Persistent pain is an underreported morbidity after cardiac surgery. We sent pain surveys to all patients who underwent coronary artery bypass graft surgery from 1997 to 1999 from a single surgeon’s experience. Two analgesia strategies were used: high thoracic epidural (HTEA) or IV and oral opiates (OPIOID) for 48–72 h after surgery. Persistent pain was defined as pain still present two or more months after surgery, and all questions referred to the time of survey only. From 356 questionnaires, 305 patients responded, and 61 of them refused consent, leaving 244 patients with complete surveys (HTEA, 150 patients [69%]; OPIOID, 94 patients [68%]). The incidence of persistent pain at any site was 29% and for sternotomy was 25%. The intensity of pain reported was mild, with only 7% reporting interference with daily living. Other common locations of persistent pain were the shoulders (17.4%), back (15.9%), and neck (5.8%). Twenty patients (8%) described symptoms suggestive of the internal mammary artery syndrome. A comparative audit of the HTEA and OPIOID groups showed no significant differences in the frequency or intensity of pain, although the time of survey from operation was longer in the OPIOID group. Mild persistent chest pain after sternotomy is common but infrequently interferes with daily life.
*Department of Anaesthesia, Monash Medical Centre; †Department of Pharmacology, University of Melbourne; and Departments of ‡Anaesthesia and Pain Management and §Cardiothoracic Surgery, The Royal Melbourne Hospital, Melbourne, Australia
May 30, 2002.
Address correspondence and reprint requests to Dr. Colin Royse, PO Box 1022, Research, Victoria, Australia, 3095. Address e-mail to Colin.Royse@mh.org.au.
Long-term postoperative wound pain is a potential morbidity of cardiac surgery, with a reported incidence of more than 50%(1). The incidence of severe chronic pain is less common but is frequently disabling (2,3). The cause of persistent pain after sternotomy is multifactorial but includes tissue destruction, intercostal nerve trauma, scar formation, rib fractures, sternal infection, stainless-steel wire sutures, and costochondral separation (1,3–5). This represents a very important problem after cardiac surgery, especially after internal mammary artery (IMA) harvest. Our aim was to audit the incidence and severity of persistent pain after coronary artery bypass surgery (CABG) by using high thoracic epidural analgesia (HTEA) and opioid-based analgesia regimens.
After approval from the Human Ethics Committee, all patients who underwent primary and reoperative CABG from 1997 until the end of 1999 from a single surgeon’s experience at the Royal Melbourne Hospital were sent surveys, and written consent was obtained. Two primary analgesia strategies were used: HTEA or IV and oral opiates (OPIOID) for 48–72 h after surgery. The group sizes were different because more patients received HTEA in that time period. The OPIOID group did not receive HTEA for a variety of reasons, including patient refusal, preoperative anticoagulation, previous spinal damage or operation, randomization to a control group in a HTEA study, or being anesthetized by practitioners unfamiliar with the HTEA technique. A total of 356 surveys were sent (217 HTEA and 139 OPIOID). The audit was performed for each group on an intention-to-treat basis.
Our anesthetic technique has been previously described (6). Epidural catheters were inserted at the T2-3 vertebral level the evening before surgery. Before the induction of anesthesia, 6–10 mL of 0.5% ropivacaine and fentanyl (5 μg/mL) were administered through the epidural catheter. A maintenance epidural infusion of ropivacaine 0.2% and fentanyl 2 μg/mL at 6–12 mL/h was commenced during surgery and continued for 2–3 days. The presence of epidural blockade was confirmed with ice daily in the postoperative phase but was not tested in all patients before induction. A target-controlled infusion of propofol (2 μg/mL), supplemented with sevoflurane, was used to maintain anesthesia. Postoperative opiates were not coadministered while the epidural infusion was maintained. Of the 217 patients with HTEA, the epidural worked satisfactorily for at least 24 h in 214 (98.6%).
The OPIOID group patients received similar anesthesia but with a larger target concentration of propofol (2–4 μg/mL). Fentanyl (total dose, <10 μg/kg) was used as intraoperative analgesia and was commenced before incision. The skin wound was infiltrated with ropivacaine 0.5% at chest wall closure. Postoperative analgesia consisted of nurse-controlled morphine infusion supplemented with indomethacin, acetaminophen, and proladone as required.
The surgical technique for CABG consists of a composite pedicle Y graft, using the left (IMA) and radial artery to form the composite Y grafts (7). Apart from analgesia management, patients in both groups received postoperative care according to unit protocol.
