Continuous, Online Measurement of the Absolute Plasma Refill Rate During Hemodialysis Using Feedback Regulated Ultrafiltration: Preliminary Results

Dynamics of Plasma Refill Rate and Intradialytic Hypotension During Hemodialysis: Retrospective Cohort Study With Causal Methodology

Key Points

Directly studying plasma refill rate (PRR) during hemodialysis (HD) can offer insight into physiologic mechanisms that change throughout HD. PRR at the start and during HD is associated with intradialytic hypotension, independent of ultrafiltration rate. A rising PRR during HD may be an early indicator of compensatory mechanisms for impending circulatory instability.

Background

Attaining the optimal balance between achieving adequate volume removal while preserving organ perfusion is a challenge for patients receiving maintenance hemodialysis (HD). Current strategies to guide ultrafiltration are inadequate.

Methods

We developed an approach to calculate the plasma refill rate (PRR) throughout HD using hematocrit and ultrafiltration data in a retrospective cohort of patients receiving maintenance HD at 17 dialysis units from January 2017 to October 2019. We studied whether (1 ) PRR is associated with traditional risk factors for hemodynamic instability using logistic regression, (2 ) low starting PRR is associated with intradialytic hypotension (IDH) using Cox proportional hazard regression, and (3 ) time-varying PRR throughout HD is associated with hypotension using marginal structural modeling.

Results

During 180,319 HD sessions among 2554 patients, PRR had high within-patient and between-patient variability. Female sex and hypoalbuminemia were associated with low PRR at multiple time points during the first hour of HD. Low starting PRR has a higher hazard of IDH, whereas high starting PRR was protective (hazard ratio [HR], 1.26, 95% confidence interval [CI], 1.18 to 1.35 versus HR, 0.79, 95% CI, 0.73 to 0.85, respectively). However, when accounting for time-varying PRR and time-varying confounders, compared with a moderate PRR, while a consistently low PRR was associated with increased risk of hypotension (odds ratio [OR], 1.09, 95% CI, 1.02 to 1.16), a consistently high PRR had a stronger association with hypotension within the next 15 minutes (OR, 1.38, 95% CI, 1.30 to 1.45).

Conclusions

We present a straightforward technique to quantify plasma refill that could easily integrate with devices that monitor hematocrit during HD. Our study highlights how examining patterns of plasma refill may enhance our understanding of circulatory changes during HD, an important step to understand how current technology might be used to improve hemodynamic instability.

Pilot Study to Detect Changes in Blood Flow in the External Auditory Meatus During Hemodialysis

Blood flow to internal organs is reported to fall during hemodialysis (HD). As such, noninvasive monitoring devices are required to detect changes in perfusion, which could then be used for therapeutic interventions. We report on a pilot study monitoring blood flow in the outer auditory meatus. We measured the maximum pulse wave amplitude and indicators of blood flow by analyzing red and green color changes in the outer auditory meatus from video recordings made using an otoscope fitted with a digital camera during HD treatments. We studied 61 patients, 43 (71.5%) male, mean age 64.9 ± 12.7 years. Weight fell from 72.8 ± 22.5 kg predialysis to 71.5 ± 22.1 kg postdialysis (P < 0.001). BP did not significantly change (predialysis 142 ± 29/67 ± 18 to 143 ± 25/68 ± 17 mm Hg postdialysis). The maximum pulse wave amplitude in the external auditory meatus fell from 0.21 (0.1-0.55) to 0.14 (0.04-0.4) after 90 min, P < 0.001, and remained low thereafter, and the change at the end of the dialysis session was associated with percentage weight loss (r = -0.37, P = 0.003). Green and red pixel values did not change (predialysis 0.339 [0.333-0.345] to 0.302 [0.291-0.33] post, and 0.301 [0.293-0.328] predialysis to 0.339 [0.334-0.347] post, respectively). This pilot study showed that the maximum pulse wave amplitude measured in the external auditory meatus fell during the dialysis session, and that the fall was associated with fluid removal. This could potentially lead to the development of a monitoring device, which could fit in the ear and record during the dialysis session.

Everything we always wanted to know about furosemide but were afraid to ask

Furosemide is a widely used, potent natriuretic drug, which inhibits the Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-2 in the ascending limb of the loop of Henle applied to reduce extracellular fluid volume expansion in heart and kidney disease. Undesirable consequences of furosemide, such as worsening of kidney function and unpredictable effects on sodium balance, led to this critical evaluation of how inhibition of NKCC affects renal and cardiovascular physiology. This evaluation reveals important knowledge gaps, involving furosemide as a drug, the function of NKCC2 (and NKCC1), and renal and systemic indirect effects of NKCC inhibition. Regarding renal effects, renal blood flow and glomerular filtration rate could become compromised by activation of tubuloglomerular feedback or by renin release, particularly if renal function is already compromised. Modulation of the intrarenal renin angiotensin system, however, is ill-defined. Regarding systemic effects, vasodilation followed by nonspecific NKCC inhibition and changes in venous compliance are not well understood. Repetitive administration of furosemide induces short-term (braking phenomenon, acute diuretic resistance) and long-term (chronic diuretic resistance) adaptations, of which the mechanisms are not well known. Modulation of NKCC2 expression and activity in kidney and heart failure is ill-defined. Lastly, furosemide's effects on cutaneous sodium stores and on uric acid levels could be beneficial or detrimental. Concluding, a considerable knowledge gap is identified regarding a potent drug with a relatively specific renal target, NKCC2, and renal and systemic actions. Resolving these questions would increase the understanding of NKCCs and their actions and improve rational use of furosemide in pathophysiology of fluid volume expansion.