Continuous measurement of blood volume during hemodialysis by an optical method

Prevention of Hypovolemia-Induced Hypotension during Hemodialysis by Means of an Optical Reflection Method

In this study protocol we evaluate the clinical value of the continuous monitoring of blood volume (BV) during hemodialysis (HD) by means of an optical reflection method. In the course of a dialysis session the ratio between the ultrafiltration (UF) rate and the patient's refill capacity determines the extent of decrease of BV. A steep fall of BV and, moreover, a remaining absolute BV too low, cause the greater part of hemodialysis-induced complaints. During 23 standard HD sessions BV was monitored by means of the optical method. Nine of the sessions were complicated by hypotension (group H). Comparison of the mean BV graphs of group H with the graphs of non-complicated sessions (non-H) produces several differences. Most important is the fact that BV is better preserved in group non-H, a difference which is already significant during the first ninety minutes of dialysis. By making use of the shape of the monitored BV graph an HD patient, in that way, might be recognized as hypotension-prone during the first third of a dialysis session. To prevent the occurrence of hypovolemia-induced hypotension two strategies can be followed. First, the decrease of BV of a patient prone to hypotension can be triggered to the mean BV decrease according to the BV graph of the non-H group. This can be achieved by interventional methods, e.g. temporary lowering of the UF rate. However, for this intervention the development of a closed-loop circuit is required. Another possibility is to measure a patient's maximal refill capacity each hour of hemodialysis by taking advantage of the displayed BV graph. When the UF rate during ensuing sessions is kept in rate with the measured maximum values the occurrence of hypovolemia-induced hypotension will be minimized.

Influence of lipid emulsion for the hematocrit value measured with continuous hematocrit monitor

Continuous monitoring of hematocrit with a CRIT-LINE monitor (CLM) is used to prevent excess ultrafiltration during hemodialysis and continuous renal replacement therapy. The presence of substances affecting the scattering and absorption rates of multiple wavelengths of near infrared rays of CLM in the blood may affect the measured values with CLM. We examined the influences of lipid emulsion (LE) on hematocrit and relative blood volume (RBV) which were measured with CLM using an in vitro experimental model with human blood. Additions of 10% or 20% of LE increased the hematocrit measured by LCM and decreased the percent change of RBV in proportion to the dose. One percentage of 20% LE in the plasma increased the expected hematocrit measured with CLM by 2.9%. The decrease of initial hematocrit from 48.1% to 43.4% decreased the expected percent change of RBV from -3.4% to -3.7% with the addition of 1 ml of 20% LE to 100 ml blood. These findings indicate that additions of LE increase hematocrit that is measured with CLM in proportion to the dose of LE. Low levels of initial hematocrit will increase the degree of expected percent change of RBV. Attention should be paid to the influence of LE during monitoring with CLM.

Influence of Ultrafiltration Volume on Blood Volume Changes During Hemodialysis as Observed in Day-of-the-Week Analysis of Hemodialysis Sessions

Monitoring of relative blood volume changes (DeltaRBV) has been propagated for the prevention of hemodialysis hypotension. Although the influence of ultrafiltration volume on DeltaRBV is well-known, there is no mention in the literature that DeltaRBV results should be interpreted differently for the first, second, or third hemodialysis session of the week. To elucidate whether DeltaRBV and its derivative, DeltaRBV normalized for ultrafiltration volume (DeltaRBV/ultrafiltration ratio), vary systematically over the week, we separately analyzed these parameters for the first, second, and third hemodialysis session of the week in 13 chronic hemodialysis patients over a 17-week period. As expected, mean (+/-SD) ultrafiltration volume was significantly (p < 0.001) higher during the first session than during the second and third hemodialysis sessions (3163 +/- 615, 2622 +/- 674 and 2607 +/- 638 ml, respectively). DeltaRBV was significantly (p < 0.01) more negative at the first session than at the second and third hemodialysis sessions (-10.1 +/- 2.7, -9.3 +/- 3.0 and -9.3 +/- 3.1%, respectively). The DeltaRBV/ultrafiltration ratio was significantly (p < 0.01) less negative at the first session than at the second and third hemodialysis sessions (-3.2 +/- 0.6, -3.5 +/- 0.8 and -3.6 +/- 0.6%/l, respectively). In conclusion, DeltaRBV and the DeltaRBV/ultrafiltration ratio differ systematically between the first and other hemodialysis sessions in patients on a thrice-weekly hemodialysis schedule, most likely as a result of different ultrafiltration volumes.

