Colloid Osmotic Pressure Values Research Articles

Colloid osmotic pressure changes in human whole blood and separated plasma in vitro with changes in CO 2 content and pH

1. 1. Colloid osmotic pressure (COP) and pH were measured on the true plasma of human blood from five subjects tonometered with different concentrations of carbon dioxide. Measurements were also made on their separated plasma. 2. 2. COP (mmHg) of true plasma obtained from tonometered whole blood varied in proportion to the bicarbonate concentration (mEq/1): COP = 0.056 [HCO 3 −] + 23.3 3. 3. In separated plasma, as CO 2 concentration increased, COP decreased as pH decreased: COP = 1.99 (pH) + 11.0. 4. 4. When the change in COP due to the change in pH was subtracted from the observed change of COP due to CO 2 exposure of whole blood, the difference was the change of COP due to the shift of fluid between plasma and red cells: COP adjusted for pH = 0.131 [HCO 3 −] + 21.5. The COP values of tonometered whole blood and separated plasma are taken to be equal at a pH of 7.40 (at the mixed venous point). 5. 5. The change in COP, adjusted for pH, for a given change in pCO 2 is in keeping with the amount of fluid shift calculated from the measured changes in hematocrit and plasma protein concentration. 6. 6. An error in a previous paper (Kakiuchi et al., J. appl. Physiol. 44, 474–478, 1978) had led to an overestimation of the COP change from the exposure of whole blood to CO 2 in vitro.

Correlation between measured and calculated colloid osmotic pressure

We examined the relationship between measured colloid osmotic pressure (COP), and COP calculated from serum total protein concentration (TP). Serum COP and TP were measured in 40 patients with severe abdominal sepsis. Measured COP values were not significantly different from values calculated using three separate formulas. The correlation rate between measured COP and TP (r = .83, p less than .01) was lower than that between calculated COP and TP (r = .99, p less than .01). All three formulas were fairly reliable. Alternatively, a table of predicted COP values may be useful in severely ill patients.

An alternate method for estimating efferent arteriolar plasma colloid osmotic pressure.

The colloid osmotic pressure (COP) of efferent arteriolar plasma in glomerular dynamic studies generally is estimated from the measured protein concentration (CE) while the nephron filtration fraction (SNFF) is derived from CE and the systemic plasma protein concentration (CA) according to the equation SNFF = (1 - CA/CE). Estimates of both SNFF and COPE are quite sensitive to small errors in protein measurement, however, with a putative coefficient of variation of +/- 5% in protein measurement at a typical SNFF of 0.33, for example, providing an uncertainty (i.e., +/- SD) of +/- 14% in the SNFF estimate and +/- 2.4 mmHg in the estimated COPE value. In this study, we evaluated in vitro the precision with which the COP of plasma samples can be estimated after ultrafiltration by coupling direct oncometry of native plasma with isotopically measured filtration fractions derived employing nanoliter and microliter volumes and applying a modification of the equation of Ladegaard-Pedersen (Scand. J. Clin. Lab. Invest. 23: 153-158, 1969). The measured and estimated oncotic pressures were then compared. The mean differences between theoretic and measured COP values at filtration fractions of less than 0.1, 0.1-0.2, 0.2-0.3 and greater were: -0.4 +/- 0.8 (SE) (n = 22); 1.8 +/- 1.1; 3.9 +/- 1.0; and 6.0 +/- 1.7%, respectively. It is concluded that the coupling of direct oncometric measurement of arterial plasma colloid osmotic pressure with isotopically determined filtration fractions provides a satisfactory estimate of COPE that is suitable for studies of glomerular dynamics.

