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Departments of *Anesthesiology, Intensive Care Medicine and Pain Control and
Thoracic and Cardiovascular Surgery, J. W. Goethe University Hospital Center, Frankfurt, Germany
Address correspondence and reprint requests to Paul Kessler, MD, Department of Anesthesiology, Intensive Care Medicine, and Pain Control, J. W. Goethe University Hospital, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany. Address e-mail to p.kessler{at}em.uni-frankfurt.de
| Abstract |
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IMPLICATIONS. The sole use of high thoracic epidural anesthesia was studied in 20 patients who underwent beating-heart coronary artery bypass grafting using either median or partial lower sternotomy while awake.
| Introduction |
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| Methods |
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On the basis of angiographic findings, the cardiac surgeon first decided which patients were suitable to undergo beating-heart surgery. Surgical contraindications for this technique included near-total and distal coronary stenosis, small target vessels, diffuse coronary artery disease, highly impaired left ventricular function, and significant stenosis of the circumflex artery. Patients with isolated disease of the left anterior descending coronary artery (LAD) were scheduled to undergo MIDCAB surgery, whereas patients with coexisting disease of the first diagonal branch (RD 1), the right coronary artery (RCA), or both underwent OPCAB. Patients considered eligible for beating-heart surgery were given the opportunity to chose TEA and thus to be operated on while awake. Contraindications for TEA included patients refusal or noncompliance, unfavorable anatomy, previous surgery of the cervical or upper thoracic spine, and language barriers. Patients with compromised coagulation (thromboplastin time <80%, prothrombin time >40 s, or platelets <100/nL) or a bleeding disorder were excluded. In addition, the use of any antiplatelet drugs within the prior 10 days was considered a contraindication for TEA.
The day before surgery, an epidural catheter (20-gauge; B. Braun Melsungen AG, Melsungen, Germany) was inserted, preferably at the T1-2 interspace for OPCAB and the T2-3 interspace for MIDCAB. A midline approach was used, using the hanging-drop technique. To eliminate intrathecal catheter placement, a test dose of 2 mL of mepivacaine 1% (20 mg) was administered. Radiographic confirmation of correct placement of the catheter was not performed.
On arrival in the preoperative holding area, IV access and direct blood pressure monitoring by using catheterization of the radial artery were established. A central venous catheter was inserted via a cubital vein, and correct position was confirmed by electrocardiography. Additional monitoring consisted of continuous automated ST segment analysis at J + 60 ms for leads I, II, and V5 (Hellige Marquette Solar 8000 Patient Monitor; Marquette Medical Systems, Milwaukee, WI). An ST segment alteration of
1 mm (0.1 mV) from baseline that persisted longer than 60 s was considered significant. Oxygenation and respiration were continuously monitored with pulse oximetry and capnography. Supplemental oxygen (5 L/min) was administered via face mask during the entire procedure.
A continuous epidural infusion of ropivacaine 0.5% and sufentanil 1.66 µg/mL was started at a rate of 2030 mL/h until the desired anesthetic level was established. Sensory level was determined with warm-cold discrimination. The level of motor block was estimated in the outplaced left arm by using the epidural anesthesia scoring scale for arm movements (ESSAM) described in Table 1 (8). Both sensory and motor block were checked at 5-min intervals until the desired anesthetic level was established and at 10-min intervals thereafter.
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All patients underwent total arterial revascularization. After full median or partial lower sternotomy, the left internal mammary artery (LIMA) was dissected and subsequently grafted onto the LAD. If required, patients received an additional sequential jump graft onto RD 1 or a radial artery graft from the LIMA to the RCA. The respective coronary artery was temporarily occluded during suture of the anastomosis. No stabilizing system was used. With the exception of one patient with a preexisting heparin-induced thrombocytopenia type II in the OPCAB group, all patients received a single dose of heparin 150 IU/kg after mammary artery dissection. This one patient was anticoagulated with recombinant hirudin. A 75% reversal of heparin effect was performed with protamine at thorax closure.
