Sternotomy

Introduction

Median sternotomy is one of many incisions that can be made in the thorax and gives a wide view of the thoracic cavity. Other incisions which involve the sternum, providing access to the thoracic cavity include the hemisternotomy (upper or lower), bilateral thoracosternotomy (clamshell), thoracosternotomy (hemiclamshell) and modified thoracosternotomy. ^{[1, 2, 3]}

Indications

Although the median sternotomy is predominantly associated with cardiac surgery, it is a useful incision for a number of other operations. The incision also allows access to both pleural spaces, making it useful for some thoracic operations, retrosternal goiter access and esophagectomy. ^[1] The incision for many neurosurgical procedures that require access to thoracic vertebral bodies or discs for treatment of fracture, neoplasm, bone cysts, osteomyelitis, spinal medullary tumors, discitis, or herniated nucleus pulposus. ^{[4, 5]}

An upper hemisternotomy is used for minimally invasive aortic and mitral valve surgery, while a lower hemisternotomy can be useful to access the right internal mammary artery and mid or right distal coronary artery for coronary artery bypass grafting. ^{[2, 6, 7, 8, 9]}

Contraindications

Although not an absolute contraindication, previous surgery using the median sternotomy is associated with an increased risk of perioperative complications. In some cases, an alternative surgical approach should be considered, such as a left lateral thoracotomy or a mini thoracotomy. Other relative contraindications include obesity, COPD, radiation therapy to the chest, and cardiomegaly. ^[1]

Indications for emergency repeat sternotomy

In cardiac surgery, a 5% risk exists of bleeding or tamponade following a first cardiac operation. If the patient is having, or at risk of having, a cardiac arrest secondary to these complications, an emergency repeat sternotomy should be performed. Emergency re-exploration is required for excessive mediastinal bleeding, defined as being approximately more than 500 mL over 30 minutes, more than 7 mL/kg for an hour, more than 5 mL/kg for 2 hours, more than 3mL/kg for 3 hours, or more than 2 mL/kg for 5 hours. ^[2]

Anesthesia

General anesthesia for sternotomy is dependent upon the type of operation to be performed. If single lung ventilation is required, patients should be intubated with a double lumen endotracheal tube.

During sternotomy, high levels of sympathetic stimulation occur. Therefore, the surgeon must ensure that the patient is sufficiently anesthetized prior to commencing sternotomy to avoid hypertension and tachyarrhythmias. The lungs are usually deflated prior to sternal division.

Anesthesia for redo sternotomy

Because the risk of hemorrhage is greater with redo sternotomy compared to the initial sternotomy, large-bore venous access should be obtained and cross-matched blood should be available. External defibrillator pads are affixed to the patient prior to induction since the redo sternotomy may result in a dysrhythmia. Some surgeons may request the insertion of a femoral arterial and venous line prior to surgery in order to aid immediate cannulation for femoral-femoral cardiopulmonary bypass if redo sternotomy results in inadvertent right ventricular laceration. ^[10]

Equipment

Two saws are used for sternotomy. For first-time operations, a standard pneumatic sternal saw is used, while an oscillating saw is used in redo and pediatric surgery.

Positioning

With the anterior thorax exposed, the patient should be in the supine position with a roll positioned in the interscapular region in order to improve access to the sternum by extending the neck and elevating the sternal notch. ^{[1, 3]}

Primary median sternotomy technique

A skin incision is made with a scalpel that extends from the midpoint between the angle of Louis and the sternal notch to below the xiphoid process; following this, a diathermy incision is extended through the subcutaneous tissue down to the sternum. The sternal periosteum is then separated, and bleeding points cauterized, being careful not to strip the periosteum as this may cause difficulties with healing later. The interclavicular ligament can then be divided at the sternal notch. ^[11]

The sternum may be divided either from top to bottom or bottom to top, depending upon personal preference, using a standard pneumatic sternal saw. Following harvest of the internal mammary conduits (in CABG operations only), a sternal retractor is placed in to the incision inferiorly so as to decrease risk of damage to the brachial plexus. ^{[2, 12, 3]}

Emergency resternotomy

An emergency sternotomy is generally indicated for hemorrhage or tamponade following cardiac surgery. If possible, the operation is performed in the operating room; however, this is not always possible and emergency resternotomy is not infrequently performed in the intensive care unit.

