Year : 2015 | Volume
| Issue : 2 | Page : 142-147
Response to low-dose intrathecal clonidine in septuagenarians undergoing sub-umbilical surgeries: A study
Jayashree Sen1, Bitan Sen2
1 Department of Anesthesia, Goldfield Institute of Medical Sciences and Research, Ballabgargh, Faridabad, India
2 Department of Emergency Medicine, Apollo Hospital, New Delhi, India
Dr. Jayashree Sen
Department of Anesthesiology, Goldfield Institute of Medical Sciences and Research Ballabgargh, Faridabad
Source of Support: None, Conflict of Interest: None
|Date of Web Publication||10-Mar-2015|
Clonidine, an alpha-2-adrenergic agonist, may have a clinically relevant analgesic action but also a hypotensive action, when administered spinally. Aim: To evaluate the analgesic and circulatory effects of low-dose intrathecal clonidine co-administered with hyperbaric bupivacaine in septuagenarian patients undergoing sub-umbilical surgeries. Materials and Methods: A total of 20 patients within the age group of 70-80 years of either sex, enrolled in this study, were randomly divided into groups of 10 each. Group I received clonidine 7.5 μg as an adjuvant to 15 mg of hyperbaric bupivacaine and Group II (control group) received 15 mg of bupivacaine with saline to make volume in the two solutions equal. Result: The level of subarachnoid block was comparable in the two groups. Duration of motor blockade was longer in the clonidine group (221.4 ± 35.92 min) compared with the control group (112.3 ± 12.45 min). Request for 1 st dose of analgesic was earlier in the control group (135.5 ± 28.52 min) than the clonidine group (295 ± 18.85 min). Mean arterial pressure (clonidine 77.67 ± 6.47 vs. control 93.87 ± 3.03, P = 0.0002) and heart rate (clonidine 65.2 ± 5.20 vs. control 77.4 ± 6.06, P = 0.003) were significantly lower (P < 0.05) in the clonidine group compared with the control group from 20 mins after the block to the end of 3 h. In the clonidine group, 3 patients had postoperative headache, 4 had intra-operative shivering. 2 patients in the clonidine group also developed hypotension and 1 bradycardia and 1 of them developed bradyapnea along with acute hypotension 5 min after shifting to the postoperative ward and later recovered on resuscitation. In the control group 2 patients had bradycardia, 6 had intra-operative shivering and 3 had postoperative headache. Conclusion: We conclude that addition of clonidine in the dose of 7.5 μg to bupivacaine significantly increases the duration of spinal analgesia with clinically insignificant influence on hemodynamic parameters.
Keywords: Intrathecal, low-dose clonidine, septuagenarians
|How to cite this article:|
Sen J, Sen B. Response to low-dose intrathecal clonidine in septuagenarians undergoing sub-umbilical surgeries: A study. Saudi J Anaesth 2015;9:142-7
|How to cite this URL:|
Sen J, Sen B. Response to low-dose intrathecal clonidine in septuagenarians undergoing sub-umbilical surgeries: A study. Saudi J Anaesth [serial online] 2015 [cited 2019 Dec 6];9:142-7. Available from: http://www.saudija.org/text.asp?2015/9/2/142/152840
| Introduction|| |
A number of procedures such as combined spinal-epidural technique and/or addition of different adjuvants have been tried intrathecally to prolong and to improve the efficacy of neuraxial/regional analgesia. The agents introduced as adjuvants are adrenergic agonists (clonidine, adrenaline), N-methyl-D-aspartate antagonists (ketamine, magnesium), gamma-aminobutyric acid agonists (midazolam), cyclooxygenase-inhibitors (ketorolac), Ach-esterase inhibitor (neostigmine), Opioids etc.  Clonidine, an alpha-2-adrenergic agonist, an effective analgesic, is being extensively evaluated as an alternative to neuraxial opioids used intrathecally for control of pain and has proven to be a potent analgesic, free of at least some of the opioid related side effects. 
