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Ann Thorac Surg 2003;75:93-100
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

Prospective randomized trial of high thoracic epidural analgesia for coronary artery bypass surgery

^a Department of Anaesthesia and Pain Management, Melbourne, Australia
^b Department of Cardiac Surgery, The Royal Melbourne Hospital, Melbourne, Australia
^c Department of Pharmacology, University of Melbourne, Melbourne, Victoria, Australia

Accepted for publication July 22, 2002.

* Address reprint requests to Dr Royse, PO Box 1022, Research, Melbourne, Victoria, Australia 3095
e-mail: colin.royse{at}mh.org.au

	Abstract

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
BACKGROUND: Postoperative pain may be severe after coronary artery bypass surgery. High thoracic epidural analgesia (HTEA) provides intense analgesia.

METHODS: Eighty patients were randomized to HTEA or intravenous morphine analgesia (control). Patients received coronary artery bypass surgery (CABG) with cardiopulmonary bypass. Pain was measured by visual analogue scale 0 to 10. Psychologic morbidity, intraoperative hemodynamics, ventricular function, lung function, and physiotherapy cooperation were also assessed. On the third postoperative day HTEA and morphine were ceased and only oral medications were used. Acetaminophen, indomethacin, and tramadol were allowed as supplemental analgesics in both groups.

RESULTS: The primary endpoint of pain scores was significantly less with HTEA on postoperative days 1 and 2 at rest, 0.02 ± 0.2 versus 0.8 ± 1.8 (p = 0.008) and 0.1 ± 0.4 versus 1.2 ± 2.7 (p = 0.022), respectively, and with coughing 1.2 ± 1.7 versus 4.4 ± 3.1 (p < 0.001) and 1.5 ± 2.0 versus 3.6 ± 3.1 (p = 0.001), respectively. When HTEA and morphine were ceased on day 3, there were no significant differences. The secondary endpoints of postoperative depression (p = 0.033) and posttraumatic stress subscales (p = 0.021) of the Minnesota Multiphasic Personality Inventory were lower with HTEA. Extubation occurred earlier with HTEA, 2.6 versus 5.4 hours (p < 0.001). HTEA showed improved physiotherapy cooperation (p < 0.001), arterial oxygen tension (p = 0.041), and peak expiratory flow rate (p = 0.001). Mean arterial pressure was lower with HTEA (p = 0.036), otherwise there were no differences in intraoperative hemodynamics or ventricular function.

CONCLUSIONS: Epidural analgesia reduces pain after coronary operation and is associated with improved physiotherapy cooperation, earlier extubation, and reduced risk of depression and posttraumatic stress.

	Introduction

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Two thirds of patients undergoing coronary artery bypass surgery (CABG) report moderate or severe pain [1], particularly with ambulatory or respiratory effort [2]. The prospect of moderate or severe pain is a common concern of patients when contemplating cardiac operations. The principal intent of regional analgesic techniques is to substantially reduce or possibly eliminate postoperative pain.

Pain may also have other physical as well as psychological sequelae, including impaired respiratory function [3], long-term pain [4], depression, and posttraumatic stress reactions [5]. Major operations are a stressful psychological and physiologic event, and patients may feel traumatized despite otherwise successful operations. Most analgesia trials have focused on the intensity or location of pain, rather than assessing whether improved analgesia can modify the traumatic experience.

Our primary aim was to assess the efficacy of epidural analgesia for CABG operations in reducing pain. Secondary aims were to test the development of psychologicalmorbidity and consider the effect of epidural on cooperation with physiotherapy, respiratory function, ventilation times, ventricular function, and intensive care unit and hospital stay.

	Material and methods

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Institutional ethics committee approval and informed written consent were obtained. A single surgeon performed all operations, completed between 1998 and 2001. Eighty patients undergoing elective CABG were randomized to receive high thoracic epidural analgesia (HTEA) or a patient controlled intravenous morphine analgesic (control). Acetaminophen, indomethacin, and tramadol were allowed as supplemental analgesia in both groups.

