Colloid Osmotic Pressure: Theoretical Aspects and Background

BackgroundThe plasma colloid osmotic pressure (COP) plays a major role in transcapillary fluid balance. There is no information on plasma COP of healthy infants beyond the first post-natal week. The normal COP in healthy adult subjects (25 mmHg) is currently also applied as a reference value for healthy infants. This study was designed to test whether plasma COP values in healthy infants are the same as those in normal adults.MethodsPlasma COP was measured in 37 male and female healthy infants from 1 to 11 months old. For this purpose, 1 ml blood was collected during the patient's regularly scheduled visit if the patient required any type of blood test for routine laboratory analyses.ResultsPlasma COP levels correlated slightly with increasing age from 1 to 9 months old (linear regression analysis; r2 = 0.1, P < 0.049). We found no correlation between plasma COP and body weight at the same age (r2 = 0.05, P = 0.155). The mean and standard deviation of COP in all infants was 25.1 ± 2.6 mmHg, which is almost identical to an average COP of 25 mmHg in healthy adult subjects. Arbitrary division of the infants into three different age groups (1–3 months [n = 11], 5–8 months [n = 13] and 9–11 months [n = 13]) showed an average increase of approximately 2 mmHg in COP of 9-month-old to 11-month-old infants, compared with 1-month-old to 3-month-old infants (one-way analysis of variance; P = 0.26). There was no gender difference in the COP level (unpaired t-test), with an average of 25.1 ± 2.4 mmHg in 19 male infants compared with 25.2 ± 2.9 in 18 female infants. The 95% confidence interval for COP in both male and female infants (n = 37) was between 24.3 to 26.0 mmHg, ranging from 19.5 to 30.3 mmHg, with a median value of 25.2 mmHg.ConclusionsThe data accept the null hypothesis that the COP range in infants younger than 1 year old is similar to those observed in adult subjects. Our observations, compared with previously reported neonatal COP values, suggest that there is a sharp increase in COP within the first months after birth.

ObjectiveThe colloid osmotic pressure (COP) of plasma and interstitial fluid play important roles in transvascular fluid exchange. COP values for monitoring fluid balance in healthy and sick children have not been established. This study set out to determine reference values of COP in healthy children.Materials and MethodsCOP in plasma and interstitial fluid harvested from nylon wicks was measured in 99 healthy children from 2 to 10 years of age. Nylon wicks were implanted subcutaneously in arm and leg while patients were sedated and intubated during a minor surgical procedure. COP was analyzed in a colloid osmometer designed for small fluid samples.ResultsThe mean plasma COP in all children was 25.6 ± 3.3 mmHg. Arbitrary division of children in four different age groups, showed no significant difference in plasma or interstitial fluid COP values for patients less than 8 years, whereas patients of 8-10 years had significant higher COP both in plasma and interstitial fluid. There were no gender difference or correlation between COP in interstitial fluid sampled from arm and leg and no significant effect on interstitial COP of gravity. Prolonged implantation time did not affect interstitial COP.ConclusionPlasma and interstitial COP in healthy children are comparable to adults and COP seems to increase with age in children. Knowledge of the interaction between colloid osmotic forces can be helpful in diseases associated with fluid imbalance and may be crucial in deciding different fluid treatment options.Trial RegistrationClinicalTrials.gov NCT01044641

Changes in colloid osmotic pressure as a function of anesthesia and surgery in the presence and absence of isotonic fluid administration in dogs

