Oxytocin

Oxytocin is a hypothalamic polypetide stored in the posterior Pituitary Gland
1. Oxytocin is encoded by the human OXT gene
Oxytocin release is triggered by reflex response to Hypothalamus from infant sucking nipple
Oxytocin acts to stimulate Smooth Muscle in the Uterus and in the Breast
1. Increases force and frequency of uterine contractions
2. Stimulates milk ejection in lactating women (contraction of alveolar myepithelium of the mammary glands)
Oxytocin is similar in structure to the other posterior pituitary Hormone, Vasopressin (ADH)
1. Oxytocin and Vasopressin differ by only 2 Amino Acid residues (out of 9 Amino Acids)
2. Oxytocin may have Vasopressin-like effects (e.g. SIADH) with prolonged continuous infusion

See Labor Induction
Precautions
1. Use with a intravenous pump to maintain consistent and safe doses
2. Continuous Fetal Monitoring
Preparation: Oxytocin in Normal Saline Infusion
1. Oxytocin 10 units in 1000 ml Normal Saline
  1. Starting rate of 6-12 ml/hour delivers 1-2 mU/minute
  2. Increasing rate 6 ml/hour delivers another 1 mU/min
2. Oxytocin 20 units in 1000 ml Normal Saline
  1. Starting rate of 3-6 ml/hour delivers 1-2 mU/minute
  2. Increasing rate 3 ml/hour delivers another 1 mU/min
Protocol: Low Dose (preferred)
1. Start: 0.5 to 2 mU/minute
2. Increase: 1-2 mU/minute every 15-40 minutes
  1. Base Pitocin rate changes on contractions
  2. After 8 mU/minute, may then increase by 2 mIU/minute
3. Maximum: 40 mU/minute
Protocol: High Dose
1. See Monitoring below
2. Precautions
  1. Low dose protocol is preferred in all patients (see Labor Induction for efficacy)
  2. As of 2019, evidence is against the use of high dose Oxytocin (see Labor Induction for efficacy)
  3. Use only in Nulliparous patients only
3. Protocol
  1. Start: 6 mU/minute
  2. Increase: 3-6 mU/minute every 15-40 minutes
  3. Maximum: 40-42 mU/minute

Postpartum Hemorrhage prevention after Vaginal Delivery
1. Oxytocin 10 units IM after delivery
2. Oxytocin 10-40 units in 1 L IV fluid (NS, LR, D5W)
Postpartum Hemorrhage prevention after Cesarean Section
1. High dose Oxytocin prevents uterine atony
2. Dose: Oxytocin 2667 mU/min for 30 minutes
3. Munn (2001) Obstet Gynecol 98:386-90 +PMID: 11530117 [PubMed]

Anaphylaxis
Uterine hypertonicity
1. Uterine tetanic contractions and Fetal Distress
2. Uterine Rupture
Water Intoxication (SIADH)
1. Associated with slow infusion >24 hours

Avoid in Lactation
In pregnancy, contraindicated, of course, prior to peripartum (at which point its primary use is pregnancy)
Monitoring
1. Continuous Fetal Monitoring

Sympathomimetics
1. Increased risk of Postpartum Hemorrhage when combined with Oxytocin