Calcium Chloride in the Prevention of Uterine Atony During Cesarean in Women at Increased Risk of Hemorrhage: a Pilot Randomized Controlled Trial and Pharmacokinetic Study
Phase: PHASE1
Conditions: Uterine Atony, Uterine Atony With Hemorrhage, Cesarean Section Complications
Sponsor: Stanford University

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Calcium chloride for the prevention of uterine atony during 
cesarean in women at increased risk of hemorrhage 
A pilot randomized controlled trial and pharmacokinetic study 
 
Jessica R. Ansari, MD 
Neil Kalariya, MD 
Brendan Carvalho, MBBCh, FRCA 
Pamela Flood, MD, MA 
Nan Guo, PhD 
Edward Riley, MD 
 
Stanford Institutional Review Board # 43076 
Clinical trial registry NCT03867383 https://clinicaltrials.gov/ct2/show/NCT03867383 
 
KEYWORDS: calcium chloride, calcium pharmacokinetics, maternal hemorrhage, 
obstetric hemorrhage, uterine atony 

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Summary 
 
Uterine atony is the leading cause of obstetric hemorrhage. Low calcium levels diminish 
uterine muscle contractility and response to oxytocin. Our aim is to assess the 
effectiveness and pharmacokinetics of intravenous calcium chloride to prevent uterine 
atony. This will be a single-center, double blind, randomized controlled pilot trial. 
Women with at least 2 risk factors for uterine atony at the time of caesarean delivery will 
be randomized in 1:1 ratio to receive 1-gram dilute calcium chloride or saline placebo in 
addition to oxytocin after umbilical cord clamping. The primary outcome will be 
incidence of uterine atony, defined as second-line uterotonic requirement, uterine 
balloon, or estimated blood loss (EBL) >1000 mL.  
 
 

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Introduction: 
Postpartum hemorrhage (PPH) is the leading cause of maternal mortality 
worldwide.1 Uterine atony, defined as failure of the uterus to adequately contract after 
placental delivery, causes at least 70-80% of PPH.2 Current management of uterine 
atony involves prophylaxis with oxytocin and treatment with second-line uterotonics 
including methylergonovine, carboprost, and misoprostol. However, these medications 
all carry significant limitations of poor efficacy, adverse side effect profiles, expense, or 
contraindications to use.3 For example, methylergonovine is contraindicated in women 
with preeclampsia or hypertensive diseases, and carboprost, which may cost up to 
$1000 per dose, is contraindicated in women with asthma. As such, additional 
prevention or treatment modalities for uterine atony are needed. 
Calcium has an important physiological role in uterine contractility. Uterine 
myometrial contractility is dependent upon an influx of calcium from intracellular stores 
in the sarcoplasmic reticulum as well as extracellular calcium.4 A number of in vitro 
studies have established that myometrial contraction amplitude diminishes in the setting 
of low extracellular calcium.4-7 Oxytocin’s efficacy in inducing myometrial contraction 
diminishes by 60-75% in the setting of low or absent extracellular calcium levels in in 
vitro studies with human uterine strips.7 Although the safety and lack of hemodynamic 
consequences of intravenous calcium infusion in parturients has been assessed in one 
study,8 no clinical studies have been designed to assess the potential role for 
intravenous calcium in preventing or treating uterine atony or PPH as a primary 
outcome. 

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. This pilot study was designed to assess whether intravenous calcium chloride 
warrants future study as an agent for prevention of uterine atony and maternal 
hemorrhage. Our primary aim is to assess whether calcium, administered in addition to 
standard oxytocin to women with risk factors for developing uterine atony during 
caesarean delivery, warrants a large study for efficacy in the prevention of uterine 
atony. We hypothesize that providing calcium will augment uterine contraction and 
decrease the incidence of atony. Secondary aims include assessment of atony and 
hemorrhage-associated outcomes including estimated blood loss, fluid requirement, 
obstetrician assessment of tone. Other secondary aims assessed include potential side 
effects of calcium infusion including hemodynamic changes, discomfort at the site of the 
intravenous catheter, nausea, and vomiting. Finally, population pharmacokinetics will be 
assessed as a secondary aim to guide dosing in future studies.  
 
