Reinforcement of subarachnoid block by epidural volume effect in lower abdominal surgery: A comparison between fentanyl and tramadol for efficacy and block properties.

BACKGROUND: Epidural volume extension (EVE) is claimed to increase the block height and decrease the dose requirement for intrathecal drug. However, almost all studies have been done in obstetric population and none actually compares the effect of additional drugs added to epidural volume.
MATERIALS AND METHODS: Seventy-five (ASA I and II) patients scheduled for lower abdominal surgery were randomly divided into three groups. All groups received intrathecal 10 mg bupivacaine; two groups received additional 10 ml of normal saline epidurally with 25 mg tramadol or 25 mg of fentanyl. Groups were than compared for maximal block height, rate of sensory block regression to T10, and motor block regression to Bromage scale of 0. Time to first analgesia and adverse effects were also compared among the three groups.
MATERIALS AND METHODS: Seventy-five (ASA I and II) patients scheduled for lower abdominal surgery were randomly divided into three groups. All groups received intrathecal 10 mg bupivacaine; two groups received additional 10 ml of normal saline epidurally with 25 mg tramadol or 25 mg of fentanyl. Groups were than compared for maximal block height, rate of sensory block regression to T10, and motor block regression to Bromage scale of 0. Time to first analgesia and adverse effects were also compared among the three groups.
RESULTS: Groups with EVE had statistically significant higher block height, with a significant faster regression that the control group. However, both fentanyl and tramadol groups were inseparable in respect to motor or sensory block regression. Fentanyl group had maximal time to first analgesia, followed by tramadol and control groups. Hemodynamic alterations were also more common in EVE groups.
CONCLUSION: EVE can increase the block height significantly, but it seems to be limited only to the physical property of additional volume in epidural space and fentanyl or tramadol do not seem to differ in their ability to alter block properties.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Since the advent of central neuraxial blockade, various methods have been explored to decrease the doses of required drugs and prolong their anesthetic effect without adding significant adverse effects. Intrathecal drug delivery with epidural volume extension (EVE) with the above aims has attracted many researchers since the combined spinal epidural (CSE) technique was introduced into clinical practice. The studies have targeted various aspects of physiological and anatomical relation of intrathecal and epidural space to decrease drug requirements and attain effective long-lasting anesthesia/analgesia. EVE using saline has been used to achieve higher block heights;[123] however, there is not enough literature on regression of such a higher block achieved in such cases. Knowing how rapidly the block regresses will be clinically important to meet the demands of long surgeries and will also help us chart out plans for postoperative analgesia. As bupivacaine remains the most commonly used drug intrathecally and is capable of causing differential blockade, higher sympathetic block attained can be associated with increased hemodynamic instability which can be further aggravated by augmentation of subarachnoid block (SAB) by EVE. Besides use of volume expansion, epidural opioids also are used to prolong the duration and quality of SAB.[4] However, there is no conclusive evidence available on block behavior when both these methods are used together. There are also scarce data available on block regression rate and time to first analgesia, comparing different opioids, when used as adjuvant with EVE of SAB. With the above background, we decided to conduct a study to compare a non-supplemented SAB and to determine the safety and pharmacokinetic aspects of EVE when combined with opioids like fentanyl and tramadol. Such a study would help us determine if one opioid could score over another to maintain a longer effect of SAB by delaying regression of the block, and thus would prolong time to first analgesia besides lowering total analgesic requirement.

MATERIALS AND METHODS

After institutional ethical approval was obtained, 75 patients (ASA I and II) scheduled for lower abdominal surgery under neuraxial blockade were included in the study. All these patients were between 15 and 65 years of age and their height varied between 140 and 175 cm.

The exclusion criteria included the following:

Morbid obesity

Expected duration of surgery >1.5 h

Any contraindication to regional anesthesia

Patient refusal

Marked spinal deformity

Increased intracranial tension (papilledema, cerebral edema, tumors, subarachnoid hemorrhage)

Coagulopathy

Skin infections at the site of block

Pregnant women

After conducting routine investigations, patients were randomly allocated into three groups of 25 each. All patients were planned for central neuraxial blockade in left lateral position preferably at L3-4 spinal interspace. In group 1 patients, only SAB was planned, so a 25 G Sprotte spinal needle was used. In group 2 and 3 patients, a CSE technique was planned, so an 18 G CSE (B. Braun, Melsungen, Germany) set with “needle through needle” was used. An epidural catheter was threaded immediately after SAB in both these groups. Patients received the following medications in their respective groups:

Group 1: 15 mg of 0.5% hyperbaric bupivacaine intrathecally

Group 2: 15 mg 0.5% hyperbaric bupivacaine intrathecally + 10.ml normal saline with 25 mg tramadol epidurally immediately after the intrathecal drug.

Group 3: 15 mg of 0.5% hyperbaric bupivacaine intrathecally +10.ml normal saline with 25 μg fentanyl epidurally immediately after the intrathecal drug

Observations planned

Twenty minutes after the block, the highest sensory dermatome blocked was assessed using a 25 G hypodermic insulin needle.

Duration of regression of sensory block level to T10 after the end of the procedure was noted in all the groups. This was done by reassessing the level of sensory block every 10 min.

