Effect of Injection Speed of Heavy Bupivacaine in Spinal Anesthesia on Quality of Block and Hemodynamic Changes.

Background and Aims: Spinal anesthesia is a technique widely used for gynecological, lower abdominal, pelvic and lower limb procedures. Even though it causes a profound nerve block, it is associated with profound hypotension. Aims of the Study: To assess the effect of the speed of injection of heavy bupivacaine on quality of block and hemodynamic changes in patients undergoing gynecological surgeries under spinal anesthesia.
Methods: This was a prospective randomized study conducted on 40 patients. Group F patients were given 3.2 mL of 0.5% heavy bupivacaine intrathecally in 15 s and Group S patients were given the same drug over 60 s. The time to achieve T10 dermatomal block, maximum block height, block height at 5 min were recorded. Heart rate (HR), systolic, diastolic blood pressures, and mean arterial pressures (MAP) were also recorded at different time points.
Results: HR, systolic BP, diastolic BP, and MAPs and mean block height at 5 min were comparable between the two groups at all time points. The time to achieve T10 dermatome block was significantly faster in Group F (1.85 ± 1.14 min) as compared to Group S (3.98 ± 1.58 min). Majority of patients in Group F (65%) had a maximum block up to T6 and those in Group S (45%) had a block upto T4. The usage of vasopressors was found to be significantly higher in Group F compared to Group S with P = 0.041.
Conclusion: Using faster speed of injection of heavy bupivacaine during spinal anesthesia can lead to faster achievement of blockade but with significantly higher usage of vasopressors. Copyright:

INTRODUCTION

In anesthetic practice, spinal anesthesia is the most often used technique for gynecological, lower abdominal, pelvic and lower limb procedures.[1] The advantage of spinal anesthesia is that it can cause a profound nerve block[2] with only a modest dose of local anesthetic injection. The technique's greatest problem, however, is controlling the distribution of the anesthetic drug through the cerebrospinal fluid (CSF), to provide appropriate degree and extend of block for the planned procedure without causing unnecessary spread, thereby leading to an increase in the risk of complications.[2]

The impact of the rate of local anesthetic injection on the anesthetic characteristics of spinal anesthesia is still debated. Isobaric local anesthetic solutions have been studied extensively in the literature.[3] However, there is a scarcity of data on the effect of speed of injection while administering hyperbaric solutions for spinal block. Although higher distribution of sensory blockade has been observed with a slower speed of injection, most researches using hyperbaric local anesthetics have not reported difference in the anesthetic characteristics.[3]

A number of factors affect the spread of local anesthetic within the intrathecal space. Physical features of the injectate and the injection technique are the two factors over which the anaesthesiologist has some control.[24]

The primary objective of the present study was to compare the effect of injection speed of heavy bupivacaine in spinal anesthesia (15 s vs. 60 s) on the time to achieve T10 dermatome block. The secondary objectives were to compare the incidence of hypotension, onset of hypotension, heart rate (HR) changes, and adequacy of blockade.

METHODS

The present study was a randomized, prospective, and single-blinded study which was conducted after ethics committee approval (IEC-AIMS-2020-ANES-050 dated 11-05-2020) and was registered in the Clinical Trial Registry of India (CTRI/2020/09/027676). Informed consent was obtained from all patients.

Forty patients with the American Society of Anesthesiologists physical status classes I and II and height between 155 and 165 cm undergoing uncomplicated gynecological surgeries under spinal anesthesia were included. Hypertensive patients on medications, those with ischemic heart disease, large intra-abdominal mass, and ascites were excluded from the study.

As there were no similar studies in the existing literature comparing the same dosage of drug and rate of injection, a pilot study with 20 patients was conducted to calculate sample size. Based on the mean and standard deviation (SD) of injection speed of spinal anesthesia between fast (2.175 ± 0.6876 min) and slow (4.33 ± 1.732 min) heavy bupivacaine injection in spinal anesthesia obtained from the pilot study and with 95% confidence interval and 80% power, the minimum sample size was calculated to be 6 in each group to get statistically significant results.

