After ethical committee clearance from the institute, informed consent from all the patients enrolled for the study was obtained. A total of 60 patients of either sex in the age group of 18-65 years belonging to American society of Anaesthesiologists physical status I or II scheduled for elective discectomy/laminectomy of the lumbosacral spine between Jan 2013 and Nov 2013 were included. Based on previous literature on VAS for two group randomised controlled study for the detection of minimum difference of 2.0 VAS score with 90% statistical power and 5% level of significance the sample size required was 58 with 28 in each group. But for better results and to account for any drop outs we chose 60 patients with 30 in each group. Patients with sacral anomaly, known hypersensitivity to local anaesthetics, those on cardiovascular medication, and with conditions contraindicating neuraxial blockade were excluded from the study.

During the preoperative evaluation all patients were familiarised with the linear Visual Analogue Scale (VAS) {0 – no pain and 10–worst imaginable pain}. Two anaesthesiologists and a blinded observer were involved with each patient. The patients were randomly allocated using a computer generated randomisation table into Ropivacaine (R) group and Ropivacaine with Dexmedetomedine (RD) group. After ensuring that all standard monitors like electrocardiogram, non-invasive blood pressure and pulseoximetry were in place anaesthesia was induced with inj fentanyl 2μg/kg, inj propofol 2mg/kg and endotracheal intubation facilitated by inj vecuronium 0.1mg/kg and then turned prone for the surgery. Caudal epidural injection was performed in the prone position under strict aseptic precautions. Position in the epidural space was confirmed using loss of resistance technique. Needle placement was also confirmed by the use of an image intensifier. The anaesthetist blinded to the contents of the syringe injected the same into the epidural space. Patients in the R group were given 20 ml of 0.2% ropivacaine and patients in group RD were given 1μg/kg of inj dexmedetomidine with 0.2% inj ropivacaine. Surgical incision was placed at least 20 minutes after the block giving sufficient time for the drug to get fixed.

Haemodynamic parameters like Heart Rate (HR), Systolic Blood Pressure (SBP), Mean Blood Pressure (MBP) and Diastolic Blood Pressure (DBP) were recorded before the block which was considered as the baseline and at regular intervals intraoperative and postoperatively. Hypotension was defined as 20% reduction in the systolic blood pressure from the baseline value and was treated with 6 mg of inj mephentermine. Inj atropine 0.6 mg iv was administered when the heart rate dropped to less than 20% of baseline or less than 50 beats/min. Anaesthesia was maintained (Minimum Alveolar Concentration- MAC 1 to 1.2) using oxygen, nitrous oxide and isoflurane along with intermittent boluses of vecuronium 1mg and inj fentanyl 25 μg every hour. Intravenous paracetamol 1 gm was given to all patients intraoperatively and the same was continued eight hourly for the first 24 hours. The patients underwent either a discectomy or a single level laminectomy. Injection neostigmine 0.04 mg/kg and inj glycopyrrolate 0.01 mg/kg were used for reversal of neuromuscular blockade. All patients were extubated awake after fulfilment of the extubation criteria. Patients were monitored for postoperative pain after they had completely recovered and regained consciousness from general anaesthesia and subsequently at 30 min, 1, 2, 4, 8, 12 and 24 hours thereafter. Pain was quantified using the VAS at regular intervals. Patients with VAS more than 3 were given the rescue analgesic inj diclofenac 75mg as an infusion. Associated side effects like nausea, vomiting, urinary retention, motor blockade were documented in the first 24 hours.

The results were averaged (mean±SD) for continuous numerical data. The unpaired student t-test and chi-square test was used to determine whether there was a statistical difference between groups in the parameters (VAS and haemodynamics) measured. The ‘p’ < 0.05 was accepted as statistically significant. Sample size was determined by a cross over pilot study of 8 patients in both the groups to detect a projected difference of 35% between the two groups for duration of analgesia for Type 1 error (α) of 0.05 and power of study 0.8. Data analysis was carried out using Statistical Package for Social Science (SPSS, V 10.5 package).

Total of 60 patients were enrolled in our study. No difference in the demographic profile was detected between the two groups as shown in [Table/Fig-1].

The difference between the two groups with regard to the duration of surgery was not statistically significant. The number of patients undergoing laminectomy and discectomy in both the groups were comparable.

[Table/Fig-2] shows the mean VAS scores of the RD group were statistically lower at 4, 8 and 12 hours (p=0, 0, 0.006) compared to R group.

