3,
P2
41
Xylocaine
2%
Normotension
65
18
35
G3,
I’2
41
Xylocaine
2%
Hypotension -80
G3,
G3,
G4,
Pl,
Al
Remarks Low forceps, 2.860 grams, Apgar 10 Diabetes, hydramnios, low forceps, cord around neck, 4,060 grams Apgar 5 Difficult midforceps, 3,621 grams, Apgar 10 Low forceps, 3,200 grams, Apgar 9 Low forceps, 3.175 grams, Apgar 10 Mid forceps, 3.510 grams, Apgar 10 Spontaneous, 3010 grams, Apgar 10 Low forceps, 3,360 grams, Apgar 9 Spontaneous, 3,180 grams, Apgar 9 Low forceps, 3.600 grams, Apgar 9 Low forceps, 4,000 grams, Apgar 10 Spontaneous, 2.960 grams, Apgar 10 Spontaneous, 3,680 grams, Apgar 10 Spontaneous, 3,180 grams, Apgar 10 Spontaneous, 3,960 grams, Apgar 10 Rh negative with antibodies. spontaneous, 3,760 grams, Apgar 10 Low forceps, 3,190 grams. Apgar 10 Spontaneous, 3,360 grams, .4pgar 10
352
Henry, Kingston,
All our patients graphic examination and fetal maturity. centas had already study.
February 1, 1967 Am. J. Obst. & Gynec.
and Maughan
are submitted to radiofor placental position Those with anterior plabeen excluded from the
Methods
Before instrumentation for recording, each patient received a continuous infusion of Demerol and chlorpromazine at the initial rate of 0.1 mg. of Demerol and 0.05 mg. of chlorpromazine per minute and this continued until the epidural anesthetic was given. Analgesia in this amount does not significantly influence normal contractility.6* 7 Contractions were recorded by means of a fluid-filled polyvinyl catheter passed transabdominally into the amniotic cavity. The fetal heart rate was recorded with a cardiotachometer fed from the fetal ECG complex obtained by direct electrode contact with the fetus. Amniotic pressure and fetal heart rate were recorded on a Sanborn polygraph (Fig. 1). The fetal heart rate served in these cases
Fig.
1. Sample
tracing
of amniotic
fluid
pressure
as a monitor of fetal well-being. Its relation to contractility with epidural anesthesia was the subject of a previous study.* Labor was induced with a constant rate infusion of oxytocin beginning at 1 or 2 milliunits per minute and increasing to rates of 4 or 8 milliunits as needed. Cervical dilatation was assessed by sterile vaginal examination, and at a suitable point in the labor the membranes were ruptured artificially. At a suitable level of contractility the infusion rate of oxytocin was maintained constant and the patient’s position was not changed,9 in an effort to reduce to a minimum the variables which might affect contractility. Lumbar epidural anesthesia was performed by staff anesthetists and continued until after delivery. under their supervision. Maternal blood pressure and level of anesthesia were determined by the usual clinical methods. Anesthesia was begun when the patient became uncomfortable (rather than at a uniform dilatation) in order to simulate the
and fetal
heart
rate.
Volume Number
97 3
Epidural
clinical situation. The level of anesthesia was from T,, or T,, to L, or L, in all patients. Blood pressure was maintained at the preanesthetic level in all but one patient, who exhibited a fall to 80/O mm. Hg. This was rest.ored to normal with Methedrine. Results Contractility. First fifteen contractions during anesthsia. The fifteen contractions INTENSITY
BEFORE
I
WRING
,
PhttMO Multipam Awage
50
[BEFORE
~ DURING
t ‘\
‘\.
----Y--1 1 ‘\
---. I
, CABEB SNWtNG
mmH9
70
1
epidural before
IO
I
I
I
CASES SHOWHG
MXEABE
DECREASE
Fig. 2. Intensity of 15 contractions before compared with 15 contractions during epidural anesthesia.
BEFORE
Primipom Multipam Abropr
in oxytocin-induced
labor
353
and the first fifteen contractions during the epidural anesthesia were compared for changes in intensity, frequency, and uterine activity (Figs. 2, 3, and 4). In 5 cases the intensity rose and in 13 it fell. In 11 cases the frequency increased and in 7 it decreased. Uterine activity, the product of intensity and frequency, increased in 7 cases and in 11 there was a decrease. There was no significant difference between the primiparas and the multiparas. The degree of change in each parameter of contractility was analyzed and expressed as per cent of change from the pre-epidural values (Fig. 5). Intensity varied from an increase of 31 per cent to a decrease of 57 per cent. The average value was a decrease of 13.5 per cent. Frequency varied from an increase of 83 per cent to a decrease of 16 per cent with an average value of 9 per cent increase. Uterine activity varied between a 64 per cent increase and a 41 per cent decrease. The average value was a decrease of 4.3 per cent. There was no relationship between the degree of change in any parameter and the cervical dilatation at the initiation of the epidural anesthesia. An analysis of the relationship between the
IO FREQUENCY
anesthesia
UTERINE ACTIVITY
contrllmin.