Hemodialysis monitoring in whole blood using transmission and diffuse reflection spectroscopy: A pilot study

Visible and near infrared transmission and diffuse reflection spectroscopy were used to monitor changes in whole blood resulting from hemodialysis treatment for end-stage renal disease. Blood samples from 8 patients on chronic hemodialysis therapy were measured in the 500- to 1700-nm wavelength range immediately before and after a single treatment. Principal component scores characteristic of each spectrum were derived, and mean pre- and posttreatment scores of the first principal component indicated a significant treatment-dependent change in both optical transmission (P = 0.004) and diffuse reflection (P < 0.001). Significant treatment-induced change persisted (P < 0.05) when the first four principal components were used to account for >97% of the treatment-dependent spectral variation. Some blood spectral changes expressed in terms of difference spectra (posttreatment - pretreatment) were consistent with standard clinical indicators of weight reduction, urea reduction, and potassium change, with probable origins at a molecular level. The results indicate the feasibility of using optical transmission and diffuse reflection spectroscopy to characterize clinically relevant blood changes for the future development of more comprehensive indicators of hemodialysis efficacy and long-term clinical outcomes. Moreover, the optical techniques employed are adaptable for potential online monitoring of blood changes during the hemodialysis treatment.

Comparison of markers of circulating blood volume in hemodialysis patients

BACKGROUND

Pulse dye-densitometry (PDD) is a newly developed technique for monitoring the arterial concentration of indocyanine green (ICG). By using this method, the circulating blood volume (CBV) can be measured as accurately as by established dilution methods using (131)I-labeled human serum albumin in healthy subjects. In the present study, we estimated the CBV in hemodialysis (HD) patients, using PDD, and compared the utility of this method with that of other markers of the CBV.

METHODS

We measured the CBV in seven HD patients and eight healthy volunteers, using PDD, and evaluated the correlation between the CBV measured by PDD (CBV-PDD) and the calculated CBV (CBV-Cal), using a prediction formula (CBV (l) = 2.68 x BSA, where BSA is body surface area (m(2))). We also investigated the correlation between CBV-PDD and the maximal inferior vena cava diameters in quiet expiration (IVCe), and the plasma levels of atrial and brain natriuretic peptides (ANP and BNP, respectively) in the HD patients.

RESULTS

CBV-Cal was closely correlated with CBV-PDD in the healthy volunteers, but there was no such correlation in the HD patients. On the other hand, IVCe was significantly correlated with the CBV-PDD in the healthy volunteers as well as in HD patients. ANP and BNP were not correlated with the CBV-PDD in the HD patients.

CONCLUSIONS

We concluded that CBV-PDD and IVCe were useful parameters in evaluating the CBV in HD patients, while CBV-Cal was not a useful parameter. Also, as a marker of changes in the CBV in HD patients, IVCe was considered to be more sensitive than either ANP or BNP.