HTEA group
An epidural catheter was inserted the night before the operation at T2/3 or T1/2 spinal levels. Eight mL of 0.5% ropivacaine with 20 µg of fentanyl was administered prior to induction of anesthesia, and sensory spread was tested with ice. Thereafter, ropivacaine 0.2% with fentanyl 2 µg/mL was infused at a rate of 5 to 14 mL per hour, adjusted to attain a sensory blockade of T1 to T10, and was ceased at 6:00 AM on postoperative day 3, with day 0 as the day of operation. Anesthesia consisted of midazolam (3 to 5 mg), fentanyl (200 µg), and a target-controlled infusion of propofol (Diprifusor algorithm; AstraZeneca; North Ryde, Australia) (set for a blood concentration of 2 µg/mL and ceased after the last skin suture).

Control group
Anesthesia consisted of midazolam (3 to 5 mg), propofol (2 to 4 µg/mL), and a 2-stage target controlled alfentanil infusion (2 µg/mL, reduced to 0.05 µg/mL after cardiopulmonary bypass, and ceased after sternal wiring) [6]; this anesthetic avoided high dose opiates so that there would be a low opiate component at the end of the procedure to facilitate early extubation. The target was designed for extubation theoretically to be possible 15 minutes after chest closure. Nurses were permitted to administer boluses of morphine in the intensive care unit until the patient was awake. This was followed by demand patient controlled intravenous morphine (1 mg bolus with 5 minute lockout period), which was continued until 6:00 AM on postoperative day 3.

Postoperative ventilation
Spontaneous ventilation was commenced if respiratory effort was adequate at the end of operation, otherwise mechanical ventilation was continued during transfer to the intensive care unit. Postoperative sedation with propofol was only administered if required, and extubation was performed when the patient was awake, cooperative, normothermic (core body temperature > 36°C), pH > 7.3 and PaO₂ > 75 mm Hg on 40% inspired oxygen.

Surgical details
All patients received arterial grafts constructed from the left internal mammary artery and left radial artery as a Y graft used to graft all coronary territories [7]. We performed epiaortic screening with ultrasound to detect and avoid ascending aortic atheroma to reduce cerebral atheroemboli [8, 9]. Cerebral atheroembolism could act as a confounding variable during psychological testing. This technique has been found to have a very low neurocognitive dysfunction rate [9]. Operations were performed with cardiopulmonary bypass using a membrane oxygenator and 40 µm arterial filter. Perfusion temperature was 35°C with rewarming to 36.5°C prior to removal of the aortic clamp. Myocardial protection was given by intermittent anterograde and retrograde blood cardioplegia. All patients were monitored with a pulmonary artery catheter, indwelling radial arterial catheter, and transesophageal echocardiography (Sonos 2500 or 5500; Phillips Medical Systems, Andover, MA).

Study endpoints
Primary endpoint
Pain
Patients self-rated their sternotomy pain daily, at rest, and after coughing, by sliding a marker on a horizontal 10 cm visual analogue scale (VAS) in which 0 represents no pain and 10 represents the worst pain imaginable.

Secondary endpoints
Physiotherapy cooperation
The following ratings were made by the attending physiotherapist: Poor = unable to cough, requiring full assistance to ambulate; Moderate = poor cough, requiring limited assistance to ambulate; and Good = cough without limitation and ambulation without assistance.

Depression and posttraumatic stress
Patients completed the Minnesota Multiphasic Personality Inventory 2 (MMPI 2), 6 weeks after operation; this time was selected because patients most likely would be free from analgesic therapy and it coincided with the routine postoperative visit to the surgeon. To avoid excessive family-wise type-1 error, we only selected the subscales relevant to our hypothesis (ie, depression and posttraumatic stress disorder).

