Initial plasma disappearance and distribution volume of [131I]albumin and [125I]fibrinogen in man

Errors of measurement for blood volume parameters: a meta-analysis

The volume of red blood cells (V(RBC)) is used routinely in the diagnostic workup of polycythemia, in assessing the efficacy of erythropoietin administration, and to study factors affecting oxygen transport. However, errors of various methods of measurement of V(RBC) and related parameters are not well characterized. We meta-analyzed 346 estimates of error of measurement of V(RBC) for techniques based on Evans blue (V(RBC,Evans)), 51chromium-labeled red blood cells (V(RBC,51Cr)), and carbon monoxide (CO) rebreathing (V(RBC,CO)), as well as hemoglobin mass with the carbon-monoxide method (M(Hb,CO)), in athletes and active and inactive subjects undergoing various experimental and control treatments lasting minutes to months. Subject characteristics and experimental treatments had little effect on error of measurement, but measures with the smallest error showed some increase in error with increasing time between trials. Adjusted to 1 day between trials and expressed as coefficients of variation, mean errors for M(Hb,CO) (2.2%; 90% confidence interval 1.4-3.5%) and V(RBC,51Cr) (2.8%; 2.4-3.2%) were much less than those for V(RBC,Evans) (6.7%; 4.9-9.4%) and V(RBC,CO) (6.7%; 3.4-14%). Most of the error of V(RBC,Evans) was due to error in measurement of volume of plasma via Evans blue dye (6.0%; 4.5-7.8%), which is the basis of V(RBC,Evans). Most of the error in V(RBC,CO) was due to estimates from laboratories with a relatively large error in M(Hb,CO), the basis of V(RBC,CO). V(RBC,51Cr) and M(Hb,CO) are the best measures for research on blood-related changes in oxygen transport. With care, V(RBC,Evans) is suitable for clinical applications of blood-volume measurement.

On the active vascular absorption of plasma proteins from tissue: rethinking the role of the lymphatic system

According to Starling's hypothesis, the osmotic pressure of plasma proteins in the capillary is the principal force for fluid absorption. The leakage of plasma proteins from capillaries to tissue during 24 h accounts for the total amount of plasma proteins in the vascular system. The same amount must therefore be reabsorbed by the lymphatic system, which is considered to be the sole absorber of proteins from tissue. However, it is a well-established routine in all kinds of organ transplantation to not restore the lymphatic system of the transplant. Experience has shown that this reconstruction is unnecessary, which consequently implies that the lymphatics are not of crucial importance for the survival of the organ. Inevitably, we must therefore question the vital role that the lymphatic system has been attributed in maintaining homeostasis as the sole absorber of proteins. Instead, it is proposed that the major part of plasma proteins in tissue is actively absorbed by the capillaries.

Clinical evaluation of circulating blood volume in critically ill patients--contribution of a clinical scoring system

The circulating blood volume (CBV) of critically ill patients may be difficult to estimate on the basis of history and physical examination. The aim of this study was to evaluate the ability of seven clinical signs and central venous pressure (CVP) to predict CBV in critically ill patients; CBV was evaluated with the [125I]human serum albumin technique. A scoring system was constructed using a combination of independence Bayes method and logistic regression. Sixty-eight patients constituted a 'model development' sample and 30 patients a validation sample. Thirty-six patients (53%) in the model development sample were found to have a low CBV (measured CBV at least 10% lower than the predicted mean normal CBV). Neither the haemodynamic variables monitored in ICU, nor the spot urinary sodium concentrations were different between patients with and without a low CBV. Individually, none of the clinical signs tested have a good positive or negative predictive value. For CVP, only extreme values seem to have clinical significance. To construct the score, the signs tested were ranked according to their discriminating efficacy. The probability of a low CBV was obtained by adding the weights of each sign tested and converting the score obtained into a probability. On a validation sample of 30 patients, the predictions are reliable as assessed by Z statistics ranging between -2 and +2. Our results suggest that: (1) individually, no clinical sign presented a clinical useful predictive value; and (2) a clinical scoring system may be helpful for the evaluation of CBV in critically ill patients.

