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Instrument delivery and the fetal heart rate
Instrument delivery and the fetal heart rate JOHN Los
“Here
V.
Angeles,
KELLY,
M.D.
California
the heart
may
give
a useful
lesson
to the head
. . . .”
The Task, William
0 B s T E T R I c s is a field which is characterized by a scarcity of objective measurements. Despite the current advancements in scientific methodology, there is a disturbing absence of techniques which could precisely quantitate factors such as fetal size, the degree of flexion of the fetal head, the amount of moulding, and the station of the head. Consequently, obstetricians are compelled to rely on inaccurate assessments and unreliable estimates. Subjective practices are particularly apparent in the procedure of instrument delivery. Prevalent therein are such personal biases as to which forceps is the most appropriate to use and as to what constitutes a difficult pull. The adoption of a more objective approach is imperative for the practice of optimal obstetrics and the elimination of birth trauma. Every instrument birth involves physical forces: an extractive device is mechanically applied to the fetal head; intermittent traction forces are then exerted upon the head until the resistive forces of the perineum are overcome. Since these forces can be measured, it should be possible to define the mechanics involved so that delivery can be accomplished with maximal efficiency. This must be combined with a constant awareness of the fetal status, since the forces involved must be subservient to fetal wellbeing.
From the Department Gynecology, University Medical Center.
of Obstetrics of California
Cowper
Concomitant assessment of both should provide information for a scientific approach to instrument delivery. Present-day practices of birth by force are not much more advanced than those of a century ago. Only recently has the operative delivery by the vaginal route been invested with an atmosphere of scientific objectivity. The inauguration of the Apgar scoring system1 and the introduction of the metric forceps? are laudable advances. Even further expansion of objectivity in obstetrics is desirable particularly in regard to the association of instrument birth and fetal trauma. What is the physiologic status of the fetus during instrument delivery? Does the fetus react when it is subjected to potentially dangerous compression of its brain? Is there some indication from the fetus when its margin of cerebral safety is being surpassed ? In an effort to obtain answers to these questions it was planned to monitor a series of vaginal deliveries in which instruments were used to achieve birth. Attention was focused on evaluating the condition of the infant while it was being delivered, the amount of compression being exerted on its head during birth, and the status of the infant during its neonatal and subsequent course. Method Determination of the status of the fetus is restricted to one measurable index-its cardiac activity. To observe this criterion, the
and
529
530
Fig.
1. Calibrated
Fig. 2. gauges.
Fig.
October 15, 1963 Am. J. Obst. & Gynec.
Kelly
Bill
Forrrps
3. Forceps
monitorccl
with
handle.
x&traction
toe
strain
with
shank
strain
gauge.
fetal heart action was recorded with electrocardiographic techniques employing electrodes on the maternal abdomen and fetal scalp. The electrocardiographic tracings were evaluated manually, and the instantaneous rate!’ for each 4 second period was determined and recorded. The degree to which obstetrical instruments compress the fetal brain still eludes direct measurement. An indirect assessment can be obtained by mensuration of the traction exerted on the head during delivery. The instruments selected for this study were the Simpson obstetrical forceps and the Malmstrijm vacuum extractor. The amount
of traction force accomplished by each of these devices during a delivery was determined by attaching a metrically monitored Bill axis-traction handle to the forceps 01 vacuum extractor for all deliveries. This handle was equipped for measurement of pull by the incorporation of a calibrated spring-gauge, and a scale from which the amount of traction in pounds could be easily read at all times (Fig. 1). In addition, most of the forceps deliveries were accomplished by Simpson forceps to which miniature strain gauges had been applied in order to appraise electronically the forces at work (Figs. 2 and 3j. The vacuum extractor was applied to the fetal scalp by gradually increasing the negativ-e pressure inside the cup by increments of 0.1 Kg. per square centimeter over a 7 minute period to a total cup pressure of 0.7 or 0.8 Kg. per square centimeter. Patients were selected for whom elective instrument delivery was contemplated and in whom there was no detectable maternal or fetal distress. Patients were excluded who had received narcotics less than an hour before delivery or who had developed hypotension after receiving the anesthesia. Ninetytwo per cent of the deliveries in this series were accomplished under spinal, epidural, or caudal anesthesia. The deliveries were effected without the assistance of fundal pressure or expulsive efforts by the mothers. t\ttempts were made to synchronize the instrument pulls with the uterine contractions. Episiotomies were performed on all subjects. The fetal cardiac rate changes were recorded in 62 babies. There were 44 infants delivered by the forceps and 18 by the vacuum extractor. The latter device was employed unsuccessfully in 7 instances prior to delivery by forceps. Thirty-five of the 62 babies were delivered from low pelvic stations: 27 infants had mid-pelvic deliveries.*
“A mid-pelvic delivery mcnt bit-th in which the
an occiput transverse vertex is at a zwo, traction.
is herein fetal head
defined requires
as any rotation
instrufrom
or posterior position, or in which plus one or plus two station prior
the tc,
Volume Number
87 4
Table
Instrument
I. Fetal
heart
rates and instrument
application
(44 9 20 15
Tachycardia Eucardia Bradycardia During traction Tachycardia Eucardia Bradycardia
*Excludes
62 final
pulls) (20%) (47%) (33%)
( 139 pulls) 11 (8%) 23 (17%) 105 (75%)
After traction* Tachycardia Eucardia Bradycardia
and
fetal
heart
rate
531
delivery
FfWCf$S During
delivery
(95 pulls) 23 (25%) 35 (59%) 37 (39%)
Vacuum
extrattor
Total
(18 4 13 1
pull) (22%) (72%) (6%)
(62 13 33 16
pulls) (21%) (53%) (26%)
(108 14 19 75
pulls) (13%) (17%) (70%)
(247 pulls) 25 (10%) 42 (17%) 180 (73%)
(90 pulls) 26 (29%) 34 (38%) 30 (33%)
(185 pulls) 49 (27%) 69 (37%) 67 (36%)
pulls.