[Table/Fig-2]:

Mean VAS scores in at different time points between the two groups.

In [Table/Fig-3] heart rate showed a steady decline and the difference between the group reached statistically significant values at 4 hours* (R=81.75±9.89, RD=75.70±8.23, p=0.012) and 12 hours** (79.34±10.27, 74.80±6.66, p=0.046). Two patients in RD group had bradycardia.

Blood pressures were relatively stable in both the groups. Systolic BP and mean BP were comparable between the groups while diastolic BP in RD group at immediate postoperative period was statistically higher compared to the R group (R=75.13±8.38, RD= 80.22±10.91, p=0.049).

Time to rescue analgesic in Group RD ranged from 420-444 min (Avg=432, SD=6.70) and 422-490 min (Avg=456, SD=10.89) in Group R. The p-value was <0.0001.

Achieving adequate pain relief in the postoperative period not only ensures patient comfort but also optimises recovery by aiding early ambulation. Following surgeries on the spine the need to assess neurologic function while providing superior analgesia with minimal side effects remains the goal. Caudal epidural block is a simple and effective means of relieving pain after lumbosacral spine surgeries [13]. Pre-emptive caudal analgesia was used in this study as earlier studies have shown good postoperative analgesia and favourable outcome [7,13–16]. Patients are positioned prone for lumbosacral spine surgeries which also facilitated performing a caudal block [17]. Sekar c et al., compared 82 patients receiving pre-emptive caudal single shot 20 cc of bupivacaine and tramadol for lumbosacral spine surgeries. They inferred that the study group had VAS score significantly lower at all the time intervals than control group which received normal saline [7]. Kakiuchi M et al., concluded that pre-incisional caudal injection of bupivacaine and buprenorphine relieves postoperative wound pain on the lumbar spine performed under general anaesthesia [14]. Kundra et al., conducted a study in 60 patients for pain relief after lumbar laminectomies comparing pre-emptive caudal morphine with postoperative caudal morphine and found that VAS at eight hour, time for first postoperative analgesia and postoperative morphine consumption to be much lower and significant with pre-emptive caudal epidural morphine [15]. Ropivacaine 0.2% was the choice of local anaesthesia which provides an advantage over bupivacaine with respect to central nervous system and cardiovascular system safety index [9,18,19] and selectivity towards sensory rather than motor blockade [8]. Hence it is an ideal drug to assess the motor system postoperatively [9] and also helps in early mobilisation of the patient. Though a statistical analysis of the time to mobilisation was not done in our study most of the patients in both the study group were out of the bed by six hours postoperatively.

There is no proper consensus regarding dose of dexmedetomedine to be used for neuraxial blocks [20] and a dose of 1 μg/kg was used in our study which was similar to study conducted by Saravana Babu MS et al., They compared epidural ropivacaine and dexmedetomedine 1μg/kg with ropivacine and clonidine 2μg/kg in 60 patients for spine surgeries given postoperatively and found dexmedetomedine as neuraxial adjuvant is better for prolonging duration of analgesia and for cardio respiratory stability [21]. Fawzi MH et al., also used same dose with good results [13].

The 11 point linear Visual Analogue Scale (VAS) being a reliable validated score for assessing acute postoperative pain was used in our study [22,23]. The mean VAS score at postoperative 4 hour, 8 hour and 12 hour were statistically lower in RD group compared to R group. Though the difference in the score was statistically significant the mean score in both the groups was less than 3 indicating adequate analgesia upto 12 hours. The time to first rescue analgesic was prolonged in the RD group compared to the R group and it was statistically significant. Haemodynamic alterations can occur following caudal block which is attributable to ropivacaine and dexmedetomidine [13,24]. In our study heart rate and blood pressures were in a clinically acceptable range. Two patients in RD group had bradycardia which was treated with atropine 0.6mg stat. So 0.2% of ropivacaine and 1 μg/kg of dexmedetomidine seem to cause no haemodynamic disturbance of clinical significance. No other complications were noted in either of the groups.

The limitations of the present study were that the sedation scoring was not done postoperatively which is one of the commonest side-effect of α2 adrenergic agonists. The time to mobilize postoperatively was not studied either considering that the neurosurgical team had a definite protocol in this regard and randomisation was not possible.

Pre-emptively given caudal block with 0.2% ropivacaine and 1 μg /kg dexmedetomidine provides excellent analgesia for prolonged duration in lumbosacral spine surgeries with minimal haemodynamic side effects while preserving good motor function facilitating neurological assessment and early ambulation.