New Blood Volume Monitoring Method for Hemodialysis: A-V Pressure Gradient Measurement by Synchronized One-point Reading

During hemodialysis, rapid ultrafiltration often causes symptomatic hypotension. To predict the occurrence of volume-dependent hypotension as early as possible, continuous hematocrit monitoring with the Crit-Line noninvasive monitor has been widely used to measure blood volume changes during hemodialysis. As another potential method of monitoring blood volume variations, we studied blood viscosity, which is theoretically associated with the pressure gradient across the dialyzer. Blood viscosity (calculated by the Hugen-Poiseuille formula) is a major determinant of the blood flow rate and is associated with the pressure difference between the postpump arterial (A) and venous (V) pressures. The A-V pressure gradient fluctuates due to pump pulsation, so we minimized this noise by always reading the pressure gradient at the same point out of 1400 partitions on the rotary pump. To test this synchronized one-point reading method, the A-V pressure gradient was measured using 3 different xanthan gum solutions and was found to be linearly proportional to the model blood flow rate. In an experimental dialysis system using a xanthan gum solution (300 mg/L), the A-V pressure gradient showed a gradual linear increase along with the ultrafiltration rate up to 1 L/h as the viscosity slowly increased in the dialyzer. The changes of blood volume shown by this method were significantly correlated with data obtained using the Crit-Line in 8 patients undergoing hemodialysis. This simple and inexpensive method may allow monitoring of blood volume changes and thus provide data that are beneficial for fluid management in hemodialysis patients suffering from clinical dialysis intolerance.

Evaluation of the Harmonized Alert Sensing Technology Device for Hemodynamic Monitoring in Chronic Hemodialysis Patients

The Harmonized Alert Sensing Technology (HASTE) device was developed to overcome the primary shortcomings of interval based noninvasive blood pressure (BP) monitoring. This study was conducted to assess the reliability of the HASTE system compared with standard cuff BP values in patients on hemodialysis. A total of 1,370 HASTE measurements were compared with oscillometric standard cuff systolic BP values in 42 sessions of 15 patients on hemodialysis. The average discrepancy between the HASTE and cuff systolic BP was 1.41 +/- 16.90 mm Hg. Compared with cuff measurements, 31% of systolic BP fell within a range of 5 mm Hg difference, 57% of systolic BP fell within 10 mm Hg, and 73% of systolic BP fell within a 15 mm Hg band. According to British Hypertension Society standards or Association for the Advancement of Medical Instrumentation criteria, the current HASTE method did not perform well. Technology to provide noninvasive hemodynamic monitoring is, however, in its developmental stage. The effort at continuous systolic pressure monitoring using existing, readily available, and frequently used techniques is exciting. Although the HASTE system as currently configured and calibrated did not adequately perform, variations in site analysis and conversion factors may increase pressure sensitivity and tracking over the course of a standard dialysis treatment.

The role of blood volume reduction in the genesis of intradialytic hypotension

BACKGROUND

The aim of this multicenter prospective study was to investigate the role of relative blood volume (RBV) reduction on intradialytic hypotension.

METHODS

One hundred twenty-three patients on chronic hemodialysis therapy were considered a priori normotensive (reference group A), intradialytic hypotension prone (group B), and hypertensive (group C). RBV was continuously monitored, and diastolic and systolic blood pressure (SBP) and heart rate (HR) were measured at 20-minute intervals during three dialysis sessions.

RESULTS

Intradialytic RBV reduction was -13.8% +/- 7.0% and similar in the three groups (P = 0.841). SBP and RBV decreased during dialysis, with a sharp initial decrease (in the first 20 minutes for SBP and the first 40 minutes for RBV), followed by a slower decrease. The lying bradycardic response before dialysis was less in group B than group A (a decrease of 3 +/- 7 versus 9 +/- 9 beats/min; P < 0.001). When symptomatic hypotension occurred, RBV reduction was not significantly different from that recorded at the same time during hypotension-free sessions (-13.9% +/- 6.4% versus -12.7% +/- 5.2%; P = 0.149). Group, baseline plasma-dialysate sodium gradient, RBV line irregularity, and early RBV and HR reduction during dialysis influenced the relative risk for symptomatic hypotension with a sensitivity of 80% versus 30% for RBV alone.

