Comparison of the Effectiveness of Bolus Doses of Norepinephrine 4 mcg and Phenylephrine 50 mcg in Managing Hypotension After Spinal Anesthesia in Cesarean Section Patients
Phase: NA
Conditions: Hypotenstion, Cesarean Resection, Anesthesia Spinal, Pregnancy Complications, Cardiovascular
Sponsor: Universitas Sumatera Utara

COMPARISON OF THE EFFECTIVENESS OF BOLUS DOSES OF NOREPINEPHRINE 4 MCG AND 
PHENILEPHRINE 50 MCG IN MANAGING HYPOTENSION AFTER SPINAL ANESTHESIA IN CESAREAN 
SECTION PATIENTS 
 
NCT Number:  
Document Date: August 29, 2025 
 

COMPARISON OF THE EFFECTIVENESS OF BOLUS DOSES OF NOREPINEPHRINE 4 MCG AND 
PHENILEPHRINE 50 MCG IN MANAGING HYPOTENSION AFTER SPINAL ANESTHESIA IN CESAREAN 
SECTION PATIENTS 
ABSTRACT 
Background: Spinal anesthesia is the preferred method for cesarean sections but frequently 
causes maternal hypotension, posing risks to both mother and fetus. Phenylephrine has been the 
traditional vasopressor, but its association with reflex bradycardia raises concerns. Norepinephrine 
may offer a more stable hemodynamic response. This study compared the efficacy and safety of 
norepinephrine (4 mcg) and phenylephrine (50 mcg) bolus doses in managing spinal-induced 
hypotension during cesarean delivery. 
Methods: A randomized, double-blind clinical trial was conducted with 46 parturients 
undergoing elective cesarean section under spinal anesthesia. Participants received either 
norepinephrine 4 mcg or phenylephrine 50 mcg intravenously upon hypotension onset. Hemodynamic 
parameters (SBP, DBP, HR) were recorded every two minutes for 30 minutes. Vasopressor requirements 
and side effects were also assessed. Data were analyzed using SPSS v26, with significance p value < 
0.05. 
Result: Both vasopressors effectively restored SBP without significant differences in efficacy. 
However, phenylephrine caused a significant HR reduction (particularly at T2–T4 intervals, p value < 
0.01), while norepinephrine maintained stable HR. Side effects (e.g., nausea) were minimal and similar 
between groups. These findings suggest that norepinephrine provides comparable blood pressure 
control but with better HR stability, potentially improving cardiac output and placental perfusion 
compared to phenylephrine. 
Conclusion: Norepinephrine (4 mcg) and phenylephrine (50 mcg) are equally effective in 
treating spinal anesthesia-induced hypotension during cesarean sections. However, norepinephrine 
offers a more favorable hemodynamic profile by avoiding reflex bradycardia, making it a preferable 
alternative for maternal and fetal well-being. 
Keywords: norepinephrine, phenylephrine, spinal anesthesia, hypotension, cesarean section 
 
INTRODUCTION 
Cesarean section under spinal anesthesia remains the preferred anesthetic technique in 
elective deliveries due to its rapid onset and reduced risk of aspiration and fetal exposure to general 
anesthetics. However, a major complication associated with spinal anesthesia is maternal hypotension, 
with incidences reported as high as 80–90% due to sympathetic blockade and aortocaval compression 
by the gravid uterus (Šklebar, Bujas, & Habek, 2019). This condition can significantly reduce 
uteroplacental perfusion and pose risks to both mother and fetus, necessitating prompt management 
with vasopressor agents. 
Phenylephrine has long been used as a first-line vasopressor in this context. As a pure α1-
adrenergic agonist, it causes peripheral vasoconstriction and effectively increases systemic vascular 
resistance to counteract spinal-induced hypotension. However, its use is frequently accompanied by 
reflex bradycardia, which may compromise cardiac output and, in turn, fetal oxygenation (Richards, 
Lopez, & Maani, 2023; Singh et al., 2020). Although effective in blood pressure restoration, the 
bradycardic effect of phenylephrine has led to increasing interest in alternative vasopressors. 