All necessary personnel are informed of the decision to perform an emergency resternotomy, including the referring physician and a perfusionist where necessary. An antibacterial preparation is applied to the sternal area and an anesthetist is enlisted to ensure that the patient is adequately anesthetized. A suction device is made ready, internal defibrillator paddles are connected and adequate lighting is made available. After draping the patient, the sternal wound is reopened and the sternal wires are severed with wire cutters and completely pulled out so as to avoid the possibility of laceration to the right ventricle.

After gently levering the sternum, a sternal retractor should be placed to maximize exposure and identification of the bleeding source. If the source of bleeding is not apparent, then the chest is lavaged with saline and systematically packed with swabs. These swabs are then removed and noted as to whether they demonstrate any signs of bleeding in that area, so that suspect areas can be inspected more closely. Great care needs to be maintained during this examination to avoid hemodynamic compromise or damage to CABG grafts. If no bleeding source is identified or is thought to be caused by needle holes, the chest should be repeatedly repacked with dry swabs until bleeding subsides. Prior to sternal closure, the chest drain is flushed of any clots and reinserted. ^[2]

Hemisternotomy (upper sternotomy)

An incision is made from the sternal notch, down to just below the angle of Louis. From here the incision is extended toward the right fourth rib. Electrocautery is used to divide the periosteum and cauterize any bleeding points while taking care to avoid stripping the periosteum. Then the tissue is cauterized from over the fourth rib up to the pectoralis major muscle. The upper sternum (generally a length of 8-10 cm) is then divided using an oscillating saw. The rib may be divided to provide a better view. ^{[2, 3]}

Redo sternotomy

Redo sternotomy is associated with a higher risk of complications then an initial sternotomy and, therefore, requires prior planning to minimize these risks.

If the heart or great vessels are damaged with redo sternotomy then immediate cardiopulmonary bypass may be required. Often this is accomplished via the femoral approach with access gained prior to initiation of the sternotomy.

The initial incision is generally made along the course of the prior incision, even if this is not exactly central. If the scar is hypertrophic, however, it may be advisable to excise it.

The sternal wires from the initial sternotomy may either be removed by pulling the wire upwards and then using wire cutter to cut to the side of the loop. Alternatively, they may not be removed to provide some degree of protection to the right ventricle during sternal opening.

The sternum is lifted directly upward as it is divided using an oscillating saw. Risk of damage to the underlying structures is reduced if the sternum is not completely divided using the saw, and the division is completed using heavy-duty scissors. Ceasing lung ventilation is not always necessary, as it is with the initial sternotomy. The sternum is lifted gently upwards and adhesions carefully separated using electrocautery or a scalpel to separate the mediastinal tissues from the chest wall. Once the mediastinal structures have been separated from the sternum, a retractor can be inserted. ^{[2, 10]}

The standard procedure for closing the sternal incision is to place chest drains in the thoracic cavity before using wire sutures to secure the sternum. In general, two wire sutures are placed around the manubrium and four are placed around the edges of the body of the sternum. The tissues, including the pectoralis fascia, are then closed in layers with care to close all spaces and wash out the wound thoroughly in order to try to prevent infection. In neonatal cardiac surgery, the sternum is occasionally left open for 24-72 hours if there is a high risk of tamponade. ^{[2, 13]} However, this technique does not always produce an adequate closure of the sternum. Therefore, a number of new techniques have been considered including placing three interrupted stainless steel wires in the manubrium, with five wires going through costochondral joints. ^[13] This technique may cause problems with inflammation of the costochondral joints. ^[14]

More recent advances include the use of titanium plate fixation to facilitate sternal stability in select patients. Titanium plates are bent to fit the sternum and attached with locking screws prior to closure of the soft tissues. ^{[15, 16]} Another recent advance in sternal closure is the use of kryptonite bone cement which is a biocompatible polymer which can be used to adhere the bone edges. Early results appear are promising, with a reduction in sternal displacement and improved sternal perfusion by comparison to traditional techniques. ^{[17, 18]}