CONCLUSION

We found no difference in reduction in RBV in the three groups and no critical RBV level for the appearance of symptomatic hypotension. With variables easily available within 40 minutes of dialysis, RBV monitoring increases the prediction of symptomatic hypotension.

A new technique for establishing dry weight in hemodialysis patients via whole body bioimpedance

BACKGROUND

Quantitative techniques are necessary to achieve dry weight (DW) in patients with kidney failure. Bioimpedance spectroscopy (BIS) is a non-invasive method that determines the volume of body fluid compartments. The current work evaluates the use of BIS data in hemodialysis patients for the prediction of DW.

METHODS

A new technique has been devised for the estimation of DW that involves the intersection of two slopes, slope normovolemia (SNV) and slope hypervolemia (SHV). These slopes characterize the variation in extracellular water (ECW) with body weight (BW) in the states of normovolemia and hypervolemia, respectively. SNV was established via measurements of ECW and BW in 30 healthy subjects. In a longitudinal study in new hemodialysis patients, successive reduction of post-dialysis weight (PDW) was attempted until clinical signs of normovolemia were presented. Measurements of ECW and BW that were acquired at the beginning of each treatment were used to determine SHV.

RESULTS

SNV was found to be 0.239 L/kg and 0.214 L/kg for male and female healthy subjects, respectively. A significant DeltaPDW predicted by the new method (-4.98 kg) was highly correlated to the DeltaPDW achieved in the study (-5.85 kg, R = 0.839). Blood pressure was reduced (P < 0.001) and an 86% decrease in antihypertensive agents was achieved.

CONCLUSION

The method of intersecting slopes (SHV with SNV) via BIS is a new method for the prediction DW. This approach will offer considerable improvement for the routine management of DW in the dialysis setting.

Changes in major blood components after adopting the supine position during haemodialysis

BACKGROUND

In Japan, haemodialysis (HD) is usually performed with patients in the supine position. However, the effects of changing posture on major blood components have not been investigated in HD patients. It is possible that several fluid components change rapidly when patients change from the upright to the supine position. We therefore investigated the effects of posture on blood component analysis.

METHODS

A first blood sample was taken from 10 HD patients 5 min after they adopted a supine position; HD was begun immediately after sampling. Additional blood samples were collected 15 and 30 min later while patients remained in the supine position. On an alternate day, blood samples were taken from these same patients in the supine position, but not during HD. The same procedure was performed in 10 healthy volunteers.

RESULTS

Haematocrit significantly decreased in patients undergoing HD at 15 and 30 min into the HD session. Similar decreases were observed in HD patients not undergoing HD and in normal control subjects. Haematocrit changes at 15 min were not significantly different between the three groups. Serum albumin concentrations decreased in the same way as haematocrit. Consequently, the reductions in haematocrit and albumin concentrations in HD patients during the HD session were not attributable to the HD procedure or to end-stage renal disease, but rather were due to the supine position and consequent haemodilution caused by redistribution of water from the extra- to the intravascular space. Finally, WBC counts decreased significantly at 15 min in both HD patient groups and in normal controls. The relative decrease at 15 min was significantly greater in HD patients undergoing HD (61.4% of baseline) than in those not undergoing HD (88.0%) or in normal controls (94.7%). These differences were probably due to previously reported WBC sequestration in the lungs during the early phase of HD.

CONCLUSIONS

This study suggests that the change from the upright to the supine positions during HD causes changes in blood components that are critical for quality control determinations.

Variability of relative blood volume during haemodialysis

BACKGROUND

A decrease in blood volume is thought to play a role in dialysis-related hypotension. Changes in relative blood volume (RBV) can be assessed by means of continuous haematocrit measurement. We studied the variability of RBV changes, and the relation between RBV and ultrafiltration volume (UV), blood pressure, heart rate, and inferior caval vein (ICV) diameter.

METHODS

In 10 patients on chronic haemodialysis, RBV measurement was performed during a total of one hundred 4-h haemodialysis sessions. Blood pressure and heart rate were measured at 5-min intervals. ICV diameter was assessed at the start and at the end of dialysis using ultrasonography.