 

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Methods: 
Inclusion criteria: Cesarean delivery with at least two of the following established 
risk factors for uterine atony: intrapartum delivery, oxytocin infusion for 4 hours or 
longer, magnesium infusion, chorioamnionitis, multiple gestation, polyhydramnios, 
premature preterm rupture of membranes (PPROM), preterm at <34 weeks gestation, 
and prior history of postpartum hemorrhage.  
Exclusion criteria: renal dysfunction with serum creatinine >1.0 mg dL-1, maternal 
treatment with digoxin, maternal treatment with a calcium channel blocker, and maternal 
history of cardiac condition including arrhythmia, congenital cardiac disease, or 
coronary disease.  
Patients admitted to the labor and delivery ward will be provided a brief 
informational sheet regarding the study. Women who meet inclusion criteria for the 
study will be subsequently approached by the clinical staff for written informed consent 
as long as the obstetrician agrees that this discussion will not interfere with case 
urgency. Not all women who meet study inclusion criteria will be approached; the 
patients included in this pilot study will be a convenience sample approached when the 
clinical service allows.  
As part of consent, women will be asked if they will permit the team to draw 3 
blood specimens for ionized calcium assessment and nested pharmacokinetic analysis; 
however, women who declined phlebotomy are still allowed study participation.  
Patients will be informed about possible side effects including intravenous line 
discomfort during the consent process and asked to inform the anesthesiologist if they 
experience this at any point during the delivery course. The anesthesiologist is 

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instructed to assume all patients are receiving a 1 gram bolus of calcium chloride, and 
to immediately discontinue the infusion if any concerns for medication extravasation, 
arrhythmia, hemodynamic disturbance, or for severe nausea or vomiting. 
Patients will be sequentially assigned to one of two computer-generated random 
groups (Microsoft Excel, Microsoft Corporation, Redmond, WA, USA) using in a sealed, 
opaque envelope system. Patients will either receive 1 gram of intravenous calcium 
chloride or saline placebo diluted to a total volume of 60mL with normal saline in 
addition to our institution’s standard oxytocin regimen (2 U bolus and 7.5 U hr-1 infusion 
for 4 hours). All participants including the obstetrician, supervising and resident 
anesthesiologists, patient, and study investigator collecting data will be blinded to the 
study solution received. An anesthesiologist with no further involvement in patient care 
will prepare the study solution in a different operating theater. 
Upon entering the operating room, standard noninvasive monitors will be applied: 
pulse oximetry, electrocardiography (ECG), heart rate (HR), and baseline non-invasive 
blood pressure (NIBP). Mean arterial blood pressure (MAP) will be measured with an 
automated, non-invasive sphygmomanometer (Dinamap, Critikon Inc., Tampa, FL, 
USA) at 1 minute intervals until fetal delivery and hysterotomy closure and then at 2.5 
minute intervals at the discretion of the clinical anesthesiologist.  
All patients will have an 18-gauge peripheral intravenous cannula in place at the 
time of cesarean delivery per standard protocol. Lactated Ringers solution will be 
administered at the discretion of the clinical anesthesiologist with general guidelines not 
to exceed 3 L during the caesarean delivery. Total administered fluid volume will be 
recorded. Colloid infusion with 6% hydroxyethyl starch in 0.9% sodium chloride or 5% 

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albumin is also recorded. Patients receive prophylactic phenylephrine infusion (starting 
at 0.5 mcg kg-1 min-1) and phenylephrine (50-100 mcg) or ephedrine (5-10 mg) bolus 
doses as needed at the discretion of the clinical anesthesiologist to maintain MAP within 
20% of baseline. The total phenylephrine infusion dose received as well as total bolus 
doses of vasopressors will likewise be left to the discretion of the clinical 
anesthesiologist and recorded. 
Following fetal delivery and umbilical cord clamping, patients will receive 2 U 
oxytocin bolus, and oxytocin infusion will be initiated at a rate of 7.5 U hr-1. At this same 
time point, the 60 mL study drug infusion will be administered over 10 minutes using an 
Alaris syringe infusion pump (BD Alaris syringe module, Beckton, Dickinson and 
Company, Franklin Lakes, NJ, USA) through microbore infusion tubing connected to the 
intravenous injection port most proximal to the patient. Adequacy of uterine tone (yes or 
no) will be formally assessed at 3, 6, and 10 minutes after delivery by the operating 
obstetrician. If tone is deemed inadequate at 3 minutes or 6 minutes, a 2 U bolus of 
oxytocin will be administered, and the oxytocin infusion rate doubled. If at 10 minutes, 
tone is still deemed inadequate, a second-line uterotonic agent of intramuscular 
methylergonovine 200 mcg, intramuscular 250 mcg, or buccal misoprostol 600 mcg will 
be chosen at the discretion of the obstetrician and clinical anesthesiologist and 
recorded. After leaving the operating theater, all patients receive our institution’s 
standard protocol of oxytocin 7.5 U hr-1 for 4 hours. 
 
 
 

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Primary outcome: 
The primary outcome will be incidence of uterine atony, a binary composite 
outcome defined as any of the following: second-line uterotonic requirement, EBL 
>1000 mL, placement of a Bakri balloon, B-lynch suture, or O’Leary sutures by the 
obstetrician, uterine artery embolization or hysterectomy. For this pilot study, any P 
value less than 0.2 is defined a priori as indicating potential for efficacy, and thus 
warranting a future, larger study.  
 
