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Vol 11 No 2 May 2021

92

Original Article       

Hemodynamic Effects of Oxytocin when Given as Bolus or Slow 
Intravenous Infusion During Cesarean Section

Nasima Begum1, Tahamina Khanum2, Rahima Khatun3, Nelufa Tahera Rahman4
Received: 5 January 2021        Accepted: 14 April 2021

doi: https://doi.org/10.3329/jemc.v11i2.65191

Abstract

Background: Oxytocin is a uterotonic drug with profound haemodynamic effects. The effects of 
oxytocin on women undergoing cesarean section include tachycardia, hypotension and decreased 
cardiac output. These can be sufficient to cause significant compromise in high risk patients. 
Objective: This study aims to find out a simple way to decrease these risks without compromising 
the therapeutic benefits such as decreasing bleeding after delivery and uterine contraction. 
Materials and Methods: We recruited 60 women undergoing cesarean section. The subjects were 
randomly divided into two groups, 30 subjects per group, randomly selected by blind envelope 
method. Group A: parturient received 5 IU bolus (approximately over 2 seconds). Group B: 
parturient received 5 IU oxytocin IV slow infusion (diluted with 10 mL distilled water) over 2 
minutes. Results:  A significant increase in heart rate and fall in blood pressure in the group where 
oxytocin was given IV bolus compared to the slow IV infusion group. There were no differences 
in the estimated blood loss and uterine contraction between the two groups.  Conclusion: The 
haemodynamic changes are more marked in the IV bolus than the slow IV infusion of oxytocin. 
Slower injection of oxytocin can effectively minimize the cardiovascular side effects without 
compromising the therapeutic benefits. 

Key words: Obstetric anaesthesia; Anaesthetic techniques; Regional; Spinal; Complications;    
Haemodynamic; Oxytocin

J Enam Med Col 2021; 11(2): 92−98

1. Assistant Professor, Department of Gynaecology and Obstetrics, Enam Medical College & Hospital, Savar, Dhaka
2. Associate Professor, Department of Gynaecology and Obstetrics, Enam Medical College & Hospital, Savar, Dhaka
3. Assistant Professor, Department of Gynaecology and Obstetrics, Ad-din Women’s Medical College & Hospital, Dhaka 
4. Medical Officer, Department of Anesthesiology & ICU, Enam Medical College & Hospital, Savar, Dhaka
Correspondence Nasima Begum, Email: nasimadr1975@gmail.com

Introduction

The hemodynamic changes in parturient women after 
cesarean delivery may be caused by the elimination 
of the aorta-caval compression, autotransfusion of 
blood immediately after delivery, haemorrhage, and 
vasoconstriction and excitation, but some studies 
have reported that uterotonic drug is the main factor.1,2 
Uterotonic drug, which is most frequently used for 
cesarean section, is oxytocin which induces uterine 

contraction during cesarean section and peripheral 
vasodilation along with a decrease in arterial pressure 
after delivery and thus reduces hemorrhage.3,4 
However, intravenous injection of oxytocin during 
cesarean section may cause cardiovascular side 
effects such as tachycardia or hypotension1,2 and is 
reported to cause even cardiovascular collapse and 
death in the most severe cases.5,6 Moreover, various 



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other side effects have been reported including fluid 
pooling or pulmonary edema by the antidiuretic effect 
of oxytocin.7−9

Hence, determining the oxytocin concentration 
for cesarean section is important. However, since 
the activity of oxytocin varies from individual to 
individual10 and an appropriate dose has not been 
established, 5−20 IU is intravenously injected based 
on experience.11,12 There is recent assertion that bolus 
intravenous injection or bolus-continuous parallel 
intravenous injection of oxytocin is more effective 
than continuous intravenous injection in cesarean 
section.13,14 There is also report that a great quantity 
of bolus intravenous injection requires caution 
because it causes hemodynamic changes related to 
hypotension.1,2 Therefore, research is necessary on 
the method of oxytocin injection and the effective 
minimum concentration for cesarean section to induce 
uterine contraction without side effects. 