RESULTS

The changes in RBV showed considerable inter-individual variability. The average change in RBV ranged from -0.5 to -8.2% at 60 min and from -3.7 to -14.5% at 240 min (coefficient of variation (CV) 0.66 and 0.35 respectively). Intra-individual variability was also high (CV at 60 min 0.93; CV at 240 min 0.33). Inter-individual as well as intra-individual variability showed only minor improvement when RBV was corrected for UV. We found a significant correlation between RBV and UV at 60 (r= -0.69; P<0.001) and at 240 min (r= -0.63; P<0.001). There was a significant correlation between RBV and heart rate (r= -0.39; P<0.001), but not between RBV or UV and blood pressure. The level of RBV reduction at which hypotension occurred was also highly variable. ICV diameter decreased from 10.3+/-1.7 mm/m(2) to 7.3+/-1. 5 mm/m(2). There was only a slight, although significant, correlation between ICV diameter and RBV (r= -0.23; P<0.05). The change in ICV-diameter showed a wide variation.

CONCLUSIONS

RBV changes during haemodialysis showed a considerable intra- and inter-individual variability that could not be explained by differences in UV. No correlation was observed between UV or changes in RBV and either blood pressure or the incidence of hypotension. Heart rate, however, was significantly correlated with RBV. Moreover, IVC diameter was only poorly correlated with RBV, suggesting a redistribution of blood towards the central venous compartment. These data indicate that RBV monitoring is of limited use in the prevention of dialysis-related hypotension, and that the critical level of reduction in RBV at which hypotension occurs depends on cardiovascular defence mechanisms such as sympathetic drive.

Comparison of optical, electrical, and centrifugation techniques for haematocrit monitoring of dialysed patients

Haematocrits were measured as a function of ultrafiltration in a simulated haemodialysis circuit using bovine blood (plasma conductivity 12 mS cm-1) and hypotonic (8.6 mS cm-1) or hypertonic (16 mS cm-1) dialysates as well as in the absence of dialysate. A comparison was made between measurements by light absorption due to haemoglobin, by impedance in the blood line at 5 kHz using Hanai's model of blood conductivity, by conductivity measurements of blood samples at 1.2 kHz using a conductimeter, by centrifugation of blood samples and by calculations using fluid conservation. The validity of Hanai's model was verified to be satisfactory by direct blood and plasma conductivity measurements. In the absence of ionic transfer the impedance device underestimated the haematocrit by 5 to 7%. This underestimation reached 18% in the case of hypertonic dialysate, but this effect can be minimised if the haematocrit necessary for calibration is measured by centrifugation after 15 min of dialysate circulation when ionic balance is achieved. It was found that the optical method monitors haemoglobin concentration rather than red cell volume changes and is not affected by osmotic red cell swelling in the case of hypotonic dialysate. It can be concluded that the light absorption technique is both more accurate and more convenient to use than impedance.

Hemodynamic monitoring during hemodialysis

Intradialytic monitoring of hemodynamic parameters is an active area of research; future developments in this field will decrease intradialytic morbidity and the mortality of end-stage renal disease patients treated by hemodialysis. Recent investigations have been assisted by the development of devices that can continuously and noninvasively measure hematocrit and plasma protein concentration during the treatment. Intradialytic morbidity, fluid overload, and hypertension in chronic hemodialysis patients have been shown to be associated with either large or small intradialytic decreases in blood or plasma volume that can be routinely measured by these devices. The use of intradialytic changes in blood volume as a feedback control parameter to vary the ultrafiltration rate and dialysate sodium concentration, so called profiling, is now possible, but further research in this area is necessary to show how to optimize the control algorithms. Other, more preliminary studies suggest that monitoring of central blood volume, extracellular volume, and cardiac output during hemodialysis may permit improved hemodynamic stability during treatment and better control of blood pressure. Although optimal application of these techniques and devices remains to be shown, their routine use during maintenance hemodialysis therapy will likely be the standard of care in the near future.