At the end of procedure, motor blockade was reassessed every 10 min using the Bromage scale till it returned to 0.

Average duration from block to time to first analgesia at a numeric pain scale of more than 4.

Statistical analysis

Statistical analyses were performed using SPSS (version 15.0; SPSS, Inc., Chicago, IL, USA) software and graphs were produced using Origin Pro for Windows (version 8.6). In this study, parametric data were recorded as arithmetic mean ± standard deviation (SD). Chi-square analysis was used for nonparametric measurement and to compare the hemodynamic effects. Independent t test was applied for comparing motor regression in the groups with significant confidence interval of 5%. The statistical comparison with preoperative value was done by simple “t” test. Pearson's correlation coefficient was used to determine the relation of block height with the rate of motor and sensory regression.

RESULTS AND OBSERVATIONS

Patient and surgery profile

Patients in all three groups were comparable in terms of demographic parameters like age, sex, weight, and height [Table 1]. The mean duration of surgery in groups 1, 2, 3 was 84.6, 80.2, and 82.84, min, respectively, which was also found to be statistically comparable.

Table 1

Distribution of patients according to their demographical data

Block height

The median highest block height attained among groups 2 and 3 was comparable; however, it was clearly two segments higher than the highest sensory dermatome blocked in group 1. The highest block noted in groups 1, 2, and 3 was T5-6, T3-4, and T3-4, respectively, whereas the median block height in groups 1, 2, and 3 was T6-7, T4-5, and T4-5, respectively [Table 2].

Table 2

Comparison of upper level of sensory block after 20 min

Sensory block regression

In groups with EVE, the regression of sensory block was found to be significantly faster to T10 level. The mean time interval for sensory level regression to the tenth thoracic dermatome was 125.2 ± 8.718 min in group II and 125.6 ± 7.681 min in group III as compared to group I (without EVE effect), which served as our control group where the mean time was found to be 146.8 ± 9.883 min [Figure 1]. The difference in mean values between groups I and II and between groups I and III was most highly significant with “P” values <0.001, while it was insignificant between groups II and III where the “P” value was >0.05.

Figure 1

Graph comparing sensory block regression to T10 level

The Pearson's product moment correlation coefficient (“r” value) value showed that the height of the block reached correlates only moderately to regress to T10 levels in respect to time (in minutes), emphasizing that the increase in height of level of sensory blockade in the study groups due to epidural injection of normal saline is not in proportion to the time to regress to T10 levels, that is, the higher the level of blockade achieved, this shorter is the time taken to regress.

Motor block regression

It was found that time for motor recovery, that is, motor power in lower limbs to a Bromage score of 0, was significantly shorter (153.2 ± 11.446 min) in group II and group III (154 ± 12.583 min) than in group I where the mean motor recovery time was 202.8 ± 13.699 min [Figure 2].

Figure 2

Graph comparing motor block regression to a Bromage score of 0

The mean values in all the three groups were compared with a simple “t” test and significance noted in a t-test chart. It was found that difference in the mean values between groups I and II and between groups I and III was most highly significant with “P” values <0.001, while it was insignificant between groups II and III where the “P” value was >0.05.

The Pearson's product moment correlation coefficient (“r” value) showed that the height of the block reached correlated only moderately to complete motor recovery in respect to time (in minutes), emphasizing that the increase in height of level of sensory blockade in the study groups due to epidural injection of normal saline is not in proportion to complete motor recovery, that is, the higher the level of blockade achieved, the shorter is the time taken for complete motor recovery, which can be accountable to EVE effect.

Hemodynamic parameters

Hemodynamic parameters were continuously monitored in all the three groups after the block till a period of 6 h. The mean blood pressure after 10 min of the block in groups 1, 2, and 3 was 82.93, 82.01, and 80.43, respectively. Within the first half an hour of block, 8 patients in group 2 and 11 patients in group 3 had transient systolic blood pressure readings below 90 mm of Hg, while it was seen only in six patients in group 1. All these patients responded well to intravenous fluid loading or single dose of 3 mg intravenous ephedrine. One patient each in groups 2 and 3 had transient bradycardia with heart rate below 60 beats/min and responded to a single dose of intravenous atropine (0.3 mg); however, no bradycardia was seen in any patient in group 1. The pulse oximeter recordings did not show any significant variation among the three groups.

Requirement of first analgesic postoperatively

Group III, where 25 μg fentanyl was used, provided postoperative analgesia for the maximum duration since the time of administration of block, while group I, where no additional agent was given, had the shortest average duration of analgesia of around 180 min for the first analgesic postoperatively. Group II, where 25 mg tramadol was given, showed average duration to first analgesic of around 240 min as compared to 330 min in 25-μg fentanyl in Group III.

