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James C. (James Chalmers) Cameron.

The American text-book of obstetrics for practitioners and students (Volume v.1) online

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resistances of the anterior wall of the pelvis. The rapid descent of the occi-
put as compared with the sinciput thus re-establishes flexion, with the head
in a directly occipito-posterior position. Expulsion of the head in a persist-
ently posterior position by the natural forces or by the aid of forceps is then
possible, though the conditions are much less favorable than when the occiput
is rotated forward, as may be seen by reference to Figure 263. On comparing




Fig. 263.— Expulsion of the head in persistently posterior positions of the occiput ; mechanism of face
to pubes delivery.

Figure 263 with Figure 254 it will be seen that when the occiput is anterior
the curved axis of the child's head and body corresponds with the curved axis
of the pelvis, but that when the occiput is posterior these curves are reversed
upon each other, and that to effect the delivery iu this position the uterine
forces must alter the shape of the child by elongating the occiput, by com-
pressing the sinciput, and by producing an exaggerated flexion uutil the normal
curve of the fetal axis is reversed. Although the fetal head is surprisingly
tolerant of the excessive compression necessary for this change of shape, the
process always results in the stillbirth of a large proportion of the children ;
while the prominence of the occiput, even after the most extreme moulding,
always exposes the soft tissues of the pelvic floor to a degree of tension that
almost invariably results in deep laceration of these structures during the
stage of expulsion. The expulsion of a persistent occiput posterior, more-
over, always requires, in addition to lax adaptation, the presence of very



498



AMERICAN TEXT-BOOK OF OBSTETRICS.



powerful uterine contractions or the application of powerful traction by the
forceps ; and even when these conditions are present the process is a long
one.

The head remains on the perineum until the processes of the change in its
shaj^e and the production of extreme flexion are sufficiently far advanced to per-
mit the occiput to travel downward along the median line of the posterior wall
under the influence of the pressure from above. The region of the small fonta-
nelle finally appears at the vulva, and the perineum retracts, or, more com-
monly, tears across the occiput to the base of the neck. The occipital end of
the head is then free from pressure, while the sincipital end is still exposed to
the driving force of the uterine contractions. The excess of pressure upon
the sincipital end of the head then causes extension, by which the forehead,
the eyes, the nose, and the chin successively appear under the arch, while the
occiput swings backward, and the head is born by extension (Fig. 263).

Restitution. — During the expulsion of the head the shoulders enter in the
second oblique diameter, and the rotation of the left (the anterior) shoulder to




Tig. 264.— Occipito-posterior position, with the head beginning to distend the pelvic floor (Smellie).

the arch produces an external restitution to the right, in accordance with the
general law that external rotation or restitution restores the head to its origi-
nal position. Abnormal or so-called " super-rotation" is, however, of especially
common occurrence in these cases.

Summary. — In reviewing the mechanism of posterior positions it is at once
apparent that the whole key to the situation is to be found in the degree of
flexion presented — that the better the flexion the more certain and the more
rapid is the execution of the normal and most favorable mechanism. It is an



THE MECHANISM OF LABOR. 499

established fact in practice that in the comparatively few cases in which good
flexion is established at the start and maintained to the end, posterior labor is
hardly less favorable than anterior ; and that the degree of difficulty increases
as the degree and persistence of flexion decrease, until we reach the fact that
when flexion is lost and is not promptly restored by art, posterior positions
invariably yield long, difficult, and exhausting labors for the mother, and a
large proportion of stillbirths among the children. It may safely be said that
there is no variety of labor in which easily-avoided ill results are so commonly
incurred as in posterior positions of the vertex ; and there is certainly no sub-
ject in obstetrics that better deserves the attention of the student than the
means of detecting extension and of preserving or re-establishing flexion in
these cases.

Mechanism of Left-posterior Positions. — Of the mechanism of O. L. P.
positions it is only necessary to say that it differs from that of O. D. P. posi-
tions simply in the substitution of one side of the pelvis for the other, and in
the fact that failure of rotation is more common in left positions.