Assessment of dry weight in hemodialysis: an overview

Fluid balance is an integral component of hemodialysis treatments to prevent under- or overhydration, both of which have been demonstrated to have significant effects on intradialytic morbidity and long-term cardiovascular complications. Fluid removal is usually achieved by ultrafiltration to achieve a clinically derived value for "dry weight." Unfortunately, there is no standard measure of dry weight and as a consequence it is difficult to ascertain adequacy of fluid removal for an individual patient. Additionally, there is a lack of information on the effect of ultrafiltration on fluid shifts in the extracellular and intracellular fluid spaces. It is evident that a better understanding of both interdialytic fluid status and fluid changes during hemodialysis is required to develop a precise measure of fluid balance. This article describes the current status of dry weight estimation and reviews emerging techniques for evaluation of fluid shifts. Additionally, it explores the need for a marker of adequacy for fluid removal.

Continuous measurement of hematocrit using an intravascular catheter equipped with a fiberoptic transmission cell

PURPOSE

The purpose of this study was to measure intravascular hematocrit values continuously by using a fiberoptic probe based on near-infrared photometry.

METHODS

We produced a catheter 1.5 mm in diameter that use a pair of plastic fibers. One of the fibers, the measuring fiber, was used to measure the optical density of blood, and the other, the reference fiber, was used to decrease the signal-to-noise ratio. We employed an 805-nm laser diode as the light source. Two photodiodes were used to measure the intensity of the light transmitted through the two fibers, and the output signals were amplified and sent to a personal computer through an analog-to-digital converter.

RESULTS

The hematocrit values obtained by this fiberoptic continuous measurement agreed well with those obtained by microcentrifugation within physiological ranges.

CONCLUSIONS

This method is effective for monitoring the rapid changes in hematocrit.

Evaluating volume status in hemodialysis patients

Accurate determination of the volume and distribution of body fluids in end stage renal disease patients will permit improved assessment of dry weight and strategies for optimal fluid removal. Certain biochemical markers and anatomical measures have been proposed as markers of dry weight, but these markers primarily reflect the volume of the intravascular compartment and may not reflect total body volume status. Noninvasive determination of total body water and extracellular fluid volumes using bioimpedance analyses has also been proposed for assessment of dry weight, but such determinations do not yet have sufficient accuracy for routine use. Several devices have been recently developed for continuously monitoring changes in blood volume on-line during routine hemodialysis. Such blood volume monitors cannot be used to determine dry weight directly; however, continuous monitoring of blood volume can be used to detect fluid overload because intradialytic changes in blood volume are small in hemodialysis patients who are overhydrated. Furthermore, continuous monitoring of blood volume can be used to predict symptoms resulting from intradialytic hypovolemia. The combined use of blood volume monitoring and time-dependent ultrafiltration and dialysate sodium profiles will be used increasingly in the future to assist in the prevention of hypotension and symptoms that result from intradialytic hypovolemia, especially when automated systems for controlling intradialytic blood volume are individualized and shown to be safe and effective.

Blood volume changes during three different profiles of dialysate sodium variation with similar intradialytic sodium balances in chronic hemodialyzed patients

