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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Any difficult delivery with or without assistance.

Pathophysiology!!navigator!!

  • Hereditary—genital tract abnormalities, twinning, ankylosis of joints, large fetal head, hydrocephalus
  • Nutrition and management—mare's pelvic size (nutritional stunting), pelvic cavity fat, failure to observe animals near term (uterine inertia), close confinement of mares during entire gestation
  • Infectious conditions of the placenta or fetus—can result in uterine inertia, incomplete cervical dilatation, postural abnormalities due to fetal death, loss of placental attachment sites, etc.
  • Traumatic—abdominal wall damage can inhibit abdominal contractions; uterine torsion, pelvic fracture, etc.
  • Miscellaneous—unexplained postural changes: posterior or transverse presentation

Primary Uterine Inertia

  • Uterine overstretching (i.e. hydrops, twins) increases in older, debilitated animals
  • Uterine infections
  • Oxytocin—failure of its release or to effect a uterine response

Secondary Uterine Inertia

  • Dystocia, uterine muscle is exhausted
  • Failure of labor due to pain
  • Prolonged dystocia with strong circular contractions in a fatigued uterus

Immediate Causes of Dystocia

  • Most often of fetal origin
  • Maternal causes—birth canal stenosis, small pelvis, hypoplasia, lacerations and scars of the genital tract, pelvic tumors, persistent hymen, failure of cervical dilatation, uterine inertia, abortions, twinning
  • Fetal causes—abnormal presentation, position, posture; excessive size; anasarca, ascites, tumors, monsters; ankylosed joints, hydrocephalus, posterior or transverse presentation, wry neck

Systems Affected!!navigator!!

  • Reproductive
  • Others possible as condition progresses, with development of systemic illness

Genetics!!navigator!!

See Pathophysiology.

Incidence/Prevalence!!navigator!!

Dystocia rates—10%. Higher incidence—miniature horse breeds.

Geographic Distribution!!navigator!!

Wherever pregnant mares are housed.

Signalment!!navigator!!

Any breed and ages.

Signs!!navigator!!

General Comments

Dystocia is always an emergency.

Historical Findings

  • Stage 2 labor >40 min or an abnormal presentation, position, and/or posture
  • May include premature placental detachment with the fetus yet in utero
  • Important—complete history
    • Mare's due date
    • Prior dystocia or abnormal gestations
    • Systemic disease during gestation
    • Duration active labor (stages 1 and 2)
    • Rupture of allantoic membrane
    • Rupture of amniotic membrane
    • Assistance given? (potential contamination)
    • Status of mare's mobility

Physical Examination Findings

  • Do routine physical examination of the reproductive tract and fetal examination before deciding how to handle a dystocia
  • If recumbent, unable to rise, determine:
    • Cause
    • Hydration status
    • In shock or into shock before procedure is complete?
    • CRT ± toxic mucous membranes
  • TRP of genital tract performed to determine possible lacerations; uterine tone; fetal presentation, position, posture before vaginal examination
  • Genital tract examination following tail wrap and meticulous perineal wash
    • Use liberal amounts of lubricant
    • Examine vulva, vagina, cervix, uterus for lacerations. Inform owner prior to palpation of the fetus or obstetric manipulation if lacerations have been identified.
  • Determine fetal viability:
    • Gentle pressure over eyes (blink reflex?)
    • Place fingers in fetal mouth (suckle reflex?)
    • Pull on fetal limb (test—fetal retraction?)
    • Maximally flex limb (stimulate fetal motion, it pulls away)
    • Test anal sphincter, contraction?
    • US examination to determine presence of heart beat or blood flow
  • Evaluate fetal presentation, position, posture
  • Determine birth canal size, permit fetal passage?
  • If fetus is dead, determine how long (may not be possible until after delivery)
    • Time of death classification—corneas cloudy (dead 6–12 h prior to delivery); emphysema and sloughing of hair of fetus (dead minimum 18 h prior to delivery)

Causes!!navigator!!

  • All posterior presentations
  • All deviations from normal position (dorsosacral)
    • Dorsoilial
    • Dorsopubic
  • Postural defects, flexion of the extremities (head, neck, limbs)
    • Most common cause of dystocia
    • Carpal, shoulder, hip flexion; lateral flexion head and neck
    • Ankylosis of joints
    • Hydrocephalic fetus, anasarca

Risk Factors!!navigator!!

  • Major causes involve fetal malposture. It is impossible to state precisely why the fetus moves from a normal to an abnormal delivery presentation
  • Increased risk in older mares and in mares with insufficient exercise

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Primary prepartum colic. Similar signs, especially in early stages of dystocia. With dystocia, the mare is not only uncomfortable but is also straining. Examination of the reproductive tract (TRP and vaginal) will help to differentiate dystocia from colic
  • With true breech delivery (posterior presentation, both rear legs flexed), stage 2 labor and straining may be absent

CBC/Biochemistry/Urinalysis!!navigator!!

CBC—blood chemistries indicated if mare is hospitalized and results rapidly available.

Imaging!!navigator!!

Depending on circumstances, US may determine fetal viability.

Other Diagnostic Procedures!!navigator!!

