Orthostatic Hypotension and Blood Pressure Variability in Persons Undergoing Hemodialysis

Background: Hypertension is an independent risk factor for development of end-stage renal disease and is the leading risk factor for cardiorenal death. It is estimated that more than 80% of patients with end-stage renal disease who undergo maintenance hemodialysis have hypertension. Intensified blood pressure control has been associated with reduced risk of death in patients with hypertension and chronic kidney disease but may increase the risk for intra-dialytic blood pressure falls in patients who undergo hemodialysis. Hemodialysis-associated hypotension has been associated with increased risks for cardiovascular disease and mortality.

Aim: The aim of this observational pilot study is to evaluate whether point-of-care ultrasound measurements may predict intradialytic hypotension and orthostatic blood pressure falls, in patients with chronic kidney disease who undergo maintenance hemodialysis.

Ethics: The study has been approved by the Swedish Ethical Review Authority (2023-05959-01).

Study participants: All patients (n=70) with chronic kidney disease who undergo maintenance hemodialysis at Vrinnevi Hospital in Norrköping, Sweden, will be invited to voluntarily participate in the study. Information about the study will be given orally and in written form. Those who opt to participate will be asked to sign a written informed consent.

Background data collection: For descriptive purposes, information will be collected regarding current and prior medical diagnoses, current medical treatment, anthropometric data, and self-perceived quality of lite (using the validated questionnaire KDQOL-SF). Blood samples will be tested for routine hematological variables, as well as for sodium, potassium, calcium, creatinine, urea and HbA1c.

Ultra-sound measurements: Before initiation of dialysis, point-of-care ultrasound measurements will be performed with the patient resting in a supine position at a 30 degrees angle, using a Sonosite SII ultrasound machine with a curvilinear probe. Measurements of the diameter of the inferior vena cava will be performed at a level approximately 2 cm from the right atrium, and breathing variability of its diameter will be assessed.

Blood pressure measurements: Systolic and diastolic blood pressure measurements will be performed after the patient has been resting for 5 minutes in the supine position, with a cuff size that is appropriate for each patient, with the arm resting at heart level, in the arm where the patient does not have a dialysis fistula, using an automated blood pressure measurement device (Fresenius 6008 CARE System) which is connected to the dialysis equipment. Two measurements (with one minute apart) will be performed 30 minutes before the dialysis session begins, three measurements will be performed after half of the planned dialysis session, and two measurements will be performed 15 minutes after the dialysis session has ended. An orthostatic test, which includes systolic and diastolic blood pressure measurements taken immediately after standing up and 1 and 3 minutes after standing up, will also be performed 30 minutes before the dialysis session begins and 15 minutes after the dialysis session has ended.

Statistics: Background information (demographics, anthropometrics, medical history, medication, biochemical evaluation) will be presented for the entire study population as means with standard deviations, medians with inter-quartile ranges, or as counts with percentages, as appropriate. These variables will also be presented in patients with and without intradialytic blood pressure falls (defined as an intradialytic reduction of systolic blood pressure ≥ 20 mmHg or of diastolic blood pressure ≥10 mmHg), and in patients with and without orthostatic blood pressure falls (defined as an orthostatic reduction of systolic blood pressure ≥ 20 mmHg or of diastolic blood pressure ≥10 mmHg), respectively. Between-group differences will be tested for statistical significance using Student´s t-test, Mann-Whitney U-test, Chi-square test or Fisher´s exact test, as appropriate.

Temporal changes in supine systolic and diastolic blood pressures (assessed prior to dialysis, during dialysis and after dialysis) will be visualized with regression slopes, and mixed models will be used to assess their associations with ultrasound measurements of the inferior vena cava. Associations between ultrasound measurements of the inferior vena cava and the blood pressure changes during the orthostatic blood pressure tests will be visualized with scatter plots and tested for statistical significance with correlation analysis.

The predictive ability of ultrasound measurements of the inferior vena cava and the occurrence of intra-dialytic blood pressure falls and of orthostatic blood pressure falls, respectively, will be assessed with logistic regression.