If the use of the cup is expected to be difficult, it must be done in the cesarean theater or near to it, and in the presence of an anesthetist and a pediatrician.
The obstetrical cup is applied to the fetal skull, and does not make it any bigger.
The obstetrical cup avoids the problems inherent in general anesthesia.
Most studies have found that the cup produces less harmful effects on the soft tissues of the woman than the use of forceps. The only lesions observed are those resulting from inadequate monitoring of disengagement, or failing to check that the device has been installed properly.
However, it should be noted that vaginal and perineo-vulvar damage occurs more often than during spontaneous childbirth, and this is because of the speed of expulsion, which does not allow good perineal ampliation to occur.
The cup does not constitute a risk factor for these lesions in contrast to forceps. Promoting factors include a fetal weight in excess of 4 kg, primiparity, and occipito-sacral disengagement.
Blood loss is often related to iatrogenic or traumatic perineal lesions.
Damage of the vaginal mucosa if a fold remains trapped between the cup and the presentation.
Cervical damage (if the cup has been positioned before complete cervical dilatation has occurred) which involves the same mechanism.
Incidents of this type can easily be avoided by carefully checking the position of the cup when it is inserted.
Some very rare forms of damage have been reported in the literature:
Annular detachment of the cervix
Bladder-vagina or bladder-uterine fistula
In some cases, these two complications seem to occur for the same reason: ischemic necrosis induced by prolonged pressure of the fetal head engaged in the pelvic tract.
The obstetrical cup does not seem to be responsible for these complications: in fact, had it been applied earlier, it could have abolished the vascular compression and thus avoided the necrosis.
Damage of the pudendal nerve, which innervates the external anal sphincter and the peri-urethral sphincter, seems to be responsible for disorders affecting pelvic statics. Childbirth increases the risk of such lesions.
Instrumental extractions are a promoting factor, especially forceps deliveries.
As in the case of forceps deliveries, few statistical studies have demonstrated any isolated responsibility of vacuum cup-assisted extraction in neonatal accidents, particularly in a context of concomitant fetal distress.
The most serious and unusual complications can occur after the prolonged and difficult use of vacuum cups during which maximum traction forces may have been applied to the scalp.
The praiseworthy intention of seeking to reduce the number of C-sections obviously does not justify running any neonatal risk in borderline indications for the vacuum cup.
The forces applied by the cup to the fetal scalp can lead to secondary injuries. Four types of force are applied to the fetal skull: negative suction pressure, traction force, a circular force in the context of rotation, and shear forces. The combination of these phenomena accounts for the various different lesions observed and reported on the neonate.
Figure17 : anatomy of the fetal scalp
The first layer is the skin, which is thinner in neonates than in adults, and is resistant, dense and hairy.
The second layer is the subcutaneous tissue immediately beneath the skin, consisting of cellulo-adipose tissue, crossed by thick, resistant fibrous trabeculae, which are anastomosed with one another and which extended from the underside of the dermis to the upper surface of the epicranial aponeurosis and of the occipito-frontal muscle. The main branches of the vessels and nerves are located in this part of the adipose tissue. It is in this layer that the caput succedaneum occurs.
This is a musculo-aponeurotic plane that is located beneath the subcutaneous adipose tissue, and consists of the occipito-frontal digastric muscle and the epicranial aponeurosis. The posterior bulge of this muscle is formed by the occipital muscles, and the anterior bulge by the frontal muscles; the intermediate tendon is a fibrous membrane known as the "epicranial aponeurosis". It is the anterior edge of this aponeurosis that provides the insertion for the frontal muscles, and its posterior edge that for the occipital muscles; on the edges, the aponeurosis provides an attachment for the auricular muscles and extends, getting thinner, over the temporal region, and continues with the fascia superficialis on the mastoid region.
The top surface or the aponeurosis and the connective sheath of the frontal and occipital muscles are closely bound to the skin by fibrous trabeculae that enclose the subcutaneous tissue.
Skin + adipose membrane + aponeurosis thus form a single layer known as the scalp.
The fourth layer is a slack cellular tissue located between the epicranial aponeurosis and the periosteum. This is a thin layer of very slack cellular tissue, which makes it easier for the scalp to slide over the periosteum of the skull, and which continues as the cellular tissue of the nape of the neck, the back, the face, neck, chest and mastoid.
This cellular layer is crossed by branches of blood vessels, especially of the Santorini emissary veins, which link the veins of he scalp with the blood pools of the cranial bones and the superior longitudinal sinus via the foramina in the parietal bone.
It is rupture of these veins that triggers hemorrhage beneath the aponeurosis that spreads in all directions to form a diffuse sub-cutaneous hematoma of the scalp.
The fifth layer is the periosteum.
Caput succedaneum
This is fairly common and usually banal, it can correspond to a simple "bun" corresponding to the concavity of the vacuum cup (Figure 18), which disappears within a few hours (12 to 18 hours), or alternatively can be a visible and palpable hematoma bounded by a major supporting cellulo-adipose tissue. In large examples, 20 to 40 ml of blood may collect, which results in anemia and accentuation of the physiological jaundice due to an excess of unconjugated bilirubin that has to be resorbed. A puncture should not be carried out.
Figure 18 : caput succedaneum induced by the vacuum cup
Abrasion and laceration of the skin occurs when the cup pops off or slips. These skin lesions can provide an entry point for infection, but the outcome is usually benign. The neonate may be agitated as a result of the pain, analgesics should be prescribed. Local antiseptic treatment and sterile fields are called for. Serious lesions are rare, and often secondary to the causes of failure of the cup discussed above. In exceptional cases, local alopecia has been observed subsequently. The risk factors are application of the cup for more than ten minutes, paramedian application and a prolonged second stage of labor.
This involves a caput succedaneum plus detachment of the skin extending over several cm2 where the skin is limp and fluctuating. Within a few days, this will become taut again and spontaneously adhere to the scalp.
Figure 19 :
cephalhematoma
Diffuse, subcutaneous hematomas of the scalp are promoted by fetal distress, infection, coagulation disorders, a persistent occipito-posterior position and a difficult vacuum-assisted delivery. Their rarity (4 to 20 per 10,000 births) should not lead us to forget that they can be extremely serious if they are not diagnosed early and do not receive intensive care that can be very onerous.
This condition involves bleeding from damage of Santorini's emissary veins that develops insidiously and continuously, since it is not restricted by any anatomic structure: the blood spreads between the epicranial aponeurosis and the periosteum in a slack cellular space, without any supporting tissue, and this can contain up to 260 mL of blood in a neonate. The entire scalp becomes detached, masking the bone sutures (Figure 20).
Figure 20: diffuse, subcutaneous hematoma of the scalp
Sub-dural, extra-dural, intra-parenchymatous or intra-ventricular bleeding does not seem to be directly linked to vacuum-assisted childbirth, but can be secondary to prolonged cerebral anoxia in the context of acute fetal distress or of a congenital clotting disorder.
Retinal hemorrhage has been more frequent with obstetrical vacuum cups. They have usually been correlated with the duration of labor. They are resorbed spontaneously, and no sequelae have been reported in the literature.
Jaundice has been reported in a context of vacuum-assisted extraction, requiring more phototherapy
It does not look as though any infective role can be attributed to vacuum cups.
Lesions affecting the brachial plexus are not specific to the use of vacuum cups; but are linked to dystocia of the shoulders. Nevertheless, in children suspected of having macrosomy, the risk of damaging the brachial plexus is markedly increased in an instrumental extraction of the middle part using forceps or with an obstetrical vacuum cup.
