Central neuraxial blockade is very popular for lower abdominal and lower limb surgeries. The cost effectiveness, ease of administration, rapidity of onset, adequacy of muscle relaxation and profound analgesia during the operative as well as during the post-operative period provide excellent operating conditions and make it an indispensable technique to provide anaesthesia for the surgeries below umbilicus. It blunts the ‘stress response’ to surgery, decreases intra-operative blood loss, lowers the incidence of postoperative thromboembolic events and decreases morbidity in high-risk surgical patients. It also avoids the disadvantages associated with general anaesthesia like airway manipulation, poly pharmacy and other untoward effects like postoperative nausea, vomiting and need for supplemental intravenous analgesics. ^[1]

Bupivacaine is popularly used in epidural space. The onset of action with bupivacaine is rapid and anaesthesia is long-lasting. The duration of anaesthesia is significantly longer with bupivacaine than with other commonly used local anaesthetics. However, this long duration of action delays recovery of motor function and prolongs post anaesthesia care unit (PACU) stay after surgery. ^[3] Several studies have shown that bupivacaine has more CNS and cardiac toxicity compared to other local anaesthetics. In addition; there have been reports of fatal cardiovascular toxicity following use of bupivacaine in regional anaesthesia.

Ropivacaine, a new amide local anaesthetic has been produced as a pure‘S’ isomer of the propyl analogue of bupivacaine. It is a long-acting local anaesthetic with low lipid solubility, low potency and low cardiovascular and CNS toxicity compared to bupivacaine. It blocks nerve fibres involved in pain transmission (Aδ and C fibres) to a greater degree than those controlling motor function (Aβ fibres). Therefore, ropivacaine has been found to induce less intense motor blockade than bupivacaine. ^[4]

Dexmedetomidine is a new addition to the class of alpha‑2 agonist which has got numerous beneficial effects when used through epidural route. It suppresses the activity in the descending noradrenergic pathway which modulates nociceptive neurotransmission and terminates propagation of pain signals leading to analgesia. The hypnotic and supraspinal analgesic effects are mediated by the hyperpolarization of noradrenergic neurons, which suppresses neuronal firing in the locus coeruleus along with inhibition of norepinephrine release and activity in the descending medullospinal noradrenergic pathway, secondary to activation of central α2-adrenergic receptors. ^[5]

Magnesium is the fourth most plentiful cation in our body. It has antinociceptive effects in animal and human models of pain. The biological basis for potential antinociceptive effect of magnesium is its voltage-dependent regulation of calcium influx in to the cell, and non-competitive antagonism of N-methyl-D aspartate (NMDA) receptors. N‑methyl‑d‑aspartate (NMDA) receptors present in dorsal horn of spinal cord have a role in the modulation of central sensitization of noxious stimulus. ^[6]

This is a Double blind, Prospective, Randomised controlled study was conducted int he Department of Anaesthesia and Critical Care and Orthopaedics, Tertiary Care Teaching Hospital.

Study sample size - 90 patients of ASA I and II undergoing lower abdominal and lower limb surgeries.

Sample age group- 18-55 years

Group allocation - After taking written informed consent patients were divided into three groups by computer generated random numbers.

1. GROUP (R) (n =30): received bolus of 19 ml epidural injection of 0.75% ropivacaine plus 1ml normal saline.
2. GROUP (D) (n =30): received bolus of 19 ml epidural injection of 0.75% ropivacaine plus injection dexmedetomidine 25 mcg (25 mcg /ml).
3. GROUP (M) (n =30): received bolus of 19 ml epidural injection of 0.75% ropivacaine plus injection magnesium sulfate 50 mg (50mg/ml).

Each of the solution was made to a total volume of 20 ml.

