Low Dose and the Conventional Dose Of 0.5% Hyperbaric Bupivacaine Produce Comparable Outcomes in the Lower Segment Caesarean Section. An Observational Study (2024)

Language: English | French

Abstract

Keywords: Analgesic, bupivacaine, hemodynamics, lower segment cesarean section, spinal anesthesia, visual analog scale

Résumé

Mots-clés: Rachianesthésie, Bupivacaïne, Césarienne du segment inférieur, Hémodynamique, Echelle visuelle analogique, antalgique

INTRODUCTION

Spinal anesthesia with 0.5% hyperbaric bupivacaine is a well-accepted technique for cesarean sections.[1] However, this strategy is associated with a higher incidence of maternal hypotension due to sympathetic blockade and fall in systemic vascular resistance.[2] Maternal hypotension may lead to uteroplacental hypoperfusion with the possibility of fetal academia.[3] Besides, maternal hypotension frequently leads to nausea and vomiting, which is very distressing to the parturient.[4] Early recovery from motor blockade will facilitate postoperative early mobilization of the patient, which is highly desirable. Conventional studies prove that low-dose spinal anesthesia provides adequate analgesia with fewer adverse effects.[5]

In our study, we compared two different doses of bupivacaine in spinal anesthesia for cesarean sections. We aimed to observe whether there was an added advantage of using a lower dose of bupivacaine for spinal anesthesia in lower segment cesarean sections.

METHODS

This was a comparative observational study involving patients with singleton pregnancy undergoing elective cesarean section. The study was conducted for one year. Institutional Ethics Committee approval (IEC No; 08-19/340) was obtained for the study and was registered at clinicaltrials.gov (CTRI/2020/01/022648).

Inclusion criteria included pregnant patients belonging to ASA II category within the age group of 25 and 35 years. Patients also belonged to the height range within 150 to 160 cm. Exclusion criteria included patients with cardiovascular comorbidities, patients with obstetric complications, patients with known central nervous system disease, patients in active labor, and patients with contraindication to the neuraxial blockade.

Written informed consent was obtained from the study participants. Seventy parturients were taken up for the study and they were divided into two groups by convenience nonprobability sampling. The group low dose bupivacaine (LB) had 35 patients who received 1.8 ml of 0.5% hyperbaric bupivacaine (Sensorcaine heavy 5 mg/ml AstraZeneca Pharma LTD, UK) intrathecally and group high dose bupivacaine (HB) had 35 patients who received 2.2 ml of 0.5% hyperbaric bupivacaine intrathecally. All the patients underwent a thorough pre anesthetic evaluation.

Before administering neuraxial blockade, standard monitors, namely pulse oximeter, noninvasive blood pressure (NIBP), and ECG were connected to each patient. Baseline heart rate and NIBP at T₀ were recorded. An 18 gauge intravenous cannula was inserted for giving fluids and intravenous drugs if required. Under all aseptic precautions, spinal anesthesia was conducted with the patient in the left lateral position and a 25 gauge Quincke Babco*ck spinal needle was inserted at L2-3 or L3-4 interspace. A fixed-dose of 0.5% hyperbaric bupivacaine was given.

All patients were coloaded with Ringer's lactate 500ml. Immediately after the procedure, patients were made supine with a left lateral tilt of 15 degrees. Hemodynamic parameters like heart rate and systolic and diastolic blood pressure were recorded every 2 min for the first 10 min, every 5 min until 20 min, and thereafter every 10 min throughout the surgery. The upper sensory level was assessed using the loss of sensation to pinprick along the anterior axillary line bilaterally every 2 min until the maximum level was reached. The time required to reach this level was noted. The degree of motor block was assessed according to the modified Bromage scale (0 = no motor block, 1 = inability to raise the extended leg, 2 = inability to flex the knee, 3 = inability to flex ankle) every 2 min until grade three power was reached. Any intraoperative pain or discomfort was assessed using a visual analog scale (VAS) of 0-10.

