Edmunds Aortic Arch Anaesthesia
In general, anesthesia for repair of aortic arch aneurysms is not different from that for conventional open heart surgery, which relies primarily on the use of high doses of narcotics. Routine hemodynamic monitoring includes a Swan-Ganz catheter, a jugular venous bulb catheter, and left radial and femoral arterial catheters. Transesophageal echocardiography is used to monitor left ventricular function and distention, to confirm adequate flow in the arch and arch vessels, and to guard against malperfusion. Although we do not rely on EEG surveillance, it is still used by some surgeons to determine maximum cerebral metabolic suppression in conjunction with hypothermic circulatory arrest, and to assess adequacy of cerebral protection.
We no longer administer barbiturates because, at the doses recommended to enhance cerebral protection, they significantly depress myocardial function, and also because there are conflicting laboratory data with regard to their effectiveness in the presence of hypothermia. We give 2 g of methylprednisolone at the beginning of the case and before the start of perfusion in all cases where use of HCA is anticipated. If HCA exceeds 30 minutes, we continue to administer steroids for 48 hours postoperatively (125 mg every 6 hours for 24 hours, then 125 mg every 12 hours for 24 hours).
In patients in whom a thoracotomy is utilized, use of a double-lumen tube that permits selective ventilation of the right lung is helpful if substantial dissection and mobilization of the descending thoracic aorta are necessary before institution of cardiopulmonary bypass.
Although some controversy exists about whether pH during cooling should be maintained according to alpha stat or pH stat principles, we continue to utilize values uncorrected for temperature, the alpha stat approach. We rely on a long duration of cooling, a low esophageal temperature, a high jugular venous oxygen saturation, and topical hypothermia to ensure adequate cerebral protection during HCA.
The routine perfusion protocol for intracardiac operations is also utilized for repair of arch aneurysms; a membrane oxygenator is used in all cases. In the past, for all arch aneurysm cases, we placed a shunt between the arterial and venous perfusion lines. By moving clamps appropriately, this setup allowed us to institute whole body retrograde perfusion. Although we no longer use retrograde cerebral perfusion routinely, some surgeons still advocate its use, and it may have a role in de-airing and flushing out atheroembolic debris. For aortic arch reconstruction, a "Y" connector in the arterial line enables a second antegrade perfusion catheter to be used if needed. With right axillary artery cannulation, the site of arterial perfusion is constant and allows retrograde flushing of the brachiocephalic vessels. Distal arch descending aneurysms require transfer of the perfusion cannula from the femoral artery to the proximal graft following DHCA.