Applications in Cardiothoracic Surgery

Minimally invasive surgery, also referred to as endoscopic surgery, is an emerging field in the medical community. Minimally invasive surgery describes a category of procedures in which significant internal operations are conducted through small natural and artificial orifices. The miniature incisions decrease the severity of the surgery and therefore result in a smooth and timely preparation, operation, and recovery progression for the patient. The nature of endoscopic surgery, however, makes it difficult for the surgeon to perform manually. As a result, robotics have been introduced to aid doctors in performing endoscopic surgery.

The advantages of endoscopic surgery have made it an increasingly popular technique within a variety of specialty areas. It has most notably revolutionized cardiac operations, and more specifically the coronary artery bypass surgery. Robotic systems such as da Vinci and Zeus have enhanced the efficiency and success of these procedures in the last two decades.

Overview
Endoscopic surgery appears to be a routine procedure because it follows a simple model of mechanical maneuvering supported by informational imaging. The first step in endoscopic surgery is to make small incisions in the patient. The surgeon then inserts an endoscope, composed of stiff tube with a camera fixed at the tip, into the opening (1). The camera recordings are sent via wireless internet to the operating room computer, where the data input is converted into visual output. The final live image is projected onto a display screen located on the far side of the patient. After visual orientation is established, the surgeon inserts long, stiff instruments into the incisions to follow the path of the endoscope towards the target anatomical structure. Once localized to the surgical area, the surgeon maneuvers the instrument from outside the incision in order to create the intended motion of the internal ends of the instruments (2).

Although minimally invasive surgery appears to be routine, every facet of endoscopic surgery is extremely vulnerable to human flaw and error. First, the small incisions, which serve as the portals into the surgical area, impose severe limitations on human dexterity. In contrast to the large openings of fully invasive surgery (typically 15 cm – 30 cm), minimally invasive surgery keeps the incisions between 0.5 cm and 5 cm. The small slits maintain skin tension in the horizontal direction and the instruments, therefore, cannot move laterally. In addition to the small incision, the instruments themselves restrict motion. Since the endoscopic tools reside mainly in the body cavity, there can be no joints in the instrument. If there were points of rotation on the instrument, the surgeon could not control the motion of the instrument from the external ends. The instruments are therefore long and stiff, which makes it difficult to perform precise tasks. Since the surgeons have less flexibility in motion, they are often forced to assume awkward and uncomfortable positions as they try to achieve the type of motion that is necessary to perform the task. The surgeons must also perform movements with extreme geometric accuracy because the overextension of a motion will not be compensated for by the flexibility of the instrument (3). These mechanical demands for precision make the procedure more vulnerable to human fatigue and tremor.

Endoscopic surgery also requires the surgeon to perform a complex level of multitasking and multiprocessing that pushes the limits of human capacities. Since the surgery is performed through a small incision, all visualization comes from the live imaging on the screen located on the far side of the patient. The doctor must make a difficult mental transformation between the information on the screen and the motor movements of the instruments (4). The proportions on the screen do not identically represent the movements of the tools, requiring the doctor to integrate the two different systems instantaneously. In addition to this multiprocessing, endoscopic surgery also requires physical multitasking. The surgeries typically require two surgical instruments and a camera instrument. The doctor must then maneuver all three instruments smoothly, while maintaining proper visuals and precise motion. If a camera assistant is utilized to move the endoscope, the surgeon must provide clear instructions and communications to the assistant while simultaneously performing all other tasks.

Robotic Systems
Robotics has been incorporated in endoscopic surgery to extend human capabilities and lessen the demands put on the surgeons during this procedure. Robots have good geometric accuracy, are stable and untiring, and can be manufactured to all sizes. Robots can also utilize different technological sensors (chemical, force, acoustic) to gain control unlike the limited senses of the human hand (4). These sensors maintain the same precision from the external cut to the center of the target organ and do not deteriorate with increasing depth or decreasing visualization. These advantages allow robots to augment the efficiency and safety of human-directed endoscopic surgery. The four main goals of robotic endoscopy are to: (a) provide a stable camera platform, (b) replace 2D with 3D imaging, (c) simulate the fluid motions of a surgeon’s wrist, thereby triumphing over the motion constraints of the stiff endoscopic instruments, and (d) allow the surgeon to control the robotic movements from a comfortable and optimal operating position (1).