This study was undertaken in the patients who are more vulnerable to the trauma of anesthesia, the septuagenarians, undergoing sub-umbilical surgeries. The aim of this study is to evaluate the effect of addition of a small dose (7.5 μg) clonidine to hyperbaric bupivacaine for spinal anesthesia in the spread and duration of sensory block, duration of motor block, time to first analgesic request, the degree of analgesia and circulatory effects.
| Materials and Methods|| |
This prospective study was conducted in a teaching hospital during the period of April 2010 to January 2011. After informing the Ethical Committee and written informed consent was obtained from all the participants, 20 patients of either sex, aged between 70 and 80 years of American Society of Anesthesiologists Grade I and II, undergoing herniorrhaphy, dynamic hip screw fixation for inter-trochanteric fracture femur, open reduction internal fixation for distal femoral fracture, interlocking nailing for fracture tibia and hip replacement were included. The patients having metabolic disorder, psychiatric illness, neurologic disease, on cardiovascular medications, those with history of hypersensitivity to clonidine or local anesthetics, alcoholics, also patients with a body weight of >120 kg, a height of <150 cm, and those with conditions that preclude spinal anesthesia were excluded from the study. Preanesthetic check-up of the patients under the study, were done a day before surgery and were counseled regarding adequate starvation, sedation, local anesthesia, the operative procedures and also were educated about the visual analog scale (VAS)  regarding the rate of experience with the analgesia. VAS (0-10 cm).
Patients were randomly divided equally in two groups of 10 each. Investigations were done according to the institution's protocol. Patients were not premeditated. On arrival in the operation theater, multipara monitor was connected (Philips-Intellivue MP20) for recording the patient's oxygen saturation (SpO 2 ), heart rate (HR), electrocardiography, noninvasive arterial blood pressure, and respiratory rate. Intravenous (IV) line was established with an 18-G bore cannula and IV preloading was done with 15 ml/kg of Ringer's solution about 15 min before the intended time of intrathecal drug administration. Under all aseptic and antiseptic precautions, spinal anesthesia was administered in sitting position at the L3-L4 interspace using midline approach with a 25 gauge Quincke spinal needle. After ensuring a free flow of cerebro spinal fluid, the Clonidine group (group I) received a single dose of 15 mg of 0.5% bupivacaine (heavy) plus 7.5 μg of preservative free clonidine. The patients in the Control group (group II) were given 15 mg of 0.5% bupivacaine (heavy) mixed with an identical volume of saline. Patient was then made to lie down immediately and the level of sensory block was assessed by pin-prick method using a 25-G short beveled needle and reassessed every 3 min for 15 min to record the highest level of block and the time taken to achieve the highest level. Degree of motor block, at the same intervals as sensory block, was assessed as per modified Bromage scale: 
- Free movement of legs and feet
- Just able to flex knees with free movement of feet
- Unable to flex knees, but with free movement of feet
- Unable to move legs or feet after intrathecal drug injection, data recording was performed during the first half an hour at 5 min interval, then at the 60 th min, followed by every hour up to 5 th h.
Both the groups were similar in respect of age, body mass index, and duration of surgeries [Table 1]. The baseline values of HR, mean blood pressure (MAP) and blood SpO 2 are presented in [Table 2]. [Table 3] presented a comparison of type of surgery, number and gender in both the groups. The data included the hemodynamic parameters, SpO 2 [Table 2] duration and onset of analgesia which were calculated and compared with baseline values. Time taken to achieve maximum degree of block as per Bromage scale was noted [Table 4]. Intramuscular diclofenac sodium 75 mg was administered as rescue analgesia whenever VAS was >4.  The time to first analgesic request (rescue analgesia) was noted. Patients who demanded rescue analgesia intra-operatively were excluded from the study [Table 4].
|Table 1: Patient characteristics data and duration of surgery (mean ± SD and P value)|
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|Table 2: Comparison of baseline vital signs in both groups (mean ± SD and P value)|
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|Table 3: Comparison of type of surgery, number and gender in both groups|
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Descriptive statistics for all continuous variables are denoted as mean (M) and ± standard deviation (SD). The comparisons for testing significant differences between the two groups I and II (for continuous variables) were performed using the Student's t-test. While, Chi-square test was used for categorical variables. Statistical significance was set at P < 0.05.