Patients were enrolled in the study after undergoing a thorough preanesthesia evaluation. They were premedicated with alprazolam 0.25 mg orally on the night before the surgery as well as pantoprazole 40 mg and metoclopramide 10 mg orally on the night before and on the morning of surgery. Patients were then randomized into Group F and Group S by computer generated random sequence of numbers. Concealment of group allocation was ensured with sequentially numbered opaque sealed envelopes. On reaching the operating room, standard preinduction monitors such as pulse oximeter, electrocardiogram, and noninvasive blood pressure were attached. Intravenous access was secured. Baseline HR and blood pressure were recorded. Patients were then given 10 mL.kg−1 of lactated Ringer's solution.

Patients were positioned in the left lateral position. Under strict aseptic precautions and using midline approach, dural puncture was done at the L3-L4 interspace with 25 G Whitacre needle. After free flow of CSF was confirmed, 3.2 mL of 0.5% hyperbaric bupivacaine was administered. The time period between start and end of injection was measured by an anesthesiologist using a stopwatch. Patients in Group F received the spinal drug in 15 s and Group S received the spinal drug in 60 s.

The patients were then turned into supine position and a second anesthesiologist, who was not aware of the patient group allocation, collected the data. All subarachnoid blocks were performed by one anesthesiologist. Sensory block was assessed by loss of cold sensation using ice cube. Systolic blood pressure, diastolic blood pressure, mean arterial pressure (MAP), and HR were measured at 2 min intervals for the first 10 and 5 min interval thereafter for 1 h following the spinal injection. The time to achieve T10 dermatome block, maximum sensory level, and block height at 5 min were recorded. A modified Bromage score was used for evaluation of the degree of motor block – Grade 1: Free movement of legs and feet implied no motor block, Grade 2: Just able to flex knees with free movement of feet implied partial (33%) block, Grade 3: Unable to flex knees but free movement of feet implied (66%) partial block, and Grade 4: Unable to move legs or feet implied complete paralysis. Surgery was allowed to proceed if a dermatomal blockade of T6 level and above was achieved.

Statistical analysis

Descriptive statistics of both groups were expressed as mean and SD for continuous variables and frequency and percentage for categorical variables. To test the statistical significance of the difference in the proportion of categorical variables between the groups, Chi-square with Fisher's exact test was applied. To test the statistical significance of the difference in the mean or median comparison of numerical variables between groups, Independent sample t-test was applied for normal data and Mann–Whitney U-test was used for nonnormal data. A P < 0.05 was considered to be statistically significant.

RESULTS

The data of 40 patients were analyzed [Figure 1]. Mean age, weight, height, and ASA PS were comparable in both groups. The mean time to achieve T10 dermatomal blockade was significantly faster in Group F (1.85 ± 1.14 min) as compared to Group S (3.98 ± 1.58 min) with a P < 0.001 [Table 1]. There was no statistically significant difference in block height between the two groups with P = 0.184 [Table 2]. Majority of patients in Group F (65%) had a maximum block up to T6 and majority of patients in Group S (45%) had a block up to T4 [Table 3]. The MAPs were comparable between the two groups [Table 4]. The patients in Group F required more usage of vasopressor compared to those in Group S which was significant with a P = 0.041 [Table 5].

Figure 1

CONSORT diagram

Table 1

Mean time to achieve T10 dermatome block between groups in minutes

Groups	Mean time (min)±SD	P2
Group F (n=20)	1.85±1.14	<0.001
Group S (n=20)	3.98±1.58

SD=Standard deviation

Table 2

Distribution of block height at 5 min between the groups

Block height at 5 min	Group F, n (%)	Group S, n (%)	Total	P
T10	1 (5)	5 (25)	6	0.184
T12	0	1 (5)	1
T8	3 (15)	5 (25)	8
T7	0	1 (5)	1
T6	9 (45)	7 (35)	16
T5	1 (5)	0	1
T4	5 (25)	1 (5)	6

Table 3

Distribution of maximum block height between groups

Maximum block height	Group F (n=20), n (%)	Group S (n=20), n (%)
T10	0	2 (10)
T8	1 (5)	4 (20)
T7	1 (5)	0
T6	2 (10)	9 (45)
T5	1 (5)	0
T4	13 (65)	5 (25)
T3	1 (5)	0
T2	1 (5)	0