Management of Labor in Posterior Positions of the Vertex. — Prophy-
laxis. — Since posterior labor is so much less favorable than anterior, it is evi-
dent that every effort should be made to prevent the occurrence of posterior
positions, or, when they do occur, to convert them into anterior positions
before the occurrence of labor or during its early stages. We are, fortunately,
able to effect this end in the great majority of cases, provided the position is
diagnosticated before the ruptui'e of the membranes or the engagement of the
head. For this reason, if for no other, the obstetrician should in every case
endeavor to ascertain the position of the fetus by making an abdominal pal-
pation some days before the advent of labor. If a posterior position is dis-
covered at this time, it is usually possible to' rectify it by postural treatment
of the patient.

If the patient is placed in the knee-chest position, the anterior wall and
the fundus are the lowest portions of the uterus. So long as the patient
remains in this position there is a tendency for the child to sag away from the
brim under the influence of gravity ; and since the recession of the head from
the brim leaves the child free to turn upon its own axis, while the presence of
the spinal column makes the dorsal side the heavier, there is also a tendency
toward a rotation of the fetus as a whole until its dorsum is in apposition to
the anterior wall of the uterus.

The woman should in such cases be instructed to assume the knee-chest
posture several times daily during the last few weeks of pregnancy, to remain
as long in this position as is possible without fatigue, and, on relinquishing it,
to recline on the right side for a short time before rising, in the hope that as
the child's head again settles down against the brim it may become fixed in an
anterior position.

The enlarged abdomen of the gravida at term may prevent the assumption
of the true geuu-pectoral position and compel her to adopt the knee-elbow atti-
tude ; but in either event it is essential that the abdomen should be free from



500 AMERICAN TEXT-BOOK OF OBSTETRICS.

pressure against either the bed or the thighs of the patient ; that is, the thighs
should be vertical (Fig. 265).

The postural treatment is especially powerful when instituted before any
labor-pains have occurred. If this treatment is conscientiously carried out for
several davs, the physician will almost surely find the position anterior when
summoned to the patient in labor.

Even if the patient is not seen until labor is present, it is still worth while
to adopt a postural treatment so long as the membranes are unruptured and

the head is unengaged. The patient

^ ^ should then be encouraged to maintain

^j/\^ this position so long as her strength

permits, or until a vaginal examination

B without alteration of her attitude dem-

-~s>^~^ onstrates the fact that rotation has

occurred. She should then be placed

^j^ in the latero-proue position upon the

c =-^- ^ =a — side to which the occiput is directed,

Fig. 265-Correct (A) and incorrect (B and aQ( \ should remain ill that position
C) methods of assuming the genu-pectoral posi- ., , , , . „ , ■■ . ,

tion until the head is firmly engaged m the

new position. Should the head, after
once becoming anterior, show any tendency to revert to the posterior position,
it mav even be wise to rupture the membranes in order to prevent any such
reversion.

Should the postural treatment fail, no special treatment is necessary until
after the rupture of the membranes has occurred ; but both before and after
rupture frequent examinations are to be advised, in order to detect early any
tendency to the production of marked extension.

Passage of the Superior Stf-'ait. — In the majority of cases the head in pos-
terior positions passes the superior strait by the natural efforts only after some
delay, and often only after the occurrence of some extension and of considerable
moulding of the head.

The attitude of the phvsician should be determined by the degree of exten-
sion presented. When the extension is not extreme, he should not be alarmed
by a failure of progress, but should avoid interference, and expect the best
results so long as the condition of both patients remains good.

When extension becomes so extreme that the eyebrows are below the
brim of the pelvis, there is but little prospect that the head will pass the
superior strait by the natural efforts, aud unless active progress is present it
is wise, after a single hour has passed without alteration of the condition, to
abandon the expectant method of treatment and resort at once to the operative
treatment of a high arrest of the posterior occiput.

Operative treatment at the superior strait subdivides itself into the operative
re-establishmeut of flexion and the delivery through the superior strait of the
flexed but arrested head.