Adverse events like bradycardia (HR <45 bpm), hypotension (drop in systolic blood pressure >20% of baseline or mean arterial pressure (MAP) <60 mmHg sustained for >10 min), nausea, vomiting shivering, pain and also blood loss, urine output, IV fluid input during the procedure were noted. Bradycardia was treated with IV atropine sulfate 0.01 mg/kg, hypotension with trendelenberg position, fluid replacement in the form of Ringer's lactate in calculated doses as per the weight of the patient and further adjusted according to the blood loss during surgery. If there was no response to fluid administration, IV mephentermine sulfate 3 mg aliquots of injection in incremental doses was administered. All patients were observed in the post anesthesia recovery room for 5 h and then in the ward. Severity of pain was measured using a 10 cm VAS at hourly interval for next 24 h by the nursing staff that was unaware of the group the patient belonged to. The first request for pain killer drug was recorded.
| Result|| |
A total of 20 patients were studied. The variations in the mean HR and arterial pressure have been shown graphically in [Figure 1] and [Figure 2], respectively. The decrease in mean HR from 20 min until the end of 3 h was greater in clonidine group (65.2 ± 5.20) than in the control group (77.4 ± 6.06) (P = 0.003), which is statistically significant (P < 0.05). In addition, the decrease from baseline value within the clonidine group was also statistically significant at 5 min to end of 3 h. The MAP also showed a similar trend and there was a significant low MAP in the clonidine group (77.67 ± 6.47), compared with the control group (93.87 ± 3.03) (P = 0.0002) from 20 min after the test drug administration until the end of 3 h (P < 0.05).
|Figure 1: Comparison of heart rate between clonidine group and control group|
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|Figure 2: Comparison of mean arterial pressure between clonidine group and control group|
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|Figure 3: Peroperative complications in the clonidine group and control group|
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There was no significant change in respiratory rate and SpO 2 from the baseline in both the groups.
Supplemental oxygen through nasal prongs, at the rate of 2 L/min was administered to all the septuagenarian patients as long as the surgery continued. The parameters regarding onset and regression of sensory block, onset and regression of motor block were observed and compared (mean ± SD) [Table 4].
A sensory block of T7-T10 and a complete motor blockade of the lower extremities (Bromage 3) were observed in all patients. The mean time to achieve sensory block of T10 was significantly shorter in the clonidine group (8.4 ± 1.26 min) than the control group (12.5 ± 2.54 min). The time of achievement of complete motor block between groups (clonidine group 8.7 ± 1.41 min, control group 13.7 ± 2.66 min), was less in clonidine group and was highly significant (P = 0.0002). We also observed that the duration of motor blockade in group I and II was 221.4 ± 35.92 min versus 112.3 ± 12.45 min, which again goes in favor of clonidine.
The first request for supplemental analgesia (VAS scores at >2-3) on regression of sensory block was longer in the clonidine group than in the control group (295 ± 18.85 min vs. 135.5 ± 28.52 min). During the surgical procedures in the control group, incidence of hypotension was nil, 2 had bradycardia, 6 had postoperative shivering and 3 had headache in the postoperative period. In the clonidine group 2 patients had hypotension, 1 had bradycardia, 4 had shivering and 3 had post-operative headache [Figure 3]. 1 patient of hypotension and bradycardia suffered a marked fall in blood pressure and bradyapnea in the postoperative room 5 min after discharge from the operation theater and required emergency resuscitation, later recovered.
| Discussion|| |
Clonidine, a centrally acting selective partial agonist for α2 -adrenoreceptor, activates post junctional α2 -adrenoceptors which are located:
- On primary afferent terminals at peripheral and spinal endings,
- On neurons in the superficial laminae of the spinal cord which contain important structures for pain transmission, receiving most of their primary sensory input from Aδ and C fibers and
- Within several brainstem nuclei implicated in analgesia in the dorsal horn of the spinal cord and thus inhibits nociceptive impulses, the postulated mechanism for which may be that:
- Clonidine blocks conduction of Aδ and C fibers and increases potassium conductance in isolated neurons in vitro, thus intensifying conduction block.
- Clonidine causes local vasoconstriction in the clinical setting, thereby reducing vascular uptake of local anesthetic from around the neural structures.
- Clonidine enhances analgesia from intraspinal opioids by interactions within the spinal cord both pre- and postsynaptically.