Norepinephrine, a mixed α1- and β1-adrenergic agonist, has been proposed as a more 
physiologically favorable alternative. Its α1 action provides vasoconstriction, while its β1 component 
helps maintain heart rate and myocardial contractility, potentially preserving cardiac output more 
effectively than phenylephrine. Multiple studies have evaluated its utility. For instance, Vallejo et al., 
(2017) found norepinephrine to be as effective as phenylephrine in preventing hypotension, with 
improved heart rate preservation. Similarly, Hassani et al., (2018) and Xue et al., (2023)reported in 
their trials that norepinephrine was associated with fewer incidences of bradycardia and better 
maternal hemodynamic stability. 
Further support comes from recent systematic reviews. Wang, Mao, Liu, Xu, & Yang, (2019) 
and Xue et al., (2023) concluded that norepinephrine offers a more balanced hemodynamic profile 
and may be preferable in clinical scenarios requiring sustained cardiac output. Their meta-analyses 
indicated that norepinephrine and phenylephrine are equally effective in controlling hypotension, but 
norepinephrine results in fewer episodes of bradycardia and less need for rescue medication. 
Despite these encouraging findings, relatively few randomized studies have directly compared 
fixed bolus doses of norepinephrine and phenylephrine during cesarean section. The current study 
seeks to address this gap by comparing 4 mcg of norepinephrine to 50 mcg of phenylephrine for the 
treatment of spinal anesthesia-induced hypotension in cesarean section patients. The objective is to 
evaluate their comparative effectiveness in blood pressure restoration, heart rate control, and overall 
safety to inform optimal vasopressor selection in obstetric anesthesia. 
 
METHODS 
Study Design 
This research adopted a randomized, double-blind clinical trial approach to assess and 
compare the efficacy of intravenous bolus doses of norepinephrine 4 mcg and phenylephrine 50 mcg 
in treating hypotension following spinal anesthesia in cesarean section patients. The study was carried 
out at three healthcare facilities in Medan, Indonesia: Prof. dr. Chairuddin P. Lubis Hospital, Dr. Pirngadi 
General Hospital, and Haji General Hospital. Ethical approval was granted by the Ethics Committee of 
the Faculty of Medicine, Universitas Sumatera Utara. 
Population and Samples 
The target population comprised pregnant women between 18 and 40 years old undergoing 
elective cesarean delivery under spinal anesthesia with an ASA physical status of II. Inclusion criteria 
required stable baseline hemodynamics and no use of inotropic, chronotropic, or vasoactive drugs 
preoperatively. Exclusion criteria included emergency procedures, fetal distress, preeclampsia or 
eclampsia, contraindications to spinal anesthesia, allergic history to the study drugs, and 
hemodynamic instability. Subjects were excluded if they withdrew, experienced significant clinical 
deterioration, or did not develop post-spinal hypotension. 
Sample size was calculated based on unpaired numerical analysis, resulting in a minimum of 
23 participants per group. Subjects were randomly assigned into one of two groups: Group N 
(norepinephrine 4 mcg) or Group P (phenylephrine 50 mcg), using computerized block randomization 
via the website www.randomizer.org. The vasopressors were administered intravenously when 
hypotension occurred, defined as a ≥20% drop in systolic blood pressure from the pre-anesthesia 
baseline. 

