Dysfunctional Labor Flashcards
What physiologic changes occur during labor?
- Each smooth muscle cells becomes a contractile element when the the intracellular ionic calcium concentration increases to trigger an enzymatic process that results in the formation of the actin-myosin element
- Stimulation of oxytocin receptors on the plasma membrane further activates the actin-myosin element
What causes the relaxations during contractions?
- Maintained by factors that increase cyclic adenosine monophosphate (cAMP)
What causes the contractions during contractions?
- Increase intracellular calcium stores
- Promote interaction of actin and myosin causing uterine contractions
What are the two segments of the uterus during labor?
- Upper segment: actively contracts and retracts to expel the fetus
- Lower segment along with the cervix: Becomes thinner and passive
How does the cervix change in labor?
- Contains collagen and smooth muscle
- In labor it changes from frim, intact sphincter to soft, pliable, dilatable structure
What is the mechanism for cervix changes in labor?
- Collagenolysis
- Increase in hyaluronic acid
- Decrease in dermatan sulfate, which favors increased water content
What is the latent phase during the first stage?
- Cervical softening and effacement occurs with minimal dilation (less than 6cm)
What is the active phase during the first stage?
- Start when the cervix is dilated to 6cm
- Includes both an increased rate of cervical dilation and ultimately, descent of the presenting fetal part
- Acceleration phase
- Deceleration phase
What are abnormal patterns of labor defined as?
- Deviation from the norms for the phases of labor
What may an abnormality of labor be?
- Protraction: slower than normal rate
- Arrest: complete cessation of progress (no further dilation or descent)
What are some etiologies of an abnormal latent phase?
- Most patients will be those who have entered labor without substantial cervical change
- Excessive use of sedatives or analgesic
- Fetal malposition
What are some management options for abnormalities of the latent phase?
- Therapeutic rest (sleep) which can provide patient with relief and aid in distinction between true and false labor
- Morphine (15-20mg): majority will go into active phase, few will stop having contractions due to false labor
What are some abnormalities during the active phase in regards to dilation?
- Cervical dilation is less than norms is a protraction disorder of dilation
- If 2 or more hours elapsed with no cervical dilation
What are some abnormalities during the active phase in regards to fetal descent?
- Fetal descent of less than norms is a protraction disorder of descent
- If no change in descent/station has occurred within 1 hour an arrest of descent has occurred
Can abnormalities in the active phase have an effect on perinatal mortalitiy?
- Yes
What are some etiologies of abnormalities of the active phase?
- Inadequate uterine activity
- Cephalopelvic disproportion
- Fetal malposition
- Anesthesia
What is dystocia?
- “Difficult labor”
- It can be used interchangeably with dysfunctional labor characterizing that labor is not progressing normally
What does dystocia result from?
- Three P’s
What are the three P’s?
- Power
- Passenger
- Passage
What is power in the three Ps?
- Uterine contractions or maternal expulsive forces
What is passenger in the three Ps?
- Position, size, or presentation of the fetus
What is passage in the three Ps?
- Maternal pelvic bone contractions
When should a diagnosis of dystocia be made?
- Not until an adequate trial of labor has been tried
How are abnormalities of the active phase managed?
- Augmentation refers to stimulation of uterine contraction when spontaneous contractions have failed to result in progressive cervical dilation or descent of fetus
When is augmentation considered?
- If contractions are less than 3 in a 10 minute period and/or the intensity is less than 25 mm Hg
When does the ACOG recommend oxytocin?
- In protraction and arrest disorders after assessing maternal pelvis, fetal position, station, and maternal and fetal status
How is power assessed?
- Intrauterine pressure catheter which gives precise measurement of the intensity of the uterine contractions in mm Hg
What is required for use of an intrauterine pressure catheter? Risks vs benefits?
- Requires membranes to be ruptured
- Benefits: augment labor, allows assessment of meconium status
- Risks: Cord prolapse, prolonged rupture is associated with chorioamnionitis
What are montevideo units?
Calculated by measuring the peaks of contractions in mm Hg in a 10 min period
- > 200 mm Hg for at least 2 hours
- Before proceeding to cesarean section, should document adequate contractions for at least 4 hours
What is the MOA of pitocin?
- Increases intracellular calcium which results in increased actin/myosin activity
- Sensitivity of uterus to oxytocin increases between 20-40 gestational weeks
How is Passage assessed?
- Cephalopelvic disproportion (CPD)
- Refers to a disparity between the size of the maternal pelvis and the fetal head
- Causes failure of descent and sometimes engagement of the head
What increases the likelihood of CPD?
- Nulliparous women who present in labor with an unengaged head
What pelvices are good for delviery?
- Gynecoid and anthropoid
- Pubic arch: >90º
- Ischial tuberosity: >8.5 cm
- Diagonal conjugate: >11.5 cm
- Prominence of ischial spines
How is passage assessed?
- Presentation other than vertex occiput anterior are considered to be abnormal in the laboring patient
What is the usual path of the fetal head during descent?
- Enters and engages the maternal pelvis in OT position then rotates to OA
- Can persist in the OT position
- Or rotate to the OP positions
What else can cause dystocia?