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CASES SHOWING
MMipam
INCREASE
CASES
SHOWING DECREASE
Fig., 3. Frequency
of 15 contractions
pared
contractions
with
anesthesia.
15
during
before comepidurai
Fig. 4. Uterine activity of 15 contractions before compared with 15 contractions during epidural anesthesia.
354
Henry,
Kingston,
and
February 1, 1967 Am. J. Obst. & Gynec.
Maughan
changes in the various parameters shows that the small over-all decrease in uterine activity is primarily the result of the depression of the intensity (Fig. 6). Effect of epidural anesthesia beyond the first fifteen contractions. The analysis of
uterine activity was carried out where possible to include the thirty contractions following the onset of the epidural anesthesia (Fig. 7). There was an average decrease of 32 Montevideo units, or 20 per cent in the primiparas, an average increase of 6 Monte-
60
60
60
INTENSITY
40
(%)
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FREPUENCY
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FIGURE 5:
Fig. with
5. Per cent 15 contractions
change in preceding
-60
CERVICAL
values for it. (Cervical
6
6
-60 4
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between
6
IO
15 contractions after epidural anesthesia dilatation is expressed in centimeters.)
-40
variation
6
DILATATION
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Fig. 6. Relationship anesthesia.
60
.
in
intensity
and
20 IN INTENSITY
uterine
40
compared
.
W
activity
caused
by
epidural
Volume
97
Number
3
Epidural
in oxytocin-induced
I --I
PRIMIPARAS
250
I50 i
20
15
IO
5
5
BEFORE
and during
IO
15 WRING
CONTRACTIONS
Fig. 7. Uterine activity before
labor
355
Cervical dilatation and uterine work. Cervical dilatation was then plotted against “uterine work.” This is the effort exhibited by the uterus during a given interval and is measured in millimeters of mercury by adding the intensities of all the contractions during that period.‘O When uterine work is plotted against dilatation, the slope of the line serves as an index of the efficiency of the uterus. Time-dilatation curves can only record the result without taking into account the contractility required to produce it. In Figs. 10 and 11, the cervical dilatation-uterine work curves of these groups are displayed. For the primiparous group the curves show greater efficiency in 6 cases, no change in one, and a period of reduced efficiency in the one who exhibited stationary dilatation. The remaining patient had epidural anesthesia in the second stage. In the multiparous group, 6 cases showed greater efficiency, one showed a period of decreased efficiency although progress was maintained, and 2 showed a period of more markedly decreased efficiency.
video units, or 4 per cent, in the multiparas. The over-all change for the series was a fall of 13 Montevideo units or 8.5 per cent. Progress of labor. Each case was then examined for the effect epidural anesthesia might have on the progress of labor. Cervical dilatation and time. Cervical dilatation was plotted against time to delivery. In Figs. 8 and 9, the “curves” have been separated along the ordinate of dilatation to exhibit each one individually. The time scale on the abscissa is maintained. In the primiparous group, 6 patients exhibited an accleration of dilatation during epidural anesthesia. In one the rate of dilata.tion remained steady. In one there was a period of one hour and 7 minutes of stationary dilatation; the ninth received her epidural anesthesia in the second stage. In the multiparous group the rate of dilatation accelerated in 5 cases; in one there was a slight decrease, but progress was maintained. In one there was a period of 40 minutes of stationary dilatation following the and in 2 cases the epiepidural anesthesia, dural anesthesia was given too close to full dilatation to assess the effect on progress. 350
anesthesia
epidural
anesthesia.
20
25
30
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and
I 6
b I
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February 1,1967 Am. J. Obst. & Gynec.
I 5
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Fig. 8.
TIME-DILATATION
h
I
CURVES FOR MULTIWRAS
41
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Fig. 9.
To
#LIVERY
2.
I I
8
Volulne 97 Number 3
Epidural
UTERINE
WORK -DlLAlAlIoW
anesthesia
in oxytocin-induced
labor
357
CURVES FOR PRIMIPARAS
CERYICAL D)LAIATIoW
UTERINE
WRK
T O DELIVERY
Fig. 10. UTERINE
WORK--MLATATION
CURVES
FOR MULTIPARAS
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T O DELIVERY
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358
Henry, Kingston,
and Maughan
Postepidural hypotension. The one patient who exhibited postepidural hypotension showed a decrease of 25.5 per cent in the intensity of her contractions, an increase of 19 per cent in their frequency, and a resultant fall of 5.8 per cent in uterine activity. Her labor exhibited a slight decreasein the rate of dilatation after the epidural anesthesia and the efficiency fell slightly as well. Comment
In this small seriesof induced labors there were minimal to marked individual variations in the parameters of contractility mentioned. There was not, however, a trend in either the primiparas or the multiparas suggesting a significant change in contractility with epidural anesthesia. The progress of labor, whether measured against time or against uterine work, did not appear to be materially affected by the epidural anesthesia. If any generalization may be drawn it should be to say that the labors tended to exhibit a slight acceleration of progressand greater efficiency. These are the conclusions to be drawn from the measurementsmade. On theoretical grounds how should we expect epidural anesthesia to affect induced labor? There is evidence that uterine contractility may be influenced in a number of ways: 1. Ferguson reflex. Although there has been no convincing proof to date of the existence in women of the reflex which Fergusonll observed in rabbits, it is probable that it plays a part in the augmentation of uterine activity which accompaniesdilatation in spontaneous labor. Certainly the total uterine activity observed as induced labor progressesis commonly greater than that expected of the infused oxytocin alone. The epidural anesthesiasin our casesdid not descendbelow L, or L, until the perineal dose was given during the second stage. It is unlikely then that an active Ferguson reflex, if present, would have been interfered with. 2. Effect of epinephrine and norepinephrine. The work of Garrett’2 and of Alvarez
February 1, 1967 Am. J. Obst. & Gym.
