Physiology of delivery. Analgesia in labor.

LaborLabor is the physiologic process

by which a fetus is expelled from the uterus to the outside world.

It involves the sequential integrated changes in the uterine decidua, and myometrium.

Changes in the uterine cervix tend to precede uterine contractions

Dilatation: the enlarging of the cervix to 10 centimeters.

Effacement: the thinning of the cervix. cervix starts out being two inches long, and 50% effaced would be a 1 inch cervix.

Cervical effacement and dilation

Labor - Mechanics Uterine contractions have two major goals:1. To dilate cervix2. To push the fetus through the birth canal

Success will depend on the three P’s: Powers

Passenger Passage

PowerUterine contractionsPower refers to the force

generated by the contraction of the uterine myometrium

Activity can be assessed by the simple observation by the mother, palpation of the fundus, or external tocodynamometry.

Contraction force can also be measured by direct measurement of intrauterine pressure using internal manometry.

Power

Generally 3-5 contractions in a 10 minute period is considered adequate labor

Passenger Passenger =fetus

Fetal variables that can affect labor:Fetal Lie – the relationship of the long axis of the fetus to the long

axis of the mother:longitudinal, transverse or oblique

Fetal size

40 weeks 20.16 inches 7.63 pounds 51.2 cm3462 grams

41 weeks 20.35 inches 7.93 pounds 51.7 cm3597 grams

42 weeks 20.28 inches 8.12 pounds 51.5 cm3685 grams

Fetal presentationthe part of the fetus that lies

closest to or has entered the true pelvis. Cephalic presentations are vertex, brow, face, and chin. Breech presentations include frank breech, complete breech, incomplete breech, and single or double footling breech. Shoulder presentations are rare and require cesarean section or turning before vaginal birth. Compound presentation involves the entry of more than one part in the true pelvis,

Attitude – degree of flexion or extension of the fetal head

A--Complete flexion. B-- Moderate flexion. C--Poor flexion. D--Hyperextension

Position - the relationship of the part of the fetus that presents in the pelvis to the four quadrants of the maternal pelvis, identified by initial L (left), R (right), A (anterior), and P (posterior). The presenting part is also identified by initial O (occiput), M (mentum), and S (sacrum)

Number of fetusesPresence of fetal anomalies –

hydrocephalus, sacrococcygeal teratoma

The Fetal Skull

Fetal Positions for Labor and Birth

Left Occiput Anterior (LOA)

Left Occiput Transverse (LOT)

Left Occiput Transverse (LOT)

Left Occiput Posterior (LOP)

Right Occiput Anterior (ROA)

Right Occiput Transverse (ROT)

Right Occiput Posterior (ROP)

Leopold's Maneuvers

StationStation – degree of

descent of the presenting part of the fetus, measured in centimeters from the ischial spines in negative and positive numbers.

-5 is a floating baby,

0 station is said to be engaged in the pelvis,

and +5 is crowning.

PassagePassage = PelvisConsists of the bony

pelvis and soft tissues of the birth canal (cervix, pelvic floor musculature)

Small pelvic outlet can result in cephalopelvic disproportion

Bony pelvis can be measured by pelvimetry but it not accurate and thus has been replaced by a clinical trial of labor

Passage

The Stages of Labor

First StageInterval between the

onset of labor and full cervical dilation

Two phases:Latent phase – onset of

labor with slow cervical dilation to ~4 cm and variable duration

Active phase – faster rate of cervical change, 1-1.2 cm /hour, regular uterine contractions

The Labor Curve

First stage - A: latent phase; B + C + D: active phase; B: acceleration; C: maximum slope of dilation; D: deceleration; E: second stage.

LaborFreidman’s

curve is a good guideline for expected progression in labor and therefore helpful to note abnormal labor patterns.

Labor NulliG MultiG

1st Stage Active phase

Duration 6-18 h 2-10 h

Dilation ~1 cm/h ~1.5 cm/h

2nd Stage 0.5-3 h 5-30 min

3rd Stage 0-30 min 0-30 min

Fig 1:  An idealized labor pattern.  The normal patterns of cervical dilation (solid line) and descent (broken line) as they are traced against elapsed time in labor. The distinctive phases of the first stage are shown. The active phase comprises the interval from the onset of the acceleration phase to the beginning of the second stage.

Labor – Second Stage Interval between full

cervical dilation to delivery of the infant.

Characterized by descent of the presenting part through the maternal pelvis and expulsion of the fetus.