Changes in circulating blood volume after infusion of hydroxyethyl starch 6% in critically ill patients

BACKGROUND

The cardiovascular response to a volume challenge with hydroxyethyl starch (HES) (200/0.5) 6% depends on the relation between the volume of HES 6% infused and the expansion of the blood volume in critically ill patients. However, only relatively limited data exist on the plasma expanding effect of infusion of HES 6% in critically ill patients. The purpose of the study was to evaluate the variation in the expansion of the circulating blood volume (CBV) in critically ill patients after infusion of 500 ml of colloid (HES (200/0.5) 6%) using the carbon monoxide method.

METHODS

In 20 consecutive patients admitted to the ICU requiring mechanical ventilation and volume expansion, 500 ml of HES (200/0.5) 6% was infused. The CBV was measured immediately before the infusion, 10 min after completing the infusion and then hourly for 8 h.

RESULTS

The median volume expansion immediately after infusion was 470 ml (range 270 ml to 840 ml). The corresponding values after 4 h and 8 h were 265 ml (range -30 ml to 460 ml) and 120 ml (range -210 ml to 360 ml), respectively. The increase in CBV was only statistically significant for 4 h. The coefficient of variation of the method for estimation of CBV was 3.6%.

CONCLUSIONS

The large interindividual variation of the volume expansion after infusion of HES 6% in critically ill patients illustrates one of the difficulties in optimizing colloid therapy and interpretating the changes in hemodynamic variables after a colloid challenge.

Urinary albumin excretion and transcapillary escape rate of albumin in malignancies

Transcapillary escape rate of albumin was determined in 22 patients with different malignancies. In addition, urinary albumin excretion rate was measured in 24-h urine samples using a sensitive immunoassay. Increased urinary albumin excretion was defined as >/=20 microg/min according to conventional standards. Renal glomerular filtration and tubular function was estimated by 51Cr-EDTA plasma clearance and urinary beta 2-microglobulin, respectively. Median urinary albumin excretion rate was 15.0 microg/min (range 6-510 microg/min) and the frequency of increased urinary albumin excretion was 41%. This agrees with other studies showing increased albuminuria in several types of malignant diseases. Patients with advanced disease (tumour, node, metastasis (TNM) stage II-IV) had a significantly higher urinary albumin excretion rate than patients with localized disease (TNM stage I). Serum creatinine, glomerular filtration rate and urinary beta 2-microglobulin were all within normal limits. Median transcapillary escape rate of albumin was 5.5 %/h (range 2-8 %/h) and this level is comparable with values in healthy subjects. There was no significant difference in transcapillary escape rate between patients with elevated urinary albumin excretion and the normoalbuminuric group. Median value of the absolut outflux of albumin was 10.6 g/h with similar levels in patients with increased urinary albumin excretion and patients with normoalbuminuria. Our results indicate a high prevalence of minor glomerular dysfunction with a slightly elevated urinary albumin excretion in patients with malignancies. The normal endothelial function, as estimated by the transcapillary escape rate of albumin, suggests an overall unaffected capillary permeability and increased urinary albumin loss appears to be an isolated renal phenomenon in cancer patients.

Blood volume determination by the carbon monoxide method using a new delivery system: accuracy in critically ill humans and precision in an animal model

OBJECTIVE

To evaluate accuracy and repeatability of blood volume determinations made by the carbon monoxide method, using a ventilator-driven administration system.

DESIGN

Prospective within-patient comparison, using simultaneous measurements by two methods to determine accuracy. Prospective laboratory investigation in animals to estimate repeatability.

SUBJECTS

For accuracy: Nineteen ventilated critically ill patients in a university hospital intensive care unit. For repeatability: Six anesthetized, mechanically ventilated normovolemic pigs because this is impossible to perform in humans.

