What Causes an Obstetrical Brachial Plexus Injury?

There are many sites that will go into detail of how a baby sustains a brachial plexus injury (BPI). There is much controversy in the obstetrical field regarding causation. Simply put, the overwhelming evidence is that the delivering practitioner applies too much traction on the baby's head and/or uses contraindicated procedures while trying to dislodge the baby’s shoulders (shoulder dystocia) from behind the pelvic rim or from the bony sacral promontory (tail bone) while the woman is usually lying on her back and/or sitting on her tail bone.

In doing so, the nerves that innervate the shoulder, arm, wrist and/or hand can be severely damaged, resulting in partial to complete paralysis. Sometimes the force is so great that the nerves are actually pulled completely out of the spinal cord-reducing most possibilities of any useful function of the arm, and necessitating numerous surgical interventions in an attempt to gain even the slightest function.

Also, the nerve to the eye may be damaged, resulting in Horner’s Syndrome. In severe cases the nerve to the diaphragm (phrenic nerve) may also be injured.

Shoulder dystocia is described as an obstetric emergency involving the lack of rapid, spontaneous delivery of the anterior shoulder of the fetus. The accepted proposal is that the shoulder gets lodged against the mother's pelvis symphysis (Inlet), although there is evidence to suggest that it can be a pelvic outlet phenomenon -a proposal that could support either shoulder being impacted. If it is a pelvic outlet issue, then either shoulder could be damaged from the traction, whether it be upward or downward traction that is applied. Rotational toruque on the babies head must be avoided during any manual manipualtions to free the shoulders.
Risk Factors:
Prepregnancy:

* Maternal birth weight
* Prior shoulder dystocia
* Prior macrosomia (large baby)
* Pre-existing diabetes
* Obesity
* Multiparity (a woman birthing her second child or who has had two or more children)
* Prior gestational diabetes
* Advanced maternal age

Antepartum (while pregnant):

* Excessive maternal weight gain
* Macrosomia
* Short stature
* Postdatism

Intrapartum(during birth):

* Prolonged second stage
* Protracted descent
* Failure of descent of head
* Abnormal first stage
* Need for mid-pelvic or assisted delivery

Weight and weight gain during pregnancy are critical factors during pregnancy. Mothers that weigh more than 81kg (~180 lbs) pre-pregnancy, experience 30% of all shoulder dystocias. In addition, more than a 20kg (44 lbs) pregnancy weight gain shows an increase in shoulder dystocia from 1.4% to 15.2%. This is an area that must be stressed by the OB/GYN during pre-pregnancy discussions and throughout the pregnancy. Screening for maternal diabetes must be the standard protocol, not an elected option.

For infants of non-diabetic mothers, the risk of shoulder dystocia is approximately 10 percent for infants weighing 4,000 to 4,499 grams (8.8-9.9 lbs)and 23 percent for infants >4,500 grams (9.9 lbs) . For infants of diabetic mothers the risk is 31 percent for infants >4,000 grams (8.8 lbs). Unfortunately, these statistics are only retrospective, since there is no adequate method for determining the accurate fetal weight.

Maternal weight gain, and the development of a macrosomic fetus are not the only predisposing factors.

The use of epidurals has been implicated to cause an increase in the incidence of cesarean sections for shoulder dystocias (10% vs. 3.8 % without epidurals). In addition, Stoddart et al., in a well-controlled randomized prospective study, showed that epidural anesthesia affects rotation of the shoulders because it relaxes the pelvic floor. Being in a recumbent position (lying down) has also been implicated in slowing down the baby's descent, prolonging the labor process, and potentially closing the birthing canal by up to 30%.
Positioning

Using the proper positioning during labor will help reduce the incidence of shoulder dystocia, by allowing the sacrum to move back freely and by allowing the birth canal to fully open. Thus, using the recumbent position (lying down) or semi-reclined position exacerbates the shoulder dystocia.

Borell and Fernstroms' (1957a) x-ray studies showed that the sacroiliac joint (part of the tailbone) moved during labor in relation to the descent of the fetus, and that these movements were not brought about by a change of maternal position at the particular time, but by the freedom of the joints to spread and open more.

In other words, the sacroiliac joints were free to move back as the baby passed through the birthing canal, because the women were not lying on their sacrum’s thus restricting such movement. They found that as the fetal head passes the pelvic inlet, i.e. at engagement, a movement of rotation occurs within the sacroiliac joint that increases the sagittal diameter of the pelvic inlet.

At the time the fetus passes the pelvic outlet, this movement of rotation is reversed, increasing the sagittal diameter of the pelvic outlet.

Basically, by keeping off her back (tailbone) the woman is giving her baby the widest possible opening for passage thus reducing the risks of trauma.

If a woman is sitting on her sacrum and sacroiliac joints during delivery, then there is an increased chance of precipitating a shoulder dystocia, and an increased likelihood of a brachial plexus injury.

Significantly closing the birth canal in the lying down or semi-reclined position, also increases the likelihood of a forceps or vacuum delivery, which in turn increases the risk of a brachial plexus injury and other birth trauma as well.

In an article from the Perinatal Institute, shoulder dystocia is discussed:

“Shoulder dystocia needs to be distinguished from a mere difficulty with delivery of the shoulder. The latter occurs because of the prevailing delivery practice, with the mother in a semi-recumbent position on the delivery bed. There may be insufficient room for appropriate lateral, i.e., downward flexion for delivering the anterior shoulder. In addition, the weight of the mother is in part taken on the sacrum that is therefore pushed upwards, thus decreasing the diameter of the pelvic outlet. Many of these cases require only a positional change, into left side lying, or kneeling, which frees the sacrum and allows lateral flexion”.
Prevention

The BPIPP’s main goal is to provide information for the Prevention of shoulder dystocia and hence brachial plexus injuries.

There are many publications that describe medical interventions to try and resolve a shoulder dystocia, such as McRoberts Maneuver (which is used to reopen the pelvis after it has been previously closed by lying on the tail bone).

We hope to convey that by taking a birthing position that allows for maximum pelvic opening, that shoulder dystocia and brachial plexus injuries will drastically be reduced.

“Prevention” is always a much more sensible and successful approach than attempted “interventions” after the fact.

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