Children undergoing tympanomastoid surgery experience pain that can be treated with IV opioids or a peripheral nerve block of the great auricular nerve (GAN-Block), a branch of the superficial cervical plexus (Figure 1). Our previous investigation demonstrated that a GAN-block provides analgesia equivalent to that provided by IV morphine (0.1 mg/kg) while reducing the incidence of postoperative vomiting (1). The concept of preemptive analgesia was first described by Clifford Woolf as a method to reduce the magnitude and duration of postoperative pain (2). Recently a meta-analysis questioned the efficacy of preemptive analgesia (3). The purpose of this study was to determine if preemptive blockade of the sensory supply to the mastoid area could increase the quality and duration of postoperative analgesia in children undergoing tympanomastoid surgery.
After IRB approval and written informed consent and assent (if age appropriate), 40 children between the ages of 2 and 18 yr with ASA physical status I–II who were scheduled to have tympanomastoid surgery (mastoidectomy or cochlear implant) were enrolled in this prospective, randomized, double-blinded study. A power analysis estimated that a sample size of 40 patients would have an 80% power at the 0.05 significance level to detect a 50% reduction in the number of patients requiring pain rescue between patients who received a preemptive nerve block with local anesthetic solution compared with those who received a preemptive nerve block with normal saline (from 80% to 40%). Patients with known allergies to amide-type local anesthetics or a history of clinically important renal, hepatic, respiratory, cardiac, or neurological conditions were excluded. Patients were divided into 2 groups using a computer-generated table of random numbers such that each group would contain 20 patients.
After induction of anesthesia, the airway was secured with an endotracheal tube. Anesthesia was maintained with N2O, O2, and a volatile anesthetic (halothane or isoflurane). Using a sterile technique, one group received a GAN-block with 2 mL of 0.25% bupivacaine with 1:200,000 epinephrine before surgical incision followed by a second GAN-block with the same dose and concentration of bupivacaine approximately 1 h before the end of surgery (Block-block [BB] group). The second group received a sham preoperative GAN-block with 2 mL preservative free saline followed by a second GAN-block approximately 1 h before the end of the procedure with 0.25% bupivacaine with 1:200,000 epinephrine (Sham block-block [SB-B] group). No additional analgesics, including opioids, non-opioids (nonsteroidal antiinflammatory drugs or acetaminophen), antiemetics, or steroids, were administered during the procedure. All nerve blocks were performed by one of two investigators (SS or SB).
All individuals involved in the study were blinded to the solution that was injected in the preincision period. The depth of anesthesia was titrated to patient’s requirements intraoperatively, and they were tracheally extubated using standard criteria. The patients were transported to the postanesthesia care unit (PACU), where a blinded observer evaluated pain using an objective pain score (OPS). 1 The OPS scores were obtained at admission to the PACU and every 5 min thereafter for 60 min. They were further recorded every 60 min for the next 6 h in the short-stay unit after discharge from the PACU. Parents were allowed to visit their children in the PACU after initial vital signs were recorded. If the objective pain score was ≥6 for 2 consecutive 5-min intervals or if the patient complained of pain localized to the surgical site, an IV pain rescue bolus of morphine (0.05 mg/kg) was administered. If the pain relief was still inadequate, an additional 0.05 mg/kg of morphine was administered. Patients were also observed for vomiting; active vomiting was the only indication for intervention with IV ondansetron (0.1 mg/kg up to a maximum of 4 mg). The need for additional opioid as well as interventions for vomiting in the PACU and the short-stay unit were recorded. The patients’ nursing team, who were blinded as to the study groups, determined the need for additional interventions for pain or vomiting.
Statistical analysis was performed with a statistical package (SPSS version 11.0; SPSS, Chicago, IL). Demographic data were compared using Student’s t-tests; comparison of incidence data between groups was performed using Fisher’s exact tests. A P value ≤ 0.05 was considered significant.