Study Instruments 
To monitor patient status, non-invasive, calibrated multiparameter monitors were used to 
assess systolic and diastolic blood pressure, heart rate, and mean arterial pressure. Spinal anesthesia 
was performed using 10 mg hyperbaric bupivacaine with 25 mcg fentanyl administered intrathecally 
via a 25G Quincke needle at the L3-L4 interspace. Norepinephrine and phenylephrine solutions were 
diluted to a concentration of 2 mcg/mL and 25 mcg/mL, respectively, to standardize the 2 mL bolus 
doses given for each episode of hypotension. 
Data Collection 
Data were collected starting from baseline (T0), followed by continuous hemodynamic 
recordings every two minutes for 30 minutes post-spinal anesthesia (T1–T15). The total number of 
vasopressor administrations and any side effects—such as nausea, bradycardia, vomiting, or 
shivering—were documented by trained observers blinded to group allocation. 
Data Analysis 
Statistical analyses were performed using SPSS version 26.0 (IBM). Data normality was 
assessed using the Shapiro-Wilk test. Continuous variables were presented as mean ± standard 
deviation for normally distributed data, or as medians and ranges otherwise. Inter-group comparisons 
of continuous data were analyzed using independent samples t-tests or Mann-Whitney U tests as 
appropriate. Categorical variables were compared using Chi-square tests. A p-value below 0.05 was 
deemed statistically significant. 
 
RESULTS 
Table 1. Patient Characteristics 
Characteristics 
Norepinephrine 
(n: 23) 
Phenilephrine 
(n: 23) 
p-value 
Age (year) (Mean±SD) 
30,2 ± 3,8 
31,4  ± 2,5 
0,33 
Gestational Age (week) 
(Mean±SD) 
37,91 ± 1,1 
37,78 ± 1,5 
0,21 
Number of Pregnancies 
(per time) (Mean±SD) 
2,3 ± 0,9 
1,95 ± 0,8 
0,02 
 
As shown in table 1, This study included 46 parturients scheduled for elective cesarean section 
under spinal anesthesia who met the inclusion criteria and were randomized equally into two groups: 
norepinephrine 4 mcg (n = 23) and phenylephrine 50 mcg (n = 23). Baseline demographic data 
including maternal age, gestational age, and parity were statistically similar between the groups (p > 
0.05), indicating appropriate comparability for evaluating intervention outcomes. 
Table 2. Systolic Pressure Data in the Norepinephrine Group 
Time 
Examination 
Norepinephrine 
p-value 
T0 
122,8 ± 6,3 
0,71 

T1 
92,3 ± 4,9 
0,22 
T2 
114,8 ± 6,9 
0,59 
T3 
117,6 ± 7,5 
0,17 
T4 
117,9 ± 12,4 
0,07 
T5 
123,6 ± 6,6 
0,11 
T6 
123,5 ± 5,2  
0,07 
T7 
123,3 ± 3,8 
0,31 
T8 
122,6 ± 4,6 
0,58 
T9 
123,1 ± 4,9 
0,81 
T10 
121,9 ± 3,3 
0,34 
T11 
120,5 ±2,1 
0,28 
T12 
119,5 ± 2,4 
0,50 
T13 
119,3 ± 1,7 
0,06 
T14 
118,4 ± 1,8 
0,06 
T15 
119,0 ± 2,5  
0,08 
 
Table 3. Systolic Pressure Data in the Phenilephrine Group 
Time 
Examination 
Phenilephrine 
p-value 
T0 
123,6 ± 6,8 
0,31 
T1 
96,1 ± 5.9 
0,41 
T2 
118,7 ± 6,7 
0,51 
T3 
122,0 ± 8,2 
0,18 
T4 
123,1 ± 12,2 
0,11 
T5 
128,1 ± 3,7 
0,18 
T6 
125,6 ± 6,5  
0,33 
T7 
123,1 ± 6,8 
0,09 
T8 
122,6 ± 7,5 
0,06 
T9 
123,6 ± 5,3 
0,44 
T10 
122,0 ± 4,9 
0,69 
T11 
117,8 ± 5,4 
0,79 
T12 
116,2 ± 6,8 
0,52 
T13 
109,9 ± 3,8 
0,49 
T14 
112,3 ± 6,9 
0,33 

T15 
113,8 ± 7,1 
0,11 
 
Table 4. Effect of Phenilephrine and Ephedrine Administration on Systolic Pressure 
Group 
Time Examination 
p-value 
T1 
T2 
Norepinephrine 
92,3 ± 4,9 
114,7 ± 6,9 
0,001 
Phenilephrine 
96,1 ± 5.9 
118,7 ± 6,7 
0,001 
 
