Dexmedetomidine as epidural adjuvant to Ropivacaine in elective lower limb surgeries

 

Darshan MS¹, Sri Devi S^2*, G M Sanjeev³

 

Abstract               Epidural adjuvants are used to prolong the action of local anesthetic agent so as to have prolongation of motor and sensory block. Dexmedetomidine a newer α₂ agonistic agent with predominant affinity to α₂receptor, α₂:α₁ affinity is 1600:1.Ropivacaine an amide local anesthetic agents.Which is an ‘S’ isomer of the propyl analogue of Mepivacaine and Bupivacaine with long acting potential. Pharmacologically it has similar properties to Bupivacaine, but with lesser cardiotoxicity profile. In our study we divided 40 patients posted for elective lower limb surgeries into two group of 20 patients each. Patients in Group R received total of (150 mg) 20ml of 0.75% Inj.Ropivacaine with 1 ml of Normal saline epidurally. Patients in Group RD received total of (150 mg) 20ml of 0.75%  Inj.Ropivacaine with 1 ml of 1 microgram per kg of Inj.Dexmedetomidine and saline to make up volume of 1 ccepidurally. We compared the onset of motor and sensory block; duration of motor block and post-operative analgesia, two segment regression time and sedation scores of both the groups. From our study we found that not only the onset of sensory and motor blockade were hastened in Group RD but also, duration of motor block, duration of post-operative analgesia were prolonged. Sedation scores were higher in Group RD and two segment regression was prolonged in Group RD.

Key Words:ropivacaine. dexmedetomidine., epidural anesthesia.

 

INTRODUCTION

Epidural blockade is very versatile technique in hands of anaesthesiologist; virtually epidural catheter can be placed in any segment of spine from cervical region to sacral region. It outscores spinal anaesthesia by its capability of producing continuous anaesthesia and analgesia and also has a better hemodynamic stability. Orthopedic patients pose their own problems to anesthetist and there is need to deal with geriatric age group of patients with post trauma physiology. Most of the patients posted for lower limb surgeries are administered regional anaesthesia, and for managing post-operative pain epidural analgesia is often used. Use of epidural adjuvants not only attenuates the dose requirement for local anaesthetic agents and but also by synergestic effectprolongs the duration of the block.

 

MATERIAL AND METHODS

After obtaining institutional ethics committee approval, a double blinded prospective study involving 40 patients was carried out.

Duration of Motor Block: It is time interval between onset of motor block and grade 0 in Bromage motor scale. It was checked at interval of every 15 minutes in post op ward.

Sedation Score: It is calculated by using Ramsay sedation score at end of one hour following injection of epidural local anaesthetic mixture.

1. Anxious or agitated patient
2. Patient is Co-operative, oriented
3. Patient responds to commandsonly
4. A Brisk response to light glabellar tap
5. A Sluggish response to a light glabellar tap
6. No response

Post-Op Analgesia Duration: It is the time duration from the administration of local anesthetic agent to first dose of analgesic usage in PACU when Visual Analogue Scale score was 3.

If there was hypotension, (measured as systolic blood pressure less than 30 % of its initial value or below 90 mmHg or MAP less than 60 mm of Hg)during anesthesia, it was treated with administration of Inj.Ephedrine 6mg. Bradycardia(heart rate<50bpm) was treated with Inj.Atropine, 0.6 mg.

Statistical Analysis: In our double blind randomized controlled study, statistical tabulations were done with Student‘t’ test, Chi Square test‘p’ value less than 0.05 was taken as significant. Demographic variables like age, sex, weight, height and duration of surgery were compared using Levene’s test for equality of variance.

 

RESULTS

There was no significant difference between groups in demographic parameters like age, gender distribution, weight, height, and duration of surgery. The groups were comparable also on the ASA risk stratification. Mean age of patients in Group R was 40.6 years and in Group RD was 39.65 years; the variation between the groups was not statistically significant with p value of 0.549.

 

Table 3:

There were 4 female patients and 16 male patients in Group R and 5 female patients and 15 male patients in Group RD, the p value for above distribution was 0.705 and was statistically insignificant.

 

Table 4:

Mean height of patients in Group R was 162.25cm, and in Group RD was 159.75cm this variation carried the significance of 0.189, and was statistically insignificant. Similarly mean weight of patients in kg showed that mean weight in Group R was 60.3 kg and in Group RD was 60.1 kg with p =0.897, and was statistically insignificant.

 

Table 5:

There were 7 patients in Group R and 8 patients in Group RD who belonged to ASA 1 risk stratification group and 13 patients in Group R and 12 patients in Group RD belonged to ASA risk grade 2, the variation did not carry any statistical significance with p value of 0.744.Mean duration of surgery in both groups were similar with p value of 0.742.

