Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 9  |  Issue : 2  |  Page : 159-164

The effects of dexmedetomidine added to bupivacaine for parasternal intercostal block in pediatric open heart surgery


1 Department of Anesthesia and Surgical Intensive Care, Faculty of Medicine, Mansoura University, Mansoura, Egypt
2 Department of Cardiothoracic Surgery, Faculty of Medicine, Mansoura University, Mansoura, Egypt

Date of Submission20-Feb-2015
Date of Acceptance21-Jun-2015
Date of Web Publication11-May-2016

Correspondence Address:
Ibrahim I Abd El Baser
Department of Anesthesia and Surgical Intensive Care, Faculty of Medicine, Mansoura University, 2 El-Gomhouria Street, Mansoura 35516
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1687-7934.182221

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  Abstract 

Background
Regional analgesia is used for pain relief after pediatric open heart surgery. This study was designed to compare the analgesic effect of dexmedetomidine added to bupivacaine in performing parasternal block after sternotomy.
Patients and methods
Sixty American Society of Anesthesiologists (ASA) III-IV patients who were submitted to corrective open cardiac surgery were enrolled in this study and randomly allocated either into the dexmedetomidine group in which patients were given a mixture of 0.25% bupivacaine, 0.6 ml/kg and dexmedetomidine 1 mg/kg (dexmedetomidine group, n = 30) or into the control group in which patients were given 0.25% bupivacaine and 0.6 ml/kg (control group, n = 30). Postoperative pain (FLACC) scores, hemodynamics, opioid consumption, and hospital length of stay were evaluated in all patients.
Results
Heart rate, mean arterial pressure, and FLACC score were significantly lower in the dexmedetomidine group compared with the control group after 4 and 8 h in ICU. Duration of intubation and ICU stay were significantly shorter in the dexmedetomidine group compared with the control group. Ramsay sedation score was lower in the dexmedetomidine group compared with the control group at 4 h in ICU. Bradycardia and hypotension incidence were higher in the dexmedetomidine group compared with that in the control group.
Conclusion
Adding dexmedetomidine to bupivacaine for parasternal block in pediatric patients submitted to open heart surgery leads to good pain control, less analgesic consumption, early extubation, and short ICU length of stay.

Keywords: analgesia, bupivacaine, dexmedetomidine, fentanyl, open cardiac surgery, opioid requirements, parasternal block


How to cite this article:
Taman HI, Abd El Baser II, El Gamal MA. The effects of dexmedetomidine added to bupivacaine for parasternal intercostal block in pediatric open heart surgery. Ain-Shams J Anaesthesiol 2016;9:159-64

How to cite this URL:
Taman HI, Abd El Baser II, El Gamal MA. The effects of dexmedetomidine added to bupivacaine for parasternal intercostal block in pediatric open heart surgery. Ain-Shams J Anaesthesiol [serial online] 2016 [cited 2019 May 23];9:159-64. Available from: http://www.asja.eg.net/text.asp?2016/9/2/159/182221


  Introduction Top


Pain relief after surgery performed in children psychologically decreases the pain experienced by these children in subsequent surgical procedures [1]. It is known that pediatric patients submitted to open heart surgery may have significant pain, limited movements, impaired respiratory functions, and inability to cough as a result of median sternotomy and chest tube insertion incisions resulting in a significant increase in the duration of mechanical ventilation, endotracheal intubation, and length of stay of both ICU and hospital [2,3].

Optimal pain management after open heart surgery not only improves patient comfort and satisfaction, but also, more importantly, has several physiologic benefits. Parenteral opioid analgesics supplemented with NSAIDs are the classic method of pain control after cardiac surgery. The doses of opioid required to provide effective pain control may delay tracheal extubation as a result of undesirable side effects including respiratory depression, sedation, and gastrointestinal side effects [4].

Regional anesthetic blocks are the methods of choice as they reduce opioid consumption and their side effects. Parasternal intercostal block and infiltration of local anesthetics around the sternum may be helpful in providing short-term postoperative analgesia even in anticoagulated patients [5,6]. One study by McDonald et al. [5] using parasternal intercostal blocks resulted in a significant decrease in opioid requirements, although this study showed no significant reduction in pain scores.

This prospective randomized study was conducted based on the hypothesis that parasternal blocks with dexmedetomidine as an adjunct to bupivacaine 0.25% administered in pediatric patients undergoing cardiac surgery through median sternotomy can provide better postoperative analgesia, thereby reducing the requirement of opioids for postoperative pain relief than parasternal intercostal blocks with pure bupivacaine 0.25%.

