| Abstract|| |
Aims and objectives: We studied efficacy of caudal dexmedetomidine (DEX) on attenuation of perioperative stress response and postoperative pain in pediatric patients undergoing cardiac surgery. Materials and Methods: Forty patients, (ASA II, III), 1-3-years old were randomly allocated into two groups; group BD received caudal bupivacaine 0.25%, 2.5 mg/kg and DEX 0.5 μg/kg and group BF received bupivacaine 2.5 mg/kg and fentanyl 1 μg/kg. Results: Serum cortisol and blood glucose levels increased in both groups but increases were significantly less in group BD. Poststernotomy cortisol level (ug/dl) was 55.3 ± 5.1 vs. 90.4 ± 6.5; after cardio-pulmonary bypass (CPB) 84.1 ± 6.2 vs. 153.1 ± 8.5; after operation 78.3 ± 8.1 vs. 150.2 ± 9.8. Poststernotomy blood glucose level (mg/dl) was 93.6 ± 7.2 vs. 125.6 ± 5.5; after CPB 115.3 ± 3.7 vs. 175.3 ± 10.4; and after operation 97.3 2 ± 3 vs. 162.2 ± 12. Heart rate and mean arterial pressure decreased significantly after caudal block in group BD relative to the baseline and compared with group BF ( P < 0.05). Group BD had lower pain scores at first hour 2 ± 0.7 vs. 3 ± 1.1 ( P = 0.04); second hour 1.9 ± 0.5 vs. 3.7 ± 0.8, ( P = 0.008); fourth hour 2.4 ± 0.8 vs. 4.3 ± 0.5 ( P = 0.03); and eighth hour 2.5 ± 0.5 vs. 4.2 ± 1.1 ( P = 0.03). Conclusions: Caudal DEX attenuated stress response to surgical trauma and provided better postoperative analgesia.
Keywords: Caudal dexmedetomidine, Pediatric cardiac surgery, Stress hormone
|How to cite this article:|
Nasr DA, Abdelhamid HM. The efficacy of caudal dexmedetomidine on stress response and postoperative pain in pediatric cardiac surgery. Ann Card Anaesth 2013;16:109-14
|How to cite this URL:|
Nasr DA, Abdelhamid HM. The efficacy of caudal dexmedetomidine on stress response and postoperative pain in pediatric cardiac surgery. Ann Card Anaesth [serial online] 2013 [cited 2020 Feb 20];16:109-14. Available from: http://www.annals.in/text.asp?2013/16/2/109/109744
This article is accompanied by an invited commentary by Dr. Vipul Krishen Sharma
| Introduction|| |
The stress response associated with cardiac surgery in neonates and small children may cause subtle changes in hormonal secretion. Enhanced plasma cortisol level and suppressed anabolic hormones, such as insulin may have deleterious effects during the perioperative period  and if not attenuated may result in higher postoperative morbidity and longer intensive care unit (ICU) stay.  Stress response hormone levels can be used as an objective surrogate to assess the analgesic efficacy of the anesthetic techniques used in children as the assessment of pain in children can be difficult and unreliable.  It has been suggested that regional anesthesia can reduce stress response associated with surgical trauma. , Caudal epidural anesthesia with narcotics has been shown to inhibit the stress response to surgery and can influence postoperative outcome.  It is also an effective method for control of postoperative pain in children undergoing open heart surgery; the main disadvantage of single shot caudal technique being its short duration of action,  which can be prolonged by addition of various adjuvants.  The routine use of opioids for prolongation of bupivacaine duration has been critically challenged for various reasons, the most important is respiratory depression.  Fentanyl has been suggested the opioid least likely to cause respiratory depression when administered caudally. 
Alpha-2-adrenoceptor agonists have been used as an adjuvant to regional anesthesia. Dexmedetomidine (DEX) is a highly specific and selective α2 -adrenoceptor agonist with high ratio of α2 /α1 activity (1620:1 as compared with 220:1 for clonidine).  This ensures that its action is selective for the central nervous system (CNS) without unwanted cardiovascular effects from receptor activation.  This study was designed to compare the efficacy of single shot caudal DEX or fentanyl added to bupivacaine on attenuation of stress response and postoperative pain in pediatric patients undergoing open heart surgery. Our primary outcome was stress hormone levels, the secondary outcomes were postoperative pain scores and extubation time.
| Materials and Methods|| |
After approval of the institutional ethics committee and written informed parental consent, 40 pediatric patients, 1-3-years old, ASA status II and III undergoing elective surgical repair for ventricular septal defect (VSD), were enrolled in this prospective, randomized, observer-blinded study. The study was done in Ain Shams University hospitals at the pediatric cardiac surgery unit from January 2011 to February 2012. Exclusion criteria included previous cardiac surgery, hemodynamic instability requiring administration of vasoactive drugs and inotropes, patients with co-morbidities, such as heart failure, patients receiving digoxin or anticoagulants preoperatively and platelet count less than 100,000/liter.