INTERVENTIONS

In the accuracy study, a small mass of carbon monoxide was administered via a closed breathing system and arterial blood samples were taken from existing cannulas. In the repeatability study, an intramuscular sedative was given, followed by an inhalational anesthetic induction and mechanical ventilation via a tracheal tube. Left axillary artery and external jugular vein cannulas were sited. Anesthesia was maintained using an intravenous infusion. Five sequential circulating hemoglobin and blood volume estimations were made using the carbon monoxide method.

MEASUREMENTS AND MAIN RESULTS

The small carboxyhemoglobin increase produced by uptake of a small, known mass of carbon monoxide was used to estimate the circulating blood volume. Simultaneous measurement, using 51Cr-labeled red blood cells, was performed. Twenty measurements were made in 19 patients. The bias (mean difference between blood volume measurements by the two methods) was 397 mL (5.53 mL x kg(-1)) +/-415 mL (+/-5.95 mL x kg(-1)); the limits of agreement (mean difference +/-2 SD) were -433 mL and 1227 mL (-6.36 mL x kg(-1) and 17.42 mL x kg(-1)). Therefore, 95% of expected differences will lie between these limits. The mean blood volume was 75.8 mL x kg(-1) in the animals. The coefficient of variation of repeated estimates was 9.49%. Mean circulating hemoglobin mass was 7.31 mmol with a coefficient of variation of 10.18%. The mean hemoglobin concentration, by co-oximetry, was 5.014 mmol x L(-1), coefficient of variation, 2.99%.

CONCLUSION

This arrangement is a potential bedside method of estimating blood volume and circulating hemoglobin mass. We have rendered the technique more acceptable clinically by creating a ventilator-driven administration system.

A critique of the overfill hypothesis of sodium and water retention in the nephrotic syndrome

Recent reviews have claimed that the majority of patients with the nephrotic syndrome have plasma volume expansion (that is, they are overfilled). Here we attempt to re-establish balance to the debate on body fluid volume status in nephrotic patients by: (a) discussing the conflicting literature on plasma volume measurements in the nephrotic syndrome; (b) providing alternate explanations for data purporting to support an overfill hypothesis in the nephrotic syndrome; (c) emphasizing secondary neurohumoral responses that support underfilling at least as frequently as overfilling; and (d) emphasizing the clinical importance of fluid assessment in the individual patient with the nephrotic syndrome particularly in relation to diuretic use.

Transcapillary escape rate of albumin in humans during exercise-induced hypervolemia

To test the hypotheses that plasma volume (PV) expansion 24 h after intense exercise is associated with reduced transcapillary escape rate of albumin (TERalb) and that local changes in transcapillary forces in the previously active tissues favor retention of protein in the vascular space, we measured PV, TERalb, plasma colloid osmotic pressure (COPp), interstitial fluid hydrostatic pressure (Pi), and colloid osmotic pressure in leg muscle and skin and capillary filtration coefficient (CFC) in the arm and leg in seven men and women before and 24 h after intense upright cycle ergometer exercise. Exercise expanded PV by 6.4% at 24 h (43.9 +/- 0.8 to 46.8 +/- 1.2 ml/kg, P < 0.05) and decreased total protein concentration (6.5 +/- 0.1 to 6.3 +/- 0.1 g/dl, P < 0.05) and COPp (26.1 +/- 0.8 to 24.3 +/- 0.9 mmHg, P < 0.05), although plasma albumin concentration was unchanged. TERalb tended to decline (8.4 +/- 0.5 to 6.5 +/- 0.7%/h, P = 0.11) and was correlated with the increase in PV (r = -0.69, P < 0.05). CFC increased in the leg (3.2 +/- 0.2 to 4.3 +/- 0.5 microl . 100 g-1 . min-1 . mmHg-1, P < 0. 05), and Pi showed a trend to increase in the leg muscle (2.8 +/- 0. 7 to 3.8 +/- 0.3 mmHg, P = 0.08). These data demonstrate that TERalb is associated with PV regulation and that local transcapillary forces in the leg muscle may favor retention of albumin in the vascular space after exercise.