There was a total of 139 forceps pulls and 108 vacuum extractor pulls. The average duration of traction was 40 seconds in both groups. Individual pulls ranged from 5 seconds to 90 seconds in the forceps group, and 10 seconds to 105 seconds in the vacuum extractor group. The intensity of individual forceps pulls varied from 10 to 80 pounds (with an average of 43.8 pounds); with vacuum extraction pulls, the extractive forces ranged from 10 to 40 pounds (with an average of 30 pounds). The vacuum extractor will detach from the fetal scalp when traction force on it exceeds 40 pounds (with cup pressure of 0.8 Kg. per square centimeter) .I’ The condition of each newborn infant w’as evaluated at one minute of life and the infant was scored according to the Apgar system.l Results Heart rate changes during instrument application. The frequencies of appearance of tachycardia (a fetal heart rate over 160) and bradycardia (a fetal heart rate under 100) during the periods in which the forceps or vacuum extractor was being applied are listed in Table I. It should be noted that a rapid fetal heart rate occurred nearly as often with the positioning of forceps (20 per cent) as it did with the application of the vacuum extractor (22 per cent). However, a slowing of the baby’s pulse was induced much more often during the manipu-
lation of forceps (Fig. 4) than it was during attachment of the vacuum extractor; 1 of every 3 forceps applications was associated with a fetal bradycardia, whereas in only 1 of the 18 cases of vacuum extraction . . . apphcatron did the fetal heart rate slow. Heart rate changes during traction. A comparison of the effects of forceps and vacuum extractor traction on the fetal heart rate is given in Table I. The striking effect of instrument traction was that it very often evoked a slowing of the fetal heart rate. Bradycardia occurred in the distinct majority of pulls (73 per cent) and it appeared as commonly with forceps traction as with vacuum extractor traction. The severity of the bradycardia induced by both types of instruments did not seem to be correlated with the intensity of traction, except that the fetal heart rate slowed when the pull reached between 10 and 20 pounds of force and remained below 100 until the pull was reduced to less than 20 pounds. The fetal heart rate during traction usually ranged between 60 and 90 with occasional drops to the 40 to 60 range. These very slow rates occurred as often with 30 pound pulls as with 70 pound efforts (Fig. 5) Regardless of the type of instrument being used, when bradycardia appeared its onset was usually rapid, with the heart rate slowing some 40 to 50 beats within a few seconds (Fig. 5). Tachycardia, on the other hand, was usually gradual in onset.
532
October Am. J. Obst.
Kelly
IOSEC. / I+- 717" 112
FETAL HEARTRATE 7$
v
FORCEPS Fig. 4. Forceps
APPLICATION
application
and fetal
heart
t
ROTATION
AND
rate.
FETAL HEART RATE
0 Ibs.
15
35
50
60
5
15
traction
and
the fetal
20 Ibs.
78
35
60
80
70
heart
rate.
FORCEPS TRAGTION
8+
ARRHYTllMlA
88
FETAL HEART RATE Fig. 6. Forceps
traction
0 Ibs.
FOIVXPS TRACTION-
Fig. 5. Forceps
IO
and arrhythmia
of fetal
heart
rate.
0 Ibs.
IS0
ILO
15, 1963 & Gynec.
Volume
87
Number
4
Table
II. Fetal heart
Instrument
rates and infant No.
During
heart
rate
533
scores
infants
High
Apgar
Low
Apgar
13 (21%) 33 (53%) 16 (26%) 62
12 (25%) 29 (60%) 8 (15%) 49
1 (8%‘) 4 (32%) 8 (607~) 13
4 (7%) 6 (9%) 52 (84%) 62
4 (8%) 6 (12%) 39 (80%‘) 49
0 (0%) 0 (0%) 13 (100%) iii-
5 (9%) 30 (51%) 23 (40%) -’ 58”
5 (11%) 24 (53%) 16 (36%) 45
traction
Tachycardia Eucardia Bradycardia *Excludes
fetal
traction
Tachycardia Eucardia Bradycardia
Aft er
of
and
application
Tachycardia Eucardia Bradycardia During
Apgar
delivery
4 infants
who
were
delivered
with
only
one
-
0 (0%)
6 (46%) 7 (54%) 13
pull
Heart rate changes following traction. The status of the fetal heart rates in the 30 second periods immediately following cessation of instrument traction is listed in Table I. (The time periods following the final traction efforts of the 62 deliveries are not included because of the changes in pulmonary and cardiovascular dynamics which occurred upon birth of the baby’s head and its initial respiration.) A rapid heart rate occurred approximately as often after forceps traction as after vacuum extractor traction; the same held true for the appearance of a slow heart rate. In regard to the relation of the posttraction heart rate to the pattern during the preceding traction, the following changes were observed: The majority of heart rates during instrument traction (73 per cent) were slow; after cessation of traction approximately one third persisted with bradycardia (for only a short time), and one quarter developed a rapid increase in rate to levels above 160 which persisted for a short time before eventual return to normal levels. The remainder promptly resumed normal rates when the pull was stopped. A resimilar fractionation of posttraction sponses was noted in both the forceps and the vacuum extractor groups. In instances where the heart rates during traction were
normal or rapid, they usually were normal in the posttraction periods. Irregularities in the fetal heart rate. Cardiac rate irregularities were occasionally observed in this series of monitored instrument deliveries (Fig. 6). Four infants demonstrated arrhythmias, 2 in the forceps group and 2 in the vacuum extractor group. In these 4 infants, irregularities had not been observed in the prenatal periods and were not present after birth. Two of these babies had pressure applied to their heads after delivery without eliciting an arrhythmic response in the heart rate. Apgar scores and fetal heart rate changes. An Apgar score of below 7 is accepted as an indication of infant depression at one minute of life.” In this series of 62 instrument-delivered babies, there were 13 who had an Apgar score of less than 7. If the changes in the fetal heart rate are to provide help to the physician in predicting possible asphyxia of the infant at birth, then we must scrutinize the fetal heart rate changes, in the deliveries of the 13 depressed babies, for clues which might allow us to predict the development of neonatal apnea. In Table II the heart rate alterations during the application, traction, and posttraction phases of instrument delivery are listed for both normal and depressed babies. It is
534
Table
Kelly
III.