The aim of this study was to evaluate the effects on blood volume (BV) preservation of three different profiles of dialysate sodium variation with similar intradialytic sodium balances. Ten uremic patients aged 50 +/- 11 years receiving regular bicarbonate hemodialysis for 49 +/- 57 months were studied. Each patient underwent three hemodialysis treatments with different modalities of dialysate sodium profiles: constant sodium hemodialysis (CHD), high-low sodium hemodialysis (H-LHD), and low-high sodium hemodialysis (L-HHD). In CHD, the dialysate sodium concentration was 141 mEq/L and did not change during treatment. In H-LHD and L-HHD, the dialysate sodium concentration at the start of dialysis was 160 mEq/L and 133 mEq/L, respectively, and remained constant for 60 minutes. At this time, a single-step break point of variation of dialysate sodium concentration occurred. The dialysate sodium concentration changed according to a model aimed to keep identical the amount of dialysate sodium exchanged in the three different dialysis procedures. The duration of hemodialysis, the blood flow rate, the dialysate flow rate, and the dialysis membrane were the same for all three different hemodialysis modalities. The ultrafiltration rate was kept constant during treatment. Total dialysate collection and intradialytic sodium balance were calculated for each hemodialysis session. Blood pressure and heart rate were monitored at 10-minute intervals; percent reductions of BV (%R-BV) were continuously monitored by an online optical reflection method (Hemoscan; Hospal-Dasco, Medolla, Italy). The results have shown a lower intradialytic %R-BV with H-LHD compared with L-HHD and CHD. No differences in total ultrafiltration rate, systolic and diastolic blood pressures, and heart rate were observed among the three different dialysis procedures. The total dialysate sodium collected and the intradialytic sodium balances were very similar among the three different dialysis procedures, confirming the accuracy of the precision of the sodium model used. The H-LHD sodium profile may be a useful tool in the prevention of excessive %R-BV and of dialysis intolerance episodes.

Continuous measurements by impedance of haematocrit and plasma volume variations during dialysis

A technique for continuous measurements of haematocrit and plasma volume in the arterial line of dialysed patients has been tested in vitro and in vivo. This method uses impedance measurements at 5 kHz and requires a single haematocrit measurement. It relies on two assumptions: that plasma resistivity does not change during dialysis and that blood resistivity obeys Hanai's model. Both assumptions are verified during in vitro tests. Haematocrits measured in vivo by this method are found to be in good agreement with direct measurements from blood samples. The haematocrit variation is then used to monitor changes in plasma volume, assuming conservation of erythrocyte volume. In addition, it is possible to obtain the variation in interstitial volume by combining these data with body impedance measurements.

Cardiac output and circulating blood volume analysis by pulse dye-densitometry

OBJECTIVE

Pulse dye-densitometry (PDD) is a newly developed method for monitoring the indocyanine green (ICG) concentration in an artery with which cardiac output (CO) and circulating blood volume (CBV) can be determined. We evaluated its accuracy for clinical use.

METHODS

In 7 patients under general anesthesia, ICG-sensitive optical probes (805 and 890 nm) were attached to a finger. Following injection of ICG, the arterial concentration of dye was recorded optically by the non-invasive test instrument and sampled arterial blood ICG concentration was also measured photometrically for comparison. In order to validate the PDD analysis, CO was also measured by both the dye dilution cuvette method and by thermodilution in 8 patients scheduled for coronary artery bypass grafting. In 30 other patients, CBV assessed by PDD was compared with its value estimated from body size.

RESULTS

The blood dye concentration correlated well with the values obtained by PDD (r = 0.953, p < 0.01). Mean bias for the test PDD CO was +0.15 +/- 0.72 min l-1 (not significant (n.s.)) compared with the cuvette method while the mean bias of the thermodilution method vs the cuvette method was +0.79 +/- 0.84 min l-1 (p < 0.0001.). The average value of CBV obtained by PDD was 3.81 +/- 1.39 L compared with that estimated value, 3.72 +/- 0.77 L (n.s.).

CONCLUSIONS

CO determined by PDD agrees well with cuvette densitometry, and somewhat less well with CO by thermodilution. The new method, by not requiring a pulmonary arterial catheter, is less invasive than either older method, and yields in addition a value of CBV.