Somatosensory sensitization
Von Frey hairs were placed on the left chest wall lateral to the midclavicular line (operative site), and the left leg (remote site). The chest wall lateral to the midclavicular line was selected to avoid altered sensation from nerve injury during left internal mammary artery harvest. Von Frey hairs are a series of graded monofilaments with calibrated application pressure before they buckle. Patients indicated when they first detected light touch, and second, when touch first became painful in response to stimulation with a graded series of the hairs [10]. Measurements were performed preoperatively and on day 3 after cessation of both morphine and HTEA.

Lung function
Bedside spirometry and oxygen saturation (breathing room air for 5 minutes) was performed preoperatively and on each postoperative day. Arterial blood was analyzed at the same time on day 1.

Intraoperative hemodynamic parameters
Mean arterial pressure (MAP), right atrial pressure (RAP), mean pulmonary artery pressure (MPAP), pulmonary capillary wedge pressure (PCWP), cardiac index (CI), temperature, and ST segment deviation on the electrocardiogram (leads II and V5) were recorded at the following time intervals: prior to induction, after intubation, during sternotomy, during conduit harvest, at the start of the last distal anastomosis, while weaning from cardiopulmonary bypass, during chest closure, and after arrival in the intensive care unit. Left ventricular function was assessed before and after revascularization with transesophageal echocardiography, recording the midpapillary end-diastolic area (EDA) and end-systolic area (ESA), fractional area change, and a relatively load independent index of contractility—afterload corrected fractional area change (FACac) [11], and an index of myocardial stiffness—instantaneous end-diastolic stiffness (IEDS) [12]:

Protocol violations
Three HTEA patients were withdrawn after randomization, (2 because of absence of sensory block prior to induction, and 1 who did not have an operation). One control patient withdrew after randomization, requesting the epidural instead. Minor protocol violations are listed in Table 1.

	Results

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Eighty patients were randomized, and 3 patients from the HTEA group were withdrawn (1 patient withdrew themself from the study after randomization, deciding not to participate in research, and 2 patients failed epidurals prior to induction), and 1 patient from the control group withdrew from the study after randomization and requested the epidural instead. Hence, analysis was performed on 37 HTEA and 39 control patients. There were no differences in demographic variables or the number of grafts performed, but there were shorter aortic clamp and cardiopulmonary bypass times in the control group (Table 2).

Primary endpoint
Pain
The principal reason for using a regional analgesia technique is to attempt to provide improved analgesia. We found a large and significant reduction in pain experienced by patients at rest and with coughing with HTEA compared with intravenous opioid infusions (Table 3, Fig 1). The differences in pain relief were more pronounced with coughing on day 1 (1.2 ± 1.7 versus 4.4 ± 3.1 [p' < 0.001]) than on day 2 (1.5 ± 2.0 versus 3.6 ± 3.1 [p' = 0.005]). When HTEA and opioid infusions were ceased on day 3, there was no significant difference in pain experienced between the two groups.

View larger version (25K): [in this window] [in a new window]   Fig 1. Pain scores at rest and with coughing on first 3 postoperative days. Visual analogue pain score (0 = no pain and 10 = the worst pain). The solid lines are the mean ± 2 standard deviations to indicate the range of pain scores; and the shaded boxes are the 95% confidence intervals of the mean. (HTEA = high thoracic epidural analgesia.)

Secondary endpoints
Physiotherapy cooperation
Physiotherapy cooperation was better with HTEA (p < 0.001), with most patients in the HTEA group who were able to undertake good cooperation (Fig 2).

View larger version (34K): [in this window] [in a new window]   Fig 2. Degree of cooperation with postoperative physiotherapy. Physiotherapy cooperation was better with high thoracic epidural analgesic (HTEA) (p < 0.001).

