Oxytocin /Introduction Mechanism of Action Mode of Administration Indications Postpartum Hemorrhage Active Management of the Third Stage of Labor Induction of Labor Uterine Inertia Breast Engorgement Oxytocin Challenge Test Adverse Effects Contraindications Nursing role
Oxytocin
Outlines
Introduction
Mechanism of Action
Mode of Administration
Indications
Postpartum Hemorrhage
Active Management of the Third Stage of Labor
Induction of Labor
Uterine Inertia
Breast Engorgement
Oxytocin Challenge Test
Adverse Effects
Contraindications
Nursing role
OXYTOCIN:
Oxytocin is a nonapeptide, released by the posterior pituitary in
the body. It is synthesized within the nerve cell bodies in supraoptic and
paraventricular nuclei of hypothalamus. It is transported down the axon and
stored in the nerve endings within the neurohypophysis. Stimuli such as coital
activity, parturition, suckling, etc. help in the release of oxytocin molecule.
The synthetic form of oxytocin (syntocinon or pitocin) used as a drug is a
decapeptide.
Mechanism of Action
Uterus: Oxytocin, which has uterotonic action, helps in increasing
the force and frequency of uterine contractions. In the full-term gravid
uterus, oxytocin causes physiological uterine contractions, i.e. the
contraction of upper uterine segment and retraction of the lower segment. With
low doses, full relaxation occurs in between the uterine contractions. Basal
tone increases only with high doses of oxytocin.
Nonpregnant uterus and
that during early pregnancy is rather resistant to oxytocin; sensitivity
increases progressively in the third trimester, with a sharp increase occurring
near term.
The sensitivity quickly
falls during the puerperium.
Action of oxytocin on
myometrium is related to the specific G-protein coupled oxytocin receptors,
which mediate the response mainly by depolarization of muscle fibers and influx
of Ca2+ ions, through phosphoinositide hydrolysis as well as IP3-mediated
intracellular release of Ca2+ ions.
Breasts: In the breast tissues, oxytocin contracts the
myoepithelial cells of mammary alveoli, thereby forcing the milk into the
bigger milk sinusoids, resulting in the “milk ejection reflex”. This reflex is
initiated by suckling so that the ejected milk may be easily sucked by the
infant.
Mode of Administration
Being a peptide molecule, oxytocin is inactive orally and is most
commonly administered by IV route, rarely by intranasal/intrabuccal spray.
Oxytocin can also be administered by intramuscular/subcutaneous routes.
However, these routes are not commonly used because the response through these
routes may be erratic and the dose cannot be titrated to the response. Oxytocin
is available in the form of ampoules of Pitocin (5 units/0.5 mL) and syntocinon
(5 units/mL), where 1 IU of oxytocin is equal to 2 μg of pure hormone. In order
to preserve their potency, synthetic oxytocin ampoules must be stored in a
refrigerator.
(1 IU of oxytocin = 2 μg
of pure hormone). The oxytocin ampoules need to be stored in a refrigerator at
2−6°C
Indications
Prerequisites to be fulfilled before starting oxytocin infusion
• Fetus is in cephalic
presentation
• Fetal lungs are
adequately mature
• There is no
cephalopelvic disproportion
• There is no placenta
previa
• There is no fetal
distress
• No uterine scar due to
previous surgery
Postpartum Hemorrhage
Oxytocin (syntocinon) is an effective first-line treatment for
PPH. Oxytocin 10−20 IU/500 mL of Ringer’s lactate or normal saline may be
administered by IV infusion for an immediate response, especially in
hypertensive women in whom ergometrine is contraindicated. It is infused at a
rate of 125 mL/hour (60 drops/minute) over 4 hours. As much as 500 mL can be
infused over 10 minutes without complications.
For a sustained effect,
continuous infusion of oxytocin is usually preferred. In cases of circulatory
collapse, 10 units may be administered intramyometrially. Oxytocin acts by
forcefully contracting the uterine muscle, which compresses the blood vessels
passing through its mesh work to arrest hemorrhage from the inner surface
exposed by placental separation.
Active Management of the Third Stage of Labor
It is used for the active management of third stage of labor.
Oxytocin is recommended as the first-line drug in active management of third
stage of labor due to its short half-life and good intensity of action. Also,
its action can be quickly terminated and it does not cause contraction of the
lower segment.
Induction of Labor
It may be required to induce the labor in cases of postmaturity,
preeclampsia, gestational diabetes, erythroblastosis, ruptured membranes or
placental insufficiency.
Oxytocin titration technique: For this purpose, oxytocin is
administered via slow IV infusion wherein 5 IU of oxytocin is diluted in 500 mL
of glucose or normal saline solution (10 mIU/mL). Infusion is started at a low
rate (1–2 mIU/minute) and progressively accelerated at an interval of 20–30
minutes according to response (1–2 mIU/minute). When the optimal response is
achieved, i.e. there are about three uterine contractions in 10 minutes, with
each uterine contraction being sustained for about 45 seconds; the particular
oxytocin concentration which was being used is continued. The oxytocin infusion
is described
in terms of
milliunits/minute. The oxytocin infusion rate can either be manually regulated
by counting the number of drops per minute or the other option is to use an
oxytocin infusion pump, which automatically controls the infusion rate. Before
starting oxytocin infusion, the following prerequisites
Continuous monitoring: While inducing the patient with oxytocin
infusion, uterine contractions, fetal heart rate and any other complications
must be closely monitored after every 5–10 minutes. The drug is discontinued
when the uterine contractions become strong enough. The oxytocin dose can
be increased in the range of 1–32 mIU/minute. Majority of patients respond to
the dose of 16 mIU/minute or less.