Mean arterial blood pressure (MAP), central venous pressure, heart rate (HR), arterial oxygen saturation (SpO2), and the end-tidal partial pressure of carbon dioxide were recorded before the start of the epidural infusion as a baseline value, at skin incision, during sternotomy, and after wound closure. At the same time points, arterial blood samples were obtained and immediately analyzed for arterial partial pressure of carbon dioxide (ABL3, Acid Base Laboratory/Hemoximeter; Radiometer, Copenhagen, Denmark). All patients were asked for subjective discomfort and pain as determined by a visual analog scale (0, no pain; 100, worst imaginable pain) at the same time points. In addition, the degree of motor block was assessed according to the ESSAM score (Table 1).
Data are presented as mean ± SD or median and range when appropriate. Calculation and data analysis were performed with a statistical package (GraphPad InStat 3.0; GraphPad Software, San Diego, CA). Statistical significance was determined with Wilcoxons matched pairs test, the Friedman test with Dunns multiple comparisons test, or the Wilcoxon-Mann-Whitney test, where appropriate. Differences were considered to be statistically significant if P was <0.05.
| Results |
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Unplanned intraoperative conversion to general anesthesia was required in one of the OPCAB patients because of acute respiratory insufficiency caused by pneumothorax. One patient in the MIDCAB group underwent tracheal intubation because of TEA-related phrenic nerve palsy. One MIDCAB patient complained of incomplete anesthesia on skin incision and also underwent tracheal intubation. Because these patients were not awake and spontaneously breathing throughout the entire surgical procedure, hemodynamic and respiratory data, as well as visual analog scale and ESSAM scores, were excluded from further analysis, leaving nine OPCAB patients and eight patients in the MIDCAB group.
With epidural infusion of the anesthetic solution, a significant decrease in HR was noted in both groups that recovered to baseline at the end of surgery, as depicted in Table 3. With the exception of a significant decrease during coronary anastomosis, MAP remained stable throughout the procedure in both groups. Because of severe hypotension during coronary anastomosis, with a sudden decrease of MAP to 34 mm Hg, one OPCAB patient complained of dizziness and required fractionated IV administration of 80 µg of epinephrine and 20 µg of norepinephrine. Although statistically significant, the observed alterations in central venous pressure were not of clinical relevance (Table 3). No statistically significant differences were observed among groups. During occlusion of the respective coronary arteries, significant ST segment changes were observed in all patients. All ST segment changes normalized completely after revascularization.
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No patient was admitted to the cardiosurgical intensive care unit. Postoperative monitoring was performed at the intermediate care unit for 224 h after OPCAB (MIDCAB, 222 h; P not significant). All patients were mobilized immediately on arrival on the intermediate care unit and were allowed to eat and drink as desired. The epidural catheter was withdrawn on postoperative Day 3 (median; range, Day 24) in all patients (P not significant between groups). No TEA-related complication, such as puncture site infection, respiratory arrest, epidural hematoma, or lower-limb motor block, was observed. Likewise, no clinically relevant surgical complication (bleeding, redo thoracotomy, myocardial infarction, or arrhythmia) occurred. All patients were discharged from our hospital on postoperative Day 5 (median; range OPCAB, Day 37; range MIDCAB, Day 310; P not significant).
| Discussion |
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Because of the increasing popularity of minimally invasive surgical strategies, some anesthesiologists have focused on developing similar "minimally invasive" anesthetic techniques to be used for minimally invasive CABG. Karagoz et al. (7) were the first to describe the successful use of sole TEA without general anesthesia in five patients undergoing beating-heart CABG via small lateral thoracotomy while fully awake. A single radial artery graft was interposed between either the left or right internal thoracic artery and the respective coronary vessel. Previously, only three case reports were published with regard to awake CABG (1921). However, in those cases, the heart was approached through a small left or right lateral thoracotomy, usually allowing only revascularization of a single coronary artery. More sophisticated anastomoses in patients with multivessel disease often require full sternotomy. There are no reports of the use of TEA as a sole anesthetic technique in conscious patients undergoing median sternotomy.
