F PAN1,2, P CHAMPION DE CRESPIGNY1, N TOUSSAINT1,2, S HOLT1,2
1The Royal Melbourne Hospital, Parkville, Melbourne, Australia, 2The University of Melbourne, Parkville, Melbourne, Australia
Aim: To show how bioimpedance cardiography (BIC) might help us predict and prevent intradialytic hypertension and hypotension.
Background: Intradialytic hypotension (IDHypo) complicates up to 30% of haemodialysis (HD) sessions. Intradialytic hypertension (IDHyper) complicates a similar percentage of dialysis sessions but is less frequently reported. Both IDHypo and IDHyper are unpleasant for patients and have an adverse prognostic significance, portending an increase in morbidity and mortality. The mechanisms for IDHypo/IDHyper include ultrafiltration rates (UFR) that exceed capillary refill capacity, reduced coronary blood flow, dialysis of drugs and changes in systemic vascular resistance (SVR). Current monitoring techniques are relatively crude (haematocrit monitoring or conductivity testing) or are difficult or invasive (pulmonary artery catheterisation and cardiac MRI). Simple bioimpedance spectroscopy (BIS) has not been found to be clinically helpful in defining target weights or ultrafiltration rates.
Methods: Bioimpedance cardiography (BIC) combines thoracic BIS, and electrocardiography to monitor changes in transthoracic fluid content (TFC), cardiac function and SVR. Remarkably little data exists around the use of BIC monitoring during HD.
Results: In pilot studies using BIC we have shown;
1) a consistent slope in TFC between dialysis sessions with similar UF rates, despite differences in baseline and absolute measurements;
2) in cases of IDHypo, a reduction in systolic time ratios (<0.4), SVR and Heather index (dropping <7Ohms/s²) BEFORE the blood pressure drops;
3) in cases of IDHyper, increases in SVR or apparent movement back along the Starling curve.
Conclusion: BIC holds promise as a non-invasive method of helping refine maximum tolerated UF rates, as well as predicting IDHypo and responding appropriately to IDHyper.
Mary completed her Nephrology training in Melbourne, and is now enguaged in a PhD looking at the vascular and other effects of phosphate binders at The Royal Melbourne Hospital and University of Melbourne. Part of this project PhD involves the novel use of bioimpedadance cardiography in haemodialysis patients to study haemodynamics during dialysis and the effects of phosphate binders on these measurements.