Comparison of weight based versus fixed dose oxytocin infusion for preventing uterine atony during cesarean section in laboring patients

Oxytocin is used as a uterotonic to prevent uterine atony during cesarean section, but higher doses of oxytocin can cause serious maternal side effects. One of the accepted ways to optimize efficacy of a drug in clinical practice is to use it according to the patients body weight. There is however no published data regarding weight-based doses of oxytocin infusion.

Aim: To compare the efficacy of weight-based versus fixed-dose oxytocin infusion during cesarean section conducted in laboring patients.

Primary Objective:To compare the effect of weight-based (0.4 IU/Kg/hr) versus fixed-dose (34 IU/hr) oxytocin infusion for achieving adequate uterine tone during cesarean section conducted in laboring patients.

Secondary Objective:To compare effect of weight-based (0.4 IU/Kg/hr) versus fixed-dose (34 IU/hr) oxytocin infusion on associated side-effects during cesarean section conducted in laboring patients (including hypotension, tachycardia, nausea/vomiting, chest pain or ST-T changes).

Materials and Methods:

Inclusion Criteria**:** Laboring parturients with use of preoperative oxytocin for labor induction/augmentation, >18 years, and posted for cesarean section will be enrolled.

Exclusion criteria**:** Will include patient refusal, gestational age <37 weeks, preeclampsia, use of general anesthesia, preexisting uncontrolled systemic illness .

Methodology:

Anesthetic management: The anesthetic management for these patients will be standardized as per routine practice. This will include standardized aspiration prophylaxis, non-invasive monitoring and single-shot spinal block using hyperbaric bupivacaine (0.5%).

Oxytocin administration: The oxytocin infusion, with dose as per allocated group, will be initiated upon clamping of the umbilical cord, via a separate dedicated intravenous line or a three-way attached to the 18 G cannula used for fluid therapy. The same will be continued till end of surgery. The uterine tone will be assessed and graded as adequate or inadequate by the obstetrician, 4 minutes after the initiation of the oxytocin infusion. Any incidence of an inadequate tone reported subsequently till end of surgery will also be noted. For an inadequate uterine tone reported by obstetrician at the 4 minutes observation or at any time thereafter, a rescue bolus of 3 U of oxytocin over 30 seconds will be administered. If uterine tone does not improve after another 3 minutes, an additional uterotonic agent will be administered. In all patients, the predetermined oxytocin infusion as per group allocation will be continued till end of surgery, irrespective of the outcome of the dose.

After initiation of oxytocin infusion, associated side effects including hypotension, tachycardia (>10 bpm), ST-T changes, nausea/vomiting, flushing and chest pain will also be observed, till end of surgery or prior to rescue bolus whichever is earlier.

Sample size: Considering that oxytocin infusion of 34 IU/hr would be expected to attain adequate uterine tone in 90% patients, to detect a 33% change in this incidence (two-tailed) 32 patients would be required in either group at power of 80% and alpha error of 5%.

Statistical Analysis: Continuous variables will be summarized as mean ± standard deviation (SD) and/or median (IQR), depending upon skewness of data; and discrete as percentage or ratios. Incidence of achieving an adequate uterine tone at 4 minutes of oxytocin initiation, incidence of hypotension, tachycardia, ST-T changes, nausea/vomiting, and chest pain will be compared between both groups using Chi-square or Fishers exact test as appropriate. A P < 0.05 will be considered as statistically significant.