It was shown that clonidine suppresses the generation of action potentials in tonic-firing spinal dorsal horn neurones, and therefore could contribute to increase both sensory and motor blocks of local anesthetics  by 30-50% using doses as high as 1 or 2 μg/kg. This is possibly due to the fact that α2 adrenoreceptor agonists induce cellular modification in the ventral horn of the spinal cord and facilitate the local anesthetic action. Prolongation in sensory block can be due to vasoconstrictive effect of clonidine.  Improved analgesia, at these doses is associated with systemic side effects such as sedation, bradycardia, and hypotension.  Following intrathecal administration of clonidine, its analgesic effect is mediated spinally through activation of post synaptic α2 -receptors in substantia gelatinosa of spinal cord. , Clonidine administered through neuraxial route also has a local effect on sympathetic nerves in the spinal cord.  The α2 -adrenergic agonists reduce arterial blood pressure and produce sympathicolysis through effects at specific brainstem nuclei and on sympathetic preganglionic neurons in the spinal cord. These effects are counteracted by direct vasoconstriction resulting from the α2 -adrenergic agonists on the peripheral vasculature. α2 -adrenergic agonists in combination with local anesthetic can potentially increase the degree of sympatholysis resulting hypotension.  Clonidine thus affects arterial blood pressure in a complex manner because of opposing actions at multiple sites. Racle et al. studied clonidine 150 μg and isobaric bupivacaine with epinephrine in spinal anesthesia for hip surgery, for patients aged 75 years or more and found a decrease in systolic blood pressure of 15% from resting values.  Niemi studied clonidine intrathecally in the dose of 3 μg/kg added to 15 mg of 0.5% bupivacaine in patients undergoing knee arthroscopy.  Niemi  and Acalovschi et al.  observed significant sedation in their patients because they used higher doses of clonidine.
Filos et al. demonstrated that clonidine used intrathecally, as a sole analgesic in doses ≥150 μg maintains relative hemodynamic stability but causes marked sedation.  Grace et al. and Chiari et al. demonstrated that, the optimal dose of intrathecal clonidine in terms of effects versus side effects is controversial in adults. , Grubb et al. found that intrathecal clonidine may provide adjunct analgesia without additional respiratory depression. 
De Kock et al. recommended a dose of 15-45 μg of clonidine as optimal for supplementing spinal anesthesia. 
Dobrydnjov et al. added 0, 15, or 30 μg clonidine to 6 mg of intrathecal hyperbaric bupivacaine for inguinal hernia repair and found increase in duration of motor block (146, 155, and 182 min, respectively), but not the duration of analgesia. 
Dobrydnjov et al., in another study, performed a double-blinded randomized control trial with low-dose (15 μg) intrathecal clonidine added to local anesthetic in patients during combined spinal-epidural anesthesia for hip arthroplasty and observed a better quality of anesthesia and longer-lasting analgesia.  Dobryndjov et al. noted postoperative nausea and vomiting in four patients (one each in group B and BC30 and two patients in BC30).  Jeon et al. found that intrathecal clonidine 150 μg failed to prevent postspinal shivering and confirmed that IV clonidine 1 μg/kg is an effective method to prevent shivering in patients undergoing spinal anesthesia for orthopedic surgery.  Dobrydnjov et al. recorded 45-120 min after spinal injection, a significant decrease in MAP, but not in HR in groups BC15 and BC30 in comparison to group B.  Grandhe et al. also observed significant decrease in MAP from 45 min to 8 h after intrathecal injection in groups BC1 and BC2 when compared with group B.  Dobryndjov et al. and Grandhe et al. reported dose dependent sedative effect of clonidine. Wolff et al., had investigated the local anesthetic-like action of clonidine in superficial dorsal horn neurones in his experimental study.  Kaabachi et al., used clonidine 1 μg/kg as an adjuvant to plain bupivacaine for spinal anesthesia in adolescents and found the duration of sensory block achieved was prolonged by 30 min and postoperative analgesia by 120 min without severe adverse events.  Sethi et al. observed that 1 patient in the control group and 3 patients in the clonidine group had nausea, 11 patients complained of dryness of mouth,  which was possibly because of a large dose of clonidine (1 mcg/kg) used in their study.