Table 5. Comparison of Systolic Pressure Between Intervention Groups 
Time 
Examination 
Norepinephrine 
Phenilephrine 
p-value 
T0 
122,7 ± 6,3 
123,6 ± 6,8 
0,49 
T1 
92,3 ± 4,9 
96,1 ± 5.9 
0,02 
T2 
114,7 ± 6,9 
118,7 ± 6,7 
0,01 
T3 
117,6 ± 7,5 
122,0 ± 8,2 
0,06 
T4 
117,9 ± 12,4 
123,1 ±12,2 
0,44 
T5 
123,6 ± 6,6 
128,1 ± 3,7 
0,11 
T6 
123,4 ± 5,1  
125,6 ± 6,5  
0,22 
T7 
123,2 ± 3,8 
123,1 ± 6,8 
0,55 
T8 
122,5 ± 4,6 
122,6 ± 7,5 
0,44 
T9 
123,1 ± 4,9 
123,6 ± 5,3 
0,93 
T10 
121,9 ± 3,3 
122,0 ± 4,9 
0,18 
T11 
120,4 ±2,1  
117,8 ± 5,4 
0,12 
T12 
119,5 ± 2,4 
116,2 ± 6,8 
0,33 
T13 
119,3 ± 1,7 
109,9 ± 3,8 
0,43 
T14 
118,3 ± 1,8 
112,3 ± 6,9 
0,55 
T15 
119,1 ± 2,5  
113,8 ± 7,1 
0,65 
 
 
Table 6. Difference in Systolic Pressure Between Intervention Groups 
Time 
Examination 
Group 
Mean 
Difference 
P value 
T1 
Norepinerphine 
Phenilephrine 
-3.8 
0,07 
T2 
Norepinerphine 
Phenilephrine 
-4.1 
0,11 
 
Hemodynamic parameters were assessed at baseline (T0) and at 2-minute intervals for 30 
minutes post spinal anesthesia (T1–T15) (Table 3). Initial systolic blood pressures (SBP) in the 
norepinephrine and phenylephrine groups were 122.8 ± 6.3 mmHg and 123.6 ± 6.8 mmHg, 

respectively. Following the onset of spinal anesthesia, a decrease in SBP was noted in both groups at 
T1, reaching 92.3 ± 4.9 mmHg in the norepinephrine group and 96.1 ± 5.9 mmHg in the phenylephrine 
group. A significant increase in SBP was observed at T2 in both groups, with values rising to 114.8 ± 
6.9 mmHg and 118.7 ± 6.7 mmHg, respectively (p = 0.01) (Table 4 and 5). The increase confirmed both 
agents’ effectiveness in restoring blood pressure following spinal anesthesia-induced hypotension 
(Table 6 and 7). 
Table 7. Difference in Systolic Pressure Between Intervention Groups 
Time 
Examination 
Group 
Mean 
Difference 
P value 
T1 
Norepinerphine 
Phenilephrine 
-3.8 
0,07 
T2 
Norepinerphine 
Phenilephrine 
-4.1 
0,11 
 
