Pitocin is the drug we love and hate. If a laboring patient on pitocin for a long time end up in cesarean section, you often find that pitocin infusion after the baby is born is less effective in giving you the firm uterine tone. Your surgeon may ask you to give more pitocin in the hope of improving the uterine tone. Rarely, giving more pitocin would help in that scenario. Have you ever wondered why? Here below are some quick facts that will help you understand why pitocin would be less effective.
- Receptor modulation is time-dependent (not dose-dependent)
- Phaneuf (J Reprod Fert 2000)
- 60- to 300-fold decrease mRNA expression due to receptor desensitization when exposed to prolonged pitocin infusion.
- Robinson (2003)
- Loss of Ca2+ flux after 6 hours (50% at 4.2hr)
- Receptors remained responsive to PGF2
Now you see why less is more. In addition, with quick infusion of pitocin, it may cause HOTN, flushing, headache, nausea etc.
There are a few RTC studies which have demonstrated the effectiveness of rule of threes. If pitocin of IV push 3units is ineffective, then you can repeat 2 more times. If the uterine tone is still inadequate, time to switch to other medications to modulate different receptors on the myometrium.
- Rule of Threes (Tsen, 2010 and 2015)
- Based on extensive reviews and RCT conducted in 2015
- step-wise algorithm
- 3IU over 15s; repeat q3min PRN tone (total 3 doses)
- 3IU/hr infusion (50ml/hr)
- if inadequate tone, Δ to 3 pharmacologic alternatives
- RCT study (Anesthesiology 2015): A “rule of threes” algorithm using oxytocin 3 IU results in lower oxytocin doses when compared with continuous-infusion oxytocin in women undergoing elective cesarean delivery.
Sometimes, LESS is MORE.