Patients were fasted for 6 h before the procedure. All operations were scheduled as the first case in the morning to equalize the circadian changes in the stress hormone levels. EMLA cream was applied to the dorsum of both hands 1 h before surgery with no pre-medication given. After insertion of a 22-G cannula, general anesthesia was induced with fentanyl 10 μg/kg, midazolam 0.1 mg/kg, and propofol 3-4 mg/kg. Pancuronium 0.15 mg/kg was administered to facilitate endotracheal intubation and was repeated during surgery as required to ensure muscle relaxation. Anesthesia was maintained using 0.5 -1.5% sevoflurane in an oxygen-air mixture (1:1 ratio). The concentration of sevoflurane was titrated to maintain mean arterial pressure (MAP) and heart rate (HR) in the range of ± 20% baseline values. Mechanical ventilation was provided by a Narkomed anesthesia machine (North American Drδger, Telford, PA) using a tidal volume of 10 ml/kg to maintain PaCO 2 between 30 and 35 mmHg. Standard monitoring included electrocardiography (ECG), non-invasive and invasive blood pressure, pulse oximetry, capnography, temperature (central-peripheral), urine output, tidal volume, and airway pressure.
The study drugs were prepared in an unlabeled syringe by an anesthetist who did not participate in the study and handed to the anesthesiologist performing the caudal block blinded to the identity of the drug. The patients were divided randomly using computer-generated randomization numbers into two equal groups, Group BD (20 patients) received a caudal injection of bupivacaine 0.25%, 2.5 mg/kg with DEX (Precedex, Hospira Inc., Lake Forest, IL) 0.5 μg/kg diluted in normal saline to a volume of 1.6 ml/kg and Group BF (20 patients) received the same dose of bupivacaine mixed with 1 ug/kg fentanyl diluted in normal saline to a volume of 1.6 ml/kg. Caudal block was performed with the patients in the lateral position using a 23-G short-beveled needle under sterile conditions. Insertion of a central venous and an arterial catheter was done after caudal block.
All patients received 5-6 ml/kg of lactated Ringer's solution before initiating the CPB. Median sternotomy was performed in all patients. After at least 60 min of caudal block, heparin 3 mg/kg was administered. CPB was initiated after aorto-bicaval cannulation and cold blood cardioplegia (20 ml/kg, St Thomas Hospital solution) was administered into the aortic root and repeated every 20 min, the patients were cooled to 31-33°C. Priming fluids consisted of lactated Ringer ' s solution supplemented with heparin and fresh whole blood was added to the priming solution in appropriate amounts to achieve a hematocrit of 20-22% during CPB. The MAP was maintained between 40 and 60 mmHg during CPB. Aortic cross-clamping time, total bypass time, and the dose of vasodilators (sodium nitroprusside) required at weaning off CPB were recorded. Blood samples were taken to determine serum cortisol and blood glucose levels immediately after induction of anesthesia (baseline), poststernotomy, after CPB and finally 24 hours after operation. The serum cortisol levels were measured by a microtiter strip enzyme-linked immunosorbent assay (ELISA) kit (Stat Fax 2100-Microplate Reader.® , USA), and blood glucose levels were measured by Blood Glucometer (Advantage Health Services Inc., Horsham, PA, USA). Hemodynamic variables (HR and MAP) were recorded at T1 (baseline, after induction of general anesthesia), T2 (10 min after caudal injection), T3 (10 min after sternotomy), T4 (on CPB, time of maximum cooling), T5 (after termination of CPB), T6 (on ICU admission) and T7 (at extubation). After surgical repair, patients were transferred to the ICU, the ICU residents were blinded to the anesthetic technique used; pain scores were assessed by an anesthetist experienced to use the objective pain scale (OPS) for children less than 3-years-old, at 1, 2, 4, 8, 12, and 24 h postoperative. This scale uses five criteria: crying, agitation, movement, posture, and localization of pain. Each criterion was given a score of 0-2, with 2 being the worst, to give a total score of 0-10.  Intravenous ketorolac 1-2 mg/kg was administered if HR or MAP increased > 15% of baseline or OPS was ≥ 4. The criteria for extubation were hemodynamic stability, absence of arrhythmias, adequate airway reflexes, normothermia, mediastinal drainage < 1 ml/kg over 30 min and acceptable blood gas analysis (pH > 7.30, arterial oxygen tension > 60 mmHg and arterial carbon dioxide tension < 50 mmHg) at an inspired oxygen fraction of 0.4.
