Total Occlusion of Both Internal Carotid Arteries in a Patient Undergoing CPB

Cerebrovascular disease (CVD) is a concomitant disorder commonly found among cardiac surgery patients, and appears to be on the rise. For instance, the Society of Thoracic Surgeons (STS) National Adult Cardiac Surgery Database reports that the preoperative incidence of CVD in isolated CABG patients increased from 11.2% in 1999 to 13.2% in 2002.1 A similar trend can be seen in the combined procedures (CABG + AVR and CABG + MVR) where the rate of preoperative CVD rose from approximately 15% in 1999 to nearly 18% in 2002. Fortunately, the number of patients presenting for cardiac surgery with a documented history of cerebrovascular accident (CVA) has remained steady over the years (7.1% in the isolated CABG group and 8.7% in the CABG + AVR group) or has declined (from 10.5% in 1999 to 8.5% in 2002 in the CABG + MVR group). In Hays, our observed preoperative incidence of CVD in isolated CABG patients is 19.3%, well above the STS benchmark. Described herein is the surgical course of one such patient who presented for CABG surgery with both internal carotid arteries 100% blocked.

Patient History

A 75 year-old male patient with symptoms of angina, shortness of breath, and lightheadedness was admitted for cardiac catheterization. Past medical history included hypertension and occasional PVC’s. The patient had suffered a CVA eleven years prior which resulted in a right body deficit, grand maul seizures, and the need for wheelchair assistance. Cardiac catheterization revealed severe three-vessel disease, previously undiagnosed myocardial infarction including apical left ventricular aneurysm, and an ejection fraction of 30%. The patient reluctantly consented to undergo CABG surgery, and remained in the hospital for further evaluation and workup. Given the patient’s history of CVA and seizures, a carotid duplex Doppler study was ordered which showed total bilateral occlusion of both internal carotid arteries. A carotid and cerebral arteriogram was then performed, confirming that both internal carotid arteries were occluded throughout their length to the level of the ophthalmic arteries. The external carotid arteries were patent bilaterally, and branches of the external carotid arteries serving the posterior occipital, facial, and maxillary regions of the brain appeared to be hypertrophied. No right vertebral artery could be found, however antegrade flow was evident in the left vertebral artery, and this vessel supplied the posterior circulation of the brain fairly adequately. The principle pattern of blood supply to the anterior and middle circulation systems of the brain was faint retrograde flow through hypertrophied ophthalmic arteries bilaterally.

Surgical Course

A coated CPB circuit, including hardshell venous reservoir, membrane oxygenator, and centrifugal pump (Terumo Cardiovascular Systems), was used to perform CABG x 5 and left ventricular aneurysm resection. Activated clotting times were kept above 400 seconds. The patient’s hematocrit was not allowed to fall below 24%. Mean perfusion pressure was maintained at 70 mmHg or greater, and asynchronous pulsatile flow was employed once the aortic cross-clamp was applied. Moderate hypothermia (venous temperature 30° C) was induced shortly after initiation of CPB. Gradual rewarming commenced at a rate of 1° C every 3-5 minutes while carefully observing the temperature gradient between water bath and patient.2 Blood gas management during CPB included hypercarbia (pCO2 levels 50-55 mmHg) to further increase cerebral blood flow as much as possible.

Discussion

It is understood that the ‘pH stat’ method of blood gas management results in higher levels of cerebral blood flow than the ‘alpha stat’ method.3 In fact, investigators have determined that a 1 mmHg increase in pCO2 results in an approximate 3% increase in cerebral blood flow during periods of both hypothermic and normothermic perfusion.4,5 This ‘luxus’ of cerebral blood flow provoked by the ‘pH stat’ method, however, has been shown to increase cerebral embolization, resulting in more disturbances in the patient’s postoperative cognitive functions.6 It should be noted that these studies were performed on animals or humans presumed to be free of CVD. Because of the severity of our patient’s occlusive disease we chose the ‘pH stat’ method as a means of increasing cerebral blood flow as much as possible. Pulsatile flow during CPB remains a controversial topic. According to Taylor, when pulsatility is removed, despite maintenance of total arterial flow and mean arterial pressure, capillary perfusion is reduced, microcirculatory shunting develops, and cell metabolism becomes disordered with the prospect of reduced oxygen consumption, progressive acidosis, and lactate accumulation.7 For many years, the autoregulation of cerebral blood flow has been assumed to protect brain cells down to a mean perfusion pressure of, say, 50 mmHg. However, the mechanisms of cerebral autoregulation may be interfered with by such factors as temperature, blood viscosity, oxygen and carbon dioxide tensions, and various drugs. Certainly in our patient, cerebral blood flow was not distributed uniformly. We chose, therefore, to use pulsatile flow as a means of minimizing microcirculatory shunting and reducing cerebral vascular resistance as suggested by Kono et al.8 Our use of a large metal-tip arterial cannula and low compliant oxygenator ensured that transmission of the pulse wave occurred.

Outcome

Following surgery, the patient awoke uneventfully and was extubated fourteen hours following admission to the intensive care unit. The patient had full range of motion of all extremities, and was fully oriented to time and place. On the third postoperative day, the patient experienced several petit maul seizures which were successfully treated with medication. The patient was discharged to home on the ninth postoperative day, and is now strong enough to use a walker for ambulation.