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294 P R I N C I P L E S A N D P R A C T I C E O F C R I T I C A L C A R E

the robotic instruments. Avoiding true thoracotomy or from porcine, bovine or human cardiac tissue. Mechani-
sternotomy improves postoperative pain experiences and cal valves are more durable but have an increased risk
shortens length of stay. 9 of thromboembolism, so lifelong anticoagulation is
required. Biological valves suffer from the same problems
Although CABG is the most common cardiac surgical
procedure undertaken in Australia, the incidence has as the patient’s valve (i.e. calcification and degeneration).
declined since 2005/06 to be 61 procedures/100,000 The choice of valve depends on the age of the patient and
10
population in 2007–08. The decline in surgery rates is potential difficulties with taking anticoagulants.
due to changes in the treatment of CHD, including the Mortality for valvular surgery is higher than for CABG,
advent of percutaneous coronary intervention (PCI). reflecting the underlying loss of ventricular function and
More procedures are now being performed in older additional procedures that are common. Risk stratifica-
patients, with 73% of current patients aged over 60 years. tion models have been developed to help determine the
1
CABG is used to relieve the symptoms of angina by patients that are most likely to have poor recovery and
14
increasing coronary blood flow distal to occlusive coro- outcomes. The major factors that contribute to poor
nary lesions. It is a palliative, not curative, treatment as outcomes are worse left ventricular function and age over
11
the underlying disease process continues. CABG is more 70 years old.
effective than PTCA in patients with extensive, multi-
vessel disease. 9,11 CABG is also used in left main vessel
lesions due to the high risk of extensive infarction associ- Cardiopulmonary Bypass
ated with PTCA in this area. Women do not appear to CPB was developed to enable surgery to be performed on
have the same access to CABG surgery, as men are three a still, relatively-bloodless heart, while preserving the
times more likely to have surgery, although only twice as patient’s circulation. CPB temporarily performs the func-
12
likely as women to have CHD. CABG surgery is com- tions of the heart in circulating blood and of the lungs
monplace, and many cardiothoracic centres have highly by enabling gas exchange with the blood. Silicone can-
efficient, effective systems in place with mortality rates as nulae are inserted into the venae cavae and venous blood
low as 2%.
circulated through a circuit outside the body. In this
circuit the blood is oxygenated, carbon dioxide removed
and blood temperature controlled. Drugs and anaesthet-
Valve Repair and Replacement ics may be added. A roller pump is generally used to
Valve surgery is usually undertaken to repair the patient’s provide the pressure to create blood flow in the circuit
valve or, more often, to replace the valve with either a and back to the patient’s aorta.
mechanical or tissue prosthesis. The clinical decision for Adverse effects of CPB are diverse, and include the
valve surgery is primarily based on the clinical state of the following: 15
patient using the New York Heart Association (NYHA)
classification system and echocardiographic findings. ● Haematological effects due to exposure of the blood
5
The type of surgery used will depend on the valves to tubing and gas exchange surfaces, which initiates
involved, the valvular pathology, the severity of the surface activation of the clotting cycle. Also blood
condition and the patient’s clinical condition. Often component damage due to shear stress from the roller
valve surgery is not a single procedure, and it may action of the pump, which reduces haematocrit, leu-
involve multiple valves, CABG and implantable cardio- cocyte and platelet counts.
verter defribillator (ICD). Valve surgery is palliative, not ● Pulmonary effects due to activation of systemic inflam-
curative, and patients will require lifelong health care. matory response syndrome (SIRS) that increases capil-
lary leakage, and lung deflation during surgery leading
Valve repair may involve resecting and/or suturing pro- to post-operative atelectasis.
lapsed or torn leaflets (valvuloplasty) and repairing the ● Cardiovascular effects due to volume changes, fluid
ring of collagen the valve sits in (annuloplasty), and is shifts and decreased myocardial contractility, which
commonly used for mitral and tricuspid regurgitation. decreases cardiac output. This is most severe during
Commissurotomy (incising valve leaflets and debriding the first 6 hours, but usually resolves within 48–72
calcification) is the treatment of choice for mitral steno- hours.
sis. Both repair processes have demonstrated lower opera- ● Neurological effects due to poor cerebral perfusion
tive mortality than replacement, although complete valve and generation of thromboemboli from aortic
competence may not be able to be achieved. Open pro- cannulation, which can lead to cerebrovascular
cedures are preferred because thrombi and calcification accidents.
can thereby be removed.
● Renal effects due to decreases in cardiac output during
Valve replacement may be necessary, but could be associ- initiation of CPB, which decreases renal perfusion.
ated with higher risks due to long-term disease process ● Post-pump delirium or psychosis, which occurs in
and poor underlying left ventricular function. The most 32% of CPB patients although the cause has not been
common indication for valve replacement is aortic steno- identified. Symptoms include short-term memory
sis, and accounts for 60–70% of valve surgery. Prosthetic deficit, decreased attention, and inability to respond
13
valves may be mechanical or biological. Mechanical to and integrate sensory information.
valves are made of metal alloys, pyrolite carbon and ● Activation of a systemic inflammatory response, which
Dacron (Figure 12.3). Biological valves are constructed may cause vasodilation and increased cardiac output.