Now, two widely used systems will be discussed that have been created to achieve the goals of robotic endoscopy and have been used particularly in minimally invasive cardiac surgery. Zeus and da Vinci both employ the same general principles of telerobotics but carry them out in different ways and to varying degrees of robotic involvement. The two systems replace human control of instruments with robotic control. Although the human directs the robot, the automated tools perform the task alone. As a result, the surgeon no longer acts as the intermediary, converting visual imaging into instrument motion. The first technological step implemented in Zeus and da Vinci is the employment of a computer program that integrates instrument motion based on the image with instrument motion performed on the patient. This program essentially connects the surgeon’s command with robotic response and performance.

The computer programs have two stages of integration that adequately provide a continuum between patient and image information. The computer analysis is performed during patient preparation prior to the utilization of the robotic system for surgery. The first step is to determine the location of the pathological tissue or organ on the image display. This is done by taking a preoperative image and segmenting the data into physiologically important regions. These regions are then matched with an anatomical atlas and the locations of the surgical area and boundaries are marked on the image. The second step is the registration of the pathological image data, gathered from the first step, with the patient’s true anatomy (4). There are various ways to correspond points on the image with points on the patient.

A common approach in registering the surgeon/image domain with the robot/patient domain is to match the shapes of anatomical structures to the shapes of the image data. This can be achieved through lasers and probes. A computational algorithm then finds the transformation that minimizes the error between the real shape and the shape that is seen on the image. This algorithm is used as the formula to integrate image and patient (4). Computation integration systems have become a competitive technological field in themselves. Without smooth transition between human commands based on the image and the robotic response on the patient, the robotic systems would be extremely harmful and ultimately useless to the medical community.

Zeus
Zeus is a machine used in endoscopic surgeries which utilizes robotic arms to control the endoscope and the instruments. The robotic arm that holds the endoscope is voice activated. The surgeon looks at the live imaging and vocally directs the robot with commands regarding where to move the internal camera (2). The technology of the camera has advanced over those used in normal endoscopic surgeries as the camera can work in either two dimensions or three dimensions (2). The surgeon can therefore use two dimensions when a certain structure needs visualization, such as the replacement artery. Yet it can also call for three dimensions when relational information between structures is required, such as the placement of the new artery to bypass the blocked one. This advancement allows the imaging system to give more information to the surgeon.

In addition to endoscope robotic control, Zeus utilizes robotic arms to hold the instruments as well. The surgeon moves these robotic arms by controlling a remote joystick. Motion-scaling is built into the program that connects the joystick with the robot. Motion-scaling allows miniscule motions to be performed so that, for example, a 1 cm surgeon movement of the joystick can result in a 0.1 cm movement of the robotic arm on the patient (2). This advancement allows for greater geometric accuracy without the tremors and fatigue of the human hand.

Despite these advances, there are limitations to the Zeus system as well. Surgeons report that it is difficult to simultaneously give voice commands to the endoscope and mechanically maneuver the joystick. The audio and the tactile requirements together form the same multitasking difficulties as the non-robotic systems. Additionally, the system requires the surgeons to wear polarizing glasses when they choose to view the image in 3D. These glasses bring the right and left side of the images in phase to form a 3D image. The glasses, however, can impede the vision of the surgeons and cause motion sickness when they look at off-screen objects (1).

da Vinci
The limitations of Zeus prevented it from becoming widely distributed and fully FDA approved. Yet, with the advantages of telerobotic endoscopic surgery clearly laid out, the demand for a robotic system remained. In response, Intuitive Surgical created the da Vinci robot to address the limitations of Zeus and introduce new programs that greatly enhance the efficiency of robots in endoscopic surgery. The da Vinci system has two main parts. The first part is the surgeon’s console. The console has the “masters” of the robot and viewing screen. The surgeon looks through binoculars and is immersed into a 3D image of the internal cavity. His or her hands slip into “masters,” which take the movement of each finger and translate it into the movement of the remote instruments (1). The “masters” are more detailed than the joystick of the Zeus system and provide more range in motion.

The second part of the da Vinci system is the robot, which is attached to the patient operating table. The da Vinci system uses instruments that have joints in them. These joints are automatically controlled by the computer system to achieve the motion intended by the surgical “masters”. The instruments have 7 degrees of freedom and 2 degrees of axial rotation, a large advancement from the stiff, long instruments of human performed surgery. The robot also has an arm that holds the endoscope. Da Vinci uses two 5mm telescopes that run together through one trocar (hollow cylinders with sharp points at the ends that introduce objects into the cavity). A computer program then keeps the two images in phase and reflects them into the console. This imaging modality simulates a surgeon’s eyes and maintains the highest level of human science engineering. The right part of the brain processes the right image and the left part the left image just as human eyes do instantaneously every day. The two-camera system gives the best depth of field and real life representations of any system to date (1). The da Vinci system is commercially available and used primarily on cardiac endoscopic surgeries.

