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Departments of *Anaesthesia, Cardiothoracic Surgery, and Cardiology, Westmead Hospital, Westmead, Australia
Address correspondence and reprint requests to Mark Priestley, Department of Anaesthesia, Westmead Hospital, Westmead NSW 2145, Sydney, Australia.
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Abstract |
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IMPLICATIONS: We found that epidural analgesia was more effective than IV morphine for cardiac surgery. Epidural anesthesia also allowed earlier weaning from mechanical ventilation, but it did not affect hospital discharge time.
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Introduction |
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Despite acknowledgment of the theoretical advantages of epidural analgesia in facilitating more rapid recovery in surgery (15), this hypothesis has not been formally tested in the cardiac surgical population. Previous authors have demonstrated earlier extubation with TEA (10,12,13,16,17); however, the general perioperative management did not attempt to fast-track patients. Our aim in this study was to determine the effect of TEA on extubation time in the setting of a currently accepted fast-track cardiac anesthetic technique and to determine whether any advantage in postoperative analgesia from TEA could decrease the time taken to achieve set criteria for hospital discharge. We implemented an accelerated mobilization program to take advantage of any improvements in analgesia in either group of this randomized study.
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Methods |
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Block randomization using sealed envelopes was used, and patients at high risk were randomized separately. High-risk classification criteria were poor left ventricular function (ejection fraction <0.4), repeat sternotomy, coexisting significant valvular heart disease, age older than 70 yr, morbid obesity (body mass index >35 kg/m2), chronic renal dysfunction (creatinine >200 µmol/L), chronic airflow limitation (forced expiratory volume <50% of predicted), or severe diabetes (defined as having three or more of the following: previous myocardial infarction, symptomatic peripheral vascular disease, peripheral or autonomic neuropathy, or renal dysfunction). Blinding of patients or investigators was not considered feasible.
All patients were given lorazepam 2 mg on the evening before surgery and morphine 0.1 mg/kg IM plus midazolam 0.05 mg/kg IM 1 h before arrival in the operating suite, followed by oxygen delivered via face mask. Supplemental IV midazolam was administered in the anesthetic bay if necessary to assist the institution of invasive monitoring.
Monitoring of all patients included five-lead electrocardiography (ECG), a three-channel Holter recorder (Medilog MR-FD3; Oxford, UK) for 24 h commencing at the induction of anesthesia, radial intraarterial catheter, central venous pressure (CVP) via the internal jugular vein (or pulmonary artery catheterization in high-risk patients, as defined previously), oximetry, capnography, and nasopharyngeal and rectal temperature.
The TEA group had a side-holed epidural catheter (B. Braun, Melsungen, Germany) via an 18-gauge Tuohy needle inserted the evening before surgery in the thoracic region between T1 and T4, with a test dose of 2% lidocaine 3–4 mL used to confirm placement. In the event of a bloody tap, an alternative level was attempted for epidural placement, but surgery was not postponed. On the day of surgery, after monitoring devices were inserted, an epidural bolus of 4 mL ropivacaine 1% and fentanyl 100 µg was administered, with supplemental ropivacaine 1% given as necessary to obtain blockade of pain or cold sensation to ice in the distribution of the T1 to T6 dermatomes. Failure to obtain such a block with 10 mL of 1% ropivacaine constituted failure of the epidural technique; alternative methods of anesthesia and analgesia were implemented, and the patient was excluded from per-protocol analysis. After the bolus, an epidural infusion was commenced with ropivacaine 1% and fentanyl 5 µg/mL, and this continued for 48 h at 3–5 mL/h. General anesthesia (GA) in the TEA group consisted of IV fentanyl 2 µg/kg plus propofol 15 mg · kg-1 · h-1 until consciousness was lost, followed by a propofol infusion at 6 mg · kg-1 · h-1, which continued until wiring of the sternum was completed.
The GA group received fentanyl 15 µg/kg in divided doses from the induction of anesthesia to sternotomy, in addition to propofol 15 mg · kg-1 · h-1 until loss of consciousness, followed by a propofol infusion of 5 mg · kg-1 · h-1 (the larger fentanyl dose allowed a slightly smaller propofol dose than in the TEA group) until sternal closure. During cardiopulmonary bypass (CPB), a morphine infusion was commenced at 40 µg · kg-1 · h-1.