Elia et al., in a systematic review of randomized trials, studied clonidine (15-150 μg) as an adjuvant to intrathecal local anesthetics for surgery and found better intra-operative analgesia, delayed regression of the sensory block as well as the time to first analgesic request and increase in the duration of the motor block. The most prominent adverse effect was intra-operative hypotension. 
Van Tuijl et al.  observed that peak sensory level was comparable among the groups who used higher dose of clonidine but lower dose of bupivacaine. Similar trend of peak sensory level was studied by Grandhe et al. despite the use of large dose of clonidine (1 mcg/kg),  suggesting that the dose of intrathecal clonidine does not affect the peak sensory level. The data obtained from our study indicates that addition of 7.5 μg of clonidine to 0.5% hyperbaric bupivacaine in a sample size of septuagenarians significantly prolongs the analgesia and motor block and thus reduces the postoperative analgesic requirement. Even though a statistically significant decrease in MAP and HR was noted in the clonidine group compared to the control group, only 1 patient required therapeutic intervention. It is pertinent to mention that the dose of intrathecal clonidine, in our study, is significantly low than the studies conducted by Racle et al.,  Niemi,  Acalovschi et al.,  Filos et al.,  De Kock et al.,  Dobrydnjov et al.  We observed that peak sensory level was comparable among the groups in our study and the findings were similar to the study conducted by Van Tuijl et al.  In our study longer duration of analgesia observed was same as with Dobrydnjov et al.  when their dose of clonidine was 15 μg and motor block was also similar to Dobrydnjov et al.  when they used even higher doses. Incidence of fall of MAP was there in the studies done by Dobrydnjov et al.  and Grandhe et al.  starting from 45 min post spinal, though in our septuagenarians, the fall was from 20 min post spinal but only 1 patient required intervention. No patient in our study complained of dryness of mouth unlike Sethi et al.  or nausea vomiting unlike Dobrydnjov et al.  In our study, no septuagenarian was observed having sedation unlike the subjects of Niemi  and Acalovschi et al.  because patients in their studies received clonidine in higher doses. Our study thus implies that it is possible to achieve equally good analgesia without side effects when clonidine is used in dosages as low as 7.5 μg intrathecally.
| Conclusion|| |
To prolong spinal anesthesia in elderly patients undergoing sub-umbilical surgeries, alternative anesthetic techniques such as epidural or combined spinal-epidural, may be technically difficult and time consuming. In addition, the motor blockade during epidural anesthesia is often not as satisfactory as during spinal anesthesia. So we emphasize on that, in septuagenarians for sub-umbilical surgeries, the addition of clonidine to bupivacaine in the dose as low as 7.5 μg (approximately 0.15 μg/kg) significantly increases the duration of spinal analgesia with clinically insignificant influence on hemodynamic parameters and level of sedation.
| References|| |
Buvanendran A, Kroin JS. Useful adjuvants for postoperative pain management. Best Pract Res Clin Anesthesiol 2007;21:31-49.
Eisenach JC. Overview: First international symposium on alpha 2-adrenergic mechanisms of spinal anesthesia. Reg Anesth 1993;18:207-12.
Aldrete JA, Kroulik D. A postanesthetic recovery score. Anesth Analg 1970;49:924-34.
Gammon GD, Starr I. Studies on the relief of pain by counterirritation. J Clin Invest 1941;20:13-20.
Connor TO, Abram S. Atlas of Pain Injection Techniques. Edinburgh: Churchill Livingstone; 2003. p. 125.
Chiari A, Eisenach JC. Spinal anesthesia: Mechanisms, agents, methods, and safety. Reg Anesth Pain Med 1998;23:357-62.
Dobrydnjov I, Axelsson K, Thörn SE, Matthiesen P, Klockhoff H, Holmström B, et al
. Clonidine combined with small-dose bupivacaine during spinal anesthesia for inguinal herniorrhaphy: A randomized double-blinded study. Anesth Analg 2003;96:1496-503.
Sethi BS, Samuel M, Sreevastava D. Efficacy of analgesic effects of low dose intrathecal clonidine as adjuvant to bupivacaine. Indian J Anesth 2007;51:415-9.