Difficult
forceps
and Apgar scores (44 cases) -__-..-~~~ ~~~~-~Total
Fifty pounds or more Less than fifty pounds Total traction time more than 3 min. Total traction time less than 3 min. Total
forceps
deliveries
Apear
15 29 9 135
Apgar 0 to 6
9 (60%) 25 (86%) 8 (72%) 26_____ (74%)
44
apparent that only in the phase of instrument application did the normal group (Apgar score of 7 or greater) and depressed group (Apgar score less than 7) have widely differing incidences of fetal heart rate changes. Of the 49 infants who were alert at birth, 8 (15 per cent) had had bradycardia during positioning of the instruments. In contrast, of the 13 infants who were depressed at birth, 8 (60 per cent) had bradycardia during instrument application. During instrument application 16 babies developed bradycardia. In 15 of the 16 cases, the instruments used were forceps. It is of interest, that forceps were the instruments employed in 7 of the 8 infants who had low Apgar scores at birth. A review of the fetal heart rate patterns of these 7 depressed infants shows that 3 maintained a persistent slow heart rate from application of the forceps to birth; the remaining 3 babies had recurrent bradycardia only during the extraction efforts. Apgar scores and difficulty of delivery. It would seem that infants who required numerous extractive efforts and/or particularly intensive pulls would be likely to be depressed at birth. In Table III the effects of these factors are assessed for the 44 infants delivered by forceps. It is evident that the intensity of pull did appear to be a particularly prominent factor in the production of infant depression. On the other hand, an unusual number of extraction efforts (measured in total traction time) seemed to have no adverse effect on the baby’s condition at birth. Apropos to the danger associated with a difficult pull, the station from which the head was delivered, appeared important. Table IV points out that 1 out of every 3
7 to 10
34
6 4 1 9
(77%)
(40%) (14%) (9%) (26%)
10 (23%:)
deliveries accomplished from a mid-pelvic station resulted in the birth of an asphyxic baby. Outcome of the 62 infants. All of the 49 newborn infants with Apgar scores of 7 or above did well during their hospital courses. Follow-up has been possible on 22 of these 19 infants, and all have exhibited normal development and show no evidence of cerebral damage. All of the 13 initially depressed infants responded to resuscitative measures and their subsequent neonatal courses were uneventful. Twleve of the 13 infants were discharged as normal from the hospital during the first week of life. One baby, whose weight was 4 pounds, 4 ounces at birth, was discharged as normal at one month of age when its weight had reached 5 pounds, 9 ounces. No abnormalities other than prematurity had been observed during its hospital course. Ten of the 13 depressed babies were followed with periodic complete cxaminations in pediatric clinics during their first year of life; none demonstrated any neurological or developmental abnormalities. The other 3 infants were lost to follow-up. Comment
This explorative study of instrument delivery was carried out to assess the changes in cardiac rates of infants who were subjected to known amounts of cephalic trac-
Table Apgar
IV. Station scores
of vertex
and infant
Apgars of Station Midpelvic -Low pelvic
I cases 27 35
7 or more 18 (67%~) 31 (89%) ~-.-~--____
ApgarS below 7 9 (33%) -1 (11%)
Volume Number
87 4
tion. These results may be discussed in respect to the two types of instruments used and in regard to the three phases of instrument delivery: the application, traction, and posttraction phases. The forceps and the vacuum extractor were similar in their effects on the fetal heart rate during both the traction and the posttraction phases. However, during the application phase their effects differed: the vacuum extractor caused minimal changes in the heart rate while it was being applied, whereas positioning of the forceps was often associated with bradycardia. The slowing of the heart rate when forceps were applied seemed to be a sign of impending peril, for when bradycardia occurred at this specific phase of the delivery there was greater than a 50 per cent chance that the baby would be depressed at birth. Fifteen infants had the onset of bradycardia as the forceps were being applied, and 8 (53 per cent) of these infants had an Apgar below 7 at one minute of life. In contrast, of the 29 in whom there was no bradycardia during forceps application, only 3 (10 per cent) had neonatal asphyxia. The small number of cases in this study precludes any statements as to the significance of application-bradycardia and subsequent low Apgar scores at birth, but the findings are provocative. There may be at least two possible explanations for this association : compression of occultly prolapsed cords was evoked while the forceps were being applied, or perhaps the infants were already in a state of subclinical distress which was aggravated by the compressive manipulations of application. The changes in the fetal heart rate during instrument traction are of interest. Bradycardia was found to be very common during traction. Eighty-four per cent of the babies exhibited a slowing of their heart rates during the pull with either forceps or the vacuum extractor. This high frequency is consistent with the long-recognized obstetrical observatidn that the heart rate of the infant slows when the brain is squeezed.s, 6* I1 This myocardiocerebral affiliation has been
Instrument
delivery
and
fetal
heart
rate
535
studied by several investigators and recent evidence suggests that a reflex cardiac deceleration is triggered whenever the intracranial pressure exceeds 40 mm. Hg.ll A threshold level in this range for induction of bradycardia is substantiated by the finding in the present study that an instrumental traction of 10 to 20 pounds (equivalent to 30 to 60 mm. Hg amniotic fluid pressure) commonly elicits a slowing of the fetal heart rate. Further confirmation is to be found in the frequent clinical observation of fetal bradycardia during strong uterine contractions (an intensity of more than 50 mm. Hg amniotic fluid pressure) .4 The demonstration that bradycardia is such a common occurrence during forceps or vacuum extractor pull suggests that slowing of the fetal heart at such times does not represent fetal distress. The tentative conclusion is that cardiac deceleration during instrument traction is more to be expected than feared. The apparent lack of clinical significance to fetal bradycardia which takes place during traction probably also holds true for cardiac slowing which persists into the posttraction period. However, there is some suggestion (Table II) that there is a greater chance for asphyxia at birth in infants whose heart rates display a tardy return to normal after traction. Similar observations have been reported for fetuses who show a postcontraction bradycardia during labor.‘O The appearance of bradycardia during and after traction was consistent whether the instrument used was forceps or the vacuum extractor. In regard to the vacuum extractor, our observations are in contrast to previous reports. This device has been reported (in 13 cases) to have no effect on the fetal heart rate.s* I3 From our additional experiences with the vacuum extractor, we are convinced of its association with bradycardia during traction on the fetal head.l’ The high incidence of asphyxia with midpelvic operations needs re-emphasis. Deliveries undertaken when the vertex was in the mid-pelvis had an incidence of low Apgar scores at birth of 33 per cent. This high
536
octotwr.\rn. J. Ohe.