All patients received pancuronium 0.1 mg/kg for muscle relaxation and antibiotic prophylaxis with cephazolin 2 g. Aprotinin was given at the discretion of the surgeon. Median sternotomy and CPB were used for all cases. CPB was standardized by using membrane oxygenation, blood cardioplegia, cooling to maintain temperature at 30°C–34°C, and 
-stat pH management. Mean arterial pressure (MAP) during CPB was maintained at 50–70 mm Hg and heparin administered to maintain the activated clotting time longer than 400 s. After termination of CPB, protamine was administered to normalize the activated clotting time. Muscle relaxation was reversed with neostigmine (50 µg/kg) and atropine (20 µg/kg), and all patients were transferred to the intensive care unit (ICU), intubated, and ventilated.
Intraoperative hemodynamic management was similar for both groups and aimed to maintain the MAP pre- and post-CPB between 65 and 85 mm Hg. Hypotension was treated with IV crystalloid fluids until the CVP was >10 mm Hg or >5 mm Hg above baseline CVP. Persistent hypotension was treated with boluses of ephedrine 6 mg (for MAP <65 mm Hg) or metaraminol 0.5–1 mg (for MAP <60 mm Hg), or with an epinephrine infusion if the cardiac index was <2.4 L · min-1 · m-2. Hypertension was treated with a bolus of propofol (0.5 mg/kg) up to a maximum of three boluses per hour, or with a bolus of epidural ropivacaine 1% 2 mL in the TEA group. Persistent hypertension was treated with a further IV fentanyl 5 µg/kg bolus in the GA group and with the commencement of a nitroglycerine infusion in both groups.
Patients in the ICU were weaned from positive pressure ventilation and extubated when they met set criteria (Table 1) as assessed by the ICU nursing staff. If required, propofol (0.5–3 mg · kg-1 · h-1) was used to provide sedation before extubation. Patients were rewarmed with forced-air convection blankets to a core temperature 
37°C. The ICU had a step-down high-dependency area to which all patients were moved on Day 1 unless they were still intubated or were hemodynamically unstable. The following day (Day 2 for most patients), the patients were moved to a general ward. Attempts to adhere to ICU discharge criteria were initially considered but found not to be feasible because the time of ICU discharge was constrained by bed availability (in the step-down and general wards) and the time of day (a reluctance to discharge ICU patients late at night).
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The height, weight, age, and sex of all patients were recorded, as were perioperative surgical details, including aortic cross-clamp time and CPB time. Total doses of anesthetics, inotropes, vasodilators, and vasopressors were recorded. The time to tracheal extubation (from arrival in the ICU) was recorded, as was the time taken to achieve the mobilization goal of walking up two flights of stairs and the postoperative day on which the patient was discharged. The postoperative day on which patients met the predetermined hospital discharge criteria was also recorded in the event that it did not coincide with the day that the patients were actually discharged.
Myocardial ischemia was assessed by automated analysis of Holter monitoring (Medilog MR-FD3) for 24 h, commencing at the induction of anesthesia. Ischemia was defined as ST segment depression (at 60 ms past the J point) of >1 mm for more than 1 min (18). Abnormal traces were subsequently reviewed by a blinded cardiologist who excluded traces thought to be due to artifact. Permanent myocardial damage was assessed by detecting new Q waves (assessed by the blinded cardiologist) on a 12-lead ECG on Days 0, 1, 2, and 4 and by assessing venous blood levels of troponin T and creatine kinase MB fraction on arrival in the ICU and again at 4, 12, and 24 h and on Postoperative Day 2.