Therefore, the aim of the present study was to evaluate the effects of dexmedetomidine added as an adjuvant to bupivacaine for parasternal intercostal block in pediatric patients undergoing open heart surgery on time to extubation, postoperative pain, sedation score, total opioid requirements, and ICU length of stay.


  Patients and methods Top


After obtaining approval from local ethics committee of our institution and written consent from all patients' guardians, 60 patients (age 3-6 years) with physical status III-IV according to the American Society of Anesthesiologists (ASA), scheduled for elective corrective surgery for simple congenital cardiac defects in Mansoura University Children Hospital between March 2013 and May 2014, were enrolled in this prospective double-blind study.

Exclusion criteria included known allergy to any of the study medications, coagulopathy, psychiatric problems, severe heart failure, renal, pulmonary, liver, or endocrine disease, and any other associated congenital deformities.

Midazolam 0.1 mg/kg and atropine 0.02 mg/kg were given by intramuscular injection 30 min before the induction of anesthesia. In the operation room, before induction and during surgery, all patient parameters including heart rate and blood pressure were recorded using a Datex-OhmedaS/5 (Datex-Ohmeda Division; Instrumentarium Corp., Helsinki, Finland) monitor.

Anesthesia was induced with sevoflurane inhalation, fentanyl (3-5 mg/kg intravenously), and rocuronium (0.9 mg/kg intravenously), and maintained with sevoflurane, titrated to the patient response, inspired in oxygen 50% in air, fentanyl (1 mg/kg/h), and rocuronium (0.3 mg/kg/h).

At the end of the surgery and before sternal closure, patients were randomly allocated into two groups according to computer-generated randomization.

Dexmedetomidine group (n = 30): patients were given a mixture of dexmedetomidine 1 mg/kg and 0.6 ml/kg of bupivacaine 0.25% (injected at the junction of each rib with the sternum at five levels on both sides and at the insertion of chest tubes).

Control group (n = 30): patients were given 0.6 ml/kg of bupivacaine and 0.25% only (injected at the junction of each rib with the sternum at five levels on both sides and at the insertion of chest tubes).

Standard median sternotomy was the surgical approach to the heart in all patients. The ascending aorta, superior vena cava, and inferior vena cava were cannulated before going on cardiopulmonary bypass after giving heparin (3-4 mg/kg) to the patient through the central vein to obtain activated clotting time above 480 s. Cardiopulmonary bypass was established using membrane oxygenator and a roller, nonpulsatile pump flow with an average flow rate of around 1.6-2.4 l/m 2 /min. A a-stat carbon dioxide management strategy was employed. Moderate hemodilution and mild systemic hypothermia (32°C) were used. After aortic cross clamping, all patients received cold crystalloid cardioplegia (50 ml/kg as a single bolus dose) in anterograde manner in the aortic root. Hematocrit was maintained between 25 and 28% during cardiopulmonary bypass, with addition of blood as necessary according to ASA guidelines.

At the end of surgery, all anesthetics were discontinued and patients were transferred to the ICU where they were committed to a mechanical ventilator. All patients were given an additional dose of fentanyl, 2 mg/kg, when they experienced pain sensation or FLACC score more than 4.

In ICU, heart rate, invasive mean arterial pressure, FLACC score (Face, Legs, Activity, Cry, Consol ability) and Ramsay sedation scale (RSS) were monitored at 0, 4, 8, 12, 24 hours from ICU admission. FLACC score is an observer assessment score based on the above mentioned 5 items and each item is graded from 0 to 2, score of 0-3 = mild pain, 4-6 = moderate pain, 7-10 = severe pain (10), while Ramsay sedation scale means, (1 = anxious/restless or both, 2 = cooperative, oriented and tranquil responding to command, 3 = brisk response to stimulus, 4 = sluggish response to stimulus, 5 = no response to any stimulus). FLACC score was not assessed except when Ramsay sedation score exceeded 2.

During follow-up in ICU, patients who had the following characteristics [7] were extubated and intubation duration was recorded:

  1. Fully conscious and obeying verbal commands.
  2. Stable cardiac rhythm with systolic arterial blood pressure of 70 mmHg or more.
  3. No or nonsignificant bleeding.
  4. FLACC score of 5 or less.
  5. Arterial oxygen saturation more than or equal to 95 on 50% air-oxygen.
  6. Rate of respiration 16-25/min.
  7. Arterial pH more than or equal to 7.25 and arterial CO 2 tension less than or equal to 55 mm/Hg.
Duration between ICU admission and extubation moment was accepted as intubation duration. ICU stay, total additional dose of fentanyl, time of first analgesic requirement, and any complications (postoperative nausea and vomiting, pruritus, hypoxia, bradycardia, and hypotension) were also recorded.

