Calcium Chloride for Prevention of Blood Loss During Intrapartum Cesarean Delivery

Standardized volumetric and gravimetric assessment of blood loss during cesarean. Note: will analyze all participants, but planned subgroup analysis will also occur excluding patients with non-atonic reasons for blood loss including hysterotomy extension, placental abruption, cervical or vaginal laceration, etc

Postpartum hemorrhage was defined as quantitative blood loss > 1000 milliliters during operative course

Yes/no: did the patient require treatment with methylergonovine, carboprost, and/or misoprostol for uterine atony

Yes/no, if patient required transfusion of packed red blood cells prior to hospital discharge

Measured pre-delivery hematocrit minus measured post-operative day 1 hematocrit. Correction factor of 3 hematocrit points per unit packed red blood cells transfused

Total dose oxytocin bolus during cesarean

Uterine tone assessment: Obstetricians at the study institution use the following validated scale to grade uterine tone for all cesarean deliveries. The obstetrician places their hand directly on the uterine fundus and scores the adequacy of contraction. The interrater characteristics of this scale have been published (Cole et al, 2021).

The scale ranges from 0-10. A score of 0 is the worst possible score and represents a flaccid, atonic uterus. A score of 10 is the best possible score and represents a firmly-contracted uterus.

Uterine tone assessment: Obstetricians at the study institution use the following validated scale to grade uterine tone for all cesarean deliveries. The obstetrician places their hand directly on the uterine fundus and scores the adequacy of contraction. The interrater characteristics of this scale have been published (Cole et al, PMID 33652161).

The scale ranges from 0-10. A score of 0 is the worst possible score and represents a flaccid, atonic uterus. A score of 10 is the best possible score and represents a firmly-contracted uterus.

Total crystalloid required during cesarean delivery in mL

Baseline mean arterial blood pressure recorded as average of first 6 mean arterial blood pressures recorded in operating room. Percent change calculated as measured mean arterial blood pressure minus baseline, divided by baseline. Reported here as the maximal decrease in mean arterial pressure. Repeated measures ANOVA reported in Statistical Analysis.

Baseline heart rate recorded as average of first 6 heart rates recorded in operating room. Percent change calculated as measured heart rate minus baseline, divided by baseline. Maximal % increase in heart rate reported here. Repeated measures ANOVA used to analyze overall trend in Statistical Analysis below.

Total phenylephrine in milligrams administered while in the operating room

Measured using an Abbott istat machine and CG8+ cartridge to determine venous blood gas ionized calcium levels

Generated from a 2-compartment population pharmacokinetic model in NONMEM using serial venous blood gas ionized calcium concentrations.

Data were not collected. This measure required blood specimens to be obtained at the time of tone scores and this was not done.

Pre-specified subgroup analysis of primary outcome:

Because the proposed mechanism of calcium action-improving uterine contractility-was not expected to improve bleeding from causes such as hysterotomy extension or arterial bleeding, the trial was powered for a prespecified subgroup analysis excluding patients with nonatonic blood loss documented in the surgeon's operative report. Documented nonatonic bleeding was defined as presence in the surgeon's operative report narrative of any of the following: hysterotomy extension, hysterotomy types other than low transverse (eg classical, T- or J-shaped), invasive or abnormally adherent placenta, placental abruption, uterine rupture, bleeding from leiomyomas, grade 3 or 4 vaginal lacerations, or cervical lacerations.