Height-adjusted dose of intrathecal bupivacaine on surgical anesthesia for the cesarean section

Noyomi Saring; Tomar Basar; Ramapati Sanyal; Mihin Nania

doi:10.4103/JOACC.JOACC_54_22

ORIGINAL ARTICLE

Year : 2023 | Volume : 13 | Issue : 1 | Page : 75-79

Height-adjusted dose of intrathecal bupivacaine on surgical anesthesia for the cesarean section

Noyomi Saring¹, Tomar Basar², Ramapati Sanyal¹, Mihin Nania¹
¹ Department of Anaesthesiology, Tomo Riba Institute of Health and Medical Sciences, Naharlagun, Arunachal Pradesh, India
² Department of Obstetrics and Gynaecology, Tomo Riba Institute of Health and Medical Sciences, Naharlagun, Arunachal Pradesh, India

Date of Submission	18-Aug-2022
Date of Acceptance	03-Oct-2022
Date of Web Publication	09-Mar-2023

Correspondence Address:
Dr. Noyomi Saring
Assistant Professor Anaesthesiology, Tomo Riba Institute of Health and Medical Sciences, Naharlagun, Arunachal Pradesh
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/JOACC.JOACC_54_22

Abstract

Background: In the spinal anesthetic technique, local anesthetic dose (concentration and volume) is the main determinant of its adequacy and success of block to be achieved. The lack of pain during surgical intervention rather than on dermatome sensory block level is considered to be an appropriate indicator of surgical anesthesia. Spinal anesthesia is the most common anesthetic technique to provide anesthesia for the elective or emergent cesarean section (CS). However, spinal block-induced maternal hypotension is the most common adverse effect during single-shot spinal anesthesia. In our study, we aim to study the height-adjusted dose of 0.5% Bupivacaine Heavy (BH) in achieving surgical anesthesia and its effect on maternal hypotension. Participants and Method: One hundred parturients scheduled for elective CS were enrolled and were compared to the parallel arms of parturients receiving conventional BH. Fifty parturients in each group were included. In the conventional group (B), participants received spinal block with 12 mg of 0.5% BH, and in the height adjusted-dose group (H), participants received a dose of 0.5% BH in 0.06 mg per centimetre height. A sensory block level of T6 dermatome or higher was consider adequate to start surgery. The adequate surgical anesthesia is considered to be achieved if cesarean delivery can be performed without supplementary analgesia. The need of supplementary analgesia, conversion to general anesthesia, or no block till 15 min of intrathecal BH is considered spinal failure. Results: 4% of the height-adjusted dose group have a low block level. Two cases complained of pain, and of them, one received supplementary analgesia and one was converted to general anesthesia. Systolic hypotension of a maternal blood pressure of less than 90 mm Hg was found in 19 (38%) and 10 (20%) in the conventional group and HAD group, respectively, which was highly significant statistically (p value 0.001%). Conclusion: Intrathecal hyperbaric bupivacaine in height adjusted 0.06 mg per cm height of patient can achieve surgical anesthesia with maintainance of systolic blood pressure. However, low dosing of intrathecal BH has higher cases of block failure in comparison to the conventional fixed dose regime of spinal anesthesia.

Keywords: Bupivacaine, intrathecal, parturient, surgical anesthesia

How to cite this article:
Saring N, Basar T, Sanyal R, Nania M. Height-adjusted dose of intrathecal bupivacaine on surgical anesthesia for the cesarean section. J Obstet Anaesth Crit Care 2023;13:75-9

How to cite this URL:
Saring N, Basar T, Sanyal R, Nania M. Height-adjusted dose of intrathecal bupivacaine on surgical anesthesia for the cesarean section. J Obstet Anaesth Crit Care [serial online] 2023 [cited 2023 Apr 1];13:75-9. Available from: https://www.joacc.com/text.asp?2023/13/1/75/371320

Aims of Study

Primary: To determine the effectiveness of height-adjusted dose (HAD) of 0.5% Bupivacaine Heavy (BH) in providing surgical anesthesia as compared to the conventional dose in spinal anesthesia for cesarean delivery in parturients of Arunachal Pradesh.
Secondary: To compare hypotensive effects of intrathecal Bupivacaine H in conventional and height-adjusted dose groups.

Objective

To determine the effectiveness of HAD of BH to provide adequate surgical analgesia for cesarean delivery.