In this study, we tried to find out the effects of 
hemodynamic changes such as changes in heart 
rate, blood pressure and uterine contraction of the 
recommended dose (i.e., 5 IU) of oxytocin when 
given as IV bolus or slow IV infusion (diluted in 10 
mL of distilled water) over 2 minutes during cesarean 
section under spinal anesthesia.

Materials and Methods

This study was approved by the Hospital Ethics 
Committee. We recruited women undergoing cesarean 
section under spinal anesthesia who were 38 weeks 
or more into their pregnancy, and were classified as 
Class 1 or 2 according to the American Society of 
Anesthesiologist (ASA) physical status classification. 
The study was conducted in Obstetrics and Gynecology 
department in Dhaka Medical College Hospital 
(DMCH), Dhaka from 1 January 2009 to 30 August 
2009. Pregnant women who had contraindication for 
spinal anesthesia, those whose weight was 100 kg or 
higher, those who had fetal abnormalities, diabetes, 
gestational hypertension, cardiovascular disease, or 
cerebral hemorrhage, and those whose labor pain had 
already started, were excluded from the study. The 
subjects were visited before the operation and written 
consent was given by the subjects. The age, height 

and weight of the patients were recorded.

About 500 mL of Hartmann solution was rapidly 
dripped into all the parturient women before inducing 
anesthesia. An electrocardiograph, automated 
noninvasive blood pressure device, and a pulse 
oximeter were attached to the subjects, and oxygen 
was administered at 5 L/min through a face mask. For 
the spinal anesthesia, the L3−4 or L4−5 lumbar region 
was punctured with a 25 G Quincke needle when the 
parturient women were in the left lateral recumbent 
position, and a 0.5% hyperbaric bupivacaine 
solution (10−12 mg) was injected after verifying the 
cerebrospinal fluid leakage. Immediately after the 
anesthesia, the parturient women were asked to take 
the supine position and the maximum sensory block 
level was set to T4−6. The blood pressure and heart 
rate (HR) were measured in five-minute intervals from 
the time just after the anesthesia started to the end of 
the operation. However, during the 10 minutes after 
the oxytocin was injected, the blood pressure and HR 
were recorded in one-minute intervals, and delivery 
of the newborn was set as the baseline. The parturient 
women were asked if they felt or experienced nausea or 
vomiting after oxytocin injection and the results were 
recorded. When some of the parturient women had 
severe vomiting or continual nausea, the antiemetic 
drug, ondansetron 8 mg, was intravenously injected. 
In the cases where the systolic pressure decreased by 
more than 20% compared to the blood pressure before 
coming to the operating room, 10 mg of ephedrine 
was intravenously injected until the blood pressure 
was normalized, and these cases were excluded from 
the study. 

The subjects were randomly divided into two groups, 
30 subjects per group, randomly selected by blind 
envelope method. Group A: parturient received 5 
IU bolus (approximately over 2 seconds). Group B: 
parturient received 5 IU oxytocin IV slow infusion 
(diluted with 10 mL distilled water) over 2 minutes.

After delivery of the fetus, group A was given 5 IU 
oxytocin bolus (approximately over 2 seconds) and 
group B was given 5 IU oxytocin IV infusion slowly 
(diluted with 10 mL distilled water) over 2 minutes. 
Baseline data were taken before oxytocin was given. 



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After delivery of the fetus, patient was monitored by 
measuring systolic and diastolic BP, mean arterial 
pressure (MAP), heart rate, oxygen saturation (SPO2), 
uterine contraction, uterine bleeding and any adverse 
effects was recorded every one minute. The study 
period was started just before oxytocin was given 
and it was continued for a further 10 minutes. The 
study period of 10 minutes was set after a small pilot 
study. Patient was observed by the surgeon and the 
state of the uterine contraction was expressed as 
mild, moderate or satisfactorily contracted. Uterine 
bleeding was calculated clinically after suctioning 
amniotic fluid and blood in separate bottles. Visual 
estimation of the blood loss was done by surgical 
sponges and laparotomy pads (laps). A fully-soaked 
sponge (4″ × 4″) on each side holds 10 mL of blood 
whereas a soaked “lap” holds 100−150 mL. In case 
of cesarean section 800−1000 mL of blood loss is 
considerable. Patient can tolerate this amount of blood 
loss.  So, more than 1000 mL blood loss is considered 

as excessive blood loss.