Although the da Vinci system has been used in many procedures, it is not without limitations. For example, the existing sensors on the robotic instruments cannot detect the pressure that is being put on the tissue. This lack of tensile feedback makes it easy for the robot to avulse tissues and cause pressure injuries (1). A human, in contrast, can feel this tension directly. Tension and plasticity sensors, therefore, are an area of interest in future modalities.

Cardiothoracic Surgical Applications
The Zeus and da Vinci systems have revolutionized the area of cardiovascular surgery. Over the past two decades, these technologies have not only sharpened the procedures already in place but have allowed brand new technologies to be introduced that were previously considered impossible. The most important cardiovascular surgical area in which new technologies have come into play is the field of coronary artery bypass surgery.

Coronary Artery Bypass
The purpose of coronary artery bypass surgery is to change the route of blood flow to allow it to “bypass” clogged arteries. This procedure is done to allow for greater blood flow so that more oxygen reaches the patient’s heart (5). Patients are in need of a coronary artery bypass surgical procedure when they develop certain types of clots in arteries that transport blood to the heart (5).

Patients with clots in their arteries are usually first prescribed medicines that thin the blood or help the heart to run on a lower oxygen supply. If this treatment fails, an angioplasty is performed to attempt to widen the blocked blood vessel. Only when these attempts fail do doctors resort to coronary artery bypass surgery to fix the clot (6). Coronary artery bypass surgery is best for patients who have multiple blockages in many different coronary artery branches (7).

To perform a coronary artery bypass, surgeons take a piece of a healthy artery from another part of the patient’s body and construct a “bypass” route for blood to take so that it can go around the clot and make its way to the heart. A frequent practice is to take part of a long vein from the leg and attach one end to the aorta and one end to the clotted vessel. This process is called grafting (5).

Traditionally, coronary artery bypass surgery is done with the patient hooked up to a pump oxygenator, which is a heart-lung machine that diverts blood flow around the artery that needs repair. Conventional coronary artery bypass procedures require a large vertical incision of approximately 30 cm through the center of the chest that allows the surgeon to spread apart the patient’s ribs in order to directly access the heart. The heart is stopped by either cardioplegic arrest or fibrillatory arrest and the pump oxygenator is used to allow blood-flow to continue through the body (2, 7).

Because such a large incision is required to perform coronary artery bypass surgery using traditional methods, the breastbone can take around six weeks to heal, and poses the most difficulty during the patient’s recovery process. While the breastbone and chest area heal, patients cannot lift heavy objects or exercise strenuously. Additionally, they are discouraged from driving for four weeks to avoid chest injury. Furthermore, infection can develop inside the chest cavity as a result of the large opening, and can lead to a wide array of other medical problems (6).

Minimally invasive direct coronary artery bypass (MIDCAB) is now being put into use in an effort to fix many of the problems associated with traditional coronary artery bypass surgery. It involves no stoppage of the heart like conventional coronary artery bypass surgery does, and it only requires tiny incisions, rather than the large ones that are required for a doctor to gain access to the heart by the traditional method of spreading apart the ribs. Minimally invasive cardiothoracic surgery can be more difficult for the surgeon because it requires dexterous maneuvering through the small incision and it also requires the surgeon to operate on a beating heart with continues blood flow, which requires more skillful movements from the surgeon (2).

According to an article written in 2002 that discusses early clinical results of minimally invasive robotic surgery, “[a]t the present time, telerobotic surgical systems offer a limited selection of instruments and bulky configurations that impede many specific surgical procedures… The current generation of telerobots is not sophisticated enough to displace prevailing standard surgical practice” (1).

However, as it currently stands, MIDCAB surgery has many advantages over traditional methods. For example, MIDCAB procedures generally require only 2-3 hours while conventional methods require around 6. The reduced recovery time associated with MIDCAB surgery makes it a more favorable option. Furthermore, MIDCAB procedures avoid use of the pump oxygenator, which sometimes causes complications (2).

In addition, MIDCAB surgeries are often more cost-effective than conventional coronary artery bypass methods. Traditional coronary artery bypass may cost a total of around $35,000 for the lengthy surgery and the long hospital stay that is required while the patient is in recovery. For MIDCAB, however, studies have shown that the cost is approximately 40% less (2).

