Minimally invasive techniques for surgical treatment of coronary artery disease have gained increasing popularity within the last decade (1). Smaller incisions reduced surgical trauma (2–4), and coronary anastomosis on the beating heart reduced the use of cardiopulmonary bypass and its considerable side effects (5,6). Another option to reduce the stress of coronary artery bypass grafting (CAGB) may be avoidance of general anesthesia and mechanical ventilation. Avoiding general anesthesia and mechanical ventilation seems to be another way to decrease the invasiveness of the entire procedure. This anesthetic approach was first described by Karagoz et al. (7) in 2000, presenting five patients undergoing single-vessel CABG via minithoracotomy with high thoracic epidural anesthesia (TEA) alone while fully awake and breathing spontaneously (7). In recent beating-heart CABG techniques, the heart is usually approached via small thoracotomy, as described by Karagoz et al. (7); via partial lower sternotomy (minimally invasive direct CABG [MIDCAB]); or via full median sternotomy (off-pump CABG [OPCAB]). The MIDCAB techniques are usually limited to patients with single-vessel disease, whereas multivessel disease requires median sternotomy. The goal of our study was to investigate TEA as the sole anesthetic technique in patients who underwent either MIDCAB (single-vessel disease) or OPCAB (multi-vessel disease) procedures.
After approval by the IRB and with informed, written consent, 20 patients (ASA physical status II–IV) with symptomatic coronary artery disease underwent CABG on the beating heart via complete median sternotomy (OPCAB, n = 10) or partial lower sternotomy (MIDCAB, n = 10) with TEA alone.
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 patient’s 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 20–30 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.
To maintain anesthesia, continuous epidural infusion was reduced to an hourly rate of 2–5 mL once a sensory and motor block at the C5-6 level was established in OPCAB patients. The desired anesthetic level in the MIDCAB group was T1-2. During wound closure, the anesthetic regimen was changed to ropivacaine 0.16% and sufentanil 1 μg/mL at 2–5 mL/h to provide postoperative analgesia. All patients received lactated Ringer’s solution at 12 mL · kg−1 · h−1. A bolus of 750–1000 mL of hydroxyethyl starch 6% 200/0.5 was administered slowly between incision and coronary anastomosis.
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 Wilcoxon’s matched pairs test, the Friedman test with Dunn’s multiple comparisons test, or the Wilcoxon-Mann-Whitney test, where appropriate. Differences were considered to be statistically significant if P was <0.05.
Twenty patients with symptomatic coronary artery disease and good ventricular function underwent beating-heart CABG with high TEA only. Ten patients each were operated on either with a MIDCAB or OPCAB technique. The epidural catheter was placed at T1-2 (OPCAB, n = 8; MIDCAB, n = 5) or T2-3 in the remaining patients. Demographic characteristics and intraoperative fluid requirements are depicted in Table 2. As expected, the operating time was significantly longer in the OPCAB group (Table 2).
With the exception of one patient requiring an additional jump graft onto the RD 1, MIDCAB patients received single LIMA-LAD grafts only. LIMA-LAD grafts with sequential jump grafts onto the RD 1 were performed in five OPCAB patients. Two patients received an additional radial artery graft to the RCA, with or without (one each) a sequential LIMA-RD 1 graft. Three OPCAB patients, whose RD 1 was too small in diameter to be revascularized, received only LIMA-LAD grafts.
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.
Though in OPCAB patients the arterial partial pressure of carbon dioxide was significantly higher at the end of the procedure when compared with baseline, clinically significant arterial hypercarbia did not occur in any of our patients. Although one OPCAB patient required conversion to general anesthesia because of pneumothorax, a similar event caused a brief decrease of Spo2 to 89% in another OPCAB patient, who recovered promptly with supplemental oxygen 15 L/min. After chest tube insertion and wound closure, respiratory function normalized, and supplemental oxygen was no longer required. In the remaining patients, Spo2 was not affected significantly regardless of the type of surgery (Table 4).
On average, 16.1 ± 2.8 mL (initial dose, 10.4 ± 1.9 mL) of ropivacaine-sufentanil was applied epidurally during OPCAB (MIDCAB: total dose, 14.1 ± 2.1 mL; initial dose, 9.8 ± 1.4 mL;P not significant). The degree of motor block was determined intraoperatively according to the ESSAM score with the use of the outplaced left arm and is depicted in Figure 1, showing lower anesthetic levels in the MIDCAB group. In all but one MIDCAB patient, spontaneous breathing was not affected by anesthesia, and diaphragm-supported breathing was unaltered, in contrast to paralysis of the intercostal muscles. This one patient required tracheal intubation and mechanical ventilation because of respiratory distress caused by TEA-induced phrenic nerve palsy that was assumed on the basis of the clinical findings (ESSAM score, 3; sensory block level, C3-4). In particular, pneumothorax was excluded by the surgeons. No patient in either group experienced lower-limb paralysis.
No patient required supplemental IV anesthetics, but two OPCAB patients received additional wound infiltration (10 mL of mepivacaine 1%) by the surgeon because of pain perceptions during skin incision at the upper end of the sternum, whereas epidural anesthesia was sufficient for radial artery graft harvesting. One MIDCAB patient required general anesthesia because of insufficient TEA. Subjective pain as determined by visual analog scale was <20 on average and did not differ significantly between groups (Fig. 1). Effective analgesia, defined as a pain score of <40 of 100, was achieved in all patients. Two patients received intraoperative sedation with IV midazolam 2 mg. Eight patients—four in each group—reported a light itching sensation in the neck and face area. A patient survey on postoperative Day 3 yielded the utmost satisfaction from the patient viewpoint. All patients asked whether they would choose TEA again in their next CABG surgery answered affirmatively.
No patient was admitted to the cardiosurgical intensive care unit. Postoperative monitoring was performed at the intermediate care unit for 2–24 h after OPCAB (MIDCAB, 2–22 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 2–4) 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 3–7; range MIDCAB, Day 3–10;P not significant).
General anesthesia represents a well established and commonly used anesthetic technique for OPCAB and MIDCAB procedures and has become the anesthetic regimen of choice in patients undergoing minimally invasive CABG without cardiopulmonary bypass. Combined high TEA technique has been demonstrated to have a number of beneficial effects in CABG patients, e.g., thoracic sympatholysis with subsequent improvement of coronary perfusion, decreased HR and endogenous stress response, and the reduced risk for myocardial ischemia. Improved hemodynamic stability and postoperative pulmonary function have also been shown when combined TEA and general anesthesia was used for CABG (9–18).
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 (19–21). 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 patients—in 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 patient’s 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 1,500–150,000 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) —1:143,000—may be too small in CABG patients, even when applying moderate heparinization with 100–150 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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In the August 2002 issue, in the Brief Report “Intravenous Verapamil Blunts Hyperdynamic Responses During Electroconvulsive Therapy Without Altering Seizure Activity” by Wajima et al. (Anesth Analg 2002;95:400–2), there was an error in Figure 1 on page 401. The panels were labeled “Control” and “Diltiazem.” The correct labels should be “Control” and “Verapamil.” The authors apologize for the error.