At the end of surgery 200 microgram misoprostol was 
given per-rectally for each patient. Postoperatively 
patients’ state of uterine contraction, P/V bleeding and 
cardiovascular status were also monitored. The results 
were compiled and analyzed statistically by unpaired 
‘t’ test and ‘chi-square’ test with level of significance 
at p value <0.05.

Results

A total of 60 subjects were included in the study. Table 
I shows age, gestational age and weight  distribution 
of the subjects. Table Ⅱ shows comparison of 
hemodynamic mean parameters between group A and 
group B at 0 minute. Table Ⅲ shows comparison of 
hemodynamic mean parameters between group A and 
group B at 3 minutes. Table Ⅳ shows comparison of 
hemodynamic mean parameters between group A and 
group B at 5 minutes. 

Table I: Age, gestational age and weight  distribution of the subjects

Group A
n=30

Group B
n=30 t values p values

Mean±SD Mean±SD
Age in years 24.1±6.0 25.1±4.7 0.70 0.489ns

Gestational age (wks) 39.4±0.7 39.6±0.8 0.921 0.360ns

Weight of the patients (kg) 59.3±3.0 59.9±2.3 0.99 0.327ns

Group A: 5 IU oxytocin bolus, Group B: 5 IU oxytocin IV infusion. p value for age and weight of the patients was reached 
by unpaired t test and p value for gestational age was reached by Chi squire test.  No significant difference was found 
between group A and group B.

Table Ⅱ: Comparison of haemodynamic mean parameters between group A and group B at 0 minute (n=60)

0 min Group A(n=30)
Group B
(n=30) t values p values

Mean±SD Mean±SD
Heart rate (beats/min) 89.5±8.4 86.9±9.5 0.73 0.471
Systolic BP (mm Hg) 116.7±7.5 119.7±6.7 1.63 0.109
Diastolic BP (mm Hg) 75.7±6.8 77.8±4.9 1.42 0.160
SPO2 (%) 97.7±0.6 98.0±0.6 1.71 0.093
MAP (mm Hg) 88.9±7.0 86.8±4.4 1.93 0.059

Group A: 5 IU oxytocin bolus, Group B: 5 IU oxytocin IV infusion. p value reached from unpaired t-test. The mean 
difference of all haemodynamic parameters at 0 minute were not statistically significant (p>0.05) in unpaired t-test.



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Table Ⅲ: Comparison of haemodynamic mean parameters between group A and group B at 3 minutes (n=60)

3 minutes
Group A
(n=30)

Group B
(n=30) t values p values

Mean±SD Mean±SD
Heart rate (beats/min) 101.8±5.1 90.4±4.4 2.23 0.026S

Systolic BP (mm Hg) 95.5±5.4 108.7±4.3 2.16 0.006s

Diastolic BP (mm Hg) 60.0±9.9 73.7±8.1 2.39 0.022s

SPO2 (%) 98.7±0.5 98.8±0.5 0.25 0.802
ns

MAP (mm Hg) 64.2±6.2 74.7±7.3 2.07 0.034s

Group A: 5 IU oxytocin bolus, Group B: 5 IU oxytocin IV infusion. p value reached from unpaired t-test. The mean 
difference of all hemodynamic parameters at 3 minute were statistically significant (p<0.05) in unpaired t-test except SPO2, 
which was not statistically significant (p>0.05).