MIDCAB surgeries do have disadvantages as well. For example, MIDCAB can only repair one or two arteries, whereas traditional surgery can fix many more, so patients with multiple diseased arteries would not be candidates for MIDCAB procedures. In addition, operating on the heart while it is beating, as done for MIDCAB surgeries, can lead to ischemia (inadequate blood supply to the heart) or other problems, so doctors must be equipped to put the patient on cardiopulmonary bypass at any time during the procedure. Finally, since MIDCAB techniques are relatively new, doctors generally have less experience with them and long-term effects of this procedure have not yet been verified (2).

The Zeus robot, described above, has been tested and used for internal mammary artery harvest and artery bypass grafting. The first successful clinical application of Zeus occurred in 1999. In this instance, surgeons harvested the left internal mammary artery and then connected the internal mammary artery to the left anterior descending artery through three thoracic trocars in two patients. During this procedure, they put the heart into cardiac arrest using an endovascular cardiopulmonary bypass system.

In 1999 and 2000, a group in Germany performed closed-chest coronary artery bypass grafting on beating hearts in 13 patients using the Zeus robot (1). In 2000, researchers at the University of Western Ontario issued a report on the performance of closed chest coronary artery bypass procedures on 6 male patients using completely robotic methods. They used the voice-activated Zeus robot and video assistance to identify and dissect the left internal thoracic artery. They stabilized the left anterior descending coronary artery with an articulating endoscopic stabilizer. They used Zeus to accomplish the arterial manipulations required for this procedure. All of the patients except one ended up with excellent quality of grafts after the procedure. According to the researchers, for these operations, “[the] Zeus robotic telemaniplation system facilitated the closed-chest anastomosis by allowing precision and dexterity that is not possible with manual surgical instruments” (8). After completing these clinical applications of the Zeus robot, researchers held an optimistic outlook for the future of this technology. They stated in their report, “Totally endoscopic coronary surgery carries a great potential to improve our minimally invasive surgical results even further” (8).

The da Vinci system, which was developed after Zeus, has also shown successful results in clinical application. In 2005, a total of 2,984 surgical procedures were performed worldwide using da Vinci systems, including totally endoscopic coronary artery bypass grafting and small access coronary artery bypass procedures with thoracic artery harvesting (9). The large number of successful da Vinci operations, primarily cardiac related, has led to its FDA approval and commercial availability.
Despite many success stories, physicians and researches have some reservations regarding minimally invasive surgical techniques. For example, according to Noiseux, et al., “the reduction in incision size is often matched by a corresponding increase in technical difficulty and operating time owing to the constraints imposed by limited or incomplete cardiac exposure” (10). Nevertheless, Noiseux et al. state, “Studies have shown that patients undergoing minimally invasive surgery have less pain, less use of blood products, leave the hospital sooner, and return to preoperative functional levels sooner than comparable patients who had traditional surgery” (10).

Conclusion
Robotic systems have revolutionized endoscopic surgeries, especially for cardiothoracic procedures. In coronary artery bypass surgeries robots have allowed surgeons to achieve new levels of efficiency and quality care. Yet these emerging technologies are far from perfect. There are inherent problems with robotic systems such as computer viruses, high monetary expenses, the size of the system, a steep learning curve for surgeons, and the processing capabilities of the system in performing complex procedures. Engineers are working to address these problems, which will result in more widespread use of these technologies. While telerobotics in endoscopic surgery is an active research field, it has already proved itself as a beneficial and dynamic technology that has revolutionized the medical community.

References
1. G. H. Ballantyne, Surgical Endoscopy 16, 1389-1402 (2002).
2. Brown Biomed: The Division of Biology and Medicine (2000). Available at http://biomed.brown.edu/Courses/BI108/BI108_2000_Groups/Heart_Surgery/Robotics.html (6 March 2008).
3. H. Kim, Urologic Clinics of North America 31, 659-669 (2004).
4. R. Howe, Robert. Annual Review of Biomedical Engineering 1, 211-240 (1999).
5. Bypass Surgery, Coronary Artery (2008). Available at http://www.americanheart.org/presenter.jhtml?identifier=4484 (4 March 2008).
6. D. Kulick, Coronary Artery Bypass Graft Surgery (CABG). Available at http://www.medicinenet.com/coronary_artery_bypass_graft/article.htm (4 March 2008).
7. Coronary Artery Bypass Surgery (2008). Available at http://www.mayoclinic.com/health/coronary-bypass-surgery/HB00022 (4 March 2008).
8. W. D. Boyd, The Journal of Thoracic and Cardiovascular Surgery 120, 807-809 (2000).
9. S. Jacobs et al, Computers in Biology and Medicine 37, 1374-1376 (2007).
10. N. Noiseux et al., Techniques in Regional Anesthesia and Pain Management. 12, 72-79 (2008).