To compare perioperative trends in plasma colloid osmotic pressure (COP) between horses undergoing orthopedic and colic surgery. Prospective clinical study September 2009-January 2011. Veterinary university teaching hospital. Thirty-three healthy, client-owned horses presenting for orthopedic surgery (non-GI) and 85 client-owned horses presenting for emergency exploratory celiotomy (GI, gastrointestinal). None. Data relating to the horse's parameters on presentation, surgical lesion, post-operative management and survival were extracted from computerized clinical records. Heparinized blood samples were taken on presentation (PreOp, pre-operative), on recovery from anesthesia (T0), at 12 (T12) and 24 (T24) hours post recovery. COP was measured within 4 hours of collection. There was no significant difference in PreOp or T0 COP between groups. Both groups had a significant decrease in COP during anesthesia. When compared to their respective pre-operative values, horses in the non-GI group had significantly increased COP at T12, whereas those in the GI group had significantly reduced COP. This trend was continued at T24. Horses in the GI group placed on intravenous crystalloid isotonic fluids post-operatively had a significantly lower COP at T12 and T24. Horses in the GI group that did not survive had significantly lower post-operative COP values at T24. Horses undergoing exploratory celiotomy had significantly lower COP post-operatively than those horses undergoing orthopedic surgery. This difference was more marked in those horses receiving isotonic crystalloid intravenous fluid therapy post-operatively and in those that did not survive to discharge. In the non-GI group an increase in COP post-operatively was common.

Colloid osmotic pressure (COP) is a major determinant of fluid shift in paediatric patients undergoing corrective surgery for congenital heart disease (CHD) using cardiopulmonary bypass (CPB). However, very few baseline data are available for those patients requiring surgery within the first few weeks and months of life. Our aim was to determine if our CHD population exhibited COP similar to that of other extremely ill subsets of patients and, if so, whether this related to risk stratification model scores. Thirty consecutive patients under 10 kg underwent cardiac surgery with CPB. Data were collected on COP, albumin concentration, prime composition, post-operative length of ventilation and intensive care unit (ICU) stay as well as risk stratification utilising Risk Adjustment for Congenital Heart Surgery (RACHS-1) and Partial Risk Adjustment in Surgery (PRAiS) scoring systems. The patients had a mean pre-bypass COP of 13.9±2.5 mmHg. A significant negative correlation was observed between pre-operative baseline COP and length of ventilation (r=0.7; p<0.001) and a significant negative correlation between PRAiS (r=0.64; p<0.001) and RACHS-1 (r=0.5; p=0.004) scores and baseline COP was seen. Neonatal and paediatric patients requiring surgical correction of complex congenital cardiac malformations exhibit extremely low baseline COP, comparable to other sick neonatal populations, and are lower than those previously reported. Baseline COP correlates significantly with predicted survival rates and time spent on a ventilator.

Departments of Obstetrics and Gynecology and Anesthesia, University of Washington, and the Inland Empire Perinatal Center, Seattle and Spokane, WA

The albumin difference or gradient between serum ascites is presumed to be an effective estimate of the colloid osmotic pressure gradient, although this has never been directly demonstrated. The colloid osmotic pressure gradient is controlled by the degree of portal hypertension. Thus the albumin gradient is clinically useful in detecting patients with ascites caused by portal hypertension, although some overlap in such patients' albumin gradients exists compared with those of patients without portal hypertension. Part of this overlap is related to the inverse correlation of the albumin gradient with serum globulin; globulins also contribute to colloid osmotic pressure. The ability to calculate colloid osmotic pressure in serum and ascites with albumin and globulin concentration or to correct the albumin gradient for the impact of globulins might improve the clinical usefulness of the ascitic fluid analysis in determining the presence of portal hypertension in ascitic patients with borderline albumin gradients. Thus we developed equations to calculate colloid osmotic pressure from multivariate discriminate analyses of albumin and globulin concentrations in serial dilution samples of pooled serum and subsequently validated these equations, along with older methods of calculating colloid osmotic pressure. In an initial set of dilution experiments, globulin concentration was closely correlated with the colloid osmotic pressure to albumin concentration ratio (r = 0.956; p less than 0.001). Multivariate discriminate analysis yielded an equation for calculating colloid osmotic pressure from albumin (A) and globulin (G) concentration with a ratio of colloid osmotic pressure to albumin (calculated colloid osmotic pressure = A(1.058G + 0.163A + 3.11) and two other equations.(ABSTRACT TRUNCATED AT 250 WORDS)