Blood volume determination using hydroxyethyl starch: a rapid and simple intravenous injection method

OBJECTIVE

To develop and evaluate a new method for blood volume measurements using hydroxyethyl starch as a dilution marker.

DESIGN

Laboratory and clinical investigation.

SETTING

Neurosurgical operating rooms and anesthesiological laboratories of a university hospital.

PATIENTS

Twelve patients who underwent a neurosurgical operation.

INTERVENTIONS

Anesthesia and operations were carried out by physicians who were not involved in the study. In addition, blood samples were drawn from 50 volunteers.

MEASUREMENTS AND MAIN RESULTS

Blood volume measurements by the hydroxyethyl starch method were validated in vivo by comparison with a conventional carbon monoxide technique. Patients were intravenously injected with hydroxyethyl starch (100 mL) and received simultaneously an injection of carbon monoxide (50 mL) into a closed-circuit ventilation system. Blood samples obtained before and 5 mins after injection were analyzed for carboxyhemoglobin and glucose plasma concentrations after acidic hydrolysis of hydroxyethyl starch. Blood volume was calculated from the difference between glucose concentrations measured after hydrolysis in the plasma, before and after the addition of hydroxyethyl starch. In vitro, the hydroxyethyl starch method had an error and a precision of approximately 2%. In vivo, simultaneous measurements of blood volume using hydroxyethyl starch and carbon monoxide demonstrated a high correlation (r2 = .96, p < .001) between these methods. The mean difference between the two methods relative to their average value was 1.0 +/- 3.5%; the bias was 52.3 mL, and the 95% confidence interval was -64.0 to +168.7 mL.

CONCLUSIONS

Blood volume determination by the hydroxyethyl starch method is accurate and rapid and may enhance perioperative monitoring of fluid and blood therapy.

Effects of preoperative intentional hemodilution on the extravasation rate of albumin and fluid

OBJECTIVE

To evaluate the effects of preoperative intentional hemodilution with 4% albumin solution on the extravasation rate of intravascular albumin and fluid in surgical patients.

DESIGN

A prospective, randomized, clinical study.

SETTING

University teaching hospital.

PATIENTS

Two groups (control group [group 1] and hemodiluted group [group 2]) of 13 healthy patients were studied during a long-term (>4 hrs) surgical procedure.

INTERVENTIONS

Autologous technetium-99m (99mTc)-labeled red blood cells and indium-oxine ((111)In)-labeled human serum albumin were injected intravenously during anesthesia at T = 0 min in the two groups for the determination of total blood volume and albumin diffusion space, respectively. In addition, body tetrapolar electrical impedance was used to assess extracellular fluid volume. In the hemodiluted group (group 2), 15 mL/kg of blood was withdrawn over 30 mins (T = 20 mins to T = 50 mins) and simultaneously replaced by an equal volume of 4% albumin solution (0.6 g/kg).

MEASUREMENTS AND MAIN RESULTS

The albumin diffusion space, the colloid oncotic pressure, the plasma albumin concentration and the electrical impedance were measured before (T = 10 mins) and after (T = 60, 120, and 240 mins) hemodilution. Urine was collected from T = 10 mins to T = 240 mins. The total blood volume was calculated at T = 10 mins. No differences in the initial values were found between the two groups. In group 2, hemodilution (hematocrit 30 +/- 3%) resulted in a steeper increase in the albumin diffusion space (p < .05) and a progressive decrease in the body electrical impedance (p < .05). The extravasation rate of albumin was 0.052 +/- 0.007 mL/kg/min in group 2 vs. 0.038 +/- 0.020 mL/kg/min in group 1 (p < .05). The value of calculated plasma volume at T = 0 min did not shown any difference between the two groups. This value was then lower than expected in group 2, corresponding to a loss of plasma volume of >3 mL/kg. Urine output was significantly lower in group 2 than in group 1 (0.7 +/- 0.4 vs. 1.4 +/- 1.0 mL/min, respectively; p < .05). A comparable decrease in colloid oncotic pressure and in plasma albumin concentration was observed in both groups.