Preparation of the study drug:

The study drug was prepared aseptically just before the execution of epidural block. The neck of the commercially available ampoules of injection ropivacaine0.75%, inj dexmedetomidine or Inj magnesium sulfate were wiped with alcohol swab (isopropyl alcohol) and then we waited a while for the excess of alcohol to evaporate. After this the ampoule was broken at the designated mark on its neck. A sterile 20 ml syringe was taken and 19 ml of ropivacaine was loaded in this syringe. Preparation of inj. dexmedetomidine was done by adding 0.5 ml of dexmedetomidine (50 mcg/0.5 ml) to 1.5 ml of normal saline in a sterile 2 ml syringe to make the solution of 25 mcg/ml. Preparation of magnesium sulfate was done by adding 1 ml of Inj. magnesium sulfate (500 mg/ml) to 9 ml of normal saline in 10 ml sterile syringe to make the solution of 50 mg/ml. Now according to the group allocation, in Group R, 1 ml of normal saline, in Group D, 1 ml of dexmedetomidine and in Group M, 1 ml of magnesium sulphate was mixed with19 ml of ropivacaine to make the solution of 20 ml in each group.

Inclusion Criteria-

• Adult patient aged between 18-55 years of either sex undergoing lower abdominal and lower limb surgeries.
• Patient belonging to ASA Class I and II.
• Patients weighing between 45kg to 75 kg.
• Patients with height between 150cm and 180cm.

Exclusion Criteria-

• Unwilling patients.
• Psychiatric Diseases.
• Emergency surgeries.
• History of drug abuse and known case of hypersensitivity to local anaesthetics or adjuvants.
• Patient with medical complications like raised intracranial tension, anaemia, heart disease, diabetes mellitus, severe hypovolemia, shock, septicaemia, and hypertension.
• Patients with coagulation disorders or on anticoagulant therapy.
• Local infection at the proposed site of puncture for epidural anaesthesia.
• Spinal deformities like kypho-scoliosis, lordosis etc.
• Heart block or Dysrhythmia or patients on therapy with adrenergic receptor agonist/antagonist.

In this study, we compared epidural dexmedetomidine and magnesium sulphate as adjuvants to ropivacaine for lower abdominal and lower limb surgeries in relation to characteristics of sensory block, motor block and sedative effect. The changes in hemodynamic parameters and side effects were also observed.

This double blind, prospective, randomized controlled study was conducted on 90 adult patients of ASA physical status I-II of either sex, in the age group of 18-55 years. Patients were allocated to either of the three groups according to computer generated random numbers

Group allocation

1. GROUP (R) (n =30): received bolus of 19 ml epidural injection of 0.75% ropivacaine plus 1ml normal saline.
2. GROUP (D) (n =30): received bolus of 19 ml epidural injection of 0.75% ropivacaine plus injection dexmedetomidine 25 mcg (25 mcg/ml).
3. GROUP (M) (n =30): received bolus of 19 ml epidural injection of 0.75% ropivacaine plus injection magnesium sulfate 50 mg (50mg/ml).

Each of the solution was made to a total volume of 20 ml.

The observations were made on the basis of the data collected, and were compiled in the form of master chart.

P value was considered as follows:

Not significant (NS) >0.05

Significant (*) <0.05

Highly significant (**) <0.01

Very highly significant (***) <0.001

Table 1: Demographic data: Age group distribution

As shown in table 1, the demographic data of different age groups (20-30yrs, 31-40yrs, 4150yrs and >50yrs) distribution of the patients in all the three groups was statistically comparable (p value 0.200).

Table 2: demographic data: sex distribution

As shown in table 2, 19 patients were Female (63.3%) and 11 patients were male (36.7%), in Group R, 18 (60.0%) patients in group D were female and 12 patients (40.0%) were male and in Group M, 21 (70.0%) were female and 9 (30.0%) patients were male. Sex distribution between all the three groups was also statistically comparable (p value 0.712).

Table 3: Distribution of type of surgery

As shown in table 3, in Group R, 17 (56.7%) out of 30 patients were of lower abdominal surgeries and 13 (43.3%) patients were of lower limb surgeries, In Group D, 19 (63.3%) patients out of 30 were of lower abdominal surgeries and 11 (36.7%) patients were of lower limb surgeries and also in Group M, 17 (56.7%) patients out of 30 were of lower abdominal surgeries and 13 (43.3%) patients were of lower limb surgeries. Thus, the distribution of type of surgery amongst all the three groups was comparable with statistically no significant difference (p value 0.832).