Secondary outcomes: 
Several secondary outcomes related to uterine atony and hemorrhage will be 
assessed. At completion of study drug infusion (10 minutes after umbilical cord clamp), 
the operating obstetric attending will be asked to assess and grade the uterine tone 
based upon palpation of the fundus using a verbal numerical scale score from 0-100 
(0=completely atonic, 100=fully contracted). Blood loss will be estimated by visual 
examination of the graduated suction jars, surgical sponges, drapes, table and floor. 
The difference in preoperative and postoperative day 1 hematocrit gathered as standard 
of care at our institution will be calculated. The total volume of intravenous fluid given 
from start to conclusion of the surgical procedure will be recorded.  
For patients who consent to phlebotomy, blood specimens will be collected into a 
non-heparinized syringe at three different time intervals: once in the operating room 
prior to fetal delivery for a baseline value, once within 1-30 minutes of completing study 
drug infusion, and once 30 minutes to 3 hours after completing study drug infusion. To 
allow for painless sample collection for patients with a surgical lumbar neuraxial block, a 

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tourniquet will be placed at the patient’s lower calf, and a 21-gauge winged blood 
collection needle was utilized to collect a 3 mL venous specimen from the foot or 
saphenous vein. The ionized calcium level and pH will be immediately determined with 
an i-STAT 1 system (i-STAT Corp., Princeton, NJ, USA). 
 
Calcium pharmacokinetics will be analyzed with NONMEM (Nonlinear Mixed-
Effects Modeling; Globomax, Ellicott City, MD) using PLT Tools (PLT Soft, San 
Francisco, CA). We will evaluate calcium kinetics using a 1-compartment model with 
administration into the central compartment. We will use an exponential model for 
interindividual variability on the volume of distribution and clearance and an additive 
model of interindividual variability on the baseline calcium concentration. The model 
parameters will be estimated by NONMEM using the first order conditional estimation 
approach. Confidence intervals for each parameter will be assessed using log likelihood 
profiling and bootstrap analysis.  
 
Hemodynamic variables analyzed will include heart rate and mean arterial 
pressure at baseline, at fetal delivery, and at 5 minute intervals for the next 30 minutes. 
This will be used to calculate a maximal increase and decrease from baseline 
calculation for each patient. The clinical anesthesiologist will fill out a checklist prior to 
exiting the operating theater at case conclusion answering whether the patient 
experienced nausea, vomiting, intravenous line discomfort, changes in heart rate or 
blood pressure, any arrhythmia, or other possible side effect (with a free-text field) 
during or following the study drug infusion. 
 
 
 

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Statistical analysis: 
A sample size of 40 parturients was selected for this pilot study as most likely 
feasible to perform in approximately one year or less at our institution. Internal quality 
improvement data at our institution revealed that in patients with more than one atony 
risk factor, incidence of EBL >1000 mL or second line uterotonic use was >60%. If 
calcium were to halve the rate of uterine atony, we estimated that a sample size of 20 
subjects in the calcium and 20 subjects in the placebo group should allow sufficient data 
to show a difference between groups with 75% power and a two-sided type I error 
probability of 0.2. 
For analysis of the primary outcome, the relative risk (RR), and its 95% 
confidence interval will be calculated according to Altman.13 The number needed to treat 
(NNT) will be defined and calculated using the terminology suggested by Altman.14 The 
95% confidence interval for NNT will be calculated according to Daly,15 and P-value 
calculated according to Sheskin.16 Bootstrap analysis for sample size calculation for 
future studies will be performed using R programming and 10,000 replicates of the pilot 
dataset. 
Demographic and baseline characteristics will be reported as mean ± standard 
deviation (SD) or median and interquartile range [IQR] as appropriate for continuous 
variables. Categorical variables will be presented as percent. The mean differences and 
their 95% confidence intervals (CI) will be presented for outcomes of interest. Univariate 
comparisons between groups will be performed using Chi-square analysis or the 
Kruskal–Wallis test, as appropriate for categorical or continuous variables, respectively. 

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Statistical analyses will be performed using STATA version 14.0 (StataCorp, 
CollegeStation, TX, USA).  
 
 
 

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468-76 
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7. Papandreou L, Chasiotis G, Seferiadis K, Thanasoulias NC, Dousias V, Tsanadis G, 
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2004 Jul 15;115(1):17-22. 
8. Farber MK, Schultz R, Lugo L, Liu X, Huang C, Tsen LC. The effect of co-administration 
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Int J Obstet Anesth. 2015 Aug;24(3):217-24