If VAS score was more than three or adequate sensory block was not achieved after 10 min, the case was converted to general anesthesia. Patient satisfaction was assessed and recorded postoperatively using a two-point assessment scale where zero represented “unsatisfied” and one for “satisfied.” They were asked to mark satisfied if they were happy to accept the same anesthesia technique later.

Two dermatome regression time for sensory blockade and time for complete motor recovery were also noted postoperatively. The primary outcome measured included perioperative hypotension and the secondary outcome measured added sensory block characteristics, motor block characteristics, VAS pain score, and patient satisfaction. Any drop in mean arterial pressure below 65 mm of mercury or any heart rate reduction below 50 beats per minute was treated with ephedrine 6 mg and atropine 0.6 mg, respectively.

Once all the observations were recorded, the data was analyzed using the median and interquartile range for all parameters. Non-Parametric test (Mann–Whitney test) was performed to compare the VAS score between the two groups. A statistical package SSPS version 25.0 was used to do the analysis. P < 0.05 was considered statistically significant. The sample size of 70 patients was calculated as follows:

Z_1-α/2 = 1.96 at 5% level of significance

Z_1-β = 0.84 at 80% power

σ = pooled standard deviation (1)

d = clinical significant difference = 9

n = 35 in each group, i.e., n = 70 in two groups.

The method used for sampling was convenience non-probability sampling.

RESULTS

A total of 70 patients were included in the study. The parturients were comparable concerning age and height [Table 1].

There was no statistically significant variation in the heart rate between the two groups. Statistically significant variation in blood pressure appeared after 30 min of spinal anesthesia in the two groups. Still, the mean arterial pressure never fell below 70 mm of mercury, which showed that both group's patients were hemodynamically stable.

Time taken for two-point dermatomal regression was 106 min in the LB group and 128 min in the HB group, which was statistically highly significant [Graph 1]. Patients in the LB group took 227 min for complete recovery from motor blockade while the HB group patients took 251 min for complete recovery, which was statistically highly significant [Graph 2]. T6 level of sensory blockade was achieved by 65% of patients in both groups at 4 min. Almost 100% of the patients reached that level in 6 min [Graph 3]. Almost 60% of patients in 6 min and 100% of patients in 8 min reached a grade 3 motor blockade in both the groups [Graph 4].

The VAS score for pain was zero in both the groups throughout the procedure. All patients in both groups were satisfied with the anesthetic technique. There were no adverse effects encountered during the procedure.

DISCUSSION

Based on the collected evidence, we found that the extent of analgesia and the risks associated with the two different doses of hyperbaric bupivacaine in lower segment cesarean sections were almost the same. The only difference we found was that the low-dose group had faster recovery from spinal anesthesia.

In a study conducted on 52 parturients, two different dosages of bupivacaine were used. 4.5 mg isobaric bupivacaine and 12 mg hyperbaric bupivacaine were given intrathecally. The dosages were supplemented by similar doses of morphine and fentanyl intrathecally. The level of blockade achieved and the proportion of vasopressors used were comparable in both the groups. The only variation observed between the two groups was faster recovery from the motor blockade in the low-dose group.[6] These findings were similar to the observations that we have made in our study. We found no change in effects produced by two different bupivacaine dosages other than faster recovery in the low-dose group. The only difference between the two studies was that we avoided additives in our research.

In a retrospective study conducted by Ioannidis et al., it was found that there was no correlation between the level of the sensory blockade and the maternal height. They divided the patients into two groups based on their height (<165 cm and >165 cm) and the subarachnoid space was infiltrated with the 20 mg of ropivacaine and 10 μg of fentanyl. They found that there was no statistically significant difference in the level of blockade or hemodynamic effects between the two groups. One observation that could be made for this result was that the difference in an individual's height could be attributed to the lower limb bone's length and not the spine. Therefore, there may not be many variations in the anesthetic effect of drugs based on height.[7] In our study, we narrowed down the study participants between 150 and 160 cm height ranges, to reduce any bias that can happen with the extreme variation in participant's height. We used two different dosages of drugs and it was observed that there was no statically significant variation in the results obtained between the groups. This proves that height and dosage are two independent variables in spinal anesthesia, which was almost similar to the observations made in the above study.