Table 4: Sensory block: Time to onset

 As shown in table 4, onset of sensory block at T6 was earliest in Group D (11.27 ± 1.78 min) followed by Group M (12.20 ± 2.37 min) and longest in Group R (14.33 ± 1.83 min).  We found that the difference in the meantime to onset of sensory block at T6 dermatome was statistically very highly significant between Group R V/S Group D (p value <0.001) and between Group R V/S Group M (p value <0.001) but not statistically significant between Group D V/S Group M (p value 0.176).  

Table 5: Sensory block: Time to achieve maximum sensory level

As shown in table 5, maximum level of sensory block was achieved earliest in Group D (14.13 ± 2.35 min) followed by Group M (15.07 ± 2.96 min) and then in Group R (16.73 ± 2.85 min). We found that the difference in the meantime taken for maximum level of sensory block was statistically highly significant between Group R V/S Group D (p value 0.001). The differences were not found statistically significant between Group R V/S Group M (p value 0.053) and between Group D V/S Group M (p value 0.386).

Table 6: Motor block: Time to maximum motor block and duration of block

As shown in table 6, the total duration of motor block was longest in Group D (281.57 ±

25.89 min) followed by Group M (231.83 ± 20.44 min) and shortest in Group R (185.87 ± 18.22 min). We found that, the difference in the total duration of motor block was statistically very highly significant between Group R V/S Group D (p value <0.001), between Group R V/S Group M (p value <0.001) and also between Group D V/S Group M (p value <0.001).

Table 7: Sedation effect

In our study, sedation was assessed by Ramsay Sedation Scale (RMS 1-6) (Annexure 3) with RMS 1 being anxious, agitated or restless and RMS 6 being no response to light glabella tap or loud auditory stimulus.

As shown in table 7, maximum sedation score in Group R was score 1 in 7 (23.3%) patients and score 2 in 23 (76.7%) patients. In Group R, no patients achieved sedation score more than 2. Maximum sedation score in Group D was score 2 in 6 (20.0%) patients, score 3 in 20 (66.7%) patients and score 4 in 4 (13.3%) patients. No patients achieved sedation score 1, and more than 4 in Group D. Maximum sedation score in Group M was score 1 in 6 (20.0%) patients and score 2 in 24 (80.0%) patients. Similar to Group R no patients achieved sedation score more than 2 in Group M also. 

Central neuraxial blockade is a well-known technique to provide anaesthesia for lower abdominal and lower limb surgeries. It is a cost-effective method which provides effective sensory and motor blockade, adequate muscle relaxation and profound analgesia.  

Epidural anaesthesia can be used as sole anaesthetic for procedures involving the lower abdomen and lower limb. The major advantages of epidural anaesthesia are the ability to titrate the extent and duration of anaesthesia thus making it suitable for procedures of long duration, lesser complication of haemodynamic changes than that seen with comparable levels of spinal block and puncture of durameter associated with sub-arachnoid block. Ropivacaine was synthetized simultaneously with bupivacaine by Af Ekenstam almost 50 years ago, and is first launched in 1996, being the first pure S- enantiomer local anesthetic to be clinically introduced. It is a long-acting local anaesthetic with low cardiovascular and CNS toxicity compared to bupivacaine. It blocks nerve fibres involved in pain transmission (Aδ and C fibres) to a greater degree than those controlling motor function (Aβ fibres). Therefore, ropivacaine has been found to induce less intense motor blockade than bupivacaine. ^[7]

Demographic profile

No statistically significant differences were found among the three groups with respect to distribution of age, height, weight and sex. ASA physical status, type of surgery and duration of surgery were also comparable among all the three groups.