Introduction

Although various factors influence the appropriate sensory block for surgical anesthesia, the local anesthetic (LA) dose (concentration and volume) is the main determinant of its success in spinal anesthesia. Conventionally, the recommended dose of intrathecal (IT) bupivacaine is considered to be between 10 and 15 mg to achieve an adequate block (T6) level^[1],[2],[3] and achieve pain-free intervention under neuro-axial anesthesia. The adequacy of the spinal LA dose is usually expressed as ED 50 or ED 95 (effective dose in 50% or 95% patients, respectively) for the lack of pain during surgical intervention rather than on the dermatomal block level of sensory stimuli such as pin prick or cold or hot sensation. Because ED 95 is defined as the lack of intra-operative pain in 95% (in other words, <5% cases can feel pain) of the cases who received the concerned LA rather than on dermatome sensory block, it may be a more appropriate indicator to be used in surgical anesthesia. The ED95 of intrathecal bupivacaine is 11 mg for hyperbaric bupivacaine and 13 mg for isobaric bupivacaine,^[3],[4] but the dose in this range has been known to be associated with an incidence of adverse maternal effects such as arterial hypotension, bradycardia, nausea and vomiting, shivering, discomfort, and so on.

Maternal hypotension is claimed to be the most common adverse effect (approximately up to 80%) of the cesarean section under spinal anesthesia.^[2],[5] In recent years, there are many studies of low-dose intrathecal LA combined with opioid-like Fentanyl 25 μgm intrathecally^[2] or intravenously in increasing the dose from 25 μgm up to 100 μgm^[6] with or without the combined spinal epidural technique^[7] to increase the quality of anesthesia. Studies suggested that low-dose spinal anesthesia may have the benefit of a lower risk of maternal hypotension or nausea/vomiting, but they needed more analgesic supplementation^[2],[8] as well as conversion of spinal to general anesthesia.^[4]

In spinal anesthesia, the concentration of LA as well as the volume of LA injected should be taken into account to avoid adverse effects. Nofal et al.^[6] in their study found that the volume for spinal BH should be 2.62 for 150–159, 2.76 for 160–169, and 2.8 for >170 cm height (0.08 ml per cm) of the parturient, whereas the study of Siddiqui et al.^[5] found 0.05 ml per cm height of patient plus Fentanyl 25 μg (0.5 ml). According to the study performed by Danelli G et al.^[9] using the staircase method to determine the dose of spinal anesthesia with BH, it was found that the height-adjusted dose (HAD) of IT hyperbaric bupivacaine for adequate spinal anesthesia is 0.06 ml per cm height of the patient. Therefore, keeping in mind the volume and average height of 151 cm of women of Arunachal Pradesh,^[10] we aimed in our study to determine effectiveness of HAD at the dose of 0.06 mg per cm height of the patient for surgical anesthesia to determine the effective dose of 0.5% BH for cesarean delivery under spinal anesthesia in the population of Arunachal Pradesh who were admitted in a tertiary care center.

Methodology

Study type: Prospective, double-blinded randomized analytic interventional study.

Sample size calculation:

We have included 100 parturients in two groups of 50 to achieve 80% power (1-β = 0.84) at a confidence interval of 95% (1-α = 1.96) and attrition of 10% with a moderate degree of effect size (d = 0.5, considering <0.3 as small effect, 0.3–0.5 as moderate effect, and >0.5 as large effect).

After review from Institutional Ethics Committee, this study was conducted in the Department of Anaesthesiology, Tomo Riba Institute of Health and Medical Sciences, Naharlagun, Arunachal Pradesh. The mandatory informed consent was obtained from eligible parturients during pre-anesthetic check-up a day before the cesarean section, and they were allotted into groups by computer generated randomization. A convention dose of 0.5% Bupivacaine H of 12 mg was included in group Bupivacaine or B. The patients who received HAD of 0.5% hyperbaric bupivacaine were included in group H. The calculated dosage for HAD was adjusted to the nearest whole number after the decimal because dosage can be titrated in 0.1 ml with a conventional syringe used in institution.

Group B = 12 mg 0.5% hyperbaric bupivacaine.
Group H = HAD of 0.5% hyperbaric bupivacaine as in [Table 1].