and Caldeyro-BarciaZ3 indicates that infusions of pure epinephrine are capable of depressing uterine contractility while norepinephrine increases the frequency of contractions and introduces incoordination. Infusions of extracts of the adrenal medulla which contain 80 per cent epinephrine and 20 per cent norepinephrine reduce the intensity and increase the frequency and tonus of contractions, and they become incoordinated. Caldeyro-Barcia6 suggests that “pain, anxiety and other conditions which increase the secretion of the adrenal medulla may disturb uterine contractility in a similar manner.” Since our patients did not experience even the average amount of pain, fear, anxiety, etc., as a result of the constant presence of attendants, the analgesic infusion, and the epidural anesthesia, it is unlikely that this factor was present in any significant sense. It is our belief, however, that in patients who are experiencing fear and pain in labor, the introduction of epidural anesthesiamay be responsible for an observed improvement in the progress of labor for the reasons mentioned above. 3. Position of the mother. Caldeyro-Barcia and ’ co-worker? have described a reciprocal change in the intensity and frequency of contractions which occurs when some patients change from dorsal to lateral position. We have noted these changes in some of our monitored labors and maintained the patient’s position as much as possiblein this seriesto eliminate this source of error in our observations. 4. Oxytocin. The amount of contractility induced by a constant rate infusion of oxytotin increasesfor a period of time and then remains stabIe as long as that rate of infusion is maintained14. This principle was observed in the series; no observations were begun until the period of stable induced contractility was reached. On these grounds it might have been reasonable to predict that epidural anesthesia would not produce any marked changes in the contractility or the progress of these labors.
Volume Number
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anesthesia
in oxytocin-induced
labor
359
REFERENCES
1. Heinrichs, W. L., Kornmesser, J. G., and Tulloch, J. A.: Harper Hosp. Bull. 20: 6, 1962. 2. Nielsen, J. S., Spoerel, W. E., Keenleyside, H. B., Slater, P. E., and Clancy, P. R.: Canad. Anesth. Sot. J. 9: 143, 1962. 3. Cowles, G. T.: Obst. & Gynec. 26: 734, 1965. 4. Vasicka, A., and AM. J. Kretchmer, H.: OBST. & GYNEC. 82: 600, 1961. 5. Vasicka, A., Hutchison, H. T., Eng, M., and Allen, C. R.: AM. J. OBST. & GYNEC. 90: 800, 1964. 6. Caldeyro-Barcia, R.: Proc. Second Internat. Congr. Gynec. & Obst. vol. 1: 65, 1958. 7. Caldeyro-Barcia, R., Poseiro, J. J., Alvarez, H., and Test, P.: AM. J. OBST. & GYNEC. 75: 1088, 1958. 8. Henry, J. S., Jr., Hierz, O., Maughan, G. B., and Melanson, G. A.: Proc. Symposium on the Effect of Labor on the Fetus and
9.
10.
11. 12. 13. 14.
Newborn, Montevideo, Uruguay, October, 1964. In press. Caldeyro-Barcia, R., Noriega-Guerra, L., Cibils, L. A., Alvarez, H., Poseiro, J. J., Pose, S. V., Sica-Blanco, Y., Menda-Bauer, C., and Gonzalez-Pan&a, V. H.: Anr. J. OBST. & GYNEC. 80: 284, 1960. Alvarez, H., Cibils, L. A., and GonzalesPan&a, V. H.: In Caldeyro-Barcia, R., and Heller, H., editors: Oxytocin, New York, 1961, Pergamon Press, Inc., p. 203. Surg., Gynec. & Obst. Ferguson, J. K. W.: 73: 379, 1941. Garrett, W.: J. Obst. & Gynaec Brit. Emp. 61: 586, 1954. Alvarez, H., and Caldeyro-Barcia, R.: Maternidade e Infancia 13: 11, 1954. Sica-Blanco, Y., and Sala, N. L.: In Caldeyro-Barcia, R., and Heller, H., editors: Oxytocin, New York, 1961, Pergamon Press, Inc., p. 127.