This dose rate can be
attained by adding 2 IU of oxytocin to 500 mL of Ringer’s lactate solution,
with a drop rate of 60 drops/minute (where 15 drops =1 mL). There is no upper
limit to the permitted dose. If the uterus still remains inert at the oxytocin
dosage of 100 mIU/minute, it may be wise to consider using prostaglandins for
stimulation of the uterus. The accuracy and control of infusion can be greatly
improved by using an
oxytocin infusion pump.
Uterine Inertia
In cases where the uterine contractions are not strong enough and
labor is not progressing satisfactorily, uterine contractions can be augmented
by intravenous administration of oxytocin. Oxytocin, however, must not be used
for accelerating the labor, which is progressing normally on its own.
Before starting oxytocin infusion for strengthening the uterine contractions,
all the prerequisites as described in above
must be fulfilled.
Oxytocin is the drug of choice for inducing and augmenting labor and is usually
preferred over ergometrine/PGs for the following reasons:
• Intensity of oxytocin action can be controlled and be quickly
terminated due to its short half-life and slow IV infusion.
• When used in low concentrations, oxytocin allows normal
relaxation in between uterine contractions. Therefore, the fetal oxygenation is
not compromised.
• Since the lower uterine segment is not contracted, fetal descent
is not affected.
• Uterine contractions are consistently augmented.
Breast Engorgement
Oxytocin is effective in cases where the breast engorgement occurs
in the woman due to inefficient milk ejection reflex. Oxytocin is administered
by an intranasal spray few minutes before suckling. It does not increase milk
production, rather just causes milk ejection.
Oxytocin Challenge Test
This test is performed to determine uteroplacental adequacy in
cases of high-risk pregnancies. Oxytocin is administered via IV infusion at
very low concentrations till uterine contractions are elicited every 3–4
minutes. Marked abnormalities in fetal heart rate, particularly late
decelerations, indicate uteroplacental compromise. This test is rarely
performed nowadays.
Adverse Effects
• Strong uterine contractions: Injudicious use of oxytocin during
labor can result in strong uterine contractions. This may force the fetal
presenting part through incompletely dilated birth canal, resulting in harmful
effects such as maternal and fetal soft tissue injury, rupture of uterus, fetal
asphyxia and death.
• Tachysystole/uterine hyperstimulation: Injudicious use of
oxytocin can result in continuous uterine contractions or strong uterine
contractions. Tachysystole can be associated with a persistent pattern of more
than five uterine contractions in 10 minutes, with each contraction lasting for
2 minutes (or more) or contractions of normal duration occurring within 1
minute of each other, there being no resting tone between contractions.
• Maternal cardiovascular side effects: Administration of oxytocin
can cause certain side effects related to the cardiovascular system in the
mother. These can include side effects such as increase in the heart rate,
systemic venous return and cardiac output, cardiac arrhythmias, premature
ventricular contractions, etc.
• Water intoxication: This occurs due to its antidiuretic hormone
like action when administered in high doses (30−40 mIU/minute) along with IV
fluids, especially in conditions such as preeclampsia and renal insufficiency.
Water intoxication may manifest in the form of symptoms of hyponatremia such as
confusion, coma, convulsions, congestive cardiac failure and death.
• Hypotension: Bolus intravenous injection should be avoided in
patients with PPH where patient is hypovolemic or in patients with heart
disease because of the risk of development of hypotension. Occasionally,
oxytocin may also produce anginal pain.
• Fetal side effects: It can result in fetal side effects such as
bradycardia, neonatal jaundice, low APGAR score, etc.
Contraindications
Absolute Contraindications
The administration of oxytocin is contraindicated in the following
situations:
• Grand multipara (risk of uterine rupture)
• Vaginal delivery is contraindicated (e.g. obstructed labor)
• Evidence of intrapartum fetal distress
• Pregnant women with underlying cardiac disease (to avoid the
occurrence of fluid overload)
• Previous history of anaphylactic shock.
Relative Contraindications
• Previous uterine scar
• Vertex not fixed in the pelvis
• Unfavorable cervix
• Breech presentation
• Hydramnios
• Multiple pregnancy.
Nursing role
The importance of the nursing role in the management of oxytocin
during induction/augmentation of labor. It is nurses at the bedside of laboring
women who make oxytocin titration decisions based on their nursing assessments.
Those decisions must be based on a sound knowledge of the pharmacologic
properties of oxytocin, the physiology of uterine contractions, and the
response of the woman and fetus to contractions. In addition, nurses must be
aware of the standards and guidelines of care that govern their actions during
induction/augmentation.
References
Gynecological drug therapy
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