OXYTOCIN

Dr.Dhanalakshmy DNB (O&G)

“OXYTOCICS

are the drugs of varying chemical nature that have the power to excite contraction of the

uterine muscles

.”

OXYTOCIN OXYTOCICS ERGOT DERIVATIVES Ergometrine & Methergin PROSTAGLANDINS PGE PGF 2 & ά

Oxytocin: physiology

Human hypothalamus

PREPARATIONS

 Synthetic Oxytocin (Ptocin) 5 IU/ ml amp  Syntometrine 5 U Oxytocin + 0.5 mg Ergometrine  Desaminooxytocin buccal tablets 50 IU  Oxytocin nasal spray 40 IU/ ml

UTERUS

     Oxitocin is the

primary mediator

contractility during labor.

of myometrial During the second half of pregnancy, uterine smooth muscle shows an increase in the expression of oxytocin receptors(100-200fold) and becomes increasingly sensitive to the stimulant action of endogenous oxytocin. Stimulates PG synthesis.

Physiological uterine contraction

- fundal contraction; cervical relaxation. (law of polarity maintained) Cervical and vaginal dilatation results in an acute release of oxytocin from the posterior pituitary in a process known as the

Ferguson reflex

.

During lactation

…

Suckling STIMULUS

mechanoreceptors in the nipple/ areola RESPONSE MILK EJECTION hypothalamic neuronal activity

oxytocin

CVS

 In small doses Oxytocin produces vasodialation by direct relaxation of the vascular smooth muscles  Transient hypotension & flushing followed by tachycardia are observed

KIDNEY

 In high concentration Oxytocin has weak antidiuretic & pressor activity due to activation of vasopressin receptors

ABSORPTION, METABOLISM, AND EXCRETION       Intravenously (controlled infusion) for initiation and augmentation of labor. intramuscularly -control of postpartum bleeding. Buccal & nasal spray- Limited use.

Oxytocin is not bound to

plasma proteins eliminated by the kidneys and liver

.

and is Circulating half-life of plasma, utrine & placenta of pregnant women contain enzyme oxytocinase

max. 5 minutes

. (avg 3-4min) as Circulating half life is 10 to 15 mins in non pregnant women

ADMINISTRATION

 IV controlled infusion for initiation & augmentation of labour , abortions  IM for Post partum haemorrage  Buccal , Nasal spray for lactation

Toxicity



“ s

erious toxicity is rare

” when oxytocin is used judiciously. excessive uterine stimulation

HYPER S T I M U L A T I O N Hypertonia

(↑duration)

Polysystole (>6 in 10min) uterine rupture

.

fetal distress placental abruption Grand multipara, Malpresentation Contracted pelvis Prior uterine scar (hyterotomy)

NOTE: These complications can be detected early by means of standard

fetal monitoring equipment

.

Inadvertent activation of

vasopressin

receptors 40-50IU/min

Antidiuresis excessive fluid retention Pul. Edema Heart Failure activation of

vasopressin

receptors Seizures & death water Intoxication hyponatremia

30-40mIU/min

OXYTOCIN

BOLUS

HYPOTENSION

Transient vasodilation

To avoid hypotension, oxytocin is administered intravenously as dilute solutions at a controlled rate.

INDICATIONS EARLY PREGNANCY -To accelerate Abortion (inevitable, Missed).

-Molar preg.

-To stop bleeding.

-Induction of Abortion.

LATE THERAPEUTIC LABOUR To induce labour.

For cervical ripening.

Augmentation of labour.

Uterine inertia.

Active management of 3 rd stage PUERPERIUM To minimise blood loss.

Control PPH DIAGNOSTIC Contraction stress test (CST) Oxytocin sensitivity test (OST)

Milk ejection

•Intra nasal dose of 40 U , 2 to 5 mins before breast feeding to promote milk ejection

Contraindications

PREGNANCY      Grand multipara malpresentati on contracted pelvis cephalopelvic disproportion prior uterine scar (hysterotomy) LABOUR      All cont. in preg.

+ Obstructed labour Incoordinate uterine contraction FETAL DISTRESS prematurity ANY TIME  Hypovolemic state  Cardiac disease

For induction of labour

  Principle: Start with LOW DOSE, escalate to achieve optimal response (3contraction in 10min each lasting 45sec)   Maintain the dose-

oxytocin titration technique.

OBJECTIVE

- Maintain normal pattern of uterine activity till delivery and 30-60min beyond that.

NOTE: Start with 4mU/min & ↑every 20min Semi-Fowlers position - avoid venecaval compression.

Calculation of dose delivered in milliunits(mU) & its correlation with drop rate per minute Units of oxytocin mixed in 500ml Ringer solution 1unit=1000 miliunits(mU) Drops per minute (15drops=1ml) 15 30 60 In terms of mU/min 1 2 5 2 4 8 4 8 16 10 20 40 NOTE: In majority of cases, max. response is seen with 16 mU/min i.e 2U in 500ml RL at 60 drops per min

OBSERVATION DURING OXYTOCIN INFUSION

 RATE of flow – calculating drops/min  Uterine contraction - Finger tip palpation (hardening)  Intra uterine pressure:-peak 50to60mmHg resting 10to15mmHg  FHR  Assessment of progress of labour - descent of presenting part & dialatation of cervix

Indications for stopping the oxytocin infusion

    Nature of uterine contractions   abnormal uterine contractions occurring frequently (every 2 min or less ) lasting more than 60sec(hyperstimulation)  ↑tonus in between contractions Fetal distress Maternal complications Hyper stimulation is treated with 0.25 mg terbutalin

☻ T H A N K Y O U