Comparison of bolus phenylephrine, Ephedrine and Mephentermine for maintenance of Arterial pressure during Spinal anaesthesia in Caesarean section

 

Dr. Aruna V. Chandak, Dr. Deepjit Bhuyan*, Dr. Amol P. Singam, Dr. Bhakti Patil

Department of Anaesthesia, Jawaharlal Nehru Medical College,

DMIMS (DU), Sawangi, Wardha– 442004 Maharashtra.

 

ABSTRACT:

Background: Hemodynamic changes during cesarean delivery after spinal anesthesia are common. The hypotension seen after spinal anesthesia in a cesarean delivery can be treated by many agents. In the management of hypotension during spinal anesthesia for cesarean section, the effects of Phenylephrine, Ephedrine and Mephentermine were compared in this study based on the following parameters- 1. The efficacy of the vasopressor in treating hypotension 2. Incidence of undesirable side effects. Materials and method: This study included a total of 120 patients (ASA Grade I and II) undergoing elective cesarean section (with a normal singleton pregnancy, full term/near term) under spinal anesthesia. The patients were randomly allocated into three groups of 40 each. Group ‘P’ was given prophylactic bolus dose of Phenylephrine 100 mcg IV, Group ‘E’ was given prophylactic bolus dose of Ephedrine 10 mg IV and Group ‘M’ received prophylactic bolus dose of Mephentermine 6 mg IV. Blood pressure and heart rate was recorded every 2 minutes for 20 minutes and thereafter every 5 minutes till the end of the surgery. Results: In managing hypotension between the three groups, no difference was found between them. The incidence of bradycardia was higher in the Phenylephrine group. Conclusion: All the three vasopressors are effective (in intravenous form) in maintenance of maternal arterial pressure. Although Phenylephrine has quicker peak effect, in comparison to Ephedrine and Mephentermine and it causes reduction in heart rate.

 

 

INTRODUCTION:

Anaesthesia to a parturient is exclusive but also requires the very best degree of care because the anaesthesiologist has got to look after two individuals, the mother and foetus. In elective caesarean delivery under spinal anaesthesia hypotension has been reported in as many as 85% of patients.¹ Hypotension could also be detrimental to the mother and therefore the resulting placental hypoperfusion to the foetus. Vasopressors are used to correct hypotension swiftly.

 

Bolus doses of Phenylephrine, Ephedrine and Mephentermine for maintenance of blood pressure during spinal anesthesia in cesarean delivery are taken into consideration during this study.

 

For cesarean section, spinal anesthesia is widely used and it has been found to be efficacious and safe. Hypotension can have detrimental effects on neonate, and the effects include decrease in uteroplacental flow, impaired fetal oxygenation with asphyxial stress, and fetal acidosis.^2,3 As hypotension may be associated with both maternal and neonatal morbidity, many different methods have been investigated alone and in combination for both its prevention and treatment.^4,5 Some the measures used to prevent hypotension during spinal anesthesia include left uterine displacement, leg elevation and pre-hydration or preloading with colloid/ crystalloid.

 

To prevent hypotension during spinal anesthesia vasopressors are commonly used. Some of them are ephedrine, phenylephrine, and mephentermine. Phenylephrine is a selective α₁ receptor agonist and β agonist. The action of this drug is only seen at much higher doses. It is frequently used in obstetric anesthesia to treat the hypotension that is seen after spinal anesthesia (due to marked arterial vasoconstriction caused by its α₁ agonist action). An intravenous dose of phenylephrine has an immediate onset and duration of action of 5-10 minutes.⁶ The vasopressor drug Ephedrine, has both direct α and β agonist action. But its indirect action is more prominent due to the “release of norepinephrine from sympathetic neurons”. It increases the blood pressure via the β₁ receptor stimulation along with increased heart rate and cardiac contractility. The α agonist action causes peripheral vasoconstriction.⁶ The drug Mephentermine sulphate has a mixed α and β receptor agonist action. This causes both direct and indirect effect due to release of norepinephrine and epinephrine. Its influence on the heart rate is dependent on the vagal tone. Its use in hypotension after spinal anaesthesia in obstetrics is due to its ability to increase the blood pressures by enhancing the cardiac output.^6,7   

 

MATERIALS AND METHODS:

This study was executed in a prospective randomized manner. The patients were divided into three groups of 40 each. Patients meeting the criteria were considered ad included into the study. After taking informed consent, patients in age group of 20 – 35 years of age, healthy, ASA I and II patients with singleton full term pregnancy, undergoing elective and emergency LSCS were included in the study.

 

Group P was given a prophylactic bolus dose 100mcg i.v Phenylepherine and a rescue dose of 50mcg i.v was given whenever maternal systolic blood pressure was less than 90mmHg. Group E was given prophylactic bolus dose 10mg i.v ephedrine and a rescue dose of 6mg i.v was given whenever maternal systolic blood pressure was less than 90mmHg and Group M received prophylactic bolus dose 6mg i.v Mephentermine sulphate and a rescue dose of 3mg i.v whenever maternal systolic blood pressure was less than 90mmHg. The three drugs were prepared in identical syringes by an investigator who was not involved in subsequent patient care. The heart rate (ECG), respiratory rate, blood pressure (NIBP) and SpO₂ were being monitored as the patient arrived in the operation theatre. Normal saline infusion was started in all patients and was preloaded with 10 ml/kg of normal saline. According to their convenience, the patients were placed in lateral or sitting position.⁷ Lumbar puncture was done using a 25 gauge Quincke’s needle in L3-L4 intervertebral space. Once the free flow of cerebrospinal fluid was obtained, 0.5% bupivacaine was administered over 10–15 seconds. Time of injection of drug was noted and patient was placed in supine position immediately with a left lateral tilt of 15–20 degrees. Systolic blood pressure, diastolic blood pressure, and heart rate were recorded as soon as spinal anaesthesia was given. Whenever the systolic blood pressure decreased to less than 90mmHg, a vasopressor was administered (either 6mg of Ephedrine or 50mcg of Phenylephrine or 3mg of Mephentermine) as a rescue dose.