Table 4

Mean distribution of mean arterial pressure between groups

MAP (min)	Mean±SD		P
	Group F (n=20)	Group S (n=20)
Baseline	97.0±11.34	71.35±16.23	1.09
4	78.50±17.19	78.70±13.53	0.96
8	76.50±12.80	80.65±17.92	0.40
10	77.15±10.90	79.80±15.24	0.53
15	76.25±10.65	77.85±16.00	0.71
30	76.15±12.50	73.80±15.94	0.60

SD=Standard deviation, MAP=Mean arterial pressure

Table 5

Comparison of vasopressor usage between the groups

Vasopressor usage	Group F (n=20), n (%)	Group S (n=20) n (%)	P
Yes	17 (85)	10 (50)	0.041
No	3 (15)	10 (50)

DISCUSSION

In our study, we compared the time to achieve T10 dermatome block after injection of heavy bupivacaine at 2 different speeds (within 15 and 60 s) and its effect on hemodynamic changes.

Spinal anesthesia is an anesthetic technique which is easy, relatively inexpensive, and faster to perform but it is associated with adverse effects, the most common being hypotension. The technique to reduce the hypotension induced by spinal anesthesia is slow injection of the spinal drug.[3] Faster injection of heavy bupivacaine can cause sympathectomy-induced hemodynamic changes and nausea and vomiting. Slower injection of heavy bupivacaine can cause inadequate level of blockade for surgery and conversion to general anesthesia. Injection of spinal drug should be done with caution since faster injection can lead to significant hypotension.

Rapid injection of local anesthetic during spinal anaesthesia is thought to induce turbulences, which could alter distribution of local anesthetic in the subarachnoid space.[4] However, according to previous studies, the influence of speed of injection on anesthetic characteristics of spinal anesthesia remains controversial.

Neuraxial anesthesia blocks the sympathetic and somatic nervous systems, as well as compensatory reflexes, thus resulting in unopposed parasympathetic activity.[5] Reduced stroke volume and HR due to blocking of peripheral sympathetic fibers and peripheral vasodilation due to inhibition of thoracolumbar sympathetics[67] are two effects of spinal anesthesia on blood pressure.

In the present study, it was found that the time to achieve T10 dermatome block was significant with faster injection, i.e., injection of heavy bupivacaine in 15 s. This is in agreement with the study done by Janik et al.[8] However, in the study by Tuominen et al.,[9] it was observed that a slow injection of the spinal drug resulted in higher spread of analgesia. The probable reason for this difference could be because hypobaric solution was used in the study by Tuominen et al.,[9] whereas we used a hyperbaric solution.

In the present study, no significant difference was observed in the highest sensory level achieved between the groups. This is in agreement with the study conducted by Prakash et al.,[4] Singh et al.[10] and Kim et al.[5] In study conducted by Atchison et al.,[11] it was observed that slower injection of spinal anesthesia lead to attainment of higher sensory level. The complexity of the interaction between the various factors that may influence intrathecal drug spread is reflected in these contradictory results.

In the present study, there were no significant differences in hemodynamic changes. Similar observations were made by Prakash et al.,[4] Singh et al.,[10] Kim et al.[5] In contrary, studies by Simon et al.[12] observed that slower injection of spinal anesthesia produced less hypotension. There are numerous confounding factors, including dose, density, solution temperature, and patient posture that may affect the intrathecal drug spread and hence hemodynamics.

In this present study, the use of vasopressors between the groups was significant with more percentage of patients in the fast group requiring more amount of vasopressors. However, in the study conducted by Prakash et al.[4] Singh et al.,[10] the use of ephedrine or phenylephrine was not significant between the groups.

A limitation of the present study was that the injection speeds might not have been uniform between the groups because the injections were administered manually. The level of sensory block could be affected if the desired intervertebral space was chosen incorrectly. The possibility of incorrect intervertebral level identification cannot be ruled out, even though all blocks were given by the same anaesthesiologist.

CONCLUSION

It is concluded that using faster speed of injection of heavy bupivacaine during spinal anaesthesia can lead to faster achievement of T10 dermatomal blockade but significantly increases the usage of vasopressors.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.