This study was planned for a continuous response variable from independent control and experimental subjects with one control(s) per experimental subject. In a previous study the response within each subject group was normally distributed with SD 27. If the true difference in the experimental and control means is 13, we need to study 26 experimental subjects and 26 control subjects to be able to reject the null hypothesis that the population means of the experimental and control groups are equal with probability (power) 0.85. The type I error probability accompanied with this test of this null hypothesis is 0.5.

Statistical analysis

Statistical analysis was done by using statistical package for social scientists SPSS 18.0 (SPSS Inc., Chicago, IL, USA). Data was expressed as number, percentage, mean ± SD, and median and range as appropriate. Data was tested for normality using the Shapiro-Wilk's W-test. c2 -test was applied for qualitative data. Changes in quantitative values between two groups were compared using unpaired t-test. Changes in FLACC and Ramsay scores values between two groups were compared using the Mann-Whitney U-test. P value less than 0.05 was considered significant.


  Results Top


Sixty eligible patients were approached to be enrolled in the study. Patient demographic data are described in [Table 1] and showed no significant differences between the studied groups.
Table 1 Demographic data of the studied groups

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Heart rate and mean arterial pressure were significantly lower in the dexmedetomidine group when compared with the control group after 4 and 8 h in ICU, but they became nearly equal after 8 h and till end of study [Figure 1] and [Figure 2].
Figure 1: Heart rate (HR, beats/min), of the studied groups. Data are expressed as mean ± SD. *P < 0.05 signifi cant compared with the control group

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Figure 2: Invasive mean arterial pressure (MAP, mmHg) of the studied groups. Data are expressed as mean ± SD. *P < 0.05 signifi cant compared with the control group

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Duration of intubation and ICU stay were significantly shorter in the dexmedetomidine group relative to the control group. Time till first analgesic requirement was significantly longer and total fentanyl requirement was significantly lower in the dexmedetomidine group when compared with the control group [Figure 3] and [Figure 4].
Figure 3: Duration of intubation (h), duration of ICU stay (h), and duration till first analgesia required (h) of the studied groups. Data are expressed as mean ± SD. *P < 0.05 signifi cant compared with the control group

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Figure 4: Total dose of opioids (¦Ìg/kg) in the studied groups. Data are expressed as mean ± SD. *P < 0.05 significant compared with the control group

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FLACC score was significantly lower in the dexmedetomidine group when compared with the control group 4 and 8 h postoperatively, but the Ramsay score showed no significant difference between the studied groups all over the study apart from being significantly higher in the dexmedetomidine group compared with the control group at 4 h in ICU [Table 2] and [Table 3].
Table 2 Changes in mean FLACC score of the studied groups

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Table 3 Changes in the Ramsay score of the studied groups

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Bradychardia and hypotension incidence were significantly higher in the dexmedetomidine group compared with that in the control group. Incidence of postoperative nausea and vomiting, pruritus, and hypoxia urine retention showed no significant difference between the two studied groups [Table 4].
Table 4 Incidence of side effect in studied groups

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  Discussion Top


The main sources of pain in the cardiac surgical patients are median sternotomy incision and the mediastinal tube insertion site [8]. Therefore, local anesthetic agents infiltration near the sternotomy wound is a possible way for relieving early postoperative pain [5].

Many studies have shown that parasternal block of local anesthetics either with bupivacaine, levobupivacaine, or ropivacaine is effective in reducing postoperative pain in patients submitted to open heart surgery [4, 5, 9]. Efficacy of adding dexmedetomidine as an adjuvant to local anesthetics for parasternal nerve block has never been studied before. The current study discusses the effects of adding dexmedetomidine to bupivacaine in parasternal block in pediatric patients submitted to open heart surgery.

The present study showed that heart rate and mean arterial pressure in the dexmedetomidine group were significantly lower than in the control group 4 and 8 h after admission of patients in ICU. Dexmedetomidine is a highly selective and specific agonist for a2-adrenoceptor; this will abolish the undesired effects of a1 receptor [10]. Dexmedetomidine stimulates a2 receptor in central nervous system, decreasing the output of norepinepherine, resulting in deceleration of the spread of nerve impulses and the subsequent postsynaptic activation that inhibit sympathetic activity resulting in a decrease in heart rate and mean arterial blood pressure [10,11].