Indications of second stage:

1. Increased maternal show

2. Pelvic/rectal pressure3. Mother has active role

of pushing to aid in fetal descent.

Labor – Second StageMolding is the alteration of

the fetal cranial bones to each other as a result of compressive forces of the maternal bony pelvis.

Examining the fetal head during the second stage may become difficult due to molding

Caput is the localized edematous area on the fetal scalp caused by pressure on the scalp by the cervix.

PrimiG – 0.5-3 h; mulitG 0-30min

Cardinal Movements of Labor

This refers to the movements made by the fetus during the first and second stage of labor. As the force of the uterine contractions stimulates effacement and dilatation of the cervix, the fetus moves toward the cervix.

When the presenting part reaches the pelvic bones, it must make adjustments to pass through the pelvis and down the birth canal

Seven distinct movements:

1.Engagement2.Descent3.Flexion4.Internal

rotation5.Extension6.External

rotation/restitution

7.Expulsion

Descent: As the fetal head engages and descends, it assumes an occiput transverse position because that is the widest pelvic diameter available for the widest part of the fetal head.

Flexion: While descending through the pelvis, the fetal head flexes so that the fetal chin is touching the fetal chest. This functionally creates a smaller structure to pass through the maternal pelvis. When flexion occurs, the occipital (posterior) fontanel slides into the center of the birth canal and the anterior fontanel becomes more remote and difficult to feel. The fetal position remains occiput transverse.

Internal Rotation: With further descent, the occiput rotates anteriorly and the fetal head assumes an oblique orientation. In some cases, the head may rotate completely to the occiput anterior position

Extension: The curve of the hollow of the sacrum favors extension of the fetal head as further descent occurs. This means that the fetal chin is no longer touching the fetal chest.

External Rotation: The shoulders rotate into an oblique or frankly anterior-posterior orientation with further descent. This encourages the fetal head to return to its transverse position. This is also known as restitution.

ExpulsionDelivery of the fetusAfter delivery of the

fetal head, descent and intraabdominal pressure by mother brings shoulder to the level of the symphysis

Downward traction allows release of the shoulder and the fetus is delivered.

Suctioning the nasopharynx

Clamp the umbilical cord

Cut between the clamps

Labor – Third Stage Placental separation and delivery.

The time from fetal delivery to delivery of the placenta

Signs of placental separation:

a. The uterus becomes globular in shape and firmer.

b. The uterus rises in the abdomen.

c. The umbilical cord descends three (3) inches or more further out of the vagina.

d. Sudden gush of blood.

Labor – Third StagePlacenta is delivered using

one hand on umbilical cord with gentle downward traction. Other hand on abdomen supporting the uterine fundus.

Risk factor for aggressive traction is uterine inversion.

Obstetrical emergency!!Normal duration between 0-

30 min for both PrimiG and MultiG

Inspect the placenta for completeness

Labor – Fourth StageRefers to the time from delivery of the

placenta to 1 hour immediately postpartumBlood pressure, uterine blood loss and pulse

rate must be monitor closely ~ 15 minutesHigh risk for postpartum hemorrhage from:Uterine atony, retained placental

fragments, unrepaired lacerations of vagina, cervix or perineum.

Occult bleeding may occur – vaginal hematoma

Be suspicious with increased heart rate, pelvic pain or decreased

BP!!!!!!

Analgesia in labor Discomfort during Labor

and BirthPain and discomfort experienced during labor have

two neurologic origins: visceral and somatic Neurologic origins

Visceral pain: from cervical changes, distention of lower uterine segment, and uterine ischemia

Located over the lower portion of abdomen Referred pain: originates in uterus, radiates to abdominal wall,

lumbosacral area of back, iliac crests, gluteal area, and down the thighs

Somatic pain: pain described as intense, sharp, burning, and well localized Stretching and distention of perineal tissues and pelvic floor to

allow passage of fetus, from distention and traction on peritoneum and uterocervical supports during contractions, and from lacerations of soft tissue

Expression of painPain results in

physiologic effects and sensory and emotional (affective) responses

Emotional expressions of suffering often seenIncreasing anxietyWrithing, crying, groaning,

gesturing (hand clenching and wringing), and excessive muscular excitability

Cultural expression of pain varies

Factors influencing pain response

Physiologic factorsCultureAnxietyPrevious experience

Childbirth preparation

Comfort and support

Environment

Distribution of labor pain A. Distribution of labor pain during first stage B. Distribution of labor pain during later

phase of first stage and early phase of second stage

C. Distribution of labor pain during later phase of second stage and during birth

(Gray shading indicates areas of mild discomfort; light-colored shading indicates areas of moderate discomfort; dark-coloredshading indicates areas of intense discomfort.)

