OXYTOCIN

1. OXYTOCIN Dr.Dhanalakshmy DNB (O&G)

2. “OXYTOCICS are the drugs of varying chemical nature that have the power to excite contraction of the uterine muscles.” Ergometrine & Methergin PGE2 & PGF2ά E2&F2ά

3. Oxytocin: physiology Human hypothalamus

5. 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

6. Oxitocin is the primary mediator of myometrial contractility during labor. 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. UTERUS

7. During lactation… STIMULUS RESPONSE myoepithelial cells contract Axon terminals

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

9. KIDNEY • In high concentration Oxytocin has weak antidiuretic & pressor activity due to activation of vasopressin receptors

10. 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 and is eliminated by the kidneys and liver. • Circulating half-life of max. 5 minutes. (avg 3-4min) as plasma, utrine & placenta of pregnant women contain enzyme oxytocinase • Circulating half life is 10 to 15 mins in non pregnant women

11. ADMINISTRATION • IV controlled infusion for initiation & augmentation of labour , abortions • IM for Post partum haemorrage • Buccal , Nasal spray for lactation

12. “serious toxicity is rare” when oxytocin is used judiciously. Toxicity HYPER STIMULATION fetal distress Grand multipara, Malpresentation Contracted pelvis Prior uterine scar (hyterotomy) NOTE: These complications can be detected early by means of standard fetal monitoring equipment.

13. Inadvertent activation of vasopressin receptors- 40-50IU/min Seizures & death 30-40mIU/min

14. To avoid hypotension, oxytocin is administered intravenously as dilute solutions at a controlled rate. OXYTOCIN BOLUS HYPOTENSION Transient vasodilation

15. INDICATIONS To minimise blood loss. Control PPH -To accelerate Abortion (inevitable, Missed). -Molar preg. -To stop bleeding. -Induction of Abortion. To induce labour. For cervical ripening. Augmentation of labour. Uterine inertia. Active management of 3rd stage Contraction stress test (CST) DIAGNOSTIC Oxytocin sensitivity test (OST)

17. Contraindications PREGNANCY • Grand multipara • malpresentation • 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

18. 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.

19. Calculation of dose delivered in milliunits(mU) & its correlation with drop rate per minute NOTE: In majority of cases, max. response is seen with 16 mU/min i.e 2U in 500ml RL at 60 drops per min

20. 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

21. 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

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