The post-hoc analysis revealed a statistically significant difference in SBP at T2 between the 
norepinephrine and ephedrine groups (mean difference: −5.9 mmHg, p = 0.01) (Table 7). However, the 
difference between the norepinephrine and phenylephrine groups did not reach statistical significance 
(mean difference: −4.1 mmHg, p = 0.11), confirming that both norepinephrine and phenylephrine were 
equally effective in blood pressure recovery. 
Table 8. Comparison of Heart Rate in Phenilephrine and Ephedrine Group 
Time Examination 
Norepinephrine 
( n : 23) 
Phenilephrine 
( n : 23) 
p-value 
T0 
83,0 ± 3,7   
81,5 ± 3,5 
0,16 
T1 
91,0 ± 3,8 
91,1 ± 3,9 
0,94 
T2 
94,2 ± 3,8 
79,6 ± 3,3 
0,01 
T3 
83,7 ± 3,4 
70,3 ± 2,61 
0,01 
T4 
85,1 ± 3,3 
68,3 ± 2,5 
0,01 
T5 
87,1 ± 4,9 
66,7 ± 3,1 
0,01 
T6 
81,3 ± 3,9 
69,4 ± 3,1 
0,01 
T7 
80,1 ± 3,9 
71,1 ± 3,6 
0,01 
T8 
78,6 ± 3,8 
71,8 ± 3,1 
0,01 
T9 
79,5 ± 3,6 
76,1 ± 5,1 
0,12 
T10 
79,1 ± 4,1 
76,7 ± 3,9 
0,22 
T11 
76,7 ± 2,8 
75,6 ± 3,7 
0,25 
T12 
77,1 ±2,1 
72,1 ± 4,3 
0,35 
T13 
76,2 ± 1,9 
75,2 ± 3,2 
0,53 
T14 
75,1 ± 2,5 
76,7 ± 2,5 
0,42 
T15 
76,1 ± 2,8 
72,7 ± 1,7 
0,44 
 
Heart rate (HR) trends demonstrated more distinct group differences (Table 2). At T2, the HR 
in the norepinephrine group was 94.2 ± 3.8 bpm compared to 79.6 ± 3.3 bpm in the phenylephrine 
group (p < 0.01). This discrepancy continued at T3 (83.7 ± 3.4 bpm vs 70.3 ± 2.6 bpm) and T4 (85.1 ± 
3.3 bpm vs 68.3 ± 2.5 bpm), confirming a sustained lower HR in the phenylephrine group (p < 0.01). 
These findings illustrate a significant bradycardic effect of phenylephrine relative to norepinephrine 
across multiple time points. 

Table 9. Comparison of Diastolic Pressure of Phenilephrine and Ephedrine Groups 
Time 
Examination 
Norepinephrine 
( n : 23) 
Phenilephrine 
( n : 23) 
P Value 
T0 
71,4 ± 4,9 
74,6 ± 4,6 
0,16 
T1 
62,4 ± 3,8 
66,7 ± 6,6 
0,94 
T2 
75,8 ± 3,6 
79,3 ± 4,1 
0,34 
T3 
78,5 ± 3,4 
81,2 ± 3,8 
0,55 
T4 
77,5 ± 3,2 
81,0 ± 3,7 
0,41 
T5 
82,5 ± 6,5 
85,1 ± 2,5 
0,13 
T6 
81,6 ± 2,5 
78,9 ± 3,4 
0,06 
T7 
79,9 ± 3,3 
75,5 ± 3,8 
0,07 
T8 
78,6 ± 3,4 
72,9 ± 6,1 
0,33 
T9 
77,3 ± 3,2 
74,9 ± 3,4 
0,12 
T10 
77,0 ± 2,1 
74,3 ± 3,2 
0,22 
T11 
76,7 ± 1,8 
75,7 ± 1,8 
0,18 
T12 
76,8 ± 2,1 
        76,4 ± 2,1 
0,09 
T13 
75,8 ± 2,7 
77,1 ± 2,1 
0, 08 
T14 
76,1 ± 2,2 
77,4 ± 2,1 
0,17 
T15 
76,6 ± 2,2 
76,6 ± 2,1 
0,12 
 
There were no statistically significant differences in diastolic blood pressure (DBP) values 
between groups at any time point (Table 8). DBP at T0 was 71.4 ± 4.9 mmHg in the norepinephrine 
group and 74.6 ± 4.6 mmHg in the phenylephrine group, with consistent overlap in all subsequent 
measurements (p > 0.05). This suggests that both vasopressors comparably maintained peripheral 
vascular resistance necessary to restore DBP during spinal anesthesia-induced hypotension. 
Table 10. Side Effects in the Phenilephrine and Ephedrine Group 
Side Effect 
Intervention Group 
 
p-value 
Norepinephrine 
Phenilephrine 
 
Nausea 
Yes 
No 
 
1 ( 4,3%) 
22 ( 95,7%) 
 