Arterial blood analyses were performed pre- and post-CPB, on arrival to the ICU, after extubation, and on Postoperative Day 1. Oxygen saturation was measured by pulse oximetry continuously during surgery and afterward for 24 h. Oxygen saturation on room air was also measured daily from Postoperative Days 1 to 4. Spirometric estimation of forced vital capacity and forced expiratory volume in 1 s were measured by trained physiotherapy or research staff preoperatively; postoperatively; on Days 1, 2, and 4; and at a follow-up appointment between 4 and 6 wk postoperatively. Chest radiographs were taken preoperatively, on arrival to ICU, and postoperatively on Days 1 and 2 and were assessed by a blinded radiologist who scored the degree of atelectasis as follows: no changes, 0; small platelike changes, 1; large sublobar areas of opacification, 2; and complete lobar collapse, 3.
Analgesia was assessed by a trained research assistant with the visual analog pain score (VAS) by use of a standard 100-mm line at rest, with coughing, and with ambulation. The VAS was determined after extubation and on each postoperative day until discharge or until Day 7. Total doses of epidural ropivacaine, epidural meperidine, and IV opioid were recorded.
The main outcome variable chosen for sample size analysis was the length of hospital stay. Existing audit data from our department were used to estimate SD (1.48), and the difference thought to be clinically significant between the two groups was one postoperative day. Accepting an error of 0.05 and ß error of 0.2, the sample size required was estimated at 37 patients per group (JMP statistical program, version 3.2.1; SAS Institute Inc., Cary, NC). Allowing for protocol violations and failures to complete the study, 100 patients were recruited. Data were assessed for normality by using the Shapiro-Wilk W-test and were then analyzed with two-tailed Student’s t-tests, analysis of variance, or Wilcoxon’s ranked sum tests, as appropriate. Statistical significance was set at the 0.05 level.
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Results |
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Patient characteristics and intraoperative course did not differ significantly between the two groups, except that ephedrine requirements were greater and nitroglycerine requirements were smaller in the TEA group (Table 4). Operations performed by each cardiac surgeon were evenly distributed between the two groups. The time to tracheal extubation was significantly shorter in the TEA group (median hours [interquartile range], 3.2 [2.1–4.6] vs 6.7 [3.3–13.2]; P < 0.0001). Three patients required reintubation (one GA and one TEA required surgery for bleeding, and one TEA was reintubated for respiratory distress). The time taken to reach the final mobilization goal (usually two flights of stairs) did not differ between the two groups. The postoperative day on which patients met the criteria for discharge (eligible day of discharge) and the day they were actually discharged were documented and did not differ significantly between the two groups (Table 5). The eligible and actual discharge day differed in 33 patients (18 TEA and 15 GA patients), predominantly because of social reasons. When TEA and GA groups were analyzed together, 24% were discharged on Day 4 and another 33% on Day 5, which contrasts strongly with our hospital’s current average (2% on Day 4 and 18% on Day 5). Of these patients, one patient discharged on Day 5 was readmitted to hospital the next day with nausea and vomiting. Another patient (TEA) discharged on Day 7 was readmitted on Day 9 after a large stroke and died 2 wk later. There were no other readmissions to the hospital within a week of discharge, and there were no other postoperative deaths up to follow-up at 6 mo.
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Discussion |
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Kehlet (15) suggests that superior multimodal analgesia, including that provided by epidural local anesthesia and opioids, should allow a more rapid recovery from surgery as long as the postoperative management is organized to take advantage of the patient’s better ability to mobilize, feed, and perform other normal daily activities. We were unable to confirm this theory by use of TEA in CABG, but we believe that our use of the CABG population and our trial design may have limited the possibility of detecting differences in the speed of recovery with TEA. The median VAS for pain in both groups was always <30 mm, a small figure compared with that expected after other types of major surgery; this suggests that pain was well controlled for most patients. There were, however, significantly more patients in the GA group with a VAS >40 mm with coughing, suggesting that in this subset of patients TEA may play an important role in patient comfort. Unfortunately, this subset was too small to analyze possible meaningful effects on respiratory function, myocardial ischemia, or speed of recovery. It is equally important that in our study the care given to the GA group facilitated quick recovery. Most were extubated less than seven hours after surgery, they were mobilized aggressively, their pain scores were low throughout the postoperative period, and most were discharged home on Day 5 or earlier. In those patients in whom the hospital stay was prolonged, analgesia and mobilization were not limiting factors. We opined that it was important when studying the effects of a new analgesic regimen to manage the control group with equal intensity. That approach, however, had the consequence that further improvements would be harder to demonstrate.