Kelly
incidence appeared to be caused by the fact that these cases of mid-pelvic arrests rcquired more than average amounts of pull. In the forceps cases, the significant facto1 was the use of rxtractive forces of 50 pounds or more. When strong pulls of this degree were required there was a fetal depression rate of 40 per cent as compared to that of only 14 per cent with pulls under 50 pounds. These findings corroborate the earlier suggestions of increased fetal peril with traction of 50 pounds or more.“, ‘I The number of pulls (total duration of traction) did not seem to have any adversr efl’ect on fetal outcome. ‘The association of infant asphyxia with pulls of 50 pounds or more is a sobering statistic though its future significance, like that of fetal bradycardia during forceps application, will be dependent upon two factors. One is the validity of the Apgar score as an indication of the infant’s mental and physical well-being in the future, for only long-term follow-up will provide us with the true significance of a poor Apgar score. The other factor is the necessity of enlarging the number of monitored deliveries evaluated, so that statistically significant groups can be studied. Returning to the questions raised at the beginning of this report the following statements are possible: As an indicator of fetal jeopardy during forceps application, the appearance of bradycardia may prove to be a helpful sign; if expanded studies substantiate the present findings, then deceleration of the fetal heart rate during forceps manipulation would indicate that the mother should be given and that preparations should be oxygen made for resuscitation procedures at birth.
In regard to the baby’s cardiac response to potentially dangerous cerebral compression, it is evident that bradycardia is elicited so commonly during traction hp the, forceps or vacuum extractor that its appearance at these times can have little significance. as to ultimate fetal outcome. However. the degree. of peril represented by cerebral compression appears to be particularly high in those situations where forceps pulls exceed 50 pounds of force. To exceed this amount of traction would seem to require convincing ,justikation by the obstetrician. It is our hope that extension of these studies to a large number of deliveries with more thorough and prolonged follow-up of the children will ultimately provide us with definitive guideposts for thea safe conduct of instrument delkrerirs. Summary
1. Fetal heart rate changes were monitored in 62 births in which delivery was accomplished by the vacuum extractor and/ or Simpson forceps. 2. The intensity of each pull in these instrument deliveries was measured in pounds by both mechanical and electronic systems. ,7. Fetal bradycardia which developed during the process of applying the forceps to the fetal head was associated with a high incidence of neonatal asphyxia. 1. Slowing of the fetal heart rate during traction was a very common occurrence during both vacuum extractor and forceps deliveries. 5. Forceps deliveries in which individual pulls of 50 or more pounds were required were associated with a high rate of depressed infants at birth.
REFERENCES
1. Apgar, 2. 3. 4.
1953. Baxter, 53: 52, Brady,
V.:
Current
Res. Anesth.
32: 260,
J.: J. Obst. & Gynaec. Brit. Emp. 1946. J. P., and James, L. S.: AM. J. OBST. & GYNEC. 84: 1, 1962. Caldeyro-Barcia, R.: Research Report of the
15, 19ti3 C C.gnrc.
5. 6. 7.
Service of Obstetrical Physiology, Faculty of Medicine, Montevideo, Uruguay, October, 1961. Chong, F., and Hon. E.: Obst. & Gyner. 13: 633, 1959. Fenton, A. N., and Steer, C. M.: AM. J. OBST. & GYNEC. 83: 354, 1962. Fleming. .4. R., Brandeberry, K. R., and
Instrument
8. 9. 10.
Pearse, W. H.: AM. J. OBST. & 125, 1959. Fothergill, R. J., and Chalmers, tioner 186: 559, 1961. Hon, E. H.: AM. J. OBST. & 1255, 1958. Hon, E. H.: AM. J. OBST. & 1084, 1959.
GYNEC. J. A.:
78: Prac-
11. 12.
GYNEC.
75:
13.
GYNEC.
77:
14.
delivery
Kelly, J. V.: 331, 1963. Mishell, D., & Obst. 114: Saunders, J. 759, 1960. Scott, J. S., 1: 971, 1957.
and
AM.
J.
fetal
OBST.
heart
rate
537
& GYNEC.
87:
and Kelly, J. V.: Surg. Gynec. 609, 1962. R.: Proc. Roy. Sot. Med. 53: and
Gadd,
R.