CONCLUSIONS

These results suggest that preoperative hemodilution using 4% albumin on a 1:1 volume basis for blood substitution during a prolonged surgical procedure with reduced blood losses enhances the extravasation rate of albumin and fluid to the interstitial tissues, impeding the maintenance of isovolemia. These findings support the use of a volume of infused colloid solution higher than that of withdrawn blood during preoperative hemodilution.

Whole-body hyperhydration in endurance-trained males determined using radionuclide dilution

Despite evidence of hypervolemia following endurance training, there is little information regarding corresponding extravascular fluid volumes. Quantification of such volumes relies upon radionuclide dilution methods, previously hampered by the loss of plasma albumin. It was our purpose to measure human body-fluid distribution in eight endurance-trained males, using a simultaneous radionuclide dilution technique, incorporating radioiodinated serum fibronogen (RISF). Fluid distribution was measured on three occasions, using 2 microCi of RISF, 8 microCi of 51 Cr-labeled erythrocytes, and 20 microCi of Na82Br and 450 microCi of 3H2O; to measure PV, erythrocyte (RCV), extracellular (ECFV), and total-body water (TBW) volumes, respectively. Respective volume means, standard deviations, and coefficients of variation were: 46.6 (+/- 4.9; 8.44%), 33.3 (+/- 2.9; 3.89%), 258.1 (+/- 12.1; 4.93%), and 654.2 (+/- 13.4; 3.24%) ml.kg-1. The incorporation of RISF provided a reliable modification to previous methods, and revealed a body-fluid expansion in endurance-trained males. It was concluded that such subjects were hyperhydrated, possessing proportionately expanded fluid volumes throughout both intravascular and extravascular spaces. This was attributed to training history and accompanying reductions in adiposity.

Changes in plasma ionized calcium and magnesium in blood donors after donation of 450 mL blood. Effects of hemodilution and Donnan equilibrium

The plasma concentration of ionized calcium and ionized magnesium in 26 blood donors decreased 0.01 mmol/L during blood donation. The changes could be explained by admixture of interstitial fluid. About 162 mL or 36% of the donated blood was replaced by interstitial fluid during blood donation. From the changes in concentration and hematocrit we could estimate the composition of the added fluid. The concentration of protein was much lower than in plasma. The concentration of protein-bound and free cations was also lower, in accord with the Donnan theory. We conclude that blood donors immediately after blood donation are unsuited as a reference population for proteins and ions.

Discrepancies in pharmacokinetic parameter estimation between bolus and infusion studies in the perfused rat hindlimb

Isolated, perfused rat hindlimb consists of skeletal muscle, skin, bone, and adipose. Hence, it is a heterogeneous preparation composed of slowly equilibrating tissues of different characteristics and fractional flow rates. This paper shows how caution should be exercised in interpreting the results following bolus administration and subsequent statistical moment analysis of intravascular markers (51Cr-erythrocytes and 125I-albumin) and lipophilic barbiturates. For the intravascular markers, the events in the hindlimb are overshadowed by events in the connecting tubing and cannulas, due to their comparable volumes. For the barbiturates, these estimates appear to apply to short-term effects as the volume estimates obtained following infusion to steady state are greater than after bolus administration. For the extravascular markers, 14C-sucrose, 14C-urea, and 3H-water, no such time dependency was shown. However, it is only from the outflow profiles following bolus administration that events in the tissue beds can be elucidated.