BackgroundNaturally occurring gastrointestinal disease is an important cause of acute hypoproteinemia in adult horses and hydroxyethyl starch colloid fluid treatment is a component of supportive care in these cases to improve plasma volume and maintain colloid osmotic pressure (COP). The objectives of the present study were to compare 2 formulations of high molecular weight hydroxyethyl starch and their relative effect on COP, acid-base status, and survival of horses with acute hypoproteinemia secondary to gastrointestinal disease.MethodsTwenty adult horses, ≥ 1 year of age, were prospectively enrolled, with informed client consent, if they developed acute hypoproteinemia, defined as a plasma total protein <5.0 g/dL or albumin <2.2 g/dL during hospitalization while undergoing treatment for gastrointestinal disease. Horses were randomly assigned to receive a rapid infusion of either 6% hydroxyethyl starch in 0.9% saline or 6% hydroxyethyl starch in lactated ringers solution at a dose of 10ml/kg. Venous blood gas analysis, COP, and PCV were evaluated before and after colloid administration.ResultsFor both groups, average COP prior to treatment was 11.0 mmHg (9.7 – 12.2 mmHg) and post colloid treatment was 13.2 mmHg (12.0 -14.7 mmHg) [Normal range 18 – 22 mmHg]. COP was significantly increased with colloid treatment (p<0.001) but this increase was not significantly different between treatment groups. Venous pH did not change significantly with treatment. Twelve horses survived to hospital discharge and survival did not differ significantly between treatment groups.ConclusionsPost-treatment COP improved approximately 20% regardless of the formulation used, however, values did not reach the normal range of COP observed in healthy horses. Acid-base parameters were not significantly impacted by either treatment. Further study is needed to determine how these two products compare with regards to other outcome measures. Evaluation of the relative effects of colloid formulation in horses with clinical disease is a future area of interest.

Colloid osmotic pressure after hemorrhage and replenishment with Oxyglobin Solution, hetastarch, or whole blood in pregnant sheep

To evaluate the use of human albumin in critically ill dogs. Design-Retrospective case series. 73 client-owned hospitalized dogs. Medical records of dogs that received human albumin were reviewed to assess effects of the use of human albumin on serum albumin concentration, colloid osmotic pressure, and total protein concentration; determine the relationships between these variables and outcome; and assess its safety. Data for signalment, diagnoses, physiologic variables, dosage, amount of crystalloid fluid administered prior to human albumin administration, complications, and outcome were reviewed. Additionally, pre- and postadministration values for serum albumin, colloid osmotic pressure, and total protein were recorded. Administration of human albumin resulted in significant changes in serum albumin, colloid osmotic pressure, and total protein. The serum albumin, total protein, degree of improvement in serum albumin, colloid osmotic pressure, and dosage of human albumin were significantly greater in survivors. Seventeen of 73 (23%) dogs had at least 1 complication that could be potentially associated with the administration of human albumin that occurred during or immediately following administration of human albumin. Three of 73 (4%) dogs had severe delayed complications. Administration of human albumin significantly increased serum albumin, and total protein concentrations and colloid osmotic pressure, especially in survivors. Because of the high mortality rate of the study population and other confounding factors, it was uncertain whether complications were associated with the underlying disease or with human albumin administration. Acute and delayed complications may have been under-recognized.

