Published on 13/02/2015 by admin
Filed under Anesthesiology
Last modified 13/02/2015
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David J. Cook, MD and Eduardo S. Rodrigues, MD
Cardiopulmonary bypass (CPB) replaces heart and lung function during cardiopulmonary arrest. The basic features of the circuit are a pump, an oxygenator, and venous return and arterial inflow lines. A heat exchanger and a blood reservoir are also essential elements.
A right atrial or bicaval cannula is the source for drainage of blood into the venous reservoir. Blood exits the reservoir, goes to a pump (roller or centrifugal), and is pumped through an oxygenator (typically hollow fiber), most of which have integrated heat exchangers. For hollow-fiber oxygenators, the PaO2 is determined by the FIO2 of the fresh-gas flow passing countercurrent through the hollow fibers; the PaCO2 is determined by the total gas flow rate though the oxygenator. The pressurized oxygenated blood then typically passes through an arterial line filter before entering the aortic cannula (usually placed in the proximal aorta).
Additional features of the CPB circuit include several monitors of temperature and oxygenation, a cardioplegia delivery system, and a means for cardiotomy suctioning and ventricular venting.
The factors that control systemic oxygenation during non-CPB conditions also control oxygenation during CPB. Oxygen requirements are most profoundly affected by body temperature, whereas O2 delivery is determined by pump flow and hematocrit.
< ?xml:namespace prefix = "mml" />Arterial O2 content (Cao2)= 1 .34 (hemoglo bin) (O2sat%)+ 0.003 (Pao2)
Systemic D˙O2= cardiac output or CPB pump flow× Cao2
The temperature coefficient (Q10) describes the ratio of metabolic rates at two temperatures separated by 10° C. In humans, the Q10 is approximately 2 (i.e., when a patient’s temperature rises from 27° C to 37° C, the metabolic rate doubles. Conversely, every 10° C decrease in body temperature decreases theO2 by about 50%.
Nonpulsatile flow (2.0-2.5 L·min−1·m−2) is based on the cardiac index under anesthesia in non-CPB conditions. The flow rate may also be expressed as mL·kg−1·min−1
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is determined by pump flow and hematocrit.