Somatosensory sensitization
The thresholds for touch and pain stimulation are listed in Table 5. On day 3 the thresholds for touch increased in both groups in the remote and operative sites, indicating an absence of increased sensitivity to touch. The thresholds for painful stimulation decreased in the remote site, indicating somatosensory sensitization for both groups. There was no change in operative site thresholds for the HTEA group compared with the control group, in which there was a trend toward reduced thresholds. However, the difference between groups was not significant.

Intraoperative hemodynamic variables
Hemodynamic variables are listed in Table 6. Mean arterial pressure was lower for the HTEA group (p = 0.006), but the other variables were not different. There were no differences in ventricular function assessed by transesophageal echocardiography (Table 7) or ST segment deviation.

	Comment

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

Sixty-three percent of the HTEA patients experienced no pain or only mild pain at all times postoperatively. Conversely, the pain experienced by patients who received intravenous opioid infusions (with supplementary agents) was far more varied. Their pain ranged from mild to severe, and more so when coughing (Table 3). HTEA appeared to provide superior pain relief at all times while it was being administered.

HTEA has been used in many centers performing cardiac operations [13]. The key risk is that of spinal hematoma related to the presence of anticoagulants. There have been no reports of spinal hematoma in cardiac operations to date and there were none in this study. Paraplegia from a spinal hematoma with HTEA was mathematically modelled by Ho and colleagues [14] to have a maximal risk of 1:1,500 and a minimum risk of 1:150,000. We quote a risk of 1:10,000. This is a small risk compared with that of surgery. It is postulated that for each person suffering a spinal hematoma, 100 to 300 patients may die from their operation (1% to 3%), 100 to 300 may suffer strokes (1% to 3%) and 3,000 to 4,000 may suffer permanent neurocognitive damage (30% to 40%) [9, 15, 16]. The risk of conventional analgesia must also be considered, and although it is relatively safe, it is not risk free. The incidence of a potentially life-threatening complication after the use of patient controlled opiates is approximately 1:300 [17]. Nonsteroidal antiinflammatory drugs can cause renal failure, affect platelet function, and are ulcerogenic. In consideration of the risk and benefits of HTEA, the risks are not additional to intravenous opiate analgesics, but rather a substitution of risk. It is probable that epidural use in cardiac operations is no more dangerous than in noncardiac operations, or when compared with conventional analgesia therapies.

Secondary endpoints
Improved physiotherapy cooperation (Fig 2) is an indirect indicator of the quality of analgesia, and improved respiratory effort may account for the higher arterial oxygen partial pressure and peak expiratory flow rates (Table 4) with HTEA. Warner and colleagues [18] found that HTEA abolished intercostal but not scalene or diaphragm muscle function, resulting in increased functional residual capacity and no effect on gas exchange. In this study, postoperative ventilation time was shorter with HTEA (2.6 versus 5.4 hours), although the ventilation time in the control group would still be consistent with fast-track recovery. The alfentanil was ceased prior to chest closure and should not have influenced ventilation times. In the authors’ country of Australia, intensive care unit or hospital stay is often principally related to unit protocol rather than to the achievement of specific clinical outcome measures, and therefore it is not a good index for the consideration of pain management.

The incidence of depression (12% versus 29%) and posttraumatic stress disorder (12% versus 33%) on Minnesota Multiphasic Personality Inventory 2 criteria were reduced in the HTEA group. Only 3 patients suffered both disorders. Our study is the first to report that improved postoperative analgesia using an epidural technique may reduce the risk of psychological morbidity after CABG. Depression occurs in about one third of patients [19] after CABG. Neurocognitive dysfunction related to atheroemboli is equally common and it may be difficult to discriminate between psychological and brain injury related morbidity. Hence we used an operative strategy in which we have previously demonstrated a low incidence of neurocognitive dysfunction. Conventional CABG with manual palpation of the aorta and at least one aorta-coronary graft were associated with a neurocognitive dysfunction rate of 38.1%, but this rate was 3.8% when a composite graft technique was used (no aorta-coronary grafts) and epiaortic ultrasound was used to screen the aorta for atheroma leading to avoidance of any detected atheroma during surgery [9]. Thus, to remove operative technique as a confounding variable, we used the same technique for all patients.