 

Statistical Analysis:

Sample size was derived using software openepi.com. Assuming the systolic blood pressure of 120.24 mmHg and standard deviation of 12.35 mmHg (study by Iqra Nazir et. Al), keeping power at 80% and confidence interval at 95% (alpha error at 0.05), a sample of 34 patients would be required to detect a minimum of 20% difference in the base line mean blood pressure between the three groups. This study included 40 patients in each group to compensate for possible dropouts. Parametric data was shown as mean ± SD, thereby the inter group comparisons were made by Student’s t-test. The test was two sided and referred for P-value for its significance. P-value less than 0.05 (P< 0.05) was taken to be statistically significant. Comparability of groups will be analyzed with analysis of variance (ANOVA) test.

 

RESULTS:

This study included a total of 120 patients. The patients were randomly divided into three groups of 40 each. The three groups were matched with regard to their age and body weight (Table-1).

 

Table 1: Comparison of age and weight between group P, group E and group M

 

Table 2: Comparison of baseline heart rate, systolic, diastolic and mean blood pressure in groups E, P and M

 

Table 3: Comparison of heart rate, systolic and diastolic blood pressure between groups E, P and M

(*- significant)

 

Table 4: Comparison of mean blood pressure (mmHg) between groups E, P and M

 

The differences recorded in baseline heart rate, systolic, diastolic and mean blood pressures between the three groups were statistically insignificant (Table -2).

 

The incidence and occurrence of bradycardia was higher in patients receiving phenylephrine than those receiving ephedrine and mephentermine. The difference in mean heart rate compared between the three groups immediately after spinal anesthesia at 2, 4, 6, 8, 10, and 12 minutes were significant while it was insignificant at 0 and 14 minutes (P value < 0.05: significant) (Table -3).

 

The differences in systolic, diastolic and mean blood pressure between the three groups were statistically insignificant. Overall, 29/40 (72%) patients in the Phenylephrine group, 26/50 (65%) patients in Ephedrine group and 28/40 (70%) patients in the Mephentermine group had one or more episode of hypotension and required one or more bolus of vasopressor. The number of rescue doses required in groups P, E and M were statistically insignificant (Tables 3-4) (p value < 0.05: significant).

 

DISCUSSION:

The important physiological response to spinal anesthesia involves the cardiovascular system. The overall occurrence of hypotension during spinal anesthesia in cesarean section is about 80%. Hypotension can have detrimental effects on both mother and neonate.⁸ Left uterine displacement for decreasing the effects of aortocaval compression or leg elevation alone cannot reduce the incidence of hypotension.^8,9 Preloading is commonly administered but it has controversial results.^8,9 Despite all the conservative measures, a vasopressor drug is often required to prevent hypotension during spinal anesthesia.^10,11

 

All patients (in the three groups) in this study were proportionate with respect to age and ASA status. The differences that were seen in baseline parameters like the heart rate, systolic blood pressure, diastolic blood pressure and mean arterial pressures between the three groups were statistically insignificant, respectively. A higher incidence of bradycardia recorded in patients receiving phenylephrine than those receiving ephedrine and Mephentermine. This is due to increase in blood pressure with an α-agonist which leads to reactive bradycardia (baroreceptor reflex).^12-17

 

The results of this study were in consensus with the study of Lee et al.⁴ It was found in their study that a higher incidence of bradycardia was seen in patients receiving phenylephrine as compared with patients receiving ephedrine for prevention of hypotension during spinal anesthesia in cesarean section.  In another study done by Dinesh Sahu et al.¹⁰ concluded that Phenyephrine, Ephedrine and Mephentermine sulphate are effective in intravenous form in maintenance of arterial blood pressure within 20% limit of baseline. The study also found that Phenylephrine has faster peak effect and it causes reduction in heart rate which may be advantageous in cardiac patients and patients in whom tachycardia is undesirable. However, this study is not consistent with the study done by Magalhães et al.¹¹ on ephedrine versus phenylephrine for prevention of hypotension during spinal block for cesarean section and effects on fetus. It was seen from their study that ephedrine was more effective than phenylephrine in the prevention of hypotension. This may have been because less dose of phenylephrine was used in their study as compared with this study.

 

CONCLUSION:

In conclusion, we found that all the three vasopressors namely Ephedrine, Mephentermine and Phenylephrine are in maintenance of maternal arterial pressure within 20% limit of baseline values, though Phenylephrine has quicker peak effect, in comparison to Ephedrine and Mephentermine and it causes reduction in heart rate, which may be advantageous in patients in whom tachycardia is undesirable.

 

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Accepted on 28.07.2020           © RJPT All right reserved

Research J. Pharm. and Tech 2021; 14(3):1349-1352.