Persistent pain was defined as pain still present two or more months after surgery, and all questions referred to the time of survey only. Patients rated pain intensity by using a visual analog score, drew the site of pain on front and back diagrams of a body, and completed the McGill Pain Questionnaire. The effect of pain on activities of daily living was rated as 1, no effect on activities of daily living; 2, a little pain with, but not affecting, daily activities; 3, pain requiring oral medication, but patient was able to perform daily activities; 4, pain requiring medication and interfering with daily activities; and 5, severe pain requiring assistance to perform daily activities.
Categorical variables were analyzed with Fisher’s exact test. Continuous variables are expressed as mean ± sem and were assessed by analysis of variance by using SPSS 10 (SPSS Inc., Chicago, IL). P < 0.05 was considered significant.
From 356 questionnaires, 305 patients responded, but 61 of those refused consent, leaving 244 patients with complete surveys (HTEA, 150 patients [69%]; OPIOID, 94 patients [68%]). The incidence of persistent pain at any site was 29% (71 patients) and for sternotomy was 25% (61 patients). Other common locations of persistent pain were the shoulders (17.4%), back (15.9%), and neck (5.8%).
The pain characteristics of all responders are shown in Table 1. The intensity of pain reported was mild, with only 7% reporting interference with daily living. The most common words used to describe the pain were “annoying” (57%), “nagging” (33%), “dull” (30%), “sharp” (25%), “tiring” (22%), “tender” (22%), and “tight” (22%). The temporal nature of this pain was mostly reported as being brief or transient and periodic or intermittent. Twenty patients (8%) described symptoms of numbness, burning pain, and tenderness over the IMA harvest site, suggestive of IMA syndrome (8). The comparative audit of HTEA and OPIOID groups is shown in Table 2. There were no significant differences in the incidence or severity of persistent pain, although the time from operation was longer in the OPIOID group.
Our study shows that persistent pain after cardiac surgery is common. The most frequent site is over the sternum and IMA harvest site. For most patients, the severity of pain was mild, and the effect on daily living was minimal.
Mailis et al. (1) found that 73% of patients with IMA grafts had intercostal nerve damage at the site of harvest. Forty-nine percent of patients recalled protracted pain, with mean verbal pain scores of 8.5, and had associated neuropathic features such as hypoesthesia and allodynia. Eisenberg et al. (9) reported an incidence of persistent chest pain of 57%, with most experiencing moderate to severe pain and 28% noting interference with daily activities. We found a less frequent incidence of persistent pain, which could be due to retrospective recall rather than prospective survey. The duration from operation to survey also varied considerably in our study, and the incidence of persistent pain may have decreased with time.
Reduction of painful stimuli in the perioperative period may also reduce central sensitization at the dorsal horns and the development of chronic pain (10). Both groups surveyed received analgesia that could modulate the development of chronic pain before incision and for two or three days after surgery. Local anesthetics given epidurally have the ability to block noxious input to the spinal cord and offer a different mechanism than opiates for modulating the development of chronic pain. Obata et al. (11) demonstrated reduced persistent pain in thoracotomy patients with epidural analgesia, whereas Gottschalk et al. (12) obtained similar results with patients undergoing radical prostatectomy. Aguilar et al. (13) and Espinet et al. (14), however, failed to demonstrate this in thoracotomy and abdominal hysterectomy patients. Our audit did not show a difference in the intensity or frequency of persistent pain between patients receiving HTEA and those receiving traditional opioid-based analgesia. Local anesthetics or opioids may not provide total C-afferent blockade during surgery, and inflammation (secondary phase of injury) extends well into the postoperative period and may continue to cause central sensitization once analgesics are withdrawn (15,16).
There are many limitations inherent in the retrospective nature of our study, which may have led to underreporting of symptoms because of recall bias and misinterpretation of questions. The number of incomplete surveys was 31%, similar in both groups. It is unknown whether the nonresponders were more or less likely to have persistent pain or other comorbidities. The basic operative technique did not alter during the survey period, but the subtleties of technique may have changed, which could have influenced patients at either end of the survey period. During the early phase, the HTEA technique was becoming established in our institution, resulting in fewer patients being offered the technique compared with during the later part. Some patients in the OPIOID group were receiving anticoagulants, thereby contraindicating HTEA use. It is possible that these patients required surgery more urgently, but it is unknown whether the acuity of surgery influences the development of persistent pain syndromes. The mean duration from surgery was longer in the OPIOID group, and it is possible that persistent pain attenuates with time and that pain that was present for a year was not reported by patients surveyed at two years. The mean pain scores were low, which could bias toward not detecting any difference between analgesia methods. Persistent pain after cardiac surgery is common, but it is mostly mild and does not interfere with activities of daily living.
We thank K. Groves for her help with data management and in the preparation of this manuscript. We thank Dr. J. Ludbrook of Biomedical Statistical Consulting Service Pty. Ltd. for his advice and review of the manuscript.
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