Objective To investigate effects and its mechanisms of hypertonic saline hydroxyethyl starch 200/0.5 solution on intracranial pressure and brain water content in rats with ischemic cerebral edema. Methods All experiments were conducted in the animal experimental center of Sun Yat-sen University. The 28 male Sprague-Dawle (SD) rats were randomly (random number) divided into hypertonic saline hydroxyethyl starch group, hydroxyethyl starch group, control group and sham operation group, each n =7. Ischemic cerebral edema model was reproduced by middle cerebral artery occlusion(MCAO) , followed by reperfusion after ischemia for 2 hours (If the moldel was not successful, other rats were operated to fill the missing models) . Then reperfusion after ischemia 2 hours and received hypertonic saline hydroxyethyl starch and hydroxyethyl starch via tail vein at the beginning of reperfusion. The colloidal osmotic pressure (COP) and intracranial pressure (ICP) were evaluated on 0, 2, 6, 12, 18, 24 hours after the surgery. The water content of the right hemisphere was measured on 24 h after the surgery. Results The ICP of hypertonic saline hydroxyethyl starch group, hydroxyethyl starch group and control group were significantly higher than that of sham operation group on 2, 6, 12, 18, 24 h after the surgery. The ICP of hypertonic saline hydroxyethyl starch group was significantly lower than those of hydroxyethyl starch group and control group on 2, 6, 12, 18 and 24 h. But there was no significant difference in ICP of the hydroxyethyl starch group compared with that of control group at all time points. The COP of hypertonic saline hydroxyethyl starch group and hydroxyethyl starch group were significantly higher than the control group and sham operation group at each time point; There was no significant difference in COP (mmHg) of the hydroxyethyl starch group compared with that of hypertonic saline hydroxyethyl starch group at all time points. The brain water content (BWC) of hypertonic saline hydroxyethyl starch group, hydroxyethyl starch group and control group were significantly higher than that of sham operation group on 24 hours after the surgery [(81.24±0.36)%, (83.04±0.10)%, (83.14±0.41)% vs. (78.37±0.37)%, all P = 0.000], BWC of hypertonic saline hydroxyethyl starch group lower than these of hydroxyethyl starch group [(81.24 ±0.36)% vs. (83.04 ±0.10) %, P =0.000] and control group [(81.24 ±0.36)% vs. (83.14 ±0.41) %, P =0.000]. There was no significant difference in BWC of the hydroxyethyl starch group compared with that of control group [(83.04 ± 0.10)% vs. (83.14 ± 0.41) %, P =0.578]. Conclusion Hypertonic saline hydroxyethyl starch solution could significantly ameliorate ischemic cerebral edema and reduce ICP, but the relationship between its elevated COP and reduced ICP has not been confirmed. Key words: Hypertonic saline hydroxyethyl starch solution; Cerebral ischemia/reperfusion injury; Colloidal osmotic pressure; Intracranial pressure; Cerebral edema

BackgroundLower molecular weight and molar substitution formulations of hydroxyethyl starch (HES) solutions might maximize cardiovascular function and colloid osmotic pressure (COP) and minimize adverse effects on coagulation.Hypothesis/ObjectivesTo compare effects of 1 low and 1 high molecular weight and molar substitution HES solution on cardiovascular variables, COP, and hemostasis in normal horses.AnimalsEight healthy adult horses.MethodsRandomized, crossover designed study: 10 mL/kg bolus of 6% HES (600/0.75) (hetastarch) (HS), 6% HES (130/0.4) tetrastarch (TS), and 0.9% NaCl (NS). Variables recorded included central venous pressure (CVP), noninvasive arterial blood pressure, packed cell volume (PCV), COP, and automated platelet analysis (CT).ResultsCentral venous pressure was increased for 8 hours after all treatment (baseline = 8.4 ± 3.8; 8 hours = 10.3 ± 3.5 cm H2O; P < .001). HS and TS produced an increase in systolic arterial pressure (HS = 109.1 ± 11.9; TS = 109.5 ± 10.9 mmHg) and mean arterial pressure (HS = 80.4 ± 13.0; TS = 82.3 ± 10.1 mmHg) compared to NS (SAP = 103.2 ± 13.2 [P = .023]; MAP = 74.2 ± 11.4 mmHg [P = .048]). PCV decreased transiently with HS (baseline = 37.1 ± 4.4%; 1.5 hours = 31.6 ± 3.9%) and TS (baseline = 38.4 ± 3.9%; 1.5 hours = 32.2 ± 3.3%), but not NS (P = .007). COP was greater with HS (1 hour; 24.0 ± 2.1 mmHg) and TS (8 hours; 25.9 ± 2.1 mmHg) than NS (1 hour = 20.8 ± 2.6; 8 hours = 22.9 ± 3.1 mmHg; P < .001). CT was greater at 8 (HS = 178.6 ± 36.9; TS = 121.9 ± 33.3; NS = 108.3 ± 23.6 seconds) and 24 hours (HS = 174.2 ± 41.7; TS = 100.8 ± 26.0; NS = 118.7 ± 38.7 seconds; P < .001) in horses receiving HS than TS or NS.Conclusion and Clinical ImportanceBoth TS and HS resulted in more effective volume expansion and arterial pressure support than NS. TS produced a more sustained effect on COP with shorter duration of adverse effects on platelet function than HS.