Table 1: Calculated dose in mg per height cm of parturient and volume of intrathecal BH

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>Patients were evaluated for the general physical status along with ASA grading before enrolling them in the study. The inclusion criteria for the study were consenting adult parturients with singleton pregnancy, having no systemic illness. They should have a normal baseline heart rate (HR) in rate per minute, blood pressure (BP) in mm Hg, and oxygen saturation (SpO2) %, with mandatory airway evaluation along with routine investigation as per institutional norms. The exclusion criteria were as follows:

Refusal to include in the study
<18 years
ASA status > II
Presenting with any systemic illness
Emergent surgery and laboring parturients
Multiple or twin pregnancy
Grand multipara
Contraindication to neuro-axial block

On the day of surgery, patients were kept nil per orally at least for 6 hours pre-operatively. Intravenous cannulation was performed with 20–18G and 500–1000 ml of crystalloid solution (Ringer's lactate) administered preoperatively regardless of weight and height. Pre-medication of Ondensetron 4 mg and Pantoprazole 40 mg was administered intravenously before starting the procedure. Minimal routine monitoring was put on for all the cases with HR, BP, and SpO2% with re-evaluation of airway and fetal heart rate assessment. Spinal anesthesia with BH was given with 25 or 26 Gauge Quincke spinal needles in the lateral decubitus position at L3–L4 or L4–L5 interspaces after confirmation of cerebrospinal fluid (CSF) flow as per requirement in the group enrolled. Sensory analgesia was tested by the pin prick method at the mid-clavicular line bilaterally every minute after SA. If no analgesia was detected till 5 min of intrathecal SA, then painful stimuli are tested every 3 minutes until 15 min, and then the case will be considered as failed spinal block.

Adequate surgical anaesthesia was defined as no complaint of pain on painful surgical stimuli. The case was considered as failed spinal if the adequate block level of T6 sensory dermatome cannot be achieved within 15 minutes (time taken for LA to effect) of IT drug injection or if there was a need of supplementary analgesia or case conversion to general anesthesia for the cesarean section. However, if an adequate block level at T6 and adequate surgical anesthesia were achieved but the case was converted to general anesthesia because of other obstetrical reasons, the case was not considered as failed spinal. The study was deemed complete when the patient is shifted out of the operation room. The end point of the study was

Primary: Cesarean delivery and closure of surgical wound with pain-free surgical anesthesia with a T6 sensory block level.
Secondary: Failed spinal if an adequate block level cannot be achieved within 15 minutes of IT drug injection or there is case conversion to general anesthesia or there is a need for supplementary analgesia.

The vitals were recorded after 1 minute of the spinal procedure and thereafter every 5 minutes until the completion of the surgical procedure. Non-invasive arterial blood pressure is evaluated whenever the participant complains of discomfort, nausea, pain, or any other known adverse event. Any episode of hypotension of systolic BP <90 mm Hg or fall of >30% of baseline was treated with vasopressors (mephentermine 3 mg bolus, repeated when required in our setup). Bradycardia of less than HR 60 per min was treated with intravenous atropine with an increment dose of 0.6 mg. Low oxygen saturation of <90%, shivering, and vomiting along with hypotension during the procedure were recorded. The Apgar score of the baby at 1 and 5 minutes of delivery were recorded as per institutional norms.

Results and Observation

In our study, we included 100 participants, of which 36 (19 in group B and 17 in group H) were primigravida and 64 (31 and 33 in groups B and H, respectively) were multigravida. The time to achieve T6 sensory block was less than 5 minutes (an average mean of 3 SD ± 0.73 and 3.3 SD ± 0.84 for groups B and H, respectively) for both the groups. The demographic profile of the participants is shown in [Table 2].

Table 2: Demographic profile of the participants

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In this study, one participant with a conventional dose of BH had bradycardia after 5 min of intrathecal LA administration and was treated with Atropine 0.6 mg intravenously. Nineteen (38%) parturients in group B and ten (20%) parturients in group HAD recorded a systolic blood pressure less than 90 mm Hg, which was found to be highly significant statistically (P-value <0.001 by Chi-square using SPSS). Among the cases showing systolic hypotension as shown in [Figure 1] below, 11 and 6 parturients in conventional and HAD groups, respectively, had hypotension within the 5 min of IT LA administration. Five and two parturients had hypotension within 10 min and 15 min of SA in the conventional group, whereas two and one parturient had hypotension in the HAD group within 10 and 15 min, respectively. In both the groups, there was less occurrence of hypotension after 20 min of spinal anesthesia. Among the cases who had hypotension, eight parturients were primipara in the conventional group as compared to only one primipara in the HAD group.

Figure 1: Graph showing hypotension in two groups in relation to IT bupivacaine injection

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Total cases of participants who had block failure, complained of pain and needed supplementary analgesia or GA, or reported an adverse event, are summed up in [Table 3] below. Two cases (4%) in the HAD group had spinal failure. They had inadequate block levels of T8 and T10, respectively, after 15 min of SA. One patient was managed with spinal anesthesia with supplementary analgesia with intravenous Fentanyl 100 microgram as she did not feel pain on the incision site. The second case of spinal failure was converted to general anesthesia. There was no case of spinal failure in the conventional group in our study.