Reddy SV, Yaksh TL. Spinal noradrenergic terminal system mediates antinociception. Brain Res 1980;189:391-401.
Brandt SA, Livingston A. Receptor changes in the spinal cord of sheep associated with exposure to chronic pain. Pain 1990;42:323-9.
Strebel S, Gurzeler JA, Schneider MC, Aeschbach A, Kindler CH. Small-dose intrathecal clonidine and isobaric bupivacaine for orthopedic surgery: A dose-response study. Anesth Analg 2004;99:1231-8.
Racle JP, Benkhadra A, Poy JY, Gleizal B. Prolongation of isobaric bupivacaine spinal anesthesia with epinephrine and clonidine for hip surgery in the elderly. Anesth Analg 1987;66:442-6.
Niemi L. Effects of intrathecal clonidine on duration of bupivacaine spinal anesthesia, haemodynamics, and postoperative analgesia in patients undergoing knee arthroscopy. Acta Anesthesiol Scand 1994;38:724-8.
Acalovschi I, Bodolea C, Manoiu C. Spinal anesthesia with meperidine. Effects of added alpha-adrenergic agonists: Epinephrine versus clonidine. Anesth Analg 1997;84:1333-9.
Filos KS, Goudas LC, Patroni O, Polyzou V. Hemodynamic and analgesic profile after intrathecal clonidine in humans. A dose-response study. Anesthesiology 1994;81:591-601.
Grace D, Bunting H, Milligan KR, Fee JP. Postoperative analgesia after co-administration of clonidine and morphine by the intrathecal route in patients undergoing hip replacement. Anesth Analg 1995;80:86-91.
Chiari A, Lorber C, Eisenach JC, Wildling E, Krenn C, Zavrsky A, et al
. Analgesic and hemodynamic effects of intrathecal clonidine as the sole analgesic agent during first stage of labor: A dose-response study. Anesthesiology 1999;91:388-96.
Grubb WR, Kushins LG, Langenfeld JE, Barbella J, Pollak P. ASA Meeting Abstracts; 2000.
De Kock M, Gautier P, Fanard L, Hody JL, Lavand'homme P. Intrathecal ropivacaine and clonidine for ambulatory knee arthroscopy: A dose-response study. Anesthesiology 2001;94:574-8.
Dobrydnjov I, Axelsson K, Gupta A, Lundin A, Holmstrom B, Granath B. Improved response to low dose intrathecal clonidine in septuagenarians analgesia with clonidine when added to local anesthetic during combined spinal-epidural anesthesia for hip arthroplasty: A double-blind, randomized and placebo-controlled study. Acta Anesthesiol Scand 2005;49:538-45.
Jeon YT, Jeon YS, Kim YC, Bahk JH, Do SH, Lim YJ. Intrathecal clonidine does not reduce post-spinal shivering. Acta Anesthesiol Scand 2005;49:1509-13.
Grandhe RP, Wig J, Yaddanapudi LN. Evaluation of bupivacaine-clonidine combination for unilateral spinal anesthesia in lower limb orthopaedic surgery. J Anesth Clin Pharmacol 2008;24:155-8.
Wolff M, Heugel P, Hempelmann G, Scholz A, Mühling J, Olschewski A. Clonidine reduces the excitability of spinal dorsal horn neurones. Br J Anesth 2007;98:353-61.
Kaabachi O, Zarghouni A, Ouezini R, Abdelaziz AB, Chattaoui O, Kokki H. Clonidine 1 microg/kg is a safe and effective adjuvant to plain bupivacaine in spinal anesthesia in adolescents. Anesth Analg 2007;105:516-9.
Elia N, Culebras X, Mazza C, Schiffer E, Tramèr MR. Clonidine as an adjuvant to intrathecal local anesthetics for surgery: Systematic review of randomized trials. Reg Anesth Pain Med 2008;33:159-67.
Van Tuijl I, Giezeman MJ, Braithwaite SA, Hennis PJ, Kalkman CJ, van Klei WA. Intrathecal low dose hyperbaric bupivacaine-clonidine combination in outpatient knee arthroscopy: A randomized controlled trial. Acta Anesthesiol Scand 2008;52:343-9.
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]
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