The current study showed that FLACC score was significantly lower, time till first analgesic demand was significantly longer, total fentanyl requirement was significantly lower, and the intubation time and ICU length of stay were significantly shorter in the dexmedetomidine group than in the control group. Intravenous opioids are most often used for pain control after cardiac surgery, and the main sources of postoperative pain after cardiac surgery are median sternotomy and the sites of mediastinal tube insertion, parasternal block with bupivacaine facilitate early extubation after open heart surgery as it provides effective pain control and reduces postoperative narcotic requirements.

In animals many studies have investigated the effects of perineural dexmedetomidine as an adjuvant to local anesthetics. Brummett et al. [12] reported that the addition of dexmedetomidine to ropivacaine for sciatic nerve block in rat resulted in longer analgesia than systemic administration; they also found that local injection of dexmedetomidine alone provided a brief period of analgesia, which may be due to the peripherally mediated analgesic action of dexmedetomidine. In another study, Brummett et al. [13] assessed the efficacy and safety of adding dexmedetomidine to bupivacaine for sciatic nerve block in rat; they reported enhanced sensory and motor block duration without any histopathologic changes in the sciatic nerve.

Memis et al. [14] found that adding dexmedetomidine to lidocaine for intravenous regional anesthesia in a dose of 0.5 mg/kg resulted in an improved quality of intraoperative as well postoperative analgesia without causing side effects. Saadawy et al. [15] found that the addition of dexmedetomidine 1 mg/kg to bupivacaine for caudal anesthesia in pediatric patients leads to longer analgesia, less analgesic consumption, and improved sleep quality without adverse effects. Esmaoglu et al. [16] reported that the axillary plexus block is prolonged by adding dexmedetomidine to levobupivacaine. Dexmedetomidine also prolongs the sensory block of the posterior tibial nerve [17] and greater palatine nerve when added to local anesthetics [18].

The mechanisms of action that explain the analgesic effects of dexmedetomidine are variable. Masuki et al. [19] suggested that dexmedetomidine induces vasoconstriction at the site of injection, delaying the absorption of local anesthetics and therefore prolonging their effects. Peripherally, a2 agonist produces analgesia by reducing the release of norepinephrine and causing a2 receptor independent inhibitor effect on nerve fiber action potential. Centrally, a2 agonists produce analgesia and sedation by inhibition of substance P release in the nociceptive pathway at the level of the dorsal root neuron and by the activation of a2 adrenoreceptor in the locus coeruleus [11,20]. Other mechanisms include the direct inhibition of impulse propagation along the neurones via the interaction with axonal receptors and ion channel [21], a local decrease in inflammatory mediators [22], or an increase in anti-inflammatory cytokines via a2 adrenoreceptor stimulation [22].

In our study the Ramsay sedation score was significantly higher in the dexmedetomidine group than in the control group at 4 h in ICU. The high selectivity of dexmedetomidine for a2 receptor mediates analgesia, sedation, and anxyolysis. The incidence of postoperative sedation was evaluated in many studies that examined the intrathecal administration of dexmedetomidine [23-25]. Eid et al. [24] reported higher sedation levels in patients receiving high dose intrathecal dexmedetomidine.

In the present study, the incidence of bradycardia and hypotension was significantly higher in the dexmedetomidine group than in the control group. Bradycardia was transient and easily reversed with atropine. Esmaoglu et al. [16] showed that dexmedetomidine added to levobupivacaine for axillary brachial plexus blocks shortens the onset time and prolongs the durations of the blockade and postoperative analgesia, which also leads to bradycardia. Zhang et al. [26] found that perineural administration of dexmedetomidine in combination with ropivacaine prolongs axillary brachial plexus block and also produces bradycardia. Baroreceptor reflex and heart rate response to a pressor agent are well preserved with the use of dexmedetomidine; thus hypotension and bradycardia are easily treatable conferring hemodynamic stability. High selectivity for a2 adrenoreceptors mediates analgesia, sedation, and anxiolysis.

The limitation of this study is that the optimum dose of dexmedetomidine added to bupivacaine for parasternal block requires further studies and some of its effects may be due to systemic absorption; also, the duration of parasternal block is short and thus catheter insertion may be required.


  Conclusion Top


On the basis of the current study results, the use of dexmedetomidine as an adjuvant to bupivacaine for parasternal block in pediatric patients submitted to open heart surgery results in better pain control, less opioid consumption, earlier extubation, and shorter ICU length of stay than the use of bupivacaine alone. The optimum dose of dexmedetomidine as an adjuvant to bupivacaine for parasternal block needs further studies.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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