Hemodynamic and colloid osmotic pressure alterations in the surgical patient

Colloid osmotic pressure (COP) was measured simultaneously with cardiorespiratory measurements in 103 surgical patients suspected of having circulatory problems. In a small subset of 28 patients, measurements were taken before, during, and after surgical operations. Similarly, data sets were taken before, during, and after infusions of colloids and crystalloids to assess the interactions of these variables during the stress of surgery and the administration of fluid therapy. COP was found to decrease during and shortly after surgical operations despite reasonably well-maintained pressure, volume, and flow variables. Concentrated (25%) albumin and plasma protein fraction (PPF) increased COP, cardiac index (CI), CVP, pulmonary capillary wedge pressure (WP), and blood volume, whereas crystalloids transiently increased CI, CVP, and WP but did not significantly change COP and blood volume. Low COP values were weakly related to survival, and COP-WP differences less than or equal to 3 mm Hg were roughly related to ARDS and pulmonary edema.

Albumin Infusion Does not Alter the Intervillous Blood Flow in Severe Pre‐Eclampsia

Intervillous blood flow (IVBF) was measured by the 133Xe intravenous method before and after a 100 ml infusion of 20% human albumin in 13 cases of severe pre-eclampsia. In spite of the significant increase in serum albumin and colloid osmotic pressure values, no parallel direction of change in IVBF values could be seen to result from the immediate effects of volume expansion therapy. The results suggest that the use of albumin infusion is of no specific value in the treatment of severe pre-eclampsia in terms of evaluation at the level of placental circulation. The observation of an increase in placental blood flow in cases of real hypoalbuminemia calls for a further elucidation.

Colloid osmotic pressure changes during hypertensive pregnancy.

Colloid osmotic pressure (COP) was measured in maternal serum of normal and hypertensive gravidae, and in their amniotic fluid. Both normal and hypertensive gravidae in the third trimester at bed rest and those treated for hypertension have low COP. Likewise, postpartum women may have low serum COP values apparently unrelated to any disease process. Amniotic fluid COP is low in both normal and hypertensive gravidae. COP Measurements therefore, seemingly offers little information regarding the health of pregnant women. Serum COP may increase in some hypertensive gravidae receiving saline infusion, probably reflecting abnormal renal function and hypovolemia. High serum triglyceride values coexisting with low COP may represent hepatic efforts to produce other colloid osmotic-active substances in the semi-chronic situation, although our findings in the acute situation did not support this hypothesis.

Colloid Osmotic Pressure in Newborn Infants: Variations with Birth Weight, Gestational Age, Total Serum Solids, and Mean Arterial Pressure

Colloid osmotic pressure (COP) of blood was measured directly at birth with the Wescor membrane colloid osmometer (model 4100) in 91 appropriately grown, 11 large, and nine small for gestational age "well" newborn infants. COP correlated directly with birth weight (r = .726, P less than .00001) and gestational age (r = .753, P less than .00001). COP values for small for gestational age (SGA) and large for gestational age (LGA) infants were found to fall within the 95% prediction interval with regard to birth weight and gestational age for appropriate for gestational age (AGA) infants. Simultaneous measurements of COP, total serum solids, and central arterial mean blood pressure were made. The results showed that COP correlated directly with total serum solids (r = .89, P less than .0001) and mean arterial blood pressure (r = .660, P less than .001). Among the factors evaluated, total serum solids was the best predictor of COP.

Colloid osmotic pressure of normal newborns and premature infants.

Colloid osmotic pressure (COP) is an important regulator of fluid movement and can now be measured simply and reliably. The authors used the 4100 Wescor Colloid Osmometer to define COP values and its relation to total protein concentration (TP) in different groups of newborns. The mean COP was 19.4 +/- 2.2 (SD) torr in 99 term infants delivered vaginally and 16.0 +/- 2.1 in 40 term infants delivered by cesarean section (p less than 0.005). The COP was lower in those born operatively without preceding labor (14.9 +/- 1.8). COP correlated well with TP (r = 0.92) in term infants. In 60 sick preterm infants with 362 determinations, COP (12.5 +/- 2.5) was different from term infants (p less than 0.001) and the correlation with TP was poor (r = 0.64). Different therapeutic modalities were found to affect COP widely. Crystalloid infusion decreased COP by 22% and surgery by 32%. The authors conclude that COP varies not only with gestational age but also with mode of delivery and experience of labor. In critically ill preterm neonates, because estimations form TP are inadequate, the only way to obtain a quantitative measure of COP is by direct measurement. Repeated measurements of COP will permit precise selection of the fluids and will warn of changes that may lead to pulmonary edema.