L.:
Brit.
M.
J.
“Here
V.
Angeles,
KELLY,
M.D.
California
the heart
may
give
a useful
lesson
to the head
. . . .”
The Task, William
0 B s T E T R I c s is a field which is characterized by a scarcity of objective measurements. Despite the current advancements in scientific methodology, there is a disturbing absence of techniques which could precisely quantitate factors such as fetal size, the degree of flexion of the fetal head, the amount of moulding, and the station of the head. Consequently, obstetricians are compelled to rely on inaccurate assessments and unreliable estimates. Subjective practices are particularly apparent in the procedure of instrument delivery. Prevalent therein are such personal biases as to which forceps is the most appropriate to use and as to what constitutes a difficult pull. The adoption of a more objective approach is imperative for the practice of optimal obstetrics and the elimination of birth trauma. Every instrument birth involves physical forces: an extractive device is mechanically applied to the fetal head; intermittent traction forces are then exerted upon the head until the resistive forces of the perineum are overcome. Since these forces can be measured, it should be possible to define the mechanics involved so that delivery can be accomplished with maximal efficiency. This must be combined with a constant awareness of the fetal status, since the forces involved must be subservient to fetal wellbeing.
From the Department Gynecology, University Medical Center.
of Obstetrics of California
Cowper
Concomitant assessment of both should provide information for a scientific approach to instrument delivery. Present-day practices of birth by force are not much more advanced than those of a century ago. Only recently has the operative delivery by the vaginal route been invested with an atmosphere of scientific objectivity. The inauguration of the Apgar scoring system1 and the introduction of the metric forceps? are laudable advances. Even further expansion of objectivity in obstetrics is desirable particularly in regard to the association of instrument birth and fetal trauma. What is the physiologic status of the fetus during instrument delivery? Does the fetus react when it is subjected to potentially dangerous compression of its brain? Is there some indication from the fetus when its margin of cerebral safety is being surpassed ? In an effort to obtain answers to these questions it was planned to monitor a series of vaginal deliveries in which instruments were used to achieve birth. Attention was focused on evaluating the condition of the infant while it was being delivered, the amount of compression being exerted on its head during birth, and the status of the infant during its neonatal and subsequent course. Method Determination of the status of the fetus is restricted to one measurable index-its cardiac activity. To observe this criterion, the
and
529
530
Fig.
1. Calibrated
Fig. 2. gauges.
Fig.
October 15, 1963 Am. J. Obst. & Gynec.
Kelly
Bill
Forrrps
3. Forceps
monitorccl
with
handle.
x&traction
toe
strain
with
shank
strain
gauge.
fetal heart action was recorded with electrocardiographic techniques employing electrodes on the maternal abdomen and fetal scalp. The electrocardiographic tracings were evaluated manually, and the instantaneous rate!’ for each 4 second period was determined and recorded. The degree to which obstetrical instruments compress the fetal brain still eludes direct measurement. An indirect assessment can be obtained by mensuration of the traction exerted on the head during delivery. The instruments selected for this study were the Simpson obstetrical forceps and the Malmstrijm vacuum extractor. The amount
of traction force accomplished by each of these devices during a delivery was determined by attaching a metrically monitored Bill axis-traction handle to the forceps 01 vacuum extractor for all deliveries. This handle was equipped for measurement of pull by the incorporation of a calibrated spring-gauge, and a scale from which the amount of traction in pounds could be easily read at all times (Fig. 1). In addition, most of the forceps deliveries were accomplished by Simpson forceps to which miniature strain gauges had been applied in order to appraise electronically the forces at work (Figs. 2 and 3j. The vacuum extractor was applied to the fetal scalp by gradually increasing the negativ-e pressure inside the cup by increments of 0.1 Kg. per square centimeter over a 7 minute period to a total cup pressure of 0.7 or 0.8 Kg. per square centimeter. Patients were selected for whom elective instrument delivery was contemplated and in whom there was no detectable maternal or fetal distress. Patients were excluded who had received narcotics less than an hour before delivery or who had developed hypotension after receiving the anesthesia. Ninetytwo per cent of the deliveries in this series were accomplished under spinal, epidural, or caudal anesthesia. The deliveries were effected without the assistance of fundal pressure or expulsive efforts by the mothers. t\ttempts were made to synchronize the instrument pulls with the uterine contractions. Episiotomies were performed on all subjects. The fetal cardiac rate changes were recorded in 62 babies. There were 44 infants delivered by the forceps and 18 by the vacuum extractor. The latter device was employed unsuccessfully in 7 instances prior to delivery by forceps. Thirty-five of the 62 babies were delivered from low pelvic stations: 27 infants had mid-pelvic deliveries.*
“A mid-pelvic delivery mcnt bit-th in which the
an occiput transverse vertex is at a zwo, traction.
is herein fetal head
defined requires
as any rotation
instrufrom
or posterior position, or in which plus one or plus two station prior
the tc,
Volume Number
87 4
Table
Instrument
I. Fetal
heart
rates and instrument
application
(44 9 20 15
Tachycardia Eucardia Bradycardia During traction Tachycardia Eucardia Bradycardia
*Excludes
62 final
pulls) (20%) (47%) (33%)
( 139 pulls) 11 (8%) 23 (17%) 105 (75%)
After traction* Tachycardia Eucardia Bradycardia
and
fetal
heart
rate
531
delivery
FfWCf$S During
delivery
(95 pulls) 23 (25%) 35 (59%) 37 (39%)
Vacuum
extrattor
Total
(18 4 13 1
pull) (22%) (72%) (6%)
(62 13 33 16
pulls) (21%) (53%) (26%)
(108 14 19 75
pulls) (13%) (17%) (70%)
(247 pulls) 25 (10%) 42 (17%) 180 (73%)
(90 pulls) 26 (29%) 34 (38%) 30 (33%)
(185 pulls) 49 (27%) 69 (37%) 67 (36%)
pulls.