Sternal wound infection and dehiscence

Deep sternal wound infection (DSWI) is a significant cause of morbidity and mortality in cardiac surgery patients. DSWI occurs in 1-4% patients, although the incidence is increased with advanced patient age, diabetes, obesity, smoking, steroid therapy, and COPD. Damage to the periosteum can cause problems with healing and puts the patient at increased risk of DSWI. Prolonged surgery or reopening of the sternotomy also puts the patient at higher risk of DSWI. ^[2]

Chest hair should be clipped prior to surgery, and prophylactic antibiotics should be administered intravenously at the time of anesthesia induction. Additionally, the incidence or DSWI is reduced by preoperative chlorhexidine gluconate showers and nasal mupirocin the night prior to and the morning of surgery. Nasal mupirocin should be continued twice daily for 5 days following surgery. ^[12] Obese patients should reduce their weight prior to surgery if possible, and efforts should be made to optimize lung function.

The patient with a DSWI often has a fever, leukocytosis, a sternal "click" with movement or respiration, purulent discharge from the sternal wound, and sternal dehiscence. Patients may also have a pericardial effusion. ^[2]

Treatment is with intravenous antibiotics and analgesia. Vacuum-assisted closure dressings are of use, although they occasionally have been associated with bleeding complications due to sternal wires causing damage to the underlying structures. ^{[19, 20]} Surgical debridement and rewiring of the sternum may, ultimately, be necessary.

Superficial wound infection (SWI) is considerably more common than DSWI, with cardiac surgery patients have an incidence of around 3-10%. ^[2] The wound should be swabbed and carefully monitored for signs of DSWI. Treatment is with oral antibiotics and incision and drainage where required. Vacuum-assisted closure therapy may also be used.

Sternal dehiscence generally manifests 3-5 days postoperatively with a serosanguineous discharge from the sternal wound and sudden wound opening on straining. The patient may be treated with wound debridement and sternal rewiring, although conservative management with vacuum-assisted closure therapy is also an option. ^[2]

The images below depict infected sternal wounds.

Hemorrhage

Massive hemorrhage is a major risk in a redo sternotomy. Adhesions from the previous surgery (maximal 2-3 months postoperatively and decreasing thereafter) can result in major structures being attached to the chest wall.

Redo sternotomy carries a 1-3% risk of right ventricular trauma, which is associated with a 50% mortality rate. If the patient has had a previous CABG, inadvertent trauma to a patent coronary graft may occur (ie, severing the LIMA graft or a saphenous vein graft to the LAD). Accidental trauma can also occur to the right atrium.

If hemorrhage is catastrophic, cardiopulmonary bypass (CPB) is initiated urgently, often via the femoral approach.

A number of issues should be considered in order to reduce the bleeding and transfusion requirements. It should be considered as to whether a sternotomy incision is required or whether another method could be used to access the necessary structures. Preoperatively antiplatelet medications and antithrombotic agents should be discontinued several days prior to the sternotomy when possible.

Dysrhythmias

The sympathetic stimulation that occurs with sternotomy may result in tachyarrhythmias. Therefore, care should be taken with the anesthetic management. In redo surgery, sternotomy damage to previous grafts is a risk, and cardiac manipulation may cause dysrhythmias. If injury is caused to patent coronary grafts, intractable ventricular fibrillation may occur.

Sternal instability and pseudoarthrosis

Following sternotomy, 1-2% of patients present with features of sternal instability: costochondral pain, "clicking" sensation on movement, and palpable instability on coughing. Weaning patients from the ventilator in the postoperative period may also be difficult. Management involves antibiotics (as these patients are at risk of developing a sternal wound infection), supportive dressings, and possible rewiring of the sternum. Eventually, a pseudoarthrosis (cartilaginous union) will form. ^[2]

Brachial plexus injury

Brachial plexus injury may result from sternal retraction. Patients present with C8-T1 paresthesia and weakness, although in severe cases this may extend to C6-C7. Final diagnosis is established with electromyogram studies. Treatment is with analgesia and physiotherapy. ^[2]

Keloid and hypertrophic scars

Hypertrophic scarring is common with midline incisions, and keloid scars are especially likely to develop in patients of African descent. Topical silicone gel dressings or steroid injections may be of some benefit in certain patients. ^[2]