Oxygen status during haemodialysis. The Cord-Group

Determinants and short-term reproducibility of relative plasma volume slopes during hemodialysis

BACKGROUND AND OBJECTIVES

Hypervolemia is a major cause of morbidity, in part because of the lack of well characterized diagnostic tests. The hypothesis was that relative plasma volume (RPV) slopes are influenced by ultrafiltration rate, directly associate with improvement in arterial oxygen saturation, and are reproducible.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

RPV slopes were measured on three consecutive hemodialysis sessions. Various relationships were tested using mixed models. Reproducibility was assessed by the intraclass correlation coefficient.

RESULTS

RPV slopes averaged 1.37 ± 1.45% per hour. The mean RPV slopes were steeper on the first dialysis of the week, which correlated with a higher ultrafiltration rate; RPV slope and ultrafiltration rate were directly related. Increasing ultrafiltration rate quartiles were associated with similar change in RPV in the first 1 hour of dialysis but steeper changes in RPV subsequently. A direct relationship emerged between increasing RPV slopes and increasing arterial oxygen saturation slopes. The intraclass correlation coefficient for the relative plasma volume slope was 0.77.

CONCLUSIONS

Although ultrafiltration rate is a major determinant of RPV slope, similar ultrafiltration rates are associated with varying RPV between individuals. Because RPV is associated with little change by ultrafiltration rate during the first 1 hour of dialysis, probing dry weight during the earlier part of dialysis may be safer. RPV slopes are physiologically meaningful, because they are associated with parallel changes in arterial oxygenation saturation slopes. RPV slopes are reproducible, and therefore, RPV may serve as a useful marker to judge changes in volume status within an individual.

La population âgée hémodialysée : évaluer et prendre en charge le risque de déclin cognitif

Epidemiological data suggest a large prevalence of cognitive impairment in elderly patients on haemodialysis. They are frequently exposed to pathologies that affect the brain, and hold a plurality of risk factors for neurodegenerative and vascular dementia. Cognitive dysfunctions, because of their medical and socio-economical consequences, may led to discuss the indication for haemodialysis and its profit for the elderly patient. These facts highlight the advantage of a regular assessment of cognitive functions in this population. They also suggest the need in the future of a multidisciplinary intervention for these patients, for a better evaluation of interventions aimed on primary and secondary prevention of cognitive decline in the elderly group.

pO2 and pCO2 increment in post-dialyzer blood: the role of dialysate

Blood returning from a dialyzer during hemodialysis has a higher pO2 and pCO2 content than blood entering the dialyzer, and this has been attributed to the dialysate. The present study investigates this phenomenon. Acid-base and blood-gas parameters (pH, pO2, pCO2 and HCO3) were measured in three groups of stable chronic hemodialysis patients (A, B, and C) undergoing high-flux hemodialysis. In group A (n = 15), "arterial" (a) and "venous" (v) samples were withdrawn simultaneously before dialysis (samples A0), 5 min after circulation of the blood with the dialysate in the by-pass mode (samples A5), and 5 min after high-flux hemodialysis at a zero ultrafiltration rate (samples A10). In group B (n = 11) (a) and (v) samples were withdrawn simultaneously before dialysis (samples B0), 5 min after isolated-ultrafiltration with closed dialysate ports ("isolated-closed" ultrafiltration) (samples B5), and 5 min after high-flux hemodialysis at a zero ultrafiltration rate (samples B10). In group C (n = 14), after an initial arterial blood sample withdrawal before hemodialysis (sample C0), high-flux hemodialysis at a zero ultrafiltration rate was initiated. Five minutes later, blood and dialysate samples were withdrawn simultaneously from the hemodialysis lines (samples C5). In all cases blood and dialysate (bicarbonate) flow rates were set at 0.300 and 0.700 L/min, respectively. FLX-18 hemodialyzers (membrane PEPA 1.8 m2) were used in this study. Analysis of variance revealed significant changes only in venous samples. A comparison of arterial and venous samples revealed no differences between groups A and B before the initiation of dialysis (A0a vs. A0v and B0a vs. B0v, P = NS). The pO2 content was higher in A5v samples than in A5a samples (83.5 +/- 11.2 vs. 88.8 +/- 14.0 mm Hg, P < 0.02), while the level of HCO(3) was higher in A5a samples than in A5v samples (20.8 +/- 2.0 vs. 20.4 +/- 1.8 mEq/L, P < 0.05). A10a samples possessed a higher pH and lower levels of pO2, pCO2, and HCO3 in comparison to A10v samples (P < 0.001 for all). Mean pO2 and pCO2 values in A5v and A10v samples increased by 6.3% and 12.1% and by 1.29% and 52% in comparison to corresponding values of A5a and A10a samples, respectively. The pO2 level was the only parameter that differed significantly between B5a and B5v samples (B5a = 84.6 +/- 10.1 vs. B5v = 98.0 +/- 12.6 mm Hg, P < 0.005). B10a samples possessed a higher pH and lower levels of pCO2, pO2, and HCO3 in comparison to B10v samples (P < 0.0005 for all comparisons). Mean pO2 and pCO2 values in B5v and B10v samples increased by 16.2% and 16.3% and by -0.29% and 64.8% in comparison to corresponding values of B5a and B10a samples, respectively. C5a samples possessed a higher pH and lower levels of pCO2, pO2, and HCO3 in comparison to C5v samples (P < 0.001 for all). Mean pO2 and pCO2 values in C5v samples were, respectively, 16.0% and 65.0% higher than corresponding values of C5a samples. These results indicate that blood returning from the dialyzer after 5 min of high-flux hemodialysis has a higher pO2 and pCO2 than blood entering the dialyzer, and that this difference is due to O2 and CO2 transfer from the dialysate space into the blood.

