22-Anesthesia For Cardiac Surgery

Question 1

Why is hypothermia used for CPB?

Answer 1

To minimize organ damage during this stressful period, various degrees of systemic hypothermia may be employed. Topical hypothermia (an ice-slush solution) and cardioplegia (a chemical solution for arresting myocardial electrical activity) may also be used to protect the heart.

Question 2

Six components of CPB

Answer 2

The typical CPB machine has six basic components: a venous reservoir, an oxygenator, a heat exchanger, a main pump, an arterial filter, tubing that conducts venous blood to the venous reservoir, and tubing that conducts oxygenated blood back to the patient

Question 3

Venting the LV means:

Answer 3

Draining it

Question 4

Hemodilution moves HCT to:

Answer 4

At the onset of bypass, hemodilution decreases the hematocrit to about 22-27% in most patients

Question 5

How does blood go from the patient to the machine?

Answer 5

the driving force for flow into the pump is directly related to the difference in height between the patient and the reservoir and inversely proportional to the resistance of the cannulas and tubing. An appropriately primed CPB machine draws in blood like a siphon. Entrainment of air in the venous line can produce an air lock that may prevent blood flow.

Question 6

Why does the fluid level matter in roller vs centrifugal pumps?

Answer 6

The fluid level in the reservoir is critical. If a “roller” pump is used and the reservoir is allowed to empty, air can enter the main pump and be embolized into the patient where it may cause organ damage or fatality. A low reservoir level alarm is typically present. Centrifugal pumps will not pump air but have the disadvantage of not impelling a well-defined volume with each turn of the head (unlike roller pumps).

Question 7

Tell me about the way roller pumps work

Answer 7

The rollers pump blood regardless of the resistance encountered, and produce a nearly continuous nonpulsatile flow. Flow is directly proportional to the number of revolutions per minute.

Question 8

Tell me about centrifugal pumps

Answer 8

In contrast to roller pumps, blood flow with centrifugal pumps is pressure sensitive and must be monitored by an electromagnetic flowmeter. Increases in distal pressure will decrease flow and must be compensated for by increasing the pump speed. Because these pumps are nonocclusive, they are less traumatic to blood than roller pumps. Unlike roller pumps, which are placed after the oxygenator (Figure 22-1), centrifugal pumps are normally located between the venous reservoir and the oxygenator. Centrifugal (unlike roller) pumps have the advantage of not being able to pump air.

Question 9

Which pumps can give pulsatile flow?

Answer 9

Pulsatile blood flow is possible with some roller pumps. Pulsations can be produced by instantaneous variations in the rate of rotation of the roller heads; they can also be added after flow is generated. Pulsatile flow is not available with centrifugal pumps

Question 10

Is there a benefit to pulsatile flow?

Answer 10

Although there is no consensus and the data are contradictory, some clinicians believe that pulsatile flow improves tissue perfusion, enhances oxygen extraction, attenuates the release of stress hormones, and results in lower systemic vascular resistances (SVRs) during CPB.

Question 11

What do arterial filters do? Once filtered, blood returns to?

Answer 11

Particulate matter (eg, thrombi, fat globules, tissue debris) may enter the CPB circuit via the cardiotomy suction line. Although filters are often used at other locations, a final, in-line, arterial filter (27-40 μm) helps to reduce systemic embolism. Once filtered, the propelled blood returns to the patient, usually via a cannula in the ascending aorta, or less commonly in the femoral artery. A normally functioning aortic valve prevents blood from regurgitating into the left ventricle.

Question 12

Even with total CPB, blood can accumulate in the LV. How Sway?

Answer 12

From either AR, or the bronchial arteries

Question 13

Venous blood from CPB-usually comes from ____ and returns blood via ___.

Answer 13

Right atrium, and returns blood via ascending aorta or femoral artery

Question 14

What does hypothermia do to metabolic oxygen requirements? How is the patient rewarded after surgery?

Answer 14

Metabolic oxygen requirements are generally halved with each reduction of 10°C in body temperature. At the end of the surgical procedure, rewarming via the heat exchanger restores normal body temperature.

Question 15

Adverse effects of hypothermia:

Answer 15

The adverse effects of hypothermia include platelet dysfunction; reversible coagulopathy; and depression of myocardial contractility.

Question 16

Patients at greatest risk for reperfusion injury? How can you tell?