Nonpharmacologic Managementof Discomfort

Nonpharmacologic measures often simple, safe, and inexpensive

Provide sense of control over childbirth and measures best for woman

Methods require practice for best results

Try variety of methods and seek alternatives, including pharmacologic methods, if measure used is not effective

Nonpharmacologic Managementof Discomfort

Childbirth education Dick-Read method(recommended the need for education and his

teaching method included lectures, exercise, and a focus on breathing and relaxation techniques.

Lamaze method Bradley method

Relaxing and breathing techniques Relaxation Imagery and visualization Music Touch and massage Breathing techniques Effleurage and counterpressure Water therapy (hydrotherapy)Transcutaneous electrical nerve stimulation

Pharmacologic Managementof Discomfort

Nerve block analgesia

and anesthesiaLocal perineal infiltration

anesthesia

Prudendal nerve block

Spinal anesthesia (block) Disadvantages

Medication reactions (allergy)

Hypotension

Ineffective breathing

Headache Autologous epidural blood

patch

Sedatives

Analgesia and anesthesiaAnesthesia

Systemic analgesia Opioid agonist analgesics

Opioid (narcotic) agonist–antagonist analgesics

Co-drugs

Ataractics

Opioid (narcotic) antagonists

Pain Pathways and Sites of Pain Pathways and Sites of Pharmacologic Nerve BlocksPharmacologic Nerve BlocksA. A. Pudendal block; suitable Pudendal block; suitable

during second and third stages during second and third stages of labor and for repair of of labor and for repair of episiotomyepisiotomy

B.B. Epidural block; suitable Epidural block; suitable during all stages of labor and for during all stages of labor and for repair of episiotomyrepair of episiotomy

Membranes and spaces of spinal Membranes and spaces of spinal cord and levels of sacral, cord and levels of sacral, lumbar, and thoracic nerveslumbar, and thoracic nerves

Cross section of vertebra and Cross section of vertebra and spinal cordspinal cord

Levels of Anesthesia Necessary for Cesarean

and Vaginal Births

Cesarean birth

Vaginal birth

Administration of medicationIntravenous routeIntramuscular routeSpinal nerve block

Maternal fluid balance is essential during spinal and epidural nerve blocks

Maternal analgesia or anesthesia potentially affects neonatal neurobehavioral response

Use of opioid agonist-antagonist analgesics in women with preexisting opioid dependence may cause symptoms of abstinence syndrome (opioid withdrawal)

General anesthesia rarely used for vaginal birthMay be used for cesarean birth or when needed in

emergency childbirth situation

Expected outcome of preparation for childbirth and parenting is “education for choice”

Nonpharmacologic pain and stress management strategies are valuable for managing labor discomfort alone or in combination with pharmacologic methods

Gate-control theory of pain and stress response are bases for many of the nonpharmacologic methods of pain relief

Type of analgesic or anesthetic used is determined in part by stage of labor

and method of birth

Regarding Labour:the latent phase may last for more than four

hours the active phase should be associated with

cervical dilatation at a rate of at least 1 cm. per hour 

the active phase starts when the cervix is effaced and 2 cm. dilated 

involves artificial rupture of the membranes is best charted using a partogram epidural anaesthesia has an adverse effect on

the rate of progress in the 1st. stage of labour

the latent phase may last for more than four hours 

the active phase should be associated with cervical dilatation at a rate of at least 1 cm. per hour 

the active phase starts when the cervix is effaced and 2 cm. dilated 

involves artificial rupture of the membranes 

is best charted using a partogram epidural anaesthesia has an

adverse effect on the rate of progress in the 1st. stage of labour

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During delivery, what comes next after Engagement, Descent, and Flexion?

 1. Internal Rotation. 2. Extension. 3. External Rotation. 4. Expulsion.

During delivery, what comes next after Engagement, Descent, and Flexion?

 1. Internal Rotation. 2. Extension. 3. External Rotation. 4. Expulsion.

In SummaryKnow the different stages of laborKnow the labor curveKnow the cardinal movements of labor

Know the causes of postpartum hemorrhage

MD must understand medications, expected effects, potential adverse reactions, and methods of administration

Thank you for your attention!