1434 COLLOID OSMOTIC PRESSURE OF NORMAL NEWBORNS AND PREMATURE INFANTS

Colloid osmotic pressure (COP) is an important regulator of fluid movement and can now be measured simply and reliably. We used the 4100 Wescor Colloid Osmometer to define COP values and its relation to total protein concentration (TP) in different groups of newborns. The mean COP (torr ± S.D.) was 19.38 ± 2.17 in 99 term infants delivered vaginally and 16.0 ± 2.07 in 40 term infants delivered by cesarean section (p<0.005). The lowest COP (14.9 ± 1.8) was in those born operatively without preceding labor. COP correlated well with TP (r=0.92) in term infants. In 60 sick preterm infants with 362 determinations, COP (12.46 ± 2.45) was different from term infants (p<0.001) and the correlation with TP was poor (r=0.64). Different therapeutic modalities affected COP widely. Crystalloid infusion (10-20cc/kg) decreased COP by 22% and surgery by 32%. COP increased 63% after exchange transfusion, 23% after infusion of plasma (10-20cc/kg) and 15% one hour after Furosemide administration.We conclude that COP varies not only with gestational age but also with mode of delivery, experience of labor and therapy. In critically ill preterm neonates, since estimations from TP are inadequate, the only way to obtain a quantitative measure of COP is by direct measurement. Repeated COP measurements will permit precise selection of fluid therapy and warn of changes that may lead to pulmonary edema.

Albumin/Globulin Ratios, Colloid Osmotic Pressures and Lowry Protein Microanalysis in Rat Plasma

1. We have correlated measurements of colloid osmotic pressure with protein concentrations and albumin/globulin ratios. Plasma from normal rats of different genetic strains was used. 2. The Landis and Pappenheimer equation does not accurately predict colloid osmotic pressure properties of the normal rat plasma used, which had an albumin/globulin ratio of 0.74. Over the range 2.2−12.2 g of protein/100 ml, the measured colloid osmotic pressures vary between −5% and +10% from the value predicted by the equation. 3. In Wistar-derived genetically hypertensive and normotensive rats, albumin/globulin ratios were higher than those in common Wistar rats. Owing to the presence of higher globulins, plasma proteins were higher in Wistar than spontaneously hypertensive and normotensive rats, and colloid osmotic pressure was identical in the three groups. 4. When common Sprague—Dawley rats were obtained from two different suppliers, their albumin/globulin ratios were found to be different. 5. As the difference in albumin/globulin ratio between human and rat plasma becomes more pronounced, predicting rat plasma colloid osmotic pressure from the Landis and Pappenheimer equation becomes less accurate. Environmental and/or genetic factors play a role in the albumin/globulin ratio found in normal healthy rats. 6. Therefore albumin/globulin ratios should be measured in each experimental situation. If the ratios are close to that of human plasma, the Landis and Pappenheimer equation can be used. If not, a new colloid osmotic pressure-protein expression should be derived. 7. Calculation of glomerular capillary pressures from directly measured colloid osmotic pressure values reduces error.

PLASMA BIOCHEMISTRY IN RELATION TO OEDEMA OF PREGNANCY

SummaryBiochemical changes were measured serially throughout pregnancy in 83 women. The fall in total osmolality observed was unrelated to the development of oedema and there was little change in the levels of major electrolytes and urea with pregnancy. Decreased colloid osmotic pressure values were found, and they closely followed the changes in both total protein and serum albumin values. The degree of fall of these values appeared to be more important in the genesis of oedema than the absolute level reached. Changes in haematological indices were unrelated to the presence of oedema but a change in red cell fragility was found which appeared to be related to variations in colloid osmotic pressure. This change seemed to be of physiological rather than pathological significance.