It is interesting that the pain scores were significantly different only in the first 24 hours after surgery. In this period after conventional large-dose opioid anesthesia, most patients would still be sedated and require mechanical ventilation. This suggests that in fast-track cardiac anesthesia, TEA may play a more useful role in providing superior analgesia than it would when compared with large-dose opioid anesthesia.
The perioperative changes in spirometry, gas exchange, and changes on chest radiograph between the two groups were not statistically or clinically significant. Previous studies (10,12,13,16,17) have shown small improvements, often reaching statistical significance; however, the improvement in pain scores, when documented, in the TEA patients has been more than that observed in this study. This may account for the discrepancy in respiratory findings. It remains to be shown that improvements in such surrogate markers of respiratory outcome can be translated into a decrease in major pulmonary morbidity. Turfrey et al. (19) attempted to measure the patients’ ability to cooperate with physiotherapy and found an improvement with TEA, and although that was our anecdotal impression, we found it difficult to blind physiotherapists or other health care workers to the treatment group (which we believed would have been important for such a subjective assessment).
Although improvements with TEA have been demonstrated in myocardial ischemia in patients with unstable angina, the etiology and pathophysiology of perioperative ischemia during CABG is different, and the advantages of TEA in this setting are at this stage only theoretical (1–7). Our study showed no differences in the incidence of new Q waves on ECG or in the plasma levels of biochemical markers of myocardial injury. Loick et al. (10) found lower troponin T levels when using TEA for CABG, but we could not reproduce the differences with troponin I, despite a larger sample size. Variability in troponin levels after cardiac surgery can be large and may create difficulties in detecting subtle differences in myocardial protection if they exist. Although it was not statistically significant because the overall incidence was infrequent, we did find the total ischemic time on Holter monitoring to be 7 times shorter in the TEA group. By using a post hoc power analysis (ß = 0.2, = 0.05), we determined that more than 300 patients would be required to reach statistical significance if this trend continued; we believe that this would be a worthwhile area of future investigation, perhaps with a multicenter approach.
There were some methodological problems with the use of length of hospital stay as the main outcome variable. First, length of stay would have been influenced by many factors unrelated to anesthesia or analgesia. However, these would have been evenly distributed between the groups during randomization. Second, the decision to allow hospital discharge was made by the surgical team, who were not blinded to the treatment. We tried to overcome this by using predetermined criteria for hospital discharge and found that irrespective of the actual day of discharge, there was still no difference between the TEA and GA groups in the time taken to meet those discharge criteria. Finally, recruitment into a trial that focused on possible ways to reduce length of hospital stay may have attracted a subset of the general CABG population who were more motivated to recover quickly. This may have made improvements secondary to analgesic technique harder to demonstrate.
There were no major complications related to TEA, and it was well accepted by both patients and staff. The use of TEA during CABG is controversial because the anticoagulation required during surgery raises the concern of increasing the rare but serious risk of permanent spinal cord damage from an epidural hematoma. Such a risk must be balanced by important clinical advantages if the technique is to be justified. The focus of research has been to identify these advantages, but thus far the positive findings have been in surrogate end points, and convincing respiratory, cardiac, or other organ outcome data are lacking. Postoperative analgesia is consistently improved when TEA is used, and this is an important factor for patients when they are asked to consider different anesthetic techniques. Large multicenter outcome studies looking particularly for subgroups of patients who may benefit from superior analgesia (e.g., those at high cardiac or respiratory risk perioperatively) need to be performed. In conclusion, we found that TEA allows earlier tracheal extubation after CABG but does not allow earlier hospital discharge. Good pain relief and aggressive mobilization, when closely managed by a dedicated team, allow most patients to go home on the fourth or fifth postoperative day.
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Acknowledgments |
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Medtel Australia loaned the hardware to allow analysis from two Holter monitors (Medilog MR-FD3; Oxford, UK); Abbott Australasia loaned two Abbott Pain Managers to provide epidural PCA.
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