Operative Flexion. — If, at the time when operative flexion becomes neces-



THE MECHANISM OF LABOR. 501

sary, the membranes are still intact, it may occasionally be possible to raise the
forehead by making' pressure upon it with two ringers placed within the cervix,
the woman being in the laterally recumbent or knee-chest position, in order
to afford the assistance of gravity to the efforts of the accoucheur. Since it is
impossible, however, to obtain complete flexion of the head in this way, and
since the extension is almost certain to recur if no further change is made,
it is essential that the head as a whole should be freed from the brim by pres-
sure upon the vertex, after flexion has been secured, in the hope that on its en-
trance it may be better situated, and may thus be able to maintain its flexion.

Should extension again recur, it is best to etherize the patient, introduce
the hand into the vagina, and dilate the os manually to a degree sufficient to
permit the passage of the half hand within the uterus. Should the membranes
be ruptured at the time when interference is decided upon, this must usually
be the first maneuvre. When sufficient dilatation has been attained, the half
hand should be passed within the os until the fingers cover the forehead,
which should then be pressed gently upward until complete flexion has been
secured and the head has been freed from the brim. The hand should then
be withdrawn, the fingers placed as high upon the forehead as possible in
order to maintain flexion, and the head forced into the brim by external pres-
sure. The ether should be removed, and the fingers should maintain pressure
upon the sincipital portion of the head until a firm engagement in a flexed
position has been effected by the efforts of the uterus. Should extension be-
come re-established, an operative delivery of the head is necessary.

Operative Delivery of a High Arrest of the Posterior Occiput. — If extension
is present, flexion should be established by the introduction of the half hand.
Three methods of delivery are then possible : The child ma}' at once be turned,
the head may be rotated manually and forceps applied to the anterior occiput,
or forceps may be used while the occiput is still posterior.

The latter method is to be recommended only when the other methods are,
for one reason or another, contra-indicated or impossible, and the choice ordi-
narily rests between the procedures of a manual rotation of the occiput to the
front with a subsequent application of the forceps, and version.

Manual rotation and the application of forceps is a difficult, and version in
normal pelves is an easy, operation. The head after manual rotation not
infrequently returns to its original position during the manipulations incident
to the application of the blades, and in any event it is necessary to applv the
forceps to the head when freely movable above the brim, which operation is
always difficult. The writer believes, however, that after the forceps has
successfully been applied to the head in an anterior position, an extraction with
it is less dangerous to the soft parts of the mother than is the extraction of an
after-coming head ; the forceps operation should therefore, in his opinion, be
chosen by those who are thoroughly skilful in the use of the instrument, but
the primary performance of version should be elected by operators of small
experience.

Should manual rotation and the use of forceps be decided upon, the whole



502 AMERICAN TEXT-BOOK OF OBSTETRICS.

hand should be passed into the uterus and the head be raised gently until the
whole surface of the hand can be applied to the forehead, the fingers lying
over the face of the child ; whereupon the hand and the forearm of the operator
should be rotated with the head until the occiput is well anterior to, and even, if
possible, to the left of, the median line. During the introduction of the hand
careful counter-pressure must be made at the fundus by an assistant or by the
other hand of the operator, and during the rotation the external hand must be
used to promote the rotation of the trunk. The rotation should always be slow
and be procured with the utmost gentleness. Unless the rotation of the trunk
accompanies that of the body, the head will return to its original position as
soon as it is free from pressure. In difficult cases it may occasionally be per-
missible to apply the internal fingers to the shoulder of the child to promote
this rotation. The whole mauenvre is frequently so difficult that, unless the
waters have been but recently evacuated, it should not be attempted until a fair
experience in version has furnished the operator with some adroitness in intra-
uterine manipulations.

After rotation has been effected the head should be urged into the brim by
counter-pressure upon the fundus, and it should be maintained in position by
gentle abdominal pressure ujdou the head itself, from the hands of an assistant,
while the forceps application is made. The forceps should be applied, if pos-
sible, to the sides of the head, and, as in all high operations, the use of an
axis-traction instrument is to be recommended.