We demonstrated in small groups of 10 patients each that sole TEA was feasible for both MIDCAB and OPCAB surgery and produced high patients satisfaction. However, despite our initial enthusiasm, it should be recognized that unplanned intraoperative conversion to general anesthesia was required in three patients. In particular, intraoperative pneumothorax remains a concern, especially during OPCAB procedures, in which accidental pneumothorax is more likely than during MIDCAB surgery. In contrast to tracheally intubated patients who are ventilated with positive pressure and in whom intraoperative pneumothorax does not impair respiratory function significantly during cardiothoracic surgery, spontaneously breathing patients may develop significant respiratory distress. In addition, complete mammary artery dissection as performed in our patientsin contrast to grafting a radial artery from the undissected mammary artery onto a coronary vessel, as described by Karagoz et al. (7)conveys an increased risk of unintentional pneumothorax. Because our patients were transferred to a peripheral ward after only a few hours of monitoring, we consider chest radiograph examination essential to exclude even clinically insignificant pneumothorax before patients are transferred to a peripheral ward.
Another potential risk of high TEA is phrenic nerve palsy caused by an inadvertently high anesthetic level up to the C3-4 segments. Although Stevens et al. (22) demonstrated in a 15-patient cohort that cervical epidural anesthesia up to the C2 nerve roots did not result in clinically significant respiratory dysfunction, we believe that the risk for respiratory arrest remains, as we observed in one MIDCAB patient. Regardless of the fact that the level of motor block was checked at frequent intervals by assessment of hand and finger grip and elbow flexion, according to the ESSAM score (8), determination of the anesthetic level by relying on the motor response of the upper limbs was somewhat difficult. Because the patients right arm was fixed against its body, motor response of only the left arm could be evaluated intraoperatively. Eventual right lateral drift of anesthesia with undesirable high cranial levels could therefore be undetected for sometime. It is interesting to note that phrenic nerve palsy occurred in a MIDCAB patient who should have been at lesser risk than OPCAB patients, because the adequate anesthetic level for partial lower sternotomy is T1-2, compared with the C5-6 level required for OPCAB. However, a safe anesthetic level with regard to diaphragm function may result in pain sensations during surgical manipulation at the upper portion of the sternum. This occurred in two OPCAB patients, who required supplemental local anesthesia in that area. Finally, another MIDCAB patient required general anesthesia because of pain perception on skin incision.
Considering the potential risks, side effects, and pitfalls of sole TEA, its potential benefits should also be discussed. In one investigation, the risk for epidural hematoma formation in cardiosurgical patients was calculated to be 1 in 1,500150,000 within a 95% confidence interval (23), discouraging many anesthesiologists from use of TEA in cardiac anesthesia. A 1:143,000 incidence for adverse events was calculated for an overall population that receives epidural catheters for noncardiac surgery (24); however, estimating the "true" risk is difficult and purely speculative. The risk calculated by Renck (24)1:143,000may be too small in CABG patients, even when applying moderate heparinization with 100150 IU/kg, as in our patients. However, the maximum risk estimated by Ho et al. (23) seems far too high from clinical experience, although it is theoretically correct. Because spinal cord injury associated with TEA in cardiac surgery patients has not yet been described, a theoretical risk quantification can only be derived from the calculations of Ho et al. (23). Considering the risk of epidural hematoma, it should be remembered that patients with coronary artery disease often receive anticoagulants before surgery. In particular, platelet function is often impaired by aspirin or newer antiplatelet drugs. Although neurologic complications during cardiac surgery associated with TEA have not been reported in the literature, we were aware of potential bleeding complications and did not use TEA in patients who had received any antiplatelet medication within 10 days before surgery.
In times of steadily increasing health care costs, economic aspects become more and more prevalent. Fewer financial resources and reduced intensive care unit capacities led to the development of the fast-track concept in cardiac surgery, namely, early extubation after cardiac surgery and possibly earlier discharge from the hospital, although the actual benefit of fast-tracking remains controversial (25,26). Nonetheless, we could demonstrate that the sole use of TEA without general anesthesia in our selected patient cohorts did not require a postoperative intensive care unit stay. All patients were monitored on an intermediate care unit for a maximum of 24 hours. On arrival in the intermediate care unit, they were mobilized and allowed to eat and drink, a practice that our patients rated a major advantage of sole TEA.
Despite the encountered problems and complications, our data show that the sole use of TEA for MIDCAB and OPCAB surgery represents an alternative to general or combined general/epidural anesthesia. On completion of the learning curve, trials are mandatory to elucidate the relative importance of sole TEA in cardiac surgery. In addition, an important ethical question that remains to be answered is the extent of psychological stress to which humans should be exposed while awake and aware.
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