Power analysis was performed on the basis of stress hormone levels (serum cortisol and blood glucose levels) as they were the main outcome variable in the present study. With α-error level fixed at 0.05, with a 80% power in detecting a difference of 20U when the assumed population standard deviation value was 20, the sample size required in each group was 17 participants. Statistical analysis was done on a personal computer using the Statistical Package for Social Sciences version 16.0 (SPSS© v. 16.0, SPSS Inc., Chicago, IL, USA). Normally distributed continuous data are presented as mean and standard deviation, one way analysis of variance (ANOVA) was used to test the difference between the means at different time points in every group and between the 2 groups at different time points, Mann-Whitney test was used for the non-parametric data comparison, Qualitative data are presented as proportion. A P value of < 0.05 was considered significant.
| Results|| |
Forty patients were randomized into the study and all patients completed the study. There were no differences between the two groups with respect to weight, age, and durations of aortic cross clamping, CPB, and surgery [Table 1]. Serum cortisol and blood glucose levels were comparable between the two groups at baseline. These values increased significantly relative to baseline in both groups but the increases were significantly lower in group BD compared with group BF. Serum cortisol level measured at post-sternotomy, after CPB and after operation was 55.3 ± 5.1 vs. 90.4 ± 6.5 μg/dl; 84.1 ± 6.2 vs. 153.1 ± 8.5 μg/dl; and 78.3 ± 8.1 vs. 150.2 ± 9.8 μg/dl. Blood glucose level in mg/dl, poststernotomy was 93.6 ± 7.2 vs. 125.6 ± 5.5), after CPB 115.3 ± 3.7 vs. 175.3 ± 10.4, and 24 hours after operation 97.32 ± 3 vs. 162.2 ± 12 (P0 < 0.05; [Figure 1] and [Figure 2].
|Figure 1: Serum cortisol level in μg/dl. Columns are mean and error bars are SD|
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|Figure 2: Blood glucose level in mg/dl. Columns are mean and error bars are SD|
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The HR and MAP were comparable between groups at baseline (after induction of general anesthesia). After caudal block, the HR and MAP decreased significantly in group BD (relative to the baseline and relative to group BF) and continued to decrease till extubation (P < 0.05; [Table 2]). No patient in either group experienced bradycardia that required treatment. End-tidal sevoflurane concentration was significantly lower in group BD compared with group BF (0.7 ± 0.3 vs. 1.2 ± 0.4%, respectively, P < 0.01). The dose of sodium nitroprusside administered during rewarming was significantly lower in group BD compared with group BF (0.59 ± 0.2 μg/kg/min vs. 0.93 ± 0.3 μg/kg/min, respectively, P < 0.02) [Table 3]. During the first 8 h after operation, pediatric patients in group BD had lower pain scores compared with group BF, OPS at first hour (2 ± 0.7 vs. 3 ± 1.1, P0 = 0.04), second hour (1.9 ± 0.5 vs. 3.7 ± 0.8, P = 0.008), fourth hour (2.4 ± 0.8 vs. 4.3 ± 0.5, P = 0.03) and eighth hour (2.5 ± 0.5 vs. 4.2 ± 1.1, P = 0.03), respectively, with no statistically significant differences between the two groups in the subsequent readings [Table 4]. The number of patients requiring analgesia was significantly lower in group BD (4 patients, 20%) compared with group BF (15 patients, 75%) ( P = 0.01). The extubation time tended to be shorter in the Group BD compared with Group BF (88 ± 9.6 min vs. 114.8 ± 12.3 min, respectively, P = 0.06).
| Discussion|| |
The present study demonstrated that pediatric patients undergoing cardiac surgery who received caudal DEX had lower serum cortisol and blood glucose levels as markers of stress response, with a concomitant decrease in HR and MAP, better postoperative analgesia and shorter time to extubation compared to the patients who received caudal fentanyl. This is the first study that compared the efficacy of single shot caudal DEX versus fentanyl on both stress response levels and postoperative pain in pediatric cardiac surgery. Caudal route was chosen as there was some evidence to suggest that α 2 analgesic effects are more pronounced after neuraxial than intravenous administration,  it was also proved earlier that systemic DEX lacks analgesic efficacy for heat and electrical pain at doses causing mild to severe sedation.  Single shot caudal anesthesia without catheter placement was used to avoid hematoma formation.  Previous studies reported that patients who received DEX intramuscularly or intravenously had lower intraoperative serum cortisol levels; Aho et al., showed that adult females undergoing gynecological laparoscopy who received intramuscular DEX had significantly lower intraoperative cortisol levels as compared with those who did not receive the drug before surgery.  The same findings were shown by Mukhtar, et al., who found that intravenous infusion of DEX in pediatric cardiac anesthesia resulted in lower cortisol levels compared with placebo.  These data support our findings that patients receiving caudal DEX had lower level of cortisol compared with those receiving fentanyl, which can be explained by DEX being an imidazole that may lead to inhibition of cortisol synthesis  when administered by all routes.