There was a total of 139 forceps pulls and 108 vacuum extractor pulls. The average duration of traction was 40 seconds in both groups. Individual pulls ranged from 5 seconds to 90 seconds in the forceps group, and 10 seconds to 105 seconds in the vacuum extractor group. The intensity of individual forceps pulls varied from 10 to 80 pounds (with an average of 43.8 pounds); with vacuum extraction pulls, the extractive forces ranged from 10 to 40 pounds (with an average of 30 pounds). The vacuum extractor will detach from the fetal scalp when traction force on it exceeds 40 pounds (with cup pressure of 0.8 Kg. per square centimeter) .I’ The condition of each newborn infant w’as evaluated at one minute of life and the infant was scored according to the Apgar system.l Results Heart rate changes during instrument application. The frequencies of appearance of tachycardia (a fetal heart rate over 160) and bradycardia (a fetal heart rate under 100) during the periods in which the forceps or vacuum extractor was being applied are listed in Table I. It should be noted that a rapid fetal heart rate occurred nearly as often with the positioning of forceps (20 per cent) as it did with the application of the vacuum extractor (22 per cent). However, a slowing of the baby’s pulse was induced much more often during the manipu-
lation of forceps (Fig. 4) than it was during attachment of the vacuum extractor; 1 of every 3 forceps applications was associated with a fetal bradycardia, whereas in only 1 of the 18 cases of vacuum extraction . . . apphcatron did the fetal heart rate slow. Heart rate changes during traction. A comparison of the effects of forceps and vacuum extractor traction on the fetal heart rate is given in Table I. The striking effect of instrument traction was that it very often evoked a slowing of the fetal heart rate. Bradycardia occurred in the distinct majority of pulls (73 per cent) and it appeared as commonly with forceps traction as with vacuum extractor traction. The severity of the bradycardia induced by both types of instruments did not seem to be correlated with the intensity of traction, except that the fetal heart rate slowed when the pull reached between 10 and 20 pounds of force and remained below 100 until the pull was reduced to less than 20 pounds. The fetal heart rate during traction usually ranged between 60 and 90 with occasional drops to the 40 to 60 range. These very slow rates occurred as often with 30 pound pulls as with 70 pound efforts (Fig. 5) Regardless of the type of instrument being used, when bradycardia appeared its onset was usually rapid, with the heart rate slowing some 40 to 50 beats within a few seconds (Fig. 5). Tachycardia, on the other hand, was usually gradual in onset.
532
October Am. J. Obst.
Kelly
IOSEC. / I+- 717" 112
FETAL HEARTRATE 7$
v
FORCEPS Fig. 4. Forceps
APPLICATION
application
and fetal
heart
t
ROTATION
AND
rate.
FETAL HEART RATE
0 Ibs.
15
35
50
60
5
15
traction
and
the fetal
20 Ibs.
78
35
60
80
70
heart
rate.
FORCEPS TRAGTION
8+
ARRHYTllMlA
88
FETAL HEART RATE Fig. 6. Forceps
traction
0 Ibs.
FOIVXPS TRACTION-
Fig. 5. Forceps
IO
and arrhythmia
of fetal
heart
rate.
0 Ibs.
IS0
ILO
15, 1963 & Gynec.
Volume
87
Number
4
Table
II. Fetal heart
Instrument
rates and infant No.
During
heart
rate
533
scores
infants
High
Apgar
Low
Apgar
13 (21%) 33 (53%) 16 (26%) 62
12 (25%) 29 (60%) 8 (15%) 49
1 (8%‘) 4 (32%) 8 (607~) 13
4 (7%) 6 (9%) 52 (84%) 62
4 (8%) 6 (12%) 39 (80%‘) 49
0 (0%) 0 (0%) 13 (100%) iii-
5 (9%) 30 (51%) 23 (40%) -’ 58”
5 (11%) 24 (53%) 16 (36%) 45
traction
Tachycardia Eucardia Bradycardia *Excludes
fetal
traction
Tachycardia Eucardia Bradycardia
Aft er
of
and
application
Tachycardia Eucardia Bradycardia During
Apgar
delivery
4 infants
who
were
delivered
with
only
one
-
0 (0%)
6 (46%) 7 (54%) 13
pull
Heart rate changes following traction. The status of the fetal heart rates in the 30 second periods immediately following cessation of instrument traction is listed in Table I. (The time periods following the final traction efforts of the 62 deliveries are not included because of the changes in pulmonary and cardiovascular dynamics which occurred upon birth of the baby’s head and its initial respiration.) A rapid heart rate occurred approximately as often after forceps traction as after vacuum extractor traction; the same held true for the appearance of a slow heart rate. In regard to the relation of the posttraction heart rate to the pattern during the preceding traction, the following changes were observed: The majority of heart rates during instrument traction (73 per cent) were slow; after cessation of traction approximately one third persisted with bradycardia (for only a short time), and one quarter developed a rapid increase in rate to levels above 160 which persisted for a short time before eventual return to normal levels. The remainder promptly resumed normal rates when the pull was stopped. A resimilar fractionation of posttraction sponses was noted in both the forceps and the vacuum extractor groups. In instances where the heart rates during traction were
normal or rapid, they usually were normal in the posttraction periods. Irregularities in the fetal heart rate. Cardiac rate irregularities were occasionally observed in this series of monitored instrument deliveries (Fig. 6). Four infants demonstrated arrhythmias, 2 in the forceps group and 2 in the vacuum extractor group. In these 4 infants, irregularities had not been observed in the prenatal periods and were not present after birth. Two of these babies had pressure applied to their heads after delivery without eliciting an arrhythmic response in the heart rate. Apgar scores and fetal heart rate changes. An Apgar score of below 7 is accepted as an indication of infant depression at one minute of life.” In this series of 62 instrument-delivered babies, there were 13 who had an Apgar score of less than 7. If the changes in the fetal heart rate are to provide help to the physician in predicting possible asphyxia of the infant at birth, then we must scrutinize the fetal heart rate changes, in the deliveries of the 13 depressed babies, for clues which might allow us to predict the development of neonatal apnea. In Table II the heart rate alterations during the application, traction, and posttraction phases of instrument delivery are listed for both normal and depressed babies. It is
534
Table
Kelly
III.