Forty patients were enrolled in this study, with 20 patients assigned to each group. There were no differences in age, weight, gender, or types of surgical procedures between groups (Table 1). The OPS were not different in the PACU (Figure 2) or in the short-stay unit (Figure 3). Rescue pain medications in the PACU were required in 1 of 20 children (5%) in the BB group and 3 of 20 (15%) children in the SB-B group (P = 0.60 between groups). In the short-stay unit, 5 of 20 patients in the BB group versus 11 of 20 patients in the SB-B group required additional analgesics (P = 0.107 between groups). When we considered pain management during the entire hospital stay, 6 of 20 patients in the BB group versus 11 of 20 in the SB-B group required pain rescue (P = 0.20 between groups). There was no difference between groups in time to first pain rescue orders (226 ± 71 min BB group versus 201 ± 94 SB-B group, P = 0.607). There was no statistical difference in either group with regard to vomiting in the postoperative period (P = 0.52 between groups). There were no adverse effects from the performance of the nerve blocks.
Our experience with the use of a great auricular nerve block for tympanomastoid surgery has demonstrated that the GAN-block provides similar analgesia to 0.1 mg/kg of morphine sulfate but with a reduced incidence of postoperative vomiting (1). Having determined that the GAN-block provides adequate analgesia, we set forth to test the hypothesis: “Could a preincision GAN-block produce preemptive analgesia and therefore further improve the quality of postoperative analgesia?” Preemptive analgesia has been defined as treatment that 1) starts before surgery; 2) prevents establishment of central sensitization caused by incision; and 3) prevents establishment of central sensitization caused by incisional and inflammatory injuries (covers the period of surgery and the initial postoperative period) (4).
In 1983, using an animal model, Clifford Woolf demonstrated evidence of a central component of postinjury pain hypersensitivity (2). This has not been clearly demonstrated in humans. A recent meta-analysis included a literature search of all prospectively controlled randomized studies that examined the efficacy of preemptive analgesia (3). These included studies in which presurgical nonsteroidal antiinflammatory drugs, opioids, N-methyl-d-aspartic acid receptor antagonists, regional techniques (central neuraxial blocks and peripheral nerve blocks) were compared with these respective modalities used postsurgically. This analysis of clinical trials focused on whether the timing of conventional analgesia therapy i.e., preinjury versus postinjury initiation of analgesia had a significant impact on postoperative pain relief. Twenty-three trials compared preemptive and postincisional application of peripheral local anesthetic injection. The data did not substantiate a significant improvement in postoperative pain control in the preemptive analgesia group.
There have been only a few studies examining preemptive analgesia in pediatric patients. A preemptive caudal block has not been shown to be advantageous over a postsurgical placement in children undergoing procedures below the umbilicus (5). Two studies have examined the efficacy of preemptive analgesia with peripheral nerve blocks in pediatric patients. One study was able to demonstrate the value of preemptive analgesia with an ilioinguinal nerve block in patients undergoing hernia repair (6). A second study of axillary nerve blocks in children undergoing upper extremity procedures (7) found a decrease in the use of volatile anesthetics intraoperatively, but the pain scores were equivalent in both the pre- as well as the postsurgical axillary block groups. Our data are very similar to that of the axillary block study. The duration of analgesia and the pain scores were not significantly different between the two treatment arms. An advantage of placing a nerve block before incision is that it reduces the intraoperative use of volatile anesthetics; this also allows the anesthesiologist to be able to determine if the block has been successful because anesthetic requirements are reduced. As central sensitization observed in animal experiments has not been demonstrated in humans, the timing of regional blockade in children should not be affected by this observed phenomenon. A preoperative nerve block of the GAN does not appear to offer significant advantages for postoperative pain relief for children undergoing tympanomastoid surgery.
We conclude that postoperative analgesia is not enhanced by a preemptive GAN-block. Further studies may be required to demonstrate the efficacy of preemptive blockade of other peripheral nerves in children.
1 Broadman LM, Rice LJ, Hannallah RS. Testing the validity of an Objective Pain Scale (OPS) for infants and children [abstract]. Anesthesiology 1988;69:A770.
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