  • Determine mare's mucous membrane color (normal, injected, muddy) and CRT
  • Mare hydration status
  • Is mare ambulatory or down?
  • Is she sufficiently stable to administer local anesthetics, epidurals, general anesthesia, or sedation?
  • TRP is always indicated to determine if uterine lacerations are present prior to vaginal examination, fetal viability, the amount of uterine contracture around the fetus
  • Vaginal examination to determine presence of uterine tears, degree of cervical relaxation and uterine contracture, fetal viability, presentation, position, posture, space between the fetus and maternal pelvis
  • Field resolution is preferable when C-section is not an option and mare's straining prevents adequate room to accomplish mutation
  • Heavy sedation or light general anesthesia of the mare:
    • Elevation of mare's rear quarters (suspending by her hocks; care must be taken to protect the hocks with padding or towels before attaching chains or straps); use a lift, front-end loader, overhead beam, etc.
    • Mare placed in lateral recumbency, elevate hocks no more than 45–60 cm (18–24 inches), usually sufficient
    • Allows weight of the fetus/fluids in the relaxed uterus to fall deeper into the abdomen, creates additional space to accomplish mutation, subsequent extraction
    • An option whether fetus is alive or dead, especially when C-section is declined

Pathologic Findings!!navigator!!

Depends on the cause of the dystocia.

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Generally best handled on the farm
  • Vaginal deliveries best accomplished shortly after a dystocia is diagnosed, whether mutation, forced extraction, or fetotomy is to be performed

Nursing Care!!navigator!!

  • Thorough examination of the genital tract after delivery
  • Broad-spectrum antibiotics placed into the uterus to reduce number of organisms introduced during mutation and extraction of the fetus. Systemic antibiotics may be necessary if systemic disease develops
  • Uterine stimulants such as oxytocin can be beneficial; enhance uterine contractions and involution
  • Uterine flushes or infusions may be indicated to enhance uterine contractility

Activity!!navigator!!

Stall rest for mares undergoing C-section.

Diet!!navigator!!

  • Maintain mare's regular diet, reduce quantity fed, if indicated
  • Changing diet at the time of parturition further adds to the mare's stress; should be avoided

Client Education!!navigator!!

  • Mares should not be permitted to be in prolonged labor; reduces probability of neonatal survival
  • As soon as possible, examine location of fetal extremities during delivery; determine if fetus is in an abnormal delivery presentation, position, or posture
  • If soles of the fetus viewed at the mare's vulvar lips are pointed down:
    • Anterior presentation and dorsosacral position (=normal), or
    • Posterior presentation and dorsopubic position (=upside down; detorsion &/or C-section)
  • Must determine if fetus's head is resting on its metacarpi (normal presentation, position, posture)

Surgical Considerations!!navigator!!

  • Decide early if a C-section is the best approach for a viable fetus:
    • No other correction (mutation, extraction) possible
    • If surgical approach can be made quickly to maintain fetal viability
  • If a C-section is to be performed, timing is critical
  • If fetus cannot be delivered alive, give consideration to fetotomy, especially if fetotomy will require only 1 or 2 cuts that can be done on the farm at an early stage, before the vaginal vault diameter becomes compromised (swelling, bruising)

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Epidural anesthesia may assist the delivery; reduces contractions during assisted delivery. Approximate dose—1 mL of 2% Carbocaine (mepivacaine) per 40 kg of body weight
  • Xylazine (0.5–1.0 mg/kg) used for sedation alone or combined with acepromazine (0.04 mg/kg)
  • General anesthetic agents for C-section or to accomplish further corrective procedures
  • After delivery, administration of oxytocin at a dosage of 10–20 IU per 500 kg IM to hasten uterine contractions, involution of postpartum uterus

Contraindications!!navigator!!

Never administer oxytocin prepartum—potential to induce further uterine contracture, reducing further fetal manipulation space. Exceeding recommended doses, especially early after delivery, may result in uterine eversion (prolapse).

Precautions!!navigator!!

Regardless of approach, manipulate fetus carefully during delivery.

Alternative Drugs!!navigator!!

  • Butorphanol
  • Detomidine
  • Morphine

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • TRP is indicated daily or every other day to determine size and tone of the uterus
  • US examination plus TRP—determine presence or absence of uterine luminal fluid

Prevention/Avoidance!!navigator!!

  • Close observation of near-term mare to aid in early diagnosis of dystocia
  • There is no method to prevent dystocia

Possible Complications!!navigator!!

  • After dystocia, check for lacerations—cervix, vagina, vestibule, vulva, or uterus (with resultant peritonitis)
  • Uterine inflammation or infection may result from the dystocia or corrective methods used

Expected Course and Prognosis!!navigator!!

  • Prognosis decreases with:
    • Duration of dystocia
    • Inexperienced interference
    • Cause of dystocia
  • Mares have a grave prognosis if >24 h from onset of stage 2
  • Fetuses have a guarded prognosis >40 min from onset of stage 2
  • After initial examination of mare—discuss prognosis, fees, best approach to resolve dystocia with owner
  • Choices of approach:
    • Mare standing, lateral recumbency, rear quarters elevated—assisted forced extraction, manipulation (mutation) of fetus; fetotomy
    • C-section
    • Euthanasia of mare

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Age-Related Factors!!navigator!!

Slight increase in dystocia in aged mares, may be related to decreased uterine contractions.

Synonyms!!navigator!!

Difficult—foaling, labor, delivery, parturition.

Abbreviations!!navigator!!

  • CRT = capillary refill time
  • C-section = Caesarean section
  • TRP = transrectal palpation
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

McCue PM, Ferris RA.Parturition , dystocia and foal survival: a retrospective study of 1047 births. Equine Vet J 2012;44(Suppl. 41):22–25.

Author(s) ⬆

Author: Carla L. Carleton

Consulting Editor: Carla L. Carleton

Acknowledgment: The author/editor acknowledges the prior contribution of Walter R. Threlfall.