In another meta-analysis done, it was demonstrated that low-dose bupivacaine in spinal anesthesia had fewer adverse effects like hypotension, nausea, but at the cost of reduced anesthetic efficacy and increased analgesic consumption. These results contradicted our findings, where we found no difference in the incidence of adverse events and analgesic supplementation between the two groups.[8]

Many previous studies proved that a lower dose of bupivacaine for spinal anesthesia had a lesser risk for complications; was contradicting our research findings. Our study showed no difference in analgesia level or the incidence of complications, including hypotension between the two groups. However, the recovery rate was faster in the low-dose group, which could be the only favorable outcome.

Another study was conducted on 60 pregnant patients, and they were divided into three groups based on the dosage requirement as per their height. One group received 0.04 mg/kg, another group received 0.05 mg/kg, and the last group received 0.06 m/kg of heavy bupivacaine. It was found that the previous two groups had a higher incidence of motor blockade and hypotension compared to the first group. The surgical anesthesia was also excellent in the previous two groups. These findings were contradictory to our results.[9]

In a randomized controlled trial conducted by Marta et al., on two groups of pregnant patients, one group was the low-dose group, who received spinal anesthesia with 4.5 mg of 0.75% of hyperbaric bupivacaine with 150 μg of morphine and 15 μg of fentanyl. The conventional group received 9 mg of 0.75% hyperbaric bupivacaine with 150 μg of morphine and 15 μg of fentanyl. The primary outcome they measured was the length of stay in the recovery room, and the secondary outcome included the comparison of the cardiac indices between the groups. It was found that the change in cardiac index, the level of surgical anesthesia, and the block onset times were similar in both the groups. Only the recovery rates were faster in the conventional group.[10] These findings were similar to our study. The only difference between this study and our study was the use of additives. Thus, we can infer from both studies that even if the bupivacaine dosages vary, its effect on the cardiovascular system might remain the same.

Different strategies have been attempted to reduce the adverse effects due to spinal anesthesia. It has been observed that the extent of hypotension was directly proportional to the amount of drug instilled in the subarachnoid space.[11] Thus, one widely accepted method was to reduce the amount of drug used, especially in patients with compromised cardiovascular status. However, such a strategy could compromise the effectiveness of surgical anesthesia. Nevertheless, in our study, we found that the difference in surgical anesthesia between the two groups was the time taken for recovery from anesthesia.

Thus, with our study, we would like to convey the message that utmost care has to be exercised while performing spinal anesthesia even with low-dose bupivacaine. This method can give a false sense of security for anesthesiologists, and the consequences could be overlooked.

In the present study, we decided to keep the low dose as 9 mg of bupivacaine to attain adequate analgesia and reduce adverse effects. The effectiveness of such low-dose anesthesia for cesarean section compared to other types of lower abdominal surgeries could be attributed to the enlarging gravid uterus that may compress the blood vessels leading to venous engorgement and narrowing of the epidural space. This may result in the cephalad spread of the drug and a higher level of analgesia.[12]

One limitation of our study was that there was only a slight difference in the dosage between the conventional- and the low-dose groups. The effect might be more pronounced if a higher drug volume was used in the conventional dosage group. Nevertheless, it was cesarean section and we were not so keen on increasing the drug volume in the conventional group to avoid any adverse consequences. Besides, in our institute, we routinely use this dose for cesarean sections. Our understanding of the optimal dose for spinal anesthesia was by determining the ED95 dose, where 95% of patients have no intraoperative pain.[13] In our study, the level of blockade achieved in the low dose group was T6 as against the recommended level of T4, for lower segment cesarean sections, which could be another limitation of our study. However, none of our patients complained about pain or discomfort during the intraoperative period. Finally, yet importantly, we took only seventy patients in total for the study. We could have increased the sample size to avoid any bias that could have resulted in the present study.

As we conclude, we would like to ascertain that low-dose spinal anesthesia is not an entirely safe form of anesthesia, especially in patients with compromised cardiovascular status. The low-dose group had faster recovery and similar patient satisfaction scores compared with the conventional group.

REFERENCES