1 ( 4,3%) 
22 ( 95,7%) 
 
0,76 
Vomitting 
0 
0 
 
Bradycardia 
0 
0 
 
Shivering 
0 
0 
 
 
In the Table 9, Regarding side effects, the most common adverse event was nausea, occurring 
in one patient (4.3%) in the norepinephrine group and one patient (4.3%) in the phenylephrine group. 
No cases of vomiting, bradycardia requiring atropine, or shivering were reported in either group. Chi-
square analysis confirmed no statistically significant difference in the incidence of nausea between 
groups (p = 0.76), indicating both drugs were well-tolerated. 
The need for repeated vasopressor doses was minimal. The average frequency of vasopressor 
bolus administration was 1.3 ± 0.5 times for norepinephrine and 1.4 ± 0.6 times for phenylephrine, 

which did not differ significantly. This reflects the comparably effective pressor response of both agents 
in preventing recurrent hypotensive episodes. Overall, the primary outcomes of SBP restoration and 
HR preservation indicate that while norepinephrine and phenylephrine were both effective in 
correcting hypotension, norepinephrine was superior in preserving maternal HR. The safety profile and 
incidence of side effects were comparable between the two drugs. 
 
DISCUSSION 
This study set out to investigate and compare the clinical performance of norepinephrine and 
phenylephrine in addressing maternal hypotension triggered by spinal anesthesia during cesarean 
section. Although both agents were equally effective in restoring blood pressure, norepinephrine 
provided a clear advantage by maintaining maternal heart rate more effectively, contributing to 
improved hemodynamic balance. 
Phenylephrine acts as a selective α1-adrenergic agonist, promoting vasoconstriction in the 
arterial and venous systems. This increases systemic vascular resistance, thereby elevating arterial 
pressure. However, due to the absence of β-adrenergic effects, its rapid and potent vasoconstrictive 
action often leads to compensatory bradycardia via the baroreceptor reflex. This can diminish cardiac 
output, a significant concern in obstetric patients (Richards et al., 2023). Phenylephrine's 
pharmacokinetics include a swift onset and short duration of action, which may necessitate repeated 
bolus injections or continuous infusion during surgery (Zhang, Qiu, Huang, & Tan, 2024). 
Norepinephrine, conversely, has both α1-mediated vasoconstrictive properties and weak β1 
agonist effects, allowing it to support myocardial contractility and heart rate. Its pharmacodynamic 
profile makes it advantageous in maintaining systemic vascular resistance without sacrificing cardiac 
output. With a similarly rapid onset of action, norepinephrine better preserves cardiovascular stability, 
especially in scenarios where spinal anesthesia reduces preload and systemic tone (Singh et al., 2020; 
Wang et al., 2019). 
Cardiac output is essential in maintaining uteroplacental blood flow during cesarean section. 
The combination of vasodilation and reduced venous return following spinal anesthesia impairs 
preload and systemic vascular resistance. If compounded by bradycardia—as often seen with 
phenylephrine—cardiac output may decline significantly. Hirose et al., (2019) noted that 
phenylephrine-induced bradycardia could reduce cerebral oxygenation despite adequate systemic 
pressure. In contrast, norepinephrine’s β1-mediated support allows for greater preservation of cardiac 
output, thus ensuring sustained perfusion to the placenta and improving fetal oxygen delivery. 
Our results are supported by the meta-analysis conducted by Wang et al., (2019), which 
concluded that norepinephrine offers superior hemodynamic consistency and a lower rate of 
bradycardia compared to phenylephrine, while being equally effective in counteracting hypotension. 
Likewise, Singh et al., (2020), using a Bayesian network approach, found that among multiple 
vasopressors used in neuraxial anesthesia, norepinephrine displayed the most favorable profile 
regarding maternal safety and cardiovascular stability. 
These findings are reinforced by (Sharkey et al., 2019), who observed in a randomized trial that 
norepinephrine provided more consistent blood pressure control and better heart rate preservation 
than phenylephrine when administered via bolus. Hassani et al., (2018)  similarly reported that 
norepinephrine infusions were associated with fewer cardiovascular fluctuations and less frequent 
bradycardia episodes. Despite its established effectiveness, phenylephrine’s side effect of reducing 

