Krassimir Katzarski

Blood Pressure Control and Hemodynamic Changes in Patients on Long Time Dialysis Treatment

In dialysis patients blood pressure can be well controlled with long dialysis (3 times a week for 8 h) in contrast to a more common short dialysis regime (3 times a week for 4 h). We studied whether the good blood pressure control in patients on long dialysis as compared to patients on short dialysis was associated with a decrease in extracellular fluid volume. Two-day interdialytic ambulatory blood pressure monitoring was performed in 26 non-diabetic patients on long dialysis, in 22 patients on short dialysis, matched for the years they were on dialysis treatment, and during 24 h in 19 healthy volunteers. After full equilibration, 24 h after dialysis, echography of the inferior caval vein was performed to determine fluid state. Cardiac dimensions and stroke index were measured by echocardiography. A blood sample was drawn for the determination of electrolytes and vasoactive hormones. 73% of the patients on short dialysis were using antihypertensive medication in contrast to none of the patients on long dialysis. However, blood pressure was significantly lower in patients on long dialysis (115 ± 21/67 ± 11 mm Hg) when compared to patients on short dialysis (143 ± 26/81 ± 16 mm Hg). Indexed caval vein diameter, left ventricular diameter index, and atrial natriuretic peptide were not significantly different in patients on long dialysis compared to patients on short dialysis. Also the cardiac index was comparable in patients on long and short dialysis. However, the total peripheral resistance index was significantly lower in patients on long dialysis compared to the patients on short dialysis and normal controls. The left ventricular mass index was increased in both patients on long and short dialysis compared to controls. We conclude that patients on long dialysis have adequate blood pressure control that seems mainly to be caused by a low total peripheral resistance. These data also suggest that factors other than a lower fluid state contribute to the good blood pressure control in patients on long dialysis.

Kinetics of plasma refilling during hemodialysis sessions with different initial fluid status.

Removal of fluid excess from the plasma volume by ultrafiltration during hemodialysis (HD) is balanced by plasma refilling from the interstitium, driven mainly by the increase in plasma oncotic pressure. We calculated the plasma refilling coefficient (Kr, a parameter expressing the ratio of refilling rate to the increase in oncotic pressure) for nine patients, each undergoing two HD sessions differing by pretreatment fluid status and session time (shorter session, SH, 3.5 h, and longer session, LH, 4.5h). Relative blood volume change was measured online, and solute concentrations were measured regularly during the sessions. The volume of body compartments was measured by bioimpedance. The patients were more volume expanded before LH session (higher initial body mass and total body water). Oncotic pressure was similar for both sessions. The refilling rate, despite higher fluid overload in the LH sessions, was similar for both sessions. The final Kr values stabilized on similar levels (SH: 136.6 ± 55.6 ml/mm Hg/h and LH: 150.7 ± 73.6 ml/mm Hg/h) at similar times, notwithstanding the difference in initial fluid overload between the two groups, suggesting that Kr at dry weight is relatively insensitive to the initial fluid status of the patient.

Hemodialysis: A model for extreme physiology in a vulnerable patient population

Hemodialysis (HD) is a lifesaving treatment for patients with end‐stage renal disease, which is very efficient in the correction of abnormalities of the internal environment. However, this efficiency also induces significant hemodynamic, thermal, and respiratory stressors. These have parallels with the extreme physiologic demands which are normally mainly experienced by healthy subjects under adverse environmental conditions, with the difference that they must be endured by a vulnerable patient population. Hemodynamic stress induced by ultrafiltration leads to a decline in circulating blood volume, which may result in intradialytic hypotension (IDH) and changes in tissue perfusion, which may have long‐term consequences for the function of vital organs such as the brain and the heart. Pronounced declines in central venous oxygen saturation have been observed during routine HD, which are related to the circulatory stress imposed upon the patient. Apart from patient‐related factors, thermal stress induced by HD may lead to skin vasodilation, counteracting the normal hemodynamic response to hypovolemia, which has important pathophysiologic correlates in heat syncope. Lastly, respiratory stress is reflected by prolonged arterial hypoxemia during HD, which is both related to patient‐related factors, but may also be partly because of the treatment itself, especially during the first 30‐60 minutes. Whereas hypoxemia during HD is related to increased mortality, its role in the reduced tissue oxygen delivery during HD should be further defined. Treatment modifications, such as cool or temperature‐controlled HD, may reduce circulatory and thermal stress, which also may translate into a reduced risk of long‐term cardiac or cerebral damage. However, as circulatory stress is mainly time‐dependent, prolonged, or more dialysis treatment may reduce the homeostatic burden on the patient.