The influence of vascular pressure and different primes on the fluid balance of, and oxygen supply to, the patient during CABG.

Detrimental changes of blood and erythrocyte rheology, and fluid exchange between the vascular and interstitial spaces, which influence the rate that oxygen is supplied to the patient, occur during cardiac bypass surgery. Venous flow is subject to a pulsatile and uncertain variation, because the vena cava is more than 30 mmHg below atmospheric pressure. This occurs because the patient is about 1 m above the air-blood surface of the bypass reservoir. Before any reliable study of fluid exchange can be undertaken this effect must be controlled. It was then established that optimum oxygen exchange occurs when equilibration of the plasma oncotic pressure and the capillary hydrostatic pressure is achieved without alteration of the interstitial fluid volume. At the lower arterial blood pressures used during bypass, it is necessary to reduce the plasma oncotic pressure by using an appropriate volume of crystalloid prime.

Air handling characteristics of five membrane oxygenators.

This project looked at the potential of five different membrane oxygenators to allow passage of catastrophic quantities of air in a clinically simulated environment. All the oxygenators were set up in an identical circuit using heparinized human blood as the perfusate. The study was carried out at flow rates ranging from 1.0 to 6.0 l/min. The clinical situation of obstructed venous drainage was simulated by clamping the venous return line at each respective flow rate, while the initial level of blood in the open system hard shell venous reservoir was maintained at 600 ml. The time interval between the application of the clamp on the venous line and the first appearance of macroscopic air in the arterial line was recorded at each level of flow rate. A graph of time versus flow rate was plotted for each oxygenator type. At a flow rate of 6 l/min, the Safe II oxygenator took 20 seconds to allow passage of air after the venous line was clamped, while it took the Bentley Univox Oxygenator only 10 seconds. The Dideco oxygenator, which has a valve incorporated in its reservoir, did not, however, allow any air to be pumped forward at all. At low rates, some of the oxygenators offered protection against passage of air into the arterial line. Thus the Cobe oxygenator offered protection at flow rates of less than 2 l/min, the Safe II oxygenator at flow rates of up to 2.5 l/min and the Bard oxygenator at flow rates up to 3 l/min.(ABSTRACT TRUNCATED AT 250 WORDS)