European Journal of Cardiovascular Medicine

The geriatric population poses distinct challenges to the anesthesiologist due to age related physiological decline, reduced cardiovascular reserve, and the high prevalence of comorbid conditions. For lower limb orthopedic and general surgical procedures in elderly patients, central neuraxial blockade, particularly spinal anesthesia, is often preferred. Compared with general anesthesia, spinal anesthesia is associated with a lower incidence of deep vein thrombosis, pulmonary embolism, and respiratory complications, while also avoiding the risks of polypharmacy commonly encountered with general anesthesia.[1,2]

Hyperbaric bupivacaine is widely used for spinal anesthesia; however, when used alone, its duration of action may be insufficient for prolonged or complex procedures. Increasing the dose to extend the block can result in significant hypotension and delayed recovery, especially in elderly patients with blunted sympathetic responses and limited physiological reserve.[3]

To overcome these limitations, several intrathecal adjuvants such as opioids, neostigmine, and magnesium have been studied to enhance block quality and prolong analgesia while allowing lower doses of local anesthetics.[4] Among these, alpha 2 adrenergic agonists have emerged as effective non opioid adjuvants due to their ability to potentiate sensory and motor blockade while providing sedation. Clonidine, a partial alpha 2 agonist, has been used for decades to prolong spinal anesthesia and provide hemodynamic stability by acting on presynaptic C fibers and postsynaptic dorsal horn neurons to inhibit nociceptive transmission.[5,6]

More recently, dexmedetomidine, a highly selective alpha 2 adrenoceptor agonist, has gained increasing attention. While clonidine has an alpha 2 to alpha 1 selectivity ratio of approximately 220:1, dexmedetomidine exhibits a much higher selectivity of about 1620:1, allowing effective analgesia, sedation, and sympatholysis with fewer alpha 1 mediated adverse effects.[7] Although previous studies have compared these agents in general adult populations,[8,9] evidence focused specifically on elderly patients remains limited. In this age group, achieving prolonged analgesia without delaying functional recovery such as ambulation and voiding is particularly important. Therefore, this randomized double blind study was undertaken to compare intrathecal dexmedetomidine and clonidine as adjuvants to hyperbaric bupivacaine in elderly patients, with emphasis on both block characteristics and the timeline of functional recovery.

This Study Design and Population This prospective, randomized, double-blind study was conducted on 60 elderly patients aged 60–78 years of both genders (ASA physical status I and II) scheduled for elective lower limb surgeries. Inclusion Criteria Patients aged >60 years, weight 50–90 kg, undergoing lower limb orthopedic or general surgeries under spinal anesthesia. Exclusion Criteria Patients with contraindications to spinal anesthesia, coagulopathy, significant cardiac or renal disease, allergy to study drugs, or uncontrolled hypertension. Randomization and Blinding Patients were randomly divided into two groups of 30 each using a computer-generated randomization table: • Group D (Dex): Received Hyperbaric Bupivacaine (0.5%) + Dexmedetomidine. • Group C (Clon): Received Hyperbaric Bupivacaine (0.5%) + Clonidine. Anesthetic Procedure Under strict aseptic precautions, subarachnoid block was performed at the L3-L4 interspace using a 25G Quincke spinal needle. Heart rate (HR), non-invasive blood pressure (NIBP), and oxygen saturation (SpO2) were monitored continuously. Parameters Observed 1. Block Characteristics: Onset of sensory block (time to reach T10 dermatome), onset of motor block (Bromage 3), duration of analgesia (time to first rescue analgesic), and motor recovery (time to Bromage 0). 2. Post-operative Recovery: Time to unassisted ambulation (Time to Walk) and urinary voiding (Time to Void). 3. Sedation and Pain: Intraoperative sedation was assessed using the Ramsay Sedation Score (RSS). Post-operative pain was assessed using the Visual Analog Scale (VAS) at 6 hours. 4. Adverse Events: Incidence of hypotension (decrease in MAP >20% of baseline), bradycardia (HR <50 bpm), nausea, and vomiting. Statistical Analysis Data were entered into a spreadsheet and analyzed using standard statistical software. Continuous variables (Age, Weight, Duration, etc.) are presented as Mean ± Standard Deviation (SD) and compared using the Student's t-test. Categorical variables (Gender, Side effects) were compared using the Chi-square test. A p-value of <0.05 was considered statistically significant.

