EXTRACORPOREAL circulation for surgical repair of type A aortic dissection is performed by femoral artery cannulation and retrograde aortic perfusion. Preferential flow to the false lumen may occur due to a blind-pocket phenomenon [1]and may lead to aortic rupture, tissue hypoperfusion, or both.
In-line pressure monitoring is relatively unreliable because a gradient is generated at the tip of the cannula, and artifacts related to kinking, obstruction, or damping may alter pressure measurements. [2]Contrast ultrasonography [3]provides information on aortic blood flow and can be used to study perfusion in the true or false lumen at the beginning of cardiopulmonary bypass.
We describe a patient with type A aortic dissection extending to the thoracic aorta in whom extracorporeal circulation was initiated through the left femoral artery. Using contrast ultrasonography, we detected false lumen perfusion before the increase in in-line pressure. Cannulation through the right femoral artery restored perfusion to the true lumen.
Case Report
A 60-yr-old man weighing 100 kg who had a long history of arterial hypertension was admitted with chest pain of recent onset that extended to the back and epigastrium, causing agitation and vomiting. Type A aortic dissection had been diagnosed before admission. There were no focal neurologic signs, electrocardiographic abnormalities, or increased cardiac enzymes. Multiplane transesophageal echocardiography showed left ventricular hypertrophy, moderate aortic incompetence, and type A aortic dissection originating in the ascending aorta, 4 cm above the coronary arteries. The dissection extended retrograde near the right coronary artery, and partial occlusion of the left main coronary artery due to the intimal flap was evident during diastole. The aortic arch and the thoracoabdominal aorta were dissected, and the true lumen appeared markedly compressed during diastole. There was no evidence of blood stagnation either in the true or the false lumen. The aortic arch branches and the femoral arteries, as evaluated by surface color-Doppler imaging, were not dissected.
Just before anesthesia was induced, we placed a 14-gauge cannula in a peripheral vein and a 20-gauge catheter in the right radial artery. General anesthesia was induced using 0.1 mg/kg diazepam, 25 mcg/kg fentanyl, and 0.1 mg/kg pancuronium. After tracheal intubation, a triple lumen catheter and an 8.5-gauge introducer sheath were placed in the left and right internal jugular veins, respectively. Anesthesia was maintained with a 10-mcg [dot] kg sup -1 [dot] h sup -1 infusion of fentanyl. Aprotinin (2,000,000 KIU) was added to the prime pump; serum glucose was maintained between 110 and 150 mg/dl. During circulatory arrest, 40 mg/kg sodium thiopental and 30 mg/kg methylprednisolone were administered for cerebral protection before instituting deep hypothermia (at 16 degrees Celsius).
The left femoral artery was surgically exposed and cannulated with a 20-French cannula. No sign of local dissection was evident, and retrograde aortic perfusion was instituted at a flow rate of 2.5 L [dot] min sup -1 [dot] m sup -2. An 8-ml bolus of sonicated albumin microbubbles (mean diameter, 4 +/- 1 micron; injection rate, 2.5 ml/s) was immediately injected through a side branch of the cannula, while the descending thoracic aorta was visualized. This method is used routinely in our institution to assess retrograde aortic perfusion in patients with aortic dissection. The relative size of the true and false lumen did not change, and the false lumen alone was opacified (Figure 1). The in-line pressure was measured through the same three-way stopcock used for contrast injection. Although blood pressure at the beginning was low (130 mmHg), it started to increase, after 1 or 2 min, to 250 mmHg. Radial artery pressure decreased progressively to undetectable values after 2 min, and the pressure in the ascending aorta was markedly reduced. Ultrasound imaging of the proximal aorta showed stagnation of blood with marked spontaneous contrast both in the arch and in the ascending aorta, up to the valvular plane (Figure 2, upper). The right femoral artery was cannulated within 7 min, restoring blood perfusion in the true lumen and completely clearing the spontaneous echocontrast in the ascending aorta (Figure 2, lower).