Alpha-2 adrenoceptor agonists may cause hyperglycemia in human  as a result of postsynaptic α2 -adrenoceptor stimulation of pancreatic β cells, which inhibits insulin release, however, in our study, lower blood glucose levels were recorded in the DEX group, this is consistent with Mukhtar, et al., findings, they also found that DEX infusion inhibited the hyperglycemic response to surgery and CPB significantly more than placebo, which they attributed to attenuation of sympathoadrenal response. 
The hemodynamic effects of DEX are predictable from the pharmacology of α-adrenoceptor agonists, DEX causes postsynaptic activation of α2 -adrenoceptors in the CNS leading to decrease in sympathetic activity, hypotension, and bradycardia. Also, activation of α2-adrenoceptors in the CNS results in an augmentation of cardio-vagal activity. It causes a dose-dependent decrease in (MAP) and (HR).  Mukhtar et al., showed that DEX intravenous infusion resulted in marked bradycardia and hypotension starting after the administration of the drug and continuing to the time of the skin incision.  Hosokawa et al., found that although hypotension and bradycardia have been reported as side effects of DEX infusion during the postoperative period in pediatric patients undergoing cardiac surgery, in the author's experience, this is not of clinical significance in children following surgery for CHD  and is beneficial for them.  In our study, bradycardia and hypotension occurred in the DEX group relative to baseline and relative to the fentanyl group, this was in the range within 10-20% lower than the baseline value, this showed that the caudal route resulted in less hemodynamic changes compared with the intravenous route.
The use of caudal DEX for analgesia in pediatric non-cardiac surgery has been approved before  but reports regarding influence of caudal analgesia in reducing pain and stress response in pediatric cardiac surgery are controversial,  as the site of incision is far away from the regional technique. But, it was shown that if appropriate volume of anesthetic combined with an effective adjuvant is used, effective analgesia can be achieved with minimal side effects.  Eduardo et al., concluded that a single shot of bupivacaine 0.25%, 4 mg/kg (1.6 ml/kg) by caudal block produce preoperative analgesia level identified at T3-T4, while with bupivacaine 0.25% (1.8 ml/kg) the analgesia level reached T1 supraclavicular,  which was an appropriate level for cardiac surgery performed through sternotomy. The spinal mechanism is the principal mechanism for the analgesic action of DEX even though there is a clear evidence for both a supraspinal and peripheral sites of action.  Intrathecal DEX was reported to prolong the analgesic duration of spinal bupivacaine  and potentiate the effect of spinal morphine in cancer pain in humans.  At the spinal cord, stimulation of α2 -receptors at the substantia gelatinosa of the dorsal horn leads to inhibition of the firing of nociceptive neurons and inhibition of the release of substance P.  In our study, we found that patients in the DEX group had better postoperative pain scores and lower number of patients required analgesia compared with the fentanyl group.
Fragen and Fitzgerald noted 17% reduction in sevoflurane requirement for maintenance of anesthesia in elderly patients receiving DEX.  Our study also showed considerably less requirement of sevoflurane, in our study the end-tidal sevoflurane concentration was remarkably less in the DEX group patients as compared to fentanyl group. In addition, the patients in the DEX group required less vasodilator compared with patients in the fentanyl group, it is well established that intrathecal and epidural anesthesia produce thoracic cardiac sympathectomy and may attenuate stress response in patients undergoing cardiac surgery.  DEX has been shown to be particularly helpful in spontaneously breathing patients in the ICU as part of an anesthetic regimen suited for early extubation  as it provides effective pain relief with an opioid sparing effect, this is consistent with our study where the extubation time was shorter in the DEX group.
There are several limitations in our study, first, we did not use a placebo group for ethical concerns; second, our study duration was limited to 24 hours postoperatively and was performed on simple cardiac procedures and on relatively cardiac stable patients. We are aiming to assess the efficacy of caudal DEX on attenuation of stress response on more complex cardiac lesions.
We conclude that caudal DEX is a useful adjuvant in pediatric cardiac anesthesia, it attenuates the hemodynamic and neuroendocrinal stress response of surgical trauma and CPB, and it also provides adequate postoperative analgesia and short time to extubation. However, further studies are required to confirm these findings.
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Dalia Abdelhamid Nasr
6 Tawfikia Zone, Mostafa Elnahas, 8th District, Nasr City, Cairo
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]