Anaesthesia for Cardiac Surgery
TRENDS IN SURGICAL PRACTICE
Ischaemic Heart Disease
The concept of aorto-coronary bypass grafting for the relief of coronary ischaemia was conceived and performed in animals in the early 1900s. It was not until the 1960s, following development of the heart-lung machine and the chance discovery of coronary angiography, that direct revascularization of the ischaemic myocardium using the autologous saphenous vein (Fig. 34.1) replaced indirect therapies such as sympathectomy, thyroidectomy and pericardial poudrage.
FIGURE 34.1 Diagrammatic representation of coronary arteries. (Adapted from JH Mackay and JE Arrowsmith (2012) Core topics in cardiac anesthesia. Cambridge University Press.)
Cardiopulmonary Bypass
The essential components of a cardiopulmonary bypasshe essential components of a cardiopulmonary bypass (CPB) circuit (Fig. 34.2) are:
FIGURE 34.2 Components of a cardiopulmonary bypass circuit. (Adapted from JH Mackay and JE Arrowsmith (2012) Core Topics in Cardiac Anesthesia. Cambridge University Press.)
PREOPERATIVE ASSESSMENT
Cardiac Catheterization
Left heart catheterization typically comprises coronary angiography, aortography, left ventriculography and manometry. This provides the following information (Table 34.1):
TABLE 34.1
Technique | Procedure | Parameter |
Manometry | Pressure measurement with catheter in aortic root and LV | Aortic valve gradient LV end-diastolic pressure |
Angiography | Coronary arteries selectively cannulated, contrast injected | Coronary anatomy |
Ventriculogram | Catheter in LV, contrast injected very rapidly | LV size and function Ejection fraction Severity of mitral regurgitation |
Aortogram | Catheter in aortic root, contrast injected | Severity of aortic regurgitation |
The efficiency of ventricular contraction (ejection fraction) can be estimated using the formula:
Right heart catheterization allows measurement of right heart and pulmonary artery pressures. When combined with measurements of cardiac output, these can be used to determine the pulmonary and systemic vascular resistances (Table 34.2).
TABLE 34.2
Measurements Obtained During Cardiac Catheterization
Parameter | Normal Values | |
Left heart | Systemic arterial/aortic pressure | < 140/90 (mean 105) mmHg |
LV pressure | < 140/12 mmHg | |
Right heart | RA pressure | < 6 (mean) mmHg |
RV pressure | < 25/5 mmHg | |
PA pressure | 25/12 (mean 22) mmHg | |
PAWP | 12 mmHg | |
Cardiac index | 2.5–4.2 l min– 1 m– 2 | |
PVR | 100 dyne s cm– 5 | |
SVR | 800–1200 dyne s cm– 5 |