heart rate may be problematic in certain clinical scenarios, particularly in patients with preexisting 
bradycardia or cardiac compromise. The requirement for adjunctive drugs such as atropine adds 
complexity to intraoperative management. On the other hand, norepinephrine’s more balanced 
adrenergic effects result in fewer instances of reflex bradycardia and more stable cardiovascular 
responses throughout surgery. 
One of the strengths of this study lies in its design—a double-blinded, randomized trial with 
standardized dosing of each agent, allowing direct and unbiased comparison. The consistent 
monitoring of hemodynamic variables also provided robust and clinically relevant insights into each 
vasopressor’s profile. Nevertheless, the study is not without limitations. Firstly, cardiac output was not 
directly measured, and conclusions on its preservation were inferred from trends in heart rate. 
Including tools such as Doppler ultrasonography or non-invasive cardiac output monitors would have 
yielded more definitive data. Secondly, the absence of neonatal outcome measures, such as Apgar 
scores or umbilical cord blood gases, limited assessment of the downstream effects of improved 
maternal perfusion. Additionally, the trial focused solely on bolus administration, leaving unanswered 
questions about the comparative performance of these drugs when given via continuous infusion—a 
method gaining popularity in clinical anesthesia. Lastly, although adequately powered, the relatively 
small sample size restricts generalizability and may not capture less common adverse events. 
In terms of clinical implications, these findings contribute to a growing trend in obstetric 
anesthesia practice that favors norepinephrine over phenylephrine as the first-line vasopressor. As 
evidence accumulates regarding its balanced adrenergic action and reduced risk of bradycardia, more 
guidelines are recommending norepinephrine, particularly in cases where maintaining cardiac output 
is essential. Its practicality in bolus or infusion form and the consistency of its hemodynamic effects 
make it a promising agent for routine use in cesarean delivery. 
In summary, this study validates the use of norepinephrine 4 mcg and phenylephrine 50 mcg 
as equally effective interventions for spinal anesthesia-induced hypotension. However, norepinephrine 
offers superior heart rate preservation, potentially improving maternal cardiac output and 
uteroplacental circulation. These results are consistent with a broad array of literature and suggest 
that norepinephrine should be strongly considered as a primary vasopressor choice in cesarean section 
anesthesia. Future research should involve larger populations, include direct cardiac output and fetal 
outcome assessments, and examine continuous administration regimens to establish optimal 
protocols. 
. 
CONCLUSION 
This clinical trial confirmed that intravenous bolus doses of 4 mcg norepinephrine and 50 mcg 
phenylephrine are both effective in correcting hypotension resulting from spinal anesthesia during 
cesarean delivery. Both drugs successfully restored maternal blood pressure with similar efficacy and 
were associated with a low incidence of side effects. However, norepinephrine was notably more 
effective in maintaining heart rate stability, in contrast to the significant bradycardia observed with 
phenylephrine. This characteristic is particularly advantageous in obstetric settings, where sustained 
maternal cardiac output is vital for ensuring adequate uteroplacental circulation. Therefore, 
norepinephrine offers a more balanced hemodynamic profile and may serve as a preferable option 
over phenylephrine when heart rate preservation is clinically desirable. These findings support a shift 
toward incorporating norepinephrine as a primary vasopressor in obstetric anesthetic practice and 

suggest further investigation into its impact on neonatal outcomes to strengthen clinical 
recommendations. 
 
