Page 620 - Cardiac Nursing

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596 PA R T I V / Pathophysiology and Management of Heart Disease
which may vary from mild hypotension to full-blown anaphy-
SURGICAL TECHNIQUES laxis. Patients at greater risk for protamine reaction include those
with insulin-dependent diabetes and those with an allergy to fish.
Minimally Invasive Techniques While the patient is connected to the CPB machine, the surgeon,
anesthetist, and CPB perfusionists control many physiologic
In standard cardiac surgery, the heart is arrested and circulation variables. Hemodilution with crystalloid solutions is used to re-
is maintained by placing the patient on CPB. Although this duce hematocrit and the blood’s viscosity. CPB flow rates are
procedure has been used successfully for more than three controlled to maintain a cardiac index of 2.2 L/min/m and a
2
decades, it has drawbacks such as physiologic derangements as- mean arterial pressure around 60 mm Hg. Blood may be cooled
sociated with CPB andlong hospital stays. Minimally invasive to reduce metabolic demands or warmed to normothermia to-
cardiac surgery has evolved out oflaparoscopic techniques orig- ward the end of the procedure.
inally used in general and gynecologic surgery. The term mini- CPB produces a systemic inflammatory response that releases
mally invasive covers a variety of techniques rather than refer- biologically active substances that impair coagulation and the im-
ring only to one surgical procedure. Minimally invasive mune response. Proinflammatory cytokines contribute to neu-
techniques include CABG surgery performed by standard ster- trophil adhesion. In response to the vascular permeability
9
notomy but without the use of CPB (off-pump or OPCAB), changes that occur with CPB and to the decrease in plasma on-
CABG surgery performed off-pump through a small left anterior cotic pressure that occurs with hemodilution, large amounts of
thoracotomy (minimally invasive direct coronary artery bypass fluid move from intravascular to interstitial spaces. Movement of
[MIDCAB]), valve surgery performed on-pump but through fluid into interstitial spaces causes postoperative edema. This
“mini-sternotomy,” and computer-enhanced robotic system tech- generalized edema that occurs after CPB resolves after the first
niques that allow CABG and valve surgery to be performed on- few days postoperative or fluid mobilization may be facilitated
pump through a small incision with videoscopic assistance and with the use of diuretics. The longer the CPB time, the more se-
6
femoral bypass. Techniques are rapidly evolving that are geared vere the physiologic derangements during the postoperative
toward multivessel revascularization through port access on a recovery.
beating heart. Rather than just one approachfor all patients, car- Systemic warming is started approximately 30 minutes be-
diac surgeons have a variety of surgical techniques available de- fore the anticipated time of discontinuing CPB. If the left
pending on the patient’s anatomy, medicalhistory, and comorbid atrium, left ventricle, or aorta has been entered, air must be
conditions. Further discussion of these surgical methodologies is evacuated before aortic cross-clamp removal to prevent air em-
found in the coronary bypass and valve surgery sections of this bolism. The heart is warmed and resumes spontaneous rhythm
chapter. or is paced with epicardial wires. Ventricular fibrillation may oc-
cur and is converted with internal defibrillation. Under the di-
Cardiopulmonary Bypass rection of the surgeon and anesthesiologist, CPB weaning begins
by ventilation of the lungs. CPB is gradually weaned by de-
CPB comprises an extracorporeal circuit that circulates systemic creasing the amount of blood diverted through the CPB circuit.
throughout the body during periods of time the heart andlungs When the heart is functioning normally with adequate blood
are not functioning during cardiac surgical procedures. CPB has pressure and adequate cardiac index, CPB is discontinued, he-
been the standard method usedduring cardiac surgery for divert- parin is reversed, and cannulae are removed. If the heart cannot
ing bloodfrom the heart andlungs to provide a stationary, blood- support an adequate cardiac index and mean arterial pressure af-
less surgicalfield and to promote preservation of optimal organ ter weaning from CPB, the patient may have to be placed back
function. Blood is removedfrom the right atrium or vena cava by on CPB to rest the heart, and other measures for heart failure
one or two cannula, routed through the CPB machine, and re- may need to be instituted, such as inotropic treatment or intra-
turned to the patient by a cannula in the ascending aorta or the aortic balloon pump. In patients who continue to have severe
femoral artery. hemodynamic compromise, ventricular assist devices may be
The CPB system has several components, including venous used.
and arterial cannula; a membrane or bubble oxygenator that oxy-
genates the blood, removal of carbon dioxide, and delivery of Myocardial Protection
anesthetic gases; a heat exchanger that allows the blood to be ei-
ther heated or cooled by conduction; a pump, which keeps the Myocardial protection is the intraoperative techniques intended to
blood moving at a constant speed; filters, which remove particu- protect the myocardium from damage resultant from the ischemic
late or gas emboli and plasma protein or platelet aggregates; a left state that occurs with CPB. In cardiac surgical procedure requir-
ventricular vent to prevent distention of the left ventricle during ing CPB, cross clamping of the aorta without the use of myocar-
aortic cross-clamp; cardiotomy suction to aspirate blood from the dial protection would result in anaerobic metabolism and deple-
operative field; and sensors, which detect air bubbles, low levels tion of myocardial energy stores. Cross-clamping the aorta
of oxygen saturation, and low levels of blood in collection cham- without protection for more than 15 to 20 minutes would result
8
bers. 7,8 Heparin is usedfor anticoagulation during CPB to pre- in profound myocardial dysfunction. Cardioplegia is infused to
vent clotting in the CPB circuit. Before initiation of CPB, a he- arrest the heart and provide a bloodless, motionless operative field
parin dose of 3 mg/kg is administered through a centralline. as well as protect the heart during cardiac surgery. Cardioplegic
Activated clotting time is monitored a minimum of every solution is infused into the aorta or coronary sinus or into the
30 minutes during CPB. Once CPB is completed, heparin is coronary arteries themselves to cause cardiac arrest. Debate con-
7
reversed using protamine sulfate. Care is taken to administer tinues over the best type of cardioplegia, what is the best temper-
protamine slowly and watch for a possible protamine reaction, ature (hypothermic vs. normothermic), whether cardioplegia