The optimal fluid for priming the cardiopulmonary bypass machine is not known. Most priming solutions in adults are blood-free, as the drop in hematocrit allows substantial decreases in temperature without adversely affecting blood viscosity. Albumin has the advantage of increasing colloid oncotic pressure while at the same time attenuating the platelet-lowering effects of CPB [Russell JA et al. J Cardiothorac Vasc Anesth 18: 429, 2004]
Systemic heparinization prior to initiation of CPB is mandatory, even in emergency situations. To do otherwise is to risk a potentially fatal thrombotic event. In general, one should wait 3-5 minutes (after heparinization) before initiating CPB
The surgeon and perfusionist will attempt to identify a misplaced cannulae – when the surgeon asks the perfusionist to “test the line,” he/she is asking for a small bolus of priming solution via the aortic cannula – excessive line pressures indicate the potential for malposition (ex. dissection, migration into the subclavian), however, the anesthesiologist can assist in making this determination by examining the face for equal, bilateral coloring, palpating the carotids (gently), and measuring blood pressure bilaterally. Misplaced SVC cannulas may be identified by looking for venous engorgement of the head and neck, as well as increased SVC pressure. IVC cannula obstruction is almost impossible to identify but may be diagnosed by decreased filling pressures / venous return
Some authors recommend pulling the PA catheter back 3-5 cm prior to initiation of CPB, in order to avoid excessive distal migration. The TEE probe should be frozen (to prevent unnecessary heating of the esophagus). Additional paralytics and anesthetics may be indicated, as the priming solution contains neither, and thus has the potential to lower plasma concentrations of these important agents. The decrease in plasma protein concentrations and anesthetic requirements that accompanies CPB provides some margin of error in this regard, however there is tremendous variability in the response of various agents to CPB, so caution should be employed
Onset of Bypass
Transient hypotension (MAPs as low as 30 mm Hg) is common following initiation of CPB, and should not be treated unless prolonged. The predominant cause of hypotension following initiation of CPB is decreased SVR (secondary to reduced blood viscosity, dilution of endogenous catecholamines in priming solution, and differences in pO2, pH, and electrolyte concentrations between the priming solution and native blood).