Surgical pain can induce spinal sensitization, potentially leading to increased perception of pain, but this also induces opposing anti-nociceptive phenomena such as stress-induced analgesia. The intensity of acute postoperative pain has been shown to predict long-term pain [4], and there is much interest in modulating spinal sensitization by the use of preemptive analgesia, and by a blockade of afferent sensation by regional analgesia techniques [20]. In this study, both of the groups had preemptive analgesia therapy. We found reduced thresholds to pain in the remote site (Table 5), indicating a degree of spinal sensitization that is not inhibited by stress-induced analgesia. In the HTEA group, the thresholds for pain detection were not reduced in the operative site, whereas there was a trend toward reduced thresholds in the control group, but the difference was small and did not achieve statistical significance. Therefore we were unable to find objective evidence of prevention of spinal sensitization by using HTEA.

There has been considerable interest in whether regional anesthesia confers an outcome advantage. A recent meta-analysis found a one third mortality and morbidity advantage for patients undergoing regional versus general anesthesia [21]. Beattie and colleagues [22] reported a significant reduction in perioperative myocardial infarction in patients receiving thoracic epidural analgesia for more than 24 hours, and Scott and colleagues [3] showed reduced supraventricular arrhythmias and lower risk of chest infection, acute confusion, and acute renal failure in CABG with HTEA. High thoracic epidurals have been shown to dilate stenotic epicardial coronary arteries [23] and reduce exercise-induced ischaemia [24]. Loick and colleagues [25] demonstrated that troponin T levels were significantly lower after CABG with HTEA compared with conventional anesthesia, indicating less myocardial cell damage. Conversely, no large randomized study to date has shown a mortality outcome advantage with the use of epidurals. The MASTER trial of Rigg and colleagues [26], did not find a mortality outcome advantage for epidural use in high-risk patients undergoing noncardiac operations, but they did find less respiratory dysfunction and higher patient satisfaction in the epidural group. There were no complications associated with epidural use.

The strength of our study is the homogenous nature of the patient sample and of minimal variability in operative strategy, which may have prevented differences in neurocognitive dysfunction or pain. There are limitations to some parts of the study. Pain assessment is by nature subjective. The MMPI 2 test is self-reporting, and patients may not answer questions truthfully. It is possible that the complexity of this questionnaire or patient psychological dysfunction contributed to inadequate test completion.

Our current practice has changed in several ways. We now insert HTEA in the operating room on the day of surgery, with a minimum of 1 hour between insertion and systemic anticoagulation, which has allowed our technique to be compatible with the day of surgery admission. If a bloody tap is encountered, the epidural is inserted at a different level, and the surgery is not postponed. We use ropivacaine 0.2% solution with 0.02 mg/mL of morphine. Epidural morphine wears off over 6 to 8 hours, allowing a more gradual transition from epidural to oral analgesic therapy.

Epidural analgesia reduces pain after CABG, and this is associated with improved physiotherapy cooperation and reduced risk of depression and posttraumatic stress.

	Acknowledgments

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 
We thank Karen Groves, Dr Michael Barrington, the Department of Biomedical Engineering, Royal Melbourne Hospital for technical support, and the cardiothoracic and operating suite nursing staff for their support. Prof John Ludbrook performed the statistical analysis (Biomedical Statistical Consulting Pty, Ltd). We thank Prof John Ludbrook and Prof James Angus for manuscript review. The study is supported by grants from the National Heart Foundation of Australia; Australian Society of Anaesthetists; and AstraZeneca Pty, Ltd.

	References

Top Abstract Introduction Material and methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Colin Royse Alistair Royse Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Royse, C. Articles by Pang, J. Search for Related Content PubMed PubMed Citation Articles by Royse, C. Articles by Pang, J. Related Collections Coronary disease