Influence of hemodialysis on intravascular volume and vasoactive hormones.

BACKGROUND: The posthemodialysis plasma level of atrial natriuretic peptide (ANP) has been proposed as an index for an adequate fluid state in hemodialysis (HD) patients. PATIENTS AND METHODS: We investigated the effect of fluid removal during HD on the interaction between intravascular volume and the vasoactive hormones ANP, vasopressin, adrenaline, noradrenaline, renin and aldosterone in 16 HD patients. Intravascular volume was examined with the 131I-labeled albumin method for blood volume (BV) and ultrasound for measurement of inferior vena cava diameter (IVCD). RESULTS: There was a significant decrease in BV, IVCD and ANP, but not in the other vasoactive hormones. Based on BV and IVCD measurements, the predialysis plasma ANP levels in the normovolemic and hypovolemic patients were significantly higher than in the hypervolemic patients. There was no significant difference between the postdialysis ANP levels in the hypervolemic and normovolemic patients and no significant correlations between ANP and BV and IVCD, respectively, but postdialysis ANP correlated significantly with the ultrafiltration rate (r = -0.51, p < 0.05), noradrenaline (r = 0.54, p < 0.05) and change in vasopressin (r = -0.50, p < 0.05). There were also correlations between ANP and age before HD (r = 0.50, p < 0.05) and after HD (r = 0.70, p < 0.0025). CONCLUSION: We conclude that the usefulness of the plasma ANP level for assessment of the fluid state in HD patients is limited, since age and other factors than those directly related to volume influence the concentration of ANP.

Fluid state and blood pressure control in patients treated with long and short haemodialysis.

BACKGROUND: Patients treated at the haemodialysis (HD) centre in Tassin, France have been reported to have superior survival and blood pressure (BP) control. This control has been ascribed to maintenance of an adequate fluid state, antihypertensive drugs being required in < 5% of the patients, although it could not be excluded that a high dose of HD regarding removal of uraemic toxins might also have been of value. METHODS: The aim of the study was to assess the fluid state and BP in normotensive patients on long HD (8 h) in Tassin (group TN) using bioimpedance to measure extracellular volume (ECV), ultrasound for determining the inferior vena cava diameter (IVCD), and 'on-line' monitoring of the change in blood volume (BV), and to compare them with normotensive (group SN) and hypertensive (group SH) patients on short HD (3-5 h) at centres in Sweden. ECV was normalized (ECVn) by arbitrarily setting the median ECV (in % of body weight) in SN patients at 100% for each gender, recalculating the individual values and combining the results for male and female patients in each group. RESULTS: The dose of HD (Kt/V urea) was higher for TN patients than for Swedish patients who had a similar Kt/V, whether hypertensive or not. SH patients had significantly higher ECVn and IVCD than TN and SN patients. TN and SN patients did not differ significantly regarding ECVn and IVCD before and after HD. However, in a subgroup of eight TN patients, ECVn was below the range of that in SH and SN patients, due to obesity with a high body mass index. Another subgroup of 14 TN patients had a higher ECVn than most of the SN patients and also higher than the median ECVn in the SH group, without any difference in body mass index, but they were nevertheless normotensive. The fall in BV was greater in SN than in TN patients, presumably due to a higher ultrafiltration rate in SN patients. However, SH patients had a smaller change in BV than SN patients, presumably because their state of overhydration facilitated refilling of BV from the interstitial fluid. CONCLUSIONS: Normotension can be achieved independently of the duration and dose (Kt/V urea) of HD, if the control of post-dialysis ECV is adequate. However, this is more difficult to achieve with short than with more prolonged HD during which the ultrafiltration rate is lower, BV changes are smaller and intradialysis symptoms less frequent. The results in the subgroup of patients with high ECVn at Tassin suggest that normotension may also be achieved in patients with fluid overload provided that the dialysis time is long enough to ensure more efficient removal of one or more vasoactive factors that cause or contribute to hypertension.

A critical evaluation of ultrasound measurement of inferior vena cava diameter in assessing dry weight in normotensive and hypertensive hemodialysis patients.

The utility of measurement of the inferior vena cava diameter (IVCD) with ultrasound for the assessment of fluid status and posthemodialysis dry weight was studied in 35 hemodialysis (HD) patients, 17 with and 18 without hypertension. In 17 patients (group A), IVCD was measured before and 35 to 40 minutes after HD, pre-HD blood volume (BV) was measured with radiolabeled albumin and post-HD BV was calculated from the change in hematocrit. In 18 patients (group B), IVCD was measured repeatedly during HD and 2 hours after HD. Changes in BV were recorded by monitoring of the hematocrit "on line." Body weight, blood pressure (BP), BV, and IVCD decreased in the entire population. In group A, BV was significantly larger in the hypertensive patients than in the normotensive patients, and it was correlated with the mean BP before and after HD. In the whole population, IVCD was larger in the hypertensive than in the normotensive patients before and after HD. These results confirm that extracellular fluid overload plays an important role in the pathogenesis of dialysis-associated hypertension. In group B, BV and IVCD decreased in parallel during HD and increased during 2 hours after HD due to refilling of the intravascular space, indicating that changes in IVCD reflect changes in BV. In 8 patients studied twice, IVCD increased much more after a 3-hour HD session than after a 6-hour session. At the end of HD, several patients had IVCD below the reference range but IVCD increased during the following 1 to 2 hours, in some patients to values above the reference range. IVCD measured at the end or shortly after HD may therefore be misleading in assessing dry weight.

Monitoring of blood volume during haemodialysis treatment of acute renal and multiple organ failures.

The assessment of the level of hydration in the intravascular fluid compartment in acute renal failure (ARF) and multiple organ failure (MOF) is of an utmost importance. However, the data on monitoring of blood volume in these diseases and especially during haemodialysis treatment are lacking. This article summarizing the experience of monitoring of blood volume in chronic haemodialysis suggests that the application of such monitoring will contribute to better results in haemodialysis treatment of ARF and MOF.