The impact of obesity on the outcomes of coronary artery surgery remains a much debated point in the cardiac surgical literature. Although obesity has been associated with higher short-term and midterm mortality by some authors,1–3 this finding has been disputed by others4–9 and remains an inconsistently reported finding. Notwithstanding this variable impact that obesity may have on survival, most investigators have demonstrated a more consistent association between higher body mass index (BMI) and an increased risk for sternal wound complications3,8,10–14 and more frequent postoperative respiratory embarrassment.3,13–15 A nonsternotomy approach to coronary revascularization may thus offer an attractive alternative technique in the obese patient population because it will eliminate the possibility of postoperative sternal wound or peripheral conduit harvest site infection and it may facilitate a faster recovery.
At our institution, for almost the past two decades, we have been routinely adopting a nonsternotomy approach for isolated myocardial revascularization to the left anterior descending (LAD) coronary territory,16 although our technique has evolved with time, such that most of these cases are now being completed using robotic-assisted methods. The obese patient may potentially benefit the most from nonsternotomy coronary surgery, but they also present some particular technical challenges to endoscopic surgery. We thus sought to look at our minimal-access experience specifically to determine whether patients with a higher BMI are at greater risk for adverse perioperative outcomes than are patients who are not considered obese.
Between January 2010 and November 2011, a total of 110 consecutive patients underwent robotic-assisted off-pump coronary surgery at our institution. Those patients who had robotic-assisted minimally invasive direct coronary artery bypass (MIDCAB) had the left internal mammary artery (LIMA) harvested using the robot system, followed by a hand-sewn coronary anastomosis to the LAD completed via a left mini thoracotomy. A smaller group of patients in our series underwent totally endoscopic coronary artery bypass (TECAB), in which the entire operation was performed using the robot system inside the closed chest. All cases were completed on the beating heart, without the use of extracorporeal circulatory support.
For the purposes of our analysis, all patients were separated into two groups, defined as obese (BMI ≥30 kg/m2) or nonobese (BMI <30 kg/m2).
After selective lung isolation, the da Vinci Intuitive robot system (Intuitive Surgical Inc, Sunnyvale, CA USA) is docked to the operating table. Three ports are introduced into the left pleural cavity under vision, usually in the second, fourth, and sixth interspaces. The LIMA is then harvested as a skeletonized vessel using robotic-assisted techniques, after division of the endothoracic fascia. This is facilitated by carbon dioxide insufflation of the pleural cavity. After the LIMA has been completely mobilized off the chest wall, the patient is heparinized to achieve an activated clotting time greater than 300 seconds, and the conduit is divided distally.
For a MIDCAB procedure, a left anterior muscle-sparing minithoracotomy is performed by extending the middle (robot camera) port incision, with access to the pericardium usually optimal through the fourth interspace. Rib trauma is minimized as much as is practical and is facilitated by the use of an Alexis soft tissue wound protector (Applied Medical, Rancho Santa Margarita, CA USA). The anastomosis to the LAD coronary artery is then undertaken under direct vision, using standard off-pump coronary grafting techniques. A compression or suction myocardial stabilization system is used, depending on the preference of the surgeon. An intracoronary shunt is used for all cases, and a humidified carbon dioxide blower system is used to improve visualization at the operative field.
In a TECAB operation, after LIMA harvesting is complete, a suction cardiac stabilizer is introduced into the field and the LAD is controlled using proximal and distal silicone rubber vessel loops (Silastic, Dow Corning, Midland, MI USA). The LAD is opened using an endoscopic knife and is variably shunted. The LIMA to LAD anastomosis is performed using interrupted nitinol U-clips.
The heparin dose is usually completely reversed after completion of the graft. Graft flow and patency are assessed using a transit-time flow measurement system (Medistim VeriQ, Medistim USA Inc, Plymouth, MN USA) before wound closure. All patients are maintained on dual antiplatelet therapy postoperatively, unless specifically contraindicated.
Patients were identified from our prospectively collected cardiac surgical registry, maintained in accordance with New York State Cardiac Registry Reporting System guidelines. Approval for data review was obtained from our institutional review board.
Definitions of patient demographic characteristics, preoperative and intraoperative variables, and postoperative outcomes are obtained from the New York State Cardiac Surgery Reporting System and can be referenced online at the New York State Department of Health Web site at http://www.health.ny.gov/forms/cardiac_surgery. Data were analyzed using SPSS for Windows statistical software package, version 16.0 (SPSS Inc, Chicago, IL USA). Pearson χ2 test with Fisher exact test for categorical variables and independent-sample t test for continuous variables was used for analyzing differences between the two patient groups. Statistical significance was defined as P < 0.05.
During the study period, 110 patients underwent off-pump coronary surgery using a robotic-assisted nonsternotomy approach, 71 patients with a BMI of less than 30 kg/m2 and 39 patients with a BMI in the obese range. The preoperative characteristics of these patients are outlined in Table 1. Both patient groups were largely similar in risk profile. The same proportion of patients in each group, just more than 80%, had MIDCAB surgery, the remainder having a total endoscopic procedure, at the discretion of the operating surgeon. Interestingly, although there seemed to be a trend toward a higher incidence of diabetes mellitus in the more obese patients, as would be expected, this did not reach statistical significance, perhaps limited by our smaller sample size.