Precision of a new bedside method for estimation of the circulating blood volume

The present study is a theoretical and experimental evaluation of a modification of the carbon monoxide method for estimation of the circulating blood volume (CBV) with respect to the precision of the method. The CBV was determined from measurements of the CO-saturation of hemoglobin before and after ventilation with a gas mixture containing 20-50 ml of CO for a period of 10-15 min. A special Water's to and fro system was designed in order to avoid any leakage when measuring during intermittent positive pressure ventilation (IPPV). Blood samples were taken before and immediately after ventilation with the CO gas mixture. The amount of CO administered during each determination of CBV resulted in an increase in the CO saturation of hemoglobin of 2.1%-3.9%. A theoretical noise propagation analysis was performed by means of the Monte Carlo method. The analysis showed that a CO dose corresponding to an increase of less than 2% will result in an unacceptable coefficient of variation of repeated estimates. In the experimental study the coefficient of variation of repeated estimates of CBV was determined from duplicate measurements of CBV in nine healthy subjects and in nine intensive care patients. The coefficients of variation were 6.2% and 4.7% in healthy and diseased subjects, respectively. Furthermore, the day-to-day variation of the method with respect to the total amount of circulating hemoglobin (nHb) and CBV was determined from duplicate estimates separated by 24-48 h. In conclusion, determination of CBV can be performed with an amount of CO that gives rise to a harmless increase in the carboxyhemoglobin concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in blood and plasma volume during treatment with recombinant human erythropoietin

18 chronic dialysis patients with renal anemia were examined before and after three months of regular treatment with recombinant human erythropoietin (EPO). All patients responded with an increase in hemoglobin concentration (cHb). The target cHb of 7.0 mmol/L was subsequently maintained by one subcutaneous injection a week, obviating the need of blood transfusions. The amount of circulating hemoglobin and the volume of erythrocytes increased, but the plasma volume simultaneously decreased, maintaining a constant blood volume. Although some of the individual blood volumes varied, the relation between circulating hemoglobin and the hemoglobin concentration still existed. We conclude that the hemoglobin concentration gives an accurate measure of the degree of anemia, and measurement of circulating hemoglobin is unnecessary during routine treatment of dialysis patients with EPO.

Initial plasma disappearance and tissue uptake of 131I-albumin in normal rabbits

The simultaneous plasma disappearance curves of 131I-albumin and 125I-fibrinogen were recorded in normal rabbits for 1 hr. Using fibrinogen as a plasma reference, the disappearance curves of albumin were shown to contain two separate phases of efflux: one fast from zero to 10 min. comprising 8% of the total tracer; and one slow appearing in the interval of 10 to 60 min. containing another 9% of the tracer. Total albumin escape was analyzed to yield an initial slope of 0.024 +/- 0.004 min-1, corresponding to a wholebody unidirectional albumin clearance (Cl(0)) of 0.090 +/- 0.009 ml(min*100 g)-1. The distribution of efflux was assessed by biopsy uptakes using the same tracers in spleen, kidney, heart, lung, liver, intestine, skin, muscle, and brain. The disappearance curve generally reflects a biphasic pattern of uptake in peripheral tissue, predominantly by muscle and lung. The rapid phase has contributions from the fast near equilibration of liver, and intestine and skin are significant codeterminants of the slow phase. Due to their low body masses highly perfused organs such as kidney, spleen, and heart have little influence on the plasma disappearance. In accordance, the Cl(0) determined for the wholebody was higher than initial clearances found in skin (0.053 ml(min*100 g)-1 and muscle (0.054 ml(min*100 g)-1), but much lower than those found in the highly perfused organs. The initial (unidirectional) rates of peripheral albumin transfer demonstrated, ranged from 10 to 30 times higher than estimates of lymphatic return, suggesting that transcapillary albumin exchange is mediated by high-rate bidirectional diffusion. The rapid decrease of net albumin exchange rates suggests a second, highly significant barrier located within the interstitial matrix, which restricts plasma escape and reduces plasma to lymph albumin transport.