Sensory block characteristics- 

In our study the onset of sensory block at T6 was earliest in Group D (11.27 ± 1.78 min) followed by Group M (12.20 ± 2.37 min) and longest in Group R (14.33 ± 1.83 min). The difference was statistically very highly significant between Group R V/S Group D (p value <0.001) and between Group R V/S Group M (p value <0.001) but no statistically significant difference was found between Group D V/S Group M (p value 0.176). The result is comparable with the results of M. Thimmappa et al ^[8] in which they found the onset of sensory block significantly faster with addition of dexmedetomidine with epidural 0.75% ropivacaine. The result is also similar with the study conducted by T. Ghatak et al ^[9] in which they compared the effect of addition of magnesium or clonidine as adjuvant to epidural bupivacaine and found that the Onset of sensory block at T6 was most rapid in magnesium group (P value<0.001). Our study is also in corroboration with the study of V. Shahi et al ^[10] who conducted a comparative study of magnesium sulfate and dexmedetomidine as adjuvant to epidural bupivacaine and found that the addition of magnesium and dexmedetomidine decreased the time to onset of sensory block (P <0.05).In their study also, the difference was not significant between magnesium and dexmedetomidine group.

In our study we found that the higher number of patients achieved the level of T4 in Group D and Group M compared to Group R but the difference in maximum sensory level was statistically not significant among the three groups (p value 0.447). The result is comparable with the results of study conducted by P.F. Salgado et al ^[11] in which they did not find significant difference (p> 0.05) for the maximum analgesic block level with addition of dexmedetomidine to epidural .75% ropivacaine. S.H.R.Faiz et al ^[12] also found that the addition of magnesium sulfate to intrathecal bupivacaine increases the maximum sensory level but the difference was not significant (P>0.05). S.kaur et al ^[13] found that addition of dexmedetomidine to epidural ropivacaine increased the median maximum sensory level reached (P < 0.001). They used dexmedetomidine 1mcg /kg, higher than the dose used in our study, 0.25 mcg/kg, which might be the reason for the significant difference observed by them. 

Maximum level of sensory block was achieved earliest in Group D (14.13 ± 2.35 min) followed by Group M (15.07 ± 2.96 min) and then in Group R (16.73 ± 2.85 min). We found that the difference in the meantime taken for maximum level of sensory block was statistically highly significant between Group R V/S Group D (p value 0.001). The differences were not found statistically significant between Group R V/S Group M (p value 0.053) and between Group D V/S Group M (p value 0.386). Similar to our finding, M.Thimmappa et al ^[8] also found the time to achieve maximum sensory level significantly decreased with addition of  dexmedetomidine with epidural 0.75%  ropivacaine (p value<0.001). S.kaur et al ^[13] also found that addition of dexmedetomidine to epidural ropivacaine decreases the time to achieve maximum sensory level but the difference was not significant (p value 0.122). Similar result was shown by Yousef and Amr ^[14] who found no significant difference in the time taken to reach the highest level of sensory block by adding magnesium sulphate to epidural bupivacaine and fentanyl.

Motor block characteristics-  

The mean time to onset of motor block (Modified Bromage grade 1) was earliest in Group D (8.13 ± 1.81 min), followed by Group M (10.67 ± 3.17 min) and then in Group R (12.53 ± 2.22 min). The difference in the meantime to onset of motor block was statistically significant between Group R V/S Group D (p value <0.001), between Group D V/S Group M (p value <0.001) and also between Group R V/S Group M (p value 0.012). Similar result was found by Al-Mustafa et al ^[17] who found dose dependent effect of dexmedetomidine on the onset of motor block when used as an adjuvant to bupivacaine in spinal anesthesia. Similar result was also found by Shruti et al ^[19] that addition of magnesium sulphate to epidural bupivacaine significantly decreases the time to onset of motor block (p value <0.001). We found that only 10 patients (33.3%) patients achieved complete motor block in Group R and addition of dexmedetomidine and magnesium sulfate to ropivacaine increases the number of patients who achieved complete motor block but the difference was statistically not significant among the three groups (p value 0.128). Similar result was also found by S.Kaur et al ^[13] who found only 24% patients achieved complete motor block with 0 .75% epidural  ropivacaine and higher number of patients achieved complete motor block with addition of dexmedetomidine ( p value <0.001). They used dexmedetomidine 1 mcg/kg which might be the reason for the difference to be significant. P.F .Salgado et al ^[11] also found that only 24% patients achieved complete motor block with 0.75% ropivacaine that increased with addition of dexmedetomidine ( p value <0.05). They had also used dexmedetomidine 1mcg / kg in their study. Similar result was also found by R. Hasanein et al ^[17] who found that addition of magnesium with 125% epidural bupivacaine increases the frequency of complete motor block but the difference was not significant (p value 0.089). Since ropivacaine is less lipophilic than bupivacaine and thus less likely to penetrate large myelinated motor fibres, it has selective action on the pain-transmitting A δ and C nerves rather than Aβ fibres, which are involved in motor function. This might be the reason of not achieving complete motor block in many patients.  