As demonstrated in Table 2, those patients with a higher BMI had longer operative times, defined as time between initial skin incision and application of dressings at the completion of the procedure (mean, 218.15 vs 186.72 minutes; P = 0.034). Similarly, it took the surgeon longer to harvest and prepare the LIMA graft in the more obese patient group (mean, 51.03 vs 39.94 minutes; P = 0.007).
There were no significant differences noted in bleeding or transfusion requirements between the two patient groups. Postoperatively, time to extubation, time until the patient was first out of bed, and time until the patient was ambulating in the hallway was similar in all patients, irrespective of BMI (Table 3).
In our series, BMI was not associated with an appreciable difference in mortality or major morbidity (Table 4).
We routinely use robotic-assisted techniques to facilitate revascularization of the LAD territory, both in the primary and in the reoperative setting, mainly using a MIDCAB technique after robotic-assisted LIMA harvest. All of our cases are done completely off-pump on the beating heart. Although a proportion of these patients have single-vessel stenosis limited to the LAD, the majority tend to have more diffuse multiterritory coronary disease and thus require subsequent percutaneous coronary intervention to non-LAD vessels, comprising a “hybrid” surgical-percutaneous coronary intervention approach to coronary revascularization.
In our series, obese patients had longer overall operative times than did thinner patients, and it took longer for the surgeon to mobilize the LIMA from the chest wall (Table 2). This finding has been echoed by Vassiliades and associates17 in their analysis of 350 consecutive patients who underwent robotic-assisted MIDCAB procedures. They report a mean LIMA harvest time of 37.8 ± 12 minutes and an overall operating time of 126 ± 36 minutes, with a direct relationship observed between surgical time and increasing BMI. Our operative times are somewhat longer than those of Vassiliades and coworkers, although it is important to note that their patients exclusively underwent MIDCAB procedures, whereas our patient cohort included TECABs in almost 20% of cases, and these tend to be significantly longer operations. Interestingly, by contrast, Wiedemann and associates18 found no correlation between BMI and operative time or LIMA harvest time in their description of 127 patients who underwent total endoscopic surgery on the arrested heart. Similarly, Oehlinger and colleagues19 found no correlation between BMI and robotic-assisted LIMA harvest time in their report of 100 patients who underwent this procedure.
We maintain that the obese patient does present a more technically demanding substrate to the minimal-access surgeon, which may partially explain potentially longer operating times in these subjects.17 Surface landmarks are less readily identifiable in the obese individual. Port-site placement thus becomes not only more difficult but also more crucial. The increased thickness of the chest wall may reduce the mobility of a port-placed instrument, which may reduce the surgeon’s flexibility to mobilize the LIMA within the closed chest. In the patients with higher BMI, it becomes more important to perform a thorough debulking of the pericardial and mediastinal fat pad before beginning the actual LIMA harvest, and this can significantly add to the operative time. This becomes particularly important to obtain adequate exposure of the distal LIMA to ensure sufficient conduit length.
For the MIDCAB procedure, the location of the thoracotomy incision becomes more important in the larger patients and can be particularly challenging for the more obese women with pendulous breasts. Usually, in obese male patients, we are still able to extend the middle port site (the camera port) for use as the thoracotomy incision. In the larger female patients, if we are still aiming for a submammary skin incision, the inferior port site often becomes the basis for the thoracotomy wound, with a separate chest tube site introduced at the end of the procedure. Although we still prefer a submammary incision in these female patients, we have, on occasion, used a supramammary incision, with acceptable results.
Despite somewhat longer operative times in patients with higher BMI, we did not demonstrate more significant bleeding or transfusion requirements in these patients (Table 2), and this has similarly been reported by others.17,18 We did not encounter any significant intraoperative hurdles in our experience mandating an increased conversion rate to sternotomy in obese patients. Bonatti and coworkers20 also did not find BMI to be an independent risk factor for an intraoperative technical misadventure during a TECAB procedure on the arrested heart.
We did not demonstrate any significant difference in major postoperative outcomes between the obese versus nonobese patients. Most patients in both groups were free of postoperative complications, there was no mortality in our series at all, and both patient cohorts seemed to demonstrate similar postoperative ventilation, recovery, and hospital length-of-stay times (Tables 3 and 4). None of our patients sustained a perioperative stroke or myocardial infarction. Whereas sternal wound infection remains a substantial complication of traditional coronary surgery in the obese individual, we found no port-site infections in any of our patients, nor did we observe any thoracotomy-related wound problems in our larger patients, perhaps one of the most important potential benefits of minimal-access coronary surgery.
Our relatively small sample size remains the major limitation of our study, although we sought to counter this by including all consecutive patients undergoing either isolated MIDCAB or TECAB procedures. Nevertheless, even in our comparatively smaller sample of 110 patients, obese patients constituted more than one third (35.5%) of all cases, clearly reflecting the burden of this problem in the current coronary surgery population overall. We have demonstrated that minimal-access robotic-assisted coronary surgery can be safely undertaken in patients with higher BMIs without significantly more adverse postoperative outcomes, perhaps at the cost of slightly longer operative times. Obesity should not be a contraindication to robotic-assisted surgery, and indeed, these patients may benefit the most from a nonsternotomy technique.
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