STS Benchmark - CPB, Protection, Criculatory Support Flashcards
Coronary bypass grafting has been very successfully performed utilizing hypothermia with fibrillatory arrest (rather than cardioplegia).
What are the 3 important aspects of this technique?
A number of surgeons have very successfully used hypothermia with fibrillatory arrest as their primary system of myocardial protection during coronary artery bypass. If this technique is utilized, attention to detail is necessary.
Adequate myocardial cooling is essential. Since the heart continues to be perfused, myocardial cooling necessarily means systemic cooling. Ordinarily, systemic temperatures are reduced to 20-25 C. and the heart is allowed to fibrillate as the body is cooled. Induced electrical fibrillation of the heart is not necessary.
Active venting is always employed to prevent myocardial distention. This technique obviously cannot be used if aortic regurgitation prevents adequate decompression of the left ventricle. Venting is usually accomplished by a vent placed into the left ventricle via the right superior pulmonary vein. Such active venting poses a threat to the patient if air is introduced into the left atrium or left ventricle due to the development of negative intracavitary pressure. This air is difficult to remove at the termination of the operation. For this reason, several practitioners of this technique monitor the pressure within the left ventricle and maintain a positive intracavitary pressure of at least 5 mmHg.
A third critical principle of this technique is maintenance of adequate coronary perfusion pressure. It is generally kept at 80 mmHg by systemic infusion of alpha adrenergic agents.
Autotransfused shed blood in CPB has what characteristics?
“red cells suspended in serum”
The blood is defibrinated; platelet counts are not normal but are usually between 30,000-60,000/mm3. The hematocrit will vary with the hematocrit of the patient, ranging between 19% and 30%. Factor VIII and XI levels are somewhat diminished but not depleted to values that would affect intrinsic coagulation. However, fibrinogen levels are very low and fibrinopeptide A and other peptides, generated when fibrin is lysed by plasmin or released when thrombin cleaves fibrinogen, are elevated.
Reoperation for coronary disease is indicated for a 78-year-old man. What is the most sensitive surveillance modality to assess for atherosclerotic disease of the ascending aorta?
In one study, epi-aortic scanning detected atherosclerotic disease in 90% of patients compared to 76% by digital palpation. Epi-aortic scanning is currently the most sensitive and accurate technique, and it represents the “gold standard” for assessing atherosclerotic aortic disease in the operating room.
Severe atherosclerotic disease of the ascending aorta is the most important factor in defining stroke risk for patients who require cardiopulmonary bypass especially when an aortic crossclamp must be placed. A plain chest radiograph or cardiac catheterization may identify moderate to severe disease in about 25% of patients. Intra-operative gentle palpation of the ascending aorta is useful to detect plaques and extensive calcification, but manual findings are a gross underestimate of the actual incidence and severity. Transesophageal echocardiography is more sensitive and can accurately detect atherosclerotic disease of the descending and proximal ascending aorta. However, imaging of the distal ascending aorta and arch is poor and these are typical sites for aortic crossclamping and cannulation. Epi-aortic echocardiography does not have this limitation. Recent interest in cellular and molecular profiling studies of the peripheral blood have identified increased levels of a proinflammatory T-cell subset (CD4 (+)CD28 (-)) to be associated with stroke recurrence and death. These sorts of investigations may prove valuable to profile patient risk, to rationally use adjunctive diagnostic measures and to assist in developing therapeutic agents for primary and secondary stroke prevention.
What is the most important factor in defining stroke risk for patients who require cardiopulmonary bypass and cross clamp?
Severe atherosclerotic disease of the ascending aorta is the most important factor in defining stroke risk for patients who require cardiopulmonary bypass especially when an aortic crossclamp must be placed.
