Position, Prepping, and Draping

Conventional cardiac surgery is almost always performed with the patient flat and supine, prepped, and draped with the sterile field extending from mid-neck to the ankles (Box 15-1). Many MICS procedures, however, require different positions and sterile field setups. For example, most procedures performed through anterior minithoracotomies or exclusively thoracoscopically are done with the patient’s left or right side elevated approximately 30 degrees. Some thoracoscopic procedures are performed in the left or right lateral decubitus position, typically with the hips rotated to expose one or both groins for possible femoral vascular cannulation. Unlike conventional sternotomy procedures, surgical access to remote areas (neck, lateral chest wall, groin) may be necessary for peripheral cannulation, placement of camera/instrument ports, or transcutaneous retraction sutures. This should be taken into consideration when placing ECG leads or other items on the skin during setup.

Because, by definition, access to the heart is limited in most MICS, external defibrillator pads should be considered mandatory. Again, care should be taken with placement and draping to ensure the current passes through the heart and that burns associated with seepage of prep solution or other liquids under the pads are avoided.

Temperature Management

Because nearly all MICS and all off-pump procedures are performed under normothermic conditions, careful temperature management is critical to avoid hypothermia, which not only can lead to ventricular fibrillation and bleeding but also can negate some of the potential benefits of MICS by prolonging the time to extubation. In addition to maintaining room temperature, one of a variety of warming blankets is usually required. Although conventional water or forced warm air blankets can suffice, more innovative solutions such as the Kimberly-Clark Patient Warming System (formerly the Arctic Sun) may be particularly advantageous in MICS.

Hemodynamic Monitoring

Hemodynamic monitoring requirements for MICS are typically not different from those of conventional cardiac surgery. Most patients have radial arterial and pulmonary artery (PA) catheters placed. Some centers limit themselves to a central venous pressure catheter, especially in patients with normal ventricular function undergoing MICS. Intraoperative transesophageal echocardiography (TEE) is the standard of care for all valvular surgery, and it can be critical in MICS cases to assess ventricular preload and pick up early changes in regional or global ventricular function, because visualization of the heart may be limited. In addition, TEE is helpful and often necessary to guide placement of various catheters, cannulae, and balloons. Because access to a ventricular wall for temporary pacing wire placement can be limited in some MICS approaches, a PA catheter with a pacing port can be helpful in valve procedures or other cases in which the need for temporary cardiac pacing may arise.

Airway

Many MICS procedures, including all minithoracotomy and thoracoscopic approaches, require at least some period of one-lung ventilation. Double-lumen endotracheal tubes are generally preferred because they are less likely to be dislodged during repositioning. It is critical to take the time to confirm proper placement and lung isolation before and just after positioning, because loss of lung isolation during an anastomosis or during some other critical stage of the procedure can be extremely dangerous.

Carbon dioxide insufflation of the hemithorax is frequently used during thoracoscopic MICS procedures, especially during robotic procedures. Insufflation to a pressure of 8 to 15 cm H₂O can dramatically increase the working space in the chest by shifting the mediastinal structures posteriorly and to the contralateral chest. Because there is always some obligatory leak around ports and incisions, the constant flow of CO₂ also clears smoke generated during electrocauterization of tissues. The intrathoracic pressure should be set to the minimal value necessary to achieve adequate exposure, and very careful monitoring of hemodynamics and gas exchange is essential, because the physiology is effectively that of a controlled tension pneumothorax. Although generally well tolerated, significant hypotension, hypercapnia, or hypoxia can occur if the pressure is set too high, particularly in patients with ventricular dysfunction or lung disease.¹

Anesthetic Regimen

Because accelerated recovery and discharge are major goals of MICS, it is important to note that careful selection of the anesthetic agents is necessary to ensure that the patient obtains the full benefit from the minimally invasive approach. Most centers will use some sort of “fast-track” anesthesia regimen—typically very short-acting narcotics and muscle relaxants in conjunction with an inhalation agent.² Some have advocated precise pharmacokinetically controlled total intravenous anesthesia (TIVA) regimens. Routine intraoperative extubation of MICS patients is controversial. Although some centers have established protocols whereby nearly all patients are extubated at the completion of the procedure,³ others have argued that a clinical or economic benefit is difficult to document unless the patient recovers in a postoperative acute care unit setting without an overnight stay in the intensive care unit.⁴

Spinal/Epidural Anesthesia

Spinal and epidural anesthetics have been used as an adjunct to general anesthesia at many institutions practicing MICS. A single intrathecal dose of a long-acting narcotic can be beneficial in reducing intraoperative and postoperative parenteral or enteral narcotic requirements.⁶ A thoracic epidural catheter with narcotic or local anesthetics can be administered continuously or with patient-controlled dosing.⁷ The excellent pain control and potential cardioprotective benefits from this approach, however, are mitigated by the additional operative time, the small but finite additional risk from the epidural anesthesia, and its potential to delay the typically rapid mobilization and discharge of MICS patients.

Local Anesthesia

Every effort should be made to supplement the pain management of MICS with local measures at the surgical site. This can include conventional methods such as direct infiltration of the wound with a long-acting local anesthetic such as bupivacaine or intercostal rib blocks extending a couple of interspaces above and below the incision.

Arterial

Some MICS approaches, including most partial sternotomy incisions, permit direct cannulation of the ascending aorta in a fashion similar, if not identical, to conventional approaches. Some surgeons use aortic cannulae with tapered dilators designed to be inserted over a guidewire to facilitate direct cannulation through a limited incision. Through many MICS approaches, however, the ascending aorta cannot be safely cannulated and peripheral cannulation is necessary. The femoral approach is most commonly used. The axillary artery is a viable alternative but is not usually used in MICS because accessing it usually requires a cosmetically prominent 3- to 6-cm incision. TEE assessment of the descending aorta is important before considering femoral artery cannulation to rule out extensive atherosclerotic disease, which can lead to retrograde embolization and neurologic injury.

Femoral arterial cannulation can be achieved percutaneously but is usually performed through a very small transverse incision guided by the pulse or a Doppler signal. The cannulae can be short, with the tip sitting in the pelvis, or long, extending into the thoracic aorta with multiple side ports. Contraindications include significant peripheral vascular disease. Potential complications include retrograde dissection, embolization, and perforation with retroperitoneal hemorrhage.