If version is decided upon, the head should be flexed before it is raised, as
this always requires less force than an attempt to raise the extended head.

If version is absolutely contra-indicated and manual rotation fails, an attempt
should be made to bring the head through the superior strait by the application
of forceps without alteration of the position ; but as a preliminary even to this
operation an extended head should gently be flexed.

In the use of forceps while the occiput is still posterior, it is inadvisable to
make any attempt to apply the blades to the sides of the head, as the position
of the parietal bosses in the narrow space between the ilio-pectineal eminence
and the promoutory makes it extremely difficult to adjust the forceps to the
ends of the biparietal diameter. Even when it is so adjusted a very slight
forward inclination of the line of traction may cause the forceps to slip forward
along the head to the temporal region. In this position the forceps is extremely
likely to slip from the head altogether ; even if the forceps holds its position,
the sole and necessary result of traction is a reproduction of the extension, which,
of course, results in an arrest, or at least requires the use of increased and
unnecessary force. The blades should therefore be applied to the sides of the'
pelvis, where they will take an oblique grip upon the head. This application
is always very difficult, and the operation too frequently results in a fracture
of the skull or in the birth of a stillborn child from cranial compression. As
soon as the head has passed the brim the forceps should be removed, and if
necessary reapplied in the manner shortly to be recommended for the oper-
ative treatment of the low head in posterior positions.



THE MECHANISM OF LABOR. 503

Management of the Passage of the Excavation in Posterior Positions. —
Flexion. — As was said in the discussion of the mechanism of posterior posi-
tions, the maintenance of complete flexion is the first and most essential con-
dition of the progress of the head through the excavation. It follows that the
maintenance of flexion when possible, and its re-establishment when it has been
lost, must demand throughout the case the most careful attention from the
obstetrician.

When the adaptation is easy and good flexion is present from the start,
descent and rotation to an anterior position are sometimes so quickly performed
that no assistance is needed ; but in a large proportion of cases the head enters
the excavation in a condition of partial extension, and in such cases an early
adoption of certain very simple measures frequently makes the difference
between difficult and easy labors. The various expedients which may be used
to promote or to re-establish flexion form, then, the first and most important
division of the treatment of the low head in posterior positions; but, since it
not infrequently happens that even a well-flexed head fails to rotate from over-
tightness of adaptation, from relative inefficiency of the pains, or from minor
variations in the shape of the head and the pelvis, it is necessary to add thereto
a second division, which consists of the expedients that may be employed to
favor or to produce rotation during extraction, whenever, from any cause, a
well-flexed head is arrested in a posterior position in the excavation.

Maintenance of Flexion. — Unless progress goes on with unusual rapidity,
the maintenance of flexion by counter-pressure should be undertaken as soon
as the head has entered the excavation and the forehead is within easy reach.
As soon as the degree of descent permits, the fingers should be placed against
the frontal bones as far forward of the large fontanelle as the pelvic space allows,
and any further descent of the sinciput should be retarded by a maintenance of
pressure against the forehead throughout the whole of each pain until the occur-
rence of rotation carries the frontal bones backward and out of the reach of the
fingers. In this process a simple retardation of the descent of the sinciput is
all that is to be aimed at or desired, since flexion is supposed to be already
present, and its maintenance is all that is needed. This maintenance of flex-
ion, which is usually easy, is always a very much more simple matter than is
an attempt to raise the forehead by pressure after extension has once occurred.
If this precaution is carefully observed from the start, loss of flexion is
extremely rare, and a recourse to the more heroic methods required for its
re-establishment may usually be avoided.

Re-establishment of Flexion. — When extension occurs, it must be reduced
before any further progress is possible. Flexion may be re-established either
by pushing the sinciput up, by drawing the occiput down, or by a combination
of both methods. The forehead may occasionally be made to recede by pres-
sure upon the frontal bones with the fingers ; it should then be held in position
until the uterine efforts have effected complete flexion by descent of the occiput,
and until rotation has occurred. This method, the simplest and safest, is, how-
ever, possible only in very easy cases.