Maximum motor block was achieved earliest in Group D (19.73 ± 5.82 min) followed by Group M (20.00 ± 5.97 min) and then in Group R (21.47 ± 7.12 min) but the difference in the meantime taken for achieving maximum motor block was not found statistically significant among the three groups (p value 0.523). Similar result was also found by S.Kaur et al ^[13] that addition of dexmedetomidine decreases the time to achieve maximum motor block but the difference was not significant (p value 0.123). M. Thimmappa et al ^[9] found significant difference in time to achieve complete motor block with addition of dexmedetomidine to epidural ropivacaine (p value<0.001), finding not similar to our study. The use of higher dose of dexmedetomidine (1mcg/kg) by them might be the reason for significant difference.

The total duration of motor block was longest in Group D (281.57 ± 25.89 min) followed by Group M (231.83 ± 20.44 min) and shortest in Group R (185.87 ± 18.22 min). The difference in the total duration of motor block was statistically very highly significant between Group R V/S Group D (p value <0.001), between Group R V/S Group M (p value <0.001) and also between Group D V/S Group M (p value <0.001). Our findings are in corroboration with the finding of V. Shahi et al ^[10] who also found that the duration of motor block in epidural block was longest in dexmedetomidine group followed by magnesium group and then in control, bupivacaine group ( p value <0.001).^[12] S. Kaur et al ^[15] also found prolongation of duration of motor block with addition of dexmedetomine to epidural ropivacaine ( p value<0.001). Similar result was found by D. Shukla et al ^[10] who observed longest motor block in dexmedomidine group followed by magnesium and then in control (bupivacaine) group in spinal block ( p value< 0.001).

Sedation effect-

The level of maximum sedation score was in the range of 1-2 in Group R and Group M, and 1-4 in Group D. The difference in the maximum sedation score was found statistically very highly significant between the Group R V/S Group D and between Group D V/S Group M (p value <0.001). Similar result was also found by V.Shahi et al ^[11] that dexmedetomidine causes arousable sedation as compared to magnesium and control group (bupivacaine) (p value <0.05). Our study is also in corroboration with the study of P.F .Salgado et al ^[11] who found significant sedation (p value < 0.05) with addition of dexmedetomidine with epidural ropivacaine. S. Banwait et al in ^[16] also found that addition of magnesium to epidural fentanyl for postoperative pain does not causes sedation in both group (p=1).  Jabalameli and Pakzadmoghadam in ^[20] coducted study on different dose of magnesium sulfate to spinal bupivacaine and found the similar result that there was no significant difference between the groups with respect to sedation score all the times (P > 0.05).

Onset of the sensory and motor block was earliest in dexmedetomidine followed by magnesium and longest in control (ropivacacaine) group. Time to two segment regression, time to first rescue analgesic of sensory block and duration of motor block was found to be longest in dexmedetomidine followed by magnesium and then in control (ropivacacaine alone) group with statistically significant difference among all the three groups. The haemodynamic parameters (PR, SBP, DBP and MAP) decreased in all the groups after injecting the study drug. The difference was found significant when dexmedetomidine was compared to other two groups but no significant difference was found in the incidence of hypotension and bradycardia among all the three groups. Difference in the maximum sedation score was found significant with dexmedetomidine as compared to other two groups and no patients required additional sedation in dexmedetomidine group. Respiratory depression was not seen in any patient among all the three groups. Shivering was significantly lower in dexmedetomidine group. Occurrence of other adverse events like bradycardia, hypotension and nausea/vomiting was found similar among all the three groups.

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