Figure 1. Multiplane transesophageal echocardiography of the distal thoracic aorta after an 8-ml bolus injection of albumin microbubbles in the extracorporeal circulation conduit, showing perfusion of the false lumen alone. TL = true lumen; FL = false lumen.
Figure 1. Multiplane transesophageal echocardiography of the distal thoracic aorta after an 8-ml bolus injection of albumin microbubbles in the extracorporeal circulation conduit, showing perfusion of the false lumen alone. TL = true lumen; FL = false lumen.
Figure 2. Imaging of the ascending aorta (AO) without sonicated albumin microbubbles. (A) Spontaneous echocontrast due to stagnation of blood in the ascending aorta during perfusion of the false lumen. (B) Clearance of spontaneous echocontrast in the ascending aorta after restoration of flow in the true lumen. LA = left atrium.
Figure 2. Imaging of the ascending aorta (AO) without sonicated albumin microbubbles. (A) Spontaneous echocontrast due to stagnation of blood in the ascending aorta during perfusion of the false lumen. (B) Clearance of spontaneous echocontrast in the ascending aorta after restoration of flow in the true lumen. LA = left atrium.
Surgical inspection of the arch during circulatory arrest showed the integrity of the aortic arch branches, and thus the ascending aorta alone was replaced with a preclotted Hemabridge 26 vascular prosthesis. The anastomoses were treated with resorcine-formol glue, [4]and the aortic valve was resuspended. Circulatory arrest time was 28 min and cardiopulmonary bypass time was 95 min.
The patient was separated from cardiopulmonary bypass without electrocardiographic or wall motion abnormalities. However, the patient did not wake after operation and a computed tomograph revealed diffuse ischemic brain damage. Renal failure requiring hemodialysis also occurred, and the patient died of multiple-organ failure 12 days after operation.
Discussion
False lumen perfusion during retrograde aortic perfusion may contribute to morbid complications and death in patients with type A aortic dissection. Indeed, perfusion of the false lumen may impair renal or cerebral flow, whereas inadequate myocardial perfusion may occur when the aortic cross-clamp is removed. [5].
Our report shows the utility of intraoperative contrast ultrasonography for evaluating retrograde perfusion in the true or false lumen. In our patient, we detected perfusion of the false lumen with stagnation of blood in the arch and ascending aorta immediately after cardiopulmonary bypass began and before the increase in in-line pressure. Consequently, perfusion could be switched to the right femoral artery, with restoration of perfusion to the true lumen. Despite precautionary measures aimed at protecting the brain (e.g., high-dose sodium thiopental, methylprednisolone, and deep hypothermia), diffuse cerebral ischemic damage developed during the time required to make the diagnosis and to cannulate the contralateral femoral artery. An analogous mechanism was probably responsible for renal failure. Unfortunately, restoring blood flow to the true lumen through the right femoral artery did not help to prevent these complications.
The method we describe is easy to perform and allows imaging of false lumen perfusion before hemodynamic changes occur (such as an increase in in-line pressure). In-line pressure measurement does not provide a reliable estimate of aortic perfusion, because pressure at the arterial limb of the circuit decreases. For a typical adult patient (mean arterial pressure, 60 mmHg; systemic flow, 2.4 l/min/m2; 24 French aortic cannula), line pressure in an uncomplicated case usually ranges from 150 to 250 mmHg. [2]Pressure measurement may be also biased by kinking, obstruction, or damping artifacts, which are proportional to the distance between the artery and the transducer. Unlike Doppler imaging, contrast ultrasonography has the advantage of detecting slow flows and flows perpendicular to the ultrasound beam and may be used to measure relative perfusion in the aortic lumens. Contrast ultrasonography allows easy detection of false lumen perfusion, supporting rapid intraoperative decision making. As anesthesiologists are becoming increasingly familiar with intraoperative ultrasound imaging, the technique might be used to detect vital organ hypoperfusion during extracorporeal circulation.