Associated adverse effects

Adverse effects were divided into two groups – immediate (first 6 h after the block) and delayed (2 days postoperatively). The incidence of postoperative nausea and vomiting was the highest in the tramadol group where 10 patients either complained of severe nausea or had episodes of vomiting, while the number in groups 1 and 3 was 2 and 4, respectively. Five patients in group 1 had at least a single episode of shivering, whereas no such episode was noted in groups 2 and 3. Pruritus was noted in one patient in the tramadol group and two patients in the fentanyl group. One patient each in group 1 and fentanyl group had an episode of urinary retention requiring single time urinary catheterization postoperatively [Table 3]. Two patients only in group 1 had history of headache suggestive of post-dural puncture headache on day 1, which responded to conservative treatment.

Table 3

Comparison of side effects in all three groups

DISCUSSION

EVE is a known modality of increasing block height post spinal block.[5] It also has demonstrated additional benefits in terms of reduced dose requirements of intrathecal local anesthetic.[167] The aim of such a dose reduction is to lower the local anesthetic dose-associated side effects like hypotension after spinal blockade. Once the regular dose of spinal local anesthetic is given and an EVE is used, it rather causes the block to reach higher sensory level,[8] and thus may add to hypotension by increasing the level of associated sympathetic blockade. On the other hand, if lower dose with planned epidural extension is used, knowing the rate of block regression is very important as a rapidly receding blockade could lead to inadequate anesthesia for the surgical duration. Thus, it would be clinically relevant to find agents which when used with EVE methods could lower the rate of block regression. In our study, we used standard dose of intrathecal bupivacaine in short procedures lasting up to 1½ hours to evaluate the rate of block regression after surgery. The choice of small procedure was made as this would not require any epidural local anesthetic supplementation during the intraoperative course and would allow us to measure block regression only from the SAB component.

The block recorded in both fentanyl and tramadol groups with epidural volume was seen to be higher by around two segments than our control group, which is in accordance with the literature as the epidural volume compresses the thecal space causing the CSF to move higher, thus achieving a higher level. The similar levels attained by both fentanyl and tramadol groups highlight that this is more likely to be only associated with the physical property of volume effect in the epidural space and remains unaffected by the content injected into the epidural space.

Interestingly, both groups 2 and 3 regressed to level of T10 much faster than group 1 where no epidural volume was supplemented despite attaining a higher block level. The possible explanation to this fact is that since bupivacaine is not actually metabolized in the CSF, the action is only offset by reabsorption and circulation of CSF. In other words, if the CSF mobilization becomes faster, the likely effect will last smaller.[9] The injected volume in epidural space raises the CSF pressure and enhances its reabsorption, and thus the action offsets faster. Intrathecal fentanyl is known to enhance the duration of motor blockade in SAB.[10] However, in the present study, the block actually offset faster and also fentanyl failed to show significant block prolongation in comparison to tramadol. Tramadol and fentanyl both have been used in central neuraxial blocks to prolong the duration of analgesia. Both these, used in our groups 2 and 3, respectively, did seem to achieve higher analgesic efficacy as the mean time to first analgesic was higher than in group 1. The time to analgesic requirement, however, was statistically equivalent in both tramadol and fentanyl. Since motor block and sensory block regression was faster, it is likely that the block of pain fibers is also offset faster and the analgesic effect seen was due to the action of both the drugs used epidurally rather than improving the quality of SAB when used as an adjuvant in EVE group. The time of analgesic administration in both the groups was similar to the time of their action when used epidurally alone.[1112]

We monitored our patients continuously for hemodynamic changes, as SAB block is well known for its hypotensive effects. The block height directly correlates with the degree of hemodynamic variations. Eight of our patients in the tramadol group and 11 patients in the fentanyl group showed hypotension requiring treatment, whereas the number was 3 in group 1. This is likely due to the higher block level attained in these groups. So, if EVE is planned, one must use smaller doses of intrathecal local anesthetics.[513] A possible higher sympathetic block level also would account for bradycardia seen in two patients in groups 2 and 3. This capability of increasing the efficacy of block can be used where patchy or incomplete block is seen after CSE technique.

Other adverse effects like nausea and vomiting were more common in the tramadol group, which is more likely to be due to local properties of the drugs used. The prime reason for decreasing the use of tramadol in central neuraxial block is the high degree of nausea,[14] which was also highlighted in our study. Two patients in group 1 possibly had mild Post Dural Puncture Headache, which was not reported in any other groups; this is also in accordance with the fact that CSE technique is associated with lower incidence of PDPH and injection into epidural space helps to seal dural leaks if any.[15]

CONCLUSIONS

The “volume effect” was distinct from the block enhancement after an epidural top-up of local anesthetic in that saline extends the block height by a mechanical volume effect and does not prolong the block duration.

EVE with the help of epidural catheter can be used to achieve a higher block level when combined with SAB using a local anesthetic.

There is a moderate correlation between the highest level of sensory block and the time of regression of sensory block to T10 level, and a higher seeming block with epidural volume expansion actually regresses faster.

The motor block tested in the lower limb regresses faster in the EVE group.

The analgesic effect due to adjuvants in epidural volume unlike motor and sensory block lasts longer, highlighting that it is more likely due to pharmacology of the injected drug rather than EVE.

Since the block attained in EVE group is higher, it is more likely to be associated with hypotension.

Results between fentanyl and tramadol groups were statistically similar; hence, it is more likely that effects seem by EVE are purely due to physical property of the injected volume and are independent of the agent used.