REFERENCES 
Hassani, V., Movaseghi, G., Safaeeyan, R., Masghati, S., Yekta, B. G., & Rad, R. F. (2018). Comparison 
of ephedrine vs. Norepinephrine in treating anesthesia-induced hypotension in hypertensive 
patients: Randomized double-blinded study. Anesthesiology and Pain Medicine, 8(4). 
doi:10.5812/aapm.79626 
Hirose, N., Kondo, Y., Maeda, T., Matsui, M., Matsuda, M., & Suzuki, T. (2019). Prophylactic infusion of 
phenylephrine is effective in attenuating the decrease in regional cerebral blood volume and 
oxygenation during spinal anesthesia for cesarean section. International Journal of Obstetric 
Anesthesia, 37, 36–44. doi:10.1016/j.ijoa.2018.09.006 
Richards, E., Lopez, M. J., & Maani, C. V. (2023). Phenylephrine. XPharm: The Comprehensive 
Pharmacology Reference, 1–5. doi:10.1016/B978-008055232-3.62411-0 
Sharkey, A. M., Siddiqui, N., Downey, K., Ye, X. Y., Guevara, J., & Carvalho, J. C. A. (2019). Comparison 
of Intermittent Intravenous Boluses of Phenylephrine and Norepinephrine to Prevent and Treat 
Spinal-Induced Hypotension in Cesarean Deliveries: Randomized Controlled Trial. Anesthesia 
and Analgesia, 129(5), 1312–1318. doi:10.1213/ANE.0000000000003704 
Singh, P. M., Singh, N. P., Reschke, M., Ngan Kee, W. D., Palanisamy, A., & Monks, D. T. (2020, March 
1). Vasopressor drugs for the prevention and treatment of hypotension during neuraxial 
anaesthesia for Caesarean delivery: a Bayesian network meta-analysis of fetal and maternal 
outcomes. British Journal of Anaesthesia. Elsevier Ltd. doi:10.1016/j.bja.2019.09.045 
Šklebar, I., Bujas, T., & Habek, D. (2019). Spinal anaesthesia-induced hypotension in obstetrics: 
Prevention and therapy. Acta Clinica Croatica, 58, 90–95. doi:10.20471/acc.2019.58.s1.13 
Vallejo, M. C., Attaallah, A. F., Elzamzamy, O. M., Cifarelli, D. T., Phelps, A. L., Hobbs, G. R., … 
Ranganathan, P. (2017). An open-label randomized controlled clinical trial for comparison of 
continuous phenylephrine versus norepinephrine infusion in prevention of spinal hypotension 
during cesarean delivery. International Journal of Obstetric Anesthesia, 29, 18–25. 
doi:10.1016/j.ijoa.2016.08.005 
Wang, X., Mao, M., Liu, S., Xu, S., & Yang, J. (2019). A comparative study of bolus norepinephrine, 
phenylephrine, and ephedrine for the treatment of maternal hypotension in parturients with 
preeclampsia during cesarean delivery under spinal anesthesia. Medical Science Monitor, 25, 
1093–1101. doi:10.12659/MSM.914143 
Xue, X., Lv, X., Ma, X., Zhou, Y., Yu, N., & Yang, Z. (2023). Prevention of spinal hypotension during 
cesarean section: A systematic review and Bayesian network meta-analysis based on ephedrine, 
phenylephrine, and norepinephrine. Journal of Obstetrics and Gynaecology Research, 49(7), 
1651–1662. 
doi:10.1111/JOG.15671;SUBPAGE:STRING:ABSTRACT;REQUESTEDJOURNAL:JOURNAL:14470756
;WGROUP:STRING:PUBLICATION 

Zhang, C., Qiu, J., Huang, Y., & Tan, R. (2024). Prophylactic norepinephrine infusion to treat 
hypotension after spinal anaesthesia during caesarean section: a meta-analysis. Journal of 
Obstetrics and Gynaecology. Taylor and Francis Ltd. doi:10.1080/01443615.2024.2393379