Table Ⅳ: Comparison of hemodynamic mean parameters between group A and group B at 5 minutes (n=60)

5 minutes
Group A
(n=30)

Group B
(n=30) t values p values

Mean±SD Mean±SD
Heart rate (beats/min) 105.8±5.2 90.1±2.1 2.27 0.029S

Systolic BP (mmHg) 97.3±4.5 106.9±3.6 2.21 0.032s

Diastolic BP (mmHg) 61.3±3.6 72.6±4.9 2.21 0.032s

SPO2 (%) 98.9±0.3 98.8±0.4 1.20 0.235
ns

MAP (mmHg) 64.7±4.2 74.3±5.3 2.55 0.016s

Group A: 5 IU oxytocin bolus, Group B: 5 IU oxytocin IV infusion. P value reached from unpaired t-test. The mean 
difference of all hemodynamic parameters at 5 minute were statistically significant (p<0.05) in unpaired t-test except SPO2, 
which was not statistically significant (p>0.05).

Table Ⅴ shows amount of blood loss and occurance 
of postpartum haemorrhage in two groups. In case 
of cesarean section 800−1000 mL of blood loss is 
considerable. Patient can tolerate this amount of blood 
loss.  So, more than 1000 mL blood loss is considered 
as excessive blood loss.

Uterus was found mildly contracted in 27 (90%) 

cases in group A and in 26 (86.7%) cases in group B 
at 1 minute. However, at 2 minutes uterus was found 
moderately contracted in 29 (96.7%) in group A, and 28 
(93.3%) in group B.  Uterus was found fully contracted 
at 3 minutes and onwards in all patients in both groups. 
Regarding uterine contraction, no statistical significant 
(p>0.05) difference was found between two groups in 
chi square test (Table VI).

Table Ⅴ: Amount of blood loss and occurance of postpartum haemorrhage in two groups

Complications Group A Group B
Number Percentage Number Percentage

Ignored bleeding up to 1000 mL 30 100.0 30 100.0
Postpartum hemorrhage 0 0 0 0

Group A: 5 IU oxytocin bolus, Group B: 5 IU oxytocin IV infusion. p value reached from chi square test.



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Discussion

Oxytocin, a hormone that is secreted from the pituitary 
posterior lobe, decreases blood pressure by causing 
peripheral vasodilation and increasing the HR and 
induces uterine contraction.3,4 Uterine contraction by 
oxytocin is enhanced since there are more intrauterine 
oxytocin receptors.15 The oxytocin sensitivity of 
pregnant women reaches the maximum in the full 
term of the pregnancy because of the increase 
of intrauterine oxytocin receptors by gestational 
estrogen.10 Hence, during normal delivery, the 
oxytocin discharged from the pituitary posterior lobe 
by the obstetric canal stimulus of the fetus can induce 
labor pain and sufficient uterine contraction with an 
extreme low-dose of 10 mIU/min.16 In the case of a 
planned cesarean section, however, a relatively high-
dose of oxytocin (5−20 IU) is intravenously injected 
since the action of the oxytocin is not normal.11,12 
Since hemodynamic changes are proportional to the 
intravenously injected dose of oxytocin, studies have 
been done on effective concentrations and intravenous 
injection methods.

Sarna et al11 reported that oxytocin infusion at a rate 
of 1 IU/min did not show any difference in uterine 
contraction and blood loss with that of 5 IU/min by 
intravenous injection even though the total dose may 
have been more than 5 IU. Kim et al12 published 
the same assertion. On the contrary, Zarzur17 
recommended an infusion at a rate lower than 1 IU/
min because infusion at a rate higher than 0.25 IU/

min may cause such symptoms as hemangiectatic 
hypotension, tachycardia, increased cardiac output, 
and myocardial ischemia. 