- Abnormalities of fetal structure like macrosomia, shoulder dystocia, fetal abnormalities
What is persistent OT position?
- Head fails to rotate and flex into the OA position
- May be caused by CPD, altered pelvic architecture, or relaxed pelvic floor
What is transverse arrest of descent?
- A persistent OT position with arrest of descent for a period of 1 hour or more
Why does arrest occur in a persistent OT position?
- The deflexion that occurs could cause the occipitofrontal diameter (11 cm) to become the presenting diameter
What is the management for a persistent OT position?
- If pelvis is adequate, infant is not macrosomic, and contractions are inadequate:
- Start oxytocin
- Rotation (manually or with Kielland forceps)
- If pelvis is inadequate or infant deemed macrosomic, proceed with C section
What is a persistent OP position?
- Even if head rotates to OP initially, majority will eventually rotate spontaneously during labor to OA
- Course of labor is normal but second stage may be prolonged
- Associated with more back discomfort
What is the management of a persistent OP position?
- Observation of a prolonged second stage is appropriate
- If labor continues to be progressive and fetal heart rate is normal
- Delivery of head often occurs spontaneously
- Operative vaginal delivery will use a vacuum or forceps
What is macrosomia?
- Fetus weighing >4500 g
What is large for gestational age (LGA)?
- Birth weight equal to or greater than the 90% for a given gestational age
How is the passenger assessed?
- Look for any abnormalities that may lead to dystocia
- Hydrocephalus may cause an enlarged head, making delivery difficult and can be seen on ultrasound
- Fetal ascites can result in dystocia secondary to enlarged fetal abdomen
- Conjoined twins, locked twins
What is most common cause of fetal ascites secondary to enlarged fetal abdomen?
- Immune hydrops - Rh isoimmunization
What is nonimmune hydrops?
- Caused by congenital infections, chromosomal abnormalities, or fetal arrhythmias
What are some risk factors for macrosomia?
- Maternal diabetes
- Previous history of macrosomia
- Maternal prepregnancy obesity
- Weight gain during pregnancy
- Multiparity
- Male fetus
- Gestational age >40 weeks
- Ethnicity
- Maternal birth weight
- Maternal height
- Maternal age <17 years old
What are some maternal risks with macrosomia?
- Primary risk is increased risk for C section
- Postpartum hemorrhage
- Significant vaginal lacerations
What are some fetal risks with macrosomia?
- Shoulder dystocia
- Fracture of clavicle
- Damage to nerves of the brachial plexus (esp C5/6 which is Erb-Duschenne paralysis)
What is Erb-Duchenne palsy?
- Upper arm palsy
- Is most common brachial plexus injury
- Caused by injury to C5/6
What is Klumpke palsy?
- Lower arm palsy
- Caused by damage to C8/T1
What causes paralysis of entire arm?
- Damage to all four nerve roots
What does ACOG recommend for heavy babies?
- Prophylactic C section in babies that are >5000g in nondiabetic patients and >4500g in diabetic patients
What is shoulder dystocia?
- A delivery that requires additional obstetric maneuvers following failure of gentle downward traction on the fetal head to effect delivery of shoulders
What causes shoulder dystocia?
- Caused by the impaction of the anterior fetal shoulder behind the maternal pubic symphysis or the impaction of the post shoulder on the sacral promontory
What is the turtle sign?
- Retraction of the delivered fetal head against the maternal perineum
What are some antepartum risk factors for shoulder dystocia?
- Fetal macrosomia
- Maternal diabetes
- Obesity
- Post term gestation
- Short stature
- Previous macrosomic baby
- Previous history of shoulder dystocia
What are some risk factors during labor for shoulder dystocia?
- Labor induction
- Epidural analgesia
- Prolonged labor
- Operative vaginal deliveries
What are some neonatal risks with shoulder dystocia?
- Brachial plexus injuries (Erbs and Klumpke’s)
- Fractured clavicle or humerus
- Hypoxic - ischemic encephalopathy
- Death
What are some management techniques for shoulder dystocia?
- McRoberts maneuver
- Suprapubic pressure
- Rotational maneuvers, delivery of posterior fetal arm, fracturing fetal clavicle
- Proctoepisiotomy
- Zavanelli maneuver
What is the McRoberts maneuver?
- Hyperflexion and abduction of the maternal hip
What is done in suprapubic pressure?
- May dislodge the impacted anterior shoulder
- DO NOT apply fundal pressure
What is the Zavanelli maneuver?
- Cephalic replacement
- Last resort
- Poor prognosis with significant risk of fetal morbidity and mortality
- Head is pushed back in to pre-delivery position
- Emergent C section is done
What is the Rubin maneuver?
- Place pressure on an accessible shoulder to push it toward the anterior chest wall of the fetus to decrease the bisacromial diameter and free the impacted shoulder
What is the Wood’s corkscrew maneuver?
- Apply pressure behind the posterior to rotate the infant and dislodge the anterior shoulder
What is the procedure for shoulder dystocia?
- Obstetric emergency
- Call for help (Anesthesia and PICU)
- Can not be predicted or prevented
- Initial maneuvers are McRoberts and suprapubic pressure