A total of 60 patients were included in the study, with 30 patients in each group. Both groups were comparable regarding demographic parameters such as age, weight, and duration of surgery. There were no statistically significant differences between the groups ($p > 0.05$), ensuring a uniform baseline for comparison.

The addition of Dexmedetomidine resulted in a significantly faster onset of both sensory and motor blockade compared to Clonidine. Furthermore, the duration of analgesia was significantly prolonged in Group D (310.2 min) compared to Group C (258.1 min). Interestingly, while the motor block lasted longer in Group D (delayed motor recovery), the onset was faster.

Despite the prolonged motor block in the Dexmedetomidine group, patients in Group D achieved milestones for walking and voiding significantly earlier than Group C. The 6-hour VAS score was significantly lower in Group D (1.98) compared to Group C (2.95), indicating superior residual analgesia.

Group D patients exhibited higher sedation scores (Ramsay Sedation Score ~2.9) compared to Group C (~2.3), providing "arousable sedation" which is desirable in regional anesthesia. The incidence of bradycardia and hypotension was comparable between groups, though slightly higher in the Dexmedetomidine group, but easily managed.

The results of this study show that adding alpha 2 agonists to intrathecal bupivacaine significantly improves the quality of spinal anesthesia in elderly patients. Among the two adjuvants studied, dexmedetomidine emerged as the superior agent. It produced a faster onset of sensory and motor block, prolonged the duration of analgesia, and provided better postoperative pain control, while maintaining a hemodynamic profile comparable to clonidine.

The faster onset of sensory block (2.1 vs 2.7 minutes) and motor block (3.4 vs 4.0 minutes) observed with dexmedetomidine is consistent with previous studies by Kanazi et al. and Al-Ghanem et al.[10,11] This effect is likely related to the high lipophilicity of dexmedetomidine, which allows rapid penetration and binding at the spinal cord dorsal horn. Its mechanism involves activation of presynaptic alpha 2 receptors that inhibit the release of substance P and glutamate, along with postsynaptic receptor activation that leads to neuronal hyperpolarization through G-protein mediated potassium channels.[7,12]

An interesting and clinically relevant observation in our study was the apparent dissociation between physiological motor recovery and functional recovery. Although regression of motor block to Bromage 0 occurred later in the dexmedetomidine group, these patients were able to ambulate earlier than those receiving clonidine. This finding appears counterintuitive at first glance, but it can be explained by the superior quality of analgesia in the dexmedetomidine group. Patients in the clonidine group, despite earlier return of motor power, likely experienced higher pain scores or residual discomfort, which discouraged early mobilization. In elderly patients, adequate pain relief appears to play a more decisive role in functional recovery than motor strength alone.[13]

Hemodynamic stability is a major concern when using sympatholytic agents in geriatric patients. In the present study, the incidence of hypotension and bradycardia was comparable between the two groups, with no statistically significant differences. These findings support earlier observations by El-Hennawy et al., who suggested that the reduction in local anesthetic requirement associated with dexmedetomidine may offset its sympatholytic effects.[14] The episodes of bradycardia observed were mild, transient, and easily managed with standard treatment.

Dexmedetomidine was also associated with higher sedation scores. This sedation closely resembles natural sleep, mediated through the locus coeruleus, and is characterized by easy arousability and patient cooperation.[15] Unlike opioid-induced sedation, it was not associated with respiratory depression. This calm and comfortable state likely contributed to the higher patient satisfaction scores observed in the dexmedetomidine group, as anxiety during spinal anesthesia is a common concern in elderly patients.