According to many recent studies, oxytocin bolus 
injection was reported to be more effective than 
infusion by intravenous injection to reduce blood loss 
by inducing the appropriate uterine contraction13, and 
thus, the minimum bolus dose has been discussed.18−20 
A suggested method to reduce hemodynamic 
changes is the repeated intravenous injections of a 
small quantity of a bolus dose and bolus-continuous 
parallel intravenous injection.14,21 Svanstrom et al6 
stated that attention is required because a bolus 
injection of 10 IU oxytocin may cause temporary 
hypotension and tachycardia as well as myocardial 
ischemia, apart from the operation, pregnancy, and 
autonomic blocking by spinal anesthesia. Pinder et 
al2 recommended 5 IU as the bolus dose since 10 IU 
of bolus intravenous dose might not be considered as 
safe, either. On the contrary, Butwick et al19 asserted 
that a dose of more than 5 IU might not be necessary 
because the appropriate uterine contraction occurred 
even with a bolus dose of 0.5−3 IU. Their results were 
similar to our results and the hemodynamic changes 
were always temporary. This study shows that slower 
infusion of 5 IU oxytocin can effectively minimize the 
cardiovascular side-effects but rapid bolus oxytocin 
causes marked cardiovascular instability. 

The current study demonstrated that there was an 
average decrease in MAP of 24 mm Hg ranging from 

Table Ⅵ: States of uterine contraction in both groups

Uterine Contraction 
Group A (n=30) Group B (n=30)

p values
Number Percentage Number Percentage

1 minute
Mildly contracted 
Moderately contracted 

27 90.0 26 86.7
3 10.0 4 13.3 0.500

2 minute
Mildly contracted 1 3.3 2 6.7
Moderately contracted 29 96.7 28 93.3 0.500
3 minute
Fully contracted 30 100.0 30 100.0

Group A: 5 IU oxytocin bolus, Group B: 5 IU oxytocin IV infusion. p value reached from chi square test.



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19 to 32 mm Hg in group A during 2 to 5 minutes 
who received 5 IU of oxytocin as a rapid bolus. But 
in group B average decrease in MAP was 12 mm Hg 
ranging from 8 to 18 mm Hg during 2 to 5 minutes. 
It was observed that the changes in heart rate were 
significantly higher in group A compared to group B 
during 2 to 5 minutes. 

Thus, it was found that the hemodynamic changes 
varied by the bolus injected oxytocin dose and 
changes were recovered from in about 4−5 minutes 
after oxytocin injection. It is shown in this study that 
delivery of the newborn and the following excitement 
may affect the HR because parturient women are 
conscious during cesarean section under spinal 
anesthesia. However, the main factor of the changes 
may be the effect of oxytocin itself. 

The half-life of oxytocin is about 2−5 minutes and a 
blood steady state is reached in about 30−60 minutes 
after intravenous injection.21 Thus, the oxytocin dose 
and injection method play an important role in the 
hemodynamic changes before a steady state is reached. 
These hemodynamic changes by oxytocin are always 
temporary and the effect on healthy parturient women 
is small. However, it may be dangerous to parturient 
women who have hypovolemia or cardiovascular 
diseases. Hence, continuous intravenous injection 
of oxytocin at a low concentration is primarily 
recommended as a safe injection method for parturient 
women in a high-risk group.1,2 Nevertheless, repeated 
bolus intravenous injection with a small quantity 
of bolus or parallel intravenous injection of a small 
quantity of bolus plus continuous injection is also 
used because of rapid desensitization by which the 
hemodynamic changes are significantly decreased in 
the repeated oxytocin than in the initial injection.14,22

While the cardiovascular results of this study are 
unequivocal, it was acceptable that <1000 mL 
bleeding during cesarean section was ignored in this 
study. Uterine contraction and uterine bleeding were in 
satisfactory level in both groups. This study supports 
the need for caution in using oxytocin as a bolus in 
cardiovascular unstable patients and offers relatively 
less adverse effects when given as an infusion over 
two minutes. The hemodynamic changes are more 

marked in the IV bolus than the slow IV infusion of 
oxytocin. Slower injection of oxytocin can effectively 
minimize the cardiovascular side effects without 
compromising the therapeutic benefits.

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