Difficult
forceps
and Apgar scores (44 cases) -__-..-~~~ ~~~~-~Total
Fifty pounds or more Less than fifty pounds Total traction time more than 3 min. Total traction time less than 3 min. Total
forceps
deliveries
Apear
15 29 9 135
Apgar 0 to 6
9 (60%) 25 (86%) 8 (72%) 26_____ (74%)
44
apparent that only in the phase of instrument application did the normal group (Apgar score of 7 or greater) and depressed group (Apgar score less than 7) have widely differing incidences of fetal heart rate changes. Of the 49 infants who were alert at birth, 8 (15 per cent) had had bradycardia during positioning of the instruments. In contrast, of the 13 infants who were depressed at birth, 8 (60 per cent) had bradycardia during instrument application. During instrument application 16 babies developed bradycardia. In 15 of the 16 cases, the instruments used were forceps. It is of interest, that forceps were the instruments employed in 7 of the 8 infants who had low Apgar scores at birth. A review of the fetal heart rate patterns of these 7 depressed infants shows that 3 maintained a persistent slow heart rate from application of the forceps to birth; the remaining 3 babies had recurrent bradycardia only during the extraction efforts. Apgar scores and difficulty of delivery. It would seem that infants who required numerous extractive efforts and/or particularly intensive pulls would be likely to be depressed at birth. In Table III the effects of these factors are assessed for the 44 infants delivered by forceps. It is evident that the intensity of pull did appear to be a particularly prominent factor in the production of infant depression. On the other hand, an unusual number of extraction efforts (measured in total traction time) seemed to have no adverse effect on the baby’s condition at birth. Apropos to the danger associated with a difficult pull, the station from which the head was delivered, appeared important. Table IV points out that 1 out of every 3
7 to 10
34
6 4 1 9
(77%)
(40%) (14%) (9%) (26%)
10 (23%:)
deliveries accomplished from a mid-pelvic station resulted in the birth of an asphyxic baby. Outcome of the 62 infants. All of the 49 newborn infants with Apgar scores of 7 or above did well during their hospital courses. Follow-up has been possible on 22 of these 19 infants, and all have exhibited normal development and show no evidence of cerebral damage. All of the 13 initially depressed infants responded to resuscitative measures and their subsequent neonatal courses were uneventful. Twleve of the 13 infants were discharged as normal from the hospital during the first week of life. One baby, whose weight was 4 pounds, 4 ounces at birth, was discharged as normal at one month of age when its weight had reached 5 pounds, 9 ounces. No abnormalities other than prematurity had been observed during its hospital course. Ten of the 13 depressed babies were followed with periodic complete cxaminations in pediatric clinics during their first year of life; none demonstrated any neurological or developmental abnormalities. The other 3 infants were lost to follow-up. Comment
This explorative study of instrument delivery was carried out to assess the changes in cardiac rates of infants who were subjected to known amounts of cephalic trac-
Table Apgar
IV. Station scores
of vertex
and infant
Apgars of Station Midpelvic -Low pelvic
I cases 27 35
7 or more 18 (67%~) 31 (89%) ~-.-~--____
ApgarS below 7 9 (33%) -1 (11%)
Volume Number
87 4
tion. These results may be discussed in respect to the two types of instruments used and in regard to the three phases of instrument delivery: the application, traction, and posttraction phases. The forceps and the vacuum extractor were similar in their effects on the fetal heart rate during both the traction and the posttraction phases. However, during the application phase their effects differed: the vacuum extractor caused minimal changes in the heart rate while it was being applied, whereas positioning of the forceps was often associated with bradycardia. The slowing of the heart rate when forceps were applied seemed to be a sign of impending peril, for when bradycardia occurred at this specific phase of the delivery there was greater than a 50 per cent chance that the baby would be depressed at birth. Fifteen infants had the onset of bradycardia as the forceps were being applied, and 8 (53 per cent) of these infants had an Apgar below 7 at one minute of life. In contrast, of the 29 in whom there was no bradycardia during forceps application, only 3 (10 per cent) had neonatal asphyxia. The small number of cases in this study precludes any statements as to the significance of application-bradycardia and subsequent low Apgar scores at birth, but the findings are provocative. There may be at least two possible explanations for this association : compression of occultly prolapsed cords was evoked while the forceps were being applied, or perhaps the infants were already in a state of subclinical distress which was aggravated by the compressive manipulations of application. The changes in the fetal heart rate during instrument traction are of interest. Bradycardia was found to be very common during traction. Eighty-four per cent of the babies exhibited a slowing of their heart rates during the pull with either forceps or the vacuum extractor. This high frequency is consistent with the long-recognized obstetrical observatidn that the heart rate of the infant slows when the brain is squeezed.s, 6* I1 This myocardiocerebral affiliation has been
Instrument
delivery
and
fetal
heart
rate
535
studied by several investigators and recent evidence suggests that a reflex cardiac deceleration is triggered whenever the intracranial pressure exceeds 40 mm. Hg.ll A threshold level in this range for induction of bradycardia is substantiated by the finding in the present study that an instrumental traction of 10 to 20 pounds (equivalent to 30 to 60 mm. Hg amniotic fluid pressure) commonly elicits a slowing of the fetal heart rate. Further confirmation is to be found in the frequent clinical observation of fetal bradycardia during strong uterine contractions (an intensity of more than 50 mm. Hg amniotic fluid pressure) .4 The demonstration that bradycardia is such a common occurrence during forceps or vacuum extractor pull suggests that slowing of the fetal heart at such times does not represent fetal distress. The tentative conclusion is that cardiac deceleration during instrument traction is more to be expected than feared. The apparent lack of clinical significance to fetal bradycardia which takes place during traction probably also holds true for cardiac slowing which persists into the posttraction period. However, there is some suggestion (Table II) that there is a greater chance for asphyxia at birth in infants whose heart rates display a tardy return to normal after traction. Similar observations have been reported for fetuses who show a postcontraction bradycardia during labor.‘O The appearance of bradycardia during and after traction was consistent whether the instrument used was forceps or the vacuum extractor. In regard to the vacuum extractor, our observations are in contrast to previous reports. This device has been reported (in 13 cases) to have no effect on the fetal heart rate.s* I3 From our additional experiences with the vacuum extractor, we are convinced of its association with bradycardia during traction on the fetal head.l’ The high incidence of asphyxia with midpelvic operations needs re-emphasis. Deliveries undertaken when the vertex was in the mid-pelvis had an incidence of low Apgar scores at birth of 33 per cent. This high
536
octotwr.\rn. J. Ohe.