Microbubbles

Gas embolism is a known complication of various invasive procedures, and its management is well established. The consequence of gas microemboli, microbubbles, is underrecognized and usually overlooked in daily practice. We present the current data regarding the pathophysiology of microemboli and their clinical consequences. Microbubbles originate mainly in extracorporeal lines and devices, such as cardiopulmonary bypass and dialysis machines, but may be endogenous in cases of decompression sickness or mechanical heart valves. Circulating in the blood stream, microbubbles lodge in the capillary bed of various organs, mainly the lungs. The microbubble obstructs blood flow in the capillary, thus causing tissue ischemia, followed by inflammatory response and complement activation. Aggregation of platelets and clot formation occurs as well, leading to further obstruction of microcirculation and tissue damage. In this review, we present evidence of the biological and clinical detrimental effects of microbubbles as demonstrated by studies in animal models and humans, and discuss management of the microbubble problem with regard to detection, prevention, and treatment.

Myocardial scintigraphy using a fatty acid analogue detects coronary artery disease in hemodialysis patients

BACKGROUND

Coronary artery disease contributes significantly to mortality in end-stage renal disease (ESRD) patients. Single-photon emission computed tomography (SPECT) using an iodinated fatty acid analogue, iodine-123-methyl iodophenylpentadecanoic acid (123I-BMIPP), can assess fatty acid metabolism in the myocardium. We investigated the ability of 123I-BMIPP SPECT to detect coronary artery disease in hemodialysis patients compared with 201thallium chloride (201Tl) SPECT.

METHODS

We prospectively studied 130 ESRD patients undergoing hemodialysis for a mean of 88.6 months (male/female, 77/53; mean age, 63.8 years). Dual SPECT using 123I-BMIPP and 201Tl was performed, followed by coronary angiography. SPECT findings were graded in 17 segments on a five-point scale (0, normal uptake; 4, none) and assessed as a summed score.

RESULTS

By coronary angiography, 71.5% of patients (93/130) had significant coronary stenosis (> or =75%), and five patients showed coronary spasm without coronary stenosis. When a BMIPP summed score of 6 or more was defined as abnormal, sensitivity, specificity, and accuracy for detecting coronary artery disease by BMIPP SPECT were 98.0%, 65.6%, and 90.0%, respectively; in contrast, these parameters for detecting coronary artery disease by Tl SPECT were 84.7%, 46.9%, and 75.0%, respectively, when a Tl summed score of 1 or more was defined as abnormal. In receiver operating characteristic analysis, the area under the curve was 0.895 in BMIPP and 0.727 in Tl SPECT, respectively.

CONCLUSION

Resting BMIPP SPECT is superior to Tl SPECT for detecting coronary lesions, and provides safe screening for coronary artery disease among maintenance hemodialysis patients.

Adenosine and hemodialysis in humans

BACKGROUND

Infections and hypotension are serious complications that develop during hemodialysis (HD) treatment. Adenosine (ADO), a strong hypotensive and immunosuppressive agent, may participate in these two HD complications, because high concentrations of ADO metabolites are found in dialyzed human plasma. ADO, which is released by endothelial cells, is quickly transformed into inosine (INO) by plasmatic ADO deaminase (ADA) and mononuclear cell ADO deaminase (MCADA). In plasma, the degradation of ADO into INO and its uptake by red blood cells (RBC) are both very rapid, resulting in the short half-life of ADO in blood.

METHODS

Using liquid chromatography, we evaluated ADO and INO plasma concentrations before and after HD session.

RESULTS

Before the HD session, ADO and INO plasma concentrations were higher in hemodialyzed patients than in controls and in peritoneally dialyzed patients. At the end of the HD session, ADO plasma concentration was increased. ADO plasma concentration for the undialyzed patients was in the same range as that of the controls. Before HD, ADA activity was higher in hemodialyzed patients (559 +/- 349 IU) than in controls (219 +/- 48 IU), and the activity rose during the session (665 +/- 135 IU). ADA activity in the undialyzed patients (222 +/- 80 IU) was in the same range as that of the controls (219 +/- 48 IU). Before the HD session, the MCADA activity (247 +/- 144 IU) was lower than in controls (624 +/- 99 IU). HD did not modify ADO RBC uptake. ADO inhibited mononuclear cell proliferation and interferon-gamma production in humans. Finally, as much as 50 microM INO does not inhibit ADO uptake by RBC and does not modify ADA and MCADA activities.

CONCLUSIONS

These data indicate that chronic HD inhibited MCADA activity and increased ADO plasma concentration. Both high ADO plasma concentration and low MCADA activity may be involved in dialysis-induced immune system failure and thereby favor infectious diseases.