Limitations

This study has a few limitations. The sample size was calculated primarily to assess block duration, and a larger study may be required to detect rare adverse effects. Plasma concentrations of the intrathecal adjuvants were not measured, although the doses used were small. Long-term neurological outcomes were not evaluated beyond hospital discharge, although no neurological complications were observed during the study period.

In elderly patients undergoing lower limb surgeries, the addition of Dexmedetomidine to intrathecal Bupivacaine provides a significantly faster onset of anesthesia, prolonged analgesia, and better patient satisfaction scores compared to Clonidine. Despite a prolonged motor block duration, Dexmedetomidine facilitates earlier return to physiological functions like voiding and walking, likely due to superior pain control.

[1]           Brown DL. Spinal, epidural, and caudal anesthesia. In: Miller RD, ed. Miller’s anesthesia. 7th edn. Philadelphia: Churchill Livingstone 2010:1611-38.

[2]           Kehlet H. Modification of responses to surgery by neural blockade: clinical implications. In: Cousins MJ, Bridenbaugh PO, eds. Neural blockade in clinical anesthesia and management of pain. 3rd edn. Philadelphia: Lippincott-Raven 1998:129-75.

[3]           Racle JP, Benkhadra A, Poy JY, et al. Prolongation of isobaric bupivacaine spinal anesthesia with epinephrine and clonidine for hip surgery in the elderly. Anesth Analg 1987;66(5):442-6.

[4]           Hindle A. Intrathecal opioids in the management of acute postoperative pain. Contin Educ Anaesth Crit Care Pain 2008;8(3):81-5.

[5]           Niemi L. Effects of intrathecal clonidine on duration of bupivacaine spinal anaesthesia, haemodynamics, and postoperative analgesia in patients undergoing knee arthroscopy. Acta Anaesthesiol Scand 1994;38(7):724-8.

[6]           Eisenach JC, De Kock M, Klimscha W. Alpha (2)-adrenergic agonists for regional anesthesia. A clinical review of clonidine (1984-1995). Anesthesiology 1996;85(3):655-74.

[7]           Kamibayashi T, Maze M. Clinical uses of alpha-2 adrenergic agonists. Anesthesiology 2000;93(5):1345-9.

[8]           Mahendru V, Tewari A, Katyal S, et al. A comparison of intrathecal dexmedetomidine, clonidine, and fentanyl as adjuvants to hyperbaric bupivacaine for lower limb surgery: a double blind controlled study. J Anaesthesiol Clin Pharmacol 2013;29(4):496-502.

[9]           Bajwa SJ, Bajwa SK, Kaur J, et al. Dexmedetomidine and clonidine in epidural anaesthesia: A comparative evaluation. Indian J Anaesth 2011;55(2):116-21.

[10]         Kanazi GE, Aouad MT, Jabbour-Khoury SI, et al. Effect of low-dose dexmedetomidine or clonidine on the characteristics of bupivacaine spinal block. Acta Anaesthesiol Scand 2006;50(2):222-7.

[11]         Al-Ghanem SM, Massad IM, Al-Mustafa MM, et al. Effect of adding dexmedetomidine versus fentanyl to intrathecal bupivacaine on spinal block characteristics in gynecological procedures: A double blind controlled study. Am J Appl Sci 2009;6:882-7.

[12]         Kalso EA. Clonidine in spinal anaesthesia. Acta Anaesthesiol Scand 1994;38(7):721-3.

[13]         Gupta R, Bogra J, Verma R, et al. Dexmedetomidine as an intrathecal adjuvant for postoperative analgesia. Indian J Anaesth 2011;55(4):347-51.

[14]         El-Hennawy AM, Abd-Elwahab AM, Abd-Elmaksoud AM, et al. Addition of clonidine or dexmedetomidine to bupivacaine prolongs spinal anesthesia. Br J Anaesth 2009;103(2):268-74.

[15]         Hall JE, Uhrich TD, Barney JA, et al. Sedative, amnestic, and analgesic properties of small-dose dexmedetomidine infusions. Anesth Analg 2000;90(3):699-705.