Kelly
incidence appeared to be caused by the fact that these cases of mid-pelvic arrests rcquired more than average amounts of pull. In the forceps cases, the significant facto1 was the use of rxtractive forces of 50 pounds or more. When strong pulls of this degree were required there was a fetal depression rate of 40 per cent as compared to that of only 14 per cent with pulls under 50 pounds. These findings corroborate the earlier suggestions of increased fetal peril with traction of 50 pounds or more.“, ‘I The number of pulls (total duration of traction) did not seem to have any adversr efl’ect on fetal outcome. ‘The association of infant asphyxia with pulls of 50 pounds or more is a sobering statistic though its future significance, like that of fetal bradycardia during forceps application, will be dependent upon two factors. One is the validity of the Apgar score as an indication of the infant’s mental and physical well-being in the future, for only long-term follow-up will provide us with the true significance of a poor Apgar score. The other factor is the necessity of enlarging the number of monitored deliveries evaluated, so that statistically significant groups can be studied. Returning to the questions raised at the beginning of this report the following statements are possible: As an indicator of fetal jeopardy during forceps application, the appearance of bradycardia may prove to be a helpful sign; if expanded studies substantiate the present findings, then deceleration of the fetal heart rate during forceps manipulation would indicate that the mother should be given and that preparations should be oxygen made for resuscitation procedures at birth.
In regard to the baby’s cardiac response to potentially dangerous cerebral compression, it is evident that bradycardia is elicited so commonly during traction hp the, forceps or vacuum extractor that its appearance at these times can have little significance. as to ultimate fetal outcome. However. the degree. of peril represented by cerebral compression appears to be particularly high in those situations where forceps pulls exceed 50 pounds of force. To exceed this amount of traction would seem to require convincing ,justikation by the obstetrician. It is our hope that extension of these studies to a large number of deliveries with more thorough and prolonged follow-up of the children will ultimately provide us with definitive guideposts for thea safe conduct of instrument delkrerirs. Summary
1. Fetal heart rate changes were monitored in 62 births in which delivery was accomplished by the vacuum extractor and/ or Simpson forceps. 2. The intensity of each pull in these instrument deliveries was measured in pounds by both mechanical and electronic systems. ,7. Fetal bradycardia which developed during the process of applying the forceps to the fetal head was associated with a high incidence of neonatal asphyxia. 1. Slowing of the fetal heart rate during traction was a very common occurrence during both vacuum extractor and forceps deliveries. 5. Forceps deliveries in which individual pulls of 50 or more pounds were required were associated with a high rate of depressed infants at birth.
REFERENCES
1. Apgar, 2. 3. 4.
1953. Baxter, 53: 52, Brady,
V.:
Current
Res. Anesth.
32: 260,
J.: J. Obst. & Gynaec. Brit. Emp. 1946. J. P., and James, L. S.: AM. J. OBST. & GYNEC. 84: 1, 1962. Caldeyro-Barcia, R.: Research Report of the
15, 19ti3 C C.gnrc.
5. 6. 7.
Service of Obstetrical Physiology, Faculty of Medicine, Montevideo, Uruguay, October, 1961. Chong, F., and Hon. E.: Obst. & Gyner. 13: 633, 1959. Fenton, A. N., and Steer, C. M.: AM. J. OBST. & GYNEC. 83: 354, 1962. Fleming. .4. R., Brandeberry, K. R., and
Instrument
8. 9. 10.
Pearse, W. H.: AM. J. OBST. & 125, 1959. Fothergill, R. J., and Chalmers, tioner 186: 559, 1961. Hon, E. H.: AM. J. OBST. & 1255, 1958. Hon, E. H.: AM. J. OBST. & 1084, 1959.
GYNEC. J. A.:
78: Prac-
11. 12.
GYNEC.
75:
13.
GYNEC.
77:
14.
delivery
Kelly, J. V.: 331, 1963. Mishell, D., & Obst. 114: Saunders, J. 759, 1960. Scott, J. S., 1: 971, 1957.
and
AM.
J.
fetal
OBST.
heart
rate
537
& GYNEC.
87:
and Kelly, J. V.: Surg. Gynec. 609, 1962. R.: Proc. Roy. Sot. Med. 53: and
Gadd,
R.
L.:
Brit.
M.
J.