Table 6:

Time of onset of sensory block in two groups had a significant variation with block onset time being longer in Group R (mean 8.9 minutes) than in Group RD (mean 6.7 minutes) with p=0.00.

 

Table 7:

Motor block onset time in Group R was 14.1 minutes and in Group RD was 11.9 minutes; the variation carried a p value of 0.00 and was statistically significant. Duration of motor block in Group R was 182.75minutes and in Group RD was 247 minutes and variation had p value of 0.00 and was statistically significant.

 

Table 8:

GROUP	Motor block onset time  in minutes	Duration ofmotor block time  in minutes
GROUP R	14.1	182.75
GROUP RD	11.9	247

19 patients in Group R and 15 patients in Group RD had a Modified Bromage Scale score of 1; 1 patient in Group R and 5 patients in Group RD had a Modified Bromage Scale score of 2 and the above variation had a p value of 0.077 and was statistically insignificant.

 

Table 9:

Further 18 patients in Group R had a sedation score of 2 and 2 patients had a sedation score of 3, but 18 patients in Group RD had a sedation score of 3 and 2 had a sedation score of 4, the variation was statistically significant with p=0.00.

Table 10:

Duration of post-operative analgesia in Group R was 306.5minutes, which was significantly lesser compared to post op analgesia duration in Group RD which was 496.25minutes, and associated p (0.00) value which was statistically significant. Two segment regression time in Group R was 60.05minutes and that in Group RD was 84.75minutes, and above variation was statistically significant with p = 0.00.

Table 11:

Patients in both groups had comparable hemodynamics. Even though there was mild reduction of pulse rate and mean arterial pressures in Group RD which were statistically insignificant, none of the patients required Inj. Atropine and need for pressor agents was similar in both the groups.

 

DISCUSSION

From our study it was seen that epidurally administered Inj.Dexmedetomidine together with Inj.Ropivacaine not only hasten the onset of sensory and motor block but also prolong the duration of post op analgesia and duration of motor block. The sedation score obtained was higher, and two segment regression time was also prolonged by using epidural Dexmedetomidine with Ropivacaine.Many studies done shows the positive synergistic effect of α₂ agonistclonidine added to epidural local anaesthetic agent.^1,2,3Dexmedetomidine a newer α₂ agonistic agent. Three α₂adrenoreceptor sub types have been found namely α_2A, α_2B, and α_2C.^4,5 of which α_2Ais found in periphery and α_2b and α_2c receptors are found in brain and spinal cord. Postsynaptic α₂adrenoreceptors in peripheral blood vessels produce vasoconstriction, whereas presynaptic α₂adrenoreceptors inhibit the release of norepinephrine, potentially attenuating the vasoconstriction. The overall response to α₂adrenoreceptors agonists is predominantly related to the stimulation of α_2B andα_2C receptors which causesympatholysis, sedation, and antinociceptioneffects. Dexmedetomidine has a predominant affinity to α₂receptor,α₂:α₁affinityis 1600:1. It also exhibits a dose dependent action on epidural administration and has a better profile in neuraxial administration as compared to intravenous administration since α_2B and α_2C are located in brain and spinal cord. It also causes prolongation of action of local anesthetic agents in epidural space by causing reduced systemic absorption due to local vasoconstriction caused byα_2C adrenergic receptors stimulation in smooth muscle of epidural venous plexus^6,7,8.Cephalad spread of drug is responsible for sedation, it also causes reduction in minute ventilation but response to increased carbon dioxide is retained this can be taken as a safety feature of the drug. Dexmedetomidine additionally causes reduced histamine release and bronchoconstriction; it also has effect to reduce intra-operative shivering.Ropivacaine an amide local anesthetic agent which is an ‘S’ isomer of the propyl analogue of Mepivacaine and Bupivacaine with long acting potential. Pharmacologically it has similar properties to Bupivacaine, but with lesser cardiotoxicity profile because of its early dissociation from sodium channels.

Demographic profile of our study matched in both the groups, and the onset of sensory and motor block was hastened by epidural Dexmedetomidine which is comparable to many studies done earlier.⁹Duration of motor block and sensory block were significantly prolonged with addition of epidural Dexmedetomidine, and the results were comparable with studies done by Sarabjitetal and Bajwa etal.^10,11Two segment regression time was also prolonged by epidural Dexmedetomidine, this result was also in conjunction with previous studies of Sarbjitetal and Bajwaetal. Similarly the sedation score obtained was higher in Dexmedetomidine group and these results were also similar to study done earlier by Sarbjitetal.

CONCLUSION

Dexmedetomidine together with Ropivacaine not only hastens the onset of sensory and motor block but also prolongs the duration of post op analgesia and duration of motor block. The sedation score obtained was higher, and two segment regression time was also prolonged by using epidural Dexmedetomidine with Ropivacaine.

 

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