Table 3: Adverse effects

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In both the groups, the block level of T6 was achieved within 5 min of SA in cases of adequate surgical anesthesia except for two cases of spinal failure in the HAD group. One parturient in the conventional group had vomiting despite pre-medication with ondensetron. One parturient in each group had post-partum hemorrhage, which was treated conservatively with fluids. We found no cases of shivering post intrathecal LA in our study.

Two babies in each group born during the course of this study were admitted in a sick neonatal care unit (SNCU) because of a low Apgar score. Two babies born to the parturient in group H were post-dated and shifted to SNCU. In group B, among the neonates shifted to SNCU, one baby was born to post-dated pregnancy, whereas the other neonate had no significant history because of a low Apgar score.

Discussion

Obstetrics anesthesia by neuro-axial block has evolved tremendously after 1980s to improve maternal and neonatal outcomes.^[11] Most adverse effects concerned with neuro-axial block had been resolved by rigorous research studies and knowledge in current labor analgesia and cesarean delivery. In our study, we enrolled 100 parturients into two groups to determine if a dose of BH 0.06 mg per height (minimum dose of BH^[9]) of the parturient is adequate for cesarean delivery without supplementary analgesia with the block level corresponding to dermatome T6 or higher.

The primary end point of this study was successful completion of cesarean delivery under spinal anesthesia. The spinal block level of T6 was considered adequate and should be achieved within 15 min of intrathecal BH. All the cases of successful spinal block had loss of pain sensation to pin prick within 5 min (3 SD ± 0.73 and 3.3 SD ± 0.84 min for groups B and H, respectively) of intrathecal BH administration. No participants in the conventional group required additional analgesia nor did we encounter any case of spinal failure. Two (4%) parturients in the HAD group had an inadequate block level. Among the two (4%) cases of spinal failure, one was managed with intravenous fentanyl and the other was converted to general anesthesia. This finding was found to be corresponding with the results of meta-analysis of Arzola C and Wieczorek PM,^[2] where they mentioned that a low-dose intrathecal LA may necessitate higher chances of supplementary analgesia. However, this was found to be in contrast to the finding of the study performed by Bialowalska K,^[8] who concluded that height-adjusted and fixed dose regimes have the same outcome. Sivaram K et al.^[12] in their study mentioned that low-dose spinal BH with opioid is as effective in providing adequate anesthesia in pregnant patients as conventional high-dose BH. However, it should be noted that in our study, we used intrathecal LA without any adjuvant unlike those in the above-mentioned studies.^{[6],[8],[13],[14]}

An adequate sensory level enables adequate surgical anesthesia in the single-shot spinal anesthetic technique, but it may also associate with hypotension which may have serious maternal adverse effects as well as indirect fetal effects. Hypotension after spinal anesthesia is caused by a decrease in systemic vascular resistance along with increased cardiac output.^{[11],[13],[15],[16]} Uteroplacental blood flow lacks auto-regulation, making it directly dependent on uterine perfusion pressure and inversely proportional to uterine vascular resistance. Therefore, multiple adrenergic agents are used currently. In our study, we found hypotension in 38% (case count of 19) in the conventional fixed dose regime and 20% (case count of 10) in the HAD regime group, which was highly significant statistically (p-value of 0.001). This finding was similar to the finding of studies performed by Harten JM^[15] and Jain K et al.,^[14] who found in their studies that low-dose intrathecal BH is associated with lower incidence of maternal hypotension. In the study conducted by Bialowalska K^[8] and Ioannidis R,^[13] they found no difference in the occurrence of hypotension in conventional and low-dose spinal LA. From our study finding, we summarized that successful SA with a low-dose LA has lower incidence of spinal-induced adverse effects such as hypotension, nausea, and vomiting.

Conclusion

Intrathecal hyperbaric bupivacaine in HAD of 0.06 mg per cm height of patient can achieve surgical anesthesia while maintaining systolic blood pressure. However, cases of block failure are higher in low-dose spinal LA in comparison to the conventional fixed dose regime without an adjuvant, but adverse effects of spinal block were lower. Therefore, we recommend use of an adjusted dose regime to parturients for cesarean delivery, especially in areas where there is variation in maternal body habitus.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Clinical Trial number in CTRI

CTRI/2021/12/049559.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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