The relationship between colloid osmotic pressure (COP) and the severity of cardiopulmonary failure was investigated in 99 consecutive patients admitted to our Shock Unit including 41 survivors and 58 fatal cases. The COP was significantly lower (p less than 0.001) in fatal cases in comparison to survivors. None of 21 patients in whom COP was less than 10.5 torr survived. A progressive increase in survival with typical S-shaped distribution was observed as COP increased from 10 to 19 torr, above which all patients survived. These preliminary observations demonstrated that reduction in COP in critically ill patients is associated with increases in mortality. The mechanisms by which lowering of COP may be related to fatal progression of cardiopulmonary failure is the subject of continuing study.

The mechanisms for stress-induced changes in hematocrit and blood viscosity are unclear. Twenty-two males completed experimental (30 min baseline, 10 min mental stress, 30 min recovery) and no-stress control conditions (70 min). Hemostatic and hemodynamic activity were measured throughout. Hematocrit, colloid osmotic pressure, and blood viscosity displayed parallel patterns: a progressive increase with stress, followed by a gradual recovery. Correlational and covariance analyses indicated that the increase in hematocrit may be mediated by arterial pressure whereas recovery may be mediated by colloid osmotic pressure. Analyses also indicated that acute changes in blood viscosity may depend on hematocrit. These data suggest that stress disturbs hematocrit, colloid osmotic pressure, and blood viscosity through arterial pressure. Poststress, elevated colloid osmotic pressure may drive its own recovery and that of hematocrit and blood viscosity.

The long-term effect of elevated tail venous pressure (Pv) on interstitial fluid pressure (Pi) and colloid osmotic pressure (COPi) was studied in rats. Measurements were performed on different rats after 1-5 days of congestion, and on a sham operated control group. Two different degrees of venous stasis were obtained by means of graded ligation of tail veins and skin. Moderate degree of ligation (group 1) caused no visual oedema. More extensive ligation (group 2) gave marked oedema already on day 1 and further progression and exudation from the skin during the following 3 days. Tail venous pressure was measured by micropuncture and interstitial fluid pressure by the wick-in-needle technique. Interstitial fluid was sampled by a dry wick method, and colloid osmotic pressure was measured with a membrane osmometer. In group 1, Pv had increased from 6.5 to 21.5 mmHg on day 1, and thereafter remained unchanged. Interstitial fluid pressure increased from 3.4 to 16.9 mmHg after ligation and to 19.2 mmHg on day 1. Colloid osmotic pressure fell from 11.7 to 5.8 mmHg. From day 1, both interstitial fluid pressure and colloid osmotic pressure remained largely unchanged. In group 2 rats, tail venous pressure increased to 33.0 and 36.3 mmHg on day 1 and 2 and then fell towards control level during the following 3 days. Interstitial fluid pressure increased to 22.9 and 31.4 mmHg before a rapid decline towards control level. Colloid osmotic pressure was reduced from 11.7 to 5.6 mmHg. We conclude that hydrostatic counterpressure may provide an oedema-preventing effect of up to about 15 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)