Answer 16

Patients at greatest risk are those with poor ventricular function (as measured preoperatively) (see Table 21-13) those with ventricular hypertrophy, and those with diffuse severe coronary artery disease. Inadequate myocardial preservation is usually manifested at the end of bypass as a persistently reduced cardiac output, worsened ventricular function by TEE, or cardiac arrhythmias.

Question 17

When can cross clamping cause ischemia of the heart?

Answer 17

Myocardial ischemia during bypass may occur not only during aortic clamping, but also after release of the cross-clamp

Question 18

Ischemia causes what in the heart-like what’s depleted? How does cardioplegia help?

Answer 18

Cardioplegic solutions maintain normal cellular integrity and function during CPB by reducing energy expenditure and preserving the availability of high-energy phosphate compounds.

Question 19

The cardioplegic dose is what temperature wise?

Answer 19

The initial dose of cardioplegic solution may be hypothermic or may start warm (“hot shot”) and progress to cold.

Question 20

What’s the desired temp of cardioplega? What’s all that ice doing?

Answer 20

Maintenance of myocardial protection may be facilitated by systemic and topical cardiac hypothermia (ice slush). Myocardial hypothermia reduces basal metabolic oxygen consumption, and potassium cardioplegia minimizes energy expenditure by arresting both electrical and mechanical activity. Myocardial temperature is often monitored directly; 10-15°C is usually considered desirable

Question 21

How can mannitol help with CPB?

Answer 21

Free radical scavengers, such as mannitol, may help decrease reperfusion injury and are typical constituents of cardioplegic solutions and bypass “priming” solutions.

Question 22

What happens with pressure and acid base status prior to being off of CPB?

Answer 22

Systemic perfusion pressure is reduced just prior to clamp release; it is then brought up initially to about 40 mm Hg before gradually being increased and maintained at about 70 mm Hg. To further minimize metabolic requirement, the heart should have the opportunity to recover and resume contracting in an empty state for some additional time (5-10 min), and acidosis and hypoxia should be corrected before attempting to wean the patient from bypass perfusion.

Question 23

What does CPB do to humoral systems and stress hormones?

Answer 23

Itbincreases catecholanomes and stress hormones and activates complement, coagulation, fibrinolysis and the kallikrein system

Question 24

What does CPB do to platelets?

Answer 24

CPB alters and depletes glycoprotein receptors on the surface of platelets. The resulting platelet dysfunction likely increases perioperative bleeding and potentiates other coagulation abnormalities (activation of plasminogen and the inflammatory response described above).

Question 25

Infusions of drugs during CPB are increased or decreased during CPB? Also-what drug is an exception to this rule?

Answer 25

With the possible exception of propofol, constant infusion of a drug during CPB (even when adjusted to maintain a constant “effect site” concentration using data from patients not undergoing CPB) generally causes progressively increasing blood levels as a result of reduced hepatic and renal perfusion (reduced elimination) and hypothermia (reduced metabolism).

Question 26

For which cardiac surgeries should blood be immediately available?

Answer 26

Blood should be immediately available for transfusion if the patient has already had a midline sternotomy (a “redo”); in these cases, the right ventricle or coronary grafts may be adherent to the sternum and may be accidentally entered during the repeat sternotomy.

Question 27

When can radial arterial lines give false readings?

Answer 27

Radial arterial catheters may occasionally give falsely low readings following sternal retraction as a result of compression of the subclavian artery between the clavicle and the first rib.

Question 28

When should you avoid doing a radial artery a line?

Answer 28

The radial artery on the side of a previous brachial artery cutdown should be avoided, because its use is associated with a greater incidence of arterial thrombosis and wave distortion.

Question 29

When is a pulmonary artery catheter useful?

Answer 29

In general, pulmonary artery catheterization has been most often used in patients with compromised ventricular function (ejection fraction <40-50%) or pulmonary hypertension and in those undergoing complicated procedures.

Question 30

PCWP?

Answer 30

Pulmonary capillary wedge pressure (PCWP) provides an indirect estimate of left atrial pressure (LAP). Although left ventricular pressure can be directly measured by placing a catheter within the left ventricle, it is not feasible to advance this catheter back into the left atrium.

Question 31

Why not place catheters on the left?

Answer 31

Catheters placed through the other sites, particularly on the left side, are more likely to kink following sternal retraction (above) and are not nearly as likely to pass into the superior vena cava as those placed through the right internal jugular vein.

Question 32

E and A on TEE

Answer 32

E (ear

Question 33

What’s a normal ACT, and when is it best measured?

Answer 33

The baseline ACT (normal <130 s) is best measured after skin incision.