Blood density monitoring during dialysis

Continuous monitoring of blood density (BD) was preformed in 4 stable dialysis patients in 20 sessions using a density meter based on a mechanical oscillator technique. Mean predialysis and postdialysis BDs were 1.0427 +/- 0.0031 g/cm3 and 1.0502 +/- 0.0055 g/cm3, respectively. For similar predialysis to postdialysis total body water reduction, significant difference in the mean BD increase was found between hypotensive and nonhypotensive groups (1.29 +/- 0.07%, 0.47 +/- 0.12%, respectively; p < 0.001). Eight hypotensive episodes occurred during 6 sessions. The mean value of the blood density changes slope (dBD/dr) during the 5 min preceding a hypotensive episode increased about 2.5 times more than did the mean of the predialysis to postdialysis blood density slope (27.6 +/- 2.2 g/cm3.min.10(-5), 10.5 +/- 0.4 g/cm3.min.10(-5), respectively; p < 0.001) under the condition of a constant ultrafiltration rate of 18.9 +/- 0.6 ml/min. Continuous monitoring of blood density allows abrupt change in plasma volume to be identified and seems to have a potential utility to the prevention of symptomatic hypotension episodes in patients receiving hemodialysis.

Ultrafiltration and backfiltration during hemodialysis

Ultrafiltration is the pressure-driven process by which hemodialysis removes excess fluid from renal failure patients. Despite substantial improvements in hemodialysis technology, three significant problems related to ultrafiltration remain: ultrafiltration volume control, ultrafiltration rate control, and backfiltration. Ultrafiltration volume control is complicated by the effects of plasma protein adsorption, hematocrit, and coagulation parameters on membrane performance. Furthermore, previously developed equations relating the ultrafiltration rate and the transmembrane pressure are not applicable to high-flux dialyzers, high blood flow rates, and erythropoietin therapy. Regulation of the ultrafiltration rate to avoid hypotension, cramps and other intradialytic complications is complicated by inaccurate estimates of dry weight and patient-to-patient differences in vascular refilling rates. Continuous monitoring of circulating blood volume during hemodialysis may enable a better understanding of the role of blood volume in triggering intradialytic symptoms and allow determination of optimal ultrafiltration rate profiles for hemodialysis. Backfiltration can occur as a direct result of ultrafiltration control and results in transport of bacterial products from dialysate to blood. By examining these problems from an engineering perspective, the authors hope to clarify what can and cannot be prevented by understanding and manipulating the fluid dynamics of ultrafiltration.

Non-invasive monitoring of blood volume during hemodialysis: its relation with post-dialytic dry weight

Hemodialysis has a profound effect on fluid balance. Since fluid is initially withdrawn from the intravascular compartment, blood volume will decrease rapidly. A fluid shift (refill) from the overhydrated interstitium towards the intravascular compartment counteracts hypovolemia. Underestimation of postdialytic dry weight will cause interstitial dehydration and consequently a low refill capacity. This can cause hypovolemia-induced hypotension, a serious problem in the daily practice of hemodialysis: during one out of three sessions a hypotensive episode occurs. Clinical criteria to estimate post-dialytic dry weight are insensitive. We have developed non-invasive methods to estimate dry weight and changes in blood volume (BV) more accurately. The aim of this study was to investigate the relation between hydration state of the patient and changes in BV during treatment. Therefore, 37 hemodialysis patients were divided into three groups according to their post-dialytic extracellular fluid volume (EFV), which was measured by means of the non-invasive conductivity method: de- (N = 11), normo- (N = 18), and overhydrated (N = 8). Using an on-line optical reflection method, changes in BV were measured continuously during hemodialysis. BV decrease, corrected for ultrafiltration, was stronger in the dehydrated (4.4 +/- 1.5%/liter) than in the normohydrated (3.3 +/- 1.5%/liter) and overhydrated (2.7 +/- 1.9%/liter) groups. In the dehydrated group, the frequency of hypotensive episodes (48.5 +/- 20.2%) was significantly greater compared to the normohydrated (20.5 +/- 23.5%) or overhydrated (6.5 +/- 6.5%) group, P < 0.005.(ABSTRACT TRUNCATED AT 250 WORDS)