Separation from CPB

Although the patient's underlying disease or events during CPB may render separation from CPB problematic, in most patients, separation should be relatively uneventful. However, even in these more "routine" patients, several criteria should be fulfilled before separation is undertaken. These criteria are listed in Table 50-16 .

Many practitioners use low doses of their selected inotropic agent to augment inotropy, chronotropy, and lusitropy during separation and after CPB, even in patients whose preoperative cardiac indices were entirely acceptable. This practice is motivated by the recognition that even optimal myocardial protection during aortic cross-clamping is not perfect and is not without consequence in aerobic tissue. The magnitude of the myocardial insult in a specific patient will be a function of the efficacy with which cardioplegia is delivered, the frequency of administration, the duration of aortic cross-clamping, and other factors, and will determine the threshold for the type and magnitude of myocardial support. Moreover, inotropic support may be used to optimize hemodynamics, even in patients with reasonable post-aortic cross-clamp function, with the objective of decreasing the dependency of cardiac output on preload and thus on fluid administration (with its consequences for third spacing, postoperative weight gain, requirement for diuresis, electrolyte disturbances, and postoperative ventilator weaning among other effects). Importantly, inotropic support should not be initiated during the period of maximum, obligatory, oxygen

TABLE 50-16 -- Checklist before separation from cardiopulmonary bypass

Cardiac

Surgical

Bleeding

Valve function (TEE)

Intracardiac air (TEE)

Aorta (TEE, confirm no dissection)

Rate, rhythm (ECG)

Ischemia (ECG)

Myocardial function (visual observation, TEE, cardiac output/filling pressure)

Temperature (temperature in high- and low-blood flow regions > 37°C and 35°C, respectively); inflow/outflow temperature, duration of rewarming

Hematocrit

Electrolytes, acid-base status

Ventilation, oxygenation (ability to ventilate both lungs, especially the left lung and its lower lobe)

ECG, electrocardiography; TEE, transesophageal echocardiography.

1982

Bradycardia, with or without varying degrees of heart block, is not uncommon after aortic cross-clamping and is managed with some combination of pacing (atrial, ventricular, atrioventricular sequential) depending on the circumstances. Although transient heart block can occur in any case, it occurs more frequently and is likely to have greater implications when surgery is performed adjacent to the bundle of His (i.e., after aortic valve surgery with swelling of adjacent tissue or even direct surgical injury). Ventricular dysrhythmias (most often ventricular fibrillation) are common after unclamping of the aorta and are usually managed effectively by a combination of lidocaine loading and electrical defibrillation. Amiodarone is reserved for intractable dysrhythmias. Atrial fibrillation is a common dysrhythmia after cardiac surgery, even in patients with no preoperative history of same. It has tremendous medical and social implications that can include efficacy of treatment, ventricular rate response, thromboembolic risk, anticoagulation and its risks, difficulty in monitoring anticoagulation, and length of hospital stay. Atrial fibrillation most often develops 2 to 4 days postoperatively. Currently, no intraoperative intervention acts as an effective prophylaxis against the development of atrial fibrillation.