Maximum dose of oxytocin infusion
There is no national consensus on the maximum safe dose of oxytocin for induction or augmentation of labor. Many labor and delivery units have a protocol where the maximum dose of oxytocin is 20 mU/min for women in the following clinical situations: previous vaginal delivery, prior cesarean delivery, multiple gestation, and nulliparous women in the second stage of labor. A maximum oxytocin dose of 30 mU/min may be appropriate for nulliparous women in the first stage of labor. Some units permit an oxytocin dose of 40 mU/min. Many labor nurses are concerned that an oxytocin dose that high may be associated with an increased frequency of adverse effects.
Management of the oxytocin dose when tachysystole is diagnosed
Tachysystole is defined as more than 5 uterine contractions in 10 minutes averaged over 30 minutes.5,6 Because uterine contractions cause a reduction in oxygen delivery to the fetus, tachysystole, prolonged uterine contractions, and sustained elevated intrauterine pressure can result in fetal hypoxia and an abnormal fetal heart rate (FHR) pattern. If tachysystole is detected and the FHR pattern is Category 1, the oxytocin dose should be reduced. If tachysystole is detected and the FHR pattern is a concerning Category 2 or Category 3 pattern, the oxytocin infusion should be discontinued until the concerning FHR pattern resolves. If tachysystole is diagnosed, changing the maternal position (ensuring a lateral maternal position) and administering an intravenous bolus of 500 mL of lactated Ringer’s solution may help resolve an abnormal FHR. Terbutaline 0.25 mg, administered by subcutaneous injection, may be given to reduce myometrial contractility. Following resolution of an episode of tachysystole with a concerning FHR tracing, the oxytocin infusion can be restarted at a dose less than the dose that was associated with the tachysystole.
Inadvertent excess oxytocin administration
Oxytocin only should be administered using a computerized medication infusion pump with the oxytocin line piggybacked into a main infusion line.5 Occasionally, an excessively large bolus of oxytocin is administered inadvertently because the oxytocin line was mistakenly thought to be the main line or because of an infusion pump failure. These situations usually result in a tetanic contraction that will need to be treated by the immediate discontinuation of the oxytocin infusion, a fluid bolus, and one or more doses of terbutaline.
Reduction in oxytocin dose as labor progresses
Many investigators have reported that once rapid cervical dilation is occurring, or in the second stage of labor, the dose of exogenous oxytocin often can be reduced without stalling the progress of labor. Dilation of the vagina and pelvic floor, which occurs late in the process of labor, is a powerful stimulus for the release of oxytocin from the posterior pituitary.10,11 The marked increase in endogenous secretion of oxytocin during the second stage of labor may be the reason that the exogenous oxytocin infusion can be reduced or discontinued.
In a systematic review and meta-analysis, discontinuation of oxytocin after 5 cm of cervical dilation was associated with a reduced rate of uterine tachysystole and no increase in cesarean delivery.12 A Cochrane evidence-based review also concluded that once rapid cervical dilation is occurring, the dose of oxytocin can be reduced with a decrease in the rate of tachysystole with an abnormal FHR and without an increase in the rate of cesarean delivery.13
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