it is important to limit the block level to minimise haemodynamic changes during spinal anaesthesia . low - dose local anaesthetics can limit the block level and induce rapid recovery from anaesthesia with minimal haemodynamic changes . local anaesthetics - when used alone have a relatively short duration of action . the addition of opioids to local anaesthetic produces good post - operative analgesia but has disadvantages , such as pruritus , post - operative nausea vomiting and respiratory depression . dexmedetomidine ( dmt ) , a highly selective 2-agonist , is under evaluation as a neuraxial adjuvant . it provides stable haemodynamic conditions , good quality of intra - operative analgesia and prolonged post - operative analgesia with minimal side effects . however , there may be dose - related prolongation of the duration of motor blockade thus delaying discharge from post - anaesthesia care unit in day case surgeries . this trial was conducted to investigate if reduction in dose of intrathecal dmt added to a low dose hyperbaric bupivacaine would produce clinically relevant analgesia without prolonging motor blockade in patients undergoing ambulatory perianal surgeries . time to ambulation and duration of analgesia were the primary outcomes studied and sensory regression , haemodynamic changes and effect on sedation were secondary outcomes observed . after obtaining approval from the institutional ethics committee , 50 adult patients of american society of anesthesiologists physical status i and ii undergoing elective perianal surgeries were enrolled in this prospective randomised double - blinded study . patients were randomly allocated to two groups of 25 each using a sealed envelope method . group c received dmt 3 g intrathecally and group d dmt 5 g along with the local anaesthetic agent . patients with past history of spine surgery , coagulation disorders and infection at site of lumbar puncture , neurological and psychiatric disturbances , diabetes and other endocrine disorders , hypertension and other cardiac disorders , and those on beta blockers , calcium channel blockers , 2 agonists and patients with history of drug allergy were excluded from the study . written informed consent was obtained from all the patients who fulfilled the inclusion criteria and were willing to participate in the study . premedication with oral ranitidine hydrochloride 150 mg and alprazolam 0.25 mg were given the night before the surgery and they were kept nil per oral for 8 h before induction of anaesthesia . during the pre - operative evaluation , patients were given instructions to use a 10-point visual analogue scale ( vas ) , with 0 indicating no pain and 10 indicating the worst imaginable pain . ranitidine 50 mg intravenous ( iv ) . on shifting to operation theatre , electrocardiogram , peripheral oxygen saturation ( spo2 ) , non - invasive blood pressure monitors were connected and baseline values were recorded . following infusion of 500 ml ringers lactate solution , lumbar puncture was performed at l3-l4 interspace or l4-l5 interspace with the patient in the sitting position using 27 gauge quincke needle . group c received hyperbaric bupivacaine 0.5% ( 0.8 ml ) ( 4 mg ) + dmt 3 g intrathecally and group d received hyperbaric bupivacaine 0.5% ( 0.8 ml ) ( 4 mg ) + dmt 5 g intrathecally . the required dose of dexmedetomidine was drawn using a tuberculine syringe ( 0.03 ml for 3 g and 0.05 ml for 5 g ) . the total volume of solution to be injected intrathecally was made to one ml using normal saline . the drug solutions were prepared under sterile precautions by an anaesthesiologist as per instructions in the envelope , who was not involved in administration and further monitoring of the patient . the anaesthesiologist performing the spinal block and monitoring the patient was unaware of the drug administered . after the spinal block , the patients were made to sit for 5 min and then made supine . the level of sensory block , defined as the dermatomal segment with total loss of sensation to cold swab was assessed every 2 min after intrathecal injection till 10 min and every 5 min thereafter until maximum level of sensory block level stabilised . the maximum level of sensory block was considered when the loss of sensation was recorded at the same dermatomal level for 2 consecutive time intervals . ( appendix ) onset of sensory block , defined as the time required for a sensory block to reach s1 was noted . blood pressure and heart rate , was recorded every 2 min for initial 10 min and then every 5 min until the end of surgery and then at 30 min intervals in post - operative period until regression of block . sedation was monitored using ramsay sedation scale and time for sensory and motor regression to s1 and b6 , respectively , were noted and were considered as the duration of sensory and motor blockade , respectively . if patient complained of pain during surgery , it was considered as failure of subarachnoid block and inj fentanyl 2 g / kg was given as bolus and if necessary , supplementation with general anaesthesia was done . post - operatively , pain intensity was assessed using vas scale and inj diclofenac 75 mg administered intramuscularly as rescue analgesic , once the vas score was more than three . duration of post - operative analgesia was noted from the time of sab to the first demand for rescue analgesic . patient was made ambulant when the following criteria were achieved ( 1 ) able to perform partial knee bend ( bromage scale 6 ) ( 2 ) recovery of proprioception of great toe ( 3 ) return of perianal sensation ( 4 ) no postural hypotension on making the patient stand . time for ambulation was recorded from the time of sab to the time when patient was made ambulant . time for urination , sedation and side effects if any were also observed in the post - operative period . side effects such as hypotension ( defined as a decrease in mean arterial pressure > 25% of the baseline value ) was treated with iv boluses of 6 mg ephedrine . bradycardia defined as a pulse rate of < 50 beat / min was treated with bolus of 0.6 mg atropine iv , respiratory depression ( rr < 8 or spo2 < 95% ) was treated with oxygen supplementation and respiratory support if required , vomiting and others if any were noted . we hypothesised that reduction in dose of dmt would reduce the time required for ambulation . keeping ( 1   ) error at 80% and two sided significance level (  error ) at 0.05 , to detect at least a 10% difference in time for ambulation between the two groups , the minimum sample size required was 21 in each group . independent sample t - test was used to compare parametric and continuous data , and mann  whitney u - test applied if variables were not uniformly distributed . one patient in each group was excluded from analysis due to the failure of the subarachnoid block . demographic characteristics such as age , weight , height , sex and duration of surgery were comparable . demographic characteristics duration of post - operative analgesia was 337.86  105.11 min in group c whereas 340.78  101.81 min in group d ( p = 0.9 ) and time to ambulation in group c was 252.46  93.72 min and 253.64  88.04 min in group d ( p = 0.97 ) . the onset of sensory block to s1 was 9.61  5.53 min in group c compared to 7.69  4.80 min in group d ( p = 0.35 ) . median level of cephalad spread of sensory block was l1 ( t11  s1 interquartile range ) in group c and t11 ( t10  s1 interquartile range ) in group d. duration of sensory ( 145.28  83.17 min c , 167.85  93.75 min  d , p = 0.5 ) and motor block ( 170.53  73.44 min intraoperative and post - operative haemodynamic parameters were comparable between the two groups [ figures 1 and 2 ] . the mean sedation score ( average of mean sedation score of each patient ) was 2.008  0.03 in group d compared to 2  0.05 in group c ( p = 0.5 ) , and average post - operative sedation scores were two in both groups . none of the patients had sedation scores more than four in either group at any point of time during the study period . none of the patients in either group developed hypotension or bradycardia either in intraoperative period or post - operative period . the present study showed that dmt 3 g administered as intrathecal adjuvant to a low dose hyperbaric bupivacaine provided similar duration of analgesia compared to 5 g of dmt as intrathecal adjuvant , but did not shorten the time required for ambulation . though the onset of sensory block was slightly shortened in group d , this was not statistically significant . doses varying from 3 to 15 g of dmt have been added as an adjuvant to intrathecal bupivacaine . the present study tried to assess the effects of lower doses of dmt in ambulatory surgeries , hence doses of 3 and 5 g were compared . low - dose local anaesthetic for the subarachnoid block is commonly administered to limit the block level to minimise the haemodynamic changes . a low dose of hyperbaric bupivacaine has been successfully used for ambulatory arthroscopic knee surgeries and also in perianal surgeries . the addition of an adjuvant should further potentiate analgesia without prolonging motor blockade or causing other side effects . the prolongation of sensory effect may result from synergism between local anaesthetic and 2-adrenoceptor agonist , while the prolongation of the motor block of spinal anaesthetics may result from the binding of 2-adrenoceptor agonists to motor neurons in the dorsal horn . perineural administration of dmt also is reported to prolong the duration of the motor blockade in rats . observed faster onset of sensory and motor block with addition of dmt , but the present study did not reveal any statistically significant difference in onset of sensory and motor block with 3 and 5 g of dmt . the shorter duration of motor block in the present study compared to kanazi et al . may be attributed to the lower dose of local anaesthetic used . making the patient sit for 5 min may also limit the spread of drug further limiting the motor blockade . administration of an 2-agonist like dmt via an intrathecal route provides an analgesic effect in the post - operative period without severe sedation . this effect is due to the sparing of supraspinal central nervous system sites from excessive drug exposure , resulting in robust analgesia without heavy sedation . at spinal cord level , activation of both 2-c and 2-a receptors , in the neurons of superficial dorsal horn , especially lamina ii , directly reduces pain transmission , by suppressing the release of pro - nociceptive transmitter , substance p and glutamate from primary afferent terminals , and by hyperpolarising spinal interneurons via g - protein - mediated activation of potassium channels . none of the patients in either group had excessive sedation and is comparable with other studies . dmt 5 g when used as adjuvant to bupivacaine 6 mg prolonged duration of motor block and delayed ambulation in patients undergoing perianal surgeries . in this study , an attempt was made to assess the effect of reduction in doses of both dmt and bupivacaine on ambulation and analgesia . haemodynamic parameters were comparable in both the groups and there were no incidences of hypotension and bradycardia in the intraoperative or post - operative period . the present study did not observe the effect of these doses of dmt on analgesic consumption in the 24 h period , which may be a limitation . future studies may be targeted to assess the effect of these doses on analgesic efficacy in ambulatory surgeries . intrathecal bupivacaine with dexmedetomidine 3 g does not produce faster ambulation compared to intrathecal bupivacaine with dexmedetomidine 5 g , though it produces comparable duration of analgesia for perianal surgeries .