504



AMERICAN TEXT-BOOK OF OBSTETRICS.



It is occasionally possible to reinforce this method by hooking the fingers
of the hand around the occiput, and thus drawing down upon the occiput with
one hand while the sinciput is pressed up by the other hand. This method is
possible only when the extended head is very low and the soft tissues of the
outlet are very lax ; in the majority of cases in which extension has fully been
established it is necessary to resort to instrumental methods.

The vectis (Fig. 266), which was the precursor of the forceps, was originally
used to promote the descent of the head by the application of leverage motions
to the sides of the head in alternation. The vectis is
never used to-day except for the reduction of exten-
sion, and, in the opinion of the writer, cannot be
recommended even for this purpose, since, in the first
place, its efficiency depends on its possession of an
exaggerated cephalic curve which renders its intro-
duction difficult, and, in the second place, it can rarely
be prevented from slipping, without the use of a
degree of force which exposes both the vagina of the
mother and the scalp of the child to serious risks
of laceration. If employed, the vectis is passed
around the occiput and is used to draw it down,
while the delay of the sinciput is entrusted to the
friction of the pelvic walls or to counter-pressure by
fig. 266.-The vectis. the fingers. For this purpose the hand of an assist-
ant must be utilized, since the employment of the
vectis always requires both hands; that is, while one hand makes traction
on the handle of the vectis, the fingers of the other hand must always be
placed between the vagina and the instrument to protect the tissues from
laceration. ,

Reversed Forceps. — A far better operation, when manual efforts at flexion
have failed, is to be found in the application of reversed forceps. This opera-
tion is in reality a mere extension of the ancient principle that the tips of the
forceps should always be directed toward the leading point on the presenting
part ; but when the forceps is applied to an extended head in a posterior posi-
tion with the tips directed posteriorly, its grasp is directed so far toward the
occipital end that the instrument is almost certain to slip after flexion has
occurred. It is therefore important to remember that this application should
be utilized only for the production of flexion, that during each traction the
fingers of the unemployed hand should carefully note the motions of the ,
head, and that as soon as flexion has been established the blades should be
removed, if necessary being reapplied for the delivery of the head in the
manner recommended for the delivery of a well-flexed head in posterior
positions.

Technique of the Application of Reversed Forceps. — The forceps should be
placed outside the vulva, in the position in which they are to lie when applied
to the head — that is, with the transverse axis of the blades at right angles to



THE MECHANISM OF LABOR.



505



the sagittal suture, and with the tips directed backward. If the lock is of
the ordinary form, the handle of that blade which would be the left in the
ordinary position should be held in the right hand, and, under the guidance
of two fingers of the left hand, should be inserted into the vagina and passed
into position as near as possible to the occipital end of the head (Fig. 267).




Fig. 267.— The application of reversed forceps. The arrow indicates the effect of the forceps in pro-
moting the descent of the occiput while the sinciput is delayed by friction against the anterior pelvic
wall.

The other blade should be adjusted to correspond with its fellow, and simple
traction upon the handles should be made in the direction of the handles, all
leverage motions being avoided. The force of the instrument is then directed
against the occipital end of the head alone ; the sinciput is delayed by the
friction of the pelvic walls, while the occiput descends under the force of
traction, and flexion results.

As soon as the small fontanelle has been brought to the centre of the pelvis
— that is, when the head has been flexed — the forceps should be removed and
the process of rotation be entrusted to nature, since lacerations of the vagina are
far less often produced when rotation is effected by the uterine force than
when it is procured by instrumental means; unless, indeed, the condition of
the patient necessitates an immediate delivery.

Low Forceps in Well-flexed Heads in Posterior Positions. — When rotation



Online LibraryJames C. (James Chalmers) CameronThe American text-book of obstetrics for practitioners and students (Volume v.1) → online text (page 56 of 63)