Blood and plasma volumes determined by carbon monoxide gas, 99mTc-labelled erythrocytes, 125I-albumin and the T 1824 technique

The total amount of circulating haemoglobin was measured in 12 subjects using a direct carbon monoxide (CO)-technique. O2 plus 50 ml CO gas was rebreathed in a small closed system for 10 min. Carboxyhaemoglobin (HbCO)% was measured with a diode-array spectrophotometer before and after the rebreathing. delta HBCO% and the amount of CO in moles (nCO) were used to calculate the total amount of circulating haemoglobin. Blood volume was calculated by dividing this figure with the haemoglobin concentration and plasma volume by multiplying the blood volume with 1-haematocrit. The calculated blood and plasma volumes were compared with the simultaneously measured volumes by 99mTc-labelled erythrocytes, 125I-albumin and T 1824 (Evans Blue). Mean blood volume determined with CO was 4557 ml (3251-6576 ml) compared with 4527 ml (3390-6527 ml) with 99mTc-labelled erythrocytes (r = 0.97). Mean plasma volume by T 1824 was 2895 ml (1972-3658 ml) vs 2898 ml (1815-3714) ml using 125I-albumin, (r = 0.99). The plasma volumes calculated from the blood volumes determined by the erythrocyte-labelling methods were 5-10% lower than those measured with labelled albumin. There was a better correlation between the plasma volumes by the albumin methods and by the CO-technique (r = 0.98 and r = 0.97, respectively) than between the plasma volumes by the albumin methods and by 99mTc-erythrocytes (r = 0.90 and r = 0.87, respectively).

Tissue to plasma capillary permeability of 131I-albumin in the perfused rabbit ear

The tissue to plasma transfer of 131I-albumin was recorded in perfused rabbit ears (n = 6) following equilibration for 24 hr. 125I-fibrinogen served as the plasma marker, and was introduced intravenously 15 min before clamping. The ears were rollerpump perfused with isotonic diluted plasma at a constant rate of (mean +/- SD) 5.1 +/- 1.5 ml (min.100 g)-1. The mean extravascular albumin distribution volume was 12.4 +/- 1.1 ml.100 g-1, and the fibrinogen volume (plasma volume in tissue) was 3.1 +/- 0.4 ml.100 g-1 as determined from biopsies of the contralateral ear. The initial transfer of albumin was marked, and occurred at rates corresponding to a unidirectional clearance (Cl(0)) of 0.068 +/- 0.012 ml (min.100 g)-1. However, with a reduction of mean interstitial albumin tracer content of no more than 4%, net transport decreased to reach slowly declining levels 5 to 10 times lower within 10 min of continued perfusion. The decrease was considered due to rapid exhaustion of a small interstitial pool of tracer immediately adjacent to the exchange vessel membrane, followed by an increasingly retarded outwash from more distant areas. The results suggest a bimodal structural resistance to albumin movement: a relatively low resistance in the capillary membrane, and a considerable restriction to albumin transport located within the interstitial space.

pH effect on the COHb absorption spectrum: importance for calibration of the OSM3 and measurement of circulating hemoglobin and blood volume

An easy method to measure blood volume is clinically needed. We used carbon monoxide (CO) and the OSM3 to measure circulating hemoglobin and blood volume with the indicator dilution principle. 50 mL of CO was administered into a closed rebreathing system and taken up via the lungs, and the amount of hemoglobin in the blood was calculated from the increase in carboxyhemoglobin fraction after 10 min. Blood volume was calculated by division with the concentration of hemoglobin. We observed that the absorption spectrum of carboxyhemoglobin (COHb) depends on pH and pCO2, which must be controlled when very accurate spectrophotometry is necessary. The bias is 3% COHb per pH unit during calibration of the OSM3, which may be permissible for patients with CO poisoning, but not for the present purpose. With this in mind the method is very accurate, precise and simple.