Serum oncotic pressure and oncotic-hydrostatic pressure differences in critically ill patients.

The possible influence of serum colloid oncotic pressure (COP) and the gradient between COP and pulmonary capillary wedge pressure (COP-PCWP) on respiratory insufficiency and survival was studied prospectively in 77 critically ill surgical patients by daily simultaneous measurements of COP, PCWP, and intrapulmonary shunt (Qs/Qt). Mean ages of survivors (N = 51) and nonsurvivors (n = 26) were 46 +/- 3 years (survivors) and 58 +/- 4 years (nonsurvivors), respectively (p less than 0.01). Lowest value of COP was similar in survivors (15 +/- 1 torr) and in nonsurvivors (14 +/- 1 torr). Lowest value of COP-PCWP in survivors was 3 +/- 1 torr and -1 +/- 2 torr in nonsurvivors (p less than 0.05). The difference in COP-PCWP was secondary to a significantly greater PCWP in nonsurvivors (16 +/- 1 torr) than in survivors (12 +/- 1 torr) (p less than 0.01). For each patient, Qs/Qt measured at the time of lowest measured COP was not significantly different between survivors and nonsurvivors (0.18 +/- 0.01) in survivors and 0.20 +/- 0.01 in nonsurvivors) and measured at lowest COP-PCWP (0.18 +/- 0.01 in survivors, and 0.21 +/- 0.01 in nonsurvivors). No correlation was found between either lowest COP or lowest COP-PCWP and Qs/Qt. Progressive respiratory insufficiency was not a dominant factor in determining respiratory insufficiency was not a dominant factor in determining mortality. These data suggest that COP alone is not a critical factor in